http://www2.warwick.ac.uk Physics Department Heavy flavour physics Plan Kaon physics and SM construction (bit of history) Establishing SM experimentally Looking for breakdown of SM Hard to cover everything in details in four lectures Michal Kreps
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Heavy flavour physics - University of Warwick · 2013. 3. 19. · 9 8/Sept/2011 Michal Kreps - Quark flavour physics 3 Why new physics? What we saw up to now is extreme success of
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http://www2.warwick.ac.uk
Physics Department
Heavy flavour physics
Plan
Kaon physics and SM construction (bit of history)
Establishing SM experimentally
Looking for breakdown of SM
Hard to cover everything in details in four lectures
Michal Kreps
Michal Kreps - Quark flavour physics 22 6/Sept/2011
Outline
Discuss angles and unitarity triangle
Why we need new physics
What are places to look for new physics
Michal Kreps - Quark flavour physics 23 6/Sept/2011
Angle β
Sf is in fact sin(2β)
Two-fold ambiguity exists in measurement
One way to resolve it is to use decays B0→J/ψKπ with interference between K* and s-wave Kπ
Can exclude one of the two solutions at reasonable confidence
Michal Kreps - Quark flavour physics 24 6/Sept/2011
Angle α
α is phase between Vtb
*Vtd and
Vub
*Vud
Extracted from b→uud transitions using mixing induced CPV
B0→ππ, ρρ, πρ
As those decays are suppressed, penguin contributions play also role
Isospin analysis used to correct for penguin contributions
Current (2010) value is 89±4.4°
Michal Kreps - Quark flavour physics 25 6/Sept/2011
Angle γ
Interference of B-→D0K- (Vcb
) and B-
→D0K- (Vub
) when using common final state for D0 and D0
Plays special role as it is extracted from tree level decays
Provides CKM phase without being significantly affected by new physics
Three different D final states used
GLW: Cabbibo suppressed CP-eigenstates (KK, ππ)
ADS: Doubly Cabbibo suppressed D0→K+π-
Dalitz plot: Ksππ
Michal Kreps - Quark flavour physics 26 6/Sept/2011
Angle γ
B- decays are challenging for γ measurement as
CP asymmetry is large, but rate is very small (ADS)
Rate is reasonable, but CP asymmetry is small (GLW)
Only in about last year experiments start to see significant signals
Other promising decay is Bs→D
sK
But this requires to resolve fast Bs oscillation
First measurement from LHCb
Will discuss this bit later
Michal Kreps - Quark flavour physics 27 6/Sept/2011
Angle γ
Michal Kreps - Quark flavour physics 28 6/Sept/2011
Angle γ
Dalitz plot measurements are still most sensitive
Still not very precise
Some disagreement in uncertainty between different combinations of measurements
Michal Kreps - Quark flavour physics 39 8/Sept/2011
Why new physics?
What we saw up to now is extreme success of SM
So why we are so excited about new physics if we can describe all measurements without it?
SM does not tell why we have three generations (do we?)
