The BaBarians are coming

Neil Geddes

• Standard Model CP violation • BaBar• Sin2• The future

The Aims

Complex phase in CKM matrixproduces different phases for B0anti-B0 and anti-B0B0

J/K0s

B0

B0

J/K0sB0

B0

CP

Standard Model CP Asymmetry:

ΔtΔmsinηsin2β

KJ/ ΨBNKJ/ ΨBN

KJ/ ΨBNKJ/ ΨBNA

0B

0S

00S

0

0S

00S

0

CP violation in B mesons:

w w

uct

uct

b d

b d

b c

d d

c

s

= CP of final state = -1 for J/K0

s, +1 for J/K0L

= arg[-VcdVcb * /VtdVtb

*]

Unitarity Triangle

b

s

d

VVV

VVV

VVV

b

s

d

tbtstd

cbcscd

ubusud

Quark mixing described by complex Cabibbo-Kobayashi-Maskawa matrix

VCKM unitary

V†V = 1

V*i1V1j+V*

i2V2j+V*i3V3j = 0/1

V*ubVud

V*tbVtd

V*cbVcd

(

((

(rescale sides by 1/|V*cbVcd| and choose V*

cbVcd real )

Bd±

BdJ/Ks,D*±D,..B D±K

dd BB ,...,

,...,

B

llB

,...

,..., *

DB

lDDlB

Constraining The Triangle

sin2 = (0.5, 0.8)

Asymmetric B-factories

e+e- (4s) B0B0 (50%) B+B- (50%)

PEP-II design luminosity 3x1033 cm-2sec-1

+ Continuous high precision running

9GeV e- + 3.1GeV e+ boosted in lab Y(4s)

e, K tag

+

-

e-e+

B0

K0

_B0

J/

z~t CPCP

CPCP

fBNfBN

fBNfBNtA

00

00

)(measure

Small branching ratio for fCP

PEP-II and BaBar Canada

ChinaFranceGermanyItalyNorwayRussia

UKUSA

~600 Collaborators 9 Countries~ 70 Institutions

The BaBar Detector

(4) Electromagnetic Calorimeter (6) Instrumented

Iron Yoke(3) Cerenkov- Detector

(5) 1.5 T Solenoid

(2) Drift Chamber

(1) Silicon Vertex Detectore-

e+

Chronology

1995 - Approval1998 - Construction completed1999 - Started taking data - events !!

2000 - Taking data2,000,000 events per day, 20,000 Bs per day

2001 - Taking data20,000,000 events per day 100,000 Bs per day

2002 - “Results”120,000,000 Bs

2002-20052002-2005 - Detailed results - Detailed results1,000,000 Bs per day1,000,000 Bs per day

first measurements

first results

The Method

1) Reconstruct CP eigenstates, J/K0

2) “tag” other B flavour 3) Measure z t 4) Fit A(t) for sin(2)

Complicated by:•Mistags•Finite time (vertex) resolution

Also need•B mass difference M(B0)•B0 lifetime

tt mef BB

t

B

sin2sin1

4)(

||

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

0S00

S0

0S

00S

0

KJ/ ΨBNKJ/ ΨBNKJ/ ΨBNKJ/ ΨBN

A(t)

K0, 0 and J/ Reconstruction

K0s+-

K0s0-

B Reconstruction

Completely reconstruct many (anti-)B0’s

B0 J/K*0(K+),D(*)-,D(*)- ,D(*)- a1c.c.

Flavour Sample

Total sample ~6000

From this sample determine. A) Tagging efficiency B) Mistag fraction

B Mixing

MB

Mistags di-lepton events

A =

(N

u-N

m)/

(Nu+

Nm)

Semi-leptonic decays

Dilution D = 1-2w

Ameasured = Datrue

CP B Reconstruction

B0 J/K0L

EMC

IFR

allB0 J/K0

s

All K0s modes

B0 (2s)K0s For KL:

We do not know KL momentum.We know direction•Impose MB constraint•Imply momentum•Measure E

Tagging

Non CP vertex “tagged” as B or anti-B by: •Presence of charged lepton

• Electron Pcm >1.0 GeV/c; Muon Pcm >1.1 GeV/c•Presence of charged Kaons

Kaon Charge 0•Overall event properties (l,K,slow-)

Neural Network

b c

e,

s

Time Resolution

Dominated by vertex resolution for Tagging BCommon parameterisation for CP and flavour samples• Sum of three Gaussians: Core (88%), Tail (11%), and Outliers (1%)• Parameters determined from likelihood fit and other consistency checks

