1

Daniela Bortoletto

Purdue University Introduction

SM expectations Previous measurements

The measurement of sin 2 at CDF Signal reconstruction Flavor tagging methods Fit results and cross checks

Future prospects

The measurement of sin(2)

University of Southampton 25-29 July 199

2

SM with 3 generations and the CKM ansatz can accomodate CP

if the complex phase is 0CP. Only =0.21960.023, A=0.8190.035 are measured precisely.

CP is one of the less well-tested parts of SM ( , / in the Kaon system)

CP asymmetries in the B system are expected to be large. Independent observations of CP in the B system can: test the SM

Introduction

)(O

1A)i1(A

A2/1

)i(A2/1

VVV

VVV

VVV

V 4

23

22

32

tbtstd

cbcscd

ubusud

BB00

H0

2

B

BLHB

00L

0

MBqBpBdbB

)10(OMMMBqBpBdbB

lead to the discovery of new physics

3

The goal of B-physics is to over-constrain the unitarity triangle to test the CKM ansatz or to expose new physics

B Physics and CKM matrix

Unitarity triangle

B

BJ/K0sBK

(,)

(1,0)

(1--i)(+i)

*cbcd

*tbtd

VV

VV*

cbcd

*ubud

VV

VV

(0,0)

B/ B0-B0 mixing

Vud Vub*+Vcd Vcb

*+Vtd+Vtb*=0

4

Possible manifestations of CP violation can be classified as: CP violation in the decay: It occurs

in B0/B+decays if |A(f)/|A(f)|1 CP violation in mixing: It occurs

when the neutral mass eigenstates are not CP eigenstates (|q/p|1)

CP violation in the interference between decays with and without mixing

Mixing: Vtd introduces a complex phase in the box diagram

Interfering amplitudes: direct decay B0 f B0 B0 mixing followed by B0

f

CP violation in B decays

B0

B0

f B0

B0

f

Mie

Mie

Vtd

V*td

b

b

d

dt

tB0 B0W W

Box Diagram

2i2*

td2tdd

2i2td

2tdd

e|A|Vm)BB(A

e|A|Vm)BB(A

5

Determination of sin(2)

Color suppressed modes bccs. Dominant penguin contribution has the same weak phase Negligible theoretical uncertainty

Cabibbo suppressed modes bccd such as B0/B0 DD,D*D*. Large theoretical uncertainties due to the penguin contribution

Penguin only or penguin dominated modes bsss or dds. Tree contributions absent or Cabbibbo and color suppressed penguin diagrams dominate even larger theoretical uncertainties

6

B-factories at the (4S) : B0 and B0 mesons are produced in a coherent C=-1 state time integrated CP

asymmetry = 0. Determination of CP needs A(t ) where t =t(CP)-t(tag) or z =c t Need good z resolution

pp and pp colliders: time integrated asymmetry does not vanish

Since xd=0.732 0.0032 (PDG98)

Experimental considerations

2sin5.02sinx1

xA

2d

dCP

ACP is Maximum at t=2.2 lifetimes

ACP(t)

t

Measurement of the asymmetry as a function of proper time ACP(t) is more powerful Combinatoric background

dominates small ct region

7

B0/B0J/K0s

For B0/B0 J/K0S we have CP(K0

s)=1 and CP(J/K0S )= -1. To reach a

common final state the K0 must mix additional phase Asymmetry is directly related to sin2.

ACP(t)=sin[2(M- D)]sin mdt =sin2 sin mdt and

sin2 =

0

S00

S0

0S

00S

0

CPK/JBK/JB

K/JBK/JB)t(A

*cscd

cs*cd

*cbcs

cb*cs

*tdtb

td*tb

VV

VV

VV

VV

VV

VVIm

B0 B0 Mixing Ratio of K0-K0 mixing

)f(A

)f(A

22 )1(

)1(2

8

Vub/Vcb=0.093 from semileptonic decays

K=2.2810-3

B0-B0 mixing md=0.472 ps-1

Limit on Bs-Bs mixing ms >12.4 ps-1

Indirect determination of sin2 In SM the asymmetries in the B system are expected to be large

