BB Physics and CP Violation Physics and CP Violation

Jeffrey D. RichmanJeffrey D. Richman

UC Santa BarbaraUC Santa Barbara

CTEQ Summer SchoolCTEQ Summer School

Madison, June 7-8, 2002Madison, June 7-8, 2002

Outline (Lecture 1)Outline (Lecture 1)

Overview of Overview of BB decays decays

Why B physics is interesting; overview of decay diagrams; introductory discussion of CP violation.

Accelerators and Accelerators and bb-quark production -quark production

The The BaBarBaBar Detector Detector

Identifying B decaysIdentifying B decays

BB-meson lifetimes and mixing-meson lifetimes and mixing

CP Violation (CPv) and the CKM matrixCP Violation (CPv) and the CKM matrix

the CKM hierarchy and the prediction of large CP asymmetries in B decays

Outline (Lecture 2)Outline (Lecture 2) CP Asymmetries: CP Asymmetries:

sin(2): the golden measurement

the struggle for the other angles

Rare decaysRare decays

Penguins are everywhere!

Semileptonic decays, decay dynamics, and the Semileptonic decays, decay dynamics, and the magnitudes of CKM elements.magnitudes of CKM elements.

Heavy-quark symmetry and Vcb

Prospects and future directionsProspects and future directions

A reference: J. Richman, Les Houches lectures, 1997.

http://hep.ucsb.edu/papers/driver_houches12.ps

(or send e-mail asking for a copy: richman@charm.physics.ucsb.edu)

I will be I will be unashamedly pedagogicalunashamedly pedagogical, and I will not aim for , and I will not aim for the level of impartiality that is customary in a review talk the level of impartiality that is customary in a review talk or article.or article.

I will be I will be unashamedly selective:unashamedly selective: many important topics have many important topics have been left out. been left out.

There will be a strong There will be a strong biasbias towards recent results from towards recent results from ee++ee-- colliders at the colliders at the YY(4S).(4S). This is probably not too misleading This is probably not too misleading for now, since for now, since BaBarBaBar, Belle, and CLEO have to some extent , Belle, and CLEO have to some extent defined the state of the art, especially in CPv and rare defined the state of the art, especially in CPv and rare decays. However, soon-to-come measurements from the decays. However, soon-to-come measurements from the Fermilab Tevatron (CDF, D0) will be of Fermilab Tevatron (CDF, D0) will be of major importance.major importance.

My own background in My own background in bb physics: physics: BaBarBaBar, CLEO, CLEO

I strongly encourage you to ask questions!I strongly encourage you to ask questions!

Remarks/disclaimersRemarks/disclaimers

Goals of Goals of BB (and (and BBss) Physics) Physics

1.1. Can Can CP violationCP violation be understood be understood quantitativelyquantitatively within within the Standard Model, or is new physics needed? the Standard Model, or is new physics needed? Perform a comprehensive set of measurements to Perform a comprehensive set of measurements to check for the presence non-SM CP-violating phases.check for the presence non-SM CP-violating phases.

2.2. Make precise measurements of the Standard Model Make precise measurements of the Standard Model CKM parameters: CKM parameters: ||VVcb cb |,|, || VVub ub |,|, ||VVtd td |,|, ||VVts ts |,|,

3.3. Map out and understand Map out and understand rare B decaysrare B decays, especially , especially processes with loops that can be very sensitive to processes with loops that can be very sensitive to particles outside the Standard Model. particles outside the Standard Model.

4.4. Understand the Understand the dynamicsdynamics of of BB decays: underlying decays: underlying weak interaction process with overlay of complex weak interaction process with overlay of complex strong interaction effects. Progress: HQET, lattice strong interaction effects. Progress: HQET, lattice QCD, many measurements to test predictions.QCD, many measurements to test predictions.

Overview of Overview of BB Decays Decays bb is the heaviest quark that forms bound states with other is the heaviest quark that forms bound states with other

quarks (quarks (tt-quark decays too rapidly).-quark decays too rapidly).

m(b)m(b)<<m(t)m(t) => the => the bb-quark is forced to decay outside of its own -quark is forced to decay outside of its own generationgeneration

Dominant decays are CKM suppressed:

Relatively long B lifetime:

Silicon tracking systems have been essential tools.

Largest single branching fraction:

Many interesting rare decay processes are experimentally accessible (b->uW, gluonic penguins, electroweak penguins).

1.6 ps ( 480 m)B Bc

2 2( ) (0.04)cbb cW V

*0B( ) (6.50 0.20 0.43)% (CLEO, hep-ex/0203032)B D l

Leptonic and Semileptonic DecaysLeptonic and Semileptonic Decays

Leptonic Leptonic BB++ decay not yet decay not yet observed!observed!

Largest expected mode is:Largest expected mode is:

Ignoring photon radiation: Ignoring photon radiation:

Used to measure Used to measure magnitudes of CKM magnitudes of CKM elements: elements: VVcb cb andand VVubub

Amplitude can be Amplitude can be rigorously parametrized rigorously parametrized in terms of form factors.in terms of form factors.

2222 2 2

2( ) 1

8lF

qQ M l

mGM l V f m

M

5B( ) 7 10B

sD

sD csf V2( )j cbF q V

2 2 2W lq m m

(Amp )ubV

Hadronic Decays: Tree DiagramsHadronic Decays: Tree Diagrams

Theoretical predictions Theoretical predictions very difficult.very difficult.

Naïve factorization model Naïve factorization model works reasonably well in works reasonably well in predicting pattern of predicting pattern of decays.decays.

““Color suppressed”Color suppressed”

Naïve factorization model Naïve factorization model probably breaks down. probably breaks down. (New data on (New data on B-B->D>D00and and B->DB->D**00

0

2 21

( )

( )B D

A B D

a f F q m

0 0 0

2 22

( )

( )D B D

A B D

a f F q m

The color allowed The color allowed and color suppressed and color suppressed amplitudes interfere amplitudes interfere constructively in constructively in charged charged BB decays. decays. (Opp. effect for D(Opp. effect for D++.).)

