Transcript CP Violation - Federal University of Rio de Janeiro

CP Violation
Recent results and perspectives
João R. T. de Mello Neto
Instituto de Física
Universidade Federal do Rio de Janeiro
22-26 July,2003
Outline
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Introduction
CP Violation in the SM
Measurement of β
B Factories results
Other measurements
Dedicaded hadron colliders experiments
– LHCb, BTeV
• Conclusion
Motivations
CP violation is one of the fundamental phenomena
in particle physics
CP is one of the less experimentally
constrained parts of SM
SM with 3 generations and the CKM ansatz can
accomodate CP
CP asymmetries in the B system
are expected to be large.
Observations of CP in the B system can:
test the consistency of SM
lead to the discovery of new physics
Cosmology needs additional sources of CP violation
other than what is provided by the SM.
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!)
Huge experimental effort
BTEV
2001
?
1999
A
T
L
A
S
2008
CLEO 3
Plus hundreds of experimental groups
around the World.
1999
BELLE
Matter – antimatter oscillations
Neutral B0 mesons oscillate
Bd (bd )  Bd (b d )
d
t
b
ordinary ΔB=1 interactions exchange
of virtual q (2/3)
t : dominant amplitude
ΔB=2
b
d
d
w-
w-
Bs (bs )  Bs (b s )
decay
t
b
ewc
d
e
Vtd
Δmd
fB decay constant
BB Bag factor
CKM matrix
VCKM
=
 v ud

 v cd
v
 td
v us
v cs
v ts
v ub 

v cb 
v tb 
 1  / 2

 Vub e

2
2
1  / 2
A
 
  V e i V ei
1
ts
 td
2
=
The quark electroweak eigenstates are
connected to the mass eigenstates by the
CKM matrix :
Bd  Bd
mixing phase
Bs  Bs
mixing phase
 i





Weak decay
phase
four parameters
A, λ, ρ, η
Unitarity triangles

Vtd Vtb +Vcd


Vcb +Vud Vub = 0



(,)
Vtd Vud +Vts Vus +Vtb Vub =

0
Vub

(0,0)
Vtd
Vcb
In SM:
     
Vub

(1,0)
Vtd

Vts


In SM:
• measure all the angles
• measure all the sides
SM: consistency!
     0.03
2
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 interference
between mixed and unmixed decays
time-dependent formalism for Bd
decay amplitude for Bd  f
Af  f H B 0
time evolution
Af  f H B
0
f H Bphys
(t )  e imt e
B
0
 t
2
A cos
f
1
2
0
mt  i qp Af sin 12 mt
fCP
B
0
CP violation: interference between mixing and decay
p Af

q Af

time-dependent formalism for Bd
B f (t )  Bf (t )
A (t ) 
B f (t )  Bf (t )
CP
f
A (t )  A cos mt  A
CP
f
dir
 1
2
Adir 
SM:
 1
2
C=0
C=0
A
mix
mix

B-factories: Δt
LHCb, BTeV: t
sin mt
2 Im 
 1
2
S=+sin(2β)
S=-sin(2β)
B0→J/ψKS
B0→J/ψKL
Measuring β
Decays such as B0→J/ψKS and B0→J/ψKL
0
B
b
d
W
c
c
s
d
J/
b
0
K
c
g
B0
t,c,u
c
s
W
J/
K0
d
d
theoretically well understood: tree and leading penguin have same phase
“relatively simple” experiment
CP  1
Bd   KS ,c K S ,  c1KS
CP  1
Bd  J  K L
  CP e
2 i
Measuring β
(from D. Lange)
B factories: Belle, BaBar
Assimetric e  e  colliders at  ( 4S )
 bb  1 nb
L  3 1033 cm -2s -1
One year: ~ 100 M
 Ldt
Belle 132 fb-1
March, 2003
Coherent
BB pairs
BB
BaBar 117 fb-1
production
KEKB
Luminosity achieved:
1.06 x1034 cm-2s-1
Babar detector
Mixing and lifetimes
large samples of
o hadronic decays: fully or partially reconst.
o semileptonic decays (D* l )fully or partially reconst.
o dileptons
8K events
29 fb-1
12K events
Δt distributions and lifetimes
Δt = proper time difference
between the decay times of the
two B-mesons
t  z ( c )
 ( z )  150m
 ( t )  0.9 ps
Δt resolution of ~ same order
of magnitude as lifetime
t0 = 1.554  0.030  0.019 psec
t- = 1.695  0.026  0.015 psec
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
Amix(t)
(30 fb-1)
md = 0.516  0.016  0.010 ps -1
Event samples
~1600 KS events
~500 KL signal events
60% purity
Δt distributions and asymmetries
CP=-1
B0→J/ψKS
CP=+1
B0→J/ψKL
Δt distributions and asymmetries
Summary of sin2b in b  ccs
0.734  0.055
already a precise
measurement:
7.5%
rarer B decays
b  cc d
Cabbibo supressed
c
g
B0 → J/ 0
b
B
b  sq q
B → f KS
t,c,u
0
B

