LHCb Physics Programme

LHCb Physics Programme

Marcel MerkFor the LHCb Collaboration

May 26, 2008

Contents:• The LHCb Experiment• Physics Programme:

• CP Violation• Rare Decays

CERN Theory Institute: Flavour as a window to New Physics at the LHC: May 5 –June 13, 2008

LHCb @ LHC

A Large Hadron Collider Beauty Experiment for Precision Measurements of CP-Violation and Rare Decays

CMSCMS ALICEALICE

ATLASATLASLHCbLHCb CERNCERN

√s = 14 TeVLHCb: L=2-5 x 1032 cm-2 s-1

bb = 500 binel / bb = 160=> 1 “year” = 2 fb-1

b

bb

b

The LHCb Detector

31-3-2008 3

VELO

Muon det Calo’s RICH-2 MagnetOT RICH-1

VELO

Muon det Calo’s RICH-2 MagnetOT+IT RICH-1

Installation of major structures is complete

4

A walk through the LHCb spectrometer…

B-Vertex Measurement

31-3-2008 5

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

Vertexing:• Impact parameter trigger• Decay distance (time) measurement

Ds

BsK

K

K

d

47 m 144 m

440 mPrimary vertex

Decay time resolution = 40 fs

) ~40 fs

Example: Bs → Ds K

6

Momentum and Mass measurement

Momentum meas.: Mass resolution for background suppression

7

Momentum and Mass measurement

Momentum meas.: Mass resolution for background suppression

bt

Bs K

K

K

Ds

Primary vertex

Bs→ Ds KBs →Ds

Mass resolution ~14 MeV

8

Particle Identification

RICH2: 100 m3 CF4 n=1.0005

RICH: K/ identification using Cherenkov light emission angle

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

9

Particle Identification

RICH2: 100 m3 CF4 n=1.0005

RICH: K/ identification; eg. distinguish Ds and DsK events.

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

Cerenkov light emission angle

bt

Bs K

K

,K

Ds

Primary vertex

KK : 97.29 ± 0.06%K : 5.15 ± 0.02%

Bs → Ds K

10

LHCb calorimeters

e

h

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

bt

Bs K

K

K

Ds

Primary vertex

11

LHCb muon detection

Muon system: • Level 0 trigger: High Pt muons• Flavour tagging: D2 = (1-2w)2 6% btag

Bs K

K

K

Ds

Primary vertex

12

LHCb 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. b)

B (data mining)

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

40 MHz

1 MHz

2 kHz

L0: high pT (, e, , h) [hardware, 4 s]

Storage (event size ~ 50 kB)

DetectorL0, HLT and L0×HLT efficiency

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

Proper time [ps]

Effici

ency

bt

BsKK

K

Ds

Primary vertex

12

13

Measuring time dependent decays

bt

Bs K

K

Ds

Primary vertex

Measurement of Bs oscillations:

Bs->Ds– (2 fb-1)Experimental Situation:

• Ideal measurement (no dilutions)

14


bt

Bs K

K

Ds

Primary vertex

Bs->Ds– (2 fb-1)


Experimental Situation:Ideal measurement (no dilutions)+ Realistic flavour tagging dilution

15


bt

Bs K

K

Ds

Primary vertex

Bs->Ds– (2 fb-1)


Experimental Situation:Ideal measurement (no dilutions)+ Realistic flavour tagging dilution+ Realistic decay time resolution

16


bt

Bs K

K

Ds

Primary vertex

Bs->Ds– (2 fb-1)


Experimental Situation:Ideal measurement (no dilutions)+ Realistic flavour tagging+ Realistic decay time resolution+ Background events

17


bt

Bs K

K

Ds

Primary vertex

Experimental Situation:Ideal measurement (no dilutions)+ Realistic flavour tagging dilution+ Realistic decay time resolution+ Background events+ Trigger and selection acceptance

Two equally important aims for the experiment:• Limit the dilutions: good resolution, tagging etc.• Precise knowledge of dilutions

Bs->Ds– (2 fb-1)


18

Expected Performance: GEANT MC simulation

Used to optimise the experiment and to test physics sensitivities

Simulation software:• Pythia+EvtGen• GEANT simulation• Detector response

Reconstruction software:• Event Reconstruction• Decay Selection• Trigger/Tagging• Physics Fitting

