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
_
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