S. Mele CERN-EP-98-133, 1998 findssin2=0.75 0.09

Parodi et al. sin2=0.725 0.06

Ali et al. 0.52<sin2<0.94

9

Measurement of ACP(t) requires:

Reconstruct the signal B0/B0J/K0S

Measure proper decay time (not critical in pp colliders but useful) Flavor tagging to determine if we have a B0(bd) or B0(bd) at

production Tagging algorithms are characterized by an efficiency and a dilution

D. The measured asymmetry is AobsCP=D ACP

Ntot = total number of events

NW= number of wrong tags

NR=number of right tags

D=2P-1 (P=prob. of correct tag) and D=1 if NW=0 D=0 if NW=NR

Best tagging methods has highest D2

Measurement accuracy

WR

WR

NN

NND

tot

tag

N

N

Crucial factor

10

Assume you have 200 events N=200 100 are tagged Ntag=100

tagging efficiency =Ntag/Ntot=50%

Of those 100 events 60 are right sign NR=60

40 are wrong sign NW=40

Dilution D=(NR-NW)/(NR+NW)=(60-40)/100=20%

Effective tagging efficiency D2=( 0.5)(0.2)2=2%

Statistical power of this sample ND2=200*0.02=4 events

Tagging

11

Previous Measurements

sin2=3.2 0.5

Opal Zbb D. Ackerstaff et al. Euro. Phys. Jour. C5, 379 (1998) (Jan-1998)

Flavor tagging techniques:

Jet charge on opposite side jet

Jet charge on same side B

Vertex charge of a significantly separated vertex in the opposite hemisphere

24 J/K0S candidates

Purity 60 %

1.82.0

00

00

BB

BBA

12

Previous Measurements

sin2=1.8 1.1 0.3

CDF ppbb Abe et al. PRL. 81, 5513 (1998) (June 1998)

198 17 B0/B0 J/K0S candidates with both

muons in the SVX ( S/B 1.2). Measure asymmetry with Same side tagging

Dsin2=0.31 1.1 0.3.

Using D=0.166 0.018 (data) 0.013 (MC) from mixing measurement + MC

00

00

BB

BBA

13

Run I CDF detector

Crucial components for B physics: Silicon vertex detector

proper time measurements impact parameter

resolution:

d=(13+40/pT) m

typical 2D vertex error (r-) 60 m

Central tracking chamber mass resolution. B=1.4T, R=1.4m (pT/pT)2=(0.0066)2(0.0009pT)2

typical J/K0S mass resolution

10 MeV/c2

Lepton detection (triggering and tagging)

14

CDF updated measurement

Add candidate events not fully reconstructed in the SVX Double the signal to 400 events but

additional signal has larger (ct)

Use more flavor tag methods to establish b flavor at production

Check D2 with mixing analysis

Use a maximum likelihood method to combine the tags. Weight the events: in mass (B peak versus sidebands) in lifetime (more analyzing power at

longer lifetimes) in tagging probability Account for detector biases

B

background

c

(B0)=1.5610-12 s

)mtcos(D)t(N)t(N

)t(N)t(N)t(A

mixedunmixed

mixedunmixed

15

Signal J/ -+ require two central tracks with

matching hits in the muon chambers K0

S -+ use long lifetime c(K0S)=2.7 cm

to reject background by requiring Lxy/(Lxy)>5

Perform 4-track fit assuming B J/ K0S

Constrain -+ and -+ to m(K0S) and

m(J/) world average respectively K0

S points to B vertex and B points to primary vertex

Background cc production prompt J/ ( not from b

decays) + random K0S or fake

bb production J/+X, random K0S or

fake

J/K0S Event selection

B decay

+

-

+

-

primary

16

J/K0S Signal sample

CDF run1, L=110 pb-1 202 events with both muons in SVX

(ct) 60 m. 193 with one or both muons NOT in

SVX (ct) 300-900 m

Plot normalized mass

M-MB/ error on M

Both in SVX

One or Both not in SVX

395 31 events

S/B=0.7

S/B=0.9

S/B=0.5

202 18 events

19326

17

We must determine if we had a B0 or a B0 at the time of production. Opposite-side flavor tagging (OST) bb produced by QCD Identify the

flavor of the other b in the event to infer the flavor of the B0 /B0 J/K0S.

