CP ViolationBrazilian Physical Society

Particles and Fields MeetingCaxambu, 10-14 August 1998

Tatsuya NakadaCERN

Geneva, Switzerland

On leave from Paul Scherrer Institute

I) Why CP violation is highly interesting?

- Currently observed CP violation in the kaon decays can be accommodated within the Standard Model.BUT, it cannot exclude that CP violation is partly or evenentirely due to new physics.

- Since CP violation is due to an “interference”, it is sensitiveto a small effect.

- Cosmology (baryon genesis) suggests that an additional source of CP violation other than the Standard Model is needed.

A promising place to look for new Physics

K t=00 → K t=t1

0 ≠K t=00 → Kt=t1

0

Observed CP violation in the kaon system:

CP and T

so called CP violation in K0- K0 oscillations

1) Re 2π =2π Hw KL

2π Hw KS

II) CP violation in the Kaon system

CP = 1 CP 1

CP 1

So called CP violation in the interplay between oscillations and decays

2) Im

K0t=0

K0

K02t=t1

K0t=0

K0

K02t=t1

3) Current experimental results are = 00

arg = tan1 m/ (m = mL mS, = S L )

NA31,CPLEAR (CERN)E731, E773 (FNAL)

This is compatible with Standard Modelbut also with

Superweak Model

4) Experimental attempt to exclude the Superweak model1) To show

|| |00|so called Re(/) 0

or CP violation in decay:due to penguins

NA48 (CERN), KTeV(FNAL)

2) To showBr(KL 0) 1011

Being discussed at FNAL and BNL

Standard model predictions are uncertain for and 00

hadronic effects: long range interactionspenguins etc.

Br(KL 0) is experimentally really hard.

Another place to look for CP violation?

If there is nothing else but the standard model, |Vcb|, |Vub| B-meson decaysmd Bd-Bd oscillations

will fix all the Wolfenstein’s parameters, A, and ( is well known).

b c

W

b u

W

A

A

b

d

W

t

Wt

_d

b

__

A 1

III) CP Violation and B-meson System

0 0 0

i 0 0

i 1 i 0

1 i

1

i 1

VCKM =

CKM matrix relevant for B Physics(CP violation is all due to ≠ 0)

CKM Unitarity Triangles

VtdVtb + VcdVcb

+ VudVub = 0 VtdVud

+ VtsVus + VtbVub

= 0

Vub

Vcb

Vtd

Vub

Vtd

Vts

arg Vcb = 0, arg Vub = , arg Vtd = , arg Vts =

bu

1

mdBfB2F(mt)|VtdVtb|2

From the neutral kaon system > 0

Unitarity triangle

Vtd ei

Vub ei

and aredefined by thesides

NB: Br(K ) measuresalso |Vtd|

CP violation in Bd J/ KS v.s. Bd J/ KS

measures the phase of Vtd, i.e.

compare two measurements = consistency test

b

d

W

t

Wt

_d

b

__HB-B (Vtb

Vtd )2 ei

Bd- Bd

_b c

d d

c

sBd

J/

KS

b s

d d

cc

Bd KS

W

g

Wt,c,u Penguin effect

is negligible

_ ABJ/Ks Vcb Vcs e0i

Bd

Bd J/KS

Bd

J/

By 2005, CLEO, BaBar, BELLE, CDF, D0 and HERA-B will have

-accurate |Vub|, |Vcb| and - from CP violation in Bd J/ KS with ~ 0.025(Expected range in the Standard Model: 0.3<sin2<0.8)

Possibilities area) There will be already a sign of new physics:

-precision measurements in different decay modes in order to pin down the details of new physics.

b) Measurements look “consistent” with the Standard model.-what could happen?Let’s make the following “interesting” scenario.

b

d

W

t

Wt

_d

b

__

b

s

W

t

Wt

_s

b

__

HB-B 1 rdb] ei( db)

b

d

_d

b

_

b

s

_s

b

_

newFCNC

newFCNC

Bd- BdBd- Bd

Bs- Bs

_

_

A model for new physics

_

HB-B rsb ] ei( sb)_

Measured bu

1

Measured m(Bd) 1 + rdb

1 from SM box

defined by the measured triangle.

defined bythe CKM triangleVtd ei

=

=

CP violation in Bd J/ KS v.s. Bd J/ KS

measures J/K = db

If the model is such that numerically db ≈ “J/K = ”

CP measurement and triangle measurements agreeeach other.

Look consistent with the Standard Model!

