Transcript No Slide Title

CP violation in B decays:
prospects for LHCb
Werner Ruckstuhl, NIKHEF, 3 July 1998
CP Violation
Aim: Understand sources of CP Violation
Theory:
• Standard Model: CP implemented by complex phase
in CKM matrix
Natural: no reason for CKM matrix to be real
• Beyond Standard Model: many extensions predict
new interactions which produce CP
Natural: Standard Model is not complete
Combination ???
Measurement:
• Precise measurement of many complementary channels
with reliable Standard Model prediction:
• No (small) QCD corrections due to final state
interaction
• CP in oscillations and decays (and interferences)
• Different combinations of CKM elements
• Channels with large and small (no) CP within Standard
Model
“Measure all angles of CKM matrix”
3 July 1998
Hyperons98, Genoa
Werner Ruckstuhl
Detector Requirements
Efficient trigger and reconstruction of many
different channels, both hadronic and
leptonic final states
Robust and flexible trigger
• high pT leptons and hadrons
• secondary verteces
Good proper time resoution
• CP asymmetries in fast oscillating Bs
• reduce background
Good mass resolution
• reduce background
Particle Identification
• tagging (muons, electrons and kaons)
• reduce background (/K separation in RICH)
3 July 1998
Hyperons98, Genoa
Werner Ruckstuhl
Detector Acceptance
Single arm forward spectrometer:
Easy access to all detector components for
maintenance and fexible for upgrades
3 July 1998
Hyperons98, Genoa
Werner Ruckstuhl
LHCb Detector
Tracking System:
Vertex Detector: Silicon Microstrip
Main: MSGC or MCSC (inner) + Honeycombs (outer)
Muon: Cathode Pads and Multigap Resistive Pads
RICH system (3 radiators):
 - K separation at >3 for momenta between
1 GeV/c (K tag) and 150 GeV/c (Bd + -)
Calorimeters:
Preshower + ECAL (Shashlik) + HCAL(Scintillating-tile)
Average Luminosity: 2 x 10-32 cm-2s-1
3 July 1998
Hyperons98, Genoa
Werner Ruckstuhl
Vertex Detector
Precise Vertex Determination:
• Precise Detector: Silicon Microstrip Counters
• First point of measurement close to decay point
• No material between measurement and decay vertex
Install silicon counters in
LHC vacuum, as close as
possible to the beams
(10 mm), limited by
radiation damage.
For injection of beam move
silicon out by 3 cm.
In LHCb Vertex information is used in Level 1 Trigger:
r- geometry, which also makes occupancy per strip more
homogenous.
3 July 1998
Hyperons98, Genoa
Werner Ruckstuhl
Main Tracking Station
Modular Design to keep all cell occupancies < 10%
Multilayer with y u v y orientations (5 stereo)
Inner Tracker:
Size 40 x 60 cm2
High granularity
MSGC or MCSC
Outer Tracker:
Strawtube-like drift chambers (Honeycombs)
Cell radius: 5mm (Module type I and II) and 8 mm (type III)
Resolution: < 200 m
Perfomance:
p/p = 0.3 %, constant between 5 GeV/c and 200 GeV/c
Mass resolution:
mB = 15.2 MeV/c2 in Bd +mD = 4.2 MeV/c2 in DS K+K-- from BS decays
3 July 1998
Hyperons98, Genoa
Werner Ruckstuhl
RICH Detectors
Cover full kinematic range: three radiators
Aerogel
C4F10 CF4
Pthres() [GeV/c]
0.6
2.6
4.4
Pthres(K) [GeV/c]
2.0
9.3
15.6
3 July 1998
Hyperons98, Genoa
Werner Ruckstuhl
RICH Detectors
pmin ~ 1 GeV/c
K tag
pmax~ 150 GeV/c
two-body B decays
T itle:
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-K separation (in ) vs. Momentum
(full pattern recognition)
3 July 1998
Hyperons98, Genoa
Werner Ruckstuhl
RICH Beam Test
T itle:
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• Beam Test RICH 1 prototype
(1/4 scale)
• Resolution and Nb. Photon as expected
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3 July 1998
Hyperons98, Genoa
Werner Ruckstuhl
RICH Simulation
• Full GEANT simulation of tracks
• Details Simulation of Cherenkov photons
• Full pattern recognition of rings
3 July 1998
Hyperons98, Genoa
Werner Ruckstuhl
CKM Triangles
3 July 1998
Hyperons98, Genoa
Werner Ruckstuhl
LHCb Physics Menu
T itle:
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Creator:
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:
Bd  J/ KS
:
Bd + Bd D*
Bd 
+: BS  DSK
:
Bd DK*
:
Bs  J/ 
Non CP physics:
• rare B and  decays
• D meson oscillations
• BC decays
• …….
