B Physics and CP Ise-Shima, Japan February 19, 2001 Summary of - - PowerPoint PPT Presentation

Stewart Smith Princeton University

for the BABAR Collaboration

B Physics and CP Ise-Shima, Japan February 19, 2001

February 19, 2001 BCP4 Ise-Shima, Japan 2

Summary of PEP-II/BaBar performance Basics of measuring CP violation at an

asymmetric B Factory

Details of the data sample and analysis Extracting sin 2β Cross-checks and error analysis Looking to the future Conclusion

February 19, 2001 BCP4 Ise-Shima, Japan 3

• Running began Jan 2000

~24 fb-1 total by Oct 31

~21 fb-1 Υ

Υ Υ Υ(4S);

• ~3 fb-1 continuum
• Shutdown Nov1 – Feb1

PEPII improvements BaBar repair/maintenance Computing development

for 5 x 1033

• 2001 Run is underway

Began 3 Feb 1.5 1033 As of 15 Feb Expect ~40 fb-1 in CY ‘01

February 19, 2001 BCP4 Ise-Shima, Japan 4

CESR/CLEO (from CESR Web page)

PEPII/BABAR

6 12 18 (fb-1)

‘80 ‘90 ‘00

Extremely fast PEP-II Turnon

February 19, 2001 BCP4 Ise-Shima, Japan 5

By end of 2000 run, peak & average luminosity were

above design and climbing:

DESIGN: 3.0 nb-1/s 135 pb-1/d ~0.80 fb-1/w ~ 3.3 fb-1/m ACHIEVED: 3.28 184 1.03 3.8

BaBar performed just fine at 3.2 ×

× × × 1033

This year we expect to reach 5 ×

× × × 1033

Luminosity profile - next few (calendar)years:

2000 2001 2002 2003 2004 2005 25 43 80 110 130 180 fb-1

• Ldt >

> > > 500 fb-1 by end of 2005

We’re going to need it – life is hard.

…

Preliminary

(~2% uncertainty)

February 19, 2001 BCP4 Ise-Shima, Japan 6

A AR

February 19, 2001 BCP4 Ise-Shima, Japan 7

Neutral B and B mix into mass eigenstates, oscillating at a

frequency determined by ∆mB Concezio Bozzi talks on BaBar mixing results at 0900 Thur.

We define

, where

For a single decay amplitude with weak phase

Im λ λ λ λ = sin 2(φ φ φ φM - φ φ φ φD)

• Leads to CP-violating asymmetries interpretable by

the Standard model

B0-B0 CP

M

i td tb td tb

e V V V V p q

φ 2 * *

= =

A A p q = λ

• =

| | B H f A

• =

| | B H f A

D

φ

February 19, 2001 BCP4 Ise-Shima, Japan 8

V V

cd cb

V

td

V

ub

* * td tb cd cb

V V V V

* * ud ub cd cb

V V V V

CP

B0d→ππ →ππ →ππ →ππ

B0

s→ϕ

→ϕ →ϕ →ϕK0

S

B0d→ → → →J/ψ ψ ψ ψK0S (0,0)

* * *

= + +

tb td cb cd ub ud

V V V V V V

CP-violating Asymmetries in B decays directly measure phases α α α α, β β β β, and γ γ γ γ via– “no” hadronic uncertainties

February 19, 2001 BCP4 Ise-Shima, Japan 9

The ϒ(4S) decays into a P-wave B0 B0 state that

evolves coherently till one of the B’s decays. The B’s are almost motionless in the ϒ(4S) rest frame.