Processes with loops: sensitivity to new particlesProcesses with loops: sensitivity to new particles

Both gluonic and electoweak penguins have been observed!Both gluonic and electoweak penguins have been observed!

The SM mixing rate is dominated by The SM mixing rate is dominated by tttt (off-shell) intermediate states. (off-shell) intermediate states.

,Z

Processes used for sin2Processes used for sin2 measurement measurement

b

d d

s

c

cW+

0B c/ , (2S), J 0 0 *, , S LK K K

0 0Direct decay of (or ) to CPB B f

A color suppressed decay! However, in this case, the rate isenhanced by the relatively large decay constant of the J/

( / ) 400 MeVf J

Decay modes for sin2Decay modes for sin2 measurement measurement

The C, P, and T TransformationsThe C, P, and T Transformations C, P, and T are discrete transformations: there is no

continuously varying parameter, and these operations cannot be constructed from successive infinitesimal transformations.

In all well-behaved quantum field theories, CPT is conserved. A particle and its antiparticle must have equal mass and mean lifetime.

: ( is the antiparticle of )

: (spatial inversion)

: (motion- or time-reversal; antilinear op.)

C a a a a

P r r

T t t

( ) ( ) ( ) ( ) ( ) ( ) /M a M a a a a a

P and C violation in Weak InteractionsP and C violation in Weak Interactionsis Maximal (V-A)is Maximal (V-A)

e

e

e

e

e

e

P C

Allowed AllowedNot Allowed

A First Look at CP violation A First Look at CP violation

( ) ( ) violationB f B f CP decay rate

a particular final state (often pick )CPf f f

The discovery of CP violation in 1964 was based on the The discovery of CP violation in 1964 was based on the demonstration that the mass eigenstate demonstration that the mass eigenstate KKLL is not an is not an eigenstate of CP, so . eigenstate of CP, so .

The lifetime separation between The lifetime separation between BBHH and and BBLL is tiny, so we is tiny, so we

must use a different method, in which we compare the rates must use a different method, in which we compare the rates for CP-conjugate processes.for CP-conjugate processes.

0 3( ) (2.0 0.4) 10

( , 0) 1

L

CP

B K

L

0 0 2.7 cm 15.5 m S Lc K c K

[ , ] 0H CP Remove Ks from beam using lifetime difference.

CPv small in kaon system!

“...the effect is telling us that at some tiny level there is a fundamental asymmetry between matter and antimatter, and it is telling us that at some tiny level interactions will show an asymmetry under the reversal of time. We know that improvements in detector technology and quality of accelerators will permit even more sensitive experiments in coming decades. We are hopeful then, that at some epoch, perhaps distant, this cryptic message from nature will be deciphered.” ...J.W. Cronin, Nobel Prize lecture*. Cronin, Nobel Prize lecture*.

J.W. Cronin and V.L. Fitch, Nobel Prize 1980.

*J.W. Cronin, Rev. Mod. Phys. 53, 373 (1981).

J.H. Christenson, J.W. Cronin, V.L. Fitch, and R. Turlay,

Phys. Rev. Lett. 13, 138 (1964).

The Legacy of Kaon PhysicsThe Legacy of Kaon Physics

CP violation and alien civilizationsCP violation and alien civilizations

We can use our knowledge of CP violation to determine whether alien civilizations are made of matter or antimatter, without having to touch them.

0 03

0 0

( ) ( )3.3 10

( ) ( )L e L e

L e L e

K e K e

K e K e

Long-lived neutral kaon We have these inside of us

CP Violation and CosmologyCP Violation and Cosmology

A. Sakharov noted (1967) that CP violation has an important connection to cosmology.

3 conditions for an asymmetry between N(baryons) and N(anti-baryons) in the universe (assuming equal numbers initially due to thermal equilibrium). baryon-number-violating process

both C and CP violation (helicities not relevant to particle populations)

departure from thermal equilibrium

net ( ) ( )i i ii

B X Y X Y B

How can CP asymmetries arise? (I)How can CP asymmetries arise? (I)

When we talk about CP violation, we need to talk about the phases of QM amplitudes.

This is usually very confusing.

some phases are physical; others are not.

many treatments invoke specific phase conventions, which acquire a magical aura.

Need to consider two types of phases

CP-conserving phases: don’t change sign under CP. (Sometimes called strong phases since they can arise from strong, final-state interactions.)

CP-violating phases: these do change sign under CP.

How can CP asymmetries arise? (II)How can CP asymmetries arise? (II)

Suppose a decay can occur through two different processes, with amplitudes A1 and A2.

First, consider the case in which there is a (relative) CP-violating phase between A1 and A2 only.

1 2A A A

1 2A A A

1 1A A2A

2A

2

2

2

1 2

1 2

i

i

A A a e

A A a e

No CP asymmetry!(Decay rate is different from what is would be without the phase.)

How can CP asymmetries arise? (III)How can CP asymmetries arise? (III)

Next, introduce a CP-conserving phase in addition to the CP-violating phase.

Now have a CP asymmetry

1 2A A A

1 2A A A

1 1A A

2A

2A2

2 2

2 2

( )1 2

( )1 2

i

i

A A a e

A A a e

22

A A

Measuring a CP-violating phaseMeasuring a CP-violating phase To extract the CP-violating phase from an observed CP asymmetry, we need to know the value of the CP-conserving phase.To extract the CP-violating phase from an observed CP asymmetry, we need to know the value of the CP-conserving phase.

In direct CP-violating processes we usually do not know the relative CP-conserving phase because it is produced by strong-interaction dynamics that we In direct CP-violating processes we usually do not know the relative CP-conserving phase because it is produced by strong-interaction dynamics that we do not understand.do not understand.

2 2

1 2 1 2 1 22 2 22

1 2 1 2 1 2 1 2

2 sin( )sin( )

cos( )cos( )

A A A AAsymmetry

A A A AA A

BB production at the production at the YY(4S)(4S)

thresholdBB( (4 )) 1.1 nbS

33 21.1 10 cm

Rate of events vs. total energy in e+e- CM frame: TM

No accompanying pions!The B-meson energy is known from the beam energy.

