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Status and physics potential of the LHCb experiment
Walter M. Bonivento INFN Cagliari 14th Lomonosov Conference, Moscow 2009

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LHC and LHCb Physics Goals
Main LHC Goals:
З Search for the SM Higgs boson in mass range ~ 115 < mH < 1000 GeV З Search for New Physics beyond the SM - Explore TeV-scale directly (ATLAS & CMS) and indirectly (LHCb) Current CPV measurements in agreement with the Standard Model; still, the direct measurement of less constrained elements such as s and , might reveal NP effects Moreover rare b->s decays, mediated by penguin and box diagrams, might also reveal NP

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LHCb Collaboration
700 members 15 countries 52 institutes

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The LHCb Experiment
Advantages of beauty physics at hadron colliders:
High value of bb cross section at LHC: bb 500 b at 14 TeV (1mb latest Pythia) Access to all b-flavoured hadrons

b b

b b

The challenge
Multiplicity of tracks (~30 tracks per rapidity unit) Rate of background events: inel 100 mb

LHCb running conditions:
Luminosity limited to ~2з1032 cm-2 s-1 by focussing the beam less than ATLAS and CMS do Maximize the probability of single interaction per bunch crossing At LHC design luminosity pile-up of >20 pp interactions/bunch crossing while at LHCb ~ 0.7 pp interaction/bunch LHCb will reach nominal luminosity soon after start-up

2fb-1 per nominal year (107s), ~ 1012 bb pairs produced per year
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The LHCb Detector
Muon System RICH Detectors Vertex Locator VELO

Movable device 35 mm from beam out of physics / 7 mm from beam in physics

pp collision Point

~1 cm

B

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W Calorimeters alter

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Tracking System

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Detector Performances: Tracking
Expected tracking performance:
З Efficiency > 95% for tracks from B decays crossing entire detector З p/p: 0.3% - 0.5% (depending on p) З Proper time resolution: ~ 40 fs З B Mass resolution: 15-20 MeV/c2

Efficiency ~ 95 % >10 GeV

Bs Ds(KK)K

Proper time resolution ~ 40 fs Mass resolution ~ 20 MeV
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Detector Performances: PID
Two RICH detectors with 3 radiators to cover range 2 < p <100 GeV : RICH1 Aerogel (2-10 GeV), C4F10 (10-60 GeV) RICH2 CF4 (16-100 GeV)
ЗGood -K separation in 2100 GeV/c range ЗLow momentum З Tagging kaons ЗHigh momentum ЗClean separation of Bd,s hh modes
invariant mass

-K separation

No PID

with PID

with PID

Kaon ID 90% Pion mis-ID 3%
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invariant mass Walter M. Bonivento - INFN Cagliari K invariant mass

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LHCb Trigger
Trigger is crucial as bb is less than 1% of total inelastic cross section and B decays of interest typically have BR < 10-5
L0 e, L0 had L0

40 MHz

Level -0

Hardware level (L0) Search for high-pT , e, 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
(L0) Electromagnetic Hadronic 70 % 50 % > ~80 % > ~90 % (HLT1) (HLT2)

High-Level Trigger

1 MHz HLT1
ECAL Alley Had. Alley Muon Alley

30 kHz Global reconstruction
Inclusive selections , +track, , topological, charm, & Exclusive selections

Muon 90 % 19/08/09 Walter M. Bonivento - INFN Cagliari Storage: Event size ~35kB

2 kHz

HLT2

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LHCb Physics Programme
Main LHCb objective is to search for the effects induced by New Physics in CP violation (see talk by T.Du Pree) and Rare decays (see talk by N.Serra) using the FCNC processes mediated by loop (box and penguin) diagrams
b
0 Bs

u, c , t

s
-
0 Bs

W

?

W

?
0 Bs

s

u, c, t
s
s SM

b



Sensitivity to masses, couplings, spins and phases of New Particles
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New Physics Search Strategy

Phases CPV processes are the only measurements sensitive to the phases of New Physics e.g. measurements of , s & Magnitude of the couplings of new particles Look at specific cases with enhanced sensitivity e.g. helicity suppression in Bs decay gives increased sensitivity to SUSY with extended Higgs sector Helicity structure of the couplings Use the correlation between photon polarization and b flavour in b s b (L) + (ms/mb) з (R) Similar studies using B K*+- & K*e+e

-

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CPV measurements: UT angles
Box diagrams (I)
Note: UT geometry is such that the main constraint on NP comes from the comparison of the opposite elements i.e. angles vs sides vs |Vub / Vcb | is largely limited by theory (~10% precision in |Vub|) Note a discrepancy in |Vub| determined in inclusive and exclusive measurements : |Vub| incl ~ (4.0-4.9)з 10 -3 and |Vub| excl ~ (3.3-3.6)з 10



-3



vs md /ms is limited by experiment: is poorly measured (~30А)

Indirectly is determined to be = (68 Б 4)К from processes involving boxes
Indirect Direct measurement LHCb will measure directly in tree decays using the global fit to the rates of B D0K,D0K* decays and time-dependent measurements with Bs DsK and B0 D decays

Expected (

trees

) 4А with 2 fb-1
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CPV measurements: Bs mixing
Box diagrams (II)
(J/ ) = -2
S

is the Bs meson counterpart of 2

penguin contribution 10-3

s not measured accurately (indication of large value from CDF/D0)
Theoretical uncertainty is very small - 2s = - 0.0368Б0.0017 (CKMfitter 2009 Moriond)

LHCb prospects (2 fb-1 sample) Expected yield 117k Bs J/ events

(2s) ~ 0.03

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CPV measurements: Penguin vs Tree
2(NP) = 2(B Ks) - 2(B J/Ks) CPV(Bs )>>1% is also sign of NP

Penguin diagrams:



0

Thanks to B-factories 2(NP)) ~ - 0.23 Б 0.18 rad
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LHCb sensitivity with 2 fb-1 ~ 0.11 rad (stat. limited)
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Rare Decays
Current experiments are only now approaching an interesting level of sensitivity in exclusive decays: BR (Bs ЕЕ) (CDF /D0) BR (Bd ) Photon polarization in B AFB in B K* (BELLE/BaBar)

K*ЕЕ (BELLE/BaBar)

LHCb will study rare decays in depth !!!

