Flavour Physics
Tim Gershon
University of Warwick
3 April 2014
Outline
●
Lecture 3
–
kaon physics
●
–
current and future
charm physics
●
–
mixing
B physics
●
lifetimes and mixings
●
the sides of the Unitarity Triangle
Kaon physics – current and future
●
Measurement of |Vus| from leptonic and semileptonic K
decays
●
Tests of universality from K+→e+ν/K+→μ+ν

  K  e  e
 
me
RK =
=

  K     m 
2
2
K
2
K
m −m
m −m
2 2
e
2


 1 RQED  = 2.477±0.001 ×10 −5
R K =( 2.488±0.010 )×10 −5
( Phys.Lett.B 719(2013) 326)
●
Rare decays, especially K→πνν
|Vus| and |Vud| fit by flavianet
M.Palutan at Kaon'09
see also
http://ific.uv.es/flavianet/
KLOE, KTeV,
BNL E685,
ISTRA+, NA48
New survey of
superallowed 0+→0+ β decays
J.Hardy & I.Towner,
PRC 79 (2009) 055502
from RBC/UKQCD ’07
●
Uncertainty from |Vus|2 now comparable to that from |Vud|2
●
Significant further improvement very difficult
Future kaon physics
●
“Holy grail” of kaon physics : rare decays K→πνν
–
–
–
–
Allow precise measurements of CKM matrix parameters
Sensitive to new physics effects
Extraordinarily challenging experimentally
K+ →π+νν
●
●
–
Current measurement (1.7 ± 1.1) 10–10 BNL-E949
(expectation 0.9 10–10)
NA62 experiment (CERN) will observe O(100) SM events
K0 →π0νν
●
●
Current UL < 2.6 10–8 KEK-E391 (expectation 2.5 10–11)
KOTO experiment (JPARC) will reach SM sensitivity
Other notable kaon experiments
●
[Not a complete list]
●
Series of experiments at BNL (USA)
+ -
+ -
●
KLOE at LNF (Italy) – e e collisions (e e → φ)
●
ISTRA at IHEP (Russia)
●
CMD at BINP (Russia)
●
KEK-246 and others (Japan)
Also
●
HyperCP (hyperons) and others at FNAL (USA)
Charm physics
●
●
●
Neutral D meson offers the only chance to study
ΔF = 2 (mixing) phenomena among up-type
quarks
FCNC in decays can also be studied
CP violation in the D system is tiny in the SM,
and hence its study probes new physics
–
precise measurements needed to test realistic NP
models
Charm mixing
●
Evidence (3σ) for charm mixing in 2007 from BaBar & Belle
●
Followed by further evidence from CDF
●
●
Combined significance of mixing overwhelming, but no
single 5σ measurement until LHCb
Time-dependence of ratio of wrong-sign
(WS) to right-sign (RS) D0→Kπ decays
–
WS/RS known by D*+ → D0π tag
Charm mixing world averages
y = ΔΓ/2Γ
No mixing
Still need to determine if x>0, but main focus now on CP violation
x = Δm/Γ
Charm mixing CP violation parameters
●
●
●
Peculiar hour-glass shape due to constraints from D0→Kπ decays
Results from more channels expected soon
Searches for direct CP violation in charm also a current hot topic
Notable charm physics experiments
●
[Not a complete list]
●
Series of experiments at FNAL (USA)
●
MARK experiments at SLAC (USA)
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LEP experiments (ALEPH,DELPHI,L3,OPAL) at CERN
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Experiments at BINP (Russia)
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CLEO & CLEO-c at Cornell (USA)
●
BES experiments at IHEP (China)
●
B factory experiments (Belle, BaBar, etc.)
B physics
Some history
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1977 – discovery of the Υ
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1980 – discovery of the Υ(4S)
●
1981 – discovery of B mesons
–
●
1983 – lifetime of the B meson measured
–
●
[PRL 46, 84 (1981); PRL 46, 88 (1981)]
[PRL 51, 1022 (1983); PRL 51, 1316 (1983)]
0
1987 – observation of B mixing
–
[PLB 192, 245 (1987)]
First B meson lifetime measurement
τ(B) = (1.8 ± 0.6 ± 0.4) ps
PDG 2006 : (1.530 ± 0.009) ps
(previous best UL: τ(B) < 1.4 ps)
MAC experiment (1983)
B lifetime
●
Long lifetime of the B meson
⇒ |Vcb| is small (and |Vub| too)
0
0
Observation of B -B mixing
●
Same sign leptons
⇒ same flavour B mesons
●
Mixing probability is large
⇒ top quark is heavy
●
Mixing probability
r = 0.21 ± 0.08
●
PDG 2006:
“r” (χd) = 0.188 ± 0.003
●
From 103/pb of data
ARGUS experiment (1987)
B mixing with current data sets
-|Δt|
P(Δt) = (1±cos(ΔmΔt))e
●
Belle experiment
PRD 71, 072003 (2005)
Δm = (0.511 ± 0.005 ±