We measure the interference between direct and mixed

decays to a CP eigenstate

CP

ϒ ϒ ϒ ϒ(4S)

B

B

( )

/ f

S CP

K J ψ =

2 / sin e 2 t m d

i

∆ ∆

β

CP

A f

B

CP

A f

2 / cos t m d ∆ ∆

i

February 19, 2001 BCP4 Ise-Shima, Japan 10

For a tag B0 (B0) at time tTAG , the time distribution of the

• ther meson into a

CP eigenstate at time ∆t = tCP - tTAG

is given by

f+ f-

B0 → → → → fCP (f+) B0 → → → → fCP (f-)

Decay-time Distributions

February 19, 2001 BCP4 Ise-Shima, Japan 11

For b →

→ → → (C C ) S | λ λ λ λ|=1 and

I m λ

λ λ λ = - η η η ηf sin2β β β β β β β β = arg [VcdVcb*/ VtdVtb*]

We reconstruct the “gold / silver”CP eigenstates:

J/ ψ ψ ψ ψ K0S, ψ ψ ψ ψ (2s)K0S (η η η ηf = -1) J/ψ ψ ψ ψ K0L (η η η ηf = +1)

t-dependent

asymmetries:

ACP dt = 0

• Asymmetric B Factory!

February 19, 2001 BCP4 Ise-Shima, Japan 12

∆ ∆ ∆ ∆

E - = 9.0 GeV; E + = 3.1 GeV

Lorentz Boost βγ βγ βγ βγ = 0.56

∆ ∆ ∆ ∆t ≈ ∆ ∆ ∆ ∆z /β β β β γ γ γ γ c

e+ π+

S

K

e— π— ∆z ϒ(4S)

CP

B

ψ J/

( )

0 B

B

( ) ( ) ( ) tags

, ,

− + − + − +

K e µ

σCP ≈ ≈ ≈ ≈ 70 µ µ µ µm σtag ≈ ≈ ≈ ≈ 180 µ µ µ µm

February 19, 2001 BCP4 Ise-Shima, Japan 13

Fully reconstruct exclusive B decays to eigenstates of CP

• r flavour, and tag flavour of the other B in the event.

Select BCP candidates (B0 → J/ψ Ks , etc.) and

Bflav candidates (B0 →D* +, etc.)

Select Btag events using, primarily, leptons and K’s from

B hadronic decays, and determine the B flavour.

Measure the mistag fractions wi and determine the

dilutions

Di =1 – 2wi

Measure ∆Z between BCP and Btag to determine the signed

time difference ∆t between the decays

Determine the resolution function for ∆

∆ ∆ ∆t

February 19, 2001 BCP4 Ise-Shima, Japan 14

Crucial Elements in A(∆

∆ ∆ ∆t ) measurement:

• I. Vertex Resolution

Even at PEP-II, B’s don’t go very far! ( ≈ 250 µ µ µ µm)

5 Layer Silicon Vertex Tracker σ σ σ σz≈70 µ µ µ µm: reco’d B 180 µ µ µ µm: tagging B

(rms for 99% of events)

February 19, 2001 BCP4 Ise-Shima, Japan 15

Crucial Elements in A(∆ ∆ ∆ ∆t ) measurement:

• II. Particle ID and Tagging

J/ψ

ψ ψ ψ’s are detected by their ee and µµ µµ µµ µµ modes

KL modes are an important contributor to CP

• sample. KL‘s are detected by their strong

interaction debris in EMC and IFR

The flavour of the tagging B decay is

determined from its lepton and kaon content, and from slow pions from D*’s

February 19, 2001 BCP4 Ise-Shima, Japan 16

Particle ID:

• Track matching in the EMC
• 0.89 < E/P < 1.2
• EM shower shape requirements
• DCH dE/dx consistent with

electron hypothesis

• Efficiency and π

π π π misID probabilities determined from the data (Control Samples)

• Typical Tight Electron

selection: ~92% efficiency above 500 MeV, with 0.1% π π π π misID

February 19, 2001 BCP4 Ise-Shima, Japan 17

Particle ID: Muons

plab (GeV/c) Muon efficiency

BABAR

0.2 0.4 0.6 0.8 1 1 2 3 4 5

plab (GeV/c) Pion misidentification

BABAR

0.02 0.04 0.06 0.08 0.1 1 2 3 4

• Cut on # interaction lengths and

difference from that expected for a µ µ µ µ track

• IFR hit pattern rejects hadron

showers

• consistent with a MIP in the EMC
• Typical Tight Muon selection: ~75%

efficiency above 1.5 GeV, with ~3% pion mis ID

February 19, 2001 BCP4 Ise-Shima, Japan 18

0.2 0.4 0.6 0.8 1 1 2 3 4

plab (GeV/c) Pion misidentification y plab (GeV/c) Kaon efficiency plab (GeV/c)

