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