Prospects for New Physics in CP Violation and Rare Decays at LHCb

Prospects for New Physics in CP Violation and Rare Decays

at LHCbPascal Perret LPC Clermont

On behalf of the LHCb Collaboration

10 November 2008

2

b Production in LHCb bb pair production correlated and sharply peaked forward-backward

Pascal Perret - LPC Clermont10/11/2008

collect 2fb-1 per nominal year ~ 1012 bb pairs produced per year 1 LHCb day = 100 B-factory day

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

pp interactions/crossing

LHC

b

n=0

n=1

3

LHCb overview and performance


4

LHCb: vertex locator


VELO

Vertex Locator (Velo)Silicon strip detector 8 mm from beam with ~ 5 mm hit resolution30 mm IP resolutionDecay time resolution ~ 40 fs

5

LHCb: momentum & mass measurement

Pascal Perret - LPC Clermont10/11/2008Momentum measurement (s(p)/p ~ (0.4 + 1.5 p/TeV)%) and Mass resolution s ~14 MeV

Track reconstruction efficiency:95% for tracks with p>5 GeV

TTITOT

Magnet

Drift time tube

6

LHCb: particle identification


RICH: K/p identification (KK: ~96.8%, pK: ~3.9%) ; eg. distinguish Dsp and DsK events.

HPD

RICH1: 5 cm aerogel n=1.03 : 2-~10 GeV4 m3 C4F10 n=1.0014 : 10-~60 GeV

RICH2: 100 m3 CF4 n=1.0005 16-~100 GeV

7

LHCb: calorimeter


PS SPD

ECALHCAL

Inner Outer Middleregion

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

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

photon

8

LHCb: muon system


Muon system: • Level 0 trigger: High Pt

muons• Muon ID: ~ 95% for 5%

hadron misID

• Multi Wire Proportional Chamber

• Triple-GEM for M1-R1

• M1 under installation …

Muons

9

LHCb: beam pipe


Magnet

TTSPD

Pb

M2

HCAL

ECAL

PS

Beinox

Beam pipe:Under vacuum June – Oct.Detector closed

RICH2

10

LHCb trigger system Two levels:

1st level: hardware 4 ms latency“moderate” pT m, e, g & hadrons, e.g. pT m >1.3 GeV/c : full custom made

HLT: software ~2000 CPU


40 MHz

1 MHz

Pile-upCalorimeter

Muon + L0DU

Level 0:High pT : m, e, h, g

4 µs

HLT:L0 confirmation m, e, h, g alleys

inclusive/exclusive Selection

Full reconstruction of event

2 kHz Storage(event size ~ 35 kB)

(Interaction rate ~ 10 MHzb hadron inside LHCb ~50 kHz)

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)

11

Status of LHCb LHCb detector fully installed and commissioned, including L0

trigger All sub-detectors have undergone the first readout synchronisation

and alignment with cosmics & LHC beam induced particles


OT Calo MuonTop view

Events with LHC beam induced particles

OT

Calo

Muon

Side view

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

Clean event from halo muonsVelo

F. Dett

ori

poste

r

12 Pascal Perret - LPC Clermont10/11/2008

t,c,u

t,c,u

W W

s,d

b s,d

b

0B 0B

Box diagram

0B,K0

s

b

s,ds

s,d

ss

Penguin diagram

stsSMstd

SMd

tstdSM

VV

Vm

2arg,2arg 22

2,

New Physics in CPV Unitarity Triangles

Overconstrain the unitarity triangles (consistency checks)

Bs

Bd0 p p

Bd0 r p

BS0 DS p

Bd0 J/ KS

0

Bd

a

g

VudVub VtdVtb

VcdVcb

* *

*Bd0 DK*0

BS0 DSK

Bd0 D* p,3p

BS0 J/

s

VtsVtb

VcsVcb

*

VusVub*

*

13 Pascal Perret - LPC Clermont10/11/2008

t,c,u

t,c,u

W W

s,d

b s,d

b

0B 0B

Box diagram

0B,K0

s

b

s,ds

s,d

ss

Penguin diagram

stsSMstd

SMd

tstdSM

VV

Vm

2arg,2arg 22

2,

New Physics

?

?

d

m

s

New Physics in CPV

b-physics measurements probe New Physics and are complementary to direct searches

New particles may show up in loop process

Unitarity Triangles

Overconstrain the unitarity triangles (consistency checks)

will allow to understand the nature and flavour structure of possible New Physics ones

Bs

Bd0 p p

Bd0 r p

BS0 DS p

Bd0 J/ KS

0

Bd

a

g

VudVub VtdVtb

VcdVcb

* *

*Bd0 DK*0

BS0 DSK

Bd0 D* p,3p

BS0 J/

s

VtsVtb

VcsVcb

*

VusVub*

*

14

g Measurements from Bs Ds K+

Interference between 2 tree diagrams via Bs mixing: BsDs

K (b c) and BsDsK (b u) (+ CP conjugates)


Measure g + s in a clean way (no theoretical uncertainty) from time dependent rates

Use s from Bs J/

Include Bs Dsp (20x Br) to determine Δms ΔΓs and tagging dilution

Simultaneous fit to Bs→Dsp and Bs→DsK decay time distributions (tagged and untagged) 10 fb-1 data:

Bs→ Ds-p

Bs→ Ds-K+

(ms = 20)

Mode Sig. yield

B/S

Bs→DsK 6.2k 0.7

Bs→Dsp 140k 0.2

Sensitivity

2 fb-1 10 fb-1

s stat(g)° 10.3 4.6

15

g Measurements Different ways to measure g at LHCb:


Compare angle g measured from interfering tree decays (which should always take the value from the CKM matrix) to angle measured from penguin diagrams:

Any difference is a sign of New Physics

B mode D mode Method s(g) 2fb-1

Bs→DsK KKp Tagged, A(t) 10º

B+→D K+ Kp+ K3p +KK/pp counting, ADS+GLW 5º - 13º

B+→D K+ Kspp Dalitz, GGSZ 7-12º

B+→D K+ KKpp 4 body Dalitz 18º

B0→D K*0 Kp + KK + pp counting, ADS+GLW 9º

B→pp,KK - Tagged, A(t) 10º

2 amplitudes, b→c (dominant) & b→u (color suppressed), interfere in decays to a common D0 and D0 modes state:

Global fit of all the channels: σ(g) = 4.3-6.2° with 2fb-1Tr

ee d

ecay

s on

ly

Penguin amplitudes:Interference of b→u tree & b→d(s) penguin diagrams

Other modes under study: B+→D*(D → Kp/KK/pp) K+, B+→D(→ Kppp)K+, …

16

s measurements from Bs J/


t,c,u

t,c,u

W W

s,d

b s,d

b

0B 0B+NP?

e(1-2w)2

Muon 0.8Electron 0.4

K (OS) 1.5

K (SS) 2.1

Q vertex 1.1

Invariant mass ofBsJ/(mm)

The measure of Bs-Bs mixing phase s in BsJ/(µµ) is sensitive to New Physics effects in mixing: s = s(SM) + s(NP) in SM: s = – 2βs = arg(Vts

2) ~ –0.04 Tevatron: s ~2.2s away from SM

(central experimental value -0.77) It is not a pure CP eigenstate (VV decay).

• 2 CP even, 1 CP odd amplitude • need to fit angular distributions of decay

final states as function of proper time• Good proper-time resolution is essential: ~39fs• Good tagging of initial Bs flavour :

• Combined = 6.2%• Good mass resolution: 13 MeV• Good particle identification

• e(KK)~80% e (pK)~ 3%

17

BRvis[BsJ/(µµ)(K+K-)]= (3.1±1.1)x10-5

With 2 fb-1 (1 nominal year): 114k reconstructed events (before

tagging)S/B ~2s stat(s) ~0.03

• 5σ NP discovery, if s >0.1! Low systematic uncertainties:

• Proper time acceptance: no bias from selection• Angular resolution: very good & negligible• Mistag and proper time are crucial…

Already at the start-up with 0.5 fb-1:28.5k reconstructed eventss stat(s) ~0.06LHCb should rapidly pin down whether really sign of new physics …

s measurements from Bs J/


ηf = +, - 1 CP eigenstates

18

New Physics in rare decays


19 s = (mmm)2 [GeV2]

AFB(s), theory Forward-backward asymmetry AFB(s) in the mm rest-frame is sensitive NP probe Uncertainties from Bd→K* transition form-

factors cancel zero of AFB(s) depends on Wilson

coefficients C7eff/C9eff

New Physics in BdK*0mm


gluino, chargino,neutralino, ?

Higgs, ?

Flavour Changing Neutral Current Decay in SM: b s electroweak penguin NP diagrams could contribute at same level

Sensitive to magnetic and vector and axial semi-leptonic penguin operators

Decay described by three angles (θl, φ, θK) and di-μ invariant mass q2

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New Physics in BdK*0mm

Current Measurements: BR measured at B-factories, in

agreement with SM: 1.1 ±0.3x10-6

AFB also: Belle has ~230 K*ll events LHCb sensitivity:

Expected yields: 7.2k events/2fb–1 Background:

• dominated by b→ m, b→ m, symmetric distribution in θl observed

• b→ m, b→ c → m significant contribution, asymmetric θl distribution …

• B/S ~0.2Acceptance correction …

Simple linear fit suggests precision:


NB: Opposite sign convention w.r.t. LHCb657 MBB

0.5 fb-1 2 fb-1 6 fb-1

s(s0) 0.8 GeV2 0.5 GeV2 0.3 GeV2 More complex fit methods being evaluated

q2(GeV2)

An example 0.5fb-1 experiment

AFB

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New Physics in Bsmm


SM SM MSSM

W

W

b

s

m

t

m

? ?

~ tan6/MH2

Helicity suppressed and in SM: BR(Bs → mm) = (3.4 ± 0.5) 10-9 sensitive to New Physics; could be strongly enhanced in SUSY Current limit from CDF: BR(Bs → mm) < 4.7 10-8

Event selection Main issue is background rejection:

dominated by B → mX, B → m X decays good mass resolution and PID essential SM Yield (2 fb-1): Signal: 23 – Bkg: 150 Statistical method applied to separate signal from background using PID, vertexing, mass

CDF Sensitivity with 8fb-1?

Sensitivity

0.1 fb-1 0.5 fb-1 2 fb-1 6 fb-1

BR SM BR < 10-8

(CDF limit)Excluded <SM

3 s evidence

5 s observation

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Summary Few hints of deviation from SM in b-physics are observed …

Flavour physics at the LHC will play a central role in the understanding of any new physics signals

LHCb offers exciting prospects for precision measurement and search for new physics in CP violation & rare decays: with 10fb-1

g measurements:with trees: a combined sensitivity of sg~2-3o is expectedwith loops: g with a sensitivity of sg~5o is expected

s measurements: s (s) ~0.01 Rare decays:

BdK*0mm : s(s0) =0.3 GeV2

Bsmm :5 s observation of SM value Ready and waiting for the first collisions!

With fraction of a 1 year nominal data set LHCb can already perform important key measurements probing New Physics


Many topics not addressed in this talk: a, measurements, charm physics, radiative decays … (Many channels still to be investigated …) F. Dettori

poster

Prospects for New Physics in CP Violation and Rare Decays at LHCb

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