At CDF 60% loss in efficiency due the acceptance of the other B0. Lepton tagging :

b +X b b -X b

Jet charge tag :

Q(b-jet) > 0.2 b Q(b-jet) <- 0.2 b

Flavor tagging methods

B0(bd) J/K0S

+-

+

-

Opposite side b

+

Q(b-jet)>0.2

K0S

18

Identify the flavor of the B0/B0J/K0S through

the charge of the opposite b-jet Jet definition allows for wide low PT jets:

Cluster tracks by invariant mass (Invariant mass cutoff 5 GeV/c2 )

remove track close to primary B Weight tracks by momentum and impact

parameter

pT= track momentum TP = probability track comes from primary

vertex (low Tp more likely track comes from B )

Jet Charge Flavor tagging

i iPTi

i iPTii

jet ))T(2(p

))T(2(pqQ

Qjet>0.2 b

Qjet<-0.2 b

|Qjet|<0.2 no tag

=(40.2 3.9)%

Qjet in BJ/K

-QK*QJet

19

Soft Lepton Flavor tagging

Identify the flavor of the B0/B0J/K0S

through the semileptonic decay of the opposite B. b - X b + X

Electron: central track (PT>1 GeV/c) matched to EM cluster

Muon: central track (PT>2 GeV/c) matched to muon stub

Efficiency 6% Source of mistags:

Sequential decay b c X Mixing Fake leptons

Opposite side tagging was used at CDF to study B0 B0 mixing Ph. D. Thesis O. Long and M. Peters

md=0.50 0.05(stat)+0.05(sys) ps-1

md=0.464 0.018 ps-1 (PDG)

20

Same side tagging

du

b

B0-

su

b

BS K-

ds

b

B0K0

us

b

B-K+

ud

b

B-+

No K/ separation higher correlation for charged B

Problems with opposite side tagging Opposite b-hadron is central only 40 % of the time If opposite b-hadron is B0

d or B0s mixing degrades tagging

Same side flavor tagging (SST). Exploits the correlation between the charge of nearby and the b quark charge due to fragmentation or B** production (Gronau,Nippe,Rosner)

21

Correlation due to excited B** production

B**+ (I=1/2) resonance B**- B0 - Implementation of SST: Search for

track with minimum Ptrel in b-jet cone

SST has higher efficiency ( 70 %) than OST

Same side tagging

Candidate track Pt>400 MeV/c d/<3 wrt primary vertex

PB

B0 J/K0S

+-

+

-

Same side pion negative charge

d

b b

d

u

B0

-

B**-

Ptrrel

PB+ Ptr

Ptr

Cone R=0.7

B direction

22

Tagger calibration

Use BJ/ K sample to determine the efficiency and the dilution D of the sample:

Charge of the K b or b

Decay mode and trigger

analogous to B J/ K0S

B+/B- does not mix

23

Calibration Jet Charge Tagging

Sample of 988 J/K events 273 right-sign events 175 wrong-sign events

Tagging efficiency: =Ntag/Ntot=(44.9 2.2)%

Tagging dilution:

D=NR-NW/NR+NW= (21.5 6.6)%

Mistag fraction: w=(39.23.3)%

24

Calibration of Soft Lepton Tagging

Sample of 988 J/K events 54 right-sign events 12 wrong-sign events

Tagging efficiency: =Ntag/Ntot=(6.5 1.0)%

Tagging dilution:

D=NR-NW/NR+NW=(62.5 14.6)%

Mistag fraction: w=(18.87.3)%

25

Same Side Tagging Calibration

D+=0.270.03(stat)+0.02(syst)

D0=0.180.03(stat)+0.02(syst)

D=0.1660.022 both muons in SVX

D=0.1740.036 one/both muons NOT in SVX

Use inclusive + D* sample. This sample was used for the determination of B0/B0 mixing in F. Abe at al Phys. Rev. Lett. 80, 2057(1998) and Phys. Rev. D 59 (1999)

