LHCb early results and prospects: final states including leptons

LHCb early results and prospects: final states including leptons

Liming Zhang

(Syracuse University)

Brookhaven Forum 2010May 26-28

on behalf of the LHCb Collaboration

2

LHCb Physics Program• LHCb focus on searching for New Physics in the flavour

sector– Complementary to direct search in ATLAS and CMS

• Some key LHCb measurements– CP Violation Bs mixing phase fs, BDK : γ from loops and

trees, Bhh

– Rare Decays BR(Bs μ+μ-), B K*

For more details see the LHCb Roadmap document

http://arxiv.org/abs/0912.4179

May. 26, 2010 Brookhaven Forum 2010

http://arxiv.org/abs/0912.4179

The LHCb Experiment• LHCb is a dedicated B physics experiment

at LHC– High beauty cross section expected: 200-500

mb @ 7-14 TeV– Access to all b-hadrons: B+, B0, Bs, Bc, b-

baryons• Luminosity limited to ~ 2x1032 to limit

multiple interactions per bunch crossing– Expect to reach this in 2010– Expect ~ 2fb-1 and ~1012 bb pairs per nominal

year @ 14 TeV (107 secs)– ~200 pb-1 in 2010 and 1fb-1 in 2011 @ 7 TeV

• LHCb acceptance optimised for forward bb production: Forward single arm spectrometer 1.9<<4.9 – b-hadrons produced at low angle– Correlated bb-production in same

hemisphere

100 mb230 mb

Pythia production cross section (14TeV)

h

pT

q B (rad)q B (rad)

Production of B vs B

3May. 26, 2010 Brookhaven Forum 2010

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LHCb Detector

VELO:primary verteximpact parameterdisplaced vertex

Tracking Station: p for lower energy tracks and long lived V0 reconstruction

Tracking Stations:p of charged particles that traverse the magnet

Calorimeters:PID: h,e,, 0

Muon System

RICH:PID: primarily K, separation

Interaction region


Detector Workings

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LHCb detector ~ fully installed and commissioned walk through the detector using the example of a Bs→DsK decay


f sensors

Rsensors

B-Vertex Measurement

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 (MC simulation)

Vertex Locator (Velo)Silicon strip detector with ~ 5 mm hit resolution 30 mm IP resolution at pT~2GeV


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

7

btag

Bs K

K

p+, K

Ds

Primary vertex

Bs→ Ds KBs →Ds p(MC)

Mass resolutions ~14 MeV


Hadron 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


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

Ds

Primary vertex

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


10

m

• Physics: BsJ/ y f, Bsm+m-, etc.

• Level 0 trigger: fast information from high Pt muons• OS flavour tagging

Muon System


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Trigger

Hardware level (L0)

Search for high-pT μ, e, γ and hadron candidates

Software level (High Level Trigger, HLT)

Farm with O(2000) multi-core processors

HLT1: Confirm L0 candidate with more complete

info, add impact parameter and lifetime cuts

HLT2: B reconstruction + selections

Hig

h-L

evel

Trig

ger

2 kHz

Level -0

L0 e, g

40 MHz

1 MHz

L0 had

L0 m

ECALAlley

Had.Alley

Global reconstruction30 kHz

HLT

1H

LT2

MuonAlley

Inclusive selectionsm, m+track, , mm

topological, charm, ϕ & Exclusive selections

Storage: Event size ~35kB

e(L0) e(HLT1) e(HLT2)

Electromagnetic 70 %

> ~80 % > ~90 %Hadronic 50 %

Muon 90 %

Trigger is crucial as σbb is less than 1% of total

inelastic cross section and B decays of

interest typically have B < 10-5

Very high efficiencyMay. 26, 2010 Brookhaven Forum 2010

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p0, h and w in Data

Data 2009 MC

p0,hgg

,h wppp0

p0,hgg


13

First J/ψ data results (800mb-1)Loose selection Tight selection

Pseudo-proper time in signal peak

These are B→J/ψX candidates !Can any be fully reconstructed?


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Mass = (5326.7±10.9) MeV/c2

Momentum: p = 62.7 GeV/c, pT = 10.48 GeV/cCos(a) = 0.9999, dist = 2.03mm

Muons are magenta, kaon is red

B+→J/ψK+ candidate


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Primary vertex

B decay vertex

m+

m-K+

J/ψ

B+

XY Projection

[mm]

[mm]Tracks from primary vertex

B+→J/ψK+ candidate


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Muon identification studies

Plan to use J/ym+m- to measure muon ID efficiency.Do not have sufficient statistics yet. Muon ID efficiency: ~94% (MC)

LHCb 2010preliminary

LHCb 2010preliminary

p→μdominated bydecays in flight

p→μdominated bycombinatoricsin muon stations

Fak

e ra

te

Fak

e ra

te

Fake Rate of pm and pm


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t,c,u

t,c,u

W W

s,d

b s,d

b

0B0B

+NP?

