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Study of the B c Meson Properties using B c g J/ y e n Decay at CDF II

Study of the B c Meson Properties using B c g J/ y e n Decay at CDF II. Masato Aoki University of Tsukuba, Japan. “ Periodic Table ”. B c meson is the last meson experimentally observed. The B c meson. Only meson state with differently flavored heavy quarks

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Study of the B c Meson Properties using B c g J/ y e n Decay at CDF II

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  1. Study of the Bc Meson Properties using BcgJ/yen Decay at CDF II Masato Aoki University of Tsukuba, Japan

  2. “Periodic Table” Bc meson is the last meson experimentally observed

  3. The Bc meson • Only meson state with differently flavored heavy quarks (bottom and charm quark) • Both quarks are heavy • Similar binding interaction to heavy quarkonia families (J/y, U, etc.) • Other quarkonia decay via strong interaction • The two quarks have different flavor Only weak decay is possible Comparable timescales for decay of two heavy constituents Measurable lifetime but shorter than other B mesons (t~0.5 ps) q q J/y, U q q’ Bu,Bd,Bs

  4. The Bc properties • Quarkonia described by Quark Potential models • Opportunity to test with Bc • Expect: • Tightly bound: f(Bc) » 400 MeV • Ground state mass predictions : 6.1<M(Bc )<6.5 GeV/c2 • Rich spectroscopy of narrow states below B-D threshold

  5. Decay properties • Three dominant processes: • b decay: • J/y p+, J/y Ds+, J/y l+n • c decay: • Bs0p+, Bs0 l+n • Annihilation: • tnt, DK, multi-p • Large f(Bc) and Vcb vertex  400x larger annihilation width than for B+

  6. Decay properties • Naïvely expect factorization to apply • G=Gb+Gc+ Gann. • Expect t~0.4 - 0.7 ps • However, bound-state effects may be large • Eichten and Quigg predict t~1.3 ps

  7. Theoretical calculations • V. V. Kiselev, hep-ph/0308214 (2003) : Review paper Bc observation by CDF(1998)

  8. Rich decay modes hep-ph/0308214(2003) • Large J/ygm+m- rate provides experimental signature ( For example, BR(BugJ/yK) =0.1% )

  9. Hadronic production • Dominant process is gggBc+bc • Calculation requires 36 diagrams O(as4) • Contributions from color singlet / octet Chang et al, PRD, 71 (2005) 074012 curves represent different singlet/ octet contributions

  10. Bc production rate • Much smaller production rate than other b-hadrons Theoretical calculation : 7.4nb Phys. Lett. B605, 311(2005)

  11. Heavy Flavor Physics at CDF • Huge production cross sections at Tevatron • sb~30 mb • Currently only Tevatron can produce the Bc meson • B-factories cannot produce the Bc meson because the beam energy is not enough for the Bc generation • Large backgrounds as well B triggers are necessary • lepton trigger • displaced track trigger • and combined trigger Typical bb pair production diagrams quark annihilation gluon fusion flavor excitation gluon splitting

  12. M=6.4±0.39±0.13 GeV/c2 +0.18 –0.16 t=0.46 ±0.03 ps s(Bc)B(BcgJ/yln) =0.132 ±0.031 +0.041 –0.037 +0.032 –0.020 s(Bu)B(BugJ/yK) Bc discovery in CDF Run I (’91~’96) • Bc signal search using BcgJ/yln (l=e,m) channel • ~20 Bc signal events were observed in 110 pb-1 of J/ygmm trigger data [PRL 81, 2432 (1998) and PRD 58, 112004 (1998)]

  13. The CDF II detector @Tevatron • Silicon Detector • |h|<2.0 • svertex~30mm • Central Outer Tracker • |h|<1.0 • spT/pT=0.15% pT • Muon Chamber • |h|<0.6 (1.0) • EM, HAD Calorimeter • |h|<1.1(EM), <0.9(HAD) • sE/E=√ (13.52/ET+32) % (EM) • =√ (502/ET+32) % (HAD) Muon Chamber HAD Calorimeter EM Calorimeter Silicon Detector Central Outer Tracker All of the tracking system are replaced for Run II

  14. Bc signature in this analysis • Use semileptonic decay BcgJ/y+e+n Larger BR than other triggerable decay modes  statistical advantage Improved J/ygmm trigger • pT(m)>1.5 GeV/c (was 2 GeV/c) • Factor ~5 J/y yield (factor ~2 BgJ/y yield) No narrow mass peak due to missing neutrino… • Bc signal = excess above estimated backgrounds  More photon conversion background due to new tracking system (more material than Run I) • Establishing the Bc again and precise measurements s(Bc)B(BcJ/yen) / s(Bu)B(BugJ/yK)andlifetime (Mass to be measured in exclusive channel)