SM does not tell anything about masses of fermions
Way SM works needs quite some fine tuning (final result is often difference between two huge numbers)
Higgs mass in SM is not really stable
Cosmology argument:
No candidate for Dark matter
Not possible to generate current matter-antimatter asymmetry in Universe
Michal Kreps - Quark flavour physics 310 8/Sept/2011
Sakharov
In 1967 Andrei Sakharov formulated three necessary conditions to produce baryon-antibaryon asymmetry
Baryon number violation
CP violation
Interactions out of equilibrium
Surprisingly SM can best cope with baryon number violation – but non-perturbative QCD effect
CP violation exists in SM, but definitely not large enough
In SM there is nothing which could drive system out of equilibrium
Those are in my view strongest needs for new physics
Michal Kreps - Quark flavour physics 311 8/Sept/2011
Typical NP scenarios
SUSY – most popular
Each SM particle gets its SUSY partner
Squarks can also mix (similar to quarks) and provide additional phases
Fourth generation
Puts in additional fermion generation
Not as appealing as SUSY and cannot answer all questions, but can make huge difference on CPV
Technicolor
Gets more popular again as it can dynamically create Higgs like effect without need of Higgs
Michal Kreps - Quark flavour physics 312 8/Sept/2011
NP DNA
Michal Kreps - Quark flavour physics 313 8/Sept/2011
Bs→μ+μ-
SM prediction Br=(3.2±0.2)10-9
Extremely sensitive to new physics
Already with limits 10 times above SM one could severely restrict NP models
Michal Kreps - Quark flavour physics 314 8/Sept/2011
Experiments
Michal Kreps - Quark flavour physics 315 8/Sept/2011
LHCb is not small one
Michal Kreps - Quark flavour physics 316 8/Sept/2011
Main experimental issues
As decay is rare, main issue is to control background
Special care is needed for B→hh' decays which peak in same place as signal
Selection ranges from cut based (CMS) to BDT (LHCb) to NN(CDF, D0)
Michal Kreps - Quark flavour physics 317 8/Sept/2011
Tevatron Bs→μ+μ-
Tevatron was for long time only place to really study this decay
With final data could come close to SM
D0: <15*10-9 (exp 23*10-9)
CDF: two-sided bound (0.8—3.4)10-8 (exp 13*10-9)
Small excess, but does not look like signal
Which experiment is better?
Michal Kreps - Quark flavour physics 318 8/Sept/2011
Bs→μ+μ- with GPDs @ LHC
LHC experiments can finally probed SM values
CMS: <7.7*10-9 (8.4*10-9)
ATLAS: <22*10-9 (16*10-9)
In long run, GPD should give us best branching fraction measurement
This comes from higher luminosity compared to LHCb
Michal Kreps - Quark flavour physics 319 8/Sept/2011
Bs→μ+μ- @ LHCb First evidence for signal
(3.5σ)
Branching fraction (3.2+1.4
-1.2+0.5
-0.3)10-9
Spot on Standard model prediction
Michal Kreps - Quark flavour physics 320 8/Sept/2011
CPV induced by Bs mixing
CPV stems from interference of decays with and w/o mixing
In SM it is expected to me tine – Effect of almost real Vts
Needs some care in interpretation of what is really measured
Up to now measured with Bs→J/ψφ and Bs→J/ψf
0(980)
Difficult due to large Δms~17.8 ps-1
Needs very good time resolution
Michal Kreps - Quark flavour physics 321 8/Sept/2011
Master formulas of time evolutionA
rXiv:0 90
4.1 869
Michal Kreps - Quark flavour physics 322 8/Sept/2011
Decay Bs→J/ψf
0
This final state is CP-eigenstate
In master formula this (with some additional assumptions) means |λ
f|=1
For Bs the a is at most ~ 1% and ΔΓ is in principle non-zero
Michal Kreps - Quark flavour physics 323 8/Sept/2011
Decay Bs→J/ψf
0 - Lifetime
Michal Kreps - Quark flavour physics 324 8/Sept/2011
Decay Bs→J/ψf
0 - CPV
Takes input of Γ and ΔΓ from LHCb B
s→J/ψφ result
Consistent with SM
Michal Kreps - Quark flavour physics 325 8/Sept/2011
Decay Bs→J/ψφ
This decay was first to study as it has higher signal yield
Complication arises from the fact that both J/ψ and φ are have spin 1 => mixture of CP-even and CP-odd
Need additional work (angular analysis) to statistically distinguish two
On the other hand it also helps to gain additional sensitivity from interference
There are many details to care about, much beyond scope of this lecture
If you are interested, check CDF paper arXiv:1112.1726, it has more details than you want to know (LHCb long paper on its way)
Update from LHCb very soon
Michal Kreps - Quark flavour physics 326 8/Sept/2011
Decay Bs→J/ψφ
Michal Kreps - Quark flavour physics 327 8/Sept/2011
Decay Bs→J/ψφ
Michal Kreps - Quark flavour physics 328 8/Sept/2011
Quantum interference in action
On previous page I showed only one solution while for CDF and D0 two, which are equally good
Michal Kreps - Quark flavour physics 329 8/Sept/2011
Going back to Bs→D
sK
ArX
iv:0 904.1 869
Michal Kreps - Quark flavour physics 330 8/Sept/2011