Flavour Physics with LHCb
“When Beauty Decays and Symmetries Break”
Seminar RuG
March 31, 2008
Marcel Merk
Nikhef and VU
Contents:
• CP violation with the CKM matrix
• Bs meson and “new physics”
• B-physics with the LHCb detector
31-3-2008
1
LHCb
CERN
ATLAS
CMS
ALICE
LHC: Search for physics beyond Standard Model
Atlas
CMS
LHCb
• Atlas/CMS: direct observation of new particles
• LHCb: observation of new particles in quantum loops
LHCb is aiming at search for
new physics
in CP violation and Rare Decays
31-3-2008
Focus of this talk
3
quarks
I
II
u
c
~3
1200
d
s
b
~7
120
4300
0.511
ne
~0
t
176300
106
nm
~0
LEP 1
4 neutrino’s
3 neutrino’s
2 neutrino’s
t
m
e
leptons
III
Cross section
Flavour physics with 3 generations of fermions
1777
nt
measurements
~0
Beam energy (GeV)
31-3-2008
Note:
In the Standard Model 3 generations of Dirac particles is the
minimum requirement to create a matter - antimatter asymmetry.
4
Quark flavour interactions
• Charged current interaction with quarks:
A  g weak Wm J m 
I


5
m
I
1


1




u
d
u, c, t
2
W
d 
J
I
 
I
gweak


u
,
c
,
t
;




d, s, b
u
d
s
b
 
• Quark mass eigenstates are not identical to interaction eigenstates:
J
M
u
. .

  u   u , c, t   . M u
. .

.

.
. 
m
†
;
 dM
. .

 d  . M d
. .

.  d 
 
.  s 
.   b 
• In terms of the mass eigenstates the weak interaction changes from:
J
31-3-2008
m
I


  u 1 1   5  m  dI
2
5
Quark flavour interactions
• Charged current interaction with quarks:
A  g weak Wm J m 
I


5
m
I
1


1




u
d
u, c, t
2
W
d 
J
I
 
I
gweak


u
,
c
,
t
;




d, s, b
u
d
s
b
 
• Quark mass eigenstates are not identical to interaction eigenstates:
J
M
u
. .

  u   u , c, t   . M u
. .

.

.
. 
m
†
;
 dM
. .

 d  . M d
. .

.  d 
 
.  s 
.   b 
• In terms of the mass eigenstates the weak interaction changes to:
J m    u 1 1   5   m VCKM  d
2
31-3-2008
VCKM  M u† M d
Cabibbo Kobayashi Maskawa
quark mixing matrix
6
The CKM Matrix VCKM
 Vud

V
 cd
V
 td
31-3-2008
Vus Vub 

Vcs Vcb 
Vts Vtb 
7
The CKM Matrix VCKM
 Vud

V
 cd
V
 td
Vus Vub 

Vcs Vcb 
Vts Vtb 
Typical B-meson decay diagram:
b
d
Vcb
c
d
The B-meson has a relatively
long lifetime of 1.5 ps
Related to mass hierarchy?
31-3-2008
8
The CKM Matrix VCKM
 Vud

V
 cd
V
 td
Vus Vub 

Vcs Vcb 
Vts Vtb 
Wolfenstein parametrization: VCKM
1 2

1

l
l

2

1 2

l
1 l

2
 3
2
A
l
1

r

i
h

A
l




31-3-2008

Al 3  r  ih  


Al 2


1


From unitarity (VCKM V†CKM=1) :
CKM has four free parameters:
3 real: l 0.22 , A ( 1), r
1 imaginary: ih
Particle → Antiparticle: Vij → Vij*
=> 1 CP Violating phase!
9
The CKM Matrix VCKM
 Vud

V
 cd
V
 td
Vus Vub 

Vcs Vcb 
Vts Vtb 
Wolfenstein parametrization: VCKM
1 2

1

l
l

2

1 2

l
1 l

2
i

 3
2
A
l
1

r

i
h

A
l




e
31-3-2008
e
Al
3
i

 r  ih  
Al 2
1






From unitarity (VCKM V†CKM=1) :
CKM has four free parameters:
3 real: l 0.22 , A ( 1), r
1 imaginary: ih
Particle → Antiparticle: Vij → Vij*
=> 1 CP Violating phase!
10
Unitarity Triangle: VCKM V†CKM = 1
 Vud Vus Vub 


