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Bc at the Tevatron William Wester Fermilab for the CDF and D Ø collaborations

Bc at the Tevatron William Wester Fermilab for the CDF and D Ø collaborations. p. e , m , u, …. n e , n m , d, …. c c. J/ y. b c. B c. m + m -. Introduction. B Physics at Hadron Colliders UA1 cross section measurements CDF fully reconstructed B->J/ y K (*)

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Bc at the Tevatron William Wester Fermilab for the CDF and D Ø collaborations

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  1. Bc at the TevatronWilliam WesterFermilabfor the CDF and DØ collaborations p e,m, u, … ne, nm, d, … c c J/y b c Bc m+m- W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  2. Introduction • B Physics at Hadron Colliders • UA1 cross section measurements • CDF fully reconstructed B->J/yK(*) • Study of Bc highlights hadron collider advantages • Large cross section for producing triggerable low background decays not accessible at the B factories. Since the 1980’s … Advantages: Large s(b) x L All mesons and baryons Triggerable: l or J/y Multipurpose detectors Run 0 (88-89) No SVX 2.6pb-1 Disadvantages: (perceived) High backgrounds Limited acceptance Small Lorentz boost Unknown initial state UA1 s(b) in m channel PLB 213, 415 (1988) CDF Bu->J/yK PRL 68, 3403 (1992) W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  3. Tevatron in Run II L = 1 fb-1 CDF beautiful prairie but no hills, thanks to the organizers DØ W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  4. Innermost silicon layer CDF • CDF LayerØØ detector (beyond the baseline) • DØ will add inner silicon for Run IIb s(ip) improves especially in the hybrid region 1.35cm outside hybrid region Without LØØ With LØØ 1.61cm hybrid region prototype W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  5. Bc properties • Bc is a heavy-heavy system • Production: Factorization with two scales Mb + Mc and contributions of color singlet / octet • Softer PT distribution? • Decay: both b and c quarks can participate • Shorter c-like lifetime? • Large number of final state BR’s. • Mass: new system for potential models and new lattice QCD calculations • All aspects of the theoretical work require experimental measurement => happening now at the Tevatron Chang et al, PRD, 71 (2005) 074012 curves represent different singlet/ octet contributions W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  6. CDF: Bc in Run I (‘91-’96) • A few candidate events at LEP and the CDF observation and measurements… +6.2 20.4 signal events -5.5 CDF 0.11 fb-1 M=6.4±0.39±0.13 GeV +0.18 ct = 0.46 0.03 ps - 0.16 PRL 81, 2432 (1998) and PRD 58, 112004 (1998) Production measurement (Pt(B)>6 GeV/c |h|<0.6): s(Bc)xB(Bc->J/yln) +0.041 +0.032 = 0.132 (stat)±0.031 (syst) (ct) -0.037 -0.020 s(Bu)xB(Bu ->J/yK) Note: assuming harder Pt spectrum in MC W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  7. Run II results: semi-leptonic decays • Bc -> J/y + l with l = e, m • Not fully reconstructed (missing n) • Understanding backgrounds are key • bb events with the J/y from b and l from b • Fake muons or fake electrons • Other backgrounds • Study J/y+track and Bu->J/y K • Look for Bc excess above background and make measurements W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  8. Bc in DØ • Three muon final state: Bc -> J/y m X • 0.21 fb-1 of data • 231 J/ymX candidates (signal+background) • Use J/y+track control sample for background • prompt • non-prompt • Combined likelihood fit • Signal + background • mass • pseudo-lifetime mm Scan Monte Carlo in steps of different mass. Perform the fit with and without the Bc along with prompt and non-prompt data bkgd distributions. Cross-check the results using y(2S) + m/track (background dominated). W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  9. Fit with and w/o Bc Background-only Include Bc contribution Background-only fit is poor compared with addition of signal: D2log(likelihood) is 60 for 5 dof W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  10. DØ: fits and results Mass log likelihood ct log likelihood NCAND: 95 ±12 ±11 “first 5s Bc result” Mass: 5.95 ±0.34 GeV +0.14 -0.13 ct: 0.448 ±0.121ps +0.123 -0.096 DØ Note: 