cp violation
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CP Violation
Recent results and perspectives
João R. T. de Mello Neto
Instituto de Física Universidade Federal do Rio de Janeiro
IF – UFRJ, July/2003
Outline
• Introduction• CP Violation in the SM• Measurement of β• B Factories results• Other measurements• Hadron colliders (LHCb)• New physics• Conclusion
Motivations
SM with 3 generations and the CKM ansatz can accomodate CP
CP is one of the less experimentally constrained parts of SM
Observations of CP in the B system can:test the consistency of SMlead to the discovery of new physics
Cosmology needs additional sources of CP violation other than what is provided by the SM.
CP violation is one of the fundamental phenomena in particle physics
CP asymmetries in the B system are expected to be large.
I will not talk about:
• Kaon physics• Strong CP problem;• CP violation in the charm sector;• CP violation in Cosmology!
Concentrate in CP violation in the B sector(Only a small subset!)
CLEO 3BELLE
1999
2001BTEV A
TLAS
?
19992008
Huge experimental effort
Plus hundreds of experimental groups around the World.
Matter – antimatter oscillations
decay
ordinary ΔB=1 interactions exchangeof virtual q (2/3) t : dominant amplitude
ΔB=2
VtdΔmd
fB decay constant
BB Bag factor
CKM matrix
CKMV =
tbtstd
cbcscd
ubusud
vvv
vvv
vvv
=
mixing phase
Weak decay phase
dd BB mixing phase
ss BB
1
2/1
2/122
2
its
itd
iub
eVeV
A
eV
The quark electroweak eigenstates are connected to the mass eigenstates by the CKM matrix :
four parametersA, λ, ρ, η
Unitarity triangles
Vtd Vtb+Vcd Vcb
+Vud Vub= 0
(0,0)
Vub
Vcb
Vtd
(,)
(1,0)
Vtd Vud+Vts Vus
+Vtb Vub= 0
Vub
Vtd
Vts
In SM:
In SM:
03.02 • measure all the angles• measure all the sides SM: consistency!
CP violation
Three possible manifestations of CP violation:
Direct CP violation(interference between two decay amplitudes)
Indirect CP violation(interference between two mixing amplitudes)
CP violation in the interferencebetween mixed and unmixed decays
General time-dependent formalism
Interfering amplitudes with different CP-violating (weak) phases can give a non-zero CP asymmetry. For B0 → fCP:
Then, when one of the interfering amplitudes is B-mixing
with
S C
Only one decay amplitude (or all decay amp. same CKM phase):C=0 and S gives clean CKM phase information
• Golden modes:– clean theory– “relatively easy” experiment
• Tree and leading penguin have same phase • sinmt coeff. measures sin2 cleanly• Not just J/ KS:
– Also ’ KS, c1 KS, c KS (CP=-1)
– J/ KL (CP=+1)
– J/ K*0 (Mixed CP)
Measuring βb
d
d
W cc
s
0B /J
0K0K0B
b
dW
s
d
c
cg
u,c,t
/J
Measuring β
B factories: Belle, BaBar
Assimetric colliders at ee )( S4
nb 1bb -1-233 scm 103LOne year: ~ 100 M pairs BB
Ldt Belle 132 fb-1
March, 2003 BaBar 117 fb-1
Coherent productionBB
KEKBLuminosity achieved:
1.06 x1034 cm-2s-1
Babar detector
Mixing and lifetimesResults based on large samples of
– Fully or partially reco. hadronic decays– Fully or partially reco. D* l – Dileptons
8K events
12K events29 fb-1
Δt Distributions Lifetimes
Δt = proper time differencebetween the decay times of the two B-mesons
Δt resolution of ~ same order of magnitude as lifetime
0 = 1.554 0.030 0.019 psec- = 1.695 0.026 0.015 psec
Lifetimes results summary
• Belle and BaBar now dominate world averages• Improvement by x2 over pre B-factory era• Order 1% uncertainty on lifetimes and ratio
Adding Tagging Information
md = 0.516 0.016 0.010 ps -130 fb-1
1.6K events
~500 signal ev.
Clean ~2K KS sample
+~ 500 KL events
with ~ 60% purity
Event samples
Δt distributions and asymmetries
CP=-1 CP=+1
Events with KS Events with KL
Δt distributions and asymmetries
Summary of sin2b in b ccs
7.5% precision
B0 → J/ 0
b
d
d
W cc
d
0B /J
00B
b
dW
d
d
c
cg
u,c,t
/J
0
S = - sin2β if no penguin C = 0 if no penguin
Measuring β in b→sss
Bb
d,u
W
ss
sg
Kd,u
bW
s
s
sg
u,c,t
Kd,u d,u
B
B → KS
B → ‘ KS
• Same CKM structure as J/ψ KS
• u-penguin down by ~1/50• Expect S=sin2β to 5%
• Like ϕKS but also u-tree• Still, S~sin2b
Measuring β in b→sss
Theoretical especulations
• sin(2β) = SϕK=-0.39 +- 0.41 (2.7 σ) from the SM prediction;
• models from SUSY could explain this result!G.L. Kane et al., PRL Apr.2003
Grossman et al. hep-ph/0303171
SM is alive and well!
Confidence levels in the large (rhobar,etabar) plane
obtained from the global fit. The constraint from the
WA sin2beta (from psi Ks modes) is overlaid.
Confidence levels in the large (rhobar,etabar) plane
obtained from the global fit. The constraint from the WA
sin2beta (from psi Ks modes) is included in the fit.