BAB

AR

• dE/dx from

DCH and SVT

• θ

θ θ θC from DIRC Better than 3 σ

σ σ σ K/π

π π π separation

for pK > 250 MeV/c

February 19, 2001 BCP4 Ise-Shima, Japan 19

B

Leptons (l

l l l -→ B0 tag )

Electron Pcm >1.0 GeV/c Muon

Pcm >1.1 GeV/c

Kaons

Σ Kaon Charge ≠

≠ ≠ ≠ 0

NT1,NT2 (neural net)

slow pions (from D*) Isolated unidentified leptons

b c s

e-,µ-

K-

February 19, 2001 BCP4 Ise-Shima, Japan 20

• A negative kaon is found

in the decay products of the

• ther B meson, which is

therefore tagged as a

• ∆

∆ ∆ ∆z is measured precisely, thanks to the Silicon Vertex Detector

B

− + − +

→ → → µ µ ψ π π ψ / , / J K K J B

S S CP

with:

A candidate in the Golden Mode

February 19, 2001 BCP4 Ise-Shima, Japan 21

Reconstructed Hadronic B events for mixing and fitting (Bflav Sample)

BABAR

Energy Substituted Mass (GeV/c2) Events/0.002 GeV/c2

500 1000 1500 2000 5.2 5.22 5.24 5.26 5.28 5.3

D(*)-π π π π+, D(*)-ρ ρ ρ ρ+, D(*)- a1

+

J/ψ ψ ψ ψ K*0 (K*0→ → → → K+ π -) ~ 6700 events

February 19, 2001 BCP4 Ise-Shima, Japan 22

)

2

Beam-Energy Substituted Mass (MeV/c 5200 5210 5220 5230 5240 5250 5260 5270 5280 5290 5300

2

Events / 2.5 MeV/c 20 40 60 80 100 BABAR

B0 → J/ψ KS KS → π+π–

( )

)

2

Beam-Energy Substituted Mass (MeV/c 5200 5210 5220 5230 5240 5250 5260 5270 5280 5290 5300

2

Events / 2.5 MeV/c 10 20 30 40 50

BABAR

B0 → J/ψ KS KS → π+π– J/ψ → µ+µ–

( )

)

2

Beam-Energy Substituted Mass (MeV/c 5200 5210 5220 5230 5240 5250 5260 5270 5280 5290 5300

2

Events / 2.5 MeV/c 10 20 30 40 50

BABAR

B0 → J/ψ KS KS → π+π– J/ψ → e+e–

( )

B0 → → → → J/ψ ψ ψ ψ (Ks → → → → π π π π+π π π π-)

February 19, 2001 BCP4 Ise-Shima, Japan 23

B0 → → → →J/ψ ψ ψ ψ (Ks → → → → π π π π0π π π π0)

)

2

Beam-Energy Substituted Mass (MeV/c 5200 5210 5220 5230 5240 5250 5260 5270 5280 5290 5300

2

Events / 2.5 MeV/c 2 4 6 8 10 12 14 16 18 20 BABAR

B0 → → → → J/ψ ψ ψ ψ KS KS → → → → π π π π0π π π π0

( )

)

2

Beam-Energy Substituted Mass (MeV/c 5200 5210 5220 5230 5240 5250 5260 5270 5280 5290 5300

2

Events / 2.5 MeV/c 2 4 6 8 10

BABAR

B0 → → → → J/ψ ψ ψ ψ KS KS → → → → π π π π0π π π π0 J/ψ ψ ψ ψ → → → → µ µ µ µ+µ µ µ µ–

