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CERN Theory Institute: Flavour as a window to New Physics at the LHC: May 5 –June 13, 2008. LHCb Physics Programme. Marcel Merk For the LHCb Collaboration May 26, 2008. Contents: The LHCb Experiment Physics Programme: CP Violation Rare Decays. LHCb @ LHC. b. b. b. b.

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lhcb physics programme

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

LHCb Physics Programme

Marcel Merk

For the LHCbCollaboration

May 26, 2008

  • Contents:
  • The LHCb Experiment
  • Physics Programme:
    • CP Violation
    • Rare Decays
lhcb @ lhc
LHCb @ LHC

b

b

b

b

  • √s = 14 TeV
  • LHCb: L=2-5 x 1032 cm-2 s-1
  • sbb = 500 mb
  • inel / sbb = 160
  • => 1 “year” = 2 fb-1

CERN

LHCb

ATLAS

CMS

ALICE

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

the lhcb detector
The LHCb Detector

Muon det

Muon det

Calo’s

Calo’s

Magnet

RICH-2

RICH-2

Magnet

RICH-1

OT+IT

OT

RICH-1

VELO

VELO

Installation of major structures is complete

b vertex measurement
B-VertexMeasurement

144 mm

47 mm

K

K

Bs

K

Ds



d

440 mm

Example: Bs → Ds K

s(t) ~40 fs

Primary vertex

Decay time resolution = 40 fs

Vertex Locator (Velo)

Silicon strip detector with

~ 5 mm hit resolution

 30 mm IP resolution

  • Vertexing:
  • Impact parameter trigger
  • Decay distance (time) measurement
momentum and mass measurement
Momentum and Mass measurement

Momentum meas.: Mass resolution for background suppression

momentum and mass measurement7
Momentum and Mass measurement

p+, K

Bs

K

K

Ds



Primary vertex

bt

Momentum meas.: Mass resolution for background suppression

Mass resolution

s ~14 MeV

Bs→ Ds K

Bs →Ds p

particle identification
Particle Identification

RICH: K/p identification using Cherenkov light emission angle

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

RICH2: 100 m3 CF4 n=1.0005

particle identification9
Particle Identification

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

Cerenkov light emission angle

Bs → Ds K

,K

Bs

KK : 97.29 ± 0.06%

pK : 5.15 ± 0.02%

K

K

Ds



Primary vertex

bt

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

RICH2: 100 m3 CF4 n=1.0005

lhcb calorimeters
LHCb calorimeters

K

Bs

K

Ds

K



Primary vertex

bt

e

h

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

K

Bs

K

Ds

K



Primary vertex

btag

m

  • Muon system:
  • Level 0 trigger: High Pt muons
  • Flavour tagging: eD2 = e (1-2w)2 6%
lhcb trigger
LHCb trigger

Detector

40 MHz

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

1 MHz

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

2 kHz

Storage (event size ~ 50 kB)

L0, HLT and L0×HLT efficiency

Efficiency 

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

K

Bs

K

Ds

K



Primary vertex

bt

Proper time [ps] 

12

measuring time dependent decays
Measuring time dependent decays



Bs

K

Ds

K



Primary vertex

bt

Measurement of Bs oscillations:

  • Experimental Situation:
  • Ideal measurement (no dilutions)

Bs->Ds–p+ (2 fb-1)

measuring time dependent decays14
Measuring time dependent decays



Bs

K

Ds

K



Primary vertex

bt

Measurement of Bs oscillations:

Experimental Situation:

Ideal measurement (no dilutions)

+ Realistic flavour tagging dilution

Bs->Ds–p+ (2 fb-1)

measuring time dependent decays15
Measuring time dependent decays



Bs

K

Ds

K



Primary vertex

bt

Measurement of Bs oscillations:

Experimental Situation:

Ideal measurement (no dilutions)

+ Realistic flavour tagging dilution

+ Realistic decay time resolution

Bs->Ds–p+ (2 fb-1)

measuring time dependent decays16
Measuring time dependent decays



Bs

K

Ds

K



Primary vertex

bt

Measurement of Bs oscillations:

Experimental Situation:

Ideal measurement (no dilutions)

+ Realistic flavour tagging

+ Realistic decay time resolution

+ Background events

Bs->Ds–p+ (2 fb-1)

measuring time dependent decays17
Measuring time dependent decays



Bs

K

Ds

K



Primary vertex

bt

Measurement of Bs oscillations:

Experimental Situation:

Ideal measurement (no dilutions)

+ Realistic flavour tagging dilution

+ Realistic decay time resolution

+ Background events

+ Trigger and selection acceptance

Bs->Ds–p+ (2 fb-1)

