Study of the Bc Meson Properties using BcJ/e Decay at CDF II

Masato Aoki

University of Tsukuba, Japan

2

“Periodic Table”

Bc meson is the last meson experimentally observed

3

q

q’

The Bc meson

Only meson state with differently flavored heavy quarks

(bottom and charm quark)Both quarks are heavySimilar binding interaction to heavy quarkonia families

(J/, etc.)Other quarkonia decay via strong interaction

The two quarks have different flavorOnly weak decay is possible

Comparable timescales for decay of two heavy constituents

Measurable lifetime but shorter than other B mesons (~0.5 ps)

J/

Bu, Bd, Bs

q

q

4

The Bc properties

Quarkonia described by Quark Potential modelsOpportunity to test with Bc

Expect:•Tightly bound: f(Bc) eV

•Ground state mass predictions : 6.1<M(Bc )<6.5 GeV/c2

•Rich spectroscopy of narrow states below B-D threshold

5

Decay properties

Three dominant processes: b decay:

• J/ p+, J/Ds+, J/ l+

c decay: • Bs

0+, Bs0 l+

Annihilation: • , DK, multi-

Large f(Bc) and Vcb vertex 400x larger annihilation width than for B+

6

Decay properties

Naïvely expect factorization to applyb+c+ ann.

• Expect - psHowever, bound-state effects may be large

• Eichten and Quigg predict ps

7

Theoretical calculations

V. V. Kiselev, hep-ph/0308214 (2003) : Review paper

(Bc) [ps] Author

0.357 ~ 0.362 C. H. Chang et al. (Commun. Theor. Phys. 35, 57 (2001))

0.480.05 V. V. Kiselev et al. (Nucl. Phys. B 585, 353 (2000))

0.630.02 A. Yu. Anisimov et al. (Phys. Atom. Nucl. 62, 1739 (1999))

0.590.06 A. Yu. Anisimov et al. (Phys. Lett. B 452, 129 (1999))

0.46 ~ 0.47 A. El-Hady et al. (Phys. Rev. D 59, 094001 (1999))

0.380.03 L. P. Fulcher (Phys. Rev. D 60, 074006 (1999))

0.4 ~ 0.7 M. Beneke et al. (Phys. Rev. D 53, 4991 (1996))

0.550.1 V. V. Kiselev (Phys. Lett. B 372, 326 (1996))

< 1.0 I. I. Bigi (Phys. Lett. B 371, 105 (1996))

0.40 C. H. Chang et al. (Phys. Rev. D 49, 3399 (1994))

1.1 ~ 1.2 C. Quigg (FERMILAB-CONF-93/265-T (1993))

0.50 M. Lusignoli et al. (Z. Phys. C 51, 549 (1991))

Bc

obse

rvat

ion

by C

DF

(199

8)

8

Rich decay modes

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)

Large J/ rate provides experimental signature

( For example, BR(BuJ/K) =0.1% )

9

Hadronic productionDominant process is

ggBc+bc

Calculation requires 36 diagrams O(s

4)Contributions from color

singlet / octet

Chang et al, PRD, 71 (2005) 074012

curves representdifferent singlet/octet contributions

10

Bc production rate

Much smaller production rate than other b-hadrons

Species Prod. Fraction

B+ 40%

B0 40%

Bs 10%

b-baryons 10%

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

11

Heavy Flavor Physics at CDFHuge production cross sections

at Tevatron b~30 b

Currently only Tevatron can produce the Bc mesonB-factories cannot produce the Bc meson because the beam energy is not enough for the Bc generation

Large backgrounds as well B triggers are necessary lepton trigger displaced track trigger and combined trigger

quark annihilation gluon fusion

flavor excitation gluon splitting

Typical bb pair production diagrams

12

Bc discovery in CDF Run I (’91~’96)

Bc signal search using BcJ/l(l=e,) channel ~20 Bc signal events were observed in 110 pb-1 of

J/ trigger 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)

