Open beauty production in pp collisions at 7 TeV with CMS BACKUP
Resnick, Rosalind, Founder and CEO has reference to this Academic Journal, PHwiki organized this Journal Open beauty production in pp collisions at 7 TeV with CMS Kajari Mazumdar Tata Institute of Fundamental Research Mumbai, India. on behalf of CMS Collaboration, LHC, CERN ICPAQGP, GOA, December 2010 Open Beauty in addition to Heavy Ions Heavy flavours are important probes of QGP in heavy ion collisions. Several issues: Production time scale of heavy flavour shorter than that of the deconfined state. Lifetime of heavy flavours are larger than that of the medium b,c quarks fragment inside the hot medium. Hard partons are likely to loose energy while traversing through the dense medium. Does the energy quench depend on mass of the hadron ->Study in addition to compare the properties of J/, , B-mesons . The tussle between the heavy meson dissociation in addition to decay of c/b quark in dense medium may cause significant modification in measured b-cross-section in QGP compare with pp measurement. ICPAQGP, Goa, December 2010 LHC accelerator in addition to CMS experiment CMS recorded about 43 pb-1 integrated luminosity as long as pp collision at 7 TeV in addition to ~9 b-1 of Pb-Pb collision in 2010 . LHC instantaneous luminosity during April to October: 1027 to 1032 /cm-2 / s-1 CMS trigger strategy changed accordingly Results shown today uses only a fraction of the total pp collision data. HI collisions of 2010 just getting over. No result on open beauty measurement in HI data of CMS available as yet. ICPAQGP, Goa, December 2010 pp collisions at LHC provides the important normalization as long as HI to estimate the shadow effect. LHC provides abundant rates as long as heavy flavour production accurate measurements possible in both pp in addition to HI collision data.
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CMS: precise charged particle tracking, robust lepton identification, finely segmented calorimeter ICPAQGP, Goa, December 2010 Open beauty: double b-jet c in addition to idate CMS B-physics programme as long as p-p collisions: 1. Measure differential in addition to total cross-sections as long as beauty production. 2. Study exclusive B-decays. 3. Search as long as New Physics in rare decays. Important subdetectors Charged particle tracking in pixel layer in addition to Si-strip detectors Long lifetime in addition to large mass reconstruction Measurement of transverse momentum (pT) Primary in addition to secondary vertex reconstruction Muon measurements: 3 different sub-detector types Muon identification Muon pT measurement Semileptonic decays Particle Flow algorithm as long as jet reconstruction upto 20 GeV/c, with capability as long as b-jet identification. Minimum bias in addition to inclusive single jet triggers ICPAQGP, Goa, December 2010 B-physics studies mainly depend on: Muon trigger: pT> 3GeV/c + impact parameter d0< 2cm + dedicated quarkonia triggers pT resolution @ 1 GeV/c 0.7% @ =0, 2% @ = 2.5 Tracking Algorithmic Efficiency: The CMS Tracker feels at home in high charged particles multiplicity environment. It has been designed to tackle thous in addition to of tracks per event. It provides good tracking per as long as mance also as long as the Heavy Ion running of LHC (~104 tracks per event). Fake rate: Tracking in low in addition to high multiplicity environments of pp collision ICPAQGP, Goa, December 2010 Tracking per as long as mance ICPAQGP, Goa, December 2010 Measure upto pT ~ few hundred MeV/c Good efficiency in addition to purity as long as pT >1 GeV/c Muon identification ICPAQGP, Goa, December 2010
