Diapositive 1

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Status and Physics prospect at LHCb
Éric Conte, on behalf of LHCb collaboration Labora
toire de Physique Corpusculaire de
Clermont-Ferrand
QCD08, 7-12 July 2008, Montpellier
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Detector design
Detector and Trigger are designed for B physics
studies _at_ LHC collider

• LHC characteristics
• vs 14 TeV, stotal 100mb,
  sinelastic 80mb
• Cross-section of bb production large
  uncertainty LHCb conventions s(pp?bb) 500
  µb (0.5 of the total cross section)
• bb production is sharply peaked
  forward-backward ? LHCb single-arm forward
  spectrometer 1.9lt?lt4.9

• LHCb limits luminosity to few 1032cm-2s-1
  instead of 1034cm-2s-1 by not focusing the beam
  as much as ATLAS and CMS
• ? maximizes probability of a single interaction
  per crossing
• 1012 bb pairs produced with 2 fb-1

Status and Physics prospect at LHCb
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LHCb detector elements
HCAL
M5
ECAL
M4
PS/SPD
5m
M3
M2
RICH2
Magnet
M1
T3
T2
T1
RICH1
TT
VELO
20m 15m
10m 5m
Status and Physics prospect at LHCb
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Detector requirements performances

• B hadron signature particles with high PT (few
  GeV) coming from a displaced vertex (typically
  L1cm from primary vertex)

• Reconstruction of b hadrons decays is based on
  
• mass resolution and excellent particle id to
  reject background
• good proper time resolution to resolve B0S
  oscillations

5 µm hit resolution 30 µm IP resolution
? 40 fs resolution
B mass resolution 15-20 MeV/c2
Status and Physics prospect at LHCb
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LHCb 2-level Trigger
Status and Physics prospect at LHCb
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Installation and commissioning status

• All subdetectors are installed and cabled
  (except M1 muon station which is not required for
  the first runs)

• Integration, calibration and time-alignment of
  the different elements are performed with cosmic
  data.

In the following event, cosmic particle hits
Outer Tracker (OT), calorimeters and muon
stations. The yellow line is the track fit by
calorimeter hits, although the green line is the
track fit by OT hits.
x
y
z
z
We will be ready for the LHC start-up !!!
1rst July 2008
Status and Physics prospect at LHCb
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LHCb schedule
Status and Physics prospect at LHCb
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LHCb physics program, part I CP violation
b ? d transitions
broadly studied, in general good agreement with
Standard Model measurement and confirmation of
B0d mixing parameters still limited
knowledge, space for New Physics (NP)
effects especially, the mixing phase Fs of
B0s-B0s oscillations
b ? s transitions
Fs is predicted with precision by the Standard
Model
Could be much larger if NP contribute to B0s-B0s
transitions
Current measures must to be improved
Status and Physics prospect at LHCb
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LHCb physics program, part I CP violation
Fs can be extracted from CP time-dependent
asymmetry in decay rates

• Which signal for this measurement ?
• Pure CP eigenstates
• ex B0s?J/??, B0s?J/??, B0s??cF, B0d?DsDs-
• Low yield, high background
• Admixture of CP eigenstates
• B0s ? J/?F Large yield (130k for 2fb-1), nice
  signatures ? golden channel
• BUT requires angular analysis to disentangle even
  (?f1) and odd (?f-1) eigenstate

Yield of 2-8 k/channel with 2fb-1 s(fs)0.046
s(fs)0.023 with 2fb-1
Status and Physics prospect at LHCb
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LHCb physics program, part I CP violation
CKM mechanism parameter measurement
Unitarity triangle in the ?-? plane
g angle is poorly constraint and the LHCb
contribution to this measurement is expected !
Status and Physics prospect at LHCb
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LHCb physics program, part I CP violation
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3 independent ways to extract g angle

• from tree amplitudes B0s ? DsK
• 2 amplitudes, b?c b?u, interfere via B0s
  mixing
• Access to gFs in a very clean way
• ? s(gFs ) 9-12 with 2fb-1
• 2) from tree amplitudes B ? DK
• 2 amplitudes, b?c b?u, interfere in decays
  to a common D0 and D0 modes state, fD
• Analysis methods (GLW, ADS, Dalitz) depend on the
  fD nature
• g can extracted from the time independent
  asymmetry
• ? global fit of all the channels s(g)
  4.3-6.2 with 2fb-1
• 3) from penguin amplitudes B ? hh
• Interference of b?u tree b?d(s) penguin
  diagrams leads to CP violation effect which
  depends on g
• Sensitive to New Physics
• ? s(g )10 with 2fb-1

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Status and Physics prospect at LHCb
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LHCb physics program, part II rare decays
Rare B decays give opportunities to constrain New
Physics contributions (b?ll-, b?sll-, b?sg,
...)
We will focus on 2 relevant examples
B0s ? µ µ-
BR sensitive to NP, especially SUSY MSSM
enhancement tan6ß/MA ? larger value Standard
Model prediction BR (3.35 0.32) ? 10-9 D0
CDF results BR lt 4.7?10-8 (90 CL) ? NP can
contribute to one order of magnitude
LHCb potential
3? (blue) and 5? (red) observation of a BR as a
function of integrated luminosity
SM BR
With SM Branching ratio 2 fb1 ? 3? evidence 6
fb1 ? 5? observation
Status and Physics prospect at LHCb
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LHCb physics program, part II rare decays
10-7
2x10-8
Useful informations to constrain SUSY model
parameters
5x10-9
Status and Physics prospect at LHCb
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LHCb physics program, part II rare decays
B0d ? K0 µ µ-
Observable sensitive to NP muon
forward-backward asymmetry in the µµ- rest frame
µ
?
B K0
µ-
First measurement AFB zero point crossing
SM prediction
Status and Physics prospect at LHCb
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LHCb physics program, part III other Physics

• pp?bb cross-section estimation
• production knowledge improvement
• charm physics D0 mixing and other CP violation
  studies
• measurement Bc or ?0b particle characteristics
  (mass, lifetime, )
• spectroscopy of heavy-flavoured hadrons
• potential to observe News Physics processes with
  b-jets

Status and Physics prospect at LHCb
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LHCb physics program, part III other Physics
b cross-section measurement
Test predictions on pQCD and constrain
fragmentation models. LHCb comparison with QCD
in region of phase space not accessible to
previous hadron-collider experiments.
The cross-section of a process can be determined
by
Used process b?J/?X BR (1.160.10)
Analysis distinguish J/? from b and prompt J/?.
Discriminating variable
1 statistical precision on total b-cross section
already at 50 nb-1. This measure is limited by
the BR(b?J/?X) uncertainty.
Status and Physics prospect at LHCb
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SUMMARY
LHCb is an experiment dedicated to B physics,
searching New Physics _at_ LHC energy scale.
LHCb will extend Babar, Belle and Tevatron
results and will contribute to improve our B
physics knowledge, essentially
CP violation
Rare decays

• Fs mixing phase s0.023
• g from trees s5-10
• g from penguins s10

• B0s?mm 3s of the SM BR
• B?Kmm s(s0)0.5 GeV2

with 2fb-1
We are ready to run and to do physics !!!
Status and Physics prospect at LHCb
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