============================================================================= PHOTON2003 - Laboratori Nazionali di Frascati, April 7-11 2003. ============================================================================= LIST OF SUBMITTED ABSTRACTS Updated 1.4.2003 ============================================================================= ============================================================================= ============================================================================= Session I : Structure of the photon Convenor(s) : Maria Krawczik Summary : ALEPH(1), L3(1), OPAL(1), DELPHI(1), HERA (2), theory (1) ============================================================================= ============================================================================= ============================================================================= Author : DELPHI Collab. (Tomasz Szumlak) Type : Experimental Measurement of the Electron Structure Function The hadronic part of the Electron Structure Function (ESF) has been measured using the $e^+e^-$ data at electron scattering energy from $\sqrt{s} = 92.5-209~GeV$. The data analysis is simpler than that of the photon structure function. The ESF data are compared to phenomenological models. The GRVLO and SAS parametrizations follow the data whereas GRVHO and LAC1 do not. It is shown that quasi-real photon virtuality is important. The ESF data can serve as a cross-check of both analyses and help in refining existing parametrizations. ============================================================================= Author : Maria Krawczyk Type : Theory CJKL- A New 5-Flavour LO Analysis and Parametrization of Parton Distributions in the Real Photon New, radiatively generated, LO quark ($u,d,s,c,b$) and gluon densities in a real, unpolarized photon are presented. We perform a global 3-parameter fit, based on LO DGLAP evolution equations, to all available data for the structure function $F_2^{\gamma}(x,Q^2)$. We adopt a new theoretical approach called ACOT($\chi$), originally introduced for the proton, to deal with the heavy-quark thresholds. This defines our basic model (CJKL model), which gives a good description of the experimental data on $F_2^{\gamma}(x,Q^2)$, for both $Q^2$ and $x$ dependences. Reference : hep-ph/0212160 ============================================================================= Author : H1 Collab. Type : Experimental Photon structure as revealed in ep collisions (H1) Hard processes with sensitivity to the structure of the resolved photon are studied in collisions between real photons and protons by the HERA experiments H1 and ZEUS. Results are presented on dijet production at high transverse momentum, which gives access to high x_gamma and very large dijet invariant masses. Measurements of single-inclusive jet cross sections extend the transverse energy and pseudorapidity ranges and allow tests of the scaling violations of the invariant cross section with increasing photon-proton centre of mass energy. Prompt photon production provides an alternative method to investigate the QCD dynamics independently of jet reconstruction methods. All measurements are found to be well described by next-to-leading order QCD calculations with appropriate choices for the photon and proton parton densities. ============================================================================= Author : ZEUS Collab. Type : Experimental Results on virtual photon structure from HERA (Zeus) Similar techniques to those used to study the structure of almost real photons at HERA can be used to investigate the evolution of this structure as the "target" photon virtuality increases. New results are presented and compared to next-to-leading order QCD predictions. ============================================================================= Author : L3 Collab. Type : Experimental Double tag events in two photon Collisions at LEP L3 Collaboration Double-tag events in two-photon collisions are studied using the L3 detector at LEP centre-of-mass energies from $\sqrt{s}=189~\mathrm{GeV}$ to 209~GeV. The cross sections of the $\mathrm{e^+e^-} \rightarrow \mathrm{e^+e^-} hadrons$ and $\gamma^*\gamma^* \rightarrow hadrons$ processes are measured as a function of the photon virtualities, $Q^2_1$ and $Q^2_2$, of the two-photon mass, $W_{\gamma\gamma}$, and of the variable $Y= \ln ( W^2_{\gamma\gamma}/{Q_1 Q_2})$, for an average photon virtuality $\langle Q^2 \rangle = 16~\mathrm{GeV^2}$. The results are in agreement with next-to-leading order calculations for the process $\gamma^* \gamma^* \rightarrow \mathrm{q \bar{q}}$ in the interval $2 \le Y \le 5$. An excess is observed in the interval $5 < Y \le 7$, corresponding to $W_{\gamma\gamma}$ greater than 40~GeV . This may be interpreted as a sign of resolved photon QCD processes or the onset of BFKL phenomena. Reference : Phys.Lett.B 531 (2002) 39 ============================================================================= Author: ALEPH Collab. (Johannes Hess) Type : Experimental Measurement of $F_2^\gamma(x,Q^2)$ with the ALEPH detector The photon structure function $F_2^\gamma(x,Q^2)$ is measured with data taken with the ALEPH detector at LEP. At centre-of-mass energies between $\sqrt{s}=189\,{\rm GeV}$ and $207\,{\rm GeV}$ an integrated luminosity of $548.4\,{\rm pb}^{-1}$ is analyzed in two $Q^2$ ranges with $\langle Q^2\rangle =17.3\GeV^2$ and $67.2\GeV^2$. Detector effects and acceptance are corrected for with a standard Tikhonov unfolding procedure. The results are compared to various theoretical predictions and measurements from other experiments. ============================================================================= Author: OPAL Collab. Type : Experimental Measurement of the hadronic structure of the photon and electron at LEP OPAL collaboration The hadronic photon structure function F2g(x,Q2) and the hadronic electron structure function F2e(z,Q2) have been measured using data taken by the OPAL experiment at e+e- centre-of-mass energies sqrt(s_ee)=189-209 GeV. In case of the photon structure function the statistics of the measurement increased by a factor of more than two in comparison to the previous OPAL measurement at low x. F2g has been obtained for the average Q2 of 10.7 and 19.9 GeV2. The electron structure function has been measured at average Q2=15GeV2. This is the first measurement of F2e. The measurements are in agreement with existing phenomenological models and QED predictions for the flux of quasireal photons inside the electron. ============================================================================ ============================================================================ ============================================================================ Session II : Jets and inclusive reactions Convenor(s) : Thorsten Wengler Summary : L3(2), OPAL (3), HERMES (2), HERA (2), theory (1) ========================================================================== ========================================================================== ========================================================================== Author : ZEUS Collab. Type : Experimental Jet production and alpha_s measurements at HERA (Zeus) Collisions between protons and electrons or almost-real photons at HERA can lead to the production of high transverse energy jets. New measurements are presented of these jets for transverse energies between 6 GeV and 80 GeV. The fact that the