00

1.058 0.084 0.136f

f

(CLEO, CLNS 02/1775)

The New The New ee++ee-- B B factories factories The machines have unequal (“asymmetric”) energy The machines have unequal (“asymmetric”) energy ee++ and and ee--

beams, so two separate storage rings are required.beams, so two separate storage rings are required.

PEP-II: E(e-)=8.992 GeV E(e+)=3.120 GeV =0.55

The machines must bring the beams from the separate rings The machines must bring the beams from the separate rings into collision.into collision.

KEK-B: +-11 mrad crossing angle

PEP-II: magnetic separation

With two separate rings, the machines can store huge numbers With two separate rings, the machines can store huge numbers of beam bunches without parasitic collisions.of beam bunches without parasitic collisions.

KEK-B: 1224 bunches/beam; I(e+)=716 mA; I(e-)=895 mA

PEP-II: 831 bunches/beam; I(e+)=418 mA; I(e-)=688 mA

CESR (single ring): 36 bunches/beam; I(e+)=I(e-)=365 mA

PEP-II ePEP-II e++ee-- Ring and Ring and BaBarBaBar Detector Detector

Linac

PEP-II ring: C=2.2 kmBaBar

LER (e+, 3.1 GeV)

HER (e-, 9.0 GeV)

BaBar

May 26, 1999: 1st events recorded by BaBar

The The YY(4S) Boost(4S) Boost The purpose of asymmetric beam energies is to boost the The purpose of asymmetric beam energies is to boost the BB00BB00

system relative to the lab frame.system relative to the lab frame.

By measuring By measuring zz, we can follow time-dependent effects in B decays., we can follow time-dependent effects in B decays.

The distance scale is much smaller than in the kaon decay experiments The distance scale is much smaller than in the kaon decay experiments that first discovered CP violation!that first discovered CP violation!

1.6 psB

From CESR (1 ring, E symmetric) toFrom CESR (1 ring, E symmetric) toPEP-II (2 rings, E asymmetric)PEP-II (2 rings, E asymmetric)

Pretzel orbits in CESR(36 bunches, 20 mm excursions)

Top view of PEP-II interaction region showing beam trajectories.

(10X expansion of vertical scale)

The race between The race between BaBarBaBar/PEP-II and Belle/KEK-B/PEP-II and Belle/KEK-B

Belle

33 -2 -1

-1

(max) 7.25 10 cm s

Best day: 395 pb

L 33 -2 -1

-1

(max) 4.6 10 cm s

Best day: 303 pb

L Exceeds designluminosity!

ee++ee-- vs. pp and pp vs. pp and pp Production cross sectionsProduction cross sections

Y(4S):

pp at Tevatron:

pp at LHC:

bb fraction (ratio of fraction (ratio of bb cross section to total hadronic cross section) cross section to total hadronic cross section)

Y(4S): 0.25

pp at Tevatron: 0.002

pp at LHC: 0.0063

CommentsComments

Triggering: so far, most B branching fractions have been measured at e+e- machines, because CDF, D0 triggers were very selective in Run 1. Also, PID & detection arebetter at Y(4S) experiments so far.)

Hadron colliders produce Bs and b-baryons. (LEP also.)

New displaced-vertex triggers at hadron-collider experiments should make a dramatic improvement.

( ) 1.1 nbBB

( ) 100 bbb ( ) 500 bbb

The The BBAABBARAR Detector Detector

DIRC (particle ID)

1.5 T solenoid

CsI (Tl) Electromagnetic Calorimeter

Drift Chamber

Instrumented Flux Return

Silicon Vertex Tracker

e+ (3.1GeV)

e- (9 GeV)

SVT: 97% efficiency, 15m z resol. (inner layers, perpendicular tracks) Tracking : pT)/pT = 0.13% PT 0.45% DIRC : K- separation >3.4 for P<3.5GeV/c EMC: E/E = 1.33% E-1/4 2.1%

BaBar DetectorBaBar Detector

e- e+

center line

CsI crystals

Drift chamber

Superconducting magnet (1.5 T)

Muon detector & B-flux return

Silicon Vertex Tracker

DIRC:quartz barsstandoff boxPM tubes

BaBarBaBar Event Display Event Display(view normal to beams)(view normal to beams)

Rdrift chamber=80.9 cm

(40 measurement points, each with 100-200 m res. on charged tracks)

EM Calorimeter: 6580 CsI(Tl) crystals (5%

energy res.)

Silicon Vertex Tracker5 layers: 15-30 m res.

Cerenkov ring imaging detectors: 144 quartz bars (measure velocity)

Tracking volume: B=1.5 T

Innermost Detector Subsystem: Silicon Vertex TrackerInnermost Detector Subsystem: Silicon Vertex Tracker

Be beam pipe: R=2.79 cmInstalled SVT Modules

(B mesons move 0.25 mm along beam direction.)

BaBar Silicon Vertex TrackerBaBar Silicon Vertex Tracker 5 layers of double-sided silicon-strip detectors (340)

300m

50m

80 e-/hole pairs/m

• Measure angle of Cherenkov cone

– Transmitted by internal reflection

– Detected by PMTs

Particle Identification (DIRC)Particle Identification (DIRC)((DDetector of etector of IInternally nternally RReflected eflected CCherenkov Light)herenkov Light)

c

Particle

Quartz bar

Cherenkov light

Active Detector Surface

1cos c p m

n

1.473n No. light bounces (typical)=300

DIRC DIRC cc resolution and resolution and KK-- separation measured in data separation measured in data D D**++ D D00++ ( (KK--

++))++ decays decays

Particle Identification with the DIRC.Particle Identification with the DIRC.

