Notes from Bologna Meeting 5-6 Oct 2006

General comment

We plan to requeste the generation in DC06 of event samples WITH CP violation [at least for Bd]

Proper Time

Discussion:

• To construct the propertime I need to know the mass. So I do build the observable PT/M that can be used in the simultaneous fit. To build it the LifeTimeFitter cannot be used [does not take into account properly the correlations].
• In the fit the observable becomes PT/M * M_nominal and e_PT/M * M_nominal [PDFtime]
• How to extract the propertime PDF from data? For signal and background? First of all we can use MC and check if there are any differences. If there are relevant differences we should take them into account. So far we can assume that signal and background have PT distributions that are consistent
• The e_PT distribution is consistently different for background and signal [but statistics is poor]. And different mass regions have different shapes. Can we afford e_PT/M as mass dependent? [Argh]
• What is the best mass window? If you enlarge toward low mass values you end up in a region with partially reconstructed decays that have a different e_PT/M...
• How to evaluate the bias that comes from the trigger?
• How to extract this information from data?
  • Use J/psi mumu? e_PT/M is needed as a function of PT [J/Psi mumu can't be used].
  • Use prompt D? Contact Alison and see where are we going.
• Acceptance function:
  • There's an ongoing study on how to implement the event by event algorithm from CDF.
  • But CDF is not using it for publications: needs to check on papers what are they using.
  • In order to evaluate the trigger acceptance the ratio of TIS and TOS can be used [but at the end we want the full acceptance not just the trigger one].
  • What about a strategy that: 1) evaluates the trigger acceptance 2) uses MC to evaluate post trigger effects? [discussion]
• Key point: calibration should be done with no cuts! And this is really problematic.
• One possible solutions is to use the lifetime measurement from others and build my acceptance function on top of the exponential decay with fixed lifetime. How much can we gain with this approach?
• fitPULL can be used to evaluate the goodness of PT/M error.

Proposed studies:

[on separate Bs and Bd fits]
• Study the power of ev by ev error on PT
• Evaluate the correlation btw the wrong tagging fraction and proper time resolution
• Extract the SF on the Bs PTerr by fixing omega to the value that comes out from Bd studies and using a gaussian prior with the error extracted again from Bd decays.
• Study the acceptance effect on CP parameters: changing the parameters and the analytical form [systematics from the acceptance]

[simultaneous fit]
• How well do we need to know the proper time PDF?
• PTerr needs to be included for the background. Work is needed in the fit code [Alessio] and validating data and performing tests [Stefania and Gabriele]
• Verify that the use of a fixed sigma for Bd decays does not change anything [Stefania? Bd oscillate slowly...]
• The PT implementation should be changed into a PT/M one [in order to be M independent when dealing with simultaneous fit]. Work needed in the FitCode [Alessio]
• A double gaussian resolution model needs to be checked for PT implementation

Tagging

Discussion:

• Tagged sample
  • We proceed using the same set of tagging categories for Bd and Bs . We do not consider the SS tagging category for pions.
  • To use that information in the fit [SSkaon] a new category is needed [one more if also SSpion comes into play]. the SSkaon should be ran only if NO OS information can be extracted.
  • We should check that OS has the same omega for Bs and Bd!! [otherwise the simultaneous approach is screwed]
• UnTagged sample
  • Can be used to extract lifetime information.
  • Used for physiscs only if DeltaG is big enough.
  • Can be used to extract information about charge asymmetry: i separately fit the untagged sample, I do extract the charge asymmetry out of it, I build a prior and the run the simultanoues fit on tagged sample!
  • Can be used to extract acceptance if not used inside the fit: we know the lifetime, we assume no bias in the propertime, I make the ratio w.r.t to exponential decay and I have my acceptance function.
• Background
  • Combinatorial: Omega fixed(?) to 0.5
  • Partially reconstructed: w != 0.5?

Proposed studies:

[untagged sample]
• How to use the untagged sample in the analysis?
  • How much tagged and untagged samples do differ?
  • How much TIS and TOS proportions in the two samples are different?
  • Can we use the untagged sample to extract the acceptance on data [having fixed the mean life]?

[tagged sample]
• Finish the study on per event omega! [The per event information needs to be recomputed also in the simultanoues approach and reorganization of tagging categories]
• Rewrite the tagging in categories.
• How to extract the omegaSS if not from Dspi? [high multiplicity channels are difficult to relate to B->hh ones]

PID and momentum

Pid Discussion and proposed studies:

• Run against all the possible D*
• Study - concentrate on D* and Bhh events!
• 1 suggested study: taking from MC truth all the kaons and pions from D* and Bhh and make comparisons of DLL and momentum distributions
• 2 suggested study: Apply selection [Raluca's one via joboptions], build efficiency curves and compare again D* and Bhh! Angelo will provide Bhh data after selection. We need to weight the spectra using momentum from B2hh
• Dll distributions needs to be provided in bins of momentum or acceptance

Momentum asymmetry Discussion:

• Currently taken from Bhh itself.
• Obtain the PDF for signal and background events [differences are expected: background distribution expected much broader...]
• How to extract this distribution on data?
• Can we use the mass windowd m>mbs to extract this function for the background?

Fit Code

Discussion:

• Code needs to be fully reviewed, compactified and speed needs to be improved [Alessio, Vincenzo and Angelo]
  Possible handles:
  • Find out an integral for the acceptance * Bdecay mode
  • Analytical integral for momentum asymmetry
  • Use of histograms The aim is to end up with a 1-2 hours fit!
• Tagging in categories needs to be fully rewritten
• Comments in config file needs to be included in order to explain the meaning of all the parameters
• In the fit configuration files needs a flag to disable the fit [if you want to use it just as a toy MC data producer]
• Add the scan for the likelihood for all the fitted parameters and the extraction of chi2
• So far the pid information should be taken as integrated over the momenta [only working solution so far], undimensional PDF not depending on momentum!

Fit strategies

• What can we fix as indipendent information and what needs to be fitted directly inside the simultaneous fit
• Use the Bd->Kpi with proper time event by event error to measure omega_opposite side and then use this measurement in the Bs->KK measurement [the found SF can be used for all channels _needs to be checked_]

Fit stability

• Ask to angelo what 'stability' studies have already been carried out for the TDR:
  • Varying fit initial parameters
  • Varying statistics
• Plan to have a fit version that can be used with RooMCStudy

To do:

• Save data in rootfiles
• Add scale factor for gen event in BD and BS seprately
• Add dofit flag