CP Violation: la B epoqueelle

Stephen L.OlsenU. of Hawaii

CP studies using Beauty mesons

U-Mass Colloquium Mar 12, 2003

CP Violation:

Asymmetries Matter anti-

matter

Big Bang

matter-antimattersymmetric

all matterno

antimatter

Standard Model Symmetries

Symmetry Strong & EM Weak

C & P

CP

Gauge

Flavor

Strong& EM Weak

yesyes

yesyes

violated (maximally)

violated (small??)

violated (pretty badly)violated (~20% level)

WI: the SM’s industrial sector

Flavor violations

matter-antimatterdifferences

CPviolation

gauge symmviolations Masses

Flavor mixing

flavorviolations

Today’s talk

CP violation Flavor-mixing

B(eauty) mesons

B-meson primer(why are they interesting?)

CP-violation measurements

What’s next?

Phys 100

harder

level

Antimatter & CP

(a la Physics 100)

p = mV

xpx = mVx

E = mc22 2( )

E = ± mc2

if px is negative motion is backwards in x

if E is negative motion is backwards in

time !!!

backward time motion

t

B

when viewed forward in time:

L R

: C

: P

CP: matter

qq

J

g

J†q

qg*CP( ) =

mirror

if g g* (i.e. charge is complex):

CP operator:

(matter & antimatter behave differently)

CP symmetry is violated

“charge”

antimatter

seen as a tiny (~0.002) effect in certain K0 decays

(not in or nuclear -decays)

need a complex coupling need a complex coupling specific to strangeness-specific to strangeness-

changing processeschanging processes

CP violation discovered in 1963

Flavor-mixing

(Flavor-mixing in the 3-quark era)

Strangeness-changing weak decays circa 1963

eg: Ke p e

ud s

3 quarks:

d

u

s

q=2/3

q=1/3

4 leptons:

~

e

e

Weak interactions

Strength of the Weak interaction

Problem 1: Different weak interaction “charges” for n, and K decays:

np

K

0

GF

GdGs

Gd 0.98GF Gs 0.2GF

d

u

s

u

Cabibbo sol’n: flavors mix

d = d + s

Weak Int flavor state

Flavor mass eigenstates

Unitarity: |2 + |2 = 1

du

W

GF

Ws

uGF

=cos c; = sin c

+d’

uGF =

Cabibboangle

W

Missing neutral currents

Problem 2: no flavor-changing “neutral currents” seen.

flavor-preserving neutral currents (e.g. NX) are

allowed

flavor-changing neutral currents (e.g. K l+l) are strongly supressed

OK GN

d,u d,uK

d

s

GIM sol’n: Introduce 4th quark

2 quark doublets:

s

c

d

u

'' s

c

d

ucharmed quark

Weak eigenstates

Mass eigenstates

Unitarity: & = 1

s

d

s

d

'

'

4-quarkflavor-mixing

matrix

GIM cancellation of FCNC Charged currents

d(s)

u(c)

W

GF

Ws(d)

u(c)

GF

Neutral currents

d,(etc)

d,(etc)

Z

GN

s(d)

d(s)

Z

GN

=1 0

Flavor preserving Flavor changing

OK

forced to 0by Unitarity

Incorporating CPV via flavor mixing

a complex flavor-mixing matrix?

-

Why not incorporate

CPV by making complex?

not so simple: a 2x2 matrix has 8 parameters

unitarity: 4 conditions

4 quark fields: 3 free phases

# of irreducible parameters: 1Cabibbo

angle

2-generation flavor-mixing

-

cosCsinC

-sinC cosC

Only 1 free parameter: the Cabibbo angle

C120

not enough degrees of freedom to incorporate a

complex number

Enter Kobayashi Maskawa

a 3x3 matrix has 18 parameters

unitarity: 9 conditions

6 quark fields: 5 free phases

# of irreducible parameters: 4

three are neededfor 3-dim rotation(e.g. Euler angles)

one complexphase is possible!

suppose there are 3 quark generations:

KM (+others) circa 1973 (Kyoto)