((cc) ) 2.22.2 mrad mrad

>9

2.5

K/ Separation

Particle IdentificationParticle Identification

Electrons – p* > 0.5 GeV

•shower shapes in EMC

•E/p match

• Muons – p* > 1 GeV

• Penetration in iron of IFR

• Kaons

• dE/dx in SVT, DCH

• C in DRC

E/p from E.M.Calorimeter

Shower Shape

e e

1 < p < 2 GeV/c 0.8 < p < 1.2 GeV/cE/p > 0.5

e e

c from Cerenkov Detector

e

0.5 < p < 0.55 GeV/c

dE/dx from Dch0.8 < p < 1.2 GeV/c

mes

E

mes 3 MeV

E 15 MeV

All Ks CP modesNsig 750Purity 95%

Identifying Identifying BB Decays in BaBar Decays in BaBar• Select “candidate daughter particles” using particle ID, etc. • Compute the total 4-momentum: (E, p)=(E1+E2+E3, p1+ p2 +p3)• Compute invariant mass: m2=E2-|p|2

Gives 10x improvementin mass resolution.

sin2sin2 Signal and Control Samples Signal and Control Samples

J/ Ks (Ks +-)

J/ Ks (Ks 00)

J/ K*0 (K*0 Ks0)

c1 Ks

(2s) Ks

J/ KL

Bflav

mixing sample

J/ Ks (Ks 00)

J/ Ks (Ks )

J/ K*0 (K*0 Ks0)

CP=-1

CP=+1

The Lorentz BoostThe Lorentz Boost

The asymmetric beam energies of PEP-II allow us to measure quantities that depend on decay time.

(4s) = 0.56

Tag B

z ~ 170 m CP Bz ~ 70 m

J/

K0z

t z/c cB 250 m

e-

9.0 GeV

e+

3.1 GeV

1 ps 170 μm

Measurement of Decay Time DistributionsMeasurement of Decay Time Distributions

0

τ( )1.082 0.026 (stat) 0.011 (sys)

τ( )

B

B

B0 decay timedistribution

background

(linear scale)

B0 and anti-B0 mesons spontaneously oscillate into one another! (Mixing also occurs with neutral kaons.)

Neutral B mesons can be regarded as a coupled, two-state system.

To find the mass eigenstates we must find the linear combinations of these states that diagonalize the effective Hamiltonian.

0 0 Oscillations (Mixing)B B

0 01 0

0 1B B

Interpretation of the Effective HamiltonianInterpretation of the Effective Hamiltonian The effective Hamiltonian for the two-state system is not

Hermitian since the mesons decay.

11 12 12 12* *

21 22 12 12

12 12

* *12 12

2

01 0 2( )0 12

02

H H M M iH

H H M M

iM

iM

iM

Quark masses, strong, and EM interactions

0 0 transitions

off-shell on-shell

B f B

f f

Decays

CP Violation inCP Violation in MixingMixing Compare mixing for particle and antiparticleCompare mixing for particle and antiparticle

0 0* *212 12

0 0212 12

i

i

B H BM

M B H B

off-shell off-shell

on-shell on-shell

CP-conserving phase

20 0

20 0

CP

CP

i

i

CP B e B

CP B e B

2

2

0

0

CP

CP

i

i

eCP

e

, 0 =1 whereCP H

CP violation in mixing, continuedCP violation in mixing, continued

To produce a CP asymmetry in mixing, To produce a CP asymmetry in mixing, MM1212 and and 1212 must not must not be collinear and both must be nonzero:be collinear and both must be nonzero:

No CP violation in mixing CP violation in mixing

is a convention-dependent phaseCP

12 12

*12 12 12 12Im( ) sin( ) 0 CP violation in mixingMM M

0 0 0

0 0 0

( ) ( ) ( )

1( ) ( ) ( )

B t f t B f t B

B t f t B f t B

/ 2 / 2

/ 2 / 2

1( )

21

( )2

iM t t iM t t

iM t t iM t t

f t e e e e

f t e e e e

* *212 12

212 12

i

i

M

M

Time evolution of states that are initially flavor Time evolution of states that are initially flavor eigenstateseigenstates

General case;allows CP violation.

CP Violation in CP Violation in BB Mixing is Small Mixing is Small

When CP violation in mixing is absent (or very small), we haveWhen CP violation in mixing is absent (or very small), we have

In the neutral B-meson system, the states that both BIn the neutral B-meson system, the states that both B00 and B and B00 can decay can decay into have small branching fractions, since into have small branching fractions, since

normally lead to different final states. Can have (Cabibbo normally lead to different final states. Can have (Cabibbo suppressed) and (b->u is CKM suppressed). So the SM predictssuppressed) and (b->u is CKM suppressed). So the SM predicts

12 122 2M M

and b c b c

ccdduudd

2 212

12

0 0 -4

( / ) 1

Expect CPv in mixing to be (10 ).

b tO m mM

B B O

not yet observed

Time evolution of states that are initially flavor Time evolution of states that are initially flavor eigenstateseigenstates

In these formulas, we have assumed that /and have set

1 2

1 ( )

2M M M

The Oscillation Frequency (The Oscillation Frequency (mm)) In the neutral B-meson system, the mixing amplitude is

completely dominated by off-shell intermediate states (m) [contrast with the neutral kaon system].

Calculation of the mixing frequency

Time-dependent mixing probabilities and asymmetry

2 -1strong+weak interactions 0.5 pstb tdm V V

nomix

mix

11 cos( )

4τ1

1 cos( )4τ

t

B

t

B

dNe m t

dtdN

e m tdt

NoMix(t) - Mix(t)Asym(t)= cos( )

NoMix(t) Mix(t)m t

( 1)

TaggingTaggingCP asymmetry is between B0 fcp and B0 fcp

Must tag flavor at t=0 (when flavor of two Bs is opposite).

