beauty and the beast - mcgill university

Beauty and the Beast:Beauty and the Beast:B mesons and theB mesons and the BBAABBARAR

experimentexperimentSteven Robertson

Institute for Particle Physicsand

McGill University

Presented at Carleton UniversityNovember 29, 2005

Nov 29, 2005 2Steven Robertson, IPP, McGill Beauty and the Beast

OutlineOutline

● Physics results

– Status of sin2 constraints fromβb qqq' tree and penguin modes→

– Direct CP violation

– Electroweak penguin and raredecays results

– Exotica: pentaquarks and newstates

● Historical motivation for CP violation and B physics

● The CKM matrix and some B physics theory

● Asymmetric B factory concept


Standard ModelStandard Model

Higgs Boson(spin 0)

H0

• Describes the interactions of particles via three of the fourfundamental forces

EM: photon ( γ )Weak: Z0 W+ W-

Strong: 8 gluons

Forces (spin 1)

• ParticlesParticles interact through forcesforcesmediated by the exchange of (virtual)gauge bosons

• Weak interaction couples to weakeigenstates rather than mass eigenstatespermitting quark flavour changinginteractions between generations

Matter(spin ½)

c

s

t

b

u

d

νµ

µντ

τνee -1

0

+2/3

-1/3


A brief history of the weak interactionA brief history of the weak interaction

• 1932 - Fermi proposed “weak interaction” responsible for nuclear β decay

• 1957 - C.S. Wu et al. observed parity (P) violation inthe weak decay of polarized 60Co nuclei

• 1956 - Lee & Yang argued that parity is not conservedin weak interactions

• 1950s - Discovery of “strange” particlesproduced strongly in pairs, but decaying weakly

J=5

60Co

J=4

60Ni*

νe

+e-

J=1

e-L + νR

z

+


HistoryHistory• 1963 - Cabibbo proposed that the weak interaction couples to a

“mixture” of d and s mass eigenstates

• 1964 - Cronin & Fitch observed CP violation in K0 decays:

• 1970 - GIM predicted existence of a fourth “charmed” quark

• 1973 - Kobayashi & Maskawa proposed anexplanation for CP violation using a modelcontaining SIX quarks

• 1974 - “November revolution”: discovery ofthe J/ψ and ψ’ resonances (charm quark)

observe “forbidden” decay modeKL π+π- (0.2%)

• 1979 - discovery of the beauty (b) quark

• 1993 - observation of the top (t) quark


CKM matrixCKM matrix● CKM matrix parameterizes weak interactioncouplings to the three quark generations

– Weak eigenstates are essentially “rotated” inflavour space relative to mass eigenstates (i.e.physical quark states)

– A 3x3 unitary matrix contains a single irreduciblephase which permits CP violation in weak decays

π0

π+

K+

u

ud

s u

u

Vus

Vud

Convenient to use Wolfenstein parameterization, with = |Vλ us| ≈ 0.22acting as an expansion parameter

– Matrix fully determined by four real parameters A, , ,λ ρ and η

V=V ud V us V ub

V cd V cs V cb

V td V ts V tb= 1−1

2λ 2 λ Aλ 3ρ−iη

−λ 1−12λ 2 Aλ 2

Aλ 31−ρ−iη −Aλ 2 1O λ 4


Unitarity trianglesUnitarity trianglesUnitarity of the CKM matrix requires

VCKM = VCKMT*implying relations betweenvarious matrix elements:

Vector in complex plane

Three distinct triangles can be formed:

Vud Vus VubVcd Vcs VcbVtd Vts Vtb

Vud* Vcd* Vtd*

Vus* Vcs* Vts*

Vub* Vcb* Vtb*=1x

Σi Vid Vib* = 0

Σi Vis Vib* = 0

Σi Vid Vis* = 0

B mesons:

Bs mesons:

Kaons:

All triangles have equal areadefined by |J|/2 where|J| < ~0.1 and J=0 wouldimply no CP violation

VudVub* + VcdVcb* + VtdVtb* =0

Note that if all CKM elements are real, CP violation does not occur and areaof all triangles are zero

ReIm


Unitarity trianglesUnitarity triangles

α

γ β

VtdV

tb *

VcdVcb*V udV ub

*

B0→π+π−

B0→ ρ+ρ−

b→ ulν

b→ clνB→ψKSB→φKS

B0 D→ *πB+→ D0CP K+

B0B0 mixing

➔CP violation is permitted in the Standard Model but is small in the sensethat experimentally J is much less than the theoretical maximum

– By convention, CP violating phase is contained in Vub and Vtd (i.e. all other CKMelements are real)

– Lengths of triangle sides are related to magnitudes of CKM elements

– Angles ( , ,α β γ) are related to CP violation

● Standard Model predictsclear relationships betweenCKM matrix elements andthe expected patterns of CPviolation e.g.:

