CP violation studies at B A B AR

CP violation studies at BABAR

Philip ClarkPhilip ClarkUniversity of Colorado

Philip J. Clark CP violation studies at BaBar Page 2

Talk overview

Introduction to CP violationIntroduction to CP violationPEPII and the PEPII and the BBAABBARAR experiment experiment The charmonium systemThe charmonium systemVarious Various c c resultsresultsBBAABBARAR CP violation results CP violation resultsSummarySummary


The Standard Model

Gravitational, weak, EM and strong

1) fermions which experience the forcesquarks “confined” eg. +(ud), p(uud)leptons don’t experience strong force

2) bosons which transmit the forces

Two types of fundamental particle:

Four fundamental forces:


Symmetries and conservation laws

C = Charge Conjugation particle antiparticle

Relation between symmetry and conservation laws Noether’s theorem Symmetries conservation laws

-y

x

z-x

y

-z

q q

B. C

ahnCP =

P = Parity: x -x

T = time reversal “run the film backwards”


C and P symmetry and the weak interaction

C

P

0,0 P

1, P 1, P

0,0 P

1, P 1, P

0,0 P

1, P 1, P

0,0 P

1, P 1, P

C and P are violated maximally


CP symmetry Is CP, a good symmetry for all interactions

including the weak interaction?

Cosmology:CP violation is one of the three necessary conditions to produce aglobal excess of matter in the Universe (Andreï Sakharov, 1967)

1964 : Christenson, Cronin, Fitch and Turlay CP violation in the decay

of neutral kaons

A CP-violating process offers an absolute way of distinguishing

a world of anti-matter from a world of matter

CPLEARCPLEAR


Perhaps the answer to why the Universe looks like this not that???

Matter-antimatter asymmetry


The CKM model1973 : M. Kobayashi and T. Maskawa made the connection

CP violation third generation of quarksud

cs

tb

quark doublets

d s buct

d s buct

CP violation in the Standard Model ≠

Wolfenstein parametrization:

W

b

u

Vub

ub

Cabibbo-Kobayashi-Maskawa matrix V:

Complex matrix described by 4 independent real parameters (e.g. three angles, one phase)

W

d

u

Vud

ud


The Unitarity Triangle

Vud

Vcd

Vtd

Vus

Vcs

Vts

Vub

Vcb

Vtb

=100

010

001

Vud

Vus

Vub

Vcd

Vcs

Vcb

Vtd

Vts

Vtb

*

*

*

*

*

*

*

*

*

Vud Vub + Vcd Vcb + Vtd Vtb = 0***

Vud

Vus

Vub

Vcd

Vcs

Vcb

Vtd

Vts

Vtb

*

*

*

*

*

*

*

*

*

Vud

Vcd

Vtd

Vus

Vcs

Vts

Vub

Vcb

Vtb

=100

010

001

The CKM Matrix is complex and unitary

9 unitarity relations

The Unitarity Triangle

Experimentally: constraints on the coordinates of the apex of the Rescaled Triangle in the complex plane

The Rescaled Unitarity Triangle

CP Violation area of the Triangle


Precision test of the CKM model

Phys. Rev. Lett. 89 (2002) 201802

BABAR

World average (BABAR+Belle+…)

Heavy Flavor Averaging Group 2003

Main experimental constraints on the apex of the UT

CP violation in the kaon systemMeasurements of |Vub| (b → u transitions)B and Bs mixing frequencies


Is the CKM mechanism sufficient?CP violation in the quark sector is not enough to generate the baryon asymmetry of our Universe

Antimatter in the

Universe

?

Understand the origin of CP violation in the Standard Model The Kobayashi & Maskawa mechanism can it account for all the effects of CP violation that are observed in the quark sector?

What can we do?

and if possible, reveal inconsistencies between experimental data and theoretical predictions

Possible manifestations of New Physics? Evidence for new sources of CP violation?


PEP II/BABAR at SLACPEP II

Asymmetric B Factory

design peak: best peak: total recorded:

x cmsx cms

fb

PEP-II/BABAR at SLACLuminosity records

Started construction in1994 Completed in 1999 Reached design luminosity in 2000

9 GeV e on 3.1 GeV e+


SVTSVT-T Solenoid

The BABAR detector

SVTSVT

EMCEMC

IFRIFR

DCHDCH

DIRCDIRC


B MixingCertain mesons can do a neat little trick (K0, D0, B0)

A B0 meson can change into an anti B0 meson (B0)This is called “mixing”. It means these particles can (and do) oscillate into their anti-particles and back again

The oscillation frequency is about 0.5 ps-1!


Measurement of sin2

0tagB

e

S4

0recB

eCoherent BB

production

-K

IdentifyB or anti-B

zx

y

Full reconstruction of B cKs

0

0SK

0SK

cK+

t z/c

z


Observable CP Asymmetry

(perfect experiment with sin2 = 0.6)Different t spectrum for B0 and B0

Positive and negative t

Visible asymmetry ACP= nB0-nB0/(nB0+nB0)

t spectrum of CP eigenstates

sin 2

( ) sin(2 ) sin( )CP dA t Δm Δt


CP asymmetry


The new mode:- B0 cKs

In the c analysis group we have studied B cK and B0 cKs in the c decay modes:

c

_b

d

c_

d

cs_

K0B0 W

The two dominant modes measured have the following branching fractions BR(B0 cK0) x BR(c K0K) 36.8 36.8 11.6 11.6 6.0 x10 6.0 x10-6-6

BR(B0 cK0) x BR(c K+K-0) 11.3 11.3 5.1 5.1 2.4 x10 2.4 x10-6-6

Combining gives us our CP sample:


CP asymmetry using B→cK


Sin2 per Charmonium modeGood consistency between the measurements


Summary of “sin2” results

“reference” sin2pure penguinmostly penguin?heavily supressed tree with competing penguin

suppressed treepenguin pollution

The other BABAR measurements agree with the reference sin2

Statistical conspiracy or hint of unexpected

physics effect?within two standard deviations, or betterbut… consistently on the low side

“sin2”

0.74

1


The Charmonium system

Bound state of two spin ½ particles (fermions)The c meson consists of a charm and anti-charm quark

J = J1 + J2

the triplet statethe singlet stateJ = 0 (½ - ½ )

J = 1 (½ + ½) m = 0m = -1, 0, 1

The combined angular momenta

J = |j1-j2|, |j1-j2|+1, … , (j1+j2)-1 , (j1+j2 ) and m =m1+m2 gives:

Other examples are the: hydrogen atom (e-p)positronium (e+e-)

En

singlet

triplet

hyperfine splitting

Discrete energy levels and splittings exist andcan give information on the strong force


Striking similarity

Missing singlet state c(2S)

“Introduction to High Energy Physics” D. Perkins 4th edition April 2000

singlet

triplet

singlet

triplet

c singlet

J/ triplet

charmonium (cc)positronium (e+e-)

J/(2S) triplet


c at BABAR

photon-photonproduction

?

mass and total decay widthc widthc mass

c mass and total width

c(2S) mass and total width


Charming, but strange mesons

D+

D+sDs

+= cs Ds- = cs

mass = 1968.5 MeV

D+sJ(2317) D+

s0


Large amount of theoretical interest

32 new preprints


Summary Prequisites

The Standard ModelThe discrete symmetries C P and TC and P violated maximally in weak interationCP violation in the kaon systemCosmological implications

FormalismThe Standard Model mechanism for CP violationTesting the unitarity of the CKM matrix

Measurement of Sin2General methodologyManifestation of CP violation by BaBarComparison to other measurements

CharmoniumB c K transitions and branching fractionsUsing the c to measure sin2Charmonium system and measurement of c(2S)

New particle DsJ

+ resonance

What we have covered:What we have covered:


The c and the Charmonium System: fundamental scalar state of the charmonium system, hyperfine partner of the

to hadronsthrough virtual photon

radiative

In the c group we are studying the following decay modes:


Resonant structure

M(K± ±)

M(K0s

±)

c (KsK) resonant structure

c Dalitz analysisand

Branching fraction large 4.9 ± 1.8 % (c )1.28% (±±)cf. 1.26% (c KsK±±)

No result from Belle

resonant structure– c a0)– Should look for c )


B physics at hadron machinesGeant3 LHCb event displayAdvantages:

LHC cross-section 500 mb 1012 bb pairs/year at 2x1032 cm-2s-1 (down by 5 at Tevatron )

Challenges:Event complexityTriggering

Bunch spacing: 25 ns (LHC) 132 ns (Tevatron)

What next?


Comparison of yield and purity

Sample Ntagged Purity

J/ Ks (+-) 974 97%

J/ Ks (00) 170 89%

(2S) Ks 150 97%

c1Ks 80 95%

cKs 132 73%

Total 1506 92%


SLAC-PUB-8970

At 1036


Mixing and Sin2 analysis procedure

• Reconstruct one B fully in CP eigenstate or flavour eigenstate• Other B partially reconstructed and flavour tagged• Measure z • Fit for t z/c

PDF(t) exp(–|t|/B) ( 1 ± (1-2) sin2 sin(mt) ) R(t)

CP violation:-

PDF(t) exp(–|t|/B) ( 1 ± (1-2) cos(mt) )R(t)

B Mixing:-

(1-2) is the “dilution” due to mistag

R(t) is the vertex resolution function


Silicon Vertex Tracker (SVT)

• Five layer double-sided Si• Very low mass• Stand-alone tracking device for PT < 120 MeV/c• Radiation hard• z-resolution of 70m on CP vertex

580 mm


Drift ChamberTracking resolution


Detector of Internally Reflected Cherenkov Light (DIRC):

cosc=1/n

c resolution:


Cherenkov angles for and K from D* D0D0 K-

K


Electromagnetic calorimeter

Radiation length 1.85 cm (16 -18X0)Moliere radius 3.8 cmPeak emission 565 nmDensity 4.53 g/cm3

Time constant 940 nsLight yield 40-50k

photons/MeV

%2.1%14

EE

E


Time-Dependent Asymmetries

Use the large statistics Bflav data sample to determine the mis-tagging probabilities and the parameters of the time-resolution function

0S

0CP K/JB

CP-violating asymmetry using the BCP sample

00 BB

)cos(21)( ΔtΔm.wN(mixed)N(unmixed)N(mixed)N(unmixed)tA

dBmixing

)sin(2sin21)( 00

00ΔtΔmβ..w

)BN(B)BN(B

)BN(B)BN(BtA

dBtagtag

tagtagCP

Mixing using the Bflav sample:

for example


Large solid angle coverage for muon id (P>1 GeV/c) and to detect neutral hadrons (K0

L )

Barrel section of IFRID efficiency and fake rate

Instrumented Flux Return (IFR)


Speaking of Direct CP violation …

Uncertainty ~5%!


Separating Signal from Background (II)

The other powerful thing we can do is to exploit the “event shape” In the CM, the decay products of

the B are distributed roughly spherically. This is because the pair of B mesons weigh only slightly less than the . They are essentially produced at rest

The continuum is light quark pair production, so there is lots of extra energy. All the decay products bunch into “jets”

We define variables that measure the degree of “jettiness” of the decay to tell us how more or less likely it is to be signal or background

e+

e-

e+

e-

qq

Signal B

Other B

Documents

CP violation studies at B A B AR