photons have a continuum of energies from zero to the electron beam energy (27 GeV) means that the effects of x_T scaling can be investigated. These are measured and compared to next-to-leading-order QCD. These measurements, as well as other jet and subjet measurements, are used to determine precise values of the strong coupling alpha_s. ========================================================================== Author : H1 Collab. Type : Experimental Forward jets and particles in ep collisions and parton dynamics (H1) A study of the dynamics of QCD evolution at low values of Bjorken-x is made via the measurement of energetic jets and pi^0 mesons produced in deeply inelastic positron proton scattering. Jets and pi^0 mesons are measured at small angles with respect to the proton remnant in the laboratory frame, the so-called forward region. Differential cross sections for jet and inclusive pi^0 meson production are presented as a function of Bjorken-x and other variables. The accompanying transverse energy flow around the pi^0 is also studied. The data are compared with the predictions of NLO and modified BFKL QCD calculations as well as with LO models which use various QCD evolution schemes. ========================================================================== Author : L3 Collab. Type : Experimental Inclusive Charged Hadron Production in Two-photon Colisions at LEP L3 Collaboration Inclusive charged hadron production, e+e- ---> e+e- h+/- X, is studied using 414 pb-1 of data collected at LEP with the L3 detector at centre-of-mass energies between 189 and 202 GeV . Single particle inclusive differential cross sections are measured as a function of the particle transverse momentum, pt , and pseudo-rapidity, eta. For pt > 1.5 GeV , the data are well described by an exponential, typical of soft hadronic processes. For higher pt , the onset of perturbative QCD processes is observed. The pion production cross section for pt > 5 GeV is much higher than the NLO QCD predictions. ========================================================================== Author : L3 Collab. Type : Experimental Differential Cross-section for jet production at LEP L3 Collaboration Inclusive jet production, e+e- ---> e+e- jet X, is studied using data collected at LEP with the L3 detector at centre-of-mass energies between 189 and 209 GeV. Jet inclusive differential cross section is measured as a function of the particle transverse momentum, pt, using two different jet algorithms. At low pt, the data are well fitted by a power law. For higher pt, as already observed in pi0 and charged particle channels, a flatter distribution is observed and the measured cross-section is much higher than the NLO QCD predictions. ========================================================================== Author : OPAL Collab. Type : Experimental Di-Jet Production in Photon-Photon collisions at sqrt(s)ee from 189 to 209 GeV OPAL collaboration Di-jet producion is studied in collisions of quasi-real photons at e+e- centre- of-mass energies sqrt(s)ee from 189 to 209 GeV at LEP. The data were collected with the OPAL detector. Jets are reconstructed using an inclusive k_t clustering algorithm for all cross-section measurements presented. A cone jet algorithm is used in addition to study the different structure of the jets resulting from either of the algorithms. The inclusive di-jet cross-section is measured as a function of the mean transverse energy Etm(jet) of the two leading jets, and as a functiuon of the estimated fraction of the photon momentum carried by the parton entering the hard sub-process, xg, for different regions of Etm (jet). Angular distribution in di-jet events are measured and used to demonstrate the dominance of quark and gluon initiated processes in different regions of phase space. Furthermore the inclusive di-jet cross-section as a function of |eta(jet)| and |delta eta (jet)| is presented where eta(jet) is the jet pseudo-rapidity. Different regions of the xg+ -xg- -space are explored to study and control the influence of an underlying event. The results are compared to next-to-leading order perturbative QCD calculations and to the predictions of the leading order Monte Carlo generator PYTHIA. ========================================================================== Author : OPAL Collab. Type : Experimental Charged hadron production in photon-photon collisions at LEP OPAL collaboration The production of charged hadrons in the collisions of quasi-real photons has been measured using the OPAL detector at LEP. The data were taken at e+e- centre-of-mass energies from 183 to 209 GeV. The differential cross-sections as a function of the transverse momentum and the pseudorapidity of the hadrons are compared to recent theoretical calculations. ========================================================================= Author : OPAL Collab. Type : Experimental Measurement of isolated prompt photon production in photon-photon collisions at sqrt(s) from 183 to 209 GeV OPAL collaboration The production of prompt photons has been studied in the collisions of quasi real photons at LEP. The OPAL data taken at sqrt(s) from 183 to 209 GeV have been used. The total inclusive production cross-section for isolated prompt photons is determined. Differential cross sections are compared to the leading order predictions of PYTHIA and an NLO QCD calculation. ========================================================================== Author : HERMES Collab. (Delia HASCH - Frascati) Type : Experimental Transversity measurements at HERMES Polarised deep-inelastic lepton scattering has been the main experimental basis for our understanding of the spin structure of the nucleon. In addition to inclusive and semi-inclusive measurements, recently single-spin azimuthal asymmetries in semi-inclusive scattering have been recognized as a powerful tool to access further information about the spin structure of the nucleon. It has been suggested that these single-spin asymmetries may provide an experimental access to the so-called transversity h1, which describes the probability to find a transversely polarised quark in a nucleon polarised transverse to its (infinite) momentum. This new structure function h1 is required to allow, together with the well-known structure functions f1 and g1, for a complete description of the quark distributions in the nucleon at leading twist. Results from the HERMES experiment are presented on single-spin asymmetries in semi-inclusive hadron production from polarised targets. The azimuthal dependence of the asymmetries is discussed in relation to the transversity structure function h1 and the data are compared with a number of theoretical calculations. ========================================================================== Author : HERMES Collab. (Marco Contalbrigo) Type : Experimental A first measurement of the tensor-polarized structure function b1d The Hermes experiment studies the spin structure of the nucleon using the 27.6 GeV longitudinally polarized positron beam of HERA and an internal target of pure gases. In addition to the well-know spin structure function g1, measured precisely with longitudinally polarized proton and deuteron targets, the use of a tensor-polarized deuteron target provides access for the first time to the tensor polarized structure function b1d. The latter quantifies the dependence of the parton momentum distribution to the nuclear spin and can be used