Lifetime and Mixing

1/27

Lifetime and Mixing

Chunlei Liu / University of Pittsburgh

On behalf of CDF and D0 collaborations

FPCP 2008 May 5-9

Lifetime and Mixing / Chunlei Liu 2/27

Part I Lifetime Motivation and Experiments B0

s , Bc lifetimes

Part II Mixing B0

s mixing from D0 D0 mixing from CDF


Spectator model: all b hadron lifetimes are equal.

Pauli interference prolongs lifetimes:+5% for B+, +3% for b

Weak annihilation or scatteringreduces lifetimes -7% b

Heavy Quark Expansion (HQE):

Lifetime ratios are better predicted:

(B+)/(B0), (Bs)/B0), (b)/(B0)…

Decay of B Hadrons

kinetic and chromomagnetic operator

weak annihilation and Pauli interference


The Bc Doubly Heavy Meson

• Doubly heavy with b and c quark – interesting lab for studying QCD

• Both quarks decay or annihilate, shorter lifetime than light B mesons

theory prediction:

(Bc) :0.47 0.59 ps

arXiv:hep-ph/0308214v1Phy Rev. D 64, 14003 (2001)Phy Lett. B 452, 129 (1999)hep-ph/0002127 ( and references within)


B0s Lifetime and Decay Width Difference

b ss

cc

W WW

s

B0s →J/

Eigenstates: Bslight and Bs

heavy => L and H

s= (L+H)/2 , = L-H

Two kinds of lifetime measurements:

1) Measure 1/s and directly (need to identify CP eigenstates)

2) Treat L and H together as one exponential, measure e.g flavor specific channel:


Combine s and

: theoretically calculable and sensitive to new Physics

Probe to New Physics : = 2|12|cos(s)


Latest HFAG (by 03/08)

New measurements today:

1) Bs lifetime –direct measurement

2) Bs lifetime – flavor specific

3) Bc lifetime

Theory references:

PRD 68, 114006 (2003)

PRD 70, 094031 (2004)

hep-ph/0705.3802 (2007)


Tevatron • pp collisions at 1.96 TeV

• 3.4 fb–1 data on tape (recorded at D0)

• Initial instantaneous luminosity up to 3x1032cm–2s–1

Main Injector & Recycler

Tevatron

p source

Booster CDFDØ

Apr 2002 – Apr 2008


CDF II Detector DØ Detector

• Central tracking: silicon vertex detector drift chamber

=> pT/pT = 0.0015 pT excellent vertex resolution• Particle identification: dE/dX and TOF

• Excellent muon coverage • Good tracker coverage• Silicon layer 0 installed in 2006 improves

track parameter resolution

tracker


Measure s and from B0s→J/

ct=L/

=Lxy/sin/

=LxyM/PT

CP conservation (s=0)

|BsH> : CP odd eigenstate ~ 25%

|BsL> : CP even eigenstate ~ 75%

S, D waves: CP even

P wave: CP odd

Angular distribution in transversity basis => separate CP eigenstates


Events Selection at CDF/D0

• Di-muon trigger • Neural Network selection at CDF ~ 2500 signal events• Cuts based selection at D0 ~ 2000 signal events


Measure s and

(s=0) =1.52 ± 0.04(stat) ± 0.02(syst) ps =0.08 ± 0.06(stat) ± 0.01(syst) ps-1

World’s best measurement!

Phys. Rev. Lett. 100, 121803 (2008)

(s free)=1.52 ± 0.05(stat)±0.01(syst) ps =0.19±0.07(stat) +0.02

-0.01(syst) ps-1

s=0) =1.53 ± 0.06(stat) ps =0.14 ± 0.07(stat) ps-1

(arXiv:/0802.2255[hep-ex])


Bs Lifetime Measurement from Bs→ Ds+() - X - CDF

fully and partially reconstructed channel such as: Bs→ Ds

-1 (+ 0)

Double statistics!

“K” factor accounts for missing momentum and mass

Extensive test on B0, B+ control samples

x2 stats


Data (1.3 fb-1) collected by displaced-vertex trigger ( 120m<d0<1mm )

~ 1100 fully reconstructed events

~ 2000 partially reconstructed events

=> cut on lifetime ( events with ct<d0 removed)

modeled with “trigger efficiency curve” from MC

Two-step fit, 1)mass fit

=> relative fraction of various modes and background

2) lifetime fit (shape from MC, fraction from mass fit)

=> extract lifetime only

Events Selection and Fit Strategy


Fix fractions from mass fit

(Bs) only free parameter

= 1.518 ± 0.041(stat.) ± 0.025(syst.) ps

(http://www-cdf.fnal.gov/physics/new/bottom/080207.blessed-bs-lifetime/)

Lifetime for control samples:B0→ D-(K+--) + B0→ D*-(D0(K+-)-) + B+ →D0(K+-) +

Agrees well with PDG

Lifetime Result (CDF)

D0 had Bs semileptonic lifetime in 2006 from Bs→Ds

-+X

=1.398±0.044(stat)+0.0280.025(syst) ps

PRL 97, 241801 (2006)


Bc Semileptonic Lifetime

Missing momentum, correct pseudo-lifetime: ct= K x ct*

K= pT(J/ l)/ pT(Bc)

Main challenge is multiple backgrounds:• real J/Ψ + fake lepton• fake J/Ψ + real lepton• real J/Ψ + real lepton → from bb events • prompt J/Ψ + lepton• residual conversion (J/+e only)


