Physics@FOM Veldhoven 2009.
Focus Session F01: The start-up of the LHC at CERN
Physics with bottom quarks:
The LHCb experiment
Marcel Merk
Nikhef and the Free University
Jan 20, 2009
Contents:
• Physics with b-quarks
 CP Violation
• The LHCb Experiment
LHCb @ LHC
LHCb
CMS
CERN
ATLAS
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
I
II
III
u
c
t
~3
1200
d
s
b
~7
120
4300
176300
Cross section
quarks
Flavour physics with 3 generations of fermions
LEP 1
4 neutrino’s
3 neutrino’s
2 neutrino’s
(masses in MeV)
leptons
0.511
ne
~0
t
m
e
106
nm
~0
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 (CP violation).
4
Interactions between Quarks
Cabibbo described “V-A” quark interactions
with flavour changing charged currents:
 quark mixing
A  gweak Wm J m 
J m    u 1 1   5   m  d ,s
2
u
W
gweak
Nicola
Cabibbo
Jμ+
d,s
Interactions between Quarks
Cabibbo described “V-A” quark interactions
with flavour changing charged currents:
 quark mixing
A  gweak Wm J m 
J m    u 1 1   5   m VCKM  d
2
u,c,t
W
gweak
Jμ+
d,s,b
Matter →Antimatter
Nicola
Cabibbo
Makoto
Kobayashi
Toshihide
Maskawa
Kobayashi and Maskawa predicted in
1972 the 3rd quark generation to explain
CP-Violation within the Standard Model
 Nobel Prize 2008 (shared with Nambu)
gweak→g*weak
9 Coupling constants:
gweak → g ∙ VCKM
d
u
c
t
31-3-2008
 Vud

V
 cd
V
 td
The CKM Matrix VCKM
s
b
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 (
b
d
Vcb W
) decay diagram:
u
d
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
Benchmark Example: Bs→Ds K
 Vud

 Vcd
 V ei 
 td
31-3-2008
Vus
Vcs
Vts

Vub e

Vcb 
Vtb 
i
11
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”…..
12
The CP violating decay: Bs→Ds K
A B-meson can oscillate into an anti-B:
Due to mixing possibility the decay Bs→Ds–K+
can occur in two quantum amplitudes:
b
Bs
W
s
t
s
Bs
W
t
b
A1. Via mixing:
A2. Directly:
31-3-2008
Coupling constant with
CP odd phase 
It is straighforward to show that the interference term of the two
amplitudes have an opposite sign for the particle and antiparticle cases.
 The observable CP violation effect.
13
Double slit experiment with quantum waves
DsBs
31-3-2008
K
LHCb is a completely analogous
interference experiment using
B-mesons…
14
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
15
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
16
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 CKM phase 
17
Searching for new virtual particles
Bs  J / f
Standard Model
Standard
Model
J/
Bs
f
 Decay time
6-sept-2007
Nikhef-evaluation
18
Searching for new virtual particles
Bs  J ΔB=2
/ fB → B → D π
s
s
*μ μ
ΔB=1 Tiny
ΔB=1 Bs→μ μ
B0→KCP-odd
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
f
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 CP-odd phase in couplings!
6-sept-2007
Nikhef-evaluation
19
Searching for new virtual particles
Bs  J ΔB=2
/ fB → 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/fb
t
μ B->J/f
Bs  J s/f
g̃
s
x
ΔB=1 B0→K
b̃ *μ sμ̃
B0
f
b
b
d
s
W
t
d
K*
μ
μ
g̃
b̃
s̃
K* B
g
̃
s
μ B  Jb/f 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
20
LHCb @ LHC
√s = 14 TeV
LHCb: L=2-5 x 1032 cm-2 s-1
sbb = 500 mb
sinel / s bb = 160
=> 1 “year” = 2 fb-1
b
b
b
b
LHCb
CERN
ATLAS
CMS
ALICE
A Large Hadron Collider Beauty Experiment for Precision
Measurements of CP-Violation and Rare Decays

s
Bs  D K
Primary vertex
b-b detection in LHCb

Bs
K
Ds
btag
~1 cm
LHCb event rate: 40 MHz
1 in 160 is a b-bbar event
1012 b-bbar events per year
31-3-2008
K
K

Background Supression
Flavour tagging
Decay time measurement
• vertices and momenta reconstruction
• effective particle identification (π, К, μ, е, γ)
• triggers
22
GEANT MC simulation
Used to optimise the experiment and to test measurement sensitivities
23
A walk through the LHCb detector
~ 200 mrad
~ 300 mrad
(horizontal)
p
p
10 mrad