Sensitive to New Physics effects in mixing

s = s(SM) + s(NP)

in SM: s = – 2βs = –0.036±0.002

with 5.6 fb-1 current Tevatron result ~2.1σ away from SM value Hope to improve significance with LHCb’s first year data

Search for CPV in Bs→J/ψf

CDF public note 9798

)/arg(β **s cbcstbts VVVV-=


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Bs→J/ψ(mm)fJ/ 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

Detector Requirements Muon and Kaon ID Proper time resolution (~40 fs) Flavour tagging

LHCb expects about 2300 signal events / 100 pb-1 @ 7 TeV assuming s(bb)=219 mb

Θtr= angle between l+ and normal to decay plane

total

CP evenCP odd

flat background


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If nature agrees with Tevatron central value then LHCb can make 5σ discoveryin coming run. Statistical precision on measured CPV phase of ~0.07 with 1 fb-1

5 s non-zero CPV phase if Tevatron central value is true

This result will be complemented by equivalent measurement in CP-eigenstateBs→J/ψf0(980), f0

(980)→+-. fs sensitivity could be similar, depending on BR. [arXiv: 0909.5442]

LHCb prospects in Bs→J/ψf

• Including S-wave KK component will increase the error [Stone & Zhang arXiv: 0812.2832, 0908.3627]

• Not included in Tevatron’s measurements


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Bs→m+m- & Supersymmetry

Gaugino mass

SM

BR(Bs→μμ)SM = (3.35 ± 0.32) x 10-9

(Blanke et al., JHEP 0610:003,2006)

Very high sensitivity to NP, eg. MSSM:


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0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00

10

20

30

40

50

CDF +D0 (8 fb-1)

CDF (3.7fb-1)

BR(B

s0 ->+- )

(x10

-9)

L (fb-1)

@ 3.5 + 3.5 TeV

SM prediction

Exclusion limit @90% C.L.

• ~ 0.2 fb-1 to improve upon expected Tevatron limit with 8fb-1

• ~ 3 fb-1 for 3σ evidence and ~ 10 fb-1 for 5σ observation of SM value @ 14TeV

LHCb prospects for Bs→μμ

3σ observation* 5σ observation

BR

(Bs0

μ+μ- )

(x1

0-9)

@7+7TeV

EACH


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B0K0m+m-

• Very rare in the SM: B = (1.2 ± 0.1)×10-6 • Flavour-changing-neutral current (FCNC) process through

penguin or box diagrams• Very sensitive to probe New Physics


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• Described by three angles (ql, f, qK) and di-m invariant mass q2

Angular Distributions

qqq

qqqq

sin)1(cos2cos

cos)cos1)(1(8

3sin

4

3

cos

2L

2L2

2

lFBl2

Ll2

L2l

2

FFq

AFFq

KKK

-+µ¶¶

G¶

++-+µ¶¶

G¶PRD61 (2000) 074024

SM

ò

òò-

-

-

G

G-=

1

12

2

0

12

21

0FB

coscos

coscos

ll

ll

ddqd

d

ddqd

d

A

qq

qq

Zero point measures ratio of Wilson coeffs C9eff/C7

eff

Forward and backward asymmetry

Compare with different SUSY models


24

SM

C7=-C7SM• BELLE: 230 B →K*ℓℓ

events in 657M BB [PRL 103: 171801, 2009]

• BABAR: 60 B →K*ℓℓ events in 384M BB [PRD 79: 031102, 2009]

• CDF: 100 B →K*mm events in 4.4 fb-1 [CDF note 10047]

• LHCb expects ~350 in 300 pb-1(with m+m- only) @7TeV, B/S = 0.5±0.2

SM

C9C10=-C9SMC10

SM

C7=-C7SM

Both flipped sign

From The Other Experiments


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LHCb Prospects for AFB

• Assume Belle is right. If we measure the mean AFB in a bin 1-6 GeV2. How well can we exclude the SM?

100 pb-1: 1.5s300 pb-1: 2.4s

SM prediction - Belle - BaBar - LHCb expectation @ 7TeV

500 pb-1: 3.1s1 fb-1: 4.0s

-With more data (~2fb-1), we can do full angular analysis to access more interesting observables(Egede, et al... arXiv:0807.2589)


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Summary• LHCb is a precision heavy flavour experiment

searching for New Physics at the LHC in CP violation and rare decays

• 2010 run offers plenty of possibilities for significant measurements

– Possibly improve Tevatron’s results on fs and Bsm+m-

•

Exclusion limit @ 90% C.L.

