ICFP 2005, Taiwan Colin Gay, Yale University B Mixing and Lifetimes from CDF Colin Gay, Yale...

ICFP 2005, Taiwan Colin Gay, Yale University

B Mixing and Lifetimesfrom CDF

Colin Gay, Yale Universityfor the

CDF II Collaboration


Outline

• Status of B lifetimes• Bs “lifetime” and lifetime difference• Bs mixing


State of Lifetime

• Heavy Quark Expansion predicts

0B B Bs b

• B+, B0 in ok shape

• b a bit below expectation

• Bs on edge

• More on this later

/(B0) Expt /(B0) Theory

B0 1.528 ± 0.009 ps

B+ 1.643 ± 0.010 ps 1.076 ± 0.008 1.06±0.02

Bs 1.405 ± 0.045 ps 0.920 ± 0.030 1.00±0.01

B1.232 ± 0.072 ps 0.806 ± 0.047 0.86±0.05


Lifetime/Mixing samples

Semileptonic Hadronic

• Easy to trigger ()• 100s–1000s events•Eg

• High pt lepton•Missing complicates• ~2k-100k evts•Eg

• Low pt lepton + displaced track• ~8k events• Eg

• Two displaced tracks• ~500-10k events• Eg

/ basedJ

lifeti

me

Unbia

sed t

rig

ger

lifeti

me

bia

sed t

rigger

0 *0

/

/

/

/s

b

B J K

B J K

B J

J

s sB l D X

s sB l D X

0

0

s s

B D

B D

B D

Mixing


Measuring Lifetime

• For fully reconstructed (hadronic) modes

0 pct ct ct

p

Vertex resolution(~constant)

Momentum resolution(proportional to ct)

~ (30 ) (c.f. ~ 450 )ct O ct

~ (15%)p Op

• For semileptonic modes, missing neutrino causes

=> Resolution poor at large decay time

Important effect for Bs mixing

xy B

T

L MLc

p

Flight distance

Boost

properdecaylength


Fully Reconstructed J/ X

• Easy to trigger on, large samples, unbiased in lifetime• Fully reconstructed modes • Excellent vertex and momentum resolution

• CDF Fully reconstructs•J/+•B+ J/K+

•B0 J/K*, J/Ks

•Bs J/b J/

0 462 15 4B

c m 460.8 4.2PDG m

For example:

• See summary followingfor detailed results

1155§39 signal


Lifetimes from hadronic decays

• To get large samples of fully reconstructed hadronic decays, we use events recorded via the Secondary Vertex Trigger• Requires 2 tracks with impact

parameters between 120m and 1mm • Trigger has intrinsic lifetime bias• Events have excellent momentum and

vertex resolutions

• Final states reconstructed:• B± D0± (D0K) N=8380 evts• B0 D± D±K) N=5280 evts D± 3(D±K)N=4173evts• Bs Ds ± (Ds) N=465 evts Ds 3 (Ds) N=133 evts

B- ct-efficiency

B- D0-

• Larger statistics than J/ modes

• Larger systematics due to• Trigger Efficiency curve • Larger backgrounds


Lifetimes from hadronic decays

B+

Bs

Bs

(B+) = 1.661±0.027±0.013 ps (Bs) = 1.598±0.097±0.017 ps(B0) = 1.511±0.023±0.013 ps


Lifetime with high-pt Semileptonic sample

0sB

sD

W

b cl

s

l

s

• Trigger on 8 GeV lepton• Reconstruct• High statistics, but missing

neutrino -> “K” factor

lB Dl X

(B+) = 1.653±0.029±0.032 ps

(Bs) = 1.381±0.055±0.046 ps

(B0) = 1.473±0.036±0.054 ps

KDp

BmLct

sTxy

)(*


B Mass & Lifetime Difference

12 12* *12 122

M M iH

M M

• Second order weak diagram gives non-zero matrix element• In basis have a non-diagonal Hamiltonian

B H B

B B

• Recall Eigenstates are:

b s

bs

0sB 0

sB, ,u c t , ,u c t

*tsV

tbV

tbV

*tsV

W

W

, 12 1222Im( ) iH L M

, 12 122Re( ) iH LM M M

/ 2

/ 2

m

12

12

|

|

(| | )

(| | )

Hs

L

s s

s ss

B B

B B

B

B12

1( )L H

L H


Bs “lifetime” meaning

but SL SLH L H L

12

| ( ) (| ( ) | ( ) )H Ls s sB t B t B t

• E.g. lifetime measured in SL decays dominates the average

22 22

2

2

11

1L H

SL L L H HL H s

f f

sB

s d

2

22

2

1

1SL d d

1.47 0.05

1.53 0.01

FS

d

Unphysical value =>most likely / 0

• With the constraint (HQE says equal to 1%)

• When a significant exists,lifetime measurements aresample composition dependent

• Measured lifetime iswhere = fraction of light state

meas L L H Hf f Lf


Extracting both Bs lifetimes

• In previous cases, the sample composition, and hence relation of depends upon the unknown