as a probe of the extend of which the nuclear ground state deviates from being a composition of nucleons only. The preliminary results on the spin structure function b1d, based on the 2000 data taking period, are presented for the kinematic range 0.002Au*Au*e+e-), coherent rho0 production (AuAu->AuAu rho0), and rho0 production accompanied by mutual nuclear Coulomb excitation (AuAu->Au*Au*rho0) in ultra-peripheral relativistic gold-gold collisions. We discuss transverse momentum, mass, and rapidity distributions. The two photon-process of e+e- pair production is an important probe of strong field QED because of the large coupling Z\alpha=0.6. At sqrt{s}=200 GeV, the e+e- production cross section agrees with lowest order QED calculations. The cross sections for coherent rho0 production at sqrt{s_NN}=130 and 200 GeV are in agreement with theoretical predictions, which treat rho^0 production and nuclear excitation as independent processes. ============================================================================== Author : H1 Collab. Type : Experimental Proton structure at high Q^2 (H1) Measurements are presented of the deep-inelastic scattering charged and neutral current cross sections as measured at high Q^2 by H1 and ZEUS using the full data set taken in the first phase of HERA running, amounting to over 100 pb^-1 per experiment. The results are sensitive to the effects of W and Z boson exchange as well as to highly virtual photon exchange. They are used to extract the proton structure functions F_2, xF_3 and F_L at high Q2. Next-to-leading order QCD fits are performed to the high Q^2 data together with previous HERA data at lower Q^2, resultng in the extraction of flavour-separated parton densities of the proton using HERA data alone. ============================================================================== Author : ZEUS Collab. Type : Experimental Diffraction in ep collisions (Zeus) HERA allows the study of a wide range of inclusive and exclusive diffractive processes, many of which are amenable to perturbative approaches within QCD. New results are presented on a wide range of such processes. ============================================================================== Author : D0 Collab. (Don Lincoln) Type : Experimental Recent Run II QCD Results from D0 (including diffraction) ============================================================== Author : HERMES Collab. (Avetik Airapetian - Michigan) Type : Experimental Vector Meson Production at HERMES Recent HERMES measurements are presented on the diffractive slopes of coherent and incoherent part of the cross section for the exclusive diffractive production of $\mathbf \rho^0$'s,$\phi$'s. Based on data taken with a variety of targets, $^{1}H$, $^{2}H$,$^{3}He$,$^{14}N$, $^{20}Ne$ and Krypton, the method to extract the coherent to incoherent cross section ratios in dependence of the coherence length $l_{coh}$ and momentum transfer $Q^2$ will be presented. These measurements provide important information about interaction of quark-antiquark pairs with nuclear medium. Using the $^{2}H$ and $^{14}N$ targets, the nuclear transparency and coherent crossection ratio of $\mathbf \rho^0$ production has been measured versus coherence length and $Q^2$ . The data have been investigated on a possible onset of color transparency and are compared with recent theoretical predictions. ============================================================================= Author : OPAL Collab. (Balazs Ujvari) Type : Experimental Total Hadronic Cross-Section of Photon-Photon Interaction at LEP OPAL Collaboration The total hadronic cross-section for the interaction of real photons, gamma-gamma->hadrons, is measured for gamma-gamma invariant mass 20 e+e- gamma* gamma* -> e+e- hadrons using a luminosity function for the photon flux together with form factors for extrapolating to real photons (Q^2=0GeV^2). The data were taken with the OPAL detector at LEP at e+e- centre-of-mass energies from 189 to 209GeV. ============================================================================= Author : Martin Block (Northwestern University) Type : Theory A GLOBAL TEST OF FACTORIZATION FOR NUCLEON-NUCLEON, GAMMA P AND GAMMA GAMMA SCATTERING. ============================================================================= Author : Yogendra Srivastava Type : Theory Total Cross Sections and Bloch-Nordsieck Resummation An impact parameter representation for soft gluon radiation is applied to obtain both the initial decrease of total cross-sections as well as the later rise with energy . The non-perturbative soft part of the eikonal includes only limited low energy gluon emission and leads to the initial decrease in the cross- section. On the other hand, the rapid rise in the hard, perturbative jet part of the eikonal is tamed into the experimentally observed mild increase by soft gluon radiation whose maximum energy rises slowly with energy. ============================================================================= Author : Giulia Pancheri Type : Theory Photon total cross-sections It is planned to show how soft gluon resummation allows for better description of the photon-photon total hadronic cross-section. The technique is applied to photoproduction data as well. ======================================================================== Author : Stanislav Dubnicka Type : Theory Sum rules for proton, neutron and deuteron total photoproduction cross-sections Utilizing analytic prperties of the forward Compton scattering amplitudes on protons, neutrons and deuterons, first, one can derive sum rules bringing into relations the corresponding electromagnetic form factors with differential cross-sections of electroproduction processes on protons, neutrons and deuterons. Then for the case of small transferred momenta the derived sum rules can be transformed into the relations between charge radii and magnetic moments of the considered particles on one side and the integrals over the corresponding total photoproduction cross-sections on the other side. ============================================================================ ============================================================================ ============================================================================ Session IV : Vacuum Polarization Convenor(s) : Summary : KLOE(1), theory 1) ======================================================================== ======================================================================== ======================================================================== Author : KLOE Collab. (Speaker : S. Mueller) Type : Experimental Measurement of the e+e- hadronic cross section at Daphne via radiative return The Kloe experiment aims at a measurement of the low energy e+e- hadronic cross section with a precision such to improve the estimate of the hadronic contribution to the muon magnetic anomaly. Since the energy of the Daphne storage rings is fixed at the Phi-meson mass the scan of the lower c.m energies can be done only exploiting the Initial State Radiation (ISR). This implies a very accurate knowledge of ISR and other radiative effects. In fact the measurement is not limited by statistics but by systematic effects due to the correct modelling of the process and to the estimate of the experimental detection efficiencies. The current status of the anlysis and preliminary results from the 2001/2002 data collection will be