The LHCb Experiment

presented at Hadron99, Beijing, 24-28 August 1999

On behalf of the LHCb Collaboration

Tatsuya Nakada

CERN, Switzerland

on leave from PSI

IntroductionCP violation is observed only in the neutral kaon system:

: CP violation in K-K oscillations: CP violation in the decay-oscillation interplay: CP violation in the decay amplitudes

They are within the framework of the Standard Model: KM phase.

However, 1) no “precision” test has been made…

(difficult with the kaon system due to theoretical uncertainties)2) no real understanding, on the origin of the mass matrix…

(Why strong CP is small but weak CP not?)3) Cosmology (baryon genesis) suggests that an additional

source of CP violation other than the Standard Model is needed.

A lot of room for new physics B-meson systems

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The B-meson system is an ideal place to search for new physicsthrough CP violation.

1) For some decay modes, the Standard Model predictions can be made accurately.- precision tests -

2) CP violation can be seen in many decay channels.- consistency tests -

The system allows to extract the parameters for both the Standard Model and new physics, if it exists.

a simple demonstration to follow

CKM Unitarity Triangles

VtdVtb + VcdVcb

+ VudVub = 0 VtdVud

+ VtsVus + VtbVub

= 0

Vub

Vcb

Vtd

Vub

Vtd

Vts

arg Vcb = 0, arg Vub = , arg Vtd = , arg Vts =

newparticles

Extensions to the Standard ModelSupersymmetry, left-right symmetric model, leptoquark, … etc.

all introduces new flavour changing neutral currents

b = 1 process: Decaysthrough penguin

b = 2 process: Oscillationsthrough box

through tree

newparticles

b d, s

b d, s

newparticles

d,s b

b d, s

d,s b

lor l

lor l

HB-Brdb]ei(db)Bd-Bd oscillations_

CKM and new physics in the oscillation amplitudes

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HB-Brsb ]ei(sb)_Bs-Bs oscillations_

md

ms

CP in BdJ/KS

CP in Bs J/

HB-Bei(db)

b c

d d

c

sBd

J/

KS

W

_

Bd

Bd J/KS

Bd

_

due to the interference

ABJ/KsVcbVcsei

|VtdVtb|

2

|VtsVtb|

2

CP in Bd J/KS

CP violation in Bd J/ KS v.s. Bd J/ KS

measures 2J/K = 2(KMdb)

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CP violation in Bd Dn v.s. Bd Dn Bd Dn v.s. Bd Dn

measures 2(KMdb ) KM

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CP violation in Bs J/ v.s. Bs J/

measures 2J/ = 2(KMsb)CP violation in

Bs DsK v.s. Bs Ds

K Bs Ds

K v.s. Bs DsK

measures 2(KMsb) KM

_

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A consistency test bycomparing the two KM then combine them toimprove the precision

Measuredbu

1

|Vtd|

= CKM angle

Vtd eiKM

semileptonic decaysare least effected by

new physics

MeasuredfromCP violation inBdDn, BsDsK

2) |Vub| and KM KM or (KM, KM)

5) J/K and KM db

3) KM KM

6) J/ and KM sb

7) ms, md and (KM, KM) rdb and rsb

4) (KM, KM) |Vtd| and |Vts|

1) KM is determined

determination ofCKM parameters

determination of new physics

parameters

Both CKM and New Physics parameter sets arefully and cleanly determined.

(and many other examples)

J/KS very high statistics for a precision

Dn small asymmetries require high statistics, low background

DsK need Bs (problem for BaBar, BELLE)particle ID at large p (problem for CDF, D0)small branching fractions <require high statistics

J/ need Bs (problem for BaBar, BELLE)large statistics needed to obtain CP/CP

Potential problems for BaBar, BELLE, CDF, D0, HERA-B

The LHCb experiment

Operating at the most intensive source of Bu, Bd, Bs and Bc,i.e. LHC

with

-particle identification-trigger efficient for both leptonic and hadronic final states.(ATLAS and CMS: no real particle ID and only with lepton triggers)

Brazil

France

Germany

Italy NetherlandsPRC Romania Spain

Switzerland

Ukraine

UK

USA

The LHCb Experiment(~450 people, ~50 institutes)

Poland Russia

Finland

The LHCb Collaboration (August 99)Finland: Espoo-Vantaa Inst. Tech.

France: Clermont-Ferrand, CPPM Marseille, LAL Orsay

Germany: Humboldt Univ. Berlin, Univ. Freiburg, Tech. Univ. Dresden, Phys. Inst. Univ. Heidelberg, IHEP Univ. Heidelberg, MPI Heidelberg,

Italy: Bologna, Cagliari , Ferrara, Genoa, Milan, Univ. Rome I (La Sapienza), Univ. Rome II(Tor Vergata)

Netherlands: Univ. Amsterdam, Free Univ. Amsterdam, Univ. Utrecht, FOM

Poland: Cracow Inst. Nucl. Phys., Warsaw Univ.