ICPAQGP, Goa, December 2010 Particle flow technique in CMS Utilise: . good separation of charged particles in large tracker volume. good resolution as long as soft particles upto few hundred MeV/c. very good electromagnetic calorimeter . in multijet events only 10% of energy correspond to neutrals Big improvement in energy resolution (factor of 2 wrt measure- ments using only calorimetric info) in addition to particle identification. Reduces jet scale uncertainty by factor of 2. Correlate charged tracks with energy deposits in the calorimeter, correct For energy loss along trajectory. ICPAQGP, Goa, December 2010 Semileptonic decays, b +X B-hadron kinematics lepton is harder use relative pT of muon wrt jet to identify b-event. Use shape templates from simulation, to get fraction of b,c in addition to light quark contributions. validate with b-enriched data sample: fb = 44±1 % Consider charm decays + in-flight decays from light quarks, gluons Template as long as misidentified hadron validated with data Consider events with: pT > 6 GeV/c, wrt z-direction, < 2.1 ICPAQGP, Goa, December 2010 Estimation of b-quark production cross-section in semileptonic decays Trigger eff= 82% reconstruction=97% -jet association=77% Visible rate Models as long as fake muon + underlying effect dominate experimental uncertainty ~ 15-20% Larger discrepancy with theory at low pT in addition to central region Uncertainty in luminosity ~ 11% ICPAQGP, Goa, December 2010 Measurement of inclusive b-jets Tag/identify b-jets to include higher momentum b-events. utilise hard fragmentation, large mass, large lifetime of b. Different systematics compared to semileptonic decays ! Several algorithms as long as b-jet identification: use discriminators based on track counting, secondary vertex, semi-leptonic decays, b-jet probability threshold values in each case decide sample purity, identification efficiency. B-tagging efficiency in data, using muon spectrum in b-jets fraction of tagged, untagged events obtained from fit to samples which pass in addition to fail discriminator: Secondary vertex tagging method utilization of atleast 3 tracks to reconstruct secondary vertexbest efficiency in addition to high purity. ICPAQGP, Goa, December 2010 b-jet c in addition to idate selection: discrimination between b in addition to light-flavoured jets Basic track qualities: Number of pixel hits >2 Total number of silicon (pixel+strip) hits>8 Chi2/ndof of track fit <5 Transverse momentum >1 GeV/c Unsigned transverse impact parameter dxy <0.2 cm Unsigned longitudinal impact parameter dz < 17 cm Distance of closest approach to the jet axis < 0.07 cm Decay length < 5 cm. ICPAQGP, Goa, December 2010 Sample purity determined from secondary vertex mass fit: ~73% b-tagging in data B-fraction in tagged sample, using MC ICPAQGP, Goa, December 2010 Estimation of cross-section Stat. Uncertainty in cross-section ~ 2% Syst. Uncert. ~ 20%take ratio wrt inclusive jets to reduce systematics due to luminosity, energy resolution, energy scale of jets. Agreement good with Pythia as long as pT>40 GeV/c Shape difference with MC@NLO as long as large pT in addition to in as long as ward direction. ICPAQGP, Goa, December 2010 Exclusive B-meson decays in pp collision Reconstructed modes: B+J/ K+ , BsJ/ Several on going analyses: B0J/ K0 , J/ K0 Bs bJ/ Fit 3 gaussians as long as signal + exponential as long as background CMS DPS-2010-040 Maximum likelihood fit as long as single gaussian+ first order polynomial ICPAQGP, Goa, December 2010 Conclusion Discussed the capability of CMS experiment as long as open-b physics with pp collision data: exclusive decays in addition to measurement of b-production cross-section from low to reasonably high transverse momentum, using semileptonic decays in addition to b-tagged jets. Agreement with theoretical predictions (LO & NLO) reasonable, though some differences are significant in different kinematic regions. Measurements with larger statistics being finalised. CMS will carry as long as ward b-physics programme in heavy ion collision data. Expect interesting results in near future. Stay tuned!
ICPAQGP, Goa, December 2010 BACKUP ICPAQGP, Goa, December 2010 Tagging per as long as mance Jet pt (10,30) Jet pt (30,50) ICPAQGP, Goa, December 2010
ICPAQGP, Goa, December 2010 ICPAQGP, Goa, December 2010 ICPAQGP, Goa, December 2010 Event Displays
Resnick, Rosalind Founder and CEO
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