(towards) first physics with...

(Towards) First Physics with LHCb

presented byAndreas Schopper (CERN)

on behalf of the Collaboration

Introduction Detector overview and performanceExtracting physics from (very) first data

Bea

m in

duce

d “s

plas

h” in

LH

Cb 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

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

0B 0B

Box diagram

0Bφ,K 0

s

φb

s,ds

s,d

ss

Penguin diagram

{ } { } stsSMstd

SMd

tstdSM

VV

Vm

βφβφ 2arg,2arg 22

2,

−=−==−=

∝Δ

??

New Physics

≠

≠Δ

d

mφ ≠sφ

Andreas Schopper

Search 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 Shchutskaand Bogdan Popovici

LHCb key measurements

In CP–violation: Bs-Bs mixing angle φs

weak phase γ in treesweak phase γ in loops

In Rare Decays:branching ratio of Bs μμforward-backward asymmetry in B K*μμpolarization of photon in radiative penguin decays

(φs=-2βs)


B production in LHCb

pp interactions/crossingLH

Cb

n=0

n=1

boost

b

b

bb pair production correlated and sharply peaked forward-backwardSingle-arm forward spectrometer : θ~15-300 mrad (rapidity range: 4.9>η>1.9)Cross section of bb production in LHCb acceptance: σbb ~ 230 µbB+ (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 crossingdesign luminosity soon after start-up

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

Andreas Schopper 5

Detector overview and performance

Split, 2 October 2008 Physics at LHC 2008

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


B-Vertex Measurement

Vertex Locator (Velo)

Silicon strip detector with

~ 5 μm hit resolution

30 μm IP resolution

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

Ds

Bs K+

K−

K+

π−

d~1cm

47 μm 144 μm

440 μmPrimary vertex

Decay time resolution = 40 fs

σ(τ) ~40 fs

Example: Bs → Ds K

Andreas Schopper

Momentum and Mass measurement

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


btag

Bs K+

K−

π+, K+

π−Ds

Primary vertex

Bs→ Ds KBs →Ds π

Mass resolutionσ ~14 MeV

Andreas Schopper 8

Particle Identification

RICH2: 100 m3 CF4 n=1.0005

RICH: K/π identification using Cherenkov light emission angle

RICH1: 5 cm aerogel n=1.03

4 m3 C4F10 n=1.0014

250 mrad

Track

Beam pipe

Photon Detectors

Aerogel

VELO exit window

SphericalMirror

PlaneMirror

C4F10

0 100 200 z (cm)

Magneticshielding


btag

Bs K+

K−

π+,K+

π−Ds

Primary vertex

K K : 96.77 ± 0.06%π K : 3.94 ± 0.02%

Bs → Ds K

Andreas Schopper 9

Particle 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+

π−Ds

Primary vertex


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

Andreas Schopper

Particle identification and L0 trigger

μ

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

εD2 = ε (1‐2w)2 ≈ 6% btag

Bs K+

K−

K+

π−Ds

Primary vertex


Andreas SchopperSplit, 2 October 2008 Physics at LHC 2008

11

LHCb trigger

HLT rate Event type Physics

200 Hz Exclusive B candidates

B (core program)

600 Hz High mass di-muons

J/ψ, b→J/ψX (unbiased)

300 Hz D* candidates Charm (mixing & CPV)

900 Hz Inclusive b (e.g. b→μ)

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 (μ, e, γ, h) [hardware, 4μs]

Storage (event size ~ 35 kB)

Detector

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

Proper time [ps]

Efficiency

btag

Bs K+K−

K+

π−Ds

Primary vertex

L0 efficiency (%

)

11

Andreas Schopper

Split, 2 October 2008

OT Calo MuonTop view

Status of LHCb

Physics at LHC 2008

12

Clean event from halo muons

LHCb detector fully installed and commissioned (except M1), including L0 triggerAll 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 data

1.E-101.E-091.E-081.E-071.E-061.E-051.E-041.E-031.E-021.E-011.E+001.E+01

1.E+00 1.E+02 1.E+04 1.E+06 1.E+08 1.E+10 1.E+12 1.E+14

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 ·NmbNumber of selected signal events:

Andreas Schopper

Exploiting minimum bias data

plenty of Ks→ππ and Λ→pπ95% purity with kinematical and vertex cuts onlyclean & unbiased sample for PID studiesstudy hadron identification performance

collect 1400 J/ψ→μμuse triggered J/ψ data with pt-cut on single muonsecond muon unbiased for PID studiesstudy muon identification performance

search for D→Kπ, Kπππ, K0Sππ, Kππ0

assess background levels, resolutions & relative efficienciesdemonstrate capability to reconstruct first final states


Λ→pπ

~ 40 mins @ 1031 cm-2 s-1

~50k Λ→pπ eventsin 108 minimum bias events

Andreas Schopper

Exploiting first muon trigger data


applying J/ψ trigger with pt-cut on single muonexpect ~106 J/ψ→μμ with 1 pb-1

Reconstruct J/ψ→μμ and disentangle fraction of prompt and detached J/ψ’sdiscriminating variable:

study proper time resolution with prompt component

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

PV

μ+

μ-

dz

Andreas Schopper

Exploiting ~5 pb-1 of data with full trigger


23k B0→ D*μνtagging studies with flavour specific modes

3.2k B+→J/ψK+

selection does not require lifetime cutunbiased lifetime distribution to determine resolution

4.3k B0 → D-(K- π+π-) π +

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

trec-ttrue(fs)

σ(τ) ~34 fs

B0 → D-(K- π+π-) π +

/ ndf 2χ 62.5566 / 50norm 81.5328± 1600.2388 par_exp 0.0002± 0.0008 B/S 0.2350± 1.5942

μ 1.9518± 5367.9165 σ 1.9880± 12.7847

2MeV/c5100 5200 5300 5400 5500 5600 5700

En

trie

s

0

10

20

30

40

50

60

70

/ ndf 2χ 62.5566 / 50norm 81.5328± 1600.2388 par_exp 0.0002± 0.0008 B/S 0.2350± 1.5942

μ 1.9518± 5367.9165 σ 1.9880± 12.7847

invariant massφ ψ J/→ sB

Invariant mass ofBs→J/ψ(μμ)φ

(~days of data taking)

3.7k B→ K*γreference channel for all radiative loop decays

2.3k B→J/ψK* exercise fit machinery for analysis of Bs→J/ψφ

Select first 285 Bs→J/ψφ

σ(Bs)=13 MeV

~0.2 pb-1

B→ K*γ

Oscillation plot with 3 pb-1 of B0→ D*μν

A(t)

13 min. running

Andreas Schopper

Exploiting ~0.5 fb-1 of data with full trigger


(1/4 of a nominal year)

t,c,u

t,c,u

+W −W

s,d

b s,d

b

0B 0B+NP?

Θtr= angle between l+ and normal to φ decay plane

ηf = +, - 1 CP eigenstates

J/ψφ 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 φs in Bs→J/ψ(µµ)φ

with 28’500 reconstructed Bs→J/ψ(µµ)φ signal events (before tagging)

Sensitive to New Physics effects in mixingφs = φs(SM) + φs(NP)

in SM: φs = – 2βs = –arg(Vts2) ~ –0.04

σstat(φs)~0.06 with 0.5 fb-1


Exploiting ~0.5 fb-1 of data with full trigger

Very rare loop decay, sensitive to New PhysicsBR ~ 3.5×10–9 in SM, can be strongly enhanced in SUSY

Main issue is background rejection:dominated by B→μ+X, B→μ-X decaysgood mass resolution and PID essential

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

WWb

s μ+

t μ−ν?

?

MSSMCurrent limit from CDFBR(Bs μμ) < 4.7×10-8

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

Andreas Schopper

Conclusion


LHCb is a heavy flavour precision experiment searching for New Physics in CP-violation and rare decaysThe experiment is ready for data taking with first collisionsVery 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

(towards) first physics with...

Documents