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B

s


-9

Super rare decay in SM with precisely predicted BR(Bs ЕЕ) = (3.55Б0.33)з10

Sensitive to NP, in particular new scalars In MSSM: BR tan6 / M4A Best present limit is from Tevatron: BR(Bs ЕЕ) < 4.5з10-8 @ 95% CL (Punzi, EPS2009) For the SM prediction LHCb expects 21 signal and 180 background events with 2 fb-1. Background is dominated by muons from two different semi-leptonic b-decays LHCb sensitivity for the SM BR: 3 evidence with 3 fb-1 5 observation with 10 fb-1
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Discovery 14 TeV BR (x10-9)

5 observation
SM prediction

3 evidence L(fb-1)

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Measurement of the photon polarization in Bs decay

SM: - C = 0 direct CP-violation - S = sin2 sin - A = sin2 cos

For Bd negligible -> only S with =; flavour tagging For Bs sizeable -> but S~sin2*(~0) ->sensitivity through A i.e. independent of =s ALLOWS DISTINCTION BETWEEN NP IN MIXING AND IN RIGHT HANDED CURRENTS NO FLAVOR TAGGING REQUIRED

cfr. at B factories ~ 0.16
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B

K*

NP: modified angular distributions

Described by three angles (l, , K) and di- invariant mass q2, ''=''(q2) Forward-backward asymmetry AFB of l distribution of particular interest: - Varies between different NP models - At zero-point, dominant theor. uncert. from hadronic form-factors cancels at LO
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2 AFB s = m

(

+



-

)

=

NF - N NF + N

B B

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B

K*

AFB at B-factories defined with opposite sign w.r.t. LHCb

Forward-backward asymmetry AFB (s) in -rest frame is a sensitive NP probe Predicted zero of AFB (s) depends on Wilson coefficients C7eff / C9eff simple binned, counting analysis LHCb, 2 fb
-1

AFB

(s0) ~.5 GeV2 q2 (GeV2)

LHCb expects ~7k events / 2fb-1 with B/S~0.2 After 2 fb-1zero of AFB located to Б0.5 GeV2. Full angular analysis gives better discrimination between models.
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Commissioning of LHCb
First attempt to perform time synchronization and space alignment using cosmics and LHC beam induced events - Use of cosmics non-trivial since LHCb is horizontal and located deep underground effectively works only for big sub-systems located downward of the magnet: Outer Tracker (OT), Calorimeter and Muon

Few Hz Trigger on "horizontal" cosmic tracks - Muon & CALO synchronized to a few ns -OT aligned to ~ 1 mm - L0 trigger commissioned
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Commissioning of LHCb
Beam 2 dumped on injection line beam stopper (TED) Located 340 m away from LHCb along beam 2 High flux O(10) particles / cm2 Particles cross LHCb in a wrong direction ~40 k tracks collected and used to align high granular Vertex (VELO) and Inner Tracker (IT) detectors

IT

Ladder position in the Inner Tracker is known to 20 precision

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VELO alignment
TED tracks perfect for VELO alignment: cross detector almost parallel to z-axis

21 stations of Si wafer pairs with r and strip readout

R strips

strips Resolution estimated from VELO hit residuals agrees well with expectations Further improvement possible
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Plans with (2009)2010 data
Beam energy expectations:
Recent information from the DG: "The LHC will run at 3.5 TeV per beam until a significant data sample has been collected", then rise at 5TeV. Some LHCb studies performed at Ebeam=4TeV to assess 2010 physics potential

Early measurements
- Calibration signals and minimum bias physics: 108 events
Key channels available in min bias data with simple trigger: - Ks 95% purities achievable using - p kinematical & vertex cuts alone

~ 40 mins @ 1031 With 2 kHz random trigger
p

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Plans with (2009)2010 data
Early measurements(ii)
- J/ trigger on single muon with pt cut (600k ev./pb-1) one muon unbiased for PID studies and momentum calibration - J/ physics & production cross-sections: ~ 1-5 pb-1
Measure diff. cross-section for prompt J/ and bb production cross-section (from secondary J/) in region inaccessible to other experiments

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Prospects for most competitive measurements in 2010
LHCb can exclude BR(Bs ) at 2 з 10-8 with about 100 - 150 pb

-1

Similar limit is expected from Tevatron on this time scale Sensitive test of SUSY should be possible in a year !!!

For s from Bs J/ LHCb assumes data sets of a few 100 pb-1, but the method was shown to extrapolate down to smaller event samples (works at Tevatron as well) Present `central value' would be confirmed at 5 level with ~150-200 pb-1 collected at Ecm= 8 TeV Similar sensitivity from Tevatron with 9 fb-1
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Conclusions
З LHCb is ready for data taking З First data will be used for calibration of the detector and trigger in particular. First exploration of low Pt physics at LHC energies. Some high class measurements in the charm sector may be possible З With 150 - 200 pb-1 data sample LHCb will reach Tevatron sensitivity in a few golden channels in the beauty sector З LHCb has plenty of room for discoveries of New Physics with a ~ 10 fb-1 data sample needed to complete LHCb physics programme З Study of possible LHCb upgrade, in order to collect ~100 fb data sample, is under way
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-1