Physics Programme

LHCb is a heavy flavour precision experiment searching for new physics

in CP-Violation and Rare Decays


19

CP Violation – LHCb Program

*cd cbV V

*ud ubV V

*td tbV V

*

cs cbV V*

us ubV V*

ts tbV V s

* *

*

*

*

*

*

*

arg ; arg

arg ; arg

tb cd cb

ud tb

ud tb

td

ub td

ub ts

cd cb s cbs

c

V V VV

V VV V

V V

V

V

V V V

V

s mixing phase (SM): 2 ssB d mixing phase (SM): 2 dB

Bd triangle

Bs triangle

2 3

2 2

3 2

1 / 2

1 / 2

1

CKM

i

i d si

eA

eA A e

V A

CP Program: Is CKM fully consistent for trees, boxes and penguins?1. measurements from trees2.measurement from penguins3. s from the box: “Bs mixing phase”4. s in penguins

b q1

d, sq2W−

g

d (s)

q

q

W −

b u,c,t

b

q

u, c, tu, c, t

q

bqBqB W+ W−

V*ib Viq

Viq V*ib 20

1.a +sfrom trees: Bs→DsK

2

2

1 cos 2 sin sin

1 cosh 2 sins2 2

c ho

/ s

s

s

ss

mt mt

t tB BD K

A

• Time dependent CP violation in interference of bc and bu decays:

Bs

Bs

sD K sie

sie ie

Bs

Bs

sD K sie

sie ie

Time

21

Bs/Bs →Ds–K+ (10 fb-1)

10 fb-1 data:Bs→ Ds

-

Bs→ Ds-K+

ms = 20)

• Since same topology BsDsK, Bs Ds combine samples to fit ms, s and Wtag together with CP phase s.

Channel Yield (2 fb-1)

B/S (90% C.L.)

BsDsK 6.2 k [0.08-0.4]

BsDs 140 k [0.08-0.3]

• Use lifetime difference s to resolve some ambiguities (2 remain).

Bs→DsK

s) = 9o–12o

Decay Time →22

B →Dand Bs→DsK

Channel Yield (2 fb-1) B/S

BsD*(K ) 206 k <0.3

B->D 210 k 0.3

B D(*) measures in similar way as BsDsK• More statistics, but smaller asymmetry• No lifetime difference: 8 –fold ambiguity for solutions

Invoking U-spin symmetry (d↔s) can resolve these ambiguities in a combined analysis of DsK and D(*)pi (Fleisher)

Can make an unambiguousextraction, depending onThe value of strong phases: < 10o (in 2 fb-1)

U-s

pin

brea

king

23

LHCb-2005-036

1.b from trees: B→DK

GLW method:fD is a CP eigenstate common to D0 and D0: fD= K+K-, +-,…Measure: B→D0K, B → D0K, B→ D1K• Large event rate; small interference • Measurement rB difficult

0

0

( )

( )Bi i

BA B D K

A B D Kr e e

B–

D0K–

D0K–

fDK–

bc favoured

bu suppressed

Decay time independent analysis

Cabibbo supp.

Cabibbo allowed.

• Interfere decays bc with bu to final states common to D0 and D0

colorsuppression

BiBr e

DiDr e

ADS method:Use common flavour state fD=(K+ –

Note: decay D0→K+– is double Cabibbo suppressed• Lower event rate; large interference

24

B→D(*)K(*)

GLW: D KK (2 rates) ;

ADS: D K ( 4 rates) ;

Channel Yield (2 fb-1) B/S

B → D(hh) K 7.8 k 1.8

B → D(K) K , Favoured 56 k 0.6

B → D(K) K , Suppressed 0.71k 2

B → D(K3) K, Favoured 62k 0.7

B → D(K3) K, Suppressed 0.8k 2() = 5o to 13o

depending on strong phases.

