1 / 72

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

ivory
Télécharger la présentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related