MakotoKobayashi

ToshihideMaskawa

Original KM paper

From: Prog. of Theor. Phys. Vol. 49 Feb. 2, 1973

CP-violating phase3 Euler angles

A little history

• 1963 CP violation seen in K0 system• 1973 KM 6-quark model proposed• 1974 charm (4th ) quark discovered• 1978 beauty/bottom (5th) quark discovered• 1984 KM model makes it into PDG book• 1995 truth/top (6th) quark discovered• 2001 CPV in B-meson decays discovered

CKM matrix (in 2002)

b

s

d

VVV

VVV

VVV

b

s

d

tbtstd

cbcscd

ubusud

'

'

'

CPV phases are in the corners

t

d

W+

b

Vub

W+

u*

Unitarity

***

***

***

tbcbub

tscsus

tdcdud

VVV

VVV

VVV†

001

010

100

tbtstd

cbcscd

ubusud

VVV

VVV

VVV

VudVub* VcdVcb+ + VtdVtb = 0

1

2

3

Vtd Vtb

Vcd Vcb

Vud Vub*

*

*

phase of Vtdphase

of Vub

**

Testing the KM CPV mechanism

QM: phase measurement requires interference

1st step: show that at least one i 0

Primer on B mesons

• What are B mesons?– B0 = d b B0 = b d– B = u b B = b u– JPC = 0

= 1.5 x 10-12 s (cm)

• How do they decay?– usually to charm: |bc|2 |bu|2 100

• How are they produced?– ee (4S) B B is the cleanest process

Lesson 1: Basic properties

Lesson 2: “flavor-tagged” B decays

In ~99% of B0 decays: B0 and B0 are distinguishable by their decay products

X l

X lB0 B0

semileptonic decays:

D X

D XB0 B0

hadronic decays:

Lesson 3: B CP eigenstate decays

In ~1% of B0 decays: final state is equally accessible from B0 and B0

J/KS

J/KL

…

B0 B0

charmonium decays:

K+K

…

B0 B0

charmless decays:

Lesson 4: The (4S) resonance

(ee BB) 1nb• B0B0B+B• good S/N• BB and nothing else• EB = Ecm/2• coherent P-wave• B’s at rest in CM

3S bb bound states

(e

e)

had

ron

s

BBthreshold

• CESR/CLEO

• PEPII/BaBar

• KEKB/Belle

• ~50% of CDF & D0

• BTeV

• LHCB

• …..

Lesson 5: Recurring question:

What makes the b-quark interesting?

Lesson 5: Consider 2nd order bd(s) FCNC

b u d

Vub Vud

b c d

Vcb Vcd

b t d

Vtb Vtd * * *

A=VubVud f(mu) + VcbVcd f(mc) + VtbVtd f(mt)* * *

GIM: VubVud + VcbVcd + VtbVtd = 0* * *

A = 0 if mu = mc = mt

a big if same for bs

bd:

Lesson 6: Large mt overides GIM

but, mt >> mc & mu: GIM cancellation is ineffective

B0 B0 mixing transition is strong

(and this accesses Vtd)

V*td

V*td

Lesson 7: loops are accessible

also, because mt >> mc & mu:

GIM-forbidden “penguins” are accessible

effects of massivevirtual particles

can show up here

A. The large t-quark mass:

mt=174 GeV

B-meson primer: final exam

Q. What makes B’s interesting?

Measuring KM phases

• Use B CP eigenstate decays (fCP)

– eg BJ/ KS & BJ/ KS

• Interfere BfCP with B BfCP

Br(BfCP) are small (<10-3)need millions of B mesons

Proposed in 1981, before large t-quark mass & BB mixing was

discovered

Sanda, Bigi & Carter Technique

B0

Interfere BfCP with BBfCP

td

td

B0

Vtb

V*

Vcb

KS

J/

J/

KS

V*2

Vtb

V*td

td

Vcb

B0B0

Sanda, Bigi & Carter:

+

sin21

What do we measure?

t z/cβγ

Flavor-tag decay(B0 or B0 ?)

J/

KS

B - B

B + B

e

e

more B tags

more B tags

zt=0

fCP

(tags)

sin21

This is for CP=-1; for CP=+1, the asymmetry is opposite

Asymmetric energies

What’s needed?

