Bc mass, lifetime and BR’s at CDF

Masato AokiUniversity of Tsukuba

For the CDF Collaboration

International Workshop on Heavy Quarkonium 2006 @ BNL

Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL

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Outline1. Introduction

a. The Bc meson

b. Tevatron and CDF

2. (Bc)B(BcJ/l)/(Bu)B(BuJ/K) measurement

3. Lifetime measurement4. Mass measurement5. Summary

Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL

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• Ground state of bottom-charm quark bound system Both quarks are heavy

Similar to cc and bb families But the two quarks have different flavor

Only weak decay is possible Bc has measurable lifetime

• Bc provides unique features of heavy quark bound states

• In the future… As a Bs generator CP asymmetry measurement in D0Ds decay mode

The Bc Meson

Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL

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Bc in CDF Run I (1991~1996)• Bc signal search using BcJ/l(l=e,) channel• ~20 Bc signal events were observed in 0.11 fb-1 of J/ data

[PRL 81, 2432 (1998) and PRD 58, 112004 (1998)]

M=6.4±0.39±0.13 GeV/c2 =0.46 ±0.03 ps+0.18–0.16

=0.132 ±0.031+0.041–0.037

+0.032–0.020

(Bc)B(BcJ/l)(Bu)B(BuJ/K) * harder pT(Bc)

was assumed

Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL

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The Tevatron Collider• √s=1.98 TeV proton-antiproton collider• Tevatron has already delivered 1.6 fb-1

CDF has ~1 fb-1 available for analysis• We anticipate 4~8 fb-1 by the end of Run II

Record peak luminosity : 1.82 1032

cm-2 s-1

Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL

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B field : 1.4 T

HAD calorimeterHAD calorimeterMuon systemMuon system

Drift chamberDrift chamberSilicon microstrip detectorSilicon microstrip detector

EM calorimeterEM calorimeter

The CDF II detector

Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL

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Heavy Flavor Physics at CDF•Huge production cross

sections at Tevatron b~30 b

•Large backgrounds as well

q b

q b

bg

g b

q q

bg

bbg

g g

b

•B triggerslepton trigger displaced track trigger and combined trigger

•Trigger requirementslarge bandwidthbackground suppressiondeadtimeless

primary vertex

secondary vertex

d0

B

J/

Used for current Bc analysis

Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL

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Bc Production and Decay• Bc has differently flavored heavy quarks

Much smaller production rate Unique decay (bc,cs,annihilation…)

Rich decay modes

Species Prod. FractionB+ 40%B0 40%Bs 10%

b-baryons 10%Bc ~0.05%Theoretical calculation : 7.4nbPhys. Lett. B605, 311(2005)

Decay BR

bcBcJ/e ~1.9%BcJ/ ~0.13%

csBcBs ~16.4%BcBs

* ~20.2%

ann.Bc ~1.6%Bccs ~4.9%hep-ph/0308214(2003)

Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL

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Production Rate Measurement• BcJ/e and J/ semileptonic decays

Use J/ trigger data (0.36 fb-1)Large BR statistical advantageNo narrow mass peak due to missing neutrino (4~6GeV/c2)Need to understand all of backgrounds

fake J/…………………..J/ mass sidebandfake e, and DIF………...J/+track & fake ratebb (bJ/X,blX)….....PYTHIA Monte Carlo photon conversion e……...tagged conv. e & its efficiencyprompt J/……………….require to have a displaced vertex

• Use BuJ/K as a normalization modeTopologically similarMeasure (Bc)B(BcJ/l)/(Bu)B(BuJ/K) Cancel out most of uncertainties

Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL

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(Bc)B(BcJ/l)/(Bu)B(BuJ/K) Measurement : 0.36 fb-1

• electron mode : • 0.282 ± 0.038(stat.) ± 0.035(yield) ± 0.065(acceptance) (pT(B)>4GeV/c) • 0.242 ± 0.036(stat.) ± 0.031(yield) ± 0.051(acceptance) (pT(B)>6GeV/c)

• muon mode : • 0.245 ± 0.045(stat.) ± 0.066(syst.) +0.080/-0.032(life.) (pT(B)>6GeV/c)

J/e J/

5.9 5.2

* softer pT(Bc) was assumed

Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL

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Lifetime

• Three major decay diagrams

• Lifetime should be Bc 1/(0.6+1.2+0.1) 0.5 ps if all the three diagrams contribute to the decay

Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL

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Lifetime Measurement•BcJ/e semileptonic decay

•Perform a maximum likelihood fit to J/e decay length•Correct neutrino’s momentum using Monte Carlo•Background shapes

•Estimate # of BKGs

fake J/

conversionfake e

bb

Constrained during the fitting

(same way as B ratio measurement)

Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL

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Lifetime Measurement

(Bc) = 0.463 +0.073/-0.065(stat.) ± 0.036(syst.) ps

• BcJ/e channel• Data : ~ fb-1

accepted by PRL

Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL

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Mass• Theoretical calculations predict M(Bc) 6.3GeV/c2

• Bc full reconstruction is necessary for precise mass measurement

• CDF searches for the BcJ/ decay : (BR~0.1%)

PRL94,172001(2005)

Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL

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Observation of the BcJ/ decay and Mass Measurement

• Data : ~1.1 fb-1

• J/ selection is optimized using BuJ/K events

7.5

M(Bc) = 6276.5 ± 4.0(stat.) ± 2.7(syst.) MeV/c2

N(Bc)50

Clo

se u

p

Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL

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Summary The Bc signal has been observed in BcJ/e modes

with >5 significance in CDF Run II Measured Bc meson properties

(Bc)B(BcJ/l)/(Bu)B(BuJ/K) e : 0.282 ± 0.038 ± 0.035 ± 0.065 (pT(B)>4GeV/c) : 0.245 ± 0.045 ± 0.066 +0.080/-0.032 (pT(B)>6GeV/c)

Lifetime 0.463 +0.073/-0.065 ± 0.036 ps

Mass 6276.5 ± 4.0 ± 2.7 MeV/c2

Other studies are to follow soon… Lifetime measurements from J/, J/

Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL

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Backup slides

Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL

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Residual photon conversions

• Electrons coming from photon conversion event are removed from the J/e candidate list

• Find colinear partner track• miss-tracking in low pT region• not 100% finding efficiency residual photon conversion electrons

• Estimate using found conversions and its efficiency