  15. J/y signal region Sideband : for fake J/y study J/ygmm trigger data • Lint ~ 360 pb-1 • pT(mm) > 3 GeV/c • Reduce fake • Reduce prompt • ~2.2M J/y • Signal window |M(mm)-M(PDG:J/y)| < 50 MeV/c2 Additional requirements in this analysis…

  16. Electron reconstruction • pT(e) > 2 GeV/c, |h|<1.0 • Track-seeded reconstruction : Inside-Out algorithm • High reconstruction efficiency for low pT electrons • Calorimeter-seeded algorithm is used for high pT physics • Electron ID using both calorimeter and dE/dx measured by COT

  17. Calorimeter 10 variables E/p EHad/EEm E/p (shower max) Ewire/Estrip (shower max) — Red : electrons from gge+e- — Blue : pions from K0sgp+p- Q·DX/s (shower max) DZ/s (shower max) c2strip (shower max) c2wire (shower max) E (preradiator) DX (preradiator)

  18. Electron ID using calorimeter • 10 variables from calorimeter • Form a Joint Likelihood Function • L cut position is varied not to have any dependences for electron efficiency (isolation,pT,charge) ~70% efficiency

  19. Isolation • Isolation is defined by SpT/pT • pT in the denominator is the pT of the track of interest • SpT in the numerator is the scalar sum of pT of all other tracks in the same calorimeter tower • Calorimeter variables strongly depend on the isolation • Isolation correction is necessary • BcgJ/yen decay is expected to have similar isolation to that for BugJ/yK CDF Preliminary

  20. Electron ID using dE/dx Ze/sZ–1.3 • Energy deposit in COT p p 2GeV e 2GeV m p p K m K e ~90% efficiency e m p p K Ze=Log((dE/dx)measured/(dE/dx)pred. for e)

  21. s(Bc)B(BcJ/yen) / s(Bu)B(BugJ/yK) Measurement

  22. s(Bc)B(BcJ/yen) / s(Bu)B(BugJ/yK) measurement strategy • Reconstruct mass of J/y-e pair • Estimate all the backgrounds • Event counting above the backgrounds • Estimate the acceptance and efficiency • Use BugJ/yK as the normalization mode  BugJ/yK has similar topology to BcJ/yen  Cancel out most of uncertainties m+ m+ J/y J/y m- m- Bu+ Bc+ n K+ e+

  23. pT Secondary Vertex y R x Lxy Primary Vertex J/ye pair reconstruction m+ J/y • One displaced decay vertex • Lxy/sLxy > 3 • Prompt background becomes negligible • pT(J/y-e) > 5 GeV/c • Reduce non-B tracks • Search window • Wide mass region due to missing neutrino • 4 < M(J/ye) < 6 GeV/c2 m- n Bc+ e+ signal region

  24. Background Estimates

  25. Backgrounds and control samples • fake J/y • J/y mass sideband events • fake electron • J/y + track • bb (bgeX, bgJ/yX) • PYTHIA Monte Carlo • electron from photon conversion • J/y + electron tagged as photon conversion • prompt J/y • No control sample. There is no reliable Monte Carlo • Zero lifetime  killed by Lxy/sLxy>3 requirement

  26. Fake J/y background • Fake J/y background can be estimated by J/y mass sideband events • J/y+electron, J/y+track, J/y+conv.-e have fake J/y part each other • To avoid double counting, fake J/y events (sideband events) will be subtracted in the following background estimations

  27. Fake electron background • Control sample : J/y + track (after dE/dx requirement) • Fake rate after eID by calorimeter • Fake rates for K/p/p • Control samples from high statistics Two displaced Tracks Trigger (TTT) data • Combine them with proper fraction obtained from PYTHIA Monte Carlo • Nfake = N(J/y+track) x efake Displaced track trigger secondary vertex Long lived particle d0 primary vertex particle composition around J/y

  28. Fake rate estimates for K/p/p • Control samples in TTT data • D0gKpfor K/p • Lgppfor proton • Fitthe mass distribution to obtain # of events before and after eID by calorimeter • Fake rate = N after eID / N before eID K+ K- p+ p- after eID after eID p p after eID

  29. Particle composition in J/y+track sample • PYTHIA Monte Carlo simulation • Dominant fake source : pion CDF Preliminary Data Kaon Pion d~0.09 PYTHIA Kaon Pion Proton Proton after dE/dx requirement pion fraction from dE/dx fitting  max difference ~0.09

  30. Average fake rate Combine p+, p- CDF Preliminary The average fake rate is applied to J/y+track after dE/dx cut average fake rate positive charge negative charge K+, K- < 0.8% p, p

