LHCb

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LHCb
Sheldon Stone Syracuse Univ.

• The Large Hadron Collider beauty Experiment
  Physics

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General Physics Justification

• Expect New Physics will be seen at LHC
• Standard Model is violated by the Baryon
  Asymmetry of Universe by Dark Matter
• Hierarchy problem (why MHiggsltltMPlanck)
• However, it will be difficult to characterize
  this physics
• How the new particles interfere virtually in the
  decays of bs ( cs) with Ws Zs can tell us
  a great deal about their nature, especially their
  phases

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Example

• MSSM from Hinchcliff Kersting (hep-ph/0003090)

• Contributions to Bs mixing

Bs?J/yh
CP asymmetry ? 0.1sinfmcosfAsin(Dmst), 10 x SM
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Limits on New Physics From bs

• Is there NP in Bo-Bo mixing?
• Assume NP in tree decays is negligible
• Use Vub, ADK, SyK, Srr, Dmd, ASL
• Fit to h, r, h, s

• For New Physics via Bdo mixing, h is limited to
  lt0.3 of SM except when sBd is 0o or 180o of
  SM decays
• New physics via Bs mixing, or b?s transitions is
  unconstrained

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Most Currently Desirable Modes

• BS mixing using BS?DSp-
• High Statistics Measurement of forward-backward
  asymmetry in B ?Kmm-
• Precision measurements of CP ?s
• CP violating phase in BS mixing using BS?J/yf
• g (or f3) Using B- ?DoK- tree level decays
• g using BS?DSK- time dependent analysis
• a especially measurement of Bo ?roro
• b at high accuracy to pin down other physics
• CPV in various rare decay modes
• B(S)? mm-
• Important Other modes, not currently in vogue

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Detector Requirements - General

• Every modern heavy quark experiment needs
• Vertexing to measure decay points and reduce
  backgrounds, especially at hadron colliders
• Particle Identification to eliminate insidious
  backgrounds from one mode to another where
  kinematical separation is not sufficient
• Muon electron identification because of the
  importance of semileptonic leptonic final
  states including J/y decay
• g, po h detection
• Triggering, especially at hadronic colliders
• High speed DAQ coupled to large computing for
  data processing
• An accelerator capable of producing a large rate
  of b anti-b hadrons in the detector solid angle

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Basics For Sensitivities

• of bs into detector acceptance
• Triggering
• Flavor tagging
• Background reduction
• Good mass resolution
• Good decay time resolution
• Particle Identification

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The Forward Direction at LHC

• In the forward region at LHC the bb production s
  is large
• The hadrons containing the b b quarks are both
  likely to be in the acceptance
• LHCb uses the forward direction, 4.9 gt h gt1.9,
  where the Bs are moving with considerable
  momentum 100 GeV, thus minimizing multiple
  scattering
• At L2x1032/cm2-s, we get 1012 B hadrons in 107
  sec

pT
h
Production ? Of B vs B
q B (rad)
q B (rad)
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The LHCb Detector
Muon Detector
Tracking stations
proton beam
interaction region
Trigger Tracking
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The VELO
Sensor Half
Vacuum Tank
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Triggering

• Necessary because b fraction is only 1 of
  inelastic cross-section
• At peak luminosity interaction rate is 10 MHz,
  need to reduce to a few kHz. The B hadron rate
  into the acceptance is 50 kHz
• General Strategy
• Multilevel scheme 1st level Hardware trigger on
  moderate pT m, di-muons, e, g hadrons, e.g.
  pT m gt1.3 GeV/c veto on multiple interactions in
  a crossing except for muon triggers.
• Uses custom electronics boards with 4 ms latency,
  all detectors read out at 1 MHz
• Second level and Higher Level software triggers

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Software Triggers

• Second Level All detector information available.
  Basic strategy is to use VELO information to find
  tracks from b decays that miss the main
  production vertex also events with two good
  muons are accepted single muon with pT gt 2.1
  GeV/c. Strategies are constantly being improved.
• Higher Level Triggers Here more sophisticated
  algorithms are applied. Both inclusive selections
  and exclusive selections tuned to specific final
  states done after full event reconstruction has
  finished. Output rate is 2 kHz

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Trigger Output

• Rough guess at present (split between streams
  still to be determined)
• Large inclusive streams to be used to control
  calibration and systematics (trigger, tracking,
  PID, tagging)

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Trigger Monitoring

• Trigger lines need constant monitoring to adjust
  prescales, especially at beginning of experiment.
  