Bc→J/++X from D0 (1.35 fb-1)

Mass – lifetime simultaneous fit used to disentangle small signal fraction among large fraction of backgrounds

http://www-d0.fnal.gov/Run2Physics/WWW/results/prelim/B/B52/


Bc→J/+l+X from CDF (1.0 fb-1)

Muon channel Electron channel

c=179.1+32.6-27.2(stat) m c=121.7+18.0

-16.3(stat) m

combined (by likelihood):

=0.475+0.052-0.049(stat) ± 0.018(syst) ps

(http://www-cdf.fnal.gov/physics/new/bottom/080327.blessed-BC_LT_SemiLeptonic/)

Lifetime fit only


Combine Bc Lifetime from D0 and CDF

Bc lifetime measurements have been exclusive to Tevatron

Weighted average:=0.459 ± 0.037 ps

Theory prediction:

=0.47 – 0.59 ps


Part I Lifetime Motivation and Experiments B0

s , Bc lifetimes

Part II Mixing B0

s mixing from D0 D0 mixing from CDF


two eigenstates and

ms mH – mL , s ( H + L)/2, L – H

msTheo =19.3 ± 6.4 ± 1.9

(arXiv: 0705.3802/hep-ph)

ms/md |V∝ ts|2/|Vtd|2

HeavysB

LightsB

B0s Mixing

CDF measured at: 17.77 ± 0.10(stat) ± 0.07(syst) ps

Show D0 new result today !


Same SideOpposite Side

ms Measurement Strategy

2 2122

2

ct smS Ssignificance e

S B

D

mtetPt

BBB

cos 12

1000 ,

D


Final States Reconstruction at D0

D0 Run IIa D0 Run IIb innermost layer of silicon added resolution improved

Data collected by inclusive single and di-muon triggers, 2.4 fb-1

Final cuts maximizing S/ sqrt(S+B)


Measure ms at D0

Δms = 18.53 ± 0.93(stat) ± 0.30(syst) ps-1

2.9 significance ( DO conference note 5618) Agrees with what CDF measured in 2006: Δms = 17.77 ± 0.10(stat) ± 0.07(syst) ps-1

Introduce amplitude, P(t) ~ 1 AD cos(mst)Fit for A at different ms


D0 MixingD0 mixing in SM occurs through either: ‘short range’ processes ‘long range’ processes (negligible in SM)

M/ discovered K0 0.474 0.997 1964B0 0.77 <0.01 1987Bs 27 0.15 2006D0 < 0.01 < 0.01 2007

Recent D0 mixing evidence :1) Compare D0 → ππ, KK (CP eigenstates)

with D0 → Kπ ( Belle)

2) Compare doubly Cabibbo suppressed (DCS) D0 →K+π- with Cabibbo favored (CF) D0 →K-π+ (Babar )

Lifetime ratio:

where x=M/ , y=/2, is strong phase between DCS and CF modes


Evidence for D0 Mixing at CDF (1.5 fb-1)

CDF : probe longer D0 lifetime than B factories 3.8 significance comparing DCS D0 →K+π- to CF D0 →K-π+

RD (10-3) =3.04±0.55 x’2(10-3)=0.12±0.35 y’(10-3)= 8.5±7.6

(Phys.Rev.Lett.100:121802,2008 )

Lifetime ratio fit Bayesian probability 1-4 contour: closed circle: best fit value open diamond: highest probability point physically allowed (x’2≥0) cross : no mixing point 3.8


Conclusion

Best Bs and measurement in the world Bc lifetime provide better constraint for theory Bs mixing from D0 confirms CDF measurement D0 mixing evidence from hadron collider Expect new b lifetime result for the summer


Back Up


Angular Analysis in Transversity Basis

● Bs->J/ is P -> VV decay ➔ 3 possible angular momenta:

S, D wave: CP even P wave : CP odd● Separation by angulardistribution

➢ Transversity angles , ,


B0s Systematics and Cross Check

Systematics at CDF: 1) Background angular distribution 2) Mass model 3) Lifetime resolution function 4) B0 cross feed 5) Detector acceptance 6) Silicon detector alignment

Cross check sample at CDF:

B0→J/ K*0 for angular analyis

Lifetime: d= 1.52 ± 0.02(stat) ± 0.02(syst) ps

Systematics at D0: 1) Procedure test 2) Acceptance 3) Reconstruction algorithm 4) Background model 5) Detector alignment


Bs→ J/ angular distribution


B0 → J/ K*0

cd = 456 +/- 6 (stat) +/- 6 (syst) μm

|A0|2 = 0.569 +/- 0.009 (stat) +/- 0.009 (syst) |A|||2 = 0.211 +/- 0.012 (stat) +/- 0.006 (syst) δ|| = -2.97 +/- 0.08 (stat) +/- 0.03 (syst) δ = 2.97 +/- 0.06 (stat) +/- 0.01 (syst) ⊥


Mass components:

Single B templates (MC): (signal): Bs→ Ds() X (bkgd): B0, B+, b

Real D + track (background): template comes from fit to wrong-sign sample

Ds

Fake D + track (background): template comes from D sidebands


Bc Background Summary at CDF


One word about Λb Lifetime Status

x

expected soon x

- DØ measurements are in agreement with the theoretical predictions and with the world average

- CDF measurement in is ~3highw.r.t world average

- Expect CDF measurement updates very soon

decay mode CDF lifetime (ps), 1 fb-1 DØ lifetime (ps), 1.3 fb-1

update expected soon x

Lifetime and Mixing

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