  31. Systematic uncertainties • Isolation dependence on fake rate • ~14.5% • Difference between TTT data and J/y trigger data (tight requirement on # of silicon hits for TTT) • ~7.2% • Particle fraction in PYTHIA • ~1.9% • Sample statistics • J/y+track : ~2.0% • Fake rate : ~0.9%

  32. Estimated fake electron background • From J/y+track data with fake rate convolution • 15.43  2.54 events in the signal region

  33. Photon conversion electrons g • Control sample : J/y+e tagged as ggee • Find collinear partner track • These candidates are removed from the J/ye candidate list • Miss-tracking due to very low pT partner track  Not 100% finding efficiency  Residual photon conversion electrons • Need to understand the finding efficiency

  34. Conversion finding efficiency • Monte Carlo sample : • B0gJ/yp0 • 98% p0ggg, 2% p0geeg • etag = ~50% efficiency • Residual ggee events • Systematics study • Another MC : use pT(tracks) in J/y+track as pT(p0)

  35. Systematic uncertainties CDF Monte Carlo • pT spectrum • ~43.7% • Lifetime of B0 • ~2.0% • Dalitz decay • ~1.0% • Sample statistics • Finding efficiency : ~3.8% • J/y+conv. e : ~30.1%

  36. Estimated residual photon conversion • From J/y+conv-e data and conversion finding efficiency • 14.54  7.75 events in the signal region

  37. bb background • It is possible to make a common vertex with J/y from one B decay and e from another B decay bb background quark annihilation gluon fusion flavor excitation gluon splitting

  38. bb background estimate • PYTHIA Monte Carlo simulation • Validated using bb azimuthal correlation information [PRD71,092001 (2005) ] • Reasonable agreement with data • Normalization with data : N(BugJ/yK) Azimuthal angle distribution between J/y and electron with all kinematical requirements Bc signal MC Additional requirement : Df(J/y-e) < 90deg.

  39. Systematic uncertainties • Monte Carlo setting (PDF/ISR) • ~31.4% • Isolation dependence on eID efficiency • ~2.9% • Branching ratio of normalization mode BugJ/yK • ~0.9% • Calorimeter fiducial coverage • ~0.9% • Statistics • MC sample : ~6.5% • N(BugJ/yK) in MC : ~1.9% • N(BugJ/yK) in data : ~1.8% • e(eID by cal) : ~1.4% • e(eID by dE/dx) : ~1.0%

  40. Estimated bb background • From PYTHIA Monte Carlo • BugJ/yK for normalization to data • 33.63  11.38 events in the signal region

  41. Summary table *J/y sideband events are subtracted *before the subtraction, data has 203 events and the fake J/y is 24.5±3.5

  42. M(J/y+electron) data and excess • Total background : 63.6±14.4 events • Excess : ~115 events • Significance : 5.9s

  43. CDF Preliminary CDF Preliminary Cross check : e-track IP w.r.t. J/y vertex electron • Lxy(J/y)/sLxy> 3 • Bc decay vertex position is the same as that for J/y (J/y immediately decays) • Bc should make a peak around IP=0 m+ IP m- PV Lxy(J/y) Peak exists! BugJ/yK J/y-e

  44. s(Bc)B(BcJ/yen) / s(Bu)B(BugJ/yK) calculation • Have established the signal !! • Let’s calculate s(Bc)B(BcJ/yen) / s(Bu)B(BugJ/yK) • acceptance ratio • efficiency ratio

  45. Normalization mode : BugJ/yK • Similar reconstruction criteria as J/ye • N(Bu)=287259 was found in the same data

  46. Kinematical acceptance ratio • RK = Akin(Bu)/Akin(Bc) = 4.42±1.02 Systematic uncertainties Largest

  47. Reconstruction efficiency ratio • Most of the efficiencies are expected to be same for Bc and Bu u electron ID with calorimeter and dE/dx

  48. Kinematical limits • Choose pT(B) > 4GeV/c, |y(B)| < 1 as our cross section definition (Run1 : pT(B) > 6GeV/c, |y(B)| < 1) -1 < y(Bc) < 1 4GeV

  49. Result of sB ratio measurement s(Bc)B(BcJ/yen) / s(Bu)B(BugJ/yK) = 0.282  0.038(stat.)  0.035(yield)  0.065(acc.) (pT(B)>4GeV/c, |h(B)|<1) • Most of the difference to the Run I measurement is from the treatment of input pT(Bc) spectrum • Still consistent with Run I • Consistent with result from muon channel 0.245 ± 0.045(stat.) ± 0.066(syst.) +0.080/-0.032(life.) • The result is consistent with recent QCD calculation 0.132 ±0.031 +0.041 –0.037 +0.032 –0.020

  50. Lifetime Measurement

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