4539-CONF W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  11. CDF: Bc -> J/y m X • Use 2.7M J/y’s in 0.36 fb-1 • Combine with third track with & w/o muon ID • PT>3 GeV, ct > 60mm, and Df(J/y-trk) < 90 deg • Use Bu->J/yK from data for normalization • Use Monte Carlo of Bu and Bc for erel • Evaluate backgrounds in the data • Fake muons, bb, fake J/y • Estimate systematic uncertainties • Fit data in 4-6 GeV for signal and backgrounds • Evaluate relative production of Bc to Bu W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  12. Fake muon background • Fake muons: determine p, K, p composition vs PT (dE/dx and TOF) and then use D*, L decays to find fakes vs PT How many come from J/y+track where the track is a fake muon? 106 evts 4<M<6 Fake muons primarily from decay in flight: 16.3±2.9 estimated in 4<M<6 GeV. W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  13. More backgrounds • bb background from Pythia Monte Carlo normalized to Bu->J/yK data using Df distributions (vary production) • Fake J/y from J/y sidebands Backgrounds from the other b: 12.7±1.7 ±5.7 estimated in 4<M<6 GeV. Backgrounds from fake J/y (no double counting): 19.0±3.0 estimated in 4<M<6 GeV. W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  14. Muon channel results Use MC for relative efficiency for Bc and Bu along with Bu->J/yK to obtain: PT(B)>4 and |y| < 1 s(Bc)xB(Bc->J/yln) = s(Bu)xB(Bu ->J/yK) 5.2s Other measurements from this sample are in preparation. CDF Note: 7649 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  15. CDF: Bc -> J/y e X • Fake electron • Use J/y+track data • Estimate fake rate from data (D0Kp,L0pp) • Photon conversion • Use J/y+tagged conversion data • Conversion finding efficiency from MC • bb background • bJ/yX and beX • PYTHIA bb Monte Carlo W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  16. Photon conversions • Remove conversions by finding the partner track during the electron selection • Evaluate the conversion finding efficiency from MC • Calculate the residual conversion background as a function of M(J/ye) using J/y+tagged conversions. • Expected background • 14.54  4.38(stat)  6.39 (syst) W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  17. electron channel results • Background 63.64.9(stat)13.6(syst) • Observed 178.514.7(stat) • Excess 114.915.5(stat)13.6(syst) • Significance 5.9s s(Bc)xB(Bc->J/yln) PT(B)>4 and |y| < 1 = s(Bu)xB(Bu ->J/yK) 0.2820.038(stat.)0.035(yield)0.065(acceptance) W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  18. CDF: Bc -> J/y p • Full reconstruction determines precise mass • Estimate 10-50 events in 0.36fb-1 • Perform analysis “blind” • Optimize MC signal using a figure of merit • Collapse background into large discrete bins • Use predetermined threshold for positive result • Tight requirements • Especially on p coming from displaced J/y vertex • Perform cross-checks Bu->J/yK W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  19. 18.9 ± 5.7 candidates 10.0 ± 1.4 evts Background Results • Small excess at 6.3 GeV above predetermined threshold Monte Carlo: prob(bkgd) fluctuates to this signal is 0.3% Mass = 6287.0 ± 4.8(stat.) ± 1.1(syst.) MeV/c2 hep-ex/0505076 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  20. Cross check: partially reconstructed sample • Look at partially reconstructed decays with M < MBc. • Relax cuts • 3rd track of partially reconstructed track should still point to the J/y vertex • Upper sideband should have no Bc Bc Bu W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  21. Recent lattice QCD calculation • Recent calculation emphasizes new precision from 2+1 flavor lattice QCD with staggered quarks PLB 453, 289 (1999) PRL 94, 172001 (2005) hep-ex/0505076 mBc=6287.0±4.8±1.1 MeV D(theory-exp)= 17 MeV W. Wester, CDF, Fermilab, Beauty 2005, Assisi

  22. Summary and conclusions • The study of the Bc is happening in Run II • Semi-leptonic decays observed >5s • D0: J/y m (tri-muon) • CDF: J/y m and J/y e • Small excess in CDF’s J/y p sample • Precision mass compared with theory • Coming soon … • Production spectrum and lifetimes • Stronger fully reconstructed signal W. Wester, CDF, Fermilab, Beauty 2005, Assisi

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