Also under study:B± → DK± with D → Ks 12

B± → DK± with D → KK 1

B0 → DK*0 with D → KK, K12

B± → D*K± with D → KK, K(high background)

Normalization is arbitrary:7 observables for 5 unknows:, rB, B, D

, D3

Overall: expect precision of() = 5o with 2 fb-1 of data

2

22

22 3 33

1 2 cos

2 cos

3 2 cos

B B B

B B B D

D

D DD

B D B BD DD

B K K K

B K K r r

B K K r

r

r r r

r r

r

ADS: D (4 rates) ;

Dalitz analyses

()

See talk of Angelo Carbone

25

2. from loops: B(s)→hh• Interfere b u tree diagram with penguins:

cos sin

cosh sinh2 2

CPf

dir mixf

f

fmt mtA

A At

t tA

1 2

3 4

, ,sin ; , ,sin

', ',sin ; ', ',sin

mix dir

KK KKdir mix

d

s

A Af d f d

f d f dA A

• Strong parameters d (d’), (’) are strength and phase of penguins to tree. Weak U-spin assumption : d=d’+-20% , , ’ independent• Assume mixing phases known


B/S

B 36k 0.5

BsKK 36k 0.15

BsK+K-

BG

(1

See talk of Angelo Carbone

2 fb-1

ms=20

Time26

ACP(t) N B 0 J /KS N B0 J /KS N B 0 J /KS N B0 J /KS

(sin2 ) ~ 0.02

3. The Bd and Bs Mixing Phase

0 : ( ) sin sinCP f ddB A t m t sin sin: ( )

cosh cos sinh2

f ss CP

s sf

s

s

m tB A t

t t

s

Time dependent CP violation in interference between mixing and decay

“Yesterday’s sensation is today’s calibration and tomorrow’s background” – Val Telegdi

B

B

fCPdie

“Golden mode”

Bs

Bs

fCPsie


B/S

BdJ/Ks 216 k 0.8

27

Bs mixing phase

Decay Yield (2 fb-1)

s)

J 8.5 k 0.109

J/ 3 k 0.142

J/’ 2.2 k 0.154

J/’ 4.2 k 0.08

c 3 k 0.108

Ds+ Ds

- 4k 0.133

All CP eig - 0.046

J/ 130 k 0.023

All - 0.021

sin sin( )

cosh cos sinh2

sCP

s

f

sf

s

s

m tA t

t t

s

1. Pure CP eigenstates Low yield, high background2. Admixture of CP eigenstates: Bs→J/ “Golden mode”: Large yield, nice signature However PS->VV requires angular analysis to disentagle =+1 (CP-even) ,-1 (CP-odd)

28

Full 3D Angular analysiscos cos

cos

Study possible systematics of LHCb acceptance and reconstruction on distributions.29

Bs→ J/

time

mass

signalbackg

sum

cos tr

cos

tr

(M)= 14 MeV

)= 35 fs

• Simultaneous likelihood analysis in time, mass, full 3d-angular distribution

• Include mass sidebands to model the time spectrum and angular distribution of the background

• Model the resolution

s)=0.02

See talk of Olivier Leroy

30

4. s from Penguins• Compare observed phases in tree decays with those in penguins

Channel Yield (2 fb-1) B/S Weak phase precision

B Ks 920 0.3 < B/S < 1.1 (sin(deff) 0.23

Bs 3.1 k < 0.8 (seff ) = 0.11

• Bs requires time dependent CP asymmetry (PSVV angular analysis a la J/ )

: 2 2effs

mix decays s sB 0 2: 2eff mix dec

say

d sB K

31

See talk of Olivier Leroy

Physics Programme

LHCb is a heavy flavour precision Experiment searching for new physics



32

Rare Decays – LHCb Program

2F

eff CK ii

iM CG

H V O i=1,2: treesi=3-6,8: g penguini=7: penguini=9,10: EW penguin

Study processes that are suppressed at tree level to look for NP affecting observables: Branching Ratio’s, decay time asymmetries, angular asymmetries, polarizations, …

Weak B-decays described by effective Hamiltonian:

New physics shows up via new operators Oi or modification of Wilson coefficients Ci compared to SM.