Use decay products of other (tag) B.Leptons : Cleanest tag. Correct 91%

b c

e-

W-

b c

e+

W+

Kaons : Second best. Correct 82%

b

W-c s

u

d

K-

W+

b

W+c s

u

d

K+

W-

Effect of Mistagging and Effect of Mistagging and t Resolutiont ResolutionNo mistagging and perfect t

Nomix

Mix

t

t

D=1-2w=0.5

D=1-2w=0.5

t res: 99% at 1 ps; 1% at 8 ps

w=Prob. for wrong tag

t

t

NoMix(t)-Mix(t)NoMix(t)+Mix(t)

T=2m

~D

m = (0.516 0.016 0.010) ps-1

Measure mixing on control sample:• constrain model of t resolution• measure dilution D = (1-2w)

rec tagt t t

CP violation in the Standard ModelCP violation in the Standard Model In the SM, the couplings of quarks to the W are

universal up to factors that are elements of a unitary, 3x3 rotation matrix Vij of the quark fields. This matrix originates in the Higgs sector (mass generation of quarks).

W-

e- e b u

W-

b u

W+ubgV

*ubgV

g

The Standard Model “Unitarity Triangle”The Standard Model “Unitarity Triangle”

ud us ub

cd cs cb

td ts tb

d V V V d

s V V V s

b V V V b

Weak interaction eigenstates

Quark mass eigenstates

Cabibbo-Kobayashi-Maskawa (CKM) matrix [Col 1][Col 3]*=0

V has only 4 real parameters,including 1 CP-violating phase.

If just 2 quark generations: no CP phase allowed!

CPv

1 of 6 equal-area triangles: orientation is just an unphysical phase

The Structure of the CKM MatrixThe Structure of the CKM MatrixThe CKM matrix exhibits a simple, hierarchical structure (which we do not understand) with 4 real parameters. λ 0.22

0.04

5 *

3 3 3 *

4 2 2 *

( ) ( ) ( ) 0 (col 1) (col 2)

( ) ( ) ( ) 0 (col 1) (col 3)

( ) ( ) ( ) 0 (col 2) (col 3)

O O O

O O O

O O O

(All unitarity triangles have same area, corresponding to the sizes ofinterference terms between 1st order weak amps. But we care about CPasymmetries, so the angles of the triangles also matter.)

End of Lecture 1End of Lecture 1

Outline (Lecture 2)Outline (Lecture 2) CP Asymmetries: CP Asymmetries:

sin(2): the golden measurement

the struggle for the other angles

Rare decaysRare decays

Penguins are everywhere!

Semileptonic decays, decay dynamics, and the Semileptonic decays, decay dynamics, and the magnitudes of CKM elements.magnitudes of CKM elements.

Heavy-quark symmetry and Vcb

Prospects and future directionsProspects and future directions

A reference: J. Richman, Les Houches lectures, 1997.

http://hep.ucsb.edu/papers/driver_houches12.ps

(or send e-mail asking for a copy: richman@charm.physics.ucsb.edu)

0

0 020

0

0 020

( ) cos sin2 2

( ) sin - cos2 2

t CPiMtCP CP

CP

t CPiMtCP CP

CP

f H BM t M tf H B t e e f H B i

f H B

f H BM t M tf H B t e e f H B i

f H B

2 2 2 20 0

22 2 2 20 0

1 1( ) 1 1 cos Im( )sin

2 2

1 1 1( ) 1 1 cos Im( )sin

2 2

tCP CP

tCP CP

f H B t e f H B M t M t

f H B t e f H B M t M t

0 0* *212 12

0 0212 12

iCP CP

iCP CP

f H B f H BM

Mf H B f H B

Decay rates for Decay rates for BB00(t)(t) and and BB0 0 (t)(t) to to ffCPCP

Calculating the CP AsymmetryCalculating the CP Asymmetry

2

2 2

1 2 Im( )

1 1C S

If there is just one direct decay amplitude, we will see that

1 If CP violation is due to interference between mixing and one direct decay amp: pure sin(m t) time dependence.

Calculating Calculating

* *2 2( )12

*12

CP CP Mi itb td

tb td

M V Ve e

M V V

( )0

2 ( )0 ( )

D

CP D

iCP

i iCP CP CP

f H B a e

f H B f e a e

if just one direct decay amplitude to fCP

Piece from mixing (Piece from mixing ())

2 2 2 2

2 ( 2 )*12 02 2

( ) 12

CPiF W B B B B ttd td t t

W

G M m B f mM V V S x e x

m

Piece from decayPiece from decay

0

2 ( )

0( ) CP D

CP iCP CP

CP

f H Bf e

f H B 2 ( )( ) M Di

CP CPf e Hadronic physics divides out!

Calculating Calculating for specific final statesfor specific final states2 ( )( ) M Di

CP CPf e * *

0* *

= Im( )=sin(2 )

( )

tb td ud ub

tb td ud ub

V V V VB

V V V V

b uud

* * *

0 0* * *

0 0

/ = -1 Im( )=sin(2 )

( ) ( )

tb td cs cb cd csS

tb td cs cb cd cs

S

V V V V V VB J K

V V V V V V

b ccs K K

* * *

0 0* * *

0 0

/ = +1 Im( )=-sin(2 )

( ) ( )

tb td cs cb cd csL

tb td cs cb cd cs

L

V V V V V VB J K

V V V V V V

b ccs K K

Why it is magicWhy it is magic

0 0, ,/ /

sin 2 sinS L S LJ K J K

A t m t

CP conserving phase!

CP violating phase

asdfasdfGraphical Graphical AnalysisAnalysis

Analogy: “Double-Slit” Experiments Analogy: “Double-Slit” Experiments with Matter and Antimatterwith Matter and Antimatter

source1A

2A

1A

2A

In the double-slit experiment, there are two paths to the same point on the screen.In the B experiment, we must choose final states that both a B0 and a B0 can decay into.We perform the B experiment twice (starting from B0 and from B0). We then compare the results.

CP violation due to interference between mixing and CP violation due to interference between mixing and decay: non-exponential decay lawdecay: non-exponential decay law

Ingredients of the CP Asymmetry Ingredients of the CP Asymmetry MeasurementMeasurement

Determine initial state:“tag” using other B. Measure t dependence

Reconstruct the final state system.

0 0

0 0

( ) ( )( )

( ) ( )CP

B t f B t fA t

B t f B t f

The Lorentz BoostThe Lorentz Boost

The asymmetric beam energies of PEP-II allow us to measure quantities that depend on decay time.