B flavor eigenstates

B charmonium

z = 180 m for tagging vertex, z = 70 m for fully reconstructed vertex

Mistags and (t)

preliminary

Quality factor Q = (1-2w)2 . (sin2) 1 / QNrec

if no background

Flavour Sample Determines Mistag and t Resolution parameters

Tag Type eff’cy (%) W (%) Q(%)Lepton 10.9 0.4 11.6 2.0 6.4 0.7Kaon 35.6 0.7 17.1 1.3 15.8 1.3NT 1 7.7 0.4 21.2 2.9 2.6 0.5NT 2 13.7 0.5 31.7 2.6 1.8 0.5

Total 68.9 1.0 26.7 1.6

Parameter ValueS core 1.1 0.1S tail 3.8 0.9f tail (11 5) %f outlier (0.8 0.5) %core,lepton ( ps ) 0.08 0.10core,Kaon ( ps ) -0.21 0.05core,NT1 ( ps ) 0.010.10core,NT2 ( ps ) -0.18 0.09Tail ( ps ) -0.46 0.38

m(B0) = (0.519 ± 0.020 ± 0.016) ps-1

Fit for sin2sin2 is measured with a 35 parameter simultaneous fit to data flavour and

CP samples:

tRtmDeN

pdfmixed

tRtmDeN

pdfunmixed

iitflav

iitflav

cos14

:

cos14

:

2

1

tRtmDeN

pdftagB

tRtmDeN

pdftagB

iitCP

iitCP

sin2sin14

:

sin2sin14

:

40

30

mB andB are fixed at the PDG world average

values:mB = 0.472 ps-1

B = 1.548 ps

Fit Parameters•Sin2

•4 signal dilutions (D=1-2w)

•4 values of D for the 4 signal categories

•9 parameters for the signal t resolution function

•8 background dilutions

•3 parameters describing the background resolution function

•1 parameter for the fraction of CP background

•5 parameters for the fractions and lifetime of the Bflav background

Measured Asymmetries

• sin2 = 0.34 0.20 0.05

sin 2 0.25 0.22 (stat)b= ±2 =

sin 2 0.87 0.51 (stat)b= ±2 =

f+

f -

f -

f+

CP +1

CP -1

Cross Checks

Systematic Errors

Systematic (J/&(2s))Ks J/Y KL Full Samplet resolution function 0.04 0.04 0.04((J/& (2s))Ks bgrd 0.02 - 0.02J/ KL bgrd compostion - 0.09 0.01J/ KL bgrd fraction - 0.10 0.01B lifetime 0.01 0.01 < 0.01M 0.01 < 0.01 0.01Other 0.01 0.01 0.01

Total 0.05 0.14 0.05

BaBar, Belle and the Rest

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

Feb 2001

Belle (~10 fb-1) sin(2) = 0.58 ±0.33±0.1

BaBar (~22fb-1) sin(2) = 0.34 ±0.20±0.05

What if sin(2) is < 0.5 ?

Standard model bound ~ 0.59 sin2 0.82

SM constraints are wrong because:

SM valid but: •|Vub| smaller than theoretically favoured range •SU(3) breaking in Bd

0 /Bs0 mixing larger than favoured range

•BK larger than theoretically favoured range

SM incomplete; new flavour violating and/or CP violating physics:•New contributions to Bd

0 mixing and Bs0 mixing

•New CP violating contribution to B0 mixing•New CP violating contribution to K0 mixing (and K)

Eyal, Nir and Perez hep-ph/008009

Covering the Angles

BABAR can measure the phase angles

,

0,0 0,1

Very clean,

Eff B.R. ~ 10- 4

B.R. ~ few 10- 6

Theoretically uncertain

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

B0dJ/K0

S

B0d

B0dDK

‘80 ‘90 ‘00

Prospects

6

12

18

(fb-1)

‘80 ‘90 ‘00

CESR/CLEO (from CESR Web page)

PEPII/BABAR

‘05

30 fb-1

Conclusions

•PEP-II and BaBar collected/analysed ~25 fb-1 in 2000

•More than double our data by the end of the run in August

•By 2005, we should accumulate ~ 500 fb-1

• Measure sin 2, compare sin 2 in individual modes•Measurements of direct CP violation and rare decays.

•sin 2 = 0.34 0.20 0.05The BaBarians have already arrived !