LHC and LHCb have highly successful run so far, the luminosity is increasing very fast

log scale


27

The LHCb Collaboration

730 members15 countries54 institutes


Backup

29

B0K0m+m- Sensitivity @ 14TeV


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Other Angular Variables in K*m+m-

• Supersymmetry (Egede, et al... arXiv:0807.2589)

• Use functions of the transverse polarization

i are form factors

(4)TA

10 fb-1model 1

With more L can distinguish betweendifferent SUSY models in some cases


BSm+m-

Main concern: background suppressionHandles: mass resolution, vertex separation, use of pointing constraint

Muon misidentification dominated by decays in flight

For 2009, substitute Bsm+m- with a V0

m = (1115.7 ± 0.1stat. ) MeV/c2 PDG: 1115.683(6) MeV/c2

s = (1.4 ± 0.1stat ) MeV/c2 MC: (1.2 ± 0.2stat ) MeV/c2

m = (496.9 ± 0.2stat. ) MeV/c2 PDG: 497.61(2) MeV/c2

s = (4.1 ± 0.1stat ) MeV/c2 MC: (3.6 ± 0.2stat ) MeV/c2

Ks

Mass resolutions of the V0 observed in 2009 data agree reasonably well with MC expectations. Tracker alignment still ongoing. Alignment from magnet off data used.New alignment database for magnet on available since this week.With 3.5 TeV, we expect a Bsm+m- mass resolution of ~25 MeV/c2

BSm+m-

Main concern: background suppressionHandles: mass resolution, vertex separation,

use of pointing constraint

Muon misidentification dominated by decays in flight

For 2009, substitute Bsm+m- with a V0

Background rejection based on geometric likelihood

Geometric likelihood

Signal

Background BSm+m- MC

33

Heavy flavour studies at LHCb will begin with a measurement of the bb cross-section, as determined from production rate of displaced J/ψ mesons

μ

μΔz

pJ/ψ

zPV

Δzp J/ψ

zmJ/ψt J/ψ = t J/ψ / ps

Prompt

From b

Tail from wrong PV

Form pseudo proper-time, tJ/ψ :

Combined fit to invariant mass and pseudo proper-time allows for bothprompt J/ψ and bb production in bins of pt and pseudo-rapidity.

LHCb MC

Prompt J/ψ production a very interesting topic in its own right: Colour Octet Model (COM) predicts well cross-sections seen at Tevatron, but not polarisation

Calibrating the signal source


34

LHCb J/ψ production studies

Plan is to make study in:

• 4 pseudo-rapidity bins, with 3 < η < 5• 7 transverse momentum bins up between pt=0 and pt = 7 GeV/c LHCb inclusive J/ψ MC &

background toy MC @ 14 TeVWith 5 pb-1 all bins will havestatistical uncertainty < 10%

Largest systematic will come from unknown polarisation – varies bin to bin upto maximum of 25%. Polarisation will be measured in 2nd pass analysis.

Expected integrated luminosity uncertainty~5% through measurements of beam profile in beam-gas and beam-beam collisions. (Already determined to 15% in 2009, with uncertainty limited by knowledge ofbeam intensities)

beam 1 vs empty beam 2 vs empty

beam 1 vs beam 2

LHCb 2009 preliminary


35

Any New Physics phase contributingto Bs→J/ψФ will also be seen in

semi-leptonic flavour asymmetrymeasured in eg. Bs→Dsμ

These events are beginning to accumulate !

Bs→Dsμ n candiate in first data


36

Same side

signal Bs

K-

K+

primary vertex

Opposite side opposite B

negative lepton taggers (e-, m-) from b-quark

opposite

positive lepton taggers from bcl cascade

same side kaon tagger

vertex-charge taggerfrom inclusive vertexing

bb

s

u

s

u

Bs

K+

protonproton

kaon tagger (K-)

m+

m-

BsJ/: efficiency e~ 55.7%, mistag rate w~33.3%, e(1-2w)2~6.2%

Flavour tagging at LHCb

K/p separation using RICH critical


37

Kaon ID (MC)

btag

Bs K

K

,K

Ds

Primary vertex

KK : 96.77 ± 0.06%pK : 3.94 ± 0.02%

Bs → Ds KSS flavour tagging


38

• Described by three angles (ql, f, qK) and di-m invariant mass q2

Angular Distributions

fff

qqq

qqqq

2sin2cos)1(2

11

sin)1(cos2cos

cos)cos1)(1(8

3sin

4

3

cos

Im(2)TL2

2

2L

2L2

2

lFBl2

Ll2

L2l

2

AAFq

FFq

AFFq

K

KKK

+-+µ¶¶G¶

-+µ¶¶

G¶

++-+µ¶¶

G¶

arXiv:0807.2589

(a-d) MSSM with different inputs

SM

Transverse asymmetry AT sensitivity to right-handed current search.

(2)


Documents

LHCb early results and prospects: final states including leptons