CPV measurements with Belle/KEKB

Stephen L. OlsenUniv. of Hawai’i

Feb 17, 2003 LCPAC meeting at KEK

B0

td

td

B0

Vtb

Vcb

KS

J/

J/

KS

V*2

sin21

Vtb

V*td

Vcb

B0B0

Sanda, Bigi & Carter:

+

1 : interfere BfCP with BBfCP ()

V*td

theory errors ~1%

(aka sin2

z

more B tags B - B

B + B (tags)

t z/c βγ

more B tags

Now an established & well understood expt’l technique

sin21 = 0.719±0.074±0.035

Belle & BaBar agree

sin21 (Belle)

=0.719±0.074±0.035

sin21 (BaBar)

=0.741±0.067±0.033

sin21 (World Av.)

=0.734±0.055

theory errors ~1%

Agree on value,not name!!

Agrees with SM

What’s next?

•sin2 shift to precision measurement mode•high statistics•better control of systematics

•measure other angles•start with

•measure sin2 in non-ccs decay modes•sensitive to new physics

2 () from B+

B0

B0

V*

V*

td

td

Vtb

Vtb

V

V

+

+

B0

+ V*2 V2

td ub sin22

ub

ub

(aka sin2

Must deal with “Penguin Pollution”i.e. additional, non-tree amplitudes

with different strong & weak phases

B0

+

Vtb Vtd

*

Rq(t) 1+q [Acos(mt) + Ssin(mt)]q=+1 B0 tag

1 B0 tag

direct CPV mixing-induced CPV

t (ps)

First results from Belle (Mar 02)

+0.38 +0.160.27 0.13

+0.250.31

(stat.) (syst.)

S = 1.21

A = +0.94 0.09

• 45 million B-meson pairs (42fb-1)• 162 events in the signal region

“Study of CPV Asymmetries in B0 +– Decays” PRL 89, 071801 (2002)

Results indicate large CP asymmetries, outside of A2+S21 allowed region

-5 0 5

Outside physical region & some (~2) disagreement with

BaBar

Changes since last March

• More data ! [85106 B pairs (78 fb-1)]

• Analysis improvements:• better track reconstruction algorithm

• more sophisticated t resolution function

• inclusion of additional signal candidates by optimizing event selection

• Thorough frequentist statistical analyses • use of Monte Carlo (MC) pseudo-experiments based

on control samples

e+e- qq (q=u,d,s,c) continuum background suppression

Event topologyModified Fox-Wolfram momentsFisher discriminants

Angular distributionB flight direction

Combined into a single likelihood ratio

Select 2 regions for each flavor tag classLR > 0.825LRmin < LR 0.825

Event and time reconstruction (3)

S

S qq

LLR

L L

FlowFlavortagging

Vertexand t

Continuumsuppression

LRmin 0.825

continuum (MC)

class 1 class 2

class 3 class 4

class 5 class 6

B0 +–

Selection

B0 example

+

B0 +– candidatesLR > 0.825

+- : 57K : 22qq : 406total : 485

LRmin < LR ≤ 0.825

+- : 106K : 41qq : 128total : 275

Event and time reconstruction (4)

FlowFlavortagging

Vertexand t

Continuumsuppression

• The same algorithm as that used for sin21 meas.• Resolution mostly determined by the tag-side vtx.• B lifetime demonstration with 85 million B pairs

Example vertices

Vertex reconstruction

B0D, D*, D*, J/KS and J/K*0

B0 lifetime1.5510.018(stat) ps

Time resolution (rms)1.43ps

(PGD02: 1.5420.016 ps)

B0 +–

Selection

Time-dependent fit

Unbinned maximum-likelihood fit (no physical-region constraint)

2 free parameters (A , Sin the final fit

(1 ) {( ) }

( )

i i

m q m mi ol K K sig qq qq qq

ol ol i

L P

P f f P f P R f P R d t

f P t

E-Mbc dist.

B0D, D*, D*, J/KS and J/K*0

Lifetime fit

(single Gaussianoutlier)

The fit program reproduces our sin21 results

Reconstruction summary

Now we are able to obtain A and SBut let’s go through several crosschecks

before opening the box.

• Established techniques for• event selection

• background rejection

• flavor tagging

• vertexing

• time-difference (t) fit

• In particular, background well under control

Common techniques used forbranching fractions,md, B, sin21

B0 K+– control samplePositively-identified kaons

(reversed particle-ID requirements w.r.t. selection)

total K yield: 610 events

LR > 0.825LRmin < LR ≤ 0.825

Mixing fit using B0K+

md=0.55 ps-1+0.050.07

Consistent withthe world average(0.4890.008) ps-1

PDG2002

(OF

SF)/

(OF+

SF)

: B=(1.42 0.14) ps

K : B=(1.46 0.08) ps

BG shape fit

Lifetime measurementsworld average (PDG2002)(1.542 0.016) ps

background treatment is correct !