0.006) ps-1
●
From 140/fb of data
/2τ
Bs mixing
●
Mixing in the Bs system is large
●
Bs mixing first measurement
–
PRL 97 (2006) 242003
Δms = (17.77 ± 0.10 ± 0.07) ps-1
●
Now precision measurement
–
NJP 15 (2013) 053021
Δms = (17.768 ± 0.023 ± 0.006) ps-1
Remember The Unitarity Triangle
●
Convenient method to illustrate (dis-)agreement
of observables with CKM prediction
Constraints from mixing
●
Δmd contains information on |Vtd|
●
Δmd/Δms preferred since theoretically cleaner
Δmd
Δmd/Δms
Constraints from mixing
many theoretical uncertainties cancel
Comment on theoretical tools
●
●
Most significant theoretical uncertainties in quark
flavour physics arise due to hadronization
–
strong interaction effects – not calculable perturbatively
–
precision will be improved with lattice QCD calculations
–
alternative: QCD sum rules (parton-hadron duality)
Operator product expansion
–
●
match physics to relevant scales
For kaon physics, utilize approximate chiral symmetry
of low energy QCD
–
chiral perturbation theory
Comment on theoretical tools (2)
●
●
In B physics, can exploit the fact that mb >> ΛQCD
–
heavy quark expansion & heavy quark effective theory
–
factorization
●
QCD factorization
●
soft collinear effective theory (SCET)
Phenomenological treatments also very useful
–
SU(3)
–
isospin
–
U-spin
Ru side
●
Ru = |Vub*Vud|/|Vcb*Vcd|
–
need precise measurement of |Vub*|
●
–
also need |Vcb*|
four possibilities
●
exclusive hadronic B decays, eg. B0 → Ds+ π–
●
exclusive semileptonic B decays, eg. B0 → π- e+ ν
–
●
moderate theoretical (hadronic) uncertainties
inclusive semileptonic B decays, eg. B0 → Xu e+ ν
–
●
large theoretical (hadronic) uncertainties
experimentally challenging
leptonic B decays, eg. B+ → τ+ν
–
experimentally challenging, sensitive to new physics
Measurement of |Vcb|
●
Possible methods to measure |Vcb| very similar to those
for |Vub|
●
Current best method uses
–
inclusive semileptonic decay rates for B → Xclν
–
moments of decay distributions in m(Xc) & q2
●
–
●
fit to extract theoretical parameters from data
moments of Eγ in B → Xsγ decays also used
PDG 2013 gives |Vcb| = (40.9 ± 1.5) x 10-3
–
error inflated due to disagreement between inclusive
and exclusive measurements
Tension (crisis?) in |Vcb| measurements
|Vub| - exclusive semileptonic decays
B0 → π–l+ν
BaBar PR D83 (2011) 032007
& PR D83 (2011) 052011
Belle PR D83 (2011) 071101
B(B0 → π–l+ν) = (1.42 ± 0.04 ± 0.07) × 10–4
|Vub| = (3.23 ± 0.09 ± 0.13 +0.57–0.37) × 10–3
B(B0 → π–l+ν) = (1.49 ± 0.04 ± 0.07) × 10–4
|Vub| = (3.55 ± 0.09 ± 0.09 +0.62–0.41) × 10–3
Largest uncertainty from theory ... but more data helps to reduce theory errors
|Vub| - exclusive semileptonic decays
Simultaneous fit to BaBar & Belle data & LQCD predictions
Uses Boyd-Grinstein-Lebed (BGL) parametrization (PR D56 (1997) 303) to determine
|Vub| = (3.28 ± 0.29) × 10−3
|Vub| - exclusive semileptonic decays
Extraction of |Vub| with different
theoretical approaches
|Vub| - inclusive semileptonic decays
●
Main difficulty to measure inclusive B0 → Xu l+ ν
–
●
●
●
background from B0 → Xc l+ ν
Approaches
–
cut on El (lepton endpoint)
–
cut on M(Xu)
–
other combinations of cuts on M(Xu) and q2
Cuts ⇒ theoretical uncertainty
Ability to perform inclusive analysis depends on
detector hermiticity
|Vub| inclusive - endpoint analysis
●
One of the most precise measurements:
PRD 73, 012006 (2006)
non BB background subtracted
Xc l+ ν background subtracted
|Vub| inclusive - compilation
Different theoretical approaches
|Vub| inclusive - compilation
More different theoretical approaches
|Vub| inclusive - compilation
More different theoretical approaches
Author of
International
best-selling novel!
|Vub| average
Very hard to make an average!
PDG2013 gives: |Vub| = (4.15 ± 0.49) x 10-3
|Vub| - leptonic decays
●
●
●
Interesting alternative approach to |Vub|
Sensitive to physics BSM at tree level [also D(*)τν], but
experimentally challenging (τν, μν, & eν)
Evidence from both BaBar and Belle:
Tension (crisis?) in |Vub| measurements
CKM Matrix – Magnitudes


