W. Wester, CDF, Fermilab, Beauty 2005, Assisi Bc at the Tevatron William Wester Fermilab for the CDF and DØ collaborations p e,m, u, … ne, nm, d, … Bc b c c J/y m+ m- 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

W. Wester, CDF, Fermilab, Beauty 2005, Assisi 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) 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

Tevatron in Run II L = 1 fb-1 CDF DØ beautiful prairie but no hills, thanks to the organizers DØ 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

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 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

W. Wester, CDF, Fermilab, Beauty 2005, Assisi 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 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

W. Wester, CDF, Fermilab, Beauty 2005, Assisi 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) x B (Bc->J/y ln) +0.041 +0.032 = 0.132 (stat) ± 0.031 (syst) (ct) -0.037 -0.020 s(Bu) x B (Bu ->J/y K) Note: assuming harder Pt spectrum in MC 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

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 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

W. Wester, CDF, Fermilab, Beauty 2005, Assisi 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). 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

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 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

W. Wester, CDF, Fermilab, Beauty 2005, Assisi 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 ±0.121 ps +0.123 -0.096 DØ Note: 4539-CONF 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

W. Wester, CDF, Fermilab, Beauty 2005, Assisi 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 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

W. Wester, CDF, Fermilab, Beauty 2005, Assisi 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. 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

W. Wester, CDF, Fermilab, Beauty 2005, Assisi 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. 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

W. Wester, CDF, Fermilab, Beauty 2005, Assisi Muon channel results Use MC for relative efficiency for Bc and Bu along with Bu->J/yK to obtain: s(Bc) x B (Bc->J/y ln) PT(B)>4 and |y| < 1 = s(Bu) x B (Bu ->J/y K) 5.2s Other measurements from this sample are in preparation. CDF Note: 7649 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

W. Wester, CDF, Fermilab, Beauty 2005, Assisi 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 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

W. Wester, CDF, Fermilab, Beauty 2005, Assisi 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) 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

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) x B (Bc->J/y ln) PT(B)>4 and |y| < 1 = s(Bu) x B (Bu ->J/y K) 0.2820.038(stat.)0.035(yield)0.065(acceptance) 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

W. Wester, CDF, Fermilab, Beauty 2005, Assisi 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 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

Results Mass = 6287.0 ± 4.8(stat.) ± 1.1(syst.) MeV/c2 Small excess at 6.3 GeV above predetermined threshold 18.9 ± 5.7 candidates 10.0 ± 1.4 evts Background 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 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

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 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

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 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi

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 12/4/2018 W. Wester, CDF, Fermilab, Beauty 2005, Assisi