Very different bkgnd fracs

CP fits to the BK sample

q=+1 q=1

SK = 0.08 0.16

AK =0.03 0.11 (consistent with counting analysis)

No asymmetry

Null asymmetry tests

A = 0.0150.022S = 0.045 0.033

Null asymmetry

Null asymmetry

fit results

Afterbackgroundsubtraction

5-5 0

Still see a large CP Violation!

5-5 0

Asymmetrywith background

subtracted

Fit results

Afterbackgroundsubtraction

Asymmetrywith backgroundsubtracted

5-5 0

A = +0.77 0.27(stat) 0.08(syst) S = 1.23 0.41(stat) (syst)+0.08

0.07

data points with LR > 0.825curves from combined fit result

Likelihoods & errors

The probability for such small S errors is ~1.2%

we use most probable errors

from toy-MC

ln(L) is not parabolic

Physical region A2 + S2 ≤ 1

Probability that we have a fluctuation equal to or larger than the fit to data(input values at the physical boundary)

16.6%

[Note] prob. outside the boundary 60.1%(~independent of statistics)

How often are we outside the physical region ?

A = +0.77 0.27(stat) 0.08(syst) S= 1.23 0.41(stat) (syst)+0.08

0.07

Fit results:

Cross-checks Prev result

A S

0.94 -1.21

3.4Evidence for CP violationin B0 +–

(A,S) CL regions

2

21

21

12

212

|/|cos)cos(|/|21

,/]sin)sin(|/|2[

,/]2sin|/|

cos)sin(|/|22[sin

TPTPR

RTPA

RTP

TPS

TP

Constraining 2

| P/T| = 0. 276 0.064(Gronau-Rosner

PRD65, 013004 (2002)

S

A

2 (d

eg.)

(deg.)

allowed regions• Input values for 1 and |P/T|

1=23.5 (sin21=0.73) |P/T| = 0.3

2 constraint w/o isospin analysis !

both A and S large

• less restrictive on < 0 favored no constraint on at 3

Constraints on 2

2 (d

eg.)

(deg.)

|P/T| = 0.15 |P/T| = 0.30 |P/T| = 0.45

Consistent with theoretical predictions Larger |P/T| favored

( 1 = 23.5)|P/T| dependence

Constraints on 2 (cont’d)

Constraints on 2

78 ≤ 2 ≤ 152

2

(for: 0.15|P/T|0.45)

1 dependence is small

78 ≤ 2 ≤ 152

(95.5% C.L.)

Strategies for 3

D0CPVub

Amax ~ 2R ~ 0.2

@ 78 fb –1

47 CP-even evts

50 CP-odd evts

A = 0.12 ± 0.13

@500 fb –1: A/Amax ~0.3

Gronau,London,Wyler D0CP

Vcb

32 K

K

Strategies for 3 (cont’d)doubly Cabibbo-suppressed

Amax ~ 1; but rate is small

80 fb –1:K+

Mbc

Only ~ 15 Do evts, Cabibbo-suppressed Dodown by ~1/20

Vub

Atwood,Dunietz, Soni

Vcb

BDo

This strategy is very clean but requires lots & lots of data

Are there non-SM CPV phases?

Measure sin21 using loop-dominated processes:

Example:

, ’, KK

no SM weak phases

SM: sin21 = sin21 from BJ/ KS

unless there are other, non-SM particles in the loop

eff

eff

similar to (g-2)

• well defined technique & target

– theory & expt’l errors are well controlled

– errors on SM expectationsare small (~5%)

• SM terms are highly suppressed

– SM loops contain t-quarks & W-bosons

– effects of heavy non-SM particles can be large

look for ppm effects look for pp1 effects

(i.e.~100%)

(g-2): sin21eff

:

SM loop particle: SM loop particles: t & W

lowest-order SM diagrams

look for effects of heavy new particles in a well understood SM

loop process

These channels are very clean& the techniques are

understood

Won’t reach experimental limits until ~100 x more data

sin21eff results: (SM: sin2=+0.72± 0.05)

2.2σoff

(hep-ex/0212062)PRD(r)78fb-1

0.73 ± 0.66

B KS

S +0.52 ± 0.47 +0.76 ± 0.36

B’KSBK+KKS

OKOK

CPV with Belle (summary)

• 1 well established

– next: high precision measurements

• 2 1st expt’l limits are established– interesting near future

• 3 just beginning

• non-SM phases search has begun –

– 2.2 discrepancy seen in KS – BaBar has seen a similar discrepancy in KS

Conclusion

• We’ve accomplished a lot in CPV

• There is still a lot more to be done

• KEKB & Belle are up to the task