Bd-Bd ei( db)_

BdJ/ KS Vcb Vcs e0i

BABAR and BELLE may have difficulty to access CP violation in Bd

-experimental problemsmall branching fraction < 10 (CLEO)

-theoretical problemlarge penguin contribution

sb ud d

us

Bd

W bu

d dBd g

Wt,c,u

uK

K

CLEO: Br() < Br(K) 1.4 10 penguin is large

T (VusVub)2 P [P(mt

2)VtsVtb]2 P2(mt

2)

Top penguin dominates in Bd K P (mt2) <1)

d

b ud d

ud

Bd

Wb

u

d d

Bd g

W t,c,u

u

T (VudVub)2 P [P(mt

2)VtdVtb]2 P2(mt

2)

Br()<Br(K) penguin is large; P (mt) > = 0

VudVub ei Vtd

Vtb P(mt2)P(mc

2) + Vud

Vub P(mu2)P(mc

2) P(mt

2)P(mc2) ei

+P(mu2)P(mc

2) ei

Problem: tree and penguin have different phases

CP violation in Bd is not really possible forCDF and D0: no particle ID, HERA-B: not enough statistics

Bd can be used only if we know penguin/tree.A way out:

measure Br( 0) and Br(0 0) not enough statistics

CP violation in Bd , , 00

-experimental problemdecay time dependent Dalitz plot analysis

not enough statistics-theoretical problem

assume 0 to be always

CDF, D0 and HERA-B may be able to measure m(Bs)If m(Bs)/b <20. Does this help? Not really.

-It helps to reduce hadronic uncertainties: fB

2B (~20% error, lattice calculation)fB

2B(Bd)/fB2B(Bs) is much better known (~5% error)

-It is interesting if m(Bs) is really large; new physics.But it is out of their sensitivities.

m Bd( )Δm Bs( )

=A2λ 4 1 − ρ( )2 +η 2

[ ] + r db( )

A2λ2 + r sb( )

How can LHC attack the problem?1) Improve J/K measurement.

ATLAS, CMS: ~ 0.02/yearLHCb: ~ 0.01/year

2) Measure other angles using Bs

CP violation in BsJ/ measures J/ = + sb

ei( sb)Bs- Bs

_

b c

s s

c

s

J/

W

BsJ/ Vcb Vcs e0i

Penguin effect is negligible

If the model is such that numerically sb ≈ “J/ = ”It will still look consistent.

J/ is a easy final state to reconstructif the decay time resolution is good enough!

ATLAS, CMS: ~ 0.03/yearLHCb: ~ 0.01/year

CP = 1 (l = 0, 2)additional complication: J/

CP = 1 (l = 1) -angular momentum configuration has to be studied-

CP violation inBs Ds

K, DsK Bs Ds

K, DsK

We need to do much more!

Bs

Bs DsK

Bs DsK

b u

sc

K

WDs

s s

b c

su

Ds

WK

s s

ei

e0i

ei( sb)

+ c.c.

measures DsK = sb There is no more freedom left to make DsK = No hadronic uncertainty

Measured DsK disagrees with what one expects fromthe triangle relation New Physics

What are experimentally needed? - decay time resolution - K/ separation

Bs DsK Major background: Bs Ds (No CP violation)

Importance of particle identification and mass resolution

3) Further CP violation studies with Bd which requirevery high statistics (difficult for BaBar and Belle).

Bd D0K0, D0K0,D1,2K0

Bd D0K0, D0K0,D1,2K0

measure .

Bd D, D Bd D, D

measure 2 + db + ; 2 + i.e. inconsistent

No hadronic uncertainties.Experiment requires: K/ separation

hadron trigger

Very small visible branching fractions(10~10 )

Importance of particle identification

With signalevents

m = 13 MeV/c2

newparticles

newparticles

More generally new physics can appear inb = 1 process

through penguin

b = 2 processthrough box

through tree

b b, s

b b, snewparticles

d,s d

b d, s

d,s b

lor l

lor l

CP violation must be studied inBd decays via Oscillations bc+W and bu+WBs decays via Oscillations bc+W and bu+WBd,s,u decays via penguinsBd,s decays via box

Experimental conditions areSmall branching fractions many Bd,s,u’sRapid Bs oscillations decay time resolutionIncluding multi-body hadronic final states particle ID

mass resolution LHCb experiment

An example of shopping list: LHCb ATLAS/CMSBd JKS

Bs J Bs DSK (PID)

Bd DK (PID,Trigger)

Bd D* (PID)

Bd (PID)

Bd K (CP in gluonic penguin) (PID)

Bd ( BaBar 160 events, LHCb 670 events)Bs K (CP in radiative penguin) Bs Kll (CP in radiative penguin)

Bs oscillations, xs up to 75 38

Bs

V) Conclusions1) New results on CP violation in the neutral kaon system

will be available soon (~2000) and may indicate that the Superweak model is not valid.

2) B-meson system will provide a rich field for CP violation studies.

3) BaBar, Belle, CDF, D0 and HERA-B will observe CPviolation in BJ/KS (>2000) if CP violation is largely due to the standard model.

4) In order to look for new physics, a dedicatedexperiment at LHC, i.e. LHCb is needed.