13

The CDF II detector @Tevatron

Silicon Detector ||<2.0 vertex~30m

Central Outer Tracker ||<1.0 pT/pT=0.15% pT

Muon Chamber ||<0.6 (1.0)

EM, HAD Calorimeter ||<1.1(EM), <0.9(HAD) E/E=√ (13.52/ET +32) % (EM)

=√ (502/ET +32) % (HAD)

HAD CalorimeterHAD CalorimeterMuon ChamberMuon Chamber

Central Outer TrackerCentral Outer Tracker

Silicon DetectorSilicon Detector

EM CalorimeterEM Calorimeter

All of the tracking system are replacedfor Run II

14

Bc signature in this analysis

Use semileptonic decay BcJ/e Larger BR than other triggerable decay modes

statistical advantage

Improved J/ trigger• pT()>1.5 GeV/c (was 2 GeV/c)• Factor ~5 J/ yield (factor ~2 BJ/ yield)

No narrow mass peak due to missing neutrino…• Bc signal = excess above estimated backgrounds

More photon conversion background due to new tracking system (more material than Run I)

Establishing the Bc again and precise measurements (Bc)B(BcJ/e) / (Bu)B(BuJ/K) and lifetime

(Mass to be measured in exclusive channel)

15

J/ trigger data

Lint ~ 360 pb-1

pT() > 3 GeV/c Reduce fake Reduce prompt

~2.2M J/Signal window |M()-M(PDG:J/)| < 50 MeV/c2

Sideband : for fake J/ study

J/ signal region

Additional requirements in this analysis…

16

Electron reconstructionpT(e) > 2 GeV/c, ||<1.0Track-seeded reconstruction : Inside-Out algorithm

High reconstruction efficiency for low pT electrons Calorimeter-seeded algorithm is used for high pT physics

Electron ID using both calorimeter and dE/dx measured by COT

17

Calorimeter 10 variables

— Red : electrons from e+e

— Blue : pions from Ks

E/p EHad/EEm E/p(shower max)

Ewire/Estrip

(shower max)

2wire

(shower max)

2strip

(shower max)

Z/(shower max)

Q·X/(shower max)

E(preradiator)

X(preradiator)

18

Electron ID using calorimeter10 variables from

calorimeterForm a Joint Likelihood

Function

L cut position is varied not to have any dependences for electron efficiency (isolation,pT,charge)

~70% efficiency

19

Isolation

Isolation is defined by pT/pT

pT in the denominator is the pT of the track of interestpT in the numerator is the scalar sum of pT of all other tracks in the same calorimeter tower

Calorimeter variables strongly depend on the isolationIsolation correction is

necessaryBcJ/e decay is expected to

have similar isolation to that for BuJ/K

CDF Preliminary

20

Electron ID using dE/dxEnergy deposit in COT

Ze/Z–1.3

Ze=Log((dE/dx)measured/(dE/dx)pred. for e)

~90% efficiency

22GeVGeV

e

p K

ep

K

e

pK22GeVGeV

21

(Bc)B(BcJ/e) / (Bu)B(BuJ/K) Measurement

22

(Bc)B(BcJ/e) / (Bu)B(BuJ/K) measurement strategy

1. Reconstruct mass of J/-e pair

2. Estimate all the backgrounds

3. Event counting above the backgrounds

4. Estimate the acceptance and efficiency Use BuJ/K as the normalization mode

BuJ/K has similar topology to BcJ/e

Cancel out most of uncertainties

Bu+

J/ +

-

K+

Bc+

J/ +

-

e+

23

J/e pair reconstruction

One displaced decay vertexLxy/Lxy > 3

Prompt background becomes negligible

pT(J/-e) > 5 GeV/c Reduce non-B tracks

Search window Wide mass region due to

missing neutrino 4 < M(J/e) < 6 GeV/c2

Primary Vertex

Secondary VertexpT

Lxy

Rx

y

signal region

Bc+

J/+

-

e+

24

Background Estimates

25

Backgrounds and control samples

fake J/ J/ mass sideband events

fake electron J/ + track

bb (beX, bJ/X) PYTHIA Monte Carlo

electron from photon conversion J/ + electron tagged as photon conversion

prompt J/ No control sample. There is no reliable Monte Carlo Zero lifetime killed by Lxy/Lxy>3 requirement