( )

)

2

Beam-Energy Substituted Mass (MeV/c 5200 5210 5220 5230 5240 5250 5260 5270 5280 5290 5300

2

Events / 2.5 MeV/c 2 4 6 8 10 12

BABAR

B0 → → → → J/ψ ψ ψ ψ KS KS → → → → π π π π0π π π π0 J/ψ ψ ψ ψ → → → → e+e–

( )

February 19, 2001 BCP4 Ise-Shima, Japan 24

)

2

Beam-Energy Substituted Mass (MeV/c 5200 5210 5220 5230 5240 5250 5260 5270 5280 5290 5300

2

Events / 2.5 MeV/c 2 4 6 8 10 12 14 16 18 20 22 BABAR

B0 → ψ(2S) KS KS → π+π–

( )

ψ(2 ψ(2 ψ(2 ψ(2S) ) ) ) (KS → → → → π π π π+π π π π-) e+e- µ µ µ µ+µ µ µ µ-

)

2

Beam-Energy Substituted Mass (MeV/c 5200 5210 5220 5230 5240 5250 5260 5270 5280 5290 5300

2

Events / 2.5 MeV/c 2 4 6 8 10 12 14 16

BABAR

B0 → ψ(2S) KS KS → π+π– J/ψ → µ+µ–

( )

)

2

Beam-Energy Substituted Mass (MeV/c 5200 5210 5220 5230 5240 5250 5260 5270 5280 5290 5300

2

Events / 2.5 MeV/c 2 4 6 8 10

BABAR

B0 → ψ(2S) KS KS → π+π– J/ψ → e+e–

( )

February 19, 2001 BCP4 Ise-Shima, Japan 25

CP

K0

s

259 50 evts 54 363

February 19, 2001 BCP4 Ise-Shima, Japan 26

B0 → → → →J/ψ ψ ψ ψ K0

L events in CY 2000

sample

• K0

L signaled by isolated clusters in IFR (>1 layer) and/or EMC (>200 MeV)

• K0

L direction is combined with J/ ψ momentum to reconstruct K0 L energy

• ~ 205 total events above large background before tagging. Background shape,

amount, and CP structure studied with Monte Carlo. (182 after tagging)

February 19, 2001 BCP4 Ise-Shima, Japan 27

Simultaneous fit to BCP and Bflav samples for sin 2β (plus

34 parameters to characterize the detector and the data)

Signal ∆t resolution function (9 parameters) Signal dilutions and B0 B0 dilution differences (8

parameters)

Background ∆

∆ ∆ ∆t structure, resolution function, dilutions

and CP content (17 parameters)

Correlations between BCP and Bflav are small

Extract background parameters from: mES sidebands for golden CP modes and Bflav modes

J/ψ sidebands and inclusive B0 →J/ψ monte carlo for

K 0L modes

February 19, 2001 BCP4 Ise-Shima, Japan 28

wi Qi

• Determined from data via likelihood fit
• Qi = εi (1-2wi )2 is the effective tagging efficiency

February 19, 2001 BCP4 Ise-Shima, Japan 29

∆ ∆ ∆ ∆t

• Sum of three Gaussians: Core (88%), Tail (11%),

and Outliers (1%)

• Parameters determined from likelihood fit and other consistency checks

=

February 19, 2001 BCP4 Ise-Shima, Japan 30

∆ ∆ ∆ ∆t

Fitted for BCP and Bflav samples together

February 19, 2001 BCP4 Ise-Shima, Japan 31

0.267 ± 0.017 0.264 ± 0.018 0.255 ± 0.017

Q

0.317 ± 0.026

0.323± ± ± ± 0.027 0.364 ± ± ± ± 0.016 w [NT2]

0.212 ± 0.029

0.197 ± ± ± ± 0.030 0.216 ± ± ± ± 0.019 w [NT1]

0.171 ± 0.013

0.176 ± ± ± ± 0.014 0.180 ± ± ± ± 0.009 w [Kaon]

