fancy BackgroundText

fancy none [10.0in,6.2in]

brown Study of in Run II Data
blue George Pope

blue with Turgun Nigmanov and Paul Shepard
blue University of Pittsburgh
blue CDF Collaboration
blue contact: gpope@fnal.gov
green APS Meeting, 05/01/2004

[C]redIntroduction Production

• The high mass of the quarks allows Pertubative QCD predictions.
• Fragmentation process dominates production.
• The mass of the is predicted by nonrelativistic potential models to be in the range of .

Decay and Lifetime

• The can decay via one of three weak interactions:
  • Decay of the quark
  • Decay of the c quark
  • annihilation
• Predicted lifetimes vary from to .

Past Measurements:

• CDF measured lifetime and mass in Run I in the combined and e channels.
• OPAL observed 2 events, with a background of
• The LEP experiments have set limits on various branching ratios.

[C]redAnalysis Strategy Our signature is a and another sharing a common displaced vertex. We require:

• Hits from our silicon tracker for a good vertex
• for vertex
• lifetime
• the and the third track to be in same hemisphere ()
• for third track (good muon)

[scale=0.3]bcdecay.eps
We cannot fully resolve the in this decay mode. Our signal region is from , excluding the mass around PDG value. [scale=0.3]bcsignal.eps

[C]redData Selection We use a skim of dimuon-triggered events. The total luminosity for the data is . [scale=0.5]jpsimasswindow.eps brown mass plot showing mass window (green) and sidebands (blue) used for fake background calculation.

[C]redThe Backgrounds As the is not fully reconstructed, understanding the background is of greatest importance. The is rare, but the is plentiful. There is potential for a lot of background.

• Fake third
  • A real in coincidence with another track
  • The track - a or K, decays in-flight or punches through to muon chambers
  • This is the major background
• • One B meson decays to give a , the other gives a real
  • The unlikeliness of the and forming a good vertex makes this a small background
• Fake
  • We have some contribution of the dimuon continuum underneath our peak
  • Again, the fake must form a good vertex with another , real or fake
  • This is also a small background

We use data, when possible, to determine backgrounds.

[C]redFake Third Background We start with the distribution and apply the scaling

where is the fraction of tracks and is the fake rate for . [scale=0.20]run2mass1final3noBsi.eps
We fit a dE/dx pull distribution to determine and K fractions for the sample. [scale=0.20]bc04_kpiDedx2.eps
We use to obtain pure and K track samples. We determine how often the is reconstructed as a . The probabilities range from to . [scale=0.20]bc04_fake_prob3.eps

[C]redFake Third Validation We have validated the methodology for the fake third background with an independent dataset that is pure background.

• We use a triggered sample, and compare the distribution when is required with our prediction.

[scale=0.4]smu_allmuons2.eps brown Dimuon mass distributions for the sample, requiring , with contribution added to fake prediction overlaid. The same sign (SS) sample is a pure background.

[C]red Background

• Pythia generation of all QCD to get proper B correlation.
• B mesons with quarks forced into decay, other particles decay normally.
• Third muon verified with MC truth info.
• Only third muons with parentage other than , K considered.
• Scale MC sample using peak to normalize.
• The total contribution is events.

[scale=0.3]run2Bpeakfinal3si.eps brown peak from data using all valid analysis cuts.

[C]redFake Background

• Dilepton continuum is the source of fake .
• We take two sidebands of and pass the events through the entire analysis, omitting cut on fit.
• Surviving events must be scaled to account for effect of .
• We use the data to determine this scale factor.
• The total contribution is events.

[C]redBackground Summary The final fake third contribution is events. We are finalizing some systematics so we can not quote the exact magnitude here. For comparison we show the expected shape of the from MC. [scale=0.35]run2mass2dif3noBsi.eps [scale=0.35]bcsignal.eps brown Left: the shape of the predicted fake third background, magnitude TBD. Right: the shape of the predicted signal from a Bgen MC.

[C]redA Signal? [scale=0.5]run2mass2final3noBsi_noback.eps brown Final candidates. mass after all cuts. The high mass events are explained by and fake backgrounds, within uncertainties.

[C]redConclusions The dominant background in this study is from the decay-in-flight and punch-through of the third track which form the candidate tracks for the third muon. Although we believe that we are making correct estimates for this background there are a number of sources of systematic error (such as trigger bias effects in the analysis of the sample) which are still being considered. For this reason we are not prepared at this meeting to give a precise statement of the overall background in the signal region. Nonetheless, we fully expect that once our errors are finalized that a statistically significant signal in excess of four standard deviations for the inclusive will emerge.

About this document ...

This document was generated using the LaTeX2HTML translator Version 96.1-h (September 30, 1996) Copyright © 1993, 1994, 1995, 1996, Nikos Drakos, Computer Based Learning Unit, University of Leeds.

The command line arguments were:
latex2html aps-slides.tex.

The translation was initiated by George Pope on Thu Apr 29 19:25:35 CDT 2004