26

Fake J/ background

Fake J/ background can be estimated by J/ mass sideband events

J/+electron, J/+track, J/+conv.-e have fake J/ part each other

To avoid double counting, fake J/ events (sideband events) will be subtracted in the following background estimations

27

Fake electron background

Control sample : J/ + track

(after dE/dx requirement)Fake rate after eID by calorimeter

1.Fake rates for K//p• Control samples from high statistics

Two displaced Tracks Trigger (TTT) data

2.Combine them with proper fraction obtained from PYTHIA Monte Carlo

Nfake = N(J/+track) x fake

primary vertex

secondary vertex

d0

Long lived particle

Displaced track trigger

particle composition around J/

28

Fake rate estimates for K//p

Control samples in TTT data D0K for K p for protonFit the mass distribution to obtain # of events before and after eID by calorimeterFake rate = N after eID / N before eID

after eID

after eID

p p

after eID

29

Particle composition in J/+track sample

PYTHIA Monte Carlo simulation

Dominant fake source : pion

after dE/dx requirement

Kaon

Pion

Proton

Kaon

Pion

Proton

pion fraction from dE/dx fitting max difference ~0.09

Data

PYTHIA

~0.09

CDF Preliminary

30

Average fake rate

The average fake rate is applied to J/+track after dE/dx cut

KK

pp

positive chargenegative charge

average fake rate

< 0.8%

CDF Preliminary

CombinePPKKππaverage fεfεfεε

31

Systematic uncertainties

Isolation dependence on fake rate ~14.5%

Difference between TTT data and J/ trigger data (tight requirement on # of silicon hits for TTT) ~7.2%

Particle fraction in PYTHIA ~1.9%

Sample statistics J/+track : ~2.0% Fake rate : ~0.9%

32

Estimated fake electron background

From J/+track data with fake rate convolution15.43 2.54 events in the signal region

33

Photon conversion electrons

Control sample : J/+e tagged as ee Find collinear partner track

These candidates are removed from the J/e candidate list

Miss-tracking due to very low pT partner track

Not 100% finding efficiency

Residual photon conversion electronsNeed to understand the finding efficiency

34

Conversion finding efficiency

Monte Carlo sample : B0J/0

98% 0, 2% 0eetag = ~50% efficiency

Residual ee events

Systematics study Another MC : use pT(tracks) in J/+track as pT(0)

tag

tagtaggedresidual ε

ε1NN

35

Systematic uncertainties

pT spectrum~43.7%

Lifetime of B0

~2.0%Dalitz decay

~1.0%Sample statistics

Finding efficiency : ~3.8% J/+conv. e : ~30.1%

CDF Monte Carlo

36

Estimated residual photon conversion

From J/+conv-e data and conversion finding efficiency

14.54 7.75 events in the signal region

37

bb background

It is possible to make a common vertex with J/ from one B decay and e from another B decay

bb background

quark annihilation gluon fusion

flavor excitation gluon splitting

38

bb background estimatePYTHIA Monte Carlo simulationValidated using bb azimuthal correlation information [PRD71,092001 (2005) ] Reasonable agreement with data

Normalization with data : N(BuJ/K)

Azimuthal angle distribution between J/ and electron with all kinematical requirements

Bc signal MC

Additional requirement : J/-e< 90deg.

