(Towards) First Physics with LHCb(Towards) First Physics with LHCb

presented byAndreas Schopper (CERN)

on behalf of the Collaboration

Introduction Detector overview and performance Extracting physics from (very) first data

Be

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uce

d “

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b Physics at LHC 2008

Split, Croatia, 29 Sep - 4 Oct 2008

Andreas SchopperSplit, 2 October 2008

Physics at LHC 2008 2

LHCb is a heavy flavour precision experiment searching for new physics in CP-Violation and Rare Decays

LHCb is a heavy flavour precision experiment searching for new physics in CP-Violation and Rare Decays

New Physics models introduce new particles, dynamics and/or symmetries at a higher energy scale (expected in the TeV region) with virtual particles that appear e.g. in loop mediated processes

B-physics measurements probe New Physics and are complementary to direct searches will allow to understand the nature and flavour structure of possible New Physics

t,c,u

t,c,u

W W

s,d

b s,d

b

0B0B

Box diagram

0B

,K0s

b

s,ds

s,d

ss

Penguin diagram

stsSMstd

SMd

tstdSM

VV

Vm

2arg,2arg 22

2,

??

New Physics

d

m

s

Andreas Schopper

Search for New PhysicsSearch for New Physics

Split, 2 October 2008

Physics at LHC 2008 3

SM consistency at 7% level

CDF Public Note 9458 (August 2008)

are New physics already around the corner?

see talks by Andrei Golutvin, Alessia Satta, Val Gibson, William Robert Reece and poster by Lesya Shchutska and Bogdan Popovici

LHCb key measurements

In CP–violation: Bs-Bs mixing angle s

weak phase in trees weak phase in loops

In Rare Decays: branching ratio of Bs

forward-backward asymmetry in B K*

polarization of photon in radiative penguin decays

(s=-2βs)

Andreas SchopperSplit, 2 October 2008

Physics at LHC 2008 4

B production in LHCbB production in LHCb

pp interactions/crossing

LH

Cb

n=0

n=1

boost

b

b

bb pair production correlated and sharply peaked forward-backward Single-arm forward spectrometer : θ~15-300 mrad (rapidity range: 4.9>η>1.9) Cross section of bb production in LHCb acceptance: σbb ~ 230 µb B+ (40%), B0 (40%), Bs (10%), b-baryons (10%), Bc (< 0.1%)

LHCb limits luminosity to few 1032 cm-2s-1 instead of 1034 cm-2s-1 by not focusing the beam as much as ATLAS and CMS maximizes probability of a single interaction per crossing design luminosity soon after start-up

collect 2fb-1 per nominal year ~ 1012 bb pairs produced per year

Andreas Schopper 5

Detector overview and performance Detector overview and performance

Split, 2 October 2008

Physics at LHC 2008

walk through the detectorwith the example of a Bs→DsK decay

Andreas SchopperSplit, 2 October 2008

Physics at LHC 2008 6

B-Vertex MeasurementB-Vertex Measurement

Vertex Locator (Velo)Silicon strip detector with ~ 5 mm hit resolution 30 mm IP resolution

Vertexing:• trigger on impact parameter• measurement of decay distance (time)

Ds

BsK

K

K

d~1cm

47 mm 144 mm

440 mmPrimary vertex

Decay time resolution = 40 fs

(s t) ~40 fs

Example: Bs → Ds K

Andreas Schopper

Momentum and Mass measurement Momentum and Mass measurement

Momentum meas. + direction (VELO): Mass resolution for background suppression

Split, 2 October 2008

Physics at LHC 2008 7

btag

Bs K

K

p+, K

Ds

Primary vertex

Bs→ Ds KBs →Ds p

Mass resolutions ~14 MeV

Andreas Schopper 8

Particle IdentificationParticle Identification

RICH2: 100 m3 CF4 n=1.0005

RICH: K/p identification using Cherenkov light emission angle

RICH1: 5 cm aerogel n=1.03 4 m3 C4F10 n=1.0014

Split, 2 October 2008

Physics at LHC 2008

btag

Bs K

K

,K

Ds

Primary vertex

KK : 96.77 ± 0.06%pK : 3.94 ± 0.02%

Bs → Ds K

Andreas Schopper 9

Particle identification and L0 triggerParticle identification and L0 trigger

e

h

Calorimeter system : • Identify electrons, hadrons, π0 ,γ• Level 0 trigger: high ET electron and hadron

btag

Bs K

K

K

Ds

Primary vertexSplit, 2 October 2008

Physics at LHC 2008

ECAL (inner modules): σ(E)/E ~ 8.2% /√E + 0.9%

Andreas Schopper

Particle identification and L0 triggerParticle identification and L0 trigger

m

Muon system: • Level 0 trigger: High Pt muons• contributing to flavour tagging:

eD2 = e (1-2w)2 6% btag

Bs K

K

K

Ds

Primary vertexSplit, 2 October 2008

Physics at LHC 200810

Andreas SchopperSplit, 2 October 2008

Physics at LHC 2008

11

LHCb triggerLHCb trigger

HLT rate

Event type Physics

200 Hz Exclusive B candidates

B (core program)

600 Hz High mass di-muons

J/, bJ/X (unbiased)

300 Hz D* candidates Charm (mixing & CPV)

900 Hz Inclusive b (e.g. bm)

B (data mining)

HLT: high IP, high pT tracks [CPU farm] then full reconstruction of event

40 MHz

1 MHz

2 kHz

L0: high pT (m, e, g, h) [hardware, 4 ms]

Storage (event size ~ 35 kB)

Detector

Note: decay time dependent efficiency: eg. Bs → Ds K

Proper time [ps]

Effici

ency

btag

BsKK

K

Ds

Primary vertex

L0 e

ffici

ency

(%)

11

Andreas Schopper

Split, 2 October 2008

OT CaloMuon

Top view

Status of LHCbStatus of LHCb

Physics at LHC 2008

12

Clean event from halo muons

LHCb detector fully installed and commissioned (except M1), including L0 trigger All sub-detectors have undergone the first time and space alignment with cosmics &

LHC beam induced particles

( see talk by Olivier Callot)

Events with LHC beam induced particles

OT

Calo

Muon

Side view Splashy event from lost particles (not all tracks reconstructed...)