• In the case of the hadronic decays, there is the additional effect that the trigger turn-on affects the short-lived component of the Bs more than the long-lived

• There is a decay in which one can measure, simultaneously, the light-heavy sample composition AND each components’ lifetime:

• S,D wave amplitudes = Parity Even, (CP Even)• P wave amplitude = Parity Odd, (CP Odd)

• Since the mass eigenstates of the Bs system are

12

(| | )Hs s sB B B CP odd

12

(| | )Ls s sB B B CP even

Disentangle different L-componentsof decay amplitudes => isolate two B states

/sB J

• See D0 talk for details


Two Lifetimes

0.160.13

0.580.46

1.05 0.02ps

2.07 0.03ps

L

H

0.19 -10.24

0.250.33

0.47 0.01 ps

0.65 0.01

s

s

s

CP-odd fraction ( ) ~ 22%H

0.140.11

0.390.43

1.23 ps

1.52 ps

L

H

0.270.400.21

s

s

+ Recent D0: 1.42±0.04±0.06 psSL


The two Lifetimes

Constraint helpslow statistics H

0.080.09

1.21 0.08ps

1.68 ps

L

H

( 1.53 0.009) d

Note that L d


Experiments vs. Theory

Flavor-specific“lifetime” (SL) CDF

D0

( 1%)S d

TheoryPreferred

Theory:


Combined CDF/D0 Fit

-1

0.090.11

0.0430.047

0.23 0.08ps

0.33

11.405 ps

s

s

s

s


Lifetimes: CDF Summary

J/ modes Hadronic modes Semileptonic modes HFAG 2005

B0 1.539±0.051±0.008 1.511±0.023±0.013 1.473±0.036±0.0541.528 ± 0.009

B+ 1.662±0.033±0.008 1.661±0.027±0.013 1.653±0.029±0.0321.643 ± 0.010

Bs 1.369±0.100±0.009 1.598±0.097±0.017 1.381±0.055±0.0461.405 ± 0.045

B 1.25±0.26±0.10 1.232 ± 0.072


Mixing Analysis Strategy

•Just like a lifetime measurement, but look for change of B particle to antiparticle

•Mixing

•Bs or Bs at production?• Initial state flavor tagging (calibrated on B0)• Tagging dilution D=1-2w, w=mistag prob.• Effective sample N D2 (D2~1%)

• Bs or Bs at decay?• Decays are self-tagging (eg )

• Reconstruct proper decay time

mteN

BBdt

dN

mteN

BBdt

dN

t

t

cos12

cos12

/000

/000

Kaon

s sB D

• Fit Asymmetry (Nunmixed-Nmixed)/ N to D*A*cos(m t) at fixed m

• Expect A=1 for m ~ ms

• Limit (95% CL): m such that A+1.645A = 1


Flavor Tagging + Signals

•Opposite side tagging• Use the other B in the event• Semileptonic decay (b l-)• (1) Muon, (2) Electron

• Use jet charge (Qb = -1/3)

• (3) Jet has 2ndary vertex

• (4) Jet contains displaced track

• (5) Highest momentum Jet

• Calibrated on B0 Opposite side B

Reconstructed B

Fragmentation track

0sB

K

K

bjetQ

• Hadronic (eg ): • Less signal yield• Excellent pT resolution• Good sensitivity at higherms

•Semileptonic (eg ): • Higher signal yield• Poor pT resolution• Good sensitivity at lower ms.

0sB

sD

W

b cd

s

u

s

ss DB0

lss lDB 0

0sB

sD

W

b cl

s

l

s


CDF Limit (Semileptonic Mode)

• Bs ! Dsl X l=e/(360 pb-1)

• Ds !

• Opposite side:

• e, tag

• Jet Charge

• 7800 events

• D2 = (1.43§0.09)%


CDF Limit (Hadronic mode)

1

1Limit: 0.0 @95% CLSensitivity: 0.4

sm ps

ps

• Bs ! Ds (360 pb-1)

• Ds !

• Opposite side:

• e, tag

• Jet Charge

• ~900 events

• D2 = (1.13§0.08)%


Potential Improvements

• Increase statistics • Additional Decay Modes, More Data

• Increase tagging power

• Same Side Kaon Tagging increase D2 by 1-3%

• Lifetime resolution improve 10-20%

StatisticsR

esolution

Statistics


Conclusion

• Bs mixing search at the Tevatron is an ongoing affair• Expect improvements in technique and statistics• Observation likely still some time away

• Lifetime ratios in reasonable agreement with theory• Bs the exception?

• Lifetime difference observed. Higher than predicted, but errors still large

• In addition, the mean width differs by ~2.7 from prediction

• Could it really be that • Will repeat J/ analysis with x4 data

• Both CDF and D0 are statistics limited

~ 1.1 ?s d

ICFP 2005, Taiwan Colin Gay, Yale University B Mixing and Lifetimes from CDF Colin Gay, Yale...

Documents

Transcript of ICFP 2005, Taiwan Colin Gay, Yale University B Mixing and Lifetimes from CDF Colin Gay, Yale...