b
W
d
d
s
g

b
g
u, d
0
0
W
d
W
B
J/
c
d
s
s
f
s
u, d
B → ‘ KS
Sensitive to new physics:
• smaller amplitudes, NP through interf. terms
• virtual particles (SUSY?) in penguin loops
not theoretically clean
smaller rates, higher back.
b
B
K
t,c,u
s
s
W
u, d
c
c
J/
d
d
0
f
K
u, d
,f
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 included in the fit.
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.
2007
• More data  (sin 2 )  o(102 ) 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| ;
Strategy: new physics!
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.
statistics!!
BdJ/KS
Bd
BsJ/f
Bs DsK
Hadronic b production
B hadrons at Tevatron
• b quark pair produced

preferentially at low 
• highly correlated
tagging
low pt cuts
   ln(tan(  / 2))

for larger  the B
boost  increses rapidly
LHCb Experiment
• Dedicated B physics Experiment at the
LHC
– pp collisions at 14TeV
Muon System
Z ~ 15.0-20.0 m
• Acceptance :
– 15-300mrad
(bending)
RICH2
– 15-250mrad Z ~ 9.5-11.9 m
(non-bending)
• Particle ID
– RICH
detectors
– Calorimeters
– Muon
Detectors
Calorimeters
RICH1
Z ~ 1.0-2.2 m
Z ~ 12.5-15.0 m
One event!
Tracking performance
Average efficiency = 92 %
Efficiency for p>5GeV >95%
Ghost rate pT>0.5 GeV ~ 7%.
Mass resolution
(~13 MeV)
for the decay channel
Bs  Ds +
Ds KKπ
Momentum resolution:
p/p=0.38%
<N> = 27 tracks/event
Proper time
resolution (42 fs)
Hadron ID : Physics Performance
n
n
n
RICH essential for
hadronic decays
Example : Bs  K+K-
Sensitive to CKM angle 
No RICH
n
n
Signal Purity improved from
13% to 84% with RICH
Signal Efficiency 79%
With RICH
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/c
eff = 96.7  0.2 %
misid = 2.50  0.04 %
BTeV detector
Calorimetry
0
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
Strategies for measurements of CKM angles
and rare decays


B  J K S
0
d
2  
Bd0  D* 

Bs0  J   (/)
Bs0  J f
 ,
B  
0
d
Bd0    
Bd0    
( Bs0  K  K  )

  2

s
B D K
0
s

xs
Bs0  Ds 
γ
B      
Bd0( s )
Bd0  DK 
Bd0  K
 J K S0 , D(s ) D(s )
Rare
Bs0(d )     
Bd0  K 0    
Measuring β
B  J K S
o
d
 “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
ACP(t)
 A  0.022
 A  0.023
mix
dir
Inputs:
220 k/year signal
194 k/year back.
Amix=sin(2β)=0.73
Adir = 0
ps
Systematic errors in CP
measurements
asymmetries
• ratios
• robust
high statistical precision
• tagging efficiencies
• production asymmetries
 
f0 f0 f s f s f f
• final state acceptance
• mistag rate
 
Control channels
B   J /K 
Bd0  J / K 0
B  Ds
0
s
Monte Carlo
a(t) a (t )