β = arg (- )Vcb Vcb*Vtd Vtb*


B mesonsB mesonsB mesons are composed of a quark – antiquark pair, one of whichis b-flavoured

Neutral B mesons:

● Because B0 and B0 mesons share common final states, they areable to MIX:

B0 = db

B0 = dbB0 mass: 5.279 GeV/c2Lifetime: 1.548 ps

*tdVtbV

*tdV tbV

b

b

t

t

d

d

0B0B

∣B phys0 t ∝cos mΔ Bd

t /2 ∣B0>i e−2 iϕM sin mΔ Bd

t /2 ∣ B0>

ϕM=arg V tdV tb∗ =β


Argus experiment (1987)Argus experiment (1987)Demonstrated mixing of B0 events usingsamples of double semileptonic events:

B0→ D*-μ+ , D*ν - D→ 0 π-

B0 D*→ -μ+ , D*ν - D→ - π0

● Large observed mixing suggestedthat it might be possible to observelarge CP violating effects in Bmeson decays

– Concept of an asymmetric B factoryfirst proposed at Snowmassmeeting in 1988


CP violation in interferenceCP violation in interference● Measure CP violation in the interferencebetween the decays of mixed and unmixedB0 decays

0B

0B

CPfCP

mixing

decay

t=0

tCPfA

CPfA

~e-2iβ

– Combination of two decay amplitudes to thesame final state manifests as an “interferencepattern” in the measured decay rate as afunction of decay time

λfCP~ e-2iβ (AfCP/AfCP)


Decay modesDecay modesTree-level charmonium modes in particularhave very clean theoretical predictions

– In Standard Model, coefficient of cos term iszero, and of sin term has simple relation toCKM angle β

Also “penguin” mediated b qqq' decays→– Potential sensitivity to heavy new particles inthe loop

Goal is to overconstrain CKM parameters by measurements of unitaritytriangle sides and angles in many independent decay modes

– “New Physics” can introduce additional CP violating phases which can lead todistinctive patterns of deviations in different decay modes

0Kb

c

sc

d0B d

(quark subprocess: b(quark subprocess: b ccs)ccs)

J/Ψ

b ss

sd

d

g

, ,u c t

W +

AJ /ψ K S , L

0 t =− ηJ /ψ K

S , L0 sin 2β sin mΔ Bd

t

B0

K0


Trees and PenguinsTrees and Penguins● Time-dependent CP asymmetries in b→ccs, b→sss, b→qqs (q=u,d)

– b→ccs is tree decay: clean sin2β measurement– b→sss purely penguin decay: sin2β in Standard Model

● (~0.05 hadronic), sensitive to heavy particles in loops● “New Physics” potentially contributes at same order as Standard Model

– b→qqs proceeds via penguin diagrams and b→u tree diagrams

b ss

sd

d

g

, ,u c t

W +

K0

sds /

dd

g

b

ds /

s~b~

g~

b sd

dd

d

W +

g

, ,u c t

B0K0B0

b→ccs

b sss→ b dds→

New Physics

π0


Physics needsPhysics needs● Time dependent CP asymmetry measurements require:

1) Knowledge of the B meson flavour (B0 or anti-B0) at some time t0

✔ Υ(4S) resonance

2) Measurement of the the decay time t relative to t0

✔ Asymmetric B factory concept

3) Identification of the B decay mode to a specific CP eigenstate

✔ Exclusive event reconstruction

4) Sufficient statistics to be able to evaluate the time dependent decay rate

✔ PEP-II Collider

5) Need to do all this in a clean enough environment that any CP asymmetries arenot “washed out” by backgrounds, resolution or mistagging effects

✔ BABAR detector


The two B mesons evolve inphase until one decays

(EPR situation)

ΥΥ(4S) resonance(4S) resonance

B0B0 pair is produced ina coherent L=1 state

● The Υ(4S) is a bb resonancewhich lies just above the massthreshold for production of BBmeson pairs.

● Cross section of ~1.1nb

➔ ~1.1 million BB pairsproduced per fb-1

OffOn

PEP-IIBABAR

BBthreshold

ECM -M Υ(4S) (MeV)


Asymmetric B Factory conceptAsymmetric B Factory conceptB mesons produced via Υ(4S)→ BB are nearly at rest the centre of massframe (since very close to production threshold) and B meson lifetime isvery short (~1.5ps)

➔ flight distance prior to decay is very small

● To get around this, electron and positron beams of unequal energiesare collided so that the Υ(4S) is produced with a significant boostrelative to the centre of mass frame

● The result is that the two B mesons end up with a measurableseparation:

e.g. for a boost factor of ~0.6βγ


0tagB

0recB

B-Flavour Tagging

ExclusiveB Meson

Reconstruction

0SK

J/Ψ π+

π-

μ-

μ+

e- e+

Υ(4S)