24
B-Vertex Measurement
Example: Bs → Ds K
144 mm
47 mm
K
K

Bs
Ds
Primary vertex
d
st) ~40 fs
K
440 mm

Decay time resolution = 40 fs
Vertex Locator (Velo)
Silicon strip detector with
5 mm hit resolution
31-3-2008
Vertexing:
• Impact parameter trigger
• Decay distance (time) measurement
25
Momentum and Mass measurement
Momentum meas.: Mass resolution for
background suppression

26
Momentum and Mass measurement
Momentum meas.: Mass resolution for
background suppression
Mass resolution
s ~14 MeV
, K
Bs
Ds
Primary vertex

Bs→ Ds K
Bs →Ds 
K
K

bt
27
Particle Identification
RICH: K/ identification using Cherenkov light emission angle

RICH1: 5 cm aerogel n=1.03
RICH2:
100 m3 CF4 n=1.0005
4 m3 C4F10 n=1.0014
28
Particle Identification
RICH: K/ identification; eg. distinguish Ds and DsK events.
Cerenkov light emission angle
Bs → Ds K
,K
Bs
Ds
Primary vertex

K
K

KK : 97.29 ± 0.06%
K : 5.15 ± 0.02%
bt
RICH1: 5 cm aerogel n=1.03
RICH2:
100 m3 CF4 n=1.0005
4 m3 C4F10 n=1.0014
29
LHCb calorimeters
e
h

Calorimeter system :
• Identify electrons, hadrons, neutrals
• Level 0 trigger: high ET electron and hadron Primary vertex
K
Bs
Ds
bt
K
K

30
LHCb muon detection
m

Bs
Muon system:
• Level 0 trigger: High Pt muons
• Flavour tagging: eD2 = e (1-2w)2  6%
K
Ds
Primary vertex
btag
K
K

31
The LHCb Detector
Muon det
Muon det
Calo’s
Calo’s
RICH-2
RICH-2
OT
OT+IT
Magnet
Magnet
RICH-1
RICH-1
VELO
VELO
31-3-2008
Installation of detector is completed
32
We have seen the first events from the LHC
31-3-2008
33
First LHC Tracks in the Velo
• linked hits
• not linked hits
 Talk of Ann Van Lysebetten
15-12-2008
34
Cosmic tracks in LHCb
• Detector alignment
• T0 calibration
• RT-relation
•…
15-12-2008
35
Events from the LHC beam injection
15-12-2008
36
In Summary
Detect produced particles:
Reconstruct and select B-events:
47 mm
p
Bs
144 mm
,K
Ds
d
440 mm
K
K

Decay time spectra:
Extract CP-Violation parameters:
 Vud

 Vcd
 V e  i
 td
Vus
Vcs
Vts
Vub e  

Vcb 
Vtb 
i
MC 5 years data:
BsDs-K+
Decay time (ps)
Conclusion and Outlook
Complementary research approach:
• Atlas and CMS look for new physics via direct production of particles
• LHCb studies new physics via the couplings in B-decay loop effects
In LHCb many different B-decay studies are prepared
to examine CP violation and rare decays.
The experiment is ready for data in 2009!
31-3-2008
38
15-12-2008
39
Backup Slides
Summary of Signal Efficiencies
31-3-2008
41
Conclusions
LHCb is a heavy flavour precision experiment searching
for New Physics in CP Violation and Rare Decays
A program to do this has been developed and the methods,
including calibrations and systematic studies, are being worked out..
CP Violation: 2 fb-1 (1 year)*
•  from trees: 5o - 10o
•  from penguins: 10o
• Bs mixing phase: 0.023
• seff from penguins: 0.11
Rare Decays: 2 fb-1 (1 year)*
• BsK*mm s0 : 0.5 GeV2
• Bs  Adir , Amix : 0.11
AD
: 0.22
• Bsmm BR.: 6 x 10-9 at 5s
We appreciate the collaboration with the theory community
to continue developing new strategies.
We are excitingly looking forward to the data from the LHC.
* Expect uncertainty to scale statistically to 10 fb-1. Beyond: see Jim Libby’s talk on Upgrade
42
LHCb Detector
RICH-2 PID
MUON
ECAL
HCAL
RICH-1 PID
vertexing
Tracking (momentum)
Display of LHCb
simulated event
31-3-2008
44
ΔB=2
Bs→ Bs→ J/ψφ
First sign of New Physics
in
B
mixing?
d
s
b
t
s
B
Bs→ Bs→ Dsπ
ΔB=2
ifSM
Bs→ Bs→ J/ψφ
SM: BBs 0→K*μ μ W
ΔB=1
if