V
V
V
cd
cs
cb 

V V V 
ts
tb 
 td
31-3-2008
Vud  V  Vcd  V  Vtd  V  0
*
ub
*
cb
*
tb
Vud  Vtd*  Vus  Vts*  Vub  Vtb*  0
11
Unitarity Triangle: VCKM V†CKM = 1
 Vud Vus Vub 


V
V
V
cd
cs
cb 

V V V 
ts
tb 
 td
Vud V  Vcd V  Vtd V  0
*
ub
*
Vud Vtd
r ,h   1  l2
Im
h
Unitarity triangle:
Individual CP violating phases
in CKM are not observable
The combinations ,, are
*
tb
*
*
 Vus Vts  Vub Vtb
0

2 r ,h 

VtdVtb*
VcdVcb*
VudVub*
VcdVcb*

0
31-3-2008
*
cb

r
Amount of CP violation is proportional to surface of the triangle
1 Re
12
Unitarity Triangle and B-physics
r ,h   1  l2 2r ,h 
Im
h
: Bd mixing phase
: Bs mixing phase
: weak decay phase
B 0   , rr , r ,.....

VtdVtb*
VcdVcb*
B 0  J /K S0 , .....
VudVub*
Vcd Vcb*

0

r
Bd  DK , DK
Bs  Ds K
Bd  D *
*
  2  
  2 
Precise determination
of parameters through
study of B-decays.
Im
1 Re
h
Vud* Vtd

Vub* Vtb
VcdVcb*
+

0
VcdVcb*
r
Vus* Vts / VcdVcb*
Bs0  J /  , .....

Re
Benchmark Example: Bs→Ds K
 Vud

 Vcd
 V ei 
 td
31-3-2008
Vus
Vcs
Vts

Vub e

Vcb 
Vtb 
i
14
Benchmark Example: Bs→Ds K
 Vud

 Vcd
 V ei 
 td
Vus
Vcs
Vts
• Decay amplitudes: particles:
Bs  Ds K   Ae  i
antiparticles:
B s  Ds K   Ae  i
• But how can we observe a CP asymmetry?


s
Prob Bs  D K

  Ae
 i 2


Vub e

Vcb 
Vtb 
i

s
 Prob B s  D K

  Ae
 i 2
• Decay probabilities are equal? No CP asymmetry??
31-3-2008
Make use of the fact that B mesons “mix”…..
15
B meson Mixing Diagrams
A neutral B-meson can oscillate into an anti B-meson before decaying:
u,c,t
b
Bd
W
d
* 2
 mt VtbVtd
cc :
 mc VcbVcd
c  t ,c t :
 mc mtVtbVtd *VcbVcd *  mc mt l 6
2
* 2
Bd
W
u,c,t
b
 mt 2l 6
tt :
2
d
 mc 2l 6
GF2 2
md  2 mwh B S0 (mt2 / mW2 )mBd | Vtd |2 BBd f B2d
6
2
Dominated by top quark mass:
Sept 28-29, 2005
 mt  1
mB  0.00002  
ps
2 
 GeV c 
16
B0B0 Mixing: ARGUS, 1987
Produce a bb bound state, (4S),
in e+e- collisions:
Integrated luminosity 1983-87: 103 pb-1
e+e-  (4S)  B0B0
and then observe:
B10  D1* m1n 1, D1*  D 0 1
0
D  K1 1
B20  D2* m2n 2 , D2*  D  0
D   K 2 2 2 ,  0  
~17% of B0 and B0 mesons
oscillate before they decay
m ~ 0.5/ps, tB ~ 1.5 ps
First sign of a really large mtop!
Sept 28-29, 2005
17
Bd vs Bs mixing
The top quark and its interactions can be studied without producing it directly!
t
b
Bd
W
d
d
t
Bd mixing
B d → Bd
B d → Bd
31-3-2008
Bd
W
b
t
b
Bs
W
s
d
Bs
W
t
s
Bs mixing
Bs mixing
Bs → Bs
Bs → Bs
18
The CP violating decay: Bs→Ds K
Due to mixing possibility the decay Bs→Ds K can occur in two quantum amplitudes:
a1. Directly:
Coupling constant with
CP odd phase 
a2. Via mixing:
In addition, mixing and gluon interactions add a non-CP violating phase “d” between a1 and a2
31-3-2008
How do the phase differences between the amplitudes lead to an
observable CP violation effect…?
19
Observing CP violation
Compare the |amplitude| of the B decay versus that of anti-B decay;
 is the CP odd phase , d is a CP even phase
BDs− K+
BDs+ K−
A=a1+a2
A=a1+a2
A
+
a2
a1
d
-
A
a1
d
a2
|A||A|  Only if both  and d are not 0
Note for completeness: since the CP even phase depends on the mixing
the CP violation effect becomes decay time dependent
Sept 28-29, 2005
20
Double slit experiment with quantum waves
DsBs
31-3-2008
K
LHCb is a completely analogous
interference experiment using
B-mesons…
21
A Quantum Interference B-experiment
pp at LHCb:
100 kHz bb
“slit A”:

B  Ds K

Measure decay time
DsBs
Decay time
K
“slit B”:
6-sept-2007
B  B  Ds  K 
Nikhef-evaluation
22
CP Violation: matter – antimatter asymmetry
Bs  Ds K
Bs  Ds  K 
An interference pattern:
Ds
Bs
Decay time
Bs  Bs  Ds  K 
Bs  Ds K 
K
 Decay time
6-sept-2007
Nikhef-evaluation
23
CP Violation: matter – antimatter asymmetry
Bs  Ds K
Bs  Ds  K 
Ds
Matter
Bs
CP-mirror:
Antimatter
An interference pattern:
Decay time
Bs  Bs  Ds  K 
K
Bs  Ds K 
B s  Ds K 
Bs  Ds  K 
Ds+
Bs
Decay time
K
Bs  Bs  Ds  K 
6-sept-2007
Observation of CP Violation is a consequence
of quantum interference!!
Nikhef-evaluation
 Decay time
Difference between
curves is proportional
to the phase 
24
Searching for new virtual particles
Bs  J / 
Standard Model
Standard
Model
J/
Bs

 Decay time
6-sept-2007
Nikhef-evaluation
25
Searching for new virtual particles
Bs  J ΔB=2
/ B → B → D π
s
s
*μ μ
ΔB=1 Tiny
ΔB=1 Bs→μ μ
B0→Kweak
phase in couplings!
s
Bs→ Bs→ J/ψφ
SM: Bs
Standard
Model
b
W
t
s
t
b
b̃
s̃
s
New
g
B
g̃
̃
Physics: s
s Bs→ sB
b̃ Dsπ b
̃ xs→
ΔB=2
Bs→ Bs→ J/ψφ
SM:
Bs
b
W
t
s
NewNew
B
Physics: s
Physics
b
s
Bs
B0
W
t
b̃
g̃
s̃
x
x
s
b
s̃
g̃
b̃
s
b
d
b
s
W
t
x
b
Bs
W
s
Bs
B0
J/b
d
Bs
g̃
s
*x
Bs
B0

b
b
d
t
K*
μ
μ
g̃
b̃
K*
μ
μ
s
W
d
s
Bs
μ
ΔB=1 B0→K
b̃ μ sμ̃
B0
K*
μ
x
s
s̃
K*
μ
μ
b
s
Bs
t
W
s̃
g̃
x
b
b̃ μ
ΔB=1 Bs→μ
s
Bs
b
t
W
s̃

Bs Decay gtime
̃
s
b
x
b̃
Possible weak phase in couplings!
6-sept-2007
Nikhef-evaluation
26
Searching for new virtual particles
Bs  J ΔB=2
/ B → B → D π
s
s
ΔB=1 B0→K*μ μ
s
Bs→ Bs→ J/ψφ
SM: Bs
Standard
Model
b
W
t
s
W
t
s
b
Bs
B0
Bs
B0
Bs
B0
x
Bs
b̃
s̃
s
b
New
g
B
g̃
̃
Physics: s
s Bs→ sB
b̃ Dsπ b
̃ xs→
ΔB=2
Bs→ Bs→ J/ψφ
SM:
Bs
b
W
t
s
NewNew
B
Physics: s
Physics
6-sept-2007
b
s
W
t
b̃
g̃
s̃
x
x
s
b
s̃
g̃
b̃
s
b
Bs
b
J/b
d
d
ΔB=1 Bs→μ μ
s
*
t
Search
forsa CP K
asymmetry:
W
Bs
W
μ
B->J/b
t
μ B->J/
Bs  J s/
g̃
s
x
ΔB=1 B0→K
b̃ *μ sμ̃
B0