presented. ====================================================================== Author : Gilberto Colangelo Type : Theory The Hadronic Vacuum Polarization Contribution to g-2 ============================================================================ ============================================================================ ============================================================================ Session V : Charm and beauty production Convenor(s) : F. Kapusta Summary : D0(1), L3(2), DELPHI(1), ALEPH (1), HERA (2), theory(1) ============================================================================ ============================================================================ ============================================================================ Author : ZEUS Collaboration Type : Experimental Charm production at HERA (Zeus) New results on charm-jet cross sections in photoproduction are produced which demonstrate a large cross section for "charm excitation"-like processes. The charm fragmentation function is measured and the fragemetation fractions of many charmed hadrons are determined. In addition, new results on charm production in DIS are presented and compared to next-to-leading order QCD calculations using the latest fits to the gluon distribution in the proton. ============================================================================ Author : H1 Collaboration Type : Experimental Beauty in ep collisions (H1) The first observations of beauty production in deep inelastic ep scattering are described and measurements of the photoproduction of beauty presented. Hadrons with b flavour are detected through their semi-leptonic decays. Cross sections are extracted and compared with the expectations of NLO QCD calculations and with the predictions of QCD based models. ============================================================================ Author : D0 Collaboration (Harald Fox) Type : Experimental B-Physics at the Tevatron ========================================================================== Author : ALEPH Collaboration Type : Experimental Measurement of the inclusive D*+- production in gamma-gamma collisions at LEP The inclusive production of D$^{*\pm}$ mesons in two-photon collisions is measured with the ALEPH detector at $\epem$ centre-of-mass energies from 183$\unit{GeV}$ to 209$\unit{GeV}$. A total of $360 \pm 27$ D$^{*\pm}$ meson events were observed from an integrated luminosity of 699\unit{pb^{-1}}$. Contributions from direct and single-resolved rocesses are separated using the ratio of the transverse momentum $p_{\rm t}^{\rm D^{*\pm}}$ of the D$^{*\pm}$ to the visible invariant mass $W_{\mathrm{vis}}$ of the event. Differential cross sections of D$^{*\pm}$ production as functions of $p_{\rm t}^{\rm D^{*\pm}}$ and the pseudorapidity $|\eta^{\rm D^{*\pm}}| $ are measured in the range $ 2\unit{GeV}/c < p_{\rm t}^{\rm D^{*\pm}} < 12\unit{GeV}/c $ and $ |\eta^{\rm D^{*\pm}}| < 1.5 $. They are compared to next-to-leading order (NLO)perturbative QCD calculations. The extrapolation of the integrated visible D$^{*\pm}$ cross section to the total charm cross section, based on the Pythia Monte Carlo program, yields $ \sigma (\epem \to \epem \ccbar)_ {=197\unit{GeV}} = 731 \pm 74_{\mathrm{stat}} \pm 47_{\mathrm{syst}} \pm 157_{\mathrm{extr}} \unit{pb} $. Reference : hep-ex/0301034 ========================================================================== Author : L3 Collaboration Type : Experimental Inclusive D*+- Production in Two photon Collisions at LEP L3 Collaboration Inclusive ${\mathrm{ D^{*\pm}}}$ production in two-photon collisions is studied with the L3 detector at LEP, using 683 $\mathrm{pb^{-1}}$ of data collected at centre-of-mass energies from 183 to 208 GeV. Differential cross sections are determined as functions of the transverse momentum and pseudorapidity of the ${\mathrm{ D^{*\pm}}}$ mesons in the kinematic region ${1~\mathrm{GeV} < P_T < 12~\mathrm{GeV}}$ and ${\vert \eta \vert < 1.4}$. The cross sections $ \sigma({\mathrm{ e^{+}e^{-} \rightarrow e^{+}e^{-}D^{*\pm}X}})$ in this kinematical region is measured and the $\sigma({\mathrm{ e^{+}e^{-} \rightarrow e^{+}e^{-}c\bar{c}X}})$ cross section is derived. The measurements are compared with next-to-leading order perturbative QCD calculations. Reference : Phys.Lett. B 535 (2002) 59 ========================================================================== Author : DELPHI Collaboration (Wilfrid Da Silva) Type : Experimental Beauty production in two photon collisions at LEP with DELPHI b\bar{b} production in two-photon collisions has been studied with the DELPHI detector at LEP. The total cross section has been measured using semileptonic b decays from LEP2 data. Comparisons to existing QCD predictions have been done. ========================================================================== Author : L3 Collaboration Type : Experimental Measurement of the Cross-section for Open Charm and Beauty Production in gamma-gamma Collisions at root(s)=189-209 GeV L3 Collaboration The production of c and b quarks in $\mathrm{\gamma\gamma}$ collisions is studied with the L3 detector at LEP data collected at centre-of-mass energies from 189 GeV to 209 GeV. Hadronic final states containing c and b quarks are identified by detecting electrons or muons from their semileptonic decays. The cross sections $\mathrm{\sigma(e^{+}e^{-}\rightarrow e^{+}e^{-}c \bar{c} X)}$ and $\mathrm{\sigma(e^{+}e^{-}\rightarrow e^{+}e^{-}b \bar{b} X)}$ are measured and compared to next-to-leading order perturbative QCD calculations. The cross section of b production is in excess of the QCD prediction. ========================================================================== Author : Magno Machado Type : Theory Heavy quark production at photon-proton(photon) in the saturation approach. Abstract: We report on the calculations considering the color dipole picture and semihard approach taking into account the saturation model applied to heavy quark photoproduction and two-photon processes. ========================================================================== ========================================================================== ========================================================================== Session VI : Resonances and exclusive processes Convenor : J.H.Field Summary : KLOE(1),FOCUS(3), CLEO(2), BaBar(3),L3(7),HERA (2), BELLE(3), OPAL(2), DELPHI(2), ALEPH(1), theory (7) ======================================================================== ======================================================================== ======================================================================== Author : E835 Collab. (Claudia Patrignani) Type : Experimental Experiment E835 at FNAL has finished his second period of data taking and is now analyzing the copious data sample collected at chi_c(1P) and psi(2S) states. Preliminary results will be presented on psi(2S) branching ratios to final states including a J/psi meson and on the angular distribution of p bar p-> psi(2S)-> e+e-. ======================================================================== Author : ZEUS Collab. Type : Experimental Vector meson production (Zeus) Measurements of vector mesons at HERA allow a detailed study of diffractive and non-diffractive production mechanisms, fragmentation and decay branching ratios. New results are presented on hadronic resonance measurements. ======================================================================== Author : H1 Collab. Type : Experimental Multi-lepton production in ep collisions (H1) Events containing pairs of isolated muons at high invariant masses have been detected in electron-proton collisions at HERA. Measurements of these muon pair events are compared to Standard Model predictions. The dominant source is found to be photon-photon collisions. Multi-electron production has also been studied at high transverse momentum. Good overall agreement is found with the Standard Model predictions, again dominated by photon-photon interactions. Several events are observed with a di-electron mass above 100 GeV, a region in which the Standard Model prediction is low. ======================================================================== Author : Igor Anikin Type : Theory Exclusive gamma-gamma* -> rho rho We present the theoretical estimation for the cross-section of production of two vector mesons. We focus on the $\gamma \gamma^*\to\rho^0\rho^0$ which resently has been observed at LEP in the right kinematic domain. The spin one nature of the $\rho$-meson leads to some novel and interesting features. The compatibility of our anlysis with the experimental data is discussed. ======================================================================== Author : Rafael Escribano Type : Theory Ccalar exchange in phi->pi0pi0gamma and pi0etagamma decays The complementarity between Chiral Perturbation Theory and the Linear Sigma Model is exploited to study scalar meson exchange in $V\rightarrow P^0 P^0\gamma$ decays. The recently reported experimental data on $\phi\rightarrow\pi^0\pi^0\gamma$, $\phi\rightarrow\pi^0\eta\gamma$ can be satisfactorily accommodated in our framework ======================================================================== Author : Alexei Prokudin Type : Theory The Pomeron In Exclusive Vector Meson Production An earlier developed model for vector meson photoproduction, based on a dipole Pomeron exchange, is extended to electroproduction. Universality of the non linear Pomeron trajectory is tested by fitting the model to ZEUS and H1 data as well as to CDF data on $\bar pp$ elastic scattering. ======================================================================== Author : KLOE Collab. (Speaker: Camilla Di Donato) Type : Experimental Measurement of the Phi meson radiative decays into scalars and pseudoscalars mesons. The Kloe experiment has measured the radiative decays of the Phi meson into pi0, eta and eta'(958); these measurements are relevant to assess the mixing in the pseudoscalar nonet as well as to evaluate the gluon content in the eta'(958). Moreover also the radiative decays into pi0 pi0 gamma and eta pi0 gamma have been measured. These decays are dominated by the final states f0(980) and a0(980). The measurement of the branching ratios and of the pi0-pi0 or eta-pi0 invariant mass spectrum helps to understand the controversial nature of the above scalar mesons. ======================================================================== Author : FOCUS Collab. (Ryan Mitchell - Tennessee) Type : Experimental Light quark photoproduction results from FOCUS We present recent results from photoproduction experiment FOCUS-E831 at Fermilab on the spectroscopy of light quark states. Results include first observation of a KK(1750) state, and evidence for a state in the six-pion system at 1.9GeV. ======================================================================== Author : FOCUS Collab. (Laura Edera - Milano) Type : Experimental Light quark spectroscopy results from Dalitz plot analysis of charm decays in FOCUS The FOCUS-E831 experiment at Fermilab studies production and decays of charmed mesons and baryons. During the last Fixed Target run, FOCUS collected one million fully reconstructed charm decays. New results on light quark spectroscopy from Dalitz analysis of charm meson decays will be presented. ======================================================================== Author : FOCUS Collab. (Erik Gottschalk - Fermilab) Type : Experimental New results on diffractive photoproduction from FOCUS The FOCUS-E831 experiment at Fermilab studies production and decays of charmed mesons and baryons. Thanks to a dedicated trigger FOCUS has also collected a large sample of hidden charm mesons decaying to muon or electron pairs. We show preliminary results on diffractive photoproduction of charmonia, including first evidence for production of Psi(3770). ========================================================================= Author : CLEO Collab. Type : Experimental Search for $\eta_{c}^{\prime}$ Resonance in $\gamma\gamma$ Fusion at CLEO A knowledge of the hyperfine (spin singlet--triplet) splitting is important for the understanding of the spin--spin interaction in quarkonia. The existing knowledge is limited to the 115$\pm$2 MeV splitting between $J/\psi$(1$^{3}S_{1}$) and $\eta_{c}$(1$^{3}S_{0}$). It is important to find out the magnitude of the corresponding splitting between the radial excitations $\psi^{\prime}$(2$^{3}S_{1}$) and $\eta_{c}^{\prime}$(2$^{3}S_{0}$), which sample the confinement dominated part of the $c\bar{c}$ potential. Several unsuccessful searches for $\eta_{c}^{\prime}$ have been reported in the literature. Recently, the BELLE Collaboration presented evidence for $\eta_{c}^{\prime}$ in the decay B~$\rightarrow~K(\eta_{c}^{\prime})\rightarrow K(K_{s}K^{\pm}\pi^{\mp})$, and reported $M(\eta_{c}^{\prime})=3654\pm 6(stat)\pm 8(syst)$ MeV. At CLEO we have searched for $\eta_{c}^{\prime}$ in $\gamma\gamma$ fusion in 13.4 fb$^{-1}$ of $e^{+}e^{-}$ annihilation data at Y(4S) and its vicinity. Our sensitivity for the detection of $\eta_{c}^{\prime}$ in the reaction $\gamma\gamma \rightarrow \eta_{c}^{\prime}\rightarrow K_{s}K^{\pm}\pi^{\mp}$, which we study, is expected to be $\approx$0.3 of that for $\eta_{c}$ whose observationin the same reaction was reported by CLEO earlier. Preliminary results will be presented. ======================================================================== Author : CLEO Collab. Type : Experimental Preliminary Results on $\gamma\gamma \rightarrow K_s K^\pm \pi^\mp$ from CLEO We analyzed 13.8 ${\rm fb^{-1}}$ of the integrated $e^+e^-$ luminosity collected at 10.6 GeV center-of-mass energy with the CLEO II and II.V detectors to study exclusive two-photon production of single hadronic resonances. We searched for hadrons decaying into $K_s K^\pm \pi^\mp$ when both leptons remain undetected. In this analysis we studied the detection efficiency and evaluated systematic errors using independent data samples. We estimated 90\% CL upper limits on the products of the two-photon partial widths of (pseudo)scalar hadrons with masses below 1.7 ${\rm GeV/c^2}$ and their branching fractions into $K_s(\pi^+\pi^-)K^\pm\pi^\mp$. Our preliminary results are marginally consistent with the first observation of $\eta(1440)$ in two-photon collisions by the L3 experiment ========================================================================= Author : BABAR Collab. (Jamie Boyd - University of Bristol) Type : Experimental Charmonium production at Babar We present three analyses on charmonium production using 89 inverse femtobarns of e^+ \e^- collision data collected by the BaBar detector at the PEP-II storage ring operating at the Upsilon(4s) at SLAC. A precise measurement of the eta_c total width is obtained from the study of the invariant Ks K^+ pi^- mass spectrum for a sample of eta_c mesons produced in two-photon