(4s) = 0.56

Tag B

z ~ 170 m CP Bz ~ 70 m

J/

K0z

t z/c cB 250 m

e-

9.0 GeV

e+

3.1 GeV

1 ps 170 μm

TaggingTagging

Leptons : Cleanest tag. Correct 91%, Efficiency 11%

b c

e-

W-

b c

e+

W+

Kaons : Second cleanest. Correct 82%, Efficiency 35%

b

W-c s

u

d

K-

W+

b

W+c s

u

d

K+

W-

We must classify each neutral B according to whether it “started”as a B0 or a B0. The start time is defined as the decay time of the accompanying B meson (“tag B”). We use flavor-specific final states of the tag B.

The Correlated StateThe Correlated State

At the At the YY(4S), the two neutral (4S), the two neutral BB mesons evolve as a mesons evolve as a correlated quantum state until one of them decays.correlated quantum state until one of them decays.

As a consequence, the asymmetry of time-integrated As a consequence, the asymmetry of time-integrated rates is identically zero!rates is identically zero!

At the At the YY(4S), we (4S), we mustmust measure the CP asymmetry as measure the CP asymmetry as a function of time. The experiment would not work a function of time. The experiment would not work with the silicon vertex detector.with the silicon vertex detector.

0 0 0 01 2 1 2 1 21

1( , ) ( ); ( ); ( ); ( );

2Ct t B t p B t p B t p B t p

Acp(t)F(t) F(t)

t(ps) t(ps)

sin2

D sin2

Everything perfect

Add tag mistakes Dilution: D=1-2w

Add imperfect t resolution

Must understand tagging/mistagging and t resolution !!

Experimental aspects of the sin2 measurement:

Blind Analysis

• The whole analysis is performed blind.• All studies are performed in such a way as to hide information on the value of the final answer.• Avoids any subconscious experimenter bias

e.g. agreement with the Standard Model!

When we are ready, wehave an unblinding party…..

sin2

(cc) Ks CP = -10.76 0.10 0.04

J/ KL CP = +10.73 0.19 0.07

All modes0.75 0.09 0.04

sin2

(cc) Ks CP = -10.76 0.10 0.04

J/ KL CP = +10.73 0.19 0.07

All modes0.75 0.09 0.04

(stat) (syst)

Fit results

56 fb-1: 62 M BB pairs.

CP asymmetry in CP -1 and +1 modesCP asymmetry in CP -1 and +1 modes

J/ KL CP = +1

J/ Ks

CP = -1

Note: likelihood curves are normalized to the total number of tagged events, not B0 and anti-B0 separately.

Crosscheck: fit Crosscheck: fit BBflavflav events as a CP sample events as a CP sample

ACP = -0.004 0.027

Expect no CP asymmetry

sin2sin2fit resultsfit results

sin2

(cc) Ks CP = -10.76 0.10 0.04

J/ KL CP = +10.73 0.19 0.07

All modes0.75 0.09 0.04

sin2

(cc) Ks CP = -10.76 0.10 0.04

J/ KL CP = +10.73 0.19 0.07

All modes0.75 0.09 0.04

Systematic errorsCP = -1 background 0.019

t resolution and detector effects 0.015

md and B (PDG 2000) 0.014

Monte Carlo statistics 0.014

J/ KL background 0.013

Signal mistag fractions 0.007

Total systematic error 0.04

Systematic errorsCP = -1 background 0.019

t resolution and detector effects 0.015

md and B (PDG 2000) 0.014

Monte Carlo statistics 0.014

J/ KL background 0.013

Signal mistag fractions 0.007

Total systematic error 0.04

(stat) (syst)

Fit without ||=1 constraint (CP=-1 only)

|| = 0.92 0.06 (stat) 0.03 (syst)

Im/|| = 0.76 0.10

Fit without ||=1 constraint (CP=-1 only)

|| = 0.92 0.06 (stat) 0.03 (syst)

Im/|| = 0.76 0.10

-1: sin2 =0.82 0.12 0.05 42 fbBelle

Cross checksCross checkssin2 by decay mode sin2 in sub-samples

Individual modes and sub-samples are all consistent.

CKM interpretationCKM interpretation

Our sin2 measurement is consistent with current Standard Model constraints from measurements of other parameters.

= (1-2/2) = (1-2/2)

Method as in Höcker et al, Eur.Phys.J.C21:225-259,2001(also other recent global CKM matrix analyses)

Michael Peskin’s viewpointMichael Peskin’s viewpoint

Conclusions so far...Conclusions so far...

We have observed CP violation in the neutral-We have observed CP violation in the neutral-BB meson system.meson system.

The asymmetry is large, unlike the O(10The asymmetry is large, unlike the O(10-3-3) effects ) effects observed in the neutral-observed in the neutral-KK system. system.

The asymmetry displays consistent behavior across The asymmetry displays consistent behavior across all observed channels, including CP odd and CP even all observed channels, including CP odd and CP even final states.final states.

The time dependence of the asymmetry agrees with The time dependence of the asymmetry agrees with the expectation based on interfering amplitudes the expectation based on interfering amplitudes involving mixing and direct decay.involving mixing and direct decay.

Conclusions so far...Conclusions so far...

With the present data sample, the region allowed by With the present data sample, the region allowed by the measurement is consistent with the Standard the measurement is consistent with the Standard Model CKM framework constrained by Model CKM framework constrained by

CP-violation measurements in K decay

non-CP-violating observables in B decay

Hadronic Rare Hadronic Rare BB Decays: Towards sin(2 Decays: Towards sin(2)) B->B-> would measure sin(2 would measure sin(2)…)…

……except there is a except there is a secondsecond direct decay amplitude! direct decay amplitude!

