B mesons

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


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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
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Mixing
(and similarly for Bs)
o
b
d
W-
u, c, t
u, c, t
_
_
W
-
b
d
B0
B0
d
b
u, c, t
_
W-
W
_
_
_
_
u, c, t
d
b

• Dominated by top quark contribution

For Bo
For Bo
s
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EPS,2005
Bd Mixing
BELLE 152 106 BB . Full B reconstruction
Dmd a high precision measurement (1)
dominated by B factories results
Dmd 0.509?0.005 ps-1
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?ms
EPS 2005
Dms 22.2 ?3.1 ps-1
Dms gt 14.4 ps-1 at 95CL
Expectation from fits to the Unitarity Triangle
Amplitude method search

• LEP, SLD, Tevatron

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Bs Mixing - xs

• CDF DMs/Gs xs lt60
• SM 22lt xs lt 31
• Si detector disp. track trigger
• combine with Bd mixing - xd
• xs/xd a Vts/Vtd (s - theoretical unc.)
• constrain side of CKM triangle

Flavour at Decay Flavour at Production - other
B proper time
wtag backgroundst
LHCb
st 43 fs s DMs 8fs-1
DMs 10 ps-1
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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

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Bd?J/?Ks (CP-1)
( )
o
c
b
J/?
c
o
o
s
?
K
K
mixing
s
d
d
o

• Look at decay (ll-)(??-), Br(Bd?J/?Ks) 5x10-4

Minus for CP odd state
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Bd?J/?Ks (CP-1)
( )

• Asymmetry

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B0 ? f
B0 ? B0 ? f
B ? charmonium
B0 tag
C0 Ssin(2b)
New BELLE result for J/?K0 (386 106 BB)
EPS 2005
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Discovery of Direct CP in B system

• Look at B-gt K ?-
• Cf. anti-B-gtK- ?
• Tree and Penguin Diagrams
• Contribute
• Sign of Kaon Tags B
• rather than anti-B meson

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Sin(2a) from Bdgpp-
0

• BR 5x10-6
• No sub-mass constraint
• Other 2 body backgrounds

Tree only
Due to Penguin a, d, P/T

• Hard to interpret in terms of a
• P in BgKp, or isospin Bgp0p0

Another possibility, clean theory, complex
analysis a from Bdgrpgpp-p0
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Benchmark g
0
0
-
BsgDsK
BdgD-p

• 2b g
• Tree only
• Mixing and decay
• BR 10-3
• But bgu doubly cabibbo suppressed ( 2 bgc)

• Bs counterparts
• g-2dg
• Similar strength diagrams
• Larger asymmetry
• BS BR 10-4
• Better Bet (if RICH)
• Dsp background

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Brief Angles Prospects Summary

• ?
• BdgJ/?Ks Measured accurately by BaBar/Belle
• ?
• Bdgpp-, with P/T knowledge.
• Bdgrpgpp-p0, time dep. Dalitz plot
• ?
• As BdgD-p or BsgDsK
• Bdgpp- - What is it good for ? Comparing with
  BsgKK-
• ??
• BdgJ/??, obtain CP eigenstates from angular
  correlations
• Probe higher order unitarity r

o
o
o
o
o
-
o
o
o
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The Experiments

• B Factories (2000?)
• BaBar, Belle
• (also CLEO)
• TeVatron (2001 ?)
• CDF, D0, (proposed BTev)
• LHC (start 2007)
• LHCb (also ATLAS,CMS)

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Flavour Tagging
use particles accompanying signal B
b
s
s
u
u
e tagging efficiency w wrong tagging
fraction D1-2w, Dilution
Identify other b hadron - deduce initial flavour

• Semileptonic decay bgl
• kaon tag bgcgs
• jet charge

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Systematic Errors

• Production Asymmetries
• Initial fraction b , b
• e , e
• e.g. detector response
• asymmetry
• in magnetic field
• w , w
• Final State acceptance

• Control Channels
• e.g.
• measure e,e w,w
• Precision 10-3
• Untaggeda f / f-

-
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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)

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Why study CP at a hadron collider ?
e e- (BaBar)
pp(bar) (D0)

• Rate
• statistics limited channel

• Bs
• DMs

• Clean environment
• no additional tracks
• Initial state
• B0B0 or BB-
• B mesons 20 stot
• simpler triggering

• Bs
• Extracting g

• Bs
• J/Yf

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Hadronic b production
LHC 1012 bb per year

• h - ln (tan (q/2))
• 2 lt hlt5 LHCb/BTeV
• for larger h B boost bg increases rapidly

(B factories 108)

• B quark pair produced preferentially at small q
• highly correlated

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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
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Bdgpp-
No identification Purity 9.5
With pion identification Purity 85, Eff. 90
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Section 6 Concluding Remarks on CP Violation


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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
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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

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Not the whole picture.

• Do mixing
• Not yet observed
• Slow oscillations xlt 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 Pauls neutrino course

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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)