04/25/23 W. Wester, CDF, Fermilab, Beauty 2005, Assisi 1

Bc at the Tevatron

William WesterFermilab

for the CDF and DØ collaborations

bc

cc

e,, u, …e, , d, …

J/Bc

04/25/23 W. Wester, CDF, Fermilab, Beauty 2005, Assisi 2

Introduction• B Physics at Hadron Colliders

– UA1 cross section measurements– CDF fully reconstructed B->J/K(*)

• Study of Bc highlights hadron collider advantages– Large cross section for producing triggerable low background

decays not accessible at the B factories.

Advantages:Large (b) x LAll mesons and baryonsTriggerable: l or J/Multipurpose detectors

Disadvantages: (perceived)High backgroundsLimited acceptanceSmall Lorentz boostUnknown initial stateUA1 (b) in channel

PLB 213, 415 (1988)CDF Bu->J/K

PRL 68, 3403 (1992)

Run 0 (88-89)No SVX 2.6pb-1

Since the 1980’s …

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Tevatron in Run II

CDF

DØ

L = 1 fb-1

beautiful prairie but no hills, thanks to the organizers

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Innermost silicon layer

• CDF LayerØØ detector (beyond the baseline)

• DØ will add inner silicon for Run IIb

CDF

Without LØØWith LØØ

(ip) improvesespecially in thehybrid region

hybrid region

outside hybrid region

prototype

1.35cm

1.61cm

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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 representdifferent singlet/octet contributions

04/25/23 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… 20.4 signal events+6.2

-5.5M=6.4±0.39±0.13 GeVc = 0.46 0.03 ps+0.18

- 0.16

(Bc) x B (Bc->J/l)(Bu) x B (Bu ->J/K)= 0.132 (stat) ± 0.031 (syst) (c)+0.041 +0.032

-0.037 -0.020

Production measurement (Pt(B)>6 GeV/c ||<0.6):PRL 81, 2432 (1998) and PRD 58, 112004 (1998)

CDF 0.11 fb-1

Note: assuming harder Pt spectrum in MC

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Run II results: semi-leptonic decays

• Bc -> J/ + l with l = e, • Not fully reconstructed (missing )• Understanding backgrounds are key

– bb events with the J/ from b and l from b– Fake muons or fake electrons– Other backgrounds

• Study J/+track and Bu->J/ K• Look for Bc excess above background

and make measurements

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Bc in DØ• Three muon final state: Bc -> J/ X

– 0.21 fb-1 of data– 231 J/X candidates (signal+background)– Use J/+track control sample for background

• prompt• non-prompt

• Combined likelihood fit– Signal + background

• mass • pseudo-lifetime

Scan Monte Carlo in steps of different mass.Perform the fit with and without the Bc along with prompt and non-promptdata bkgd distributions.Cross-check the results using (2S) + /track (background dominated).

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Fit with and w/o Bc

Background-only fit is poor compared with addition of signal: 2log(likelihood) is 60 for 5 dof

Background-only Include Bc contribution

04/25/23 W. Wester, CDF, Fermilab, Beauty 2005, Assisi 10

DØ: fits and results

Mass log likelihood

c log likelihood

Mass: 5.95 ±0.34 GeV+0.14

-0.13

c:0.448 ±0.121

ps+0.123

-0.096

NCAND:

95 ±12 ±11“first 5Bc result”

DØ Note: 4539-CONF

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CDF: Bc -> J/ X• Use 2.7M J/’s in 0.36 fb-1

• Combine with third track with & w/o muon ID– PT>3 GeV, c > 60m, and Jtrk < 90 deg

• Use Bu->J/K from data for normalization• Use Monte Carlo of Bu and Bc for rel

• Evaluate backgrounds in the data– Fake muons, bb, fake J/

• Estimate systematic uncertainties• Fit data in 4-6 GeV for signal and backgrounds

– Evaluate relative production of Bc to Bu

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Fake muon background

• Fake muons: determine , K, p composition vs PT (dE/dx and TOF) and then use D*, decays to find fakes vs PT

Fake muons primarily fromdecay in flight: 16.3±2.9estimated in 4<M<6 GeV.

How many come fromJ/+track where thetrack is a fake muon?106 evts

4<M<6

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More backgrounds• bb background from Pythia Monte Carlo normalized

to Bu->J/K data using distributions (vary production)

• Fake J/ from J/ sidebands

Backgrounds from theother b: 12.7±1.7 ±5.7estimated in 4<M<6 GeV.

Backgrounds from fake J/ (no double counting): 19.0±3.0estimated in 4<M<6 GeV.

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Muon channel results

(Bc) x B (Bc->J/l)(Bu) x B (Bu ->J/K) =

Use MC for relative efficiency for Bc andBu along with Bu->J/K to obtain:

Other measurements from this sample arein preparation. CDF Note: 7649

5.2

PT(B)>4 and|y| < 1

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• Fake electron– Use J/+track data– Estimate fake rate from

data (D0K,0p) • Photon conversion

– Use J/+tagged conversion data

– Conversion finding efficiency from MC

• bb background– bJ/X and beX– PYTHIA bb Monte Carlo

CDF: Bc -> J/e X

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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/e) using J/+tagged conversions.

• Expected background– 14.54 4.38(stat) 6.39 (syst)

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electron channel results

(Bc) x B (Bc->J/l)(Bu) x B (Bu ->J/K) =

0.2820.038(stat.)0.035(yield)0.065(acceptance)

• Background63.64.9(stat)13.6(syst)• Observed178.514.7(stat)• Excess114.915.5(stat)13.6(syst)• Significance5.9

PT(B)>4 and|y| < 1

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CDF: Bc -> J/• 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 coming from displaced J/ vertex

• Perform cross-checks

Bu->J/K

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Results• Small excess at 6.3 GeV above predetermined

threshold18.9 ± 5.7 candidates10.0 ± 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

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Cross check: partially reconstructed sample

• Look at partially reconstructed decays with M < MBc.• Relax cuts• 3rd track of partiallyreconstructedtrack should still point to the J/ vertex • Upper sideband should have no Bc

Bu

Bc

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Recent lattice QCD calculation

• Recent calculation emphasizes new precision from 2+1 flavor lattice QCD with staggered quarks

PRL 94, 172001 (2005)

PLB 453, 289 (1999)

mBc = 6287.0 ± 4.8 ± 1.1 MeVhep-ex/0505076

(theory-exp)= 17 MeV

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Summary and conclusions

• The study of the Bc is happening in Run II• Semi-leptonic decays observed >5

– D0: J/ (tri-muon)– CDF: J/ and J/ e

• Small excess in CDF’s J/ sample– Precision mass compared with theory

• Coming soon …– Production spectrum and lifetimes– Stronger fully reconstructed signal