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

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

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

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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

- 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

L = 1 fb-1

CDF

beautiful prairie but no hills,

thanks to the organizers

DØ

W. Wester, CDF, Fermilab, Beauty 2005, Assisi

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

- 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

- Production: Factorization with two scales Mb + Mc and contributions of color singlet / octet
- 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

- 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

- 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

- 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

- Signal + background

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

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

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

- 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

- 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

- 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

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

- Fake electron
- Use J/y+track data
- Estimate fake rate from data (D0Kp,L0pp)

- Photon conversion
- Use J/y+tagged conversion data
- Conversion finding efficiency from MC

- bb background
- bJ/yX and beX
- PYTHIA bb Monte Carlo

W. Wester, CDF, Fermilab, Beauty 2005, Assisi

- 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

- Background
63.64.9(stat)13.6(syst)

- Observed
178.514.7(stat)

- Excess
114.915.5(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)

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

W. Wester, CDF, Fermilab, Beauty 2005, Assisi

- 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

- Especially on p coming from
- Perform cross-checks

Bu->J/yK

W. Wester, CDF, Fermilab, Beauty 2005, Assisi

18.9 ± 5.7 candidates

10.0 ± 1.4 evts Background

- 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

- 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

- 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

- 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