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Sheldon Stone Syracuse Univ. LHCb. The L arge H adron C ollider b eauty Experiment & Physics. 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 M Higgs <<M Planck )

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Sheldon Stone

Syracuse Univ.


The Large Hadron Collider beauty Experiment & Physics

general physics justification
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 MHiggs<<MPlanck)
  • However, it will be difficult to characterize this physics
  • How the new particles interfere virtually in the decays of b’s (& c’s) with W’s & Z’s can tell us a great deal about their nature, especially their phases

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Contributions to direct CP violating decay


Asym=(MW/msquark)2sin(fm), ~0 in SM

  • MSSM from Hinchcliff & Kersting (hep-ph/0003090)
  • Contributions to Bs mixing


CP asymmetry  0.1sinfmcosfAsin(Dmst), ~10 x SM

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limits on new physics from b s






From Perez

Limits on New Physics From b’s
  • 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 ~<0.3 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
Most Currently Desirable Modes
  • BS mixing using BSDS+p-
  • High Statistics Measurement of forward-backward asymmetry in B K*m+m-
  • 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DS+K- 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) m+m-
  • Important: Other modes, not currently in vogue

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detector requirements general
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
Basics For Sensitivities
  • # of b’s 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

Pythia production cross section

100 mb

230 mb

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 > h >1.9, where the B’s are moving with considerable momentum ~100 GeV, thus minimizing multiple scattering
  • At L=2x1032/cm2-s, we get 1012 B hadrons in 107 sec




 Of B vs B

q B (rad)

q B (rad)

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the lhcb detector
The LHCb Detector

Muon Detector









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the velo


R sensor: 38 mm pitch inside to

103 mm outside

f sensor: 39 mm pitch inside to

98 mm outside

1 m





3 cm separation

Interaction point






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  • 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” pTm, di-muons, e, g & hadrons, e.g. pTm >1.3 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
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 > 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
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 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
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



Traditional MC

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flavor tagging
Flavor Tagging

“opposite side”

  • For Mixing & CP measurements

it is crucial to know the b-flavor

at t=0. 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 s t
Background Reduction Using st
  • Excellent time resolution ~40 fs for most modes based on VELO simulation
  • Example

BS mixing


100 mm

Bs→Ds-π+(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

CDF data

Bd signal

Background Reduction from Particle ID
  • LHCb has two RICH detectors. Most tracks in range 100>P>2 GeV/c. Tagging kaons at lower momentum < 20 GeV/c; Bh+h- up to 200 GeV/c, but most below 100 GeV/c
  • Good Efficiencies with small fake rates


mass resolution

s=14 MeV

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the rich detectors

80 mm

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 b s j f
CP Asymmetry in BSJ/ f
  • Just as BoJ/ KS measuresCPV phase bBS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

Merged 0

Resolved 0

Neutral Reconstruction
  • Mass resolution is a useful s=~6 MeV
  • Efficiency within solid angle is OK using both merged and resolved po’s
  • Example: time dependent Dalitz Plot analysis ala’

Snyder & Quinn for Borp p+p-po

  • 14K signal events in 107 s with S/B 1/3, yielding s(a)=10o

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other physics sensitivities
Other Physics Sensitivities
  • Only a subset of modes
  • For ~1 year of running

Zero to ±0.04 GeV2


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  • Magnet installed

& mapped


& Muon Filter Installed

  • Construction on all

other items proceeding

  • Software is progressing
  • New MC-data challenges using Grid

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Overall in very good shape for startup in 2007

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view of pit

Muon system

-iron shielding

-electronics tower

Calorimeter-E-cal, H-cal modules




-HPD shielding box

OT: straw module production completedMuon: more than half of chambers produced

View of Pit

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possible improvements





Possible Improvements
  • Run at higher luminosity.

Increase to 5x1032 /cm2-s

  • Gains in event yields,

especially dimuon modes

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possible upgrades
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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  • 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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