CP Violation

Recent results and perspectives

João R. T. de Mello Neto

Instituto de Física Universidade Federal do Rio de Janeiro

IF – UFRJ, July/2003

Outline

• Introduction• CP Violation in the SM• Measurement of β• B Factories results• Other measurements• Hadron colliders (LHCb)• New physics• Conclusion

Motivations

SM with 3 generations and the CKM ansatz can accomodate CP

CP is one of the less experimentally constrained parts of SM

Observations of CP in the B system can:test the consistency of SMlead to the discovery of new physics

Cosmology needs additional sources of CP violation other than what is provided by the SM.

CP violation is one of the fundamental phenomena in particle physics

CP asymmetries in the B system are expected to be large.

I will not talk about:

• Kaon physics• Strong CP problem;• CP violation in the charm sector;• CP violation in Cosmology!

Concentrate in CP violation in the B sector(Only a small subset!)

CLEO 3BELLE

1999

2001BTEV A

TLAS

?

19992008

Huge experimental effort

Plus hundreds of experimental groups around the World.

Matter – antimatter oscillations

decay

ordinary ΔB=1 interactions exchangeof virtual q (2/3) t : dominant amplitude

ΔB=2

VtdΔmd

fB decay constant

BB Bag factor

CKM matrix

CKMV =

tbtstd

cbcscd

ubusud

vvv

vvv

vvv

=

mixing phase

Weak decay phase

dd BB mixing phase

ss BB

1

2/1

2/122

2

its

itd

iub

eVeV

A

eV

The quark electroweak eigenstates are connected to the mass eigenstates by the CKM matrix :

four parametersA, λ, ρ, η

Unitarity triangles

Vtd Vtb+Vcd Vcb

+Vud Vub= 0

(0,0)

Vub

Vcb

Vtd

(,)

(1,0)

Vtd Vud+Vts Vus

+Vtb Vub= 0

Vub

Vtd

Vts

In SM:

In SM:

03.02 • measure all the angles• measure all the sides SM: consistency!

CP violation

Three possible manifestations of CP violation:

Direct CP violation(interference between two decay amplitudes)

Indirect CP violation(interference between two mixing amplitudes)

CP violation in the interferencebetween mixed and unmixed decays

General time-dependent formalism

Interfering amplitudes with different CP-violating (weak) phases can give a non-zero CP asymmetry. For B0 → fCP:

Then, when one of the interfering amplitudes is B-mixing

with

S C

Only one decay amplitude (or all decay amp. same CKM phase):C=0 and S gives clean CKM phase information

• Golden modes:– clean theory– “relatively easy” experiment

• Tree and leading penguin have same phase • sinmt coeff. measures sin2 cleanly• Not just J/ KS:

– Also ’ KS, c1 KS, c KS (CP=-1)

– J/ KL (CP=+1)

– J/ K*0 (Mixed CP)

Measuring βb

d

d

W cc

s

0B /J

0K0K0B

b

dW

s

d

c

cg

u,c,t

/J

Measuring β

B factories: Belle, BaBar

Assimetric colliders at ee )( S4

nb 1bb -1-233 scm 103LOne year: ~ 100 M pairs BB

Ldt Belle 132 fb-1

March, 2003 BaBar 117 fb-1

Coherent productionBB

KEKBLuminosity achieved:

1.06 x1034 cm-2s-1

Babar detector

Mixing and lifetimesResults based on large samples of

– Fully or partially reco. hadronic decays– Fully or partially reco. D* l – Dileptons

8K events

12K events29 fb-1

Δt Distributions Lifetimes

Δt = proper time differencebetween the decay times of the two B-mesons

Δt resolution of ~ same order of magnitude as lifetime

0 = 1.554 0.030 0.019 psec- = 1.695 0.026 0.015 psec

Lifetimes results summary

• Belle and BaBar now dominate world averages• Improvement by x2 over pre B-factory era• Order 1% uncertainty on lifetimes and ratio

Adding Tagging Information

md = 0.516 0.016 0.010 ps -130 fb-1

1.6K events

~500 signal ev.

Clean ~2K KS sample

+~ 500 KL events

with ~ 60% purity

Event samples

Δt distributions and asymmetries

CP=-1 CP=+1

Events with KS Events with KL

Δt distributions and asymmetries

Summary of sin2b in b ccs

7.5% precision

B0 → J/ 0

b

d

d

W cc

d

0B /J

00B

b

dW

d

d

c

cg

u,c,t

/J

0

S = - sin2β if no penguin C = 0 if no penguin

Measuring β in b→sss

Bb

d,u

W

ss

sg

Kd,u

bW

s

s

sg

u,c,t

Kd,u d,u

B

B → KS

B → ‘ KS

• Same CKM structure as J/ψ KS

• u-penguin down by ~1/50• Expect S=sin2β to 5%

• Like ϕKS but also u-tree• Still, S~sin2b

Measuring β in b→sss

Theoretical especulations

• sin(2β) = SϕK=-0.39 +- 0.41 (2.7 σ) from the SM prediction;

• models from SUSY could explain this result!G.L. Kane et al., PRL Apr.2003

Grossman et al. hep-ph/0303171

SM is alive and well!

Confidence levels in the large (rhobar,etabar) plane

obtained from the global fit. The constraint from the

WA sin2beta (from psi Ks modes) is overlaid.

Confidence levels in the large (rhobar,etabar) plane

obtained from the global fit. The constraint from the WA

sin2beta (from psi Ks modes) is included in the fit.

