Philip J. Clark University of Edinburgh Rare B decays The Royal Society of Edinburgh 4th February...
-
Upload
gerard-greer -
Category
Documents
-
view
214 -
download
0
Transcript of Philip J. Clark University of Edinburgh Rare B decays The Royal Society of Edinburgh 4th February...
Philip J. ClarkUniversity of Edinburgh
Rare B decaysRare B decays
The Royal Society of Edinburgh4th February 2004
Philip J. Clark Rare B Decays Page 2
Talk overview
Introduction to rare decaysIntroduction to rare decays
Ways to measure them experimentallyWays to measure them experimentally
Theoretical methods for calculating them Theoretical methods for calculating them
Various interesting resultsVarious interesting results
SummarySummary
Philip J. Clark Rare B Decays Page 3
Small CKM matrix element
|Vub/Vcb|~
exclusive b u charmless hadronic
B0 K+...B KK*…
b
ud ,
ud ,
u
u
d*
ubV
b
uu
c
u
susV
BR~10 -5 ~ -6
B+ D0K+, ...
exclusive b c with Vus (what is rare?)
BR~10 -4~-5
exclusive b u, purely leptonic
B+ l+ BR~10 -5~-12
fB|Vub| b
u
l
What are rare B decays? (part 1)
Philip J. Clark Rare B Decays Page 4
Leading diagram involves a quantum loop (“penguin” loop)
What are rare B decays? (part 2)
gluonic loop: b s gluon (qq)
radiative loop: b (s,d)
electroweak loop
exclusiveb
ud , ud ,
sq
q
W
ud ,b
ud ,
ds ,
tcu ,,
b
ud ,ud ,
sW
Z/ll
B K* … (pure gluonic loop)B K, K’ (gluonic + small tree)
BR~10 –5 ~ -6
exclusive (b s,d )inclusive (b s )
B K*,,B s
B K, Kl lBR~10 -6
BR~10 -5 ~ -
7
BR ~10 -4
Philip J. Clark Rare B Decays Page 5
Charmless hadronic decays
JPC classification of light mesons
How can we organise them?
B K, , K, ’…
B K*, , , K, …
B , K*, …PP
PV
VV
SPB a0, f0 …
Philip J. Clark Rare B Decays Page 6
Success of the quark model
Philip J. Clark Rare B Decays Page 7
Theoretical approaches
Diagrammatic Methodology
Isospin & SU(3) Advantages:
Very intuitiveProvides powerful
approximate relations between decay channels
Disadvantages:non exact results
Effective Hamiltonian Methodology
QCD operator product expansion
Advantages:Rigorous computation using
Wilson coefficients Disadvantages
Huge uncertainties in operator matrix elements
Solution for B decays: o (QCD) factorisation
Two main methodologies
Chiang, Gronau, Luo, Rosner & SuprinBPV hep-ph 0307395BPP hep-ph 0306021
eg. Beneke & NeubertBPV, PP hep-ph 0308039
Philip J. Clark Rare B Decays Page 8
Example: rare 0 modes
Colour suppressed trees
Gluonic penguins
Singlet penguins
Electroweak penguins
Philip J. Clark Rare B Decays Page 9
Theoretical predictions
Experimental dataHeavy Flavor Averaging group (Lepton Photon 2003)
Philip J. Clark Rare B Decays Page 10
PEP II/BABAR at SLACPEP II
Asymmetric B Factory
design peak: best peak: total recorded:
x cmsx cms
fb
PEP-II/BABAR at SLAC
Luminosity records
Started construction in1994 Completed in 1999 Reached design luminosity in 2000
9 GeV e on 3.1 GeV e+
Philip J. Clark Rare B Decays Page 11
SVTSVT
-T Solenoid
The BABAR detector
SVTSVT
EMCEMC
IFRIFR
DCHDCH
DIRCDIRC
Philip J. Clark Rare B Decays Page 12
One method we use is the “event shape” The continuum is light quark pair
production, so there is lots of extra energy. All the decay products bunch into “jets”
B mesons are produced almost at rest in our case The decay products of the B are distributed roughly spherically.
e+
e-
e+
e-
Signal B
Other B
How do we find the rare decays?
There any many such event shape variables which are all correlated:
Fisher discriminants (linear weighting)
And in some cases neural networks taking advantage of hidden layers.
Philip J. Clark Rare B Decays Page 13
Time dependent meaurements
0
tagB
e
S4
0recB
eCoherent BB
production
-K
IdentifyB or anti-B
IdentifyB or anti-B
zx
y
t z/c t z/c
z
Full reconstruction of
B Ks0
Full reconstruction of
B Ks0
0SK
K+
K-
Philip J. Clark Rare B Decays Page 14
Example of a Ks event
Philip J. Clark Rare B Decays Page 15
Maximum Likelihood fits
Philip J. Clark Rare B Decays Page 16
Results: some branching fractions
Rare decays are not rare anymore!
Philip J. Clark Rare B Decays Page 17
Why do we want to study rare decays?
Phys. Rev. Lett. 89 (2002) 201802
BABAR
World average (BABAR+Belle+…)
Heavy Flavor Averaging Group 2003
Main experimental constraints on the apex of the UT
CP violation in the kaon system
Measurements of |Vub| (b → u transitions)B and Bs mixing frequencies
Philip J. Clark Rare B Decays Page 18
World-wide status of sin2
Philip J. Clark Rare B Decays Page 19
• Measurements in many charmless hadronic B decays– These modes are all sensitive
to gluonic penguin amplitudes which may interfere to produce an asymmetry
– Non-SM effects could cause potentially large asymmetries in some decays
Direct CP violation
Philip J. Clark Rare B Decays Page 20
Latest interesting result: B +-
Latest results from BELLE:S=-1.00 0.21 0.07C= 0.58 0.15 0.07 hep-ex/0401029
Philip J. Clark Rare B Decays Page 21
Summary
What are rare B decaysVarious tree diagramsSeveral penguin diagrams
Calculating themCategorisation of light mesonsThe two main theoretical approaches
Where to measure them Example: The BaBar experiment and PEPII
How to measure themMulitivariate discriminants, Particle ID, Maximum Likelihood
ResultsBranching fractions Status of Sin2Direct CP violationLatest News
Lots of new results still to comeNeed more data!
What we have covered:What we have covered:
Philip J. Clark Rare B Decays Page 22
• Need to differentiate kaons from pions. • Crucial to the analysis of many charmless decays
– Especially important at high momenta
K,
Particle Identification