b
b
d
s
W
t
d
K*
μ
μ
g̃
b̃
s̃
K* B
g
̃
s
μ B  Jb/ x
s ΔB=1 B →μ
̃
s b μ
μ
x
s
s̃
K*
μ
μ
Mission:
To search for new particles and interactions that affect the
observed matter-antimatter asymmetry in Nature, by making
precision measurementsNikhef-evaluation
of B-meson decays.
s
Bs
b
t
W
s̃

B Decay gtime
̃
s
s
b
x
b̃
27
ΔB=2
Bs→ Bs→ J/ψφ
First sign of New Physics
in
B
mixing?
s
d
b
t
s
B
Bs→ Bs→ Dsπ
ΔB=2
iSM
Bs→ Bs→ J/ψφ
SM: BBs 0→K*μ μ W
ΔB=1
i

Ae
M:
Bs
b
s
ew
B
hysics: s
b
s
W
t
W
t
x
̃
bS.M.
s̃
g̃
g̃
s̃ x b̃
s
b
s
b
d
New b
+ Bs
b
W
t s
d
g̃
Bs
B0
Bs
B0
Physics:
SM box has (to a good approx.)
no weak phase: SM = 0
31-3-2008
s
Be
b
b̃
x
NP
0
W

t
b
b
Bs
ΔB=1
Bs→μ
iμ
Ce
s
x
b̃
g̃ s
s̃ x
s̃
s 0
s̃ K*s
BW
Bs Bs
g̃
b
b̃ μ b
μ
s
*
N.P.
K
g̃
Bs
s
μ
b
μ
t d
b
s̃
x
b̃
W
t
μ
g̃
x
b̃ μ s̃
μ
μ
28
ΔB=2
Bs→ Bs→ J/ψφ
First sign of New Physics
in
B
mixing?
s
d
b
t
s
B
Bs→ Bs→ Dsπ
ΔB=2
iSM
Bs→ Bs→ J/ψφ
SM: BBs 0→K*μ μ W
ΔB=1
i

Ae
M:
Bs
b
s
ew
B
hysics: s
b
s
W
t
W
t
x
s
b
̃
bS.M.
s̃
g̃
g̃
s̃ x b̃
s
b
d
New b
+ Bs
b
W
t s
d
g̃
Bs
B0
Bs
B0
Physics:
SM box has (to a good approx.)
no weak phase: SM = 0
UTfit collab.; March 5, 2008
Combining recent results of
CDF, D0 on
s
Be
Bs  J / 
with Babar, Belle results:
b
b̃
x
NP
0
W

t
b
b
Bs
ΔB=1
Bs→μ
iμ
Ce
s
x
b̃
g̃ s
s̃ x
s̃
s 0
s̃ K*s
BW
Bs Bs
g̃
b
b̃ μ b
μ
s
*
N.P.
K
g̃
Bs
s
μ
b
μ
t d
b
s̃
x
b̃
W
t
μ
g̃
x
b̃ μ s̃
μ
μ
March 5,
2008
3.7 s
deviation
From 0
If S ≠ 0 then new physics outside
the CKM is present…
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29
The LHCb experiment
LHCb experiment:
700 physicists
50 institutes
15 countries
LHCb
ATLAS
q
CMS
b
q
b
ALICE
LHCb experiment in the cavern
Shielding wall
(against radiation)
Offset interaction point (to make
best use of existing cavern)
Electronics
+ CPU farm
Detectors can be moved
away from beam-line
for access
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31
b-b detection in LHCb
Background Supression
Flavour tagging
Decay time measurement
LHCb event rate: 40 MHz
1 in 160 is a b-bbar event
1012 b-bbar events per year
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• vertices and momenta reconstruction
• effective particle identification (π, К, μ, е, γ)
• triggers
32
GEANT MC simulation
Used to optimise the experiment and to test measurement sensitivities
33
A walk through the LHCb detector
~ 200 mrad
~ 300 mrad
(horizontal)
p
p
10 mrad