Spain: Univ. Barcelona, Univ. Santiago de Compostela

Switzerland: Univ. Lausanne

UK: Univ. Cambridge, Univ. Edinburgh, Univ. Glasgow, IC London, Univ. Liverpool, Univ. Oxford

CERN

Brazil: UFRJ

China: IHEP(Beijing), Univ. Sci. and Tech.(Hefei), Nanjing Univ., Shandong Uni.

Russia: INR, ITEP, Lebedev Inst., IHEP, PNPI(Gatchina)

Romania: Inst. of Atomic Phys. Bucharest

Ukraine: Inst. Phys. Tech. (Kharkov), Inst. Nucl. Research (Kiev)

U.S.A.: Univ. Virginia, Northwestern Univ., Rice Univ.

IP 8

The LHCb DetectorVertex detector:

Si r- strip detector, single-sided, 150m thick, analogue readoutTracking system:

Outer; drift chamber with straw technologyInner; Micro Strip Gas Chamber with Gaseous Electron Multiplier,

Micro Cathode Strip Chamber or SiRICH system:

RICH-1; Aerogel (n = 1.03) C4F10 (n = 1.0014)RICH-2; CF4 (n = 1.0005)Photon detector; Hybrid Photon Diodes (backup solution PMT)

Calorimeter system:Preshower; Single layer Pb/Si (14/10 mm)Electromagnetic; Shashilik type 25X0, ~10% resolutionHadron; ATLAS design tile calorimeter 5.6, <80% resolution

Muon system:Multi-gap Resistive Plate Chamber or Thin Gap Chamber and Cathode Pad Chamber

Physics capability of the LHCb detector is due to:-Trigger efficient for both lepton and hadron

high pT hadron trigger 2 to 3 times increase in, K, D, DK,Ds, DsK …

Ds: 34k(flexible and robust)

-Particle identification e///K/p, K, D, DK, Ds, DsK

-Good mass resolutione.g. 11 MeV for Bs Ds17 MeV for Bd

(particle ID + mass resolution redundant background rejection)-Good decay time resolution

e.g. 43 fs for Bs Ds32 fs for Bs J/

Trigger:Flexible: Multilevel with different ingredientsRobust: Evenly spread selectivities over all the levelsEfficient: High pT leptons and hadrons (Level 0)

Detached decay vertices (Level 1)

L0(%) L1(%) L2(%) Total(%) e h all

BdJ/(ee)KS + tag 17 63 17 72 42 81 24BdJ/()KS + tag 87 6 16 88 50 81 36BsDsK + tag 15 9 45 54 56 92 28

BdDKBd + tag 14 8 70 76 48 83 30

LHCb Trigger Efficiencyfor reconstructed and correctly tagged events

- trigger efficiencies are ~ 30%- hadron trigger is important for hadronic final states- lepton trigger is important for final states with leptons

Bs DsKMajor background: Bs Ds(No CP violation)

Importance of particle identification and mass resolution

Bs-Bs oscillations with BsDs

120 k reconstructed and tagged eventsmeasurements of mswith a significance >5: up topsxs

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The LHCb detector, a forward spectrometer with particle ID, will have a wide programme in heavy flavour physics.

• CP violation: Bd K±m KS K Kl+l …

Bs K+K K±m KS l+l …

• rare and forbidden decays: Bs, d , em ...

• Bc meson decays

• b-baryon spectroscopy

• etc.

tree+

penguinpenguin only

Conclusions•LHCb has been approved in September 1998,

preparing for Technical Design Reports.

•Construction will start the beginning of 2001.

•LHCb is one of the four baseline LHC experiments, taking data from the day one.

•Efficient and robust trigger the optimal luminosity

exploiting the physics potential from the day one.

•Locally tuneable luminosity long physics programme.

•Effective trigger, particle ID, decay time and mass resolution essential to reveal New Physics from CP violation.

(not possible by the general purpose LHC experiments)

LHCb CP Sensitivities in 1 year (work still in progress)

Parameter Channels No of events (1 year) LHCb feature

2(+) Bd + c.c. 6900

|P/T| = 0 2-5 PID, hadron trigger

Bd + c.c. ~1000 in progress PID, hadron trigger

2+ Bd D 446000 9 PID, hadron trigger

BdJ/Ks 45000 0.6

-2 Bs DsK 24000 6-13 PID, hadron trigger, t

Bd DK 400 10 PID, hadron trigger

Bs J/ 44000 0.6 t

Bs oscillations

xs Bs Ds 120000 upto 75 hadron trigger, t

Rare Decays

Br Bs <210-9 t

No. Bd K 26000 photon trigger