  • Two equally important aims for the experiment:
  • Limit the dilutions: good resolution, tagging etc.
  • Precise knowledge of dilutions
expected performance geant mc simulation
Expected Performance: GEANT MC simulation
  • Simulation software:
  • Pythia+EvtGen
  • GEANT simulation
  • Detector response
  • Reconstruction software:
  • Event Reconstruction
  • Decay Selection
  • Trigger/Tagging
  • Physics Fitting

Used to optimise the experiment and to test physics sensitivities

physics programme
PhysicsProgramme

LHCb is a heavy flavour precision

experiment searching for new physics

in CP-Violation and Rare Decays

  • CP Violation
  • Rare Decays
cp violation lhcb program
CP Violation – LHCb Program

q1

b

q2

W−

d, s

W −

b

u,c,t

d (s)

q

g

q

Bd triangle

Bs triangle

  • CP Program: Is CKM fully consistent for trees, boxes and penguins?
  • gmeasurementsfrom trees
  • gmeasurementfrompenguins
  • bsfrom the box: “Bsmixingphase”
  • bsin penguins

V*ib

Viq

q

u, c, t

b

W−

W+

u, c, t

q

b

Viq

V*ib

1 a g f s from trees b s d s k
1.a g +fsfrom trees: Bs→DsK
  • Time dependent CP violation in interference of bc and bu decays:

Bs

Bs

Bs

Bs

Bs/Bs →Ds–K+ (10 fb-1)

Time

b s d s k
Bs→DsK
  • Since same topology BsDsK, Bs Dsp
  • combine samples to fit Dms, DGs
  • and Wtag together with CP phase g+fs.

10 fb-1 data:

Bs→Ds-p+

Bs→ Ds-K+

(Dms = 20)

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

s(g+fs) = 9o–12o

Decay Time →

b d p and b s d s k
B →Dpand Bs→DsK
  • B  D(*)p measures g in similar way as BsDsK
  • More statistics, but smaller asymmetry
  • No lifetime difference:
  • 8 –fold ambiguity for g solutions

LHCb-2005-036

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

Can make an unambiguous

extraction, depending on

The value of strong phases:

s(g) < 10o (in 2 fb-1)

U-spin breaking

1 b g from trees b dk
1.bgfrom trees: B→DK
  • Interfere decays bc with bu
  • to final states common to D0 and D0

color

suppression

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

bc favoured

Cabibbo supp.

D0K–

fDK–

B–

bu suppressed

Cabibbo allowed.

D0K–

  • ADS method:
  • Use common flavour state fD=(K+ p –)Note: decay D0→K+p–is double Cabibbo suppressed
  • Lower event rate; large interference

Decay time independent analysis

b d k
B→D(*)K(*)

See talk of AngeloCarbone

GLW: D KK (2 rates) ;

ADS: D Kp( 4 rates) ;

ADS: DK3p(4 rates) ;

Normalization is

arbitrary:

7 observables for 5 unknows:

g, rB, dB, dDp , dD3p

s(g) = 5o to 13o

depending on strong phases.

s(g)

Also under study:

B± → DK±with D → Kspp 80-12o

B± → DK±with D → KK pp 18o

B0 → DK*0with D → KK, Kp, pp 6o -12o

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

Dalitz analyses

Overall: expect precision of

s(g) = 5owith 2 fb-1 of data

2 g from loops b s hh
2. gfrom loops: B(s)→hh

See talk of AngeloCarbone

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

2 fb-1

Dms=20

BsK+K-

BG

s ( g ) ~10o

Time

3 the b d and b s mixing phase
3. The Bd and BsMixingPhase

Time dependent CP violation in interference between mixing and decay

B

Bs

fCP

fCP

B

Bs

“Golden mode”

s(sin2b ) ~ 0.02

“Yesterday’s sensation is today’s

calibration and tomorrow’s background”

– Val Telegdi

b s mixing phase
Bsmixingphase

1. Pure CP eigenstates

Low yield, high background

2. Admixture of CP eigenstates: Bs→J/y f

“Golden mode”: Large yield, nice signature

However PS->VV requires angular analysis

to disentagle h=+1 (CP-even) ,-1 (CP-odd)

full 3d angular analysis
Full 3D Angularanalysis

cos y = cosqf

cosq

f

Study possible systematics of LHCb acceptance and reconstruction on distributions.

b s j y f
Bs→ J/y f

signal

backg

sum

  • Simultaneouslikelihoodanalysis in time, mass, full 3d-angular distribution
  • Includemasssidebands to model the time spectrum and angular distribution of the background
  • Model the tresolution
  •  s (fs)=0.02

s(t)= 35 fs

time

s(M)= 14 MeV

See talk of Olivier Leroy

mass

cosqf

cos qtr

ftr

4 b b s from penguins
4. b & bsfromPenguins
  • Compare observed phases in tree decays with those in penguins
  • Bs f f requires time dependent CP asymmetry
  • (PSVV angular analysis a la J/yf )