• General approach for a particular trigger
• Define TOS?Trigger On Signal
• Define TIS ?Trigger Independent of Signal
• Efficiency (TIS?TOS )/TIS

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Trigger Monitoring Example

• Comparison of L0 trigger efficiency on muon
  tracks that miss the IP as a function of Pt for
  both traditional Monte Carlo method (TIS?TOS
  )/TIS
• Can be done quickly with real data

TIS TOS Method
Traditional MC
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Flavor Tagging
opposite side

• For Mixing CP measurements
• it is crucial to know the b-flavor
• at t0. This can be done by
• detecting the flavor of the other B
• hadron (opposite side) or by using
• K (for BS) p (for Bd) (same side)
• Efficacy characterized by eD2, where
• e is the efficiency and D the dilution
  (1-2w)
• Several ways to do this

same side
eD2 ()
Not exactly same cuts as table
Expect eD2 7.5 for BS 4.3 for Bd
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Background Reduction Using st

• Excellent time resolution 40 fs for most modes
  based on VELO simulation
• Example
• BS mixing

Bs?Ds-p
100 mm
Bs?Ds-p (tagged as Bs)
10 mm
LHCb can measure DmS up 68 ps-1 in 2 fb-1
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Background Reduction from Particle ID

• LHCb has two RICH detectors. Most tracks in range
  100gtPgt2 GeV/c. Tagging kaons at lower momentum lt
  20 GeV/c B?hh- up to 200 GeV/c, but most below
  100 GeV/c
• Good Efficiencies with small fake rates

Excellent mass resolution s14 MeV
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The RICH Detectors

• HPD Photon Detectors

RICH I Design
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RICH II

• RICH2 installed in the pit

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CP Asymmetry in BS?J/? f

• Just as Bo?J/? KS measures CPV phase b BS?J/? f
  measures CPV BS mixing phase fS
• Since this is a Vector-Vector
• final state, must do an angular
• (transversity) analysis
• The width difference DGS/GS
• also enters in the fit
• LHCb will get 120,000 such
• events in 2fb-1. Projected errors are 0.06 in
  fS 0.02 in DGS/GS (for DmS 20 ps-1)
• Including BS?J/? h, will increase sensitivity
  (only 7K events)

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Neutral Reconstruction

• Mass resolution is a useful s6 MeV
• Efficiency within solid angle is OK using both
  merged and resolved pos
• Example time dependent Dalitz Plot analysis ala
  
• Snyder Quinn for Bo?rp ?pp-po
• 14K signal events in 107 s with S/B 1/3, yielding
  s(a)10o

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Other Physics Sensitivities
Zero to 0.04 GeV2
Afb

• Only a subset of modes
• For 1 year of running

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Status

• Magnet installed
• mapped
• ECAL, HCAL, RICH II
• Muon Filter Installed
• Construction on all
• other items proceeding
• Software is progressing
• New MC-data challenges using Grid

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Overview
Overall in very good shape for startup in 2007
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View of Pit
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Possible Improvements

• Run at higher luminosity.
• Increase to 5x1032 /cm2-s
• Gains in event yields,
• especially dimuon modes

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Possible Upgrades

• VELO needs to be replaced after 6-8 fb-1 due to
  radiation damage
• Are considering hybrid Silicon pixels as a
  replacement
• Since they are much more rad hard than current
  VELO, we could move closer to the beam getting
  better vertex s
• These could possibly allow some vertexing in
  first trigger level with minor modifications
• EM calorimeter upgrades such as having a central
  PbWO4 region
• Major modifications to readout including long
  digital pipelines that would enable extensive 1st
  level vertex triggering and allow higher
  luminosity running (very expensive)

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Conclusions

• LHCb will study CP Violation and Rare Decays in
  the BS, B-, Bd systems at an unprecedented
  level of accuracy
• These studies are crucial for specifying any new
  physics found directly
• at the Tevatron or LHC
• LHCb is on schedule
• LHCb is starting to think
• about upgrades

From Hewett Hitlin
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The End