Hadronic Rare B Decays: B->Hadronic Rare B Decays: B->, B->K, B->K++

B->B->

B->KB->K++

mES

mES E

E

6(5.4 0.7 0.4) 10

6(17.8 1.1 0.8) 10

Mixing and CP Asymmetry Measurement Mixing and CP Asymmetry Measurement in B->in B->

Mixing

Belle Mixing and Asymmetry Belle Mixing and Asymmetry Measurement in B->Measurement in B->

0.38 0.16 0.250.27 0.13 0.31: 1.21 0.94 0.09

: 0.01 0.37 0.07 0.02 0.29 0.07

Belle S C

BaBar S C

26 / 0.28P T

B B KK(*)(*)ll++ll-- in the SM and Beyondin the SM and Beyond

Flavor changing neutral current (Flavor changing neutral current (bb to to s)s): proceeds via “penguin’’ or box : proceeds via “penguin’’ or box diagrams in the SM.diagrams in the SM.

New physics at the EW scale (SUSY, technicolor, 4th generation quarks, New physics at the EW scale (SUSY, technicolor, 4th generation quarks, etc.) can compete with small SM rate.etc.) can compete with small SM rate.

Complementary toComplementary to studying studying bb to to ss due to presence of W and Z diagrams. due to presence of W and Z diagrams.

Branching Fraction Predictions in the Branching Fraction Predictions in the Standard ModelStandard Model

New Ali et al. predictions lower by 30-40%

long-distance contribution from resonances excluded

Decay rate vs. Decay rate vs. qq22 in the SM and SUSY in the SM and SUSY

J/

(2S)K

q2 q2

SM nonres SM nonres

SUSY models

B K *B K

Pole from K*even in +-

constructive interf.destructive

Generator-levelGenerator-level q q22 Distributions from Form- Distributions from Form-Factor ModelsFactor Models

B Ke e

*B K e e

B K

*B K

Ali et al. 2000(solid line)

Colangelo 1999(dashed line)

Melikhov 1997(dotted line)

Shapes are very similar!

J/ Sample: signal-like

*0K e e *0K

log LBoff resonance

J/J/ and Large Sideband Control Sample Study: and Large Sideband Control Sample Study: BB Likelihood VariableLikelihood Variable

*0K e e *0K keep

Large SB Sample: background-like

log LB-10 4

KKll++ll-- Fit Regions, Fit Regions, Unblinded Run 1+2 data (56.4 fb-1) Unblinded Run 1+2 data (56.4 fb-1)

E

mES

Fit Results (preliminary)Fit Results (preliminary)

B(BK*ee)/B(BK*)=1.21 from Ali, et al, is used in combined K*ll fit.

Belle results Belle results (29.1 fb(29.1 fb-1-1))

2.7 0.62.1 0.84.1 evts

3.7 1.03.0 1.16.3 evts

3.8 0.83.1 1.09.5 evts

2.9 0.92.1 1.02.1 evts

4.5 0.93.8 1.113.6 evts

Bkgd shape fixed from MC

ResultsResults

We obtain the following preliminary results:We obtain the following preliminary results:

The statistical significance for B The statistical significance for B K K ll++ll-- is computed is computed to be > 4to be > 4 including systematic uncertainties. including systematic uncertainties.

610.030.018.024.0 10)84.0()(

KBB

* 0.84 60.72

6

( ) (1.89 0.31) 10

3.5 10 90% C.L.

B B K

0.25 60.21: ( ) (0.75 0.09) 10Belle B B K

BaBar and Belle results are both higher than typical theoretical predictions, but the uncertainties are still very large.

Measuring Magnitudes of CKM Measuring Magnitudes of CKM Elements with Semileptonic Elements with Semileptonic BB Decays Decays

2( )Qq q q theory q Q MB M X l V

Expt. Expt.Need inputfrom theory!

Kinematic Configurations in Semileptonic Kinematic Configurations in Semileptonic DecayDecay

b->clb->cl processes are processes are dominant and are much dominant and are much easier to understand than easier to understand than b->ulb->ul decays. decays.

reliable theoretical predictions for b->cl at zero recoil (Heavy Quark Symmetry/HQET).

zero recoil: b->c without disturbing the light degrees of freedom

expansion in QCD/mQ

zero recoil

Semileptonic decays: Dalitz plotSemileptonic decays: Dalitz plot

Effect of V-A coupling on lepton angular distribution Effect of V-A coupling on lepton angular distribution and energy spectrum.and energy spectrum. *B D l

zerorecoil

Contributions of different helicities to the rateContributions of different helicities to the rate

*B D l

Zero recoil Max recoil

New CLEO measurement of |New CLEO measurement of |VVcb cb ||

0 *B D l *0B D l

CLEO Measurement of |CLEO Measurement of |VVcb cb || : w: w distribution and distribution and extrapolation to zero recoilextrapolation to zero recoil

Systematic Errors on CLEO |Systematic Errors on CLEO |VVcb cb | Measurement| Measurement

Recent |Recent |VVcb cb | measurements| measurements

Uncorrected for common inputsUncorrected for common inputs

Corrected for common inputsCorrected for common inputs

(Compilation by Artuso and Barberio, hep-ph/0205163, May 2002.)

Recent |Recent |VVcb cb | measurements| measurements

Form Factor at Zero Recoil and Form Factor at Zero Recoil and |V|Vcbcb||

The experimental extrapolation to zero recoil velocity of the The experimental extrapolation to zero recoil velocity of the daughter hadron provides the quantitydaughter hadron provides the quantity

Zero recoil form factor (“consensus value”)Zero recoil form factor (“consensus value”)

World average World average |V|Vcbcb||

( 1) 0.0383 0.005 0.009 (world average)cbF w V

21/(1) (1 ...) Luke's theorem: no 1/ corrections

1.007

0.960 0.007

(1) 0.91 0.04

QED A m

QED

A

F m

F

0.0421 0.0010 (expt.) 0.0019 (theory)cbV

Bumps in the road:Bumps in the road: Crystal Ball Crystal Ball observation of the observation of the (8.3) (1984)(8.3) (1984)

(1 ) (8.3)S

Photon energyspectrum.

