CP ViolationRecent results and

perspectives

João R. T. de Mello Neto

Instituto de Física Universidade Federal do Rio de Janeiro

22-26 July,2003

Outline

• Introduction• CP Violation in the SM• Measurement of β• B Factories results• Other measurements• Dedicaded hadron colliders

experiments– LHCb, BTeV

• 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

Neutral B0 mesons oscillateb

d

d

b

t

t

w- w-)()( dbBdbB dd

)()( sbBsbB ss

c

e-

eb

d

w-

d

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

time-dependent formalism for Bd

decay amplitude for fBd 0BHfAf 0BHfAf time evolution

mtAimtAeetBHf fpq

f

timt

phys

21

2120 sincos)(

0B0B

CPf

CP violation: interference between mixing and decay

f

f

A

A

q

p

time-dependent formalism for Bd

)()(

)()()(

tt

tttA

fBfB

fBfBCPf

B-factories: Δt

mtAmtAtA mixdirCPf sincos)(

LHCb, BTeV: t

1

12

2

dirA1

22

ImmixA

C=0 B0→J/ψKSS=+sin(2β)SM:

C=0 S=-sin(2β) B0→J/ψKL

Measuring β

b

d

d

W cc

s

0B /J

0K0K0B

b

dW

s

d

c

cg

u,c,t

/J

Decays such as B0→J/ψKS and B0→J/ψKL

theoretically well understood: tree and leading penguin have same phase

“relatively simple” experiment

ScScSd KKKB 1 ,,

Ld KJB

iCPe

2

1CP

1CP

Measuring β

(from D. Lange)

B factories: Belle, BaBar

Assimetric colliders at ee )( S4

nb 1bb-1-233 scm 103L

One 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 lifetimeslarge samples of

o hadronic decays: fully or partially reconst.o semileptonic decays (D* l fully or partially

reconst.o dileptons

8K events

12K events29 fb-1

Δt distributions and lifetimesΔt = 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

)( czt mz 150 )(pst 90.)(

proof of principle:resolution function under control.

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 -1

(30 fb-1)

Amix(t)

Event samples

~500 KL signal events

60% purity

~1600 KS events

Δt distributions and asymmetries

CP=-1 CP=+1

B0→J/ψKS B0→J/ψKL

Δt distributions and asymmetries

Summary of sin2b in b ccs

already a precisemeasurement: 7.5%

05507340 ..

rarer B decaysdccb

qqsb

Cabbibo supressed

b

d

d

W cc

d

0B /J

00Bb

dW

d

d

c

cg

u,c,t

/J

0B0 → J/ 0

B → KS B

b

d,u

W

ss

sg

Kd,u

bW

s

s

sg

u,c,t

Kd,u d,u

B

B → ‘ KS

Sensitive to new physics:• smaller amplitudes, NP through interf. terms• virtual particles (SUSY?) in penguin loops

not theoretically cleansmaller rates, higher back.

Same CKM structure as B0→J/ψKS

expect S=sin2β to 5%

B0 → J/ 0

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

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!

for the decay channelBs Ds +

Ds KKπ

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)

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

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 extrapolationFor P>3GeV/c

eff = 96.7 0.2 %

misid = 2.50 0.04 %

BTeV detector

Calorimetry

Important final states with and

Use 2x11,850 lead-tungsten crystals (PbWO4)

• technology developed for LHC by CMS• radiation hard • fast scintillation (99% of light in <100 ns)

Excellent energy, angular resolution and photon efficiency

0

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

γ B

Measuring β Sod KJB

“gold-plated” decay channel at B-factories for measuring the Bd- Bd mixing phase needed for extracting γ from Bd ππ and Bs K K in SM Adir=0, non-vanishing value (~0.01) could be a signal of Physics Beyond SM precision measurement important

Inputs:

220 k/year signal194 k/year back.

Amix=sin(2β)=0.73

Adir = 0

0230.dirA

0220.mixA

ps

ACP(t)

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 ff

from Bs J/ψϕ δγ “gold-plated” decay channel for hadron machines, measuring the Bs- Bs phase in SM expected to be ~0.03 large CP asymmetry would signal Physics Beyond SM also needed for extracting from Bs →ππ and Bs K K, or from Bs Ds K

ηλδγ 2

γ

J/ψϕ is not a pure CP eigenstate 2 CP even, 1 CP odd amplitudes contributing need to fit angular distributions of decay final states as function of proper time requires very good proper time resolutionwith input values:εtag= 30% , ωtag= 30% , Δms=20/ps

= 1.5 ps , , A = sin(-) = 0.03

σt = 38 fs

in 1 year:σ

10.

Measuring Using Bo

• A Dalitz Plot analysis gives both sin(2) and cos(2)(Snyder & Quinn)

• Measured branching ratios are:– B(B = ~10-5

– B(B + = ~3x10-5

– B(B <0.5x10-5

• Snyder & Quinn showed that 1000-2000 tagged events are sufficient

• Not easy to measure 0 reconstruction

• Not easy to analyze– 9 parameter likelihood fit

Measuring Using Bo

•Based 9.9x106 background events•Bo+- 5400 events, S/B = 4.1•Booo 780 events, S/B = 0.3

Depending of assumptions on background and value of α :

0461 ..

(from K. Honscheid)

with Bd →ππ, Bs→KK γ relies on “U-spin” symmetry assumption (ds), which is the only source of theoretical uncertainty determination of and test of U-spin symmetry using measurements of from Bs J/ψϕ and β from B J/ψ KS

sensitive to New Physics contribution by comparing with obtained from Bs Ds K

γδγ

tAt

MtAMtAtA

mixCP

dirCPth

CP

22sinhcosh

)sin()cos()(

sensitivity in 1 year

49.0),(

06.0)(

07.0)(

mixCP

dirCP

mixCP

dirCP

AACorr

A

A

1140@

0),(

04.0)()(

psM

AACorr

AA

ss

mixCP

dirCP

mixCP

dirCP

B BS

K K

with Bd →ππ, Bs→KKγ

),,,()(

),,()(

),,,()(

),,()(

40

30

20

10

ssmixCP

sdirCP

ddmixCP

ddirCP

dfKKBA

dfKKBA

dfBA

dfBA

d , (d’ ,’) parametrize P over T amplitude ratio from Bd J/ψ KS , from Bs J/ψϕ exact U-spin symmetry => d = d’ ; = ’ 3 unknowns and 4 measurements

2d γ2d

1 year

2 years

3 years

4 years

95% confidence region for d and 95% confidence region for d and

σγ after 4 years:

2.2º (for = ~60º)

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

510

CMS : 100 fb-1 (107s at 1034

cm-2s-1) ~ 26 signal events 6.4 events background

LHCb : 2 fb-1

~ 33 signal events ~ 10 events backgroundσM = 38 MeV

+-,

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

BTeV data compared to Burdman et al calculation

Conclusions

LHCb and BTeV are second generation beauty CP violation experiments;

They are 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.