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UIUC paper review

UIUC paper review. - a paper written simply and neatly with full physics concepts associated to the analysis. Introduction to Bc Event selection The blind analysis The final result The systematic error A further check. Short introduction to B c.

tara-tillman
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UIUC paper review

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  1. UIUC paper review -a paper written simply and neatly with full physics concepts associated to the analysis • Introduction to Bc • Event selection • The blind analysis • The final result • The systematic error • A further check

  2. Short introduction to Bc • Meson(bc): The highest combination of two different quark flavors • Reco. event : has not been observed in any fully reconstructed decay modes. • (CDF RunI, D0 RunII measurement of mass : using semileptonic decay.) • Mass : 6.400.39(stat)  0.13(syst) GeV/c2 (PDG-2004) • The measurement in this analysis results: • ~19 fully reconstructed BcJ/ events, J/ . • Mass : 6287.04.8(stat)  1.2(syst) MeV/c2

  3. 360 pb-1 data sample Di-muon triggered sample Level 1: CMU, CMX stubs are matched to COT axial tracks. A muon pair (CMU-CMU, CMU-CMX) is required with pT > 1.5 and 2.0 GeV/c for the CMU and CMX muons respectively. Level 2: require the opposite charge and impose requirement on the opening angle. Level 3: three dimensional tracking is done for the muon pair; require the invariant mass from 2.7 to 4.0 GeV/c2 . Online event selection

  4. Ensure good vertex resolution Three axial SVX hits. Good matching between the fitted muon tracks and the muon stubs. Di-muon invariant mass window [3.042, 3.152] GeV/c2 . pion candidate : each charged particle track that is not part of the reconstructed J/. The J/ candidate and pion candidate are constrained to a common 3-D vertex with a vertex fit cut. Bc search mass window is defined from 5.6 to 7.2 GeV/c2 . Reconstruct BcJ/ events offline

  5. The search mass window [5.6, 7.2] GeV/c2. ~ 2 standard deviation region around the CDF Run I measurement of the Bc mass. The mass values of the events in the search window are temporarily hidden Binning the invariant mass in two intervals above or below 6.4 GeV/c2.  function: Optimize the  function with MC samples: A quality requirement on the J/ three-track 3-D vertex fit. A requirement on the pion track contribution to the 3-D 2vertex fit. The impact parameter of the J/ pair with respect to the beam line. The maximum proper decay time of the J/ pair. The transverse momentum of the pion. The 3-D angle between the momentum and decay direction of the J/ pair. The significance of the transverse decay length of the J/ pair Find 390 candidate events in the search window in data sample. The blind analysis  J/  

  6. BuJ/k vs BcJ/ Same decay topology Different masses Check the understanding of the reconstruction of the relevant variables in the simulation. Mass resolution Estimate the expected Bc yield. 10 – 50 BcJ/ events in data sample Control sample: BuJ/k Three Gaussians and a linear function 2378 signal events 11.50.3MeV/c2 Agree with the mass resolution from MC simulation.

  7. The sliding search window extends from –100 to +200 MeV/c2 in mass around each nominal peak position, m. seeach mass region [5.7,7.0] In each search window, do a binned likelihood fit Signal : Gaussian with fixed width (13-19 GeV/c2) from MC. Background: linear function including two components Partially reconstructed Bc. Combinatorial background. Calculate  in each search window A sliding fit window

  8. Establish a signal or set an upper limit for the production? Toy MC determines the expected distribution of  for pure bdg samples. The overall distribution is consistent with the two mass bins of the search window Two types of backgrounds are statistically varied in each toy MC experiment.  >3.5 establishes a signal.  distribution from the sliding fit window scans Maximum value 3.6 at a mass of 6.29 GeV/c2 The background is consistent to that in the toy MC scans. The chance for a pure bgd distribution to yield  >3.6 is 0.27%. A sliding fit window to search for maximum 

  9. Use unbinned likelihood fit to the mass region containing the peak. Gaussuan + linear function Gaussian width is fixed to 15.5 MeV/c2, mean is allowed to float. Results: (within a region of  2 standard deviation of the central value) Mass: 6287.0  4.8 MeV/c2 Signal events: 18.95.7 Background: 10.01.4 The final fit BcJ/ exclusive decay signal Established.

  10. The systematic errors are evaluated from the corresponding uncertainties on the Bu mass analysis. The uncertainties on the track parameters. The uncertainty on the momentum scale. Differences in the pT spectra of the Bu and Bc mesons. Limited knowledge of the background shape used in the final mass fit. The total systematic uncertainty: 1.1 MeV/c2 Systematic error

  11. For data sample, lower mass window include both partially reconstructed Bc and the linear combinatorial bgd. The upper mass window contains mostly the linear combinatorial bgd. Lose cuts to get more events in the data sample The lower mass window should be enriched with events having small impact parameter of the pion wrt the jpsi vertex. A further check to this Bc enriched sample Data sample

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