Inner acceptance ~15 mrad (10 mrad conical beryllium beampipe)
34
LHCb Tracking: vertex region

Vertex locator around the interaction region
Silicon strip detector with ~ 30 mm impact-parameter resolution
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35
LHCb tracking: vertex region
Pile-Up
Interaction
Stations
Region
s=5.3 cm
y
y

x
x
36
LHCb tracking: momentum measurement
Tracking: Mass resolution for background suppression in eg. DsK

B [T]
y
Bfield: B dl = 4 Tm
0.15 Tm
37
LHCb tracking: momentum measurement
All tracking stations have four layers:
0,-5,+5,0 degree stereo angles.
Straw tubes
~65 m2
Silicon: ~1.41.2 m2

38
LHCb tracking: momentum measurement
Red = Measurements (hits)
Blue = Reconstructed tracks
Eff = 94%
(p > 10 GeV)
~1.41.2 m2

• Typical Momentum resolution dp/p ~ 0.4%
• Typical Impact Parameter resolution sIP ~ 40 mm
39
LHCb Hadron Identification: RICH
RICH1: 5 cm aerogel n=1.03
RICH2:
100 m3 CF4 n=1.0005
4 m3 C4F10 n=1.0014
Cerenkov light emission angle
3 radiators to cover
full momentum range:
Aerogel
C4F10
CF4

RICH: K/ separation e.g. to distinguish Ds and DsK events.
40
LHCb calorimeters
e
h

Calorimeter system :
• Identify electrons, hadrons, neutrals
• Level 0 trigger: high electron and hadron Et (e.g. Ds K events)
41
LHCb muon detection
m

Muon system:
• Identify muons
• Level0 trigger: High Pt muons
42
View of LHCb in Cavern
Muon
Muondet
det
Calo’s
Calo’s
RICH-2
RICH-2
OT
OT
Magnet
RICH-1
VELO
31-3-2008
It’s full!
Installation of major structures is essentially complete
43
Hope to soon see the first events from…
31-3-2008
44
Display of LHCb
simulated event
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45
Prepare Bs→DsK Reconstruction…
p
47 mm
144 mm
,K
K
Bs
K
Ds
d

440 mm
Invariant Mass
• Trigger :
– ET Calorimeters, Vertex topology
• Flavour Tag:
– Lepton-ID, Kaon-ID
• Background suppression:
– Mass resolution, K/ ID
• Decay time:
– Decay distance measurement
– Momentum measurement
46
… to see time dependent CP violation signal!
The amplitude of these
“wiggles“ are
proportional to the
imaginary part of the
CKM phase gamma!
5 years data:
Bs→ Ds-
Bs→ Ds-K+
 Vud

 Vcd
 V e  i
 td
31-3-2008
Decay time (ps) →
Vus
Vcs
Vts

Vub e

Vcb 
Vtb 
i
47
Conclusion: after 5 years of LHCb…
CKM Unitarity Triangle in 2007:
31-3-2008
Expected errors after 5 years
(10 fb-1) of LHCb:
To make this plot only Standard
Model physics is assumed.
48
Conclusion and Outlook LHCb
The collaboration has organised analysis groups
and identified “hot topics”:
• CP Violation
• Measure the Bs mixing phase (Bs→J/  )
• Measure the CKM angle gamma via tree method (Bs → DsK)
• Measure the CKM angle gamma via penguin loops (B(s) → hh  )
• Rare Decays
• Measure Branching Ratio Bs → m+ m • Measure angular distribution B0 → K* m+ m • Measure radiative penguins decays: b → s  B → Xs  
• Other Flavour Physics
• Angle beta, B-oscillations, lifetimes, D-physics, Higgs,…?
• Atlas and CMS look for new physics via direct production of particles
• LHCb tries to study it via the (possibly complex) couplings in B decay loop diagrams
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49
Summary of Signal Efficiencies
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50
Thank you for the attention.
31-3-2008
51
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52
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53
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54
Research Questions
• Is flavour physics fully described by the CKM mechanism
• Is CP violation in CKM sufficient to describe baryogenesis
• Many models beyond the SM include a rich flavour physics
structure
• Are the penguin, box and tree diagrams governed by the
same physics?
• Search for CP violation where SM predicts none
• Measure Branching Ratio for processes which are forbidden
in SM
• For the hypothesis that neutrinos are not massless the
lepton system has a similar flavour strcture VCKM → VPMNS
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55
Bd meson vs Bs meson
x
m
1