interactions. The total width of the J/psi meson is measured using initial state radiation, e^+ e^- -> mu^+ mu^- gamma events. Finally branching fraction measurements for the exclusive B meson decays B^0 -> J/psi p p-bar and B^+ -> J/\psi p Lambda-bar are presented. ======================================================================== Author : L3 Collab. Type : Experimental Resonances in omega-gamma Final State in Two-photon Collisions at LEP L3 Collaboration The omega-gamma final state is studied with the L3 detector at LEP, at center-of-mass energies from 183 Gev to 209 GeV. The mass spectrum is dominated by the eta'(958) and by an enhancement around 1.295 GeV, attributed to the eta(1295). ========================================================================= Author : L3 Collab. Type : Experimental Two-photon width of the etac and search for the etab L3 Collaboration The two-photon width of the $\eta_c$ is measured with the L3 detector at LEP using data collected at centre-of-mass energies from 183 GeV to 209 GeV. Several etac decay channels are analysed. The same data are used to search for the pseudoscalar meson $\eta_b$ and an upper limit for its two-photon width is derived. ========================================================================= Author : DELPHI Collab.(Valeri Pozdniakov) Type : Experimental "Production of light resonances in two-photon collisions" The f_2(1270), f_2'(1525) and f2(2010) resonances are observed, in two-photon interactions at LEP2, from their pi+pi-/K+K- decay modes . The data sample corresponds to a total integrated luminosity of 550 pb**(-1) collected by the DELPHI setup at centre-of-mass energies ranging from 189 GeV to 202 GeV. The ratio of the two-photon widths Gamma(f_2(1270)) / Gamma(f_2(1525)) and Gamma(f_2(2010) are measured. ========================================================================= Author : DELPHI Collab. (Anatoli Sokolov) Type : Experimental "Search for eta_b in two-photon collisions with the DELPHI detector" The pseudoscalar meson eta_b has been sought in two-photon interactions at LEP2. The data sample corresponds to a total integrated luminosity of 630 pb**(-1) collected at centre-of-mass energies ranging from 189 GeV to 209 GeV. Preliminary results on candidate events will be presented and discussed. ======================================================================== Author : OPAL Collab. Type : Experimental Production of chi_c2 Mesons in Photon-Photon Collisions at LEP for Centre-of-mass energies up to 209 GeV. OPAL collaboration The chi_c2 meson is a Charmonium bound state with the spin-parity of 2++. Its prodcuction in collisions of two colliding quasi-real photons is studied using the OPAL detector at LEP. The chi_c2 is reconstructed through its de-excitation to a photon and a J/psi, observed via the leptonic decay channel. The decay width of the chi_c2 to two photons is measured. Our result is in agreement with previous experimental results and theoretical calculations. ========================================================================= Author : Nicola Fabiano Type : Theory Theoretical determination of eta_b's electromagnetic decay We discuss the theoretical predictions for the two photon decay width of the pseudoscalar etab meson. Predictions from potential models are examined. It is found that various models are in good agreement with each other. Results for etab are also compared with those from Upsilon data through the NRQCD procedure. ========================================================================= Author : Sergo Gerasimov Type : Theory Sum Rules for Two-Photon Decay Widths of Meson Resonances and Quark-Gluon Configuration Structure of Low-Lying Scalar Mesons In the context of the quark-hadron duality sum rules, the relations for two-photon decay widths of scalar mesons will be reported, which are also based on diagonalization of a mass-matrix, including the mixing of isoscalar meson states of two scalar nonets and presumably existing, in approximately the same mass region, a scalar glueball state. The comparison will be given with available experimental information and the results of some other model approaches. ======================================================================= Author : L3 Collab. Type : Experimental Measurement of Exclusive rho-rho Production in Two Photon Collisions at High Q^2 at LEP L3 Collaboration Measurements by the L3 experiment at LEP of $\rho ^0\rho ^0 $ production in two-photon collisions, involving a single highly virtual photon are reported. The data were collected at centre--of--mass energies $89 \GeV < \sqrt{s} < 209 \GeV $ with a total integrated luminosity of $855~ pb ^{-1}$. The cross sections of the process $ \gamma \gamma^* \rightarrow rho^0\rho ^0 $ is determined as a function of the photon virtuality and the two-photon centre--of--mass energy, in the kinematic region $1.2 \GeV^2 < Q^2< 30 \GeV^2$ and $1.1 \GeV < \mathrm{W_{\gamma\gamma}} < 3 \GeV$. ======================================================================= Author : L3 Collab. Type : Experimental Rho-rho Production by Real Photons at LEP L3 Collaboration The reactions $\gamma\gamma \rightarrow \pi^+\pi^-\pi^+\pi^- $ and $\gamma\gamma \rightarrow \pi^+\pi^0\pi^-\pi^0 $ are studied with the L3 detector at LEP. The data sample was collected by L3 at center-of-mass energies from 161 GeV to 209 GeV. A spin-parity analysis of the $\rho ^0\rho ^0 $ and $\rho ^+\rho ^- $ systems for Wgg < 3 GeV shows the dominance of $J^P=2^+$ and helicity 2 in the first case. A contribution of $J^P=0^+$ is also observed whereas contributions of negative parity states and $(J^P,J_z)=(2^\pm,0)$ are found to be negligible. For the mass region greater than 2.7 GeV, the $f_2(1270)$ meson is also observed in the data as well as the $\rho$. ======================================================================= Author : ALEPH Collab. (Alexander Finch) Type : Experimental Exclusive production of Mesons at LEP. The exclusive production of Pion and Kaon pairs at LEP has been measured. The result is compared to QCD predictions. ======================================================================= Author : BELLE Collab. (Sadaharu Uehara) Type : Experimental Experimental studies of pi+pi-/K+K- production in two-photon collisions Production of $\pi^+\pi^-$ and $K^+K^-$ pairs in two-photon collisions has been studied using 66~fb$^{-1}$ of data collected with the Belle detector at the asymmetric-energy $e^+e^-$ collider, KEKB. The cross sections for these processes have been measured in the two-photon mass range, 2.5 - 4.1 GeV, and the c.m.-anglular range of the final-state meson $|\cos \theta^*| < 0.6$. The energy and angular dependence of the cross sections as well as the ratio of the $K^+K^-$ to $\pi^+\pi^-$ cross sections are compared to QCD predictions. ======================================================================= Author : BELLE Collab. (Augustine E. Chen, National Central University) Type : Experimental Hyperon Productions in Two-photon Collisions at Belle From ~ 90 fb-1 data collected at Belle, preliminary results of gamma gamma--> Lambda-anti-Lambda pair and gamma gamma --> Sigma-0 anti-Sigma-0 pair cross sections will be presented. The decay channels of Sigma-0 --> Lambda + gamma and Lambda --> Proton + pion- (and their charge conjugates) are used in this analysis. Due to the softness of gamma in Sigma-0 --> Lambda + gamma decay, full reconstruction of gamma gamma --> Sigma-0 anti-Sigma-0 pair becomes extremely difficult. Therefore the observed Lambda anti-Lambda pairs contain a geat portion of Sigma-0 anti-Sigma-0 pairs with missing gamma. We rely on Monte Carlo simulation to extract the cross sections of gamma gamma --> Lambda anti-Lambda and gamma gamma --> Sigma-0 anti-Sigma-0 from the observed ones. Estimation of systematic errors is still under investigation. ======================================================================= Author : BELLE Collab.