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:
o
– Bd = (bd)
– Bs = (bs)
;
;
o
Bd = (bd)
Bs = (bs)
• Difference in B1 and B2 lifetimes is small
d
s
3
yd 
 5 10 , ys 
 0.1
d
d
• Difference in B1 and B2 masses is large
M d  (3.3  0.05) 1013 GeV  (0.502  0.007) ps 1
M s  9.45 1012 GeV  14.4 ps 1
• Oscillation parameter
M d
xd 
 0.72  0.03; xs  20.6
d
Mixing
(and similarly for Bos)
0
B
b
_
d
b
_
d
d

u, c, t
W
W+
W
u, c, t
_ __
u, c, t
u, c, t
W+
_
b
d
_
b
• Dominated by top quark contribution
q

p
*
12
M
M 12
For Bo
For
Bso
q Vtb*Vtd

p VtbVtd*
q Vtb*Vts

p VtbVts*
Vtd
Vts
0

B
0
q
Bd Mixing
EPS,2005
Time-dependent probability for a B at t=0
0
to be observed as Bq0 or B q at time t

(
)0

B q (t ) 
1 t / 
e
1
2
cos( mq t ) 
BELLE 152 106 BB . Full B reconstruction
Asymmetry  cos(mdt)
P
|t| (ps)
md : a high precision measurement (~1%) dominated
by B factories results
md = 0.5090.005 ps-1
ms
EPS 2005
68%CL
95%CL
ms= 22.2 3.1 ps-1
ms > 14.4 ps-1
at 95%CL
• LEP, SLD, Tevatron
Expectation from fits to the
Unitarity Triangle
Amplitude
method search:
( )0
1 t  ( )
0
P (Bs  B s )  e 1 A cos ms t 
2
•
Bs Mixing - xs
K +K 
CDF Ms/s  xs <60
– SM 22< xs < 31

• Si detector & disp. track trigger
– combine with Bd mixing - xd
0
 +
xs/xd a |Vts/Vtd| (s  theoretical unc.)
s
s
– constrain side of CKM triangle
Flavour at Decay
wtag
Flavour at Production
background
- other B
st
proper time

•
B D 
LHCb
Ms = 10 ps-1
st = 43 fs
s 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’
(
o)
BdJ/Ks (CP=-1)
b
c
c
J/
d
s
d
o
o
K  K s mixing
o
• Look at decay (l+l-)(+-), Br(BdJ/Ks) ~ 5x10-4
 q   q   A J /K s
r     
 p  Bd0  p  K 0  AJ /K s
 Vtb*Vtd  VcsVcd*
 *
 
* 
 VtbVtd  VcsVcd




 VcbVcs* 
 * 
 VcbVcs 
Minus for CP
odd state
1
1
 1  ( Vtd e i )(1  2 )(  ) A2 (1  2 )
2
2

1
1
1  ( Vtd e +i )(1  2 )(  ) A2 (1  2 )
2
2
  e  2 i
(
)
BdJ/Ks (CP=-1)
• Asymmetry
a (t ) 
a(t )   Ιm{r} sin( mt )
 sin 2  sin( mt )
( Bd0  J / K s )  ( Bd0  J / K s )
( Bd0  J / K s ) + ( Bd0  J / K s )
 sin 2  sin( mt )
B
charmonium
_
( )
P (B (t ))  e
0
C
1 
2
1+ 
2
t /  B
A
S
2
1+ 
2
2
B0  f
1 ( +)C cos  md t 

(+)
 S sin
 md t 
2m( )
1+ 
B0 tag
_
B0 tag
2
golden mode
• Dominant penguin contribution :
same weak phase ( no direct
CP violation)
• The only diagram with a different
weak phase is suppressed by
O(2) (+OZI)
New BELLE result for J/K0 (386 106 BB)
S  sin(2 )  0.652  0.039  0.020
C  0.010  0.026  0.036
EPS 2005
B0  B0  f
C=0
S=sin(2)
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(2a) from
•
•
BR 5x10-6
No sub-mass constraint
– Other 2 body backgrounds
• Hard to interpret in terms of
a
– P in BgK, or isospin Bg00
+

Bdg 
0
Tree only:
a (t )  sin 2(  +  ) sin( mt )
Due to Penguin:
a, d, |P/T|
Another possibility, clean
theory, complex analysis
a from Bdgrg+0
Benchmark

- +
0
0
+
*
BsgDsK
BdgD 
• 2 + 
• Tree only
– Mixing and decay
• BR 10-3
– But bgu doubly
cabibbo suppressed
(~ 2% bgc)
• Bs counterparts
 -2d
• Similar strength
diagrams
– Larger asymmetry
– BS BR 10-4
• Better Bet (if RICH)
– Ds background
Brief Angles Prospects Summary
• 
– BodgJ/Ks Measured accurately by BaBar/Belle
• a
o
– Bdg+, with |P/T| knowledge.
– Bodgrg+0, time dep. Dalitz plot
• 
o
– As BodgD*-+ or BsgD-sK+
o
o
– Bdg+ - What is it good for ? Comparing with BsgK+K
• d
– BodgJ/, obtain CP eigenstates from angular
correlations
– Probe higher order unitarity r
The Experiments
• B Factories (2000):
– BaBar, Belle
– (also CLEO)
• TeVatron (2001 ):
– CDF, D0, (proposed BTev)
• LHC (start 2007)
– LHCb (also ATLAS,CMS)
Flavour Tagging
Signal B
use particles accompanying signal B
B
b
s
s
u
u
Other B
B
e – tagging efficiency
w – wrong tagging fraction
Identify other b hadron
D=1-2w, Dilution
dA 
1
D 2eN
- deduce initial flavour
•
•
•
Semileptonic decay
kaon tag
jet charge
bgl
bgcgs
0
s
B
K+
Systematic Errors
• Production Asymmetries
– Initial fraction
 e,e
b,b
• e.g. detector response
+ asymmetry
in magnetic field
• Control Channels
– e.g.
B   J /K 
– measure e,e w,w
– Precision 10-3
• w,w
• Final State acceptance
– Untaggeda
f+ / f-
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’)
Why study CP at a hadron collider ?
e+ e-
pp(bar)
(BaBar)
(D0)
• Clean environment
– no additional tracks
• Initial state
– B0B0 or B+B-
• B mesons ~ 20% stot
– simpler triggering
• Rate
– statistics limited channel
• Bs
Ms
• Bs
– Extracting 
• Bs
– J/Y
Hadronic b production
LHC 1012 bb per year
(B factories ~ 108)
 h   ln (tan (q/2
 2 < h<5 LHCb/BTeV
•
for larger |h |
B boost  increases rapidly
• B quark pair
produced
preferentially at
small q
• highly correlated
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 Discs
Detectors separated 6cm during injection
Bdg+
No identification
With pion identification
Purity = 9.5%
Purity = 85%, Eff. =90%
Section 6:
Concluding
:
Remarks on CP Violation
CKM triangle status, ICHEP 2004
Compatibility obtained between all constraints
2002: first non-trivial compatibility test for CKM triangle
Next step to measure alpha and beta angles
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 
 e 
 1 
 
 
    VCKM  2 
 
 

 
 3
• 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
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)