LHCb

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LHCb

The Large Hadron Collider beauty

Experiment & Physics

Sheldon StoneSyracuse Univ.

Aspen Winter Conference, February, 2006 2

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


Example

Contributions to Bs mixing

CP asymmetry 0.1sincossin(mst), ~10 x SM

BsJ

Contributions to direct CP violating decay

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

B-K-

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


Limits on New Physics From b’s

Is there NP in Bo-Bo mixing?

Assume NP in tree decays is negligible

Use Vub, ADK, SK, S, md, ASL

Fit to , h,

o full o

i

o SM

σ

o

B |H |B1+ e =

B |H |Bh

For New Physics via Bdo mixing,

h is limited to ~<0.3 of SM except when Bd is ~0o or ~180o of SM decaysNew physics via Bs mixing, or bs transitions is unconstrained

h

cl>5%cl>32%cl>90%

From Perez


Most Currently Desirable Modes

BS mixing using BSDS+-

High Statistics Measurement of forward-backward asymmetry in B K*+-

Precision measurements of CP ’s CP violating phase in BS mixing using BSJ/ (or 3) Using B- DoK- tree level decays using BSDS

+K- time dependent analysis especially measurement of Bo oo

at high accuracy to pin down other physics CPV in various rare decay modes B(S) +-

Important: Other modes, not currently in vogue


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/ decay

, o & 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


Basics For Sensitivities

# of b’s into detector acceptance Triggering Flavor tagging Background reduction

Good mass resolution Good decay time resolution Particle Identification


The Forward Direction at LHC

In the forward region at LHC the bb production is large

The hadrons containing the b & b quarks are both likely to be in the acceptance

LHCb uses the forward direction, 4.9 > >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

100 b230 b

Pythia production cross section

pT

B (rad) B (rad)

Production Of B vs B


The LHCb Detector

Muon DetectorTracking stations

TriggerTracking

protonbeam

interactionregion


The VELO

VacuumTank

1 m

3 cm separation sensors

Rsensors

R sensor: 38 m pitch inside to103 m outside sensor: 39 m pitch inside to98 m outside

Interaction point

Geometry

SensorHalf


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 , di-muons, e, & hadrons, e.g. pT >1.3 GeV/c; veto on multiple interactions in a crossing except for muon triggers.

Uses custom electronics boards with 4 s latency, all detectors read out at 1 MHz

Second level and Higher Level 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


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)

Output rate Trigger Type Physics Use

200 Hz Exclusive B candidates Specific final states

600 Hz High Mass di-muons J/, bJ/X

300 Hz D* Candidates Charm, calibrations

900 Hz Inclusive b (e.g. b) B data mining


Trigger Monitoring

Trigger lines need constant monitoring to adjust prescales, especially at beginning of experiment.

General approach: for a particular trigger Define TOSTrigger On Signal Define TIS Trigger Independent of Signal Efficiency =(TISTOS )/TIS


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 & (TISTOS )/TIS

Can be done quickly with real data

Traditional MC

TIS & TOSMethod


Flavor Tagging 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) ± (for Bd) (same side) Efficacy characterized by D2, where

is the efficiency and D the dilution = (1-2) Several ways to do this

Method

(For BS)

± e± K± same

K± opp

Jet charge

D2(%) 1.5 0.7 3.1 2.5 0.8

D2 (%

)

Expect D2 ~ 7.5% for BS & 4.3% for Bd

“same side”

“opposite side”

Not exactlysame cuts as table


Background Reduction Using t

Excellent time resolution ~40 fs for most modes based on VELO simulation

Example

BS mixing

Bs→Ds-π+ (tagged as Bs)

100

m10 mm

Bs→Ds-π+

LHCb can measure mS up 68 ps-1 in 2 fb-1


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; Bh+h- up to 200 GeV/c, but most below 100 GeV/c

Good Efficiencies with small fake rates

CDF data

Bd signal

Excellent mass resolution=14 MeV


The RICH Detectors

HPD Photon DetectorsRICH I Design

80 mm


RICH II

RICH2 –installed in the pit


CP Asymmetry in BSJ/ Just as BoJ/ KS measuresCPV phase BSJ/

measures CPV BS mixing phase S

Since this is a Vector-Vector final state, must do an angular (transversity) analysis The width difference S/S

also enters in the fit LHCb will get 120,000 such

events in 2fb-1. Projected errors are ±0.06 in S & 0.02 in S/S (for mS = 20 ps-1)

Including BSJ/ , will increase sensitivity (only 7K events)


Neutral Reconstruction Mass resolution is a useful

=~6 MeV Efficiency within solid

angle is OK using both merged and resolved o’s

Example: time dependent Dalitz Plot analysis ala’

Snyder & Quinn for Bo o

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

Resolved 0

Merged 0


Other Physics Sensitivities

Only a subset of modes For ~1 year of running

Afb Zero to ±0.04 GeV2


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


OverviewLHCC Milestones (October 2005)

0

50

100

150

200

250

2000

2001

2002

2003

2004

2005

2006

2007

Year

Nu

mb

er o

f m

ilest

on

es

Planned

Achieved

Projection

Overall in very good shape for startup in 2007


View of Pit

Muon system-iron shielding-electronics tower

Calorimeter-E-cal, H-cal modules

RICH2 Magnet RICH1-HPD shielding box

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


Possible Improvements

Run at higher luminosity.

Increase to 5x1032 /cm2-s Gains in event yields,

especially dimuon modes

Bo+-

BSBSJ/BSDSK

-


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 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)


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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LHCb

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