m
x

1
These B bbar oscillations allow for a beautiful CP experiment
31-3-2008
56
Result of track finding
On average:
26 long tracks
11 upstream tracks
4 downstream tracks
5 T tracks
26 VELO tracks
Typical event display:
Red = measurements (hits)
Blue = all reconstructed tracks
T1 T2
T3
TT
VELO
2050 hits assigned to a long track:
98.7% correctly assigned
Efficiency vs p :
Ghost rate vs pT :
Ghost rate = 3%
(for pT > 0.5 GeV)
Eff = 94%
(p > 10 GeV)
Ghosts:
Negligible effect on
b decay reconstruction
57
Experimental Resolution
Momentum resolution
Impact parameter resolution
sIP=
14m + 35 m/pT
dp/p =
0.35% – 0.55%
p spectrum B tracks
1/pT spectrum B tracks
58
Particle ID
RICH 1
RICH 2
e (K->K) = 88%
e (p->K) = 3%
Example:
Bs->Dsh
Bs
Prim vtx
,K
Ds
K
K

59
Event in the Simulation
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60
Zoom in on the Velo detector
31-3-2008
61
4. Expected results
• Example of an early physics measurement that is expected from
LHCb:
Measurement of Bs–Bs oscillations
Use channel Bs  Ds+
• Plot made for one year of data
 80,000 selected events
for ms = 20 ps-1 (SM preferred)
Proper time distribution for events
produced as Bs (rather than Bs)
• Need to take care of flavour
tagging, proper-time resolution,
background rejection and
acceptance correction
• Can measure frequency accurately
cf recent result ms = 17.8 ± 0.1 ps-1 [CDF]
Next step: measure the phase of the oscillation, using Bs  J/ 
decays (Bs counterpart of B0  J/KS), cleanly predicted in the SM:
s = 0.04
Roger Forty
Physics challenges of the LHC (III)
62
Penguin decays
• These are another category of decays
involving loop diagrams
New particles might appear in those loops
• Some indication from the B factory
experiments that their results for penguin
decays do not agree with expectations
 might be a hint of new physics?
Experiment
Theory
• LHCb should reach
a precision of ±0.04
on the asymmetry
of Bs  
Roger Forty
Physics challenges of the LHC (III)
63
Rare decays
• Profit from the enormous statistics
to search for very rare decays such as Bs  mm
Branching ratio ~ 3 10-9 in the Standard Model
• BR can be strongly enhanced in SUSY
[G. Kane et al, hep-ph/0310042]
• LHCb can reach the SM prediction
in a few years
BR (x10-9)
SUSY models
LHCb
5s
SM prediction
3s
Integrated Luminosity (fb-1)
Roger Forty
Physics challenges of the LHC (III)
64
Topologies in B decays
Trees
q1
b
q2
W−
Bq
d, s
Penguins
W–
b
W−
W−
u, c, t
q
b
u, c, t
d (s) b
u,c,t
l+
Z, γ
g
l−
Bq
Viq
q
u,c,t
b
W−
W+
u, c, t
q
Viq
Bq
b
V*ib
q
q
Boxes
V*ib
d (s)
Search for NP comparing observables
measured in tree and loop topologies
(tree+box) in B J/ Ks
(tree) in many channels
(tree+box) in Bs J/ 
(peng+tree) in Brr,r,
(peng+box) in B Ks
(peng+box) in Bs 
New heavy particles, which may contribute to d- and s- penguins,
could lead to some phase shifts in all three angles:
d(NP) = (peng+tree) - (tree)
d(NP) = (BKs) - (BJ/Ks)
d(NP) = (Bs) - (BsJ/)
≠ 0
B → K* μμ
?
A very important property is
forward-backward asymmetry..
..and position of its zero,
which is robust in SM:
AFB(s), fast MC, 2 fb–1
2C7eff
s0   eff
C9 ( s0 )
s = (mmm)2 [GeV2]