Malcolm John 1/17

Early physics of LHCb

Malcolm John

On behalf of the LHCb collaboration

1. Very brief introduction

2. Status of LHCb

3. A selection of the most promising results

Malcolm John 2/17

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At LHCb terms up to 5 must be considered

Major LHCb goals: Weak phase,,

Bs mixing phase s = 2arg(Vts)

B(Bs )

Malcolm John 3/17

bb• bb produced into forward region

• pp→bb(s=14TeV) 500b

• operate at ℒ = 2x1032 cm2s1

• 1012 b-hadrons a [107s] year• <momentum> 80 GeV/c• <d.o.f.(B)> = 7mm

The LHCb detector status in a nut-shell• All major sub-detector intrastructure is installed and instrumentation is well underway• LHCb will be ready to [space and time] -align during the 2007 LHC engineering run• 2008: Calibrate the complete detector and trigger for s =14TeV

Expect 0.5fb1 (50 billion b-quarks)• 2009: Full physics data-taking

Expect 2fb1/year

Malcolm John 4/17

LHCb at LHC - P8Inset: retracted HCAL & muon filter

Malcolm John 5/17

VErtex LOcator• 170 000 channels• 8.1mm from beam• (40<pitch<100)m• Z(PV) < 50m• (Bs) < 40fs

Beam’s eye view

Malcolm John 6/17

Simulation

• Expectations are evaluated using the LHCb MC simulation software: Pythia, EvtGen, GEANT4 and Gaudi-based reconstruction (2004 MC data)

– Detailed detector and material description (GEANT)– Pattern recognition, trigger simulation and offline event selection– Implemented detector inefficiencies, noise hits, effects of events from the previous

bunch crossings

Slide by Peter Vankov

Malcolm John 7/17

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Bs

→ Ds K B → D0K(*)

= (8220)° (current direct measurements)

Malcolm John 8/17

from Bs →DsK

us

sssB D*

cbV

usV

b

Kc

cs

sssB K*

cbV

csV

b

Du

• Expect 6200 DsK events in 2 fb–1

• B/S < 0.5

• Expect 6200 DsK events in 2 fb–1

• B/S < 0.5

• Expect 140 000 Ds• 98% suppression

achieved with RICH PID system in the analysis

• Used to measure ms

• 2 fb–1: (ms) 0.012ps–1

• Expect 140 000 Ds• 98% suppression

achieved with RICH PID system in the analysis

• Used to measure ms

• 2 fb–1: (ms) 0.012ps–1

+ ch.c. diagrams

• Study sensitivity by generating toy-experiments with experimental inputs derived from full MC (Decay time and mass resolution, reconstruction efficiency, tagging…)

– Sensitivity with 2 fb-1 : σ() ~ 13°

• Two tree decays (bc and bu), which interfere via Bs mixing:

– can determine (s + ), hence in a very clean way

• Fit 4 tagged, time-dependent rates– Extract s + , strong phase difference , amplitude ratio

– Bs Ds also used in the fit to constrain other parameters (, ms, s)

Malcolm John 9/17

from Bu,d →D0K• Interplay of Bu and D0 decays where interferes with

– charged Bs only (time-independent, direct CPV)– choose decay hierarchies in which large CP asymmetry is possible– “tree-level” dominates. No penguins pollution

us

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0(*)DcsV

*ubV

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s (*)K

Colour favoured bc amplitude Colour suppressed bu amplitude

)( ubVscub sucb

→ X

→ X

Also known as… → X Yield / 2 fb–1 (), 2 fb–1

ADS, GLW K ~700 (56k †)<15º

KK, 5k, 1.6k

D0-Dalitz (GGZS) KS 5.0k 8º

B0 self-tagging variant K, KK, 530, 470, 130 (3.3k †) 8º–10º

• A similar analyses possible with B0→D0K*0 decays– The b→c transition is also colour suppressed. Expect large CP-asymmetries– self-tagging (i.e. the b-quark flavour is given by the sign of the prompt signal kaon)

† favoured decay (not sensitive to )

Benefit from CLEO-c …

Malcolm John 10/17

Bs → J/…etc… and

Bs →

(0,0)

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s arg(Vts)