2007

• More data close to theory limit from penguin pollution;• Measurement of ΔmS improve |Vtd/Vcb| from near cancellation of Bd and Bs form factor;• More data from B→hulν and B→hcX together with improvement in theory will give some improvement in |Vtd/Vcb| ;

)()(sin 2102 o

Strategy: new physics!

now

2007

1 yr

LHCb

BdJ/KS Bd

BsJ/ Bs DsK

statistics!!Goal: Physics beyond the Standard model

• Measurements which provide a reference case for SM effects;• Compare this to channels that might be affected by New Physics;• Understand experimental and theoretical systematics to a level where we can draw conclusions.

for larger the B boost increses rapidly

Hadronic b productionB hadrons at Tevatron

))2/ln(tan(

• b quark pair produced preferentially at low • highly correlated

tagging low pt cuts

LHCb Experiment

• Acceptance :– 15-300mrad

(bending)

– 15-250mrad (non-bending)

• Particle ID– RICH

detectors – Calorimeters– Muon

Detectors

• Dedicated B physics Experiment at the LHC– pp collisions at 14TeV

RICH1Z ~ 1.0-2.2 m

RICH2Z ~ 9.5-11.9 m

CalorimetersZ ~ 12.5-15.0 m

Muon SystemZ ~ 15.0-20.0 m

One event!

Tracking performance

Average efficiency = 92 %Efficiency for p>5GeV >95%

Ghost rate pT>0.5 GeV ~ 7%.

Mass resolution Mass resolution ((~13 MeV)~13 MeV)

for the decay channelBs Ds +

KKπ

Momentum resolution:Momentum resolution:

p/p=0.38%

Proper timeProper time resolution resolution (42 fs)(42 fs)

<N> = 27 tracks/event <N> = 27 tracks/event

S. AmatoC. Nunes JTMN

Hadron ID : Physics Performance

No RICH With RICH

n Signal Purity improved from 13% to 84% with RICH

n Signal Efficiency 79%

n RICH essential for hadronic decays

n Example : Bs K+K-

n Sensitive to CKM angle

Muon Identification• Muons selected by searching for muon stations hits

compatible with reconstructed track extrapolations– Compare track slopes and distance of muon station hits

from track extrapolation

For P>3GeV/ceff = 96.7 0.2 %

misid = 2.50 0.04 %

M. GandelmanJTMN

Strategies for measurements of CKM angles and rare decays

Sd KJB 0

0

dB

2 *0 DBd

sx ss DB0

2KDB ss

0

0dB

)( 0 KKBs

DKBd

0

KBd 0

JBs 0

(/)0 JBs

)()(00

)( , ssSsd DDKJB

Rare 0

)(dsB 00 KBd

,

0dB

Measuring β Sod KJB

S. AmatoC. Nunes JTMN

Measuring β Sod KJB

S. AmatoC. Nunes JTMN

Systematic errors in CP measurements

high statistical precisionasymmetries • ratios• robust

• production asymmetries• tagging efficiencies

• mistag rate

• final state acceptance

Control channels

Monte Carlo Detector cross-checks

ffffff ss 00

CP eigenstates

Sd KJB /0 KJB /

00 / KJBd

)( taa(t)

ff

00 ff 00 ff

ss DB 0

ss ffL. de Paula

)2sin( 0dB

)()(

)()()(

dd

dd

BB

BBtA

• experimental: background with similar topologies

• theoretical: penguin diagrams make it harder to interpret observables in term of

tmAtmA dmix

ddir sincos

030

|P/T|=0.1

0.05

0.02

)2sin( 0dB

PeTeBA iid

)( 0

sinsin2)( 0

T

PBA d

dir

CP conserving strong phase

)sin()cos(cos

)sin()(

22

20

T

P

BA dmix

approximately

Rare B decays• flavour changing neutral currents only at loop level• very small BR ~ or smaller

In the SM:

Excellent probe of indirect effects of new physics!

SB

SM : BR ~ • observation of the decay• measurement of its BR

910

LHCb

width MeV/c2 signal backg

26 33 10

510

FrancioleS. Amato

A. Ali et al., Phys. Rev. D61074024 (2000)

Rare B decays KBd

Forward-backward asymmetry )(sAFB

)( _ pps

can be calculated in SM and other models

0)( 0 sAFB

LHCb %8.5%4.2 (1y)

H. LopesLHC Physics – Praga(B. de Paula)

Measuring γ

000 *KDBd 000 *KDBd 000 *KDBd

iiDdD eeAKDBAA )( *000

)()( *DDdD AAKDBAA 2

1000

iDdD eAKDBAA )( *000

Amplitudes of the chargeconjugated process are obtainedfrom the above ones just changingthe signal from weak phase.

DD AA

DA DA D

A

DA

Measuring γ

M. GandelmanK. Akiba

LHCb reach in one year (2 fb-1)

ChannelChannel Yield Yield PrecisionPrecision**

Bd J/Ks 119 k 0.6o

Bs DsK

Bd , Bs KK

8 k 27 k, 35 k

10o

3o

Bd 27 k 5o- 10o

Bs J/ 128 k 2o

|V|Vtdtd/V/Vtsts Bs Ds 72 k ms up to 58 ps

rare rare decaysdecays

Bd K 20 k

Numbers being updated for the Physics TDR .

Conclusions

LHCb is a second generation beauty CP violation experiment;

It is well prepared to make crucial measurements in flavour physics with huge amount of statistics;Impressive number of different strategies for measurements of

SM parameters and search of New Physics;

CP violation is a cool research topic!!

B factories established CP violation in the B sector and are making interestingmeasurements;

Exciting times: understanding the origin of CP violation in the SM and beyond.

SM is alive and being poked !