∣V ud∣ ∣V us∣ ∣V ub∣
∣V cd∣ ∣V cs∣ ∣V cb∣
∣V td∣ ∣V ts∣ ∣V tb∣
CKM Matrix – Magnitudes
superallowed 0+→0+ β decays
(
semileptonic / leptonic kaon decays
hadronic tau decays
PDG 2013
2008
PDG
semileptonic / leptonic B decays
0.97425 ± 0.00022 0.2252 ± 0.0009 ( 4.15 ± 0.49) ×10 −3
0.230 ± 0.011
1.006 ± 0.023
( 40.9 ± 1.1)×10 − 3
(8.4 ± 0.6)× 10 −3 (42.9 ± 2.6) ×10 − 3
0.89 ± 0.07
semileptonic charm decays
charm production in neutrino beams
Bd oscillations
)
semileptonic B decays
semileptonic / leptonic charm decays
Bs oscillations
single top production
theory inputs (eg., lattice calculations) required
significant progress in many of these over the last few years (including
some new results not yet in the PDG compilation)
How to measure the angles?
●
How to measure CP violation in the B system?
Measurement of γ
●
Charmless B decays, eg. B0 → K+π–
contributions from
●
P : b → suu penguin
●
T : b → usu tree
–
relative weak (CP violating) phase is γ
–
relative strong (CP conserving) phase δ
ACP = 2|P||T|sin(γ)sin(δ)/{|P|2+|T|2+2|P||T|cos(γ)cos(δ)}
●
Hadronic uncertainties:
–
even if we observe ACP ≠ 0, cannot easily extract γ
–
other processes also contribute
Direct CP violation
●
●
–
Condition for DCPV: |A/A|≠1
–
Need A and A to consist of (at least) two parts
–
●
with different weak (φ) and strong (δ) phases
Often realised by “tree” and “penguin” diagrams
i   T −T 
i   P −P 
i  T T 
i   P P 
A = ∣T ∣e
∣P∣e
A = ∣T ∣e
∣P∣ e
2
2
2 ∣T∣∣P∣ sin T − P  sin T − P 
∣ A∣ −∣ A∣
ACP =
=
2
2
2
2
∣ A∣ ∣ A∣
∣T∣ ∣P∣ 2 ∣T∣∣ P∣cos T − P cos T − P 
Example: B→Kπ
(weak phase difference is γ)
42
Clean measurement of γ
●
●
A theoretically clean measurement of γ can be
made using B → DK decays
Reconstruct D mesons in states accessible to
both D0 and D0
–
interference between b → cus and b → ucs
–
relative weak phase is γ
–
various different D decays utilized
–
large statistical errors at present
The Idea
●
–
Two possible diagrams for B →DK
∝ V cb V
●
●
∗
us
colour allowed
0
final state contains D
∝ V ub V
●
●
–
∗
cs
colour suppressed
0
final state contains D
Relative magnitude of suppressed amplitude is rB
Relative weak phase is –γ, relative strong phase is δB
0
D
Need D and
to decay to common final state
0
D→CP eigenstates
●
Neglecting CP violation in charm decay
AD 0  CP= A D 0 CP 
●
Possible states
–
CP even:
(D1) K+K–, π+π–, Ksπ0π0
–
CP odd:
(D2) Ksπ0, Ksη, Ksη', Ksρ0, Ksω, Ksφ
Experimental Summary
Constraint from γ
Best constraint from combining
all available results
●
●
B→DK, B→D(*)K, B→DK(*)
Different D decays
● D→CP eigenstates
● D→ suppressed states
● (eg. Kπ)
● D→ multibody states
+ ● (eg. K π π )
S
γ = (70.1 ± 7.1)°
NB. Other statistical approaches give much larger uncertainty
Summary
●
Mixing phenomena and types of CP violation
●
T violation
●
Existence of (tiny) direct CP violation in the kaon
system
●
Current and future kaon experiments
●
B system & the sides of the Unitarity Triangle