Malcolm John 11/17

s

s

0sB

*tbV

tsV

b

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t

*tsV

tbV

c

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ss

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/J

csV

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s

Bs mixing phase: s

• The equivalent of “sin2“ for Bs mesons• In the standard model, s is small: = -2arg(Vts) 0.0360.003

– Could be larger if New Physics is present in the box diagram– Recent D0 result s= –0.79 ±0.56(stat) +0.14–0.01(syst) with 1.1 fb–1

• To resolve Bs oscillations, excellent proper time resolution is required

• Modes sensitive to s :– CP-odd & even:

Bs→ J/– CP-even only:

Bs→ cBs→ J/ Bs→ Ds Ds

• Control channel (ms):

Bs→ Ds

Illustration of CPV:

toy-modeling LHCb data with s = 0.2 (i.e. 5SM)

events tagged as Bs

events tagged as Bs

Malcolm John 12/17

Precision on a measurement of s = 0.04

Yield in 2fb1 B/S σ (fs) mass (MeV/c2)

Comment

Bs→ J/ 131k 0.12 36 14 Large yield but full angular analysis required

0.023

Bs→ c 3k 0.6 30 12Low yield

High background

0.108

Bs→ J/ 11k <3 35 30 0.105

Bs→ Ds Ds4k 0.3 56 6 Poorest proper-time

resolution0.133

( )s rad

>90% CL

>32% CL>5% CL from hep-ph/0604112

Current, including first measurement of ms

hs

s

Arbtrary new physics parameterisation: MNP = MSM (1+hsei)

With (s)= ±0.03 (~ 2 fb–1)

(different x-scale)

hs

s

0.50.5

0.020

0.044

2fb1

0.5fb1

Malcolm John 13/17

Bs →

• FCNC gluonic penguin decay. Analogue of B0→Ks for the Bs

• Dependence on Vts in both the decay and Bs mixing amplitudes, phase cancels and leads to the SM CP-violation expectation < 1%

– Large CP asymmetry would be a signature of New Physics

• The PVV decay requires a full angular, time-dependent CP analysis

• Expect 4000 events/2 fb-1 (based on a CDF B.F. measurement: 1.40.9 x105)– Early feasibility studies suggest LHCb statistical precision on a New Physics phase

(defined at 0.2 for the purposes of this work) in 2fb1 is: ~0.10

• Current combined, B-factory measurement of sin 2β in B0 →K0S : 0.39 ± 0.18

– For comparison, the 2 fb-1 LHCb sensitivity in this mode is 0.32

s

s

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stcu ,,

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Malcolm John 14/17

Bs →

and Bs

→ K*0

New Physics enhancement of very

Z0

W

t

tb

s

Bs

W

tb

s

Bs

W

H0/A0

b

b

s

Bs

t

B.F.(Bs)MSSM tan6

B.F.(Bs)SM 3.5x109

rare B-decays

Malcolm John 15/17

Bs expected sensitivity• Very exciting possibility of sensitivity to New Physics enhancement in the early period• Current upper limit from the Tevatron is around 20 x SM prediction• The dominate background is b , b.

– Background analysis is currently limited by Monte Carlo statistics (generation)

• LHCb’s superior Bs invariant mass resolution is crucial in the background rejection

LHCb limit on BR at 90% CL (only bkg is observed)

LHCb sensitivity(signal+bkg is observed)

5 observation

3 evidence

SMB

F (

x10–9

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Integrated luminosity (fb–1)

BF

(x1

0–9)

Expected final CDF+D0 limit

SM

“early”

period

Uncertainty in bkg prediction

Uncertainty in bkg prediction

Malcolm John 16/17

NP model descrimination possible with B0 K*0

s = (m)2 [GeV2]

AFB(s), theory

AFB(s), fast MC, 2 fb–1

s = (m)2 [GeV2]

+

–

• Suppressed loop decay, BR ~1.210–6

– Forward-backward asymmetry AFB(s) in the rest-frame is sensitive probe of New Physics:

• Sensitivity (ignoring non-resonant K evts for the time being)

– 7.2k signal events/2fb–1, Bbb/S = 0.2 ± 0.1

– After 2 fb–1: zero of AFB(s) located to ±0.52 GeV2

– Other sensitive observables based on

transversity angles accessible (under study)

Malcolm John 17/17

Conclusion• LHCb is a spectrometer experiment at the LHC which instruments the forward

region of the LHC hadron collision• The final assembly and commissioning is on schedule: ready to take calibration

and alignment data this autumn

• LHCb has a rich physics program and most analyses expect good results in the early period (<2fb1):