(Chen-Cheng Kuo - National Central University, Taiwan) Type : Experimental Studies of $\gamma\gamma\to p\overline{p}$ production at Belle The $\gamma\gamma\to p \overline{p}$ events produced by the photon-photon collisions, where the two photons are emitted from the colliding $e^+ e^-$ beams of the accelerator KEKB, are collected by the Belle detector. A data sample corresponding to a toal integrated luminosity of $89$ $fb^{-1}$ is analyzed. The cross-sections and the differential cross-sections for $\gamma\gamma\to p \overline{p}$ are measured in the two-photon invariant mass range from 2 to 4 $GeV/c^2$. Better statistics are achieved, in comparison with previous measurements. This improvement can help to the test of theoretical predictions. ======================================================================== Author : L3 Collab. Type : Experimental Lambda and Sigma zero pair production in Two Photon Collisions at LEP L3 Collaboration Strange baryon pair production in two-photon collisions is studied with the L3 detector at LEP. The analysis is based on data collected at $e^+e^-$ centre-of-mass energies from 91 GeV to 208 GeV, corresponding to an integrated luminosity of 844 pb$^{-1}$. The processes $\gamma \gamma \rightarrow \Lambda \overline{\Lambda}$ and $\gamma \gamma \rightarrow \Sigma^0 \overline{\Sigma}\,\!^0$ are identified. Their cross sections as a function of the $\gamma \gamma$ centre-of-mass energy are measured and results are compared to predictions of the quark-diquark model. Reference : Phys.Lett.B 536(2002)24 ======================================================================== Author : L3 Collab. Type : Experimental Proton Antiproton Pair Production in Two Photon Collisions at LEP L3 Collaboration The reaction $e^{+}e^{-}\rightarrow e^{+}e^{-}p \bar{p} $ is studied with the L3 detector at LEP. The analysis is based on data collected at $e^{+}e^{-}$ center of mass energies from 183 GeV to 209 GeV. The $\gamma \gamma \rightarrow p \bar{p} $ cross section is measured as a function of the two-photon center of mass energy, from 2.1 GeV to 4.5 GeV and the proton production angle. The results are compared to the predictions of the three-quark and quark-diquark models. ======================================================================== Author : L3 Collab. Type : Experimental Delta++ and Delta-- Production in two-photon collisions at L3 at LEP L3 Collaboration The reaction $e^{+}e^{-}\rightarrow e^{+}e^{-} \Delta^{++} \Delta{--} $ is studied with the L3 detector at LEP. The analysis is based on data collected at $e^{+}e^{-}$ center of mass energies from 183 GeV to 209 GeV, The $\gamma \gamma \rightarrow \Delta^{++} \Delta{--}$ cross section is measured as a function of the two-photon center of mass energy. The results are compared to the predictions of the three-quark and quark-diquark models. ======================================================================== Author : OPAL Collab. Type : Experimental Measurement of the Cross-Section for the Process GammaGamma -> Ppbar at sqrt(s)_ee=183-189 GeV at LEP OPAL collaboration The exclusive production of proton-antiproton pairs in the collisions of two quasi-real photons had been studied using data taken at sqrt(s)_ee=183 GeV and 189 GeV with the OPAL detector at LEP. Results are presented for Ppbar invariant masses, W, in the range 2.15 W< <3.95 GeV. The cross-section measurements are compared with previous data and with recent analytic calculations based on the quark-diquark model. ====================================================================== Author : Markus Diehl Type : Theory Exclusive two-photon annihilation at large energy or large virtuality Two-photon annihilation into meson or baryon-antibaryon pairs admits a mechanism where the final state originates from soft hadronization of a single quark-antiquark pair. Although subleading at asymptotically large energies, this 'handbag' mechanism may dominate the process in experimentally relevant kinematics, where the leading-twist hard scattering contribution gives cross sections quite below the data. I discuss the physics of the handbag mechanism and possibilities to test it experimentally. The same mechanism dominates the annihilation gamma* gamma -> pi^0 at large photon virtuality. This process to date provides one of the cleanest contraints for the pion wave function, and investigation of gamma* gamma* -> pi^0 shows that further constraints can be obtained when one of the photons is strongly and the other weakly off-shell. When the photons have large virtualities of similar size, the sensitivity to the wave function disppears and one obtains a QCD prediction only in terms of alpha_s and the pion decay constant, if similar status as the Bjorken sum rule in deep inelastic scattering or the inclusive cross section for e+e- -> hadrons. ======================================================================= Author : Anna-Zuzana Dubnickova Type : Theory A polarization phenomena in gama-gama collisions into one and two charged lepton pairs Peripheral photon-photon collision processes into one pair of charged particles with emission of the hard photon and into two different pairs of charged particles, considering the most preferable kinematics and effects of circular and linear polarization of initial photons, are investigated. ==================================================================== ==================================================================== ==================================================================== Session VII : Related Topics Convenor : V. Khoze Summary : OPAL(1), theory(5) ====================================================================== ====================================================================== ====================================================================== Author : OPAL Collab. (Tatsuo Kawamoto) Type : Experimental Test of non-commutative QED in the process e+e -> photon photon at LEP OPAL collaboration (Please note that the speaker for this topic can only attend the conference from the 9th of April) Non-commutative QED would lead to deviations from the Standard Model depending on a new energy scale Lambda_NC and a unique direction in space defined by two angles eta and xi, where eta is the angle between the unique direction and the rotation axis of the earth. The predictions of such a theory for the process e+e -> photon photon are evaluated for the specific orientation of the OPAL detector and compared to the measurements. Distributions of the polar and azimuthal scattering angles are used to extract limits on the energy scale Lambda_NC depending on the model parameter eta. At the 95% confidence level Lamda_NC is found to be larger than 141 GeV for all eta and xi. It is shown that the time dependence of the total cross-section could be used to determine the model parameter xi if there were a detectable signal. These are the first limits obtained on non-commutative