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: fSM = 0
31-3-2008
s
Be
b
b̃
x
NP
0
W

t
b
b
Bs
ΔB=1
Bs→μ
ifμ
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
45
ΔB=2
Bs→ Bs→ J/ψφ
First sign of New Physics
in
B
mixing?
d
s
b
t
s
B
Bs→ Bs→ Dsπ
ΔB=2
ifSM
Bs→ Bs→ J/ψφ
SM: BBs 0→K*μ μ W
ΔB=1
if

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: fSM = 0
UTfit collab.; March 5, 2008
Combining recent results of
CDF, D0 on
s
Be
Bs  J / f
with Babar, Belle results:
b
b̃
x
NP
0
W

t
b
b
Bs
ΔB=1
Bs→μ
ifμ
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 fS ≠ 0 then new physics outside
the CKM is present…
31-3-2008
46
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
47
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
48
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
Dmd  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
DmB  0.00002  
ps
2 
 GeV c 
49
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
Dm ~ 0.5/ps, tB ~ 1.5 ps
First sign of a really large mtop!
Sept 28-29, 2005
50
Bd vs Bs mixing
Due to the different values of CKM couplings the Bs mixes faster then the Bd
t
b
Bd
W
d
d
Bd
W
t
Bd mixing
5.1 x 1011 Hz
B d → Bd
B d → Bd
b
t
b
Bs
W
s
s
Bs
W
t
b
Bs mixing
Bs mixing
1.8 x 1013 Hz
Bs → Bs
Bs → Bs
Both the Bd and Bs mixing have been precisely measured in experiments
31-3-2008
51
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
52
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
53
LHCb trigger
40 MHz
L0, HLT and L0×HLT efficiency
Detector
L0: high pT (m, e, , h) [hardware, 4 ms]
1 MHz
HLT: high IP, high pT tracks [software]
then full reconstruction of event
HLT
rate
Storage (event size ~ 50 kB)
Event type
200 Hz Exclusive B
candidates
Physics
B (core program)
600 Hz High mass dimuons
J/, bJ/X
(unbiased)
300 Hz D* candidates
Charm (mixing & CPV)
900 Hz Inclusive b (e.g.
bm)
B (data mining)
Efficiency 
2 kHz
Note: decay time dependent
efficiency: eg. Bs → Ds K
K
Bs
Primary vertex
Ds
bt
K
K

Proper time [ps]  54
Flavour Tagging
Efficiency e
Performance of flavour tagging:
Tagging power:
e D 2  e 1  2 w 
2
Bd
~50%
Bs
~50%
Wrong tag w Tagging power
33%
~6%
Measuring time dependent decays

Bs
Ds
Primary vertex
K
K

Measurement of Bs oscillations:
bt
Experimental Situation:
• Ideal measurement (no dilutions)
Bs->Ds–  (2 fb-1)
56
Measuring time dependent decays

Bs
Ds
Primary vertex
K
K

Measurement of Bs oscillations:
bt
Experimental Situation:
Ideal measurement (no dilutions)
+ Realistic flavour tagging dilution
Bs->Ds–  (2 fb-1)
57
Measuring time dependent decays

Bs
Ds
Primary vertex
K
K

Measurement of Bs oscillations:
bt
Experimental Situation:
Ideal measurement (no dilutions)
+ Realistic flavour tagging dilution
+ Realistic decay time resolution
Bs->Ds–  (2 fb-1)
58
Measuring time dependent decays

Bs
Ds
Primary vertex
K
K

Measurement of Bs oscillations:
bt
Experimental Situation:
Ideal measurement (no dilutions)
+ Realistic flavour tagging
+ Realistic decay time resolution
+ Background events
Bs->Ds–  (2 fb-1)
59
Measuring time dependent decays

Bs
Ds
Primary vertex
K
K

Measurement of Bs oscillations:
bt
Experimental Situation:
Ideal measurement (no dilutions)
+ Realistic flavour tagging dilution
+ Realistic decay time resolution
+ Background events
+ Trigger and selection acceptance
Bs->Ds–  (2 fb-1)
Two equally important aims for the experiment:
• Limit the dilutions: good resolution, tagging etc.
• Precise knowledge of dilutions
60
BsDsK 5 years data
BsDs-K+
BsDs+K-
BsbDs-K+
BsbDs+K-
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.
62
Conclusion and Outlook LHCb
The collaboration has organised analysis groups
and identified “hot topics”:
• CP Violation
• Measure the Bs mixing phase (Bs→J/ f )
• 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
31-3-2008
63
In the mean time:
Detector Commissioning and Analysis Preparation
47 mm
p
Bs
144 mm
,K
Ds
d
440 mm
K
K

Monte Carlo study for 5 years data:
BsDs-K+
 Vud

 Vcd
 V e  i
 td
Vus
Vcs
Vts

Vub e

Vcb 
Vtb 
i