1. Lots of B mesons (Br (BfCP) ~ 103)– very high Luminosity KEKB

2. Find CP eigenstate decays– high quality ~ detector Belle

3. “Tag” the other B’s flavor– good particle id dE/dx, Aerogel, TOF

4. Measure decay-time difference– Asymmetric energies (@KEKB: c200m)

– good vertexing silicon strip vertex detector

• Extract results

Step 1: make B mesons KEKB

•Two separate rings

e+ (LER) : 3.5 GeV

e (HER) : 8.0 GeV

•ECM : 10.58 GeV at (4S)

•Luminosity

•target: 20 B’s /sec•achieved: ~15 B’s/sec

•±11 mrad crossing angle •Small beam sizes:

• y 3 m; x 100 m

asymmetric e+e collider

KEKB

15 B’s/sec

800K B’s/day

~140M B’s

worldrecords

A World-Wide Activity Involving ~50 Institutions

The Belle Collaboration

ellela

A magnetic spectrometer based on a huge superconducting solenoid

The Belle Collaboration

~250 Authors

Step 2: Select events

B0 J/ Ks event

J/

KS

B0 J/ KL in Belle

1) J/ l+l + KL

2) Assume BJ/ KL: compute PKL

3) Plot P* =|P J/ + PKL|

B

very important because this has opposite CP and,thus, opposite asymmetry

Step3: determine the flavor of the other B

Inclusive Leptons:high-p l b c l intermed-p l+ s l

Inclusive Hadrons:high-p + B0D(*) +, D(*) +, etc.

low-p D0

intermed-p KKX…

look at the remaining tracks in the event

step 4 measure vertices

Ks+

~7cm

y-z vertices

Step 5: extract results

Combine:

•CP value (f)

•Flavor-tag (q)

•Vertex info (t)

zmore B tags

t z/c βγ

more B tags

Now an established & well understood expt’l technique

sin21 = 0.719±0.074±0.035(B0 or B0 ?)

J/

KS

e

e

z

fCP

Belle & BaBar agree

sin21 (Belle)

=0.719±0.074±0.035

sin21 (BaBar)

=0.741±0.067±0.033

sin21 (World Av.)

=0.734±0.055

theory errors ~1%

Agrees with SM

CPV in K decays

What’s next?

1.) Measure other KM angles

1

2

3

Vtd Vtb

Vcd Vcb

Vud Vub*

*

*

phase of Vtdphase

of Vub

2 () from B+

B0

B0

V*

V*

td

td

Vtb

Vtb

V

V

+

+

B0

+ V*2 V2

td ub sin22

ub

ub

(aka sin2

Must deal with “Penguin Pollution”i.e. additional, non-tree amplitudes

with different strong & weak phases

B0

+

Vtb Vtd

*

Rq(t) 1+q [Acos(mt) + Ssin(mt)]q=+1 B0 tag

1 B0 tag

direct CPV mixing-induced CPV

fit results

Afterbackgroundsubtraction

5-5 0

Still see a large CP Violation!

5-5 0

Asymmetrywith background

subtracted

2 (d

eg.)

(deg.)

allowed regions

Constraints on 2

~1580

~780

2

1

2

3

What’s next (cont’d) ?

2. Are there non-SM CPV phases?

Measure sin21 using loop-dominated processes:

Example:

, ’, KK

no SM weak phases

SM: sin21 = sin21 from BJ/ KS

unless there are other, non-SM particles in the loop

eff

eff

similar to (g-2)

• well defined technique & target

– theory & expt’l errors are well controlled

– errors on SM expectationsare small (~5%)

• SM terms are highly suppressed

– SM loops contain t-quarks & W-bosons

– effects of heavy non-SM particles can be large

look for ppm effects look for pp1 effects

(i.e.~100%)

(g-2): sin21eff

:

SM loop particle: SM loop particles: t & W

lowest-order SM diagrams

look for effects of heavy new particles in a well understood SM

loop process

sin21eff results: (SM: sin2=+0.72± 0.05)

2.2σ off!!

(hep-ex/0212062)PRD(r)78fb-1

0.73 ± 0.66

B KS

S +0.52 ± 0.47 +0.76 ± 0.36

B’KSBK+KKS

OKOK

Summary

• CPV observed in B meson decays– 1 0 & in agreement with KM expectations

• tests for non-KM-type CPV are underway:– does 1+2+3 = 180o ?

• 2 & 3 measurement results soon

– are there non-SM new physics phases?• investigate t-quark loop-processes

• stay tuned