   
f

f

f0 f0
f 0 f 0 
 
fs
fs
Detector cross-checks
CP eigenstates
Bd0  J / K S
δγ from Bs  J/ψϕ
 “gold-plated” decay channel for hadron machines, measuring the Bs- Bs phase
 in SM δγ  λ 2 η expected to be ~0.03
 large CP asymmetry would signal Physics Beyond SM
 also needed for extracting γ from Bs →ππ and Bs  K K, or from Bs  Ds K
 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 resolution
with input values:
εtag= 30% , ωtag= 30% , Δms=20/ps
t = 1.5 ps ,    0.1 , A = sin(-) = 0.03
in 1 year: σ)  3.50
σt = 38 fs
Measuring Using Bo  o
• A Dalitz Plot analysis gives both
sin(2) and cos(2)
(Snyder & Quinn)
•
Measured branching ratios are:
– B(Bo) = ~10-5
– B(Bo + ) = ~3x10-5
– B(Booo) <0.5x10-5
•
Snyder & Quinn showed that 10002000 tagged events are sufficient
•
Not easy to measure
 0 reconstruction
•
Not easy to analyze
– 9 parameter likelihood fit
Measuring Using Bo  o
•Based 9.9x106 background events
•Bo+- 5400 events, S/B = 4.1
•Booo 780 events, S/B = 0.3
Depending of assumptions on
background and value of α :
   1.6  4.0


(from K. Honscheid)
γ with Bd →ππ, Bs→KK
 relies on “U-spin” symmetry assumption (ds), which is the only source
of theoretical uncertainty
 determination of γ and test of U-spin symmetry using measurements of
δγ from Bs  J/ψϕ and β from B J/ψ KS
 sensitive to New Physics contribution by comparing with obtained from Bs  Ds K
dir
mix
ACP
 cos( Mt )  ACP
sin( Mt )
A (t ) 
  
  
cosh
t   A  sinh
t
 2 
 2 
th
CP
dir
 ( ACP
)  0.07
 (A
mix
CP
)  0.06
dir
mix
Corr ( ACP
, ACP
)   0.49
B
sensitivity in 1 year
dir
mix
 ( ACP
)   ( ACP
)  0.04
dir
mix
Corr ( ACP
, ACP
)0
@ s  0
BS  K K
M s  14 ps 1
γ
with Bd →ππ, Bs→KK
dir
( Bd0     )  f1 (d , ,  )
ACP
mix
( Bd0     )  f 2 (d , ,  , fd )
ACP
dir
( Bs0  K  K  )  f 3 (d ,  ,  )
ACP
mix
( Bs0  K  K  )  f 4 (d ,  ,  , f s )
ACP
d , (d’ ,’) parametrize P over T amplitude
ratio
 fd  2 from Bd J/ψ KS , fd  2γ
from Bs  J/ψϕ
 exact U-spin symmetry => d = d’ ;  = ’
 3 unknowns and 4 measurements
95% confidence region for d and 
1 year
2 years
3 years
4 years
σγ after 4 years:
2.2º (for  = ~60º)
Rare B decays
In the SM:
Excellent probe of indirect
effects of new physics!
• flavour changing neutral currents
only at loop level
• very small BR ~ 10 5 or smaller
BS     
, l+l-
9
SM : BR ~10
• observation of the decay
• measurement of its BR
LHCb : 2 fb-1
~ 33 signal events
~ 10 events background
σM = 38 MeV
CMS : 100 fb-1 (107s at 1034 cm-2s-1)
~ 26 signal events
6.4 events background
Rare B decays
Bd  K  



AFB (s)
s  ( p   p _ )
Forward-backward asymmetry
can be calculated in SM and other models
BTeV data compared to
Burdman et al calculation
A. Ali et al., Phys. Rev. D61
074024 (2000)
Conclusions
CP violation is a cool research topic!!
B factories established CP violation in the B sector and are making interesting
measurements;
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;
Exciting times: understanding the origin of
CP violation in the SM and beyond.