# Presentation: 549290

## Bc at the TevatronWilliam WesterFermilabfor the CDF and DØ collaborations

- Bc at the TevatronWilliam WesterFermilabfor the CDF and DØ collaborations

- b
- c

- c
- c

- e,, u,  ...

- e, , d,  ...

- J/

- Bc

- 

- 

## 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 **L**
- All mesons and baryons
- Triggerable: l or J/
- Multipurpose detectors

- _Disadvantages: __(perceived)_
- High backgrounds
- Limited acceptance
- Small Lorentz boost
- Unknown initial state

- UA1 (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 ...

## Tevatron in Run II

- CDF

- DØ

- L = 1 fb-1

- beautiful prairie but no hills,
-       thanks to the organizers

## Innermost silicon layer

- CDF LayerØØ detector          (beyond the baseline)
- DØ will add inner silicon for Run IIb

- CDF

- Without LØØ
- With LØØ

- (ip) improves
- especially in the
- hybrid region

- hybrid region

- outside hybrid region

- prototype

- 1.35cm

- 1.61cm

## 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

## 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**

**-5.5**

**M=6.4±0.39±0.13 GeV**

**c******** = 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

## 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

## 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-prompt
- data bkgd distributions.
- Cross-check the results using (2S) + /track (background dominated).

- 

## 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

## 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**

_**N**__**CAND**_**: **
**95 ±12 ±11**

- “first 5Bc result”

- DØ Note: 4539-CONF

## 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 > 60m, and Jtrk < 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

## 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 from
- decay in flight: 16.3**±**2.9
- estimated in 4<M<6 GeV.

- How many come from
- J/+track where the
- track is a fake muon?

- 106 evts
- 4<M<6

## 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 the
- other b: 12.7**±**1.7 **±**5.7
- estimated in 4<M<6 GeV.

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

## Muon channel results

- (Bc) x *B** *(Bc->J/l)

- (Bu) x *B** *(Bu ->J/K)

- =

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

- Other measurements from this sample are
- in preparation.

- CDF Note: 7649

- 5.2

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

## Fake electron
Use J/+track data
Estimate fake rate from data (D0K,0p) 
Photon conversion
Use J/+tagged conversion data
Conversion finding efficiency from MC
bb background
bJ/X and beX
PYTHIA bb Monte Carlo 

- Use J/+track data
- Estimate fake rate from data (D0K,0p)
- Photon conversion
- Use J/+tagged conversion data
- Conversion finding efficiency from MC
- bb background
- bJ/X and beX
- PYTHIA bb Monte Carlo

- CDF: Bc -> J/e X

## 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)

## electron channel results

- (Bc) x *B** *(Bc->J/l)

- (Bu) x *B** *(Bu ->J/K)

- =

**0.282********0.038(stat.)********0.035(yield)********0.065(acceptance)**

- 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
- 5.9

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

## 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

## 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

## 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/ vertex
- Upper
- sideband should
- have no Bc

- Bu

- Bc

## 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 MeV

- hep-ex/0505076

- (theory-exp)= 17 MeV

## 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