3 July 1998
Hyperons98, Genoa
Werner Ruckstuhl
Angle : Bd  J/ KS
“Golden” Decay Channel
Bd  J/ KS
 +- + -
Ideal to measure complex phase in CKM Matrix:
• solid Standard Model prediction
• large predicted asymmetry
• reasonable branching ratio
• easy signature
Aim of LHCb:
Very precise measurement on the long term:
Systematics, checks with control channels
CP reach in one year (55.6k tagged events):

0o
(sin 2) 0.017
20o
0.014
30o
0.011
When sin(2) and xS are measured (with Bd  J/ KS
and B S  DS) , the CKM matrix is fully determined:
Further measurements check Standard Model predictions
3 July 1998
Hyperons98, Genoa
Werner Ruckstuhl
Angle : Bd + Two contributions to CP:
T from oscillations, as in BdKs
P from penguin, as in Bd K+Experiment (CLEO): limit for BR(Bd +-) decreases:
• less statistics (LHC)
• more background from Bd K+- and Bs K+- (RICH)
• penguin contribution more important
 Theoretical uncertainty is large
• Measure CP in Bd K+-:
• Information about penguin contribution
• measure asymmetry in experimental background
CP reach in one year:
6.9 k tagged events with ~ 6%
background
(sin 2)  0.06 (depends on penguin)
3 July 1998
Hyperons98, Genoa
Werner Ruckstuhl
Angle 
Branching ratios:
Bd + Bd K+ Bs K+K - Bs K+ -
Other channels for  measurement under
study (theoretically clean):
Bd : involves 0 detection
Bd D*: Same method as BS  DSK, but
small || expected
3 July 1998
Hyperons98, Genoa
Werner Ruckstuhl
Angle  and 
 from BS  DSK:
Theory: Only tree diagrams involved: clean prediction
 Best candidate for precise measurement of a second
CKM angle
Experiment: not easy to measure
 from BS  J/  :
same decay diagram as “Golden” Decay Bd  J/KS
very small CP violation in SM
 sensitive to new physics
Bonus: Polarization in VV decay, used to separate
CP eigenstates: good measurement of S
BS  DS:
similar to BS  DSK, determination of mS and S
3 July 1998
Hyperons98, Genoa
Werner Ruckstuhl
Bs Decays
Detector Requirements:
• Excellent tracking to reconstruct the four particle final
states with high efficiency and low combinatorial
background (good mass and vertex resolution
• Good time resolution to resolve fast Bs Oscillations
• Excellent K identification with RICH to suppress DS in
DSK (branching ratio factor 15 higher)
3 July 1998
Hyperons98, Genoa
Werner Ruckstuhl
Angle  and 
BS  DS:
120k reconstructed and tagged decays, oscillation
measurements at > 5 possible up to xs = 75
BS  J/  :
44k reconstructed and tagged decays,  measurements at
percent level possible down to / << 0.1, depends
on ratio of decay amplitudes into CP=+1 and CP=-1
state
BS  DSK:
2.4k reconstructed and tagged decays
Background: particle identification and mass resolution
3 July 1998
Hyperons98, Genoa
Werner Ruckstuhl
Angle 
Complementary measurent: measure 6 branching ratios
Check !
Selftagging: K* flavor tags B0 flavor, no extra
tagging required
CP reach in one year depends on value of
strong phase shift T2/T1:
3 July 1998
Hyperons98, Genoa
Werner Ruckstuhl
Summary
CP reach in one year:
Channel
(sin 2) = 0.01
Bd  J/ KS
(sin 2) = 0.06
Bd +-
( +) = 0.11-0.23 Bs  DsK
( )
= 0.07-0.31 Bd DK*
( )
= 0.02
Bs  J/ 
Events
56.0k
6.9k
K/
37.1k K/, t
300
44.0k
K/
t
LHCb experiment:
• optimized to profit from the high B production at
LHC for a rich and broad B physics program
• flexibility and high efficiency in trigger and
reconstruction
• good resolutions and particle identification
• control of systematics
3 July 1998
Hyperons98, Genoa
Werner Ruckstuhl