LHCb Program: Look for deviations of the SM picture in the decays:1.b sl+l- ; Afb(BK*) , B+→K+ll (RK), Bs→ 2.b s ; Acp(t) Bs B→K*,b→γ, b→ *γ,B →0, B→γ3.Bq l+l- ; BR (Bs ) 4.LFV Bq l l‘ (not reported here) 33

1. B0→K*0µ+µ-

• Contributions from electroweak penguins• Angular distribution is sensitive to NP

2 F BFB

F B

N NA s m

N N

m2

[GeV2]

AFB(m2μμ) theory illustration

0.38 20 0.35SM: s 4.39 GeV

Observable: Forward-Backward Asymmetry in l

Zero crossing point (so) well predicted:

3 angles:l, ,K

A FB

34hep-ph:0106067v2

B0→K*0µ+µ-

Channel Yield (2 fb-1) BG (2 fb-1)

Bs→K*+ – 7200+-2200 (BR) 1770+-310

Event Selection:

Systematic study: • Selection should not distort m2

• s0 point to first order not affected

•AFB(s), fast MC, 2 fb–1

s = (m)2 [GeV2]

2 fb-1

A fb(s

)

Removeresonances

s0

See talk Mitesh Patel

(s0) = 0.5 GeV2

35

2. Bs→• Probes the exclusive b →s radiative penguin Measure time dependent CP asymmetry:

cos sin

cosh sinh2 2

ds s

Cir m

Px

s

i

s

B B mt mtA t

B

A

B At

At


B/S

Bs→ 11k <0.55

Statistical precision after 2 fb-1 (1 year)(Adir ) = 0.11 ,(Amix ) = 0.11(requires tagging) (A) = 0.22 (no tagging required)

In SM b→s is predominatly (O(ms/mb)) left handedObserved CP violation depends on the polarization


Event selection:

b (L) + (ms/mb) (R)

Adir 0, Amix sin2 sin2 , A cos 2 cos tan = |b→s R| / | b→s L| , cos 1

SM:

Measures fraction “wrong” polarization36

3. Bs → • Bs is helicity suppressed SM Branching Ratio: (3.35 ± 0.32) x 10 -9

• Sensitive to NP with S or P coupling

Channel SM Yield (2 fb-1)

Background

Bs 30 83

Event Selection:Main Backgrounds: Suppressed by:b, b Mass & Vertex resol.B hh Particle Identification

With 2 fb-1 (1 “year”):• Observe BR: 6 x 10-9 with 5 • Assuming SM BR: 3observation

37


hep-ph/0604057v5

Physics Programme

LHCb is a heavy flavour precision Experiment searching for new physics


• CP Violation• Rare Decays+ “Other” Physics

38

“Other” Physics

See the following talks for an overview:

Raluca Muresan:• Charm Physics: Mixing and CP Violation

Michael Schmelling:• Non CP Violation Physics:

– B production, multiparticle production, deep inelastic scattering, …

39

ConclusionsLHCb is a heavy flavour precision experiment searching

for New Physics in CP Violation and Rare Decays

A program to do this has been developed and the methods, including calibrations and systematic studies, are being worked out..

CP Violation: 2 fb-1 (1 year)*• from trees: 5o - 10o

• from penguins: 10o

• Bs mixing phase: 0.023• s

eff from penguins: 0.11

Rare Decays: 2 fb-1 (1 year)* • BsK* s0 : 0.5 GeV2

• Bs Adir , Amix : 0.11 A : 0.22• Bs BR.: 6 x 10-9 at 5

We appreciate the collaboration with the theory community to continue developing new strategies.

We are excitingly looking forward to the data from the LHC.

* Expect uncertainty to scale statistically to 10 fb-1. Beyond: see Jim Libby’s talk on Upgrade 40

Backup

LHCb Detector

MUON

RICH-2 PID

RICH-1 PID

Tracking (momentum)

vertexing

HCAL

ECAL

31-3-2008 43

Display of LHCb simulated event

Flavour Tagging

Performance of flavour tagging: Efficiency Wrong tag w Tagging power

Bd ~50%

Bs ~50% 33% ~6%

Tagging power:

22 1 2D w

Full table of selections

Nominal year = 1012 bb pairs produced (107 s at L=21032 cm2s1 with bb=500 b)Yields include factor 2 from CP-conjugated decaysBranching ratios from PDG or SM predictions

BsDsK 5 years data

BsDs-K+ BsDs+K-

BsbDs-K+ BsbDs+K-

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