– Observation of Bs→– ()LHCb 5 degrees– (s)LHCb 0.02 radians– Sensitivity to New Physics phase in Bs →

• In addition, (ms) 0.012ps–1 (sin(2)) 0.02 (2x105/2fb–1) [final B-factory result: σ(sin(2)) ±

0.017stat] () 10 degrees– ACP(K*) measured at % level (ACP < 1% in SM)– Charm physics:

• D0 mixing (expect ~ 45k D0 candidates in final fit sample… 5x B-factories’ combined yield)• direct CPV in D0K+K– • D0+–

• and I’m sure I’ve under-represented someone…`

Malcolm John 18/17

SupplementarySlides

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Malcolm John 19/17

bb

ss

uu

t =0

Time-dependent analysis requires B flavour tagging• We need to know the flavour of the B at a reference t=0 (at the primary vertex)• Tag (give best estimate of) the flavour by examining the rest of the event

Bs0

PV

z/c = t recKDs

t picoseconds after leaving the primary vertex, the

reconstructed B

decays.

t picoseconds after leaving the primary vertex, the

reconstructed B

decays.

K+

l (e+, )

l (e, )

K

Uses flavour conservation in the hadronization around the Brec D2 1% (B0) , 3% (Bs)

Same-side tag

ll

X b

Wc s

ll

WAssume:

Opposite side tag D2 5%

b-hadron

R Wtag

R W U

N N

N N N

Wtag

R W

N

N N

( ) ( )obsCP CPA t D A t 1 2 tagD

Malcolm John 20/17

RICH systems

• Particle ID: p~1-100 GeV provided by 2 RICH detectors

Slide by Val Gibson

Aerogel22 tiles

RICH2

Malcolm John 21/17

• Only ~1% of inelastic collisions produces b-quarks.• Branching fractions of interesting B decays are <10-4

• Properties of minimum bias events ate similar to those containing B decays

• First Level Trigger (L0) – Hardware (custom boards, 4s latency)– Largest ET hadron, e() and (di-)– Pile-up system (not for trigger)– Reduces 10 MHz inelastic rate to 1MHz

• High Level Triggers – Software trigger run on CPU farm (1800 nodes)– Access to all detector data – Full event reconstruction; inclusive and exclusive selections tuned to specific final states– Output rate 2 kHz, 35 kB per event

A successful trigger is crucial in LHCb

Output rate Trigger Type Physics Use

200 Hz Exclusive B candidates Specific final states

600 Hz High Mass di-muons J/, bJ/X

300 Hz D* Candidates Charm, calibrations

900 Hz Inclusive b (e.g. b) B data mining

Slide by Olivier Schneider

Malcolm John 22/17

VELO

TT

T1 T2 T3 RICH2

RICH1

Magnet

PYTHIA+GEANT full simulation

Expected tracking performance

• High multiplicity environment:– In a bb event, ~30 charged particles

traverse the whole spectrometer

• Track finding:– efficiency > 95%

for long tracks from B decays(~ 4% ghosts for pT > 0.5 GeV/c)

– KS+– reconstruction 75% efficient for decay in the VELO, lower otherwise

• Average B-decay track resolutions:– Impact parameter: ~30 m – Momentum: ~0.4%

• Typical B resolutions:– Proper time: ~40 fs (essential for Bs physics)

– Mass: 8–18 MeV/c2

Mass resolution

Bs 18 MeV/c2

Bs Ds 14 MeV/c2

Bs J/ 16 MeV/c2

Bs J/ 8 MeV/c2

* with J/ mass constraint

*

Slide by Olivier Schneider

Malcolm John 23/17

Particle ID performance

• Average efficiency:– K id = 88% mis-id = 3%

• Good K/ separation in 2–100 GeV/c range

– Low momentum • kaon tagging

– High momentum • clean separation

of the different Bd,shh modes

• will be best performance ever achieved at a hadron collider

invariant mass K invariant mass

With PID With PID

invariant mass

No PID

Slide by Olivier Schneider

Malcolm John 24/17

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Major LHCb goals :Weak phase,,

Bs mixing phase s = 2 2arg(Vts)

At LHCb terms up to 5 must be considered