2007
• More data close to theory limit from penguin pollution;• Measurement of ΔmS improve |Vtd/Vcb| from near cancellation of Bd and Bs form factor;• More data from B→hulν and B→hcX together with improvement in theory will give some improvement in |Vtd/Vcb| ;
)()(sin 2102 o
Strategy: new physics!
now
2007
1 yr
LHCb
BdJ/KS Bd
BsJ/ Bs DsK
statistics!!Goal: Physics beyond the Standard model
• Measurements which provide a reference case for SM effects;• Compare this to channels that might be affected by New Physics;• Understand experimental and theoretical systematics to a level where we can draw conclusions.
for larger the B boost increses rapidly
Hadronic b productionB hadrons at Tevatron
))2/ln(tan(
• b quark pair produced preferentially at low • highly correlated
tagging low pt cuts
LHCb Experiment
• Acceptance :– 15-300mrad
(bending)
– 15-250mrad (non-bending)
• Particle ID– RICH
detectors – Calorimeters– Muon
Detectors
• Dedicated B physics Experiment at the LHC– pp collisions at 14TeV
RICH1Z ~ 1.0-2.2 m
RICH2Z ~ 9.5-11.9 m
CalorimetersZ ~ 12.5-15.0 m
Muon SystemZ ~ 15.0-20.0 m
One event!
Tracking performance
Average efficiency = 92 %Efficiency for p>5GeV >95%
Ghost rate pT>0.5 GeV ~ 7%.
Mass resolution Mass resolution ((~13 MeV)~13 MeV)
for the decay channelBs Ds +
KKπ
Momentum resolution:Momentum resolution:
p/p=0.38%
Proper timeProper time resolution resolution (42 fs)(42 fs)
<N> = 27 tracks/event <N> = 27 tracks/event
S. AmatoC. Nunes JTMN
Hadron ID : Physics Performance
No RICH With RICH
n Signal Purity improved from 13% to 84% with RICH
n Signal Efficiency 79%
n RICH essential for hadronic decays
n Example : Bs K+K-
n Sensitive to CKM angle
Muon Identification• Muons selected by searching for muon stations hits
compatible with reconstructed track extrapolations– Compare track slopes and distance of muon station hits
from track extrapolation
For P>3GeV/ceff = 96.7 0.2 %
misid = 2.50 0.04 %
M. GandelmanJTMN
Strategies for measurements of CKM angles and rare decays
Sd KJB 0
0
dB
2 *0 DBd
sx ss DB0
2KDB ss
0
0dB
)( 0 KKBs
DKBd
0
KBd 0
JBs 0
(/)0 JBs
)()(00
)( , ssSsd DDKJB
Rare 0
)(dsB 00 KBd
,
0dB
Measuring β Sod KJB
S. AmatoC. Nunes JTMN
Measuring β Sod KJB
S. AmatoC. Nunes JTMN
Systematic errors in CP measurements
high statistical precisionasymmetries • ratios• robust
• production asymmetries• tagging efficiencies
• mistag rate
• final state acceptance
Control channels
Monte Carlo Detector cross-checks
ffffff ss 00
CP eigenstates
Sd KJB /0 KJB /
00 / KJBd
)( taa(t)
ff
00 ff 00 ff
ss DB 0
ss ffL. de Paula
)2sin( 0dB
)()(
)()()(
dd
dd
BB
BBtA
• experimental: background with similar topologies
• theoretical: penguin diagrams make it harder to interpret observables in term of
tmAtmA dmix
ddir sincos
030
|P/T|=0.1
0.05
0.02
)2sin( 0dB
PeTeBA iid
)( 0
sinsin2)( 0
T
PBA d
dir
CP conserving strong phase
)sin()cos(cos
)sin()(
22
20
T
P
BA dmix
approximately
Rare B decays• flavour changing neutral currents only at loop level• very small BR ~ or smaller
In the SM:
Excellent probe of indirect effects of new physics!
SB
SM : BR ~ • observation of the decay• measurement of its BR
910
LHCb
width MeV/c2 signal backg
26 33 10
510
FrancioleS. Amato
A. Ali et al., Phys. Rev. D61074024 (2000)
Rare B decays KBd
Forward-backward asymmetry )(sAFB
)( _ pps
can be calculated in SM and other models
0)( 0 sAFB
LHCb %8.5%4.2 (1y)
H. LopesLHC Physics – Praga(B. de Paula)
Measuring γ
000 *KDBd 000 *KDBd 000 *KDBd
iiDdD eeAKDBAA )( *000
)()( *DDdD AAKDBAA 2
1000
iDdD eAKDBAA )( *000
Amplitudes of the chargeconjugated process are obtainedfrom the above ones just changingthe signal from weak phase.
DD AA
DA DA D
A
DA
Measuring γ
M. GandelmanK. Akiba
LHCb reach in one year (2 fb-1)
ChannelChannel Yield Yield PrecisionPrecision**
Bd J/Ks 119 k 0.6o
Bs DsK
Bd , Bs KK
8 k 27 k, 35 k
10o
3o
Bd 27 k 5o- 10o
Bs J/ 128 k 2o
|V|Vtdtd/V/Vtsts Bs Ds 72 k ms up to 58 ps
rare rare decaysdecays
Bd K 20 k
Numbers being updated for the Physics TDR .
Conclusions
LHCb is a second generation beauty CP violation experiment;
It is well prepared to make crucial measurements in flavour physics with huge amount of statistics;Impressive number of different strategies for measurements of
SM parameters and search of New Physics;
CP violation is a cool research topic!!
B factories established CP violation in the B sector and are making interestingmeasurements;
Exciting times: understanding the origin of CP violation in the SM and beyond.
SM is alive and being poked !
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