See talk of Olivier Leroy

physics programme32
PhysicsProgramme

LHCb is a heavy flavour precision

Experiment searching for new physics

in CP-Violation and Rare Decays

  • CP Violation
  • Rare Decays
rare decays lhcb program
Rare Decays – LHCb Program

Weak B-decays described by effective Hamiltonian:

i=1,2: trees

i=3-6,8: g penguin

i=7: g penguin

i=9,10: EW penguin

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

Study processes that are suppressed at tree

level to look for NP affecting observables:

Branching Ratio’s, decay time asymmetries,

angular asymmetries, polarizations, …

LHCb Program: Look fordeviations of the SM picture in the decays:

b sl+l- ; Afb(BK*mm) ,B+→K+ll (RK), Bs→fmm

b  s g ; Acp(t) Bs fg, B→K*g, Lb→Lγ, Lb→ L*γ,B →r0g, B→wγ

Bq l+l- ; BR (Bs mm)

LFV Bq l l‘ (notreportedhere)

1 b 0 k 0
1. B0→K*0µ+µ-

AFB(m2μμ) theory illustration

m2[GeV2]

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

3 angles:

ql, f ,qK

AFB

Observable: Forward-Backward Asymmetry in ql

Zero crossing point (so) well predicted:

hep-ph:0106067v2

b 0 k 0
B0→K*0µ+µ-
  • AFB(s), fast MC, 2 fb–1

s = (m)2 [GeV2] 

See talk Mitesh Patel

Event Selection:

2 fb-1

Afb(s) 

s0

s(s0) = 0.5 GeV2

Remove

resonances

  • Systematic study:
  • Selection should not distort m2mm
  • s0 point to first order not affected
2 b s fg
2. Bs→fg

See talk Mitesh Patel

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

b   (L) + (ms/mb)  (R)

In SM b→s g is predominatly (O(ms/mb)) left handed

Observed CP violation depends on the g polarization

Event selection:

Adir 0, Amix  sin2y sin2f, AD  cos 2ycosf

tan y = |b→s gR| / | b→s gL| , cos f  1

SM:

Statistical precision after 2 fb-1 (1 year)

s(Adir ) = 0.11 , s (Amix ) = 0.11(requires tagging)

s (AD) = 0.22 (no tagging required)

Measures fraction “wrong” g polarization

3 b s m m
3. Bs →m+m-

See talk Mitesh Patel

  • Bs mm is helicity suppressed
  • SM Branching Ratio: (3.35 ± 0.32) x 10 -9
  • Sensitive to NP with S or P coupling

hep-ph/0604057v5

Event Selection:

Main Backgrounds: Suppressed by:

bm, bm Mass & Vertex resol.

B hh Particle Identification

  • With 2 fb-1 (1 “year”):
  • Observe BR: 6 x 10-9 with 5 s
  • Assuming SM BR: 3s observation
physics programme38
PhysicsProgramme

LHCb is a heavy flavour precision

Experiment searching for new physics

in CP-Violation and Rare Decays

  • CP Violation
  • Rare Decays
  • + “Other” Physics
other physics
“Other” Physics

See the followingtalksforanoverview:

RalucaMuresan:

  • CharmPhysics: Mixing and CP Violation

Michael Schmelling:

  • Non CP ViolationPhysics:
    • B production, multiparticleproduction, deepinelasticscattering, …
conclusions
Conclusions

LHCb is a heavy flavour precision experiment searching for New Physics in CP Violation and Rare Decays

CP Violation: 2 fb-1 (1 year)*

  • gfrom trees: 5o - 10o
  • gfrompenguins: 10o
  • Bsmixingphase: 0.023
  • bsefffrompenguins: 0.11

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

  • Rare Decays: 2 fb-1 (1 year)*
  • BsK*mm s0 : 0.5 GeV2
  • Bs gAdir , Amix : 0.11
  • AD : 0.22
  • Bsmm BR.: 6 x 10-9 at 5s

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

slide42

LHCb Detector

RICH-2 PID

MUON

ECAL

HCAL

RICH-1 PID

vertexing

Tracking (momentum)

slide43

Display of LHCb

simulated event

flavour tagging
FlavourTagging

Performance of flavour tagging:

Tagging power:

full table of selections
Full table of selections

Nominal year = 1012 bb pairs produced (107 s at L=21032 cm2s1 with bb=500 b)

Yields include factor 2 from CP-conjugated decays

Branching ratios from PDG or SM predictions

bs dsk 5 years data
BsDsK5 years data

BsDs-K+

BsDs+K-

BsbDs+K-

BsbDs-K+