Measurement of h® p0gg decay at KLOE.

Biagio Di Micco

Università degli Studi di Roma Tre

h production and Br measurements in past experiments;

h production mechanism @ KLOE;

h®p0 gg analysis description;

KLOE preliminary result compared with theoretical predictions.

h production and Br measurements in past experiments

p- + p ® h + n

(CERN, Brookhaven, GAMS, Crystal Ball)

p+ + d ® p + p + h (67)

p+ + p ® p+ + p +h (67,69)

K- + p ® L + h (70 AGS)

p+ + n ® h + p (71)

p- + n ® p- + n + h (80)

f ®hg (SND 01)

Most recent measurements

AGS/Crystall Ball

Phys. Lett. B 589 (2004) 14

GAMS2000

Nuovo Cimento A 71 (1982) 497

SND – Novosibirsk

Nucl. Phys. B600 (2001) 3

p- + p ® h + n

Nh = 3´107

f ® h g

Nh = 2.6´105

p- + p ® h + n

Nh = 6´105

Br(h®p0 gg)

(7.2  1.4)10-4

< 8.4 10-4

(2.7  0.9stat  0.5syst)10-4

GAMS:

evidence of the signal

L

Data

Data -2

Data - 3

L3

Data - 2 - 3

120  40 evts.

Crystall Ball:

evidence of the signal

GAMS – CB comparison

s = M = 1.02 GeV

()  3.3 b

e+e- in two separate rings with crossing angle 25mrad at IP (small  momentum p13MeV)

DEAR

The DAFNE apparatus

The KLOE detector

Electromagnetic Calorimeter (EMC)

Fine sampling Pb (0.5 mm thick) / Scifi (1 mm ø)

Hermetical coverage

High efficiency for low energy photons

E/E = 5.7%/E(GeV)

t = 54ps/E(GeV)

Central drift chamber (DCH)

Large detection volume

Uniform tracking and vertexing in all volume

Helium based gas mixture

v = 1 mm pt /pt= 0.5%

r, =200 m z = 2 mm

Quadrupoles’ calorimeter (QCAL)

Pb/Sci tile calorimeter covering quads inside KLOE











SL





BR(%)

Decay

Lint ~ 450 pb-1

Nf ~ 1.5´109

Nh ~ 1.9´107

2004 collected luminosity

Lpeack = 11´1031

Laverage = 8.3´1031

Lint = 750 pb-1

KLOE collected luminosity

2001+2002 integrated luminosity

2005 estimated luminosity

(until July)

Lint > 750 pb-1

> 5g

f ® h(®3p0)g

2 lost

1 lost – 1 merged

2 merged

h® p0gg @KLOE

5g

final sate

Background

< 5g + accidental

f ® h(®gg)g

f ® p0(®gg) g

e+ e-e+ e-(g), e+ e-gg

5g

f ® f0(®p0p0)g

f ® a0(®hp0) g

e+ e- ® w(®p0g)p0

f ®r0(®h g)g,r0(® p0g)g

The most energetic photon is in the main part of cases that coming from the f®hg decay (363 MeV)

before kinematic fit

after kinematic fit

We build the invariant mass m4g of the 4 least energetic photon to search for the signal.

