Section 5: B mesons (what are all those B factory talks really about ?)

:Section 5:

B mesons

(what are all those B factory talks really about ?)

Bo Bo systems• Decays of Bo Bo are the same,

so lifetimes of B1 and B2 are similar• Two types of neutral B mesons:

– Bd = (bd) ; Bd = (bd)– Bs = (bs) ; Bs = (bs)

• Difference in B1 and B2 lifetimes is small

• Difference in B1 and B2 masses is large

• Oscillation parameter

o o

1.0,105 3

d

ss

d

dd yy

112

113

4.141045.9

)007.0502.0(10)05.03.3(

psGeVM

psGeVM

s

d

6.20;03.072.0

s

d

dd x

Mx

Mixing

• Dominated by top quark contribution

b

du, c, t W

W_

d

b_u, c, t

b

du, c, t

W W_

d

b_

u, c, t___

B0B0

12

*12

M

M

p

q *

*

tdtb

tdtb

VV

VV

p

qFor Bo

For Bos *

*

tstb

tstb

VV

VV

p

q

(and similarly for Bs)o

ts

td

V

V

EPS,2005A

sym

me

try

co

s(

mdt)

|t| (ps)

BELLE 152 106 BB . Full B reconstruction

( )0 /1( ) 1 cos( )

2t

q qP B t e m t

Time-dependent probability for a at t=0

to be observed as or at time t 0qB

0qB

0qB

Bd Mixing

md : a high precision measurement (~1%) dominated by B factories results

md = 0.5090.005 ps-1

ms EPS 2005

ms > 14.4 ps-1 at 95%CL

68%CL

95%CL

ms= 22.2 3.1 ps-1

• LEP, SLD, Tevatron

00 1A( ) 1 cos

2t

ss sP B B e m t( )

( )

Amplitude method search:

Expectation from fits to the Unitarity Triangle

Bs Mixing - xs• CDF Ms/sxs <60

– SM 22< xs < 31• Si detector & disp. track trigger

– combine with Bd mixing - xd

• xs/xd |Vts/Vtd| (theoretical unc.)– constrain side of CKM triangle

ss DB0

Flavour at DecayFlavour at Production

- other Bproper time

tag background

t

KK

LHCb

Ms = 10 ps-1

t = 43 fs

Ms=8fs-1

CP Violation in B Decays

• TYPES:– 1) neutral to CP eigenstates– 2) neutral to non-CP eigenstates– 3) charged B-decays

• CP Possibilities:– Mixing– Decay– Interference between mixing and decay

• Channels:– Far too many to discuss!– A few well known ‘benchmark channels’

BdJ/Ks (CP=-1)

• Look at decay (l+l-)(+-), Br(BdJ/Ks) ~ 5x10-4

o( )

cb

d d

c

s

J/

Ko

Kos

mixing

o

cscb

cscb

cdcs

cdcs

tdtb

tdtb

KJ

KJ

KB

VV

VV

VV

VV

VV

VV

A

A

p

q

p

qr

s

s

d

*

*

*

*

*

*

/

/

00

i

itd

itd

e

AeV

AeV

2

222

222

)21

1())(21

1)((1

)21

1())(21

1)((1

Minus for CP odd state

BdJ/Ks (CP=-1)• Asymmetry

( )

)sin(2sin

)sin(}{)(

mt

mtrΙmta

)sin(2sin

)/()/(

)/()/()(

00

00

mt

KJBKJB

KJBKJBta

sdsd

sdsd

B charmonium

B0 f B0 B0 f

• Dominant penguin contribution : same weak phase ( no direct CP violation)

• The only diagram with a different weak phase is suppressed by O(2) (+OZI)

golden mode

New BELLE result for J/K0 (386 106 BB)

sin(2 ) 0.652 0.039 0.020

0.010 0.026 0.036

S

C

( )mS 2

2

1

C2

2

1

1

22/0 ( ) ( )

1

( ( )) 1 cos sin2

Btd dCP B t e A m t m tS

(_

)

B0 tag_B0 tag

C=0

S=sin(2)

EPS 2005

Discovery of Direct CP in B system

•Look at B-> K+ -Cf. anti-B->K- +

•Tree and Penguin Diagrams Contribute

•Sign of Kaon Tags B rather than anti-B meson

Sin(2) from Bd

• Hard to interpret in terms of – P in or isospin

00

• BR 5x10-6

• No sub-mass constraint– Other 2 body backgrounds

)sin()(2sin)( mtta Tree only:

Due to Penguin:|P/T|

Another possibility, clean theory, complex analysis from Bd

Benchmark

• 2+ • Tree only

– Mixing and decay

• BR 10-3

– But bu doubly cabibbo suppressed (~ 2% bc)

• Bs counterparts

-2• Similar strength

diagrams– Larger asymmetry– BS BR 10-4

• Better Bet (if RICH)– Ds background

BsDsK+BdD*-00 00 --

Brief Angles Prospects Summary

– BdJ/Ks Measured accurately by BaBar/Belle

– Bd, with |P/T| knowledge.

– Bdtime dep. Dalitz plot

– As BdD*-or BsDsK+

– Bd- What is it good for ? Comparing with Bs

– BdJ/, obtain CP eigenstates from angular

correlations – Probe higher order unitarity

o

oo

o

o

o

o

o

-

The Experiments• B Factories (2000):

– BaBar, Belle– (also CLEO)

• TeVatron (2001 ):– CDF, D0, (proposed BTev)

• LHC (start 2007)– LHCb (also ATLAS,CMS)

Flavour Tagging

• Semileptonic decay bl• kaon tag bcs• jet charge

B

BSignal B

Other B

K

0sB

bssuu

use particles accompanying signal B

Identify other b hadron

- deduce initial flavour

– tagging efficiency

w – wrong tagging fraction

D=1-2w, Dilution

NDA

2

1

Systematic Errors• Production Asymmetries

– Initial fraction b , b

• e.g. detector response

asymmetryin magnetic

field

• w , w

• Final State acceptance

• Control Channels– e.g.

– measure w,w– Precision 10-3

– Untaggedf+ / f-

+

-

KJB /

B Factories: BaBar/PEPII, Belle/KEKB

•Asymmetric beams boosted B

•Time difference between B decays z

•At decay time on b one bbar (c.f. EPR ‘Paradox’)

• Clean environment– no additional tracks

• Initial state– B0B0 or B+B-

• B mesons ~ 20% tot– simpler triggering

Why study CP at a hadron collider ?

• Bs

– J/

e+ e-

(BaBar)

pp(bar)

(D0)

• Rate– statistics limited channel

• Bs

Ms

• Bs

– Extracting

Hadronic b production ln (tan ( LHCb/BTeV

• for larger |boost

increases rapidly

• B quark pair produced preferentially at small

• highly correlated

LHC 1012 bb per year

(B factories ~ 108)

LHCb Detector•Forward single arm spectrometer

•Two RICH detectors for particle ID

•Multi-level Trigger system, using displaced vertices

•Precision Silicon Vertex Detector

•40MHz beam crossing rate

Series of DiscsDetectors separated 6cm during injection

Bd

No identification

Purity = 9.5%

With pion identification

Purity = 85%, Eff. =90%

:Section 6:

Concluding

Remarks on CP Violation

Compatibility obtained between all constraints

2002: first non-trivial compatibility test for CKM triangle

Next step to measure alpha and beta angles

CKM triangle status, ICHEP 2004

Final Comments

• CP violation: a fundamental symmetry broken– Good reasons to believe SM is not final

answer– Sensitive to new physics

• Next Decade– Promises to be v. exciting for CP studies– BaBar/Belle , TeVatron, LHC– Overconstrain CKM triangle

Not the whole picture….• Do mixing

– Not yet observed– Slow oscillations x< 0.01– Sensitive to new physics

• CP violation in the lepton sector– Massive neutrinos

• Neutrino mixing between flavour eigenstates to produce mass eigenstates

– Neutrino Oscillations between 3 famillies and CP phase.

– Neutrino Factory would produce enough neutrinos for CP violation test.

– See Paul’s neutrino course

3

2

1

CKM

e

V

Further Reading• SLAC-R-504 The BaBar Physics Book,

– Chapter 1, A CP Violation Primer

• CP Violation, Bigi & Sanda, Cambridge University Press, 2000

• FERMILAB-Pub-01/197 B Physics at the Tevatron: Run II and Beyond

• CERN 2000-04 Proceedings of the workshop on Standard Model Physics (and more) at the LHC– B Decays Chapter

• Hep-ph/9911321, Y. Nir, Lectures at the SLAC Summer Institute (1999)