12Split, 2 October 2008

Andreas Schopper

Extracting physics from (very) first dataExtracting physics from (very) first data

1E+00 1E+02 1E+04 1E+06 1E+08 1E+10 1E+12 1E+141E-10

1E-08

1E-06

1E-04

1E-02

1E+00

1E+02

σ∙ε/σmb

Nmb

π± production

Bd→J/ΨKs production

J/Ψ production D-meson production

Λbar production

K0 production

φ production

Λ production

π0 production

J/Ψ from bb

108 minimum bias @ 2kHz

Split, 2 October 2008

13Physics at LHC 2008

Exploit minimum bias data

S= σmb

σ∙ε∙Nmb

Number of selected signal events:

Andreas Schopper

Exploiting minimum bias dataExploiting minimum bias data

plenty of Ksππ and Λ→pπ 95% purity with kinematical and vertex cuts only clean & unbiased sample for PID studies study hadron identification performance

collect 1400 J/ use triggered J/ψ data with pt-cut on single muon

second muon unbiased for PID studies study muon identification performance search for DKπ, Kπππ, K0

Sππ, Kππ0

assess background levels, resolutions & relative efficiencies

demonstrate capability to reconstruct first final states

Split, 2 October 2008

Physics at LHC 2008 14

Λ→pπ

~ 40 mins @ 1031 cm-2 s-1

~50k Λ→pπ eventsin 108 minimum bias events

Andreas Schopper

Exploiting first muon trigger dataExploiting first muon trigger data

Split, 2 October 2008

Physics at LHC 2008 15

applying J/ψ trigger with pt-cut on single muon

expect ~106 J/ with 1 pb-1

Reconstruct J/ and disentangle fraction of prompt and detached J/’s

discriminating variable:

study proper time resolution with prompt component

Measure prompt J/ and bb cross section in a region not accessible to other collider experiments

PV

+

-

dz

Andreas Schopper

Exploiting ~5 pb-1 of data with full triggerExploiting ~5 pb-1 of data with full trigger

Split, 2 October 2008

Physics at LHC 2008 16

23k B0 D* tagging studies with flavour specific modes

3.2k B+J/K+

selection does not require lifetime cut unbiased lifetime distribution to determine resolution

4.3k B0 D-(K- π+π-) π +

measure B0 lifetime reach current precision (0.009 ps) with 60k events

trec

-ttrue

(fs)

(s t) ~34 fs

B0 D-(K- π+π-) π + Invariant mass ofBsJ/()

(~days of data taking)

3.7k B K*γ reference channel for all radiative loop decays

2.3k BJ/K* exercise fit machinery for analysis of BsJ/

Select first 285 BsJ/

σ(Bs)=13 MeV

~0.2 pb-1

B K*γ

Oscillation plot with 3 pb-1 of B0 D*

A(t

)

13 min. running

Andreas Schopper

Exploiting ~0.5 fb-1 of data with full triggerExploiting ~0.5 fb-1 of data with full trigger

Split, 2 October 2008

Physics at LHC 2008 17

(1/4 of a nominal year)

t,c,u

t,c,u

W W

s,d

b s,d

b

0B0B

+NP?

Θtr= angle between l+ and normal to decay plane

ηf = +, - 1 CP eigenstates

J/ is not a pure CP eigenstate (2 CP even, 1 CP odd amplitude) need to fit angular distributions of decay

final states as function of proper time

measure Bs-Bs mixing phase s in BsJ/(µµ)

with 28’500 reconstructed BsJ/(µµ) signal events (before tagging)

Sensitive to New Physics effects in mixing

s = s(SM) + s(NP)

in SM: s = – 2βs = –arg(Vts2) ~ –0.04

stat(s)~0.06 with 0.5 fb-1

Andreas SchopperPhysics at LHC 2008 18Split, 2 October 2008

Exploiting ~0.5 fb-1 of data with full triggerExploiting ~0.5 fb-1 of data with full trigger

Very rare loop decay, sensitive to New Physics BR ~ 3.510–9 in SM, can be strongly enhanced in SUSY Main issue is background rejection:

dominated by B+X, B-X decays good mass resolution and PID essential

LHCb expected performance: with 0.5 fb–1: exclude BR values down to SM value with 2 fb–1: 3 evidence of SM signal with 10 fb–1: > 5 observation of SM signal

W

W

b

s

t

?

?

MSSMCurrent limit from CDFBR(Bs) < 4.710-8

(1/4 of a nominal year) measure BR of rare decay Bs +–

Andreas Schopper

ConclusionConclusion

Split, 2 October 2008

Physics at LHC 2008 19

LHCb is a heavy flavour precision experiment searching for New Physics in CP-violation and rare decays

The experiment is ready for data taking with first collisions Very first data can be exploited to validate the expected

detector performance With fraction of a 1 years nominal data set LHCb can already

perform important key measurments probing New Physics