Use MC to scale for different PT spectrum in J/ K0

S wrt + D/D* sample

26

Combining Dilution: Define D=qD where q=-1 (b-quark), q=+1 (b-quark) and q=0 (no

tagging) then Deff=(D1+D2)/(1+D1D2) Tags agree Deff=(D1+D2)/(1+D1D2) Example SST and JCT D=36.8%

Tags disagree Deff=(D1-D2)/(1-D1D2) Example SST and JCT D=5.1%

Each event is weighted by the dilution in the fit

Same side SVX =(35.53.7)% D= (16.6 2.2 )% Same side non-SVX =(38.13.9)% D= (17.4 3.6 )% Soft lepton all = (5.61.8)% D= (62.5 14.6)% D2= (2.2 1.0)% Jet charge all = (40.2 3.9)% D= (23.5 6.9 )% D2= (2.2 1.3)% (if SLT do

not use Jet charge)

D2= (6.3 1.7)%

Flavor Tagging Summary

Combined flavor tagging power including correlations and multiple tags: A sample of 400 events has the statistical power of 25 perfectly tagged events

D2= (2.1 0.5)%

27

Results

Muons from J/ decay in Silicon vertex detector High resolution ct Asymmetry vs ct

Data with low resolution ct measurement Time integrated ACP

ACP=0.47 sin2 If md is fixed to the PDG world

average (md=0.4640.018 ps-1), the minimization of the likelihood function yields:

sin2=0.790.39(stat)0.16(syst) Statistical error >systematics.

Float

md

sin2=0.79+0.41

-0.44(stat.+sys.)

28

Systematic errors : Dilution 0.16 (limited by the statistics

of the calibration sample) Other sources 0.02

Cross checks: Float md :

Measure time integrated asymmetry: sin2=0.71 0.63

Only SVX events and SST: sin2=1.771.02

Verify errors and pulls with toy MC

Systematic errors and cross checks

1 contours

44.041.088.02sin

Mean:0.44

=1.01

error

Pull

29

As a check we can apply the multiple flavor tagging algorithm to the measurement of mixing in B0J/K0* decays.

The data is consistent with the expected oscillations

Measurements:md=(0.400.18) ps-1

DK=0.96 0.38 dilution due to incorrect K- assignments

Expectation:md=(0.4640.018) ps-1

DK=0.8 0.3

Cross checks

30

Measurement

Feldman-Cousin frequentist (PRD 57, 3873, 1998)

0<sin2<1 at 93 % CL Bayesian (assuming flat prior

probability in sin2)

0<sin2 <1 at 95 % CL Assume true value sin2=0.

Probability of observing sin 2 >0.79 =3.6 %.

Confidence Limits on sin(2)

Scan of the likelihood function

sin2

sin2=0.79+0.41

-0.44(stat.+sys.)

31

Results in and plane

CDF sin2 measurements fourfold ambiguity {, /2- , +, 3/2-} Solid lines are the 1 bounds, dashed lines two solutions for for

<1, >0 (shown) two solutions for >1, <0 (not-shown)

1 bounds

32

B-factories at(4S)

pp colliders:

BABAR estimates J/K0

S

(bb ) 50 b but (bb)/(total) 0.001

Tagging factor 0.063 (Run1) 0.097 (Run II-with Kaon tagging)

N(B0 /B0 J/K0S) =400 /100 pb-1

(Run 1) 15000 /2 fb-1 (run II +e triggers)

S/B =0.9 in B0/B0J/K0S

( sin2)=0.4 0.08 in Run II

(bb ) 1.05 nb but (bb)/(total) 0.26

Tagging factor 0.25-0.3(MC) N(B0/ B0 J/K0

S) =660 / 30fb-1

S/B=16 in B0/B0J/K0S

(sin2)=0.12

33

CDF reach in run II for sin2

Run I value with Run II projected error

sin2=0.79 0.084

34

Summary

CDF measures:

Mixing mediated CP will be measured precisely by CDF/D0 /BaBar/Belle/HeraB by the beginning of the new century

Precise determination of sin2 is a key step towards understanding quark mixing and CP

sin2=0.79+0.41

-0.44