39

Systematic uncertainties

Monte Carlo setting (PDF/ISR) ~31.4%

Isolation dependence on eID efficiency ~2.9%

Branching ratio of normalization mode BuJ/K ~0.9%

Calorimeter fiducial coverage ~0.9%

Statistics MC sample : ~6.5% N(BuJ/K) in MC : ~1.9% N(BuJ/K) in data : ~1.8% (eID by cal) : ~1.4% (eID by dE/dx) : ~1.0%

40

Estimated bb background From PYTHIA Monte Carlo BuJ/K for normalization to data

33.63 11.38 events in the signal region

41

Summary table

Fake e 15.430.312.52

Conversion 14.544.386.39

bb 33.632.2011.17

Total bkg 63.594.9113.59

Data 178.5014.67*J/ sideband events are subtracted

*before the subtraction, data has 203 events and the fake J/ is 24.5±3.5

42

M(J/+electron) data and excess

Total background : 63.6±14.4 eventsExcess : ~115 eventsSignificance : 5.9

43

Cross check : e-track IP w.r.t. J/ vertex

Lxy(J/)/Lxy> 3 Bc decay vertex position is the same as

that for J/ (J/ immediately decays) Bc should make a peak around IP=0

CDF Preliminary

CDF Preliminary

electron

Lxy(J/)

IP

PV

Peak exists!

J/-eBuJ/K

44

(Bc)B(BcJ/e) / (Bu)B(BuJ/K) calculation

Have established the signal !!Let’s calculate (Bc)B(BcJ/e) / (Bu)B(BuJ/K)

• acceptance ratio • efficiency ratio

45

Similar reconstruction criteria as J/eN(Bu)=287259 was found in the same data

Normalization mode : BuJ/K

46

Kinematical acceptance ratioRK = Akin(Bu)/Akin(Bc) = 4.42±1.02

MC parameters RK RK

Central value (M=6.271GeV/c2,=0.55ps) 4.4160.082

0

M(Bc)=6.291 GeV/c2 4.4030.082

0.013

M(Bc)=2.251 GeV/c2 4.3940.082

0.022

(Bc)=0.7 ps 4.0760.074

-0.34

(Bc)=0.4 ps 5.0060.096

+0.59

pT(Bc) spectrum 3.5780.062

0.838

Lxy 4.5760.086

0.16

BcJ/eX other decays 4.7690.090

+0.353

Trigger 4.2990.079

-0.117

e/K tracking 2%

Systematic uncertainties

Lar

ge

st

47

Reconstruction efficiency ratio

)/()()()/()()(

)()/()()(

dXdEcaleJvertextrigger

KJvertextriggerR

trkcccc

trkuuuu

%90~%70~

1

)/()(

1

dXdEcalR

Most of the efficiencies are expected to

be same for Bc and Bu

electron ID with calorimeter and dE/dx

48

Kinematical limits

Choose pT(B) > 4GeV/c, |y(B)| < 1 as our cross section definition

(Run1 : pT(B) > 6GeV/c, |y(B)| < 1)

4GeV -1 < y(Bc) < 1

49

Result of B ratio measurement(Bc)B(BcJ/e) / (Bu)B(BuJ/K)= 0.282 0.038(stat.) 0.035(yield) 0.065(acc.) (pT(B)>4GeV/c, |(B)|<1)

Most of the difference to the Run I measurement is from the treatment of input pT(Bc) spectrum

Still consistent with Run I

Consistent with result from muon channel 0.245 ± 0.045(stat.) ± 0.066(syst.) +0.080/-0.032(life.)

The result is consistent with recent QCD calculation

0.132 ±0.031+0.041–0.037

+0.032–0.020

50

Lifetime Measurement

51

Lifetime measurement strategy

1. Release Lxy(J/e)/Lxy > 3 requirement

2. Cut on Lxy error (Lxy < 70 m)3. Use J/e events in the signal region(4-6 GeV/c2)4. Estimate # of background events using same way

as B ratio measurement5. Un-binned maximum likelihood fit with J/e data

1. Input : pseudo-proper decay length and its error2. Background shapes from each control sample3. Prompt background shape is assumed to be a

resolution function (Gaussian)4. Signal shape with neutrino effect correction

5. Fit J/e data to extract Bc lifetime

52

Fit input value and neutrino effect correction

ct : proper decay length

X : pseudo-proper decay length

K : correction factor

KX

Bp

BM

eJM

eJp

eJp

eJML

)(Bp

)M(BL)ct(B

cT

cT

Txy

cT

cxyc

)(

)(

)/(

)/(

)/(

)/(

K-distributions for 4 M(J/e) binsInput value for the lifetime fitting

53

Background estimates (w/o decay length cut) Background events are estimated using same way as B ratio measurement