QED from an e+e- collider experiment. ====================================================================== Author : Francisco Yndurain Type : Theory How precise are chiral calculations of pi-pi scattering? We calculate the combination $2a_0^{(0)}-5a_0^{(2)}$ (the Olsson sum rule) and the scattering lengths and effective ranges $a_1$, $a_2^{(I)}$ and $b_1$, $b_2^{(I)}$ using, at low energy, the phase shifts for $\pi\pi$ scattering obtained by Colangelo, Gasser and Leutwyler from the Roy equations and chiral perturbation theory. We find mismatch, in some cases at the level of several standard deviations, irrespective of the high energy behaviour assumed. We discuss possible reasons for this inconsistency, in particular in connection with an alternate set of phase shifts. ======================================================================== Author : Valeri Khoze Type : Theory PHOTON - EXCHANGE PROCESSES AT HADRON COLLIDERS The rich structure of photon-exchange processes at hadron colliders is discussed. In particular,we consider central vector meson,W-boson and lepton pair production. Special attention is payed to the photon-photon fusion reactions at the LHC. We also address the issue of the rapidity gap survival in photon-mediated processes. ======================================================================== Author : Alexey Pak Type : Theory Quartic gauge boson anomalous couplings in the process $\gamma\gamma\to WW$ Contributions of CP-conserving and CP-violating anomalous couplings of gauge bosons are studied in the process $\gamma\gamma\to WW$ in respect to the program of the future linear colliders. Several different modes of W decay are considered. For the muon or electron decay final states of W we consider both muons (electrons) from W decay and those from cascade $W\to\nu\tau\to\mu+neutrinos$ channel (forgotten in many previos papers). The sensitivity to anomalous parameters in future experiments is estimated. Possible sources of background are discussed. Features of using two numerical calculations packages (CompHEP and WHIZARD) are discussed. ======================================================================== Author : Valery Serbo Type : Therory New method for calculating helicity amplitudes of jet--like QED processes for high--energy colliders nelastic QED processes, the cross sections of which do not drop with increasing energy, play an important role at high--energy colliders. They present an essential background and determine the beam life time. On the other hand, all these processes can serve as the calibration processes for monitoring of luminosity and polarization of colliding beams. We consider them in the region of small scattering angles $ m/E \lesssim \theta \ll 1$, which yields the dominant contribution to their total cross sections. A new effective method is presented for calculating the helicity amplitudes of these processes. Its basic idea --- the replacing of numerators of lepton propagators by vertices involving real leptons --- is similar to the well--known equivalent-lepton method. Some common properties for all jet-like processes are found and we discuss their origin. As an example, we consider in detail processes with emission of real photons. The analytical expressions for those amplitudes up to $e^8$ are derived omitting only terms of the order of $m^2/E^2,\, \theta^2$, $\theta m/E$ and smaller. The helicity amplitudes are presented in a compact form in which large compensating terms are already canceled. Based mainly on the paper: C.~Carimalo, A.~Schiller and V.G.~Serbo, Eur. Phys. J. C 23 (2002) 633--649 and some recent results. ======================================================================= Author : Ilya Ginzburg Type : Theory Charge asymmetry of muons in processes $\gamma\gamma\to\mu^+\mu^-+ neutrals$ with polarized photons. In the QED process like $\gamma\gamma\to W^+W^-$ depends only on the product of photon helicities while polarizations of $W$'s depend on separate polarizations of incident photons. In their decay polarization of $W$ transforms to the momentum distribution of muon. The result is charge asymmetry of muons related to the initial photon helicities. This charge asymmetry in SM is studied in detail to have a key for using of similar asymmetry for discovery of new physics. ======================================================================== ======================================================================== ======================================================================== Session VIII : Future Programs Convenor : A. de Roeck Summary : LC, VEPP2000, D0, SPLC, Photon collider ======================================================================== ======================================================================== ======================================================================== Author : Valery Telnov Type : Experimental Measurement of gamma-gamma and gamma-electron luminosies and polarizations at photon colliders. ======================================================================== Author : A. de Roeck Type : Experimental + Theory Two Photon Physics at Future Linear Collider ======================================================================== Author : Sergei Serednyakov Type : Experimental Physical Program for the new VEPP-2000 Collider The program of the experiments at the new VEPP-2000 e+e- collider being constructed in Novosibirsk is discussed. The CM energy is from 0.4 to 2.0 GeV, the luminosity is in the range 10**30 - 10**32 cm**-2sec**-1. The main item in the program is the careful study of the e+e- annihilation into hadrons cross section and particular hadronic production channels. Another important point is the measurement of the nucleons formfactors at the threshold in the reaction e+e--> p pbar, n nbar. Two detectors CMD-3 and SND are being upgraded for experiments at VEPP-2000. Also discussed are specific problems of soft antineutron detection with SND detector. ======================================================================== Author : D0 Collaboration Type : Experimental Recent Results on New Phenomena searches and Prospects for Higgs searches at the Tevatron ======================================================================== Author : Jeffrey Gronberg Type : Experimental A photon collider facility based on the Stanford Linear Collider The technology for photon collider experiments at a future electron-positron linear collider is maturing. It has become feasible to consider the revival of the Stanford Linear Collider (SLC) and it's conversion to a photon collider facility both as a technology test for a future linear collider experiment and as a physics experiment in it's own right. We present an estimate of the cost and schedule for such a facility, it's expected luminosity, and a preliminary analysis of the production of \eta_b and it's reconstruction in the decay mode to hadrons. ======================================================================= ======================================================================= ======================================================================= Summary Talks : --------------- Alex Finch : Experimental Summary Rohini Godbole : Theoretical Summary ======================================================================== ======================================================================== ========================================================================