0.116 ± 0.020

0.116 ± ± ± ± 0.021 0.108 ± ± ± ± 0.013 w [Lepton]

Global likelihood fit One bin hadronic

• ne bin

Parameter

B0→ → → →D*- l ν ν ν ν

16,000 events

Bflav sample

~5000 events

February 19, 2001 BCP4 Ise-Shima, Japan 32

Background

∆ ∆ ∆ ∆t B

BABAR

Unmixed Events

Events/ 0.4 ps ∆t (ps)

Mixed Events

100 200 300 400 100 200 300 400

• 10
• 5

5 10

Signal + bkgnd

|∆t| (ps) Asymmetry

BABAR

• 1
• 0.8
• 0.6
• 0.4
• 0.2

0.2 0.4 0.6 0.8 1 2 4 6 8 10 12

∆ ∆ ∆ ∆mB0 = 0.519 ± ± ± ± 0.020 ± ± ± ± 0.016 h ps-1

February 19, 2001 BCP4 Ise-Shima, Japan 33

CP

T A G G I N G C A T E G O R Y DECAY MODE

February 19, 2001 BCP4 Ise-Shima, Japan 34 T A G G I N G C A T E G O R Y DECAY MODE

February 19, 2001 BCP4 Ise-Shima, Japan 35

CP Sample: ∆

∆ ∆ ∆t distributions for

tagged K0

S events

February 19, 2001 BCP4 Ise-Shima, Japan 36

∆ ∆ ∆ ∆t vs ∆ ∆ ∆ ∆t

(Binomial Errors)

• 1
• 0.5

0.5 1 a)

• 1
• 0.5

0.5 1

• 5

5 b)

KS Modes J/ψ ψ ψ ψ KL

sin2β β β β= 0.25 ±

± ± ± 0.22 (stat)

sin2β β β β= 0.87 ±

± ± ± 0.51 (stat)

BABAR

February 19, 2001 BCP4 Ise-Shima, Japan 37

sin 2 β β β β = 0.34 ±

± ± ± 0.20(stat) ± ± ± ± 0.05(sys)

Log Likelihood vs sin 2 β

β β β

KS KL

Total

σ σ

(MC study shows 60% prob. of obtaining worse fit.)

February 19, 2001 BCP4 Ise-Shima, Japan 38

sin2β

β β β for various parts of CP sample;

crosschecks from Bflav and charged B’ s

sin2β β β β sin2β β β β

February 19, 2001 BCP4 Ise-Shima, Japan 39

February 19, 2001 BCP4 Ise-Shima, Japan 40

sin2β β β β

sin2β β β β

February 19, 2001 BCP4 Ise-Shima, Japan 41

Constraints on Unitarity Triangle

Allowed region (blue) is determined using theoretical inputs and fitting many experimental measurements

February 19, 2001 BCP4 Ise-Shima, Japan 42

CP

BABAR can measure the phase angles

γ γ γ γ

( ) η ρ, ( ) , ( ) , 1

β β β β α α α α

Very clean,

Eff B.R. ~ 10- 4 B.R. ~ few 10- 6 Theoretically uncertain

Eff B.R ~10- 7; tough!!

B0d→ → → →J/ψ ψ ψ ψK0S B0d→ππ →ππ →ππ →ππ B0d→ → → →DK

February 19, 2001 BCP4 Ise-Shima, Japan 43

‘80 ‘90 ‘00 ‘05

30 fb-1

February 19, 2001 BCP4 Ise-Shima, Japan 44

PEP-II and BaBar are operating at or above design

luminosity, and have dealt with ~25 fb-1 in 2000

The detector is performing as designed, and the

analysis teams are in full operation

We have have made the most precise measurement to

date of sin 2β, and many other analyses are underway

We expect to more than double our data by the end of

the run in August, and reduce the systematic effects to take full advantage of it.

By 2005, we should accumulate ~ 500 fb-1

Measure sin 2α, compare sin 2β in individual modes Make serious measurements of direct CP violation and rare

decays.