Prompt background and Bc signal are from the lifetime fitting directly

M(J/e) [GeV/c2] 4-6

fake J/ 164.0±9.1

fake electron 110.2±19.0

photon conversion

67.4±34.8

bb 63.0±18.4

prompt ??

Bc ??

data 783*systematic uncertainties are included

54

Background distributionsFake J/

Fake electron Photon conversion

bb

55

J/e data fit result

c=142 +22/-20 mN(Bc)237 events (N(prompt bkg) 127)

56

Systematic uncertainties on c(Bc)

Total systematic uncertainty is order of ~7% (10m)

57

Bc lifetime result

CDF Run2 (360pb-1, J/+e) c = 142 +22/-20 ±10 m = 0.474 +0.073/-0.066 ±0.033 ps

Operator Product Expansion 0.55 0.15 ps

Bethe-Salpeter Model 0.46~0.47 ps

Light-Front Constituent Quark Model

0.59 0.06 ps

Light-Front ISGW Model 0.63 0.02 ps

Hard-Soft Factorization 0.55 0.1 ps

QCD Sum Rules 0.48 0.05 ps

Recent theoretical calculations in which 3 major decay diagrams play important roles

58

Experimental results of the Bc meson lifetime measurement

This analysis

59

Summary of the Bc analysis

Have established the Bc signal in J/e final state with 5.9 significance

Measurements with good precision (world’s best) (Bc)B(BcJ/e) / (Bu)B(BuJ/K) = 0.282 0.038(stat.) 0.035(yield) 0.065(acc.) Lifetime = 0.474+0.073/-0.066(stat.) 0.033(syst.) ps

The results are consistent with CDF Run I measurements

Lifetime result agrees with theoretical models in which all the three major decay diagrams play important roles in the Bc decays

60

FIN

Thank you•This lifetime result with minor update was accepted for publication in Physical Review Letters [PRL 97, 012002 (2006)]

61

Backup slides

62

Introduction

Three major decay diagramsLifetime should be Bc 1/(0.6+1.2+0.1) 0.5 ps

if all the three diagrams contribute to the decay

*Others : – Pauli interference) + penguin) + …

63

PDF and likelihood functionSignal PDF :

Background PDF for fake J/,fake e, conv. e, bb :

Event PDF :

Log likelihood :

signal term

backgrounds term

Background shapes and the numbers are constrained

64

Fitter check before J/e data fitting

Toy MC

BuJ/K data

c=504.1 ± 9.3(stat.) mgood agreement with CDF Run II result : 498.8 ± 8(stat.) ± 4(syst.) m

Fitter returns reasonable lifetime result and error

CDF Preliminary

65

Cross check : J/+e mass distribution

Normalization : 4~6 GeV/c2 using lifetime fit result Prompt shape : Assume to be J/+track with Lxy < –3Good agreement

66

Determination of the angle from nonleptonic BcDsD0 decays

67

CP-even factors

CP-eigenstates for the oscillation D0D0

68

69

Branching ratio of BcDD

Several billion Bc events are expected at LHC 104~105 decays of Bc

70

CDF Run-II

M(J/)

M(J/)M(J/e)

ct*(J/e)0.460.08 ps62875GeV

Pub. Pub.

Pre. Pub.

71

D0 Run-II

Pre.

Pre.

72

Bc mass measurement

CDF Run-II~1.1pb-1

Bc+J/+

~50 signals>7.5sigma

6276.5 ± 4.0 ± 2.7 MeV/c2

Latest

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se u

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