First observation of exclusive B decayFirst observation of exclusive B decay CLEO I data (1983)CLEO I data (1983)

Some free adviceSome free advice

Almost every measurement is Almost every measurement is very hardvery hard, even if it is of a , even if it is of a quantity that no one cares about. So, try to find an important quantity that no one cares about. So, try to find an important measurement that will have real scientific impact.measurement that will have real scientific impact.

Never determine your event-selection criteria using the same Never determine your event-selection criteria using the same event sample that you will use to measure your signal. event sample that you will use to measure your signal.

Don’t use more cuts than you need. A simple analysis is easier Don’t use more cuts than you need. A simple analysis is easier to understand, check, duplicate, and present.to understand, check, duplicate, and present.

Look at all the distributions you can think of for your signal Look at all the distributions you can think of for your signal and compare them with what you expect.and compare them with what you expect.

Look at the distributions of events that you Look at the distributions of events that you excludeexclude. Do you . Do you understand the properties of your background?understand the properties of your background?

More free adviceMore free advice

When possible, use data rather than Monte Carlo events to When possible, use data rather than Monte Carlo events to measure efficiencies and background levels.measure efficiencies and background levels.

Do not use Monte Carlo samples blindly. Find out where the Do not use Monte Carlo samples blindly. Find out where the information came from that went into the MC. The MC may information came from that went into the MC. The MC may do well in someone else’s analysis, but in may never have been do well in someone else’s analysis, but in may never have been checked for the modes or region of phase space relevant to checked for the modes or region of phase space relevant to your analysis.your analysis.

Be careful not to underestimate the systematic errors Be careful not to underestimate the systematic errors associated with ignorance of associated with ignorance of

signal efficiency

background shapes, composition, and normalization

Yet more adviceYet more advice

Don’t be afraid to…Don’t be afraid to…

ask any question

pursue a crazy idea

jump into something you don’t already understand

question what people say is established fact

look into the details and assumptions

ConclusionsConclusions We have two remarkable new facilities forWe have two remarkable new facilities for B B physics: physics:

KEK-B/Belle

PEP-II/BaBar

The performance of these accelerators is a major The performance of these accelerators is a major achievement for the laboratories.achievement for the laboratories.

The clear observation of CP asymmetries in the The clear observation of CP asymmetries in the B B meson system is a milestone for particle physics.meson system is a milestone for particle physics.

The measurement of sin(2The measurement of sin(2) is very well accomodated ) is very well accomodated by the SM. It suggests that the dominant source of by the SM. It suggests that the dominant source of CP violation in CP violation in BB decays is due to the CKM phase. In decays is due to the CKM phase. In spite of this, we have a long way to go before we have spite of this, we have a long way to go before we have fully tested the SM/CKM framework.fully tested the SM/CKM framework.

Conclusions (continued)Conclusions (continued)

Hadron-collider experiments will soon start to play a Hadron-collider experiments will soon start to play a major role: the observation and precise measurement major role: the observation and precise measurement ofof B Bs s mixing is one of the next major goals. mixing is one of the next major goals.

We are just beginning to scratch the surface of rare We are just beginning to scratch the surface of rare BB decays. They have interesting sensitivity to new decays. They have interesting sensitivity to new physics.physics.

The next few years will be very exciting. The next few years will be very exciting.

Backup slidesBackup slides

PEP-IIPEP-II

Very high current, multibunch operation

2 rings helps avoid beam instabilities and parasitic beam crossings (crossings not at the IP)

I(e+)=1.3 A (LER), I(e-)=0.7 A (HER)

Bunch spacing: 6.3-10.5 ns

Beam spot:

x=120 m y=5.6 m z=9 mm

Number bunches/beam: 553-829 (to 1658)

High-quality vacuum to keep beam-related backgrounds tolerable for experiments

PEP-II/BaBar ConstructionPEP-II/BaBar Construction

19931993: Start of PEP-II construction: Start of PEP-II construction

19941994: Start of BaBar construction: Start of BaBar construction

Summer 1998Summer 1998: 1st e+e- collisions in PEP-II: 1st e+e- collisions in PEP-II

Spring 1999Spring 1999: BaBar moves on beamline: BaBar moves on beamline

May 26, 1999May 26, 1999: 1st events recorded by BaBar: 1st events recorded by BaBar

Oct 29, 2000Oct 29, 2000: PEP-II achieves design luminosity: PEP-II achieves design luminosity

Intense competition with KEK-B/Belle in JapanIntense competition with KEK-B/Belle in Japan

PEP-II/BaBar PEP-II/BaBar The Standard Model predicts O(1) CP asymmetries in B

decays! However, these asymmetries occur in processes that are relatively rare, so a large data sample is required.

To perform these measurements, a two-ring e+e- storage ring with unequal beam energies was built by SLAC/LBNL/LLNL with unprecedented luminosity. We now have >60 M(4S) events.

The BaBar CollaborationThe BaBar Collaboration(9 countries)(9 countries)

BaBar DIRC quartz barBaBar DIRC quartz bar

3.5 cm

Overall length (4 bars): 4.9 m

No. light bounces (typical)=300

Surface roughness (r.m.s.)= 0.5 nm

(typical) = 400 nm

BaBar DIRC PrincipleBaBar DIRC Principle

1cos C n

1.473n

0Num. r.l.=0.19 X

Number of Cherenkov photons=20-60

(C) = 3 mrad

Acp(t)F(t) F(t)

t(ps) t(ps)

sin2

D sin2

True t, Perfect tagging:

True t, Imperfect tagging:

Measured t, Imperfect tagging:

Must measure flavor tag Dilution.

D = (1-2) where w is mistag fraction.

Must measure t resolution properties.

Experimental aspects of CP measurementExperimental aspects of CP measurement

Amix(t)Fmix(t) Fnomix(t)

t(ps) t(ps)

D

True t, Perfect tagging:

True t, Imperfect tagging:

Measured t, Imperfect tagging:

BB00 mixing measurement: D and R( mixing measurement: D and R(t,t,t’)t’)

Amplitude of mixing asymmetry is the dilution factor D.

Mixing sample has 10x statistics of CP sample. Shape of t determines resolution function R(t,t’)

B->K*B->K*