CP Violation
description
Transcript of CP Violation
CP ViolationRecent results and
perspectives
João R. T. de Mello Neto
Instituto de Física Universidade Federal do Rio de Janeiro
22-26 July,2003
Outline
• Introduction• CP Violation in the SM• Measurement of β• B Factories results• Other measurements• Dedicaded hadron colliders
experiments– LHCb, BTeV
• 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
Neutral B0 mesons oscillateb
d
d
b
t
t
w- w-)()( dbBdbB dd
)()( sbBsbB ss
c
e-
eb
d
w-
d
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
time-dependent formalism for Bd
decay amplitude for fBd 0BHfAf 0BHfAf time evolution
mtAimtAeetBHf fpq
f
timt
phys
21
2120 sincos)(
0B0B
CPf
CP violation: interference between mixing and decay
f
f
A
A
q
p
time-dependent formalism for Bd
)()(
)()()(
tt
tttA
fBfB
fBfBCPf
B-factories: Δt
mtAmtAtA mixdirCPf sincos)(
LHCb, BTeV: t
1
12
2
dirA1
22
ImmixA
C=0 B0→J/ψKSS=+sin(2β)SM:
C=0 S=-sin(2β) B0→J/ψKL
Measuring β
b
d
d
W cc
s
0B /J
0K0K0B
b
dW
s
d
c
cg
u,c,t
/J
Decays such as B0→J/ψKS and B0→J/ψKL
theoretically well understood: tree and leading penguin have same phase
“relatively simple” experiment
ScScSd KKKB 1 ,,
Ld KJB
iCPe
2
1CP
1CP
Measuring β
(from D. Lange)
B factories: Belle, BaBar
Assimetric colliders at ee )( S4
nb 1bb-1-233 scm 103L
One 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 lifetimeslarge samples of
o hadronic decays: fully or partially reconst.o semileptonic decays (D* l fully or partially
reconst.o dileptons
8K events
12K events29 fb-1
Δt distributions and lifetimesΔt = 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
)( czt mz 150 )(pst 90.)(
proof of principle:resolution function under control.
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 -1
(30 fb-1)
Amix(t)
Event samples
~500 KL signal events
60% purity
~1600 KS events
Δt distributions and asymmetries
CP=-1 CP=+1
B0→J/ψKS B0→J/ψKL
Δt distributions and asymmetries
Summary of sin2b in b ccs
already a precisemeasurement: 7.5%
05507340 ..
rarer B decaysdccb
qqsb
Cabbibo supressed
b
d
d
W cc
d
0B /J
00Bb
dW
d
d
c
cg
u,c,t
/J
0B0 → J/ 0
B → KS B
b
d,u
W
ss
sg
Kd,u
bW
s
s
sg
u,c,t
Kd,u d,u
B
B → ‘ KS
Sensitive to new physics:• smaller amplitudes, NP through interf. terms• virtual particles (SUSY?) in penguin loops
not theoretically cleansmaller rates, higher back.
Same CKM structure as B0→J/ψKS
expect S=sin2β to 5%
B0 → J/ 0
S = - sin2β if no penguin C = 0 if no penguin
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!
for the decay channelBs Ds +
Ds KKπ
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)
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
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 extrapolationFor P>3GeV/c
eff = 96.7 0.2 %
misid = 2.50 0.04 %
BTeV detector
Calorimetry
Important final states with and
Use 2x11,850 lead-tungsten crystals (PbWO4)
• technology developed for LHC by CMS• radiation hard • fast scintillation (99% of light in <100 ns)
Excellent energy, angular resolution and photon efficiency
0
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
γ B
Measuring β Sod KJB
“gold-plated” decay channel at B-factories for measuring the Bd- Bd mixing phase needed for extracting γ from Bd ππ and Bs K K in SM Adir=0, non-vanishing value (~0.01) could be a signal of Physics Beyond SM precision measurement important
Inputs:
220 k/year signal194 k/year back.
Amix=sin(2β)=0.73
Adir = 0
0230.dirA
0220.mixA
ps
ACP(t)
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 ff
from Bs J/ψϕ δγ “gold-plated” decay channel for hadron machines, measuring the Bs- Bs phase in SM expected to be ~0.03 large CP asymmetry would signal Physics Beyond SM also needed for extracting from Bs →ππ and Bs K K, or from Bs Ds K
ηλδγ 2
γ
J/ψϕ is not a pure CP eigenstate 2 CP even, 1 CP odd amplitudes contributing need to fit angular distributions of decay final states as function of proper time requires very good proper time resolutionwith input values:εtag= 30% , ωtag= 30% , Δms=20/ps
= 1.5 ps , , A = sin(-) = 0.03
σt = 38 fs
in 1 year:σ
10.
Measuring Using Bo
• A Dalitz Plot analysis gives both sin(2) and cos(2)(Snyder & Quinn)
• Measured branching ratios are:– B(B = ~10-5
– B(B + = ~3x10-5
– B(B <0.5x10-5
• Snyder & Quinn showed that 1000-2000 tagged events are sufficient
• Not easy to measure 0 reconstruction
• Not easy to analyze– 9 parameter likelihood fit
Measuring Using Bo
•Based 9.9x106 background events•Bo+- 5400 events, S/B = 4.1•Booo 780 events, S/B = 0.3
Depending of assumptions on background and value of α :
0461 ..
(from K. Honscheid)
with Bd →ππ, Bs→KK γ relies on “U-spin” symmetry assumption (ds), which is the only source of theoretical uncertainty determination of and test of U-spin symmetry using measurements of from Bs J/ψϕ and β from B J/ψ KS
sensitive to New Physics contribution by comparing with obtained from Bs Ds K
γδγ
tAt
MtAMtAtA
mixCP
dirCPth
CP
22sinhcosh
)sin()cos()(
sensitivity in 1 year
49.0),(
06.0)(
07.0)(
mixCP
dirCP
mixCP
dirCP
AACorr
A
A
1140@
0),(
04.0)()(
psM
AACorr
AA
ss
mixCP
dirCP
mixCP
dirCP
B BS
K K
with Bd →ππ, Bs→KKγ
),,,()(
),,()(
),,,()(
),,()(
40
30
20
10
ssmixCP
sdirCP
ddmixCP
ddirCP
dfKKBA
dfKKBA
dfBA
dfBA
d , (d’ ,’) parametrize P over T amplitude ratio from Bd J/ψ KS , from Bs J/ψϕ exact U-spin symmetry => d = d’ ; = ’ 3 unknowns and 4 measurements
2d γ2d
1 year
2 years
3 years
4 years
95% confidence region for d and 95% confidence region for d and
σγ after 4 years:
2.2º (for = ~60º)
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
510
CMS : 100 fb-1 (107s at 1034
cm-2s-1) ~ 26 signal events 6.4 events background
LHCb : 2 fb-1
~ 33 signal events ~ 10 events backgroundσM = 38 MeV
+-,
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
BTeV data compared to Burdman et al calculation
Conclusions
LHCb and BTeV are second generation beauty CP violation experiments;
They are 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.