DATA – MC comparison

DATA

MC

the p0 peak is well reproduced

mp(MC) = 134.93 ± 0.04 MeV/c2

mp(DATA) = 135.08 ± 0.07 MeV/c2

DATA-MC comparison of energy distribution

f® hgf

p0

E(gf) = 363 MeV

p0gg

h

E(gf) = 363 MeV

f® hgf

gg

accidental clusters

Signal and accidental background topologies

< 5 g + accidental rejection

f ® h(®gg)g

f®p0(®gg) g

Inclusive energy after kinematic fit

DATA

MC

E> 20 MeV

qg > 21°

p0

f® hgf

p0 p0 p0

7g

p0

p0

g1

g2

rms, asimmetry are used to identify merged clusters

Merged clusters background topology

Merged cluster
identification

—— good

—— merged

barrel

endcap

DATA-MC comparison

—— DATA

------ MC

good-merged discrimination

Background composition

Background composition obtained by fitting mgg

distribution

Correction factors

0.704  0.008

1.07  0.04

0.4  0.1

2.9  0.3

1.50  0.09

0.68  0.04

0.76  0.06

 900 bins

c2 = 1.2

Background composition check

Correction factors obtained by the previous fit

Very nice reproduction of the w peak

w p0

p0g

Completely given by the 2 lost and 1 merged–1 lost normalization

5g rejection

f ® f0(®p0p0)g

f ® a0(®hp0) g

e+ e- ® w(®p0g)p0

f ®r0(®h g)g,r0(® p0g)g

Rejected vetoing the p0,h, w masses.

DATA-MC comparison of the S2 variables

Good DATA-MC agreement

m4g distribution for signal

and background

m4g distribution of the back-ground, obtained by the MC simulation.

m4g distribution of the signal, obtained by the MC simulation.

The signal content is evaluated by fitting the m4g distribution of the least energetic photons.

A binned likelihood approach is used, taking into account the finite size of MC statistic.

Fit result (preliminary)

The shape of background + signal after fit well reproduce the DATA.

Pbkg = 0.907  0.049

Psig = 0.093  0.031

NDATA = 735

Nbkg = 667  36 Nsig=6823

e(hp0gg) = 4.63  0.09 (only stat)

N(3p0) = 2288882

e(hp0p0p0) = 0.378  0.08syst 0.01stat

Statistical significance

68%

90%

95%

99%

Br dependence by the bin width

Bin width variation:

2 – 9 MeV

chosen bin width:

6 MeV

correction:

error:

-0.26  10-5

0.26  10-5

Br dependence by the lower cut on m4g

cut variation:

378 – 478 MeV

chosen cut:

426 MeV

correction:

error:

0.

0.44  10-5

Br dependence by the higher cut on m4g

cut variation:

570 – 720 MeV

chosen cut:

612 MeV

correction:

error:

0.

0.56  10-5

Preliminary result

Preliminary systematic error

bin width

low energy cut

high energy cut

Overall

0.26  10-5

0.44  10-5

0.56  10-5

0.8  10-5

correction

Fit result

bin width correction

Result

8.0  10-5

-0.26  10-5

7.7  10-5

Result

Br(h®p0gg) = (7.7  2.7  0.8)  10-5

Preliminary

Comparison with theoretical predictions

p6 calculation seems enough

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

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[2] J.N. Ng and D. J. Peters, Phys. Rev. D47 (1993) 4939

[3-4] L. Ametller, J. Bijnens, A. Bramon, F. Cornet, Phys. Lett. B276 (1992)

[5] S. Bellucci and C. Bruno, Nucl. Phys. B452 (1995) 626

[6] E. Oset, J. R. Pelaź and L. Roca, Phys. Rev. D67 (2003) 073013

[7] J. Bijnens, A. Fayyazuddin and J. Prades, Phys. Lett. B379 (1996) 209

[8] A. A. Belkov, A. V. Lanyov, S. Scherer, J. Phys. G 22 (1996) 1383

CB

GAMS

KLOE preliminary

KLOE and CB measurements are in disagreement with the GAMS observation;

The confirmation of KLOE result will indicate a succesfully explanation of the decay rate by the P6 ChPT ;

With 2004+2005 KLOE DATA the statistical error on the measurement can go down to 10% level.

Theoretical history

Merged clusters identification

Shower shape variables are used to identify merged clusters :

x,y,z,tmean =

rms

skewness

We find the distribution of this varibles (xk) for good clusters and for merged ones, then we build the likelihood:

and we use the ratio

as a discriminating variable:

mean

2004-10-27T18:14:05