Δ zl-

K-

Time dependent CP measurementTime dependent CP measurement

Reconstruct decayvertex positions

Exploit correlationbetween B0 flavourand lepton charge,K charge etc


• First colliding beamsFirst colliding beamsin July 1998in July 1998

• First data recordedFirst data recordedJune 1999June 1999

High Energy Ring (HER): 9.0 GeV electronsLow Energy Ring (LER): 3.1 GeV positronsPeak luminosity: 1.00 x 1034cm-2s-1

(Run 5a, Oct 2005)

PEP-II delivered 313fb-1

BaBar recorded 300.5 fb-1

Onpeak: 273.7 fb-1 offpeak: 26.8 fb-1

PEP-II Asymmetric B FactoryPEP-II Asymmetric B Factory


PEP-II OperationsPEP-II Operations● Recently exceeded 1x1034 milestone(more than three times design!)

● Addition of trickle injection of bothhigh and low energy beams in Run 4resulted in significant increase inoperational efficiency

Daily integrated luminosity

Instantaneous peakluminosity


TheThe BBAABBARAR detectordetector

e-(9.0 GeV)

e+(3.1 GeV)

EM calorimeter6580 CsI(Tl)crystals

spT/pT = (0.13 · pT /[GeV/c] + 0.45)%40 layer drift chamber (dE/dx)

1.5 Tsolenoid

5-layer siliconvertex detector

DIRC – RICH utilizingtotal internal reflection

BABAR

K-π separation

pLAB (GeV/c)

K-πseparation(σ)

Magnet flux returninstrumented withRPCs (→ LSTs)

● Operating at centre of mass energyof 10.58 GeV for Υ(4S)→ BB

● Asymmetric beam energies produceboost of βγ=0.56 in lab frame


BABAR performanceBABAR performance● Run 5 started in March 2005 afterextended shutdown

– 60fb-1 delivered prior to ~1monthshutdown in Oct 2005

– Resumed running last week and willcontinue through summer 2006

● Anticipate ~250fb-1 total in Run 5

● Hardware improvements for Run 5:

– Trigger hardware upgrade to permit z-position discrimination at Level 1

– Replacements of 2/6 of barrel RPC with LSTs (remainder during summer 2006shutdown).

● 91% single hit efficiencies and only a few dead channels seen so far

– DCH electronics upgrade to reduce deadtimes

● add waveform analysis in new front end FPGA's (expect deadtime free)

Run 5


Run 5 week 1Run 5 week 1 (Oct 2004)(Oct 2004)

Lab operations shut down for five months following an electrical accident(Oct 11, 2004) unrelated to BABAR

– Worker injured while attempting to swap a circuit breaker in an energized highvoltage panel

– Situation aggravated by a hoisting incident about a week earlier in which a loadwas dropped (about 5cm) when a sling broke

● Subsequent DOE investigationand resulting major changes toall work procedures furtherdelayed PEP-II restart


Run 5 re-start week 1Run 5 re-start week 1 (May 2005)(May 2005)● Entire SLAC site lost power for most of a week after a 33m talltree fell on the main site power lines

230 kV lines


Recovery from power outageRecovery from power outage● Gopher found eating DCH readout fibres (May 2005)


HOM heating of beamline elementsHOM heating of beamline elements

Catastrophic vacuum failure in PEP-II due to RF heating ofbeamline elements

– Beam position monitor (BPM) feedthrough failure due to HOM heating


GEANT4 dE/dx bugGEANT4 dE/dx bugMay 2005: BABAR identifies a mysterious feature in latest version ofphysics event simulation affecting low momentum pions

– reduced efficiency for low momentum particles in simulation

● Eventually traced (Aug 2005) to an undocumented bug in a specificGEANT4 toolkit release

– simulated particles don'tmake it through ~1mm Bedrift chamber inner supportcylinder

– About 1 billion newsimulated physics eventsaffected (~5 billion cpu-seconds)


Event pictureEvent picture


Charmonium modes (bCharmonium modes (b→→ccs)ccs)

sin2β =0.722±0.040±0.023PRL94,161803 (2005)

CP odd modes

CP even modes

t [ps]Δ

227M BB

World averagesin2βWA =0.685±0.032

Average from HFAG: hep-ex/0505100and Summer 2005 update

● Since 2001, sin2 in charmoniumβhas become a precisionmeasurement!

➔ Clear demonstration that KM modelof CP violation is correct

– What about New Physics???


bb→→sss, bsss, b→→qqsqqs

sin2βeff=0.63+0.28–0.32±0.04 sin2βeff=0.09±0.33+0.13–0.14±0.10

Results from B0→ Kφ 0, ’Kη 0, f0K0S,π0K0S, π0π0 K0S, Kω 0S, K+K–K0, K0SK0SK0S

hep-ex/0507087, 0508017, 0503018, 0507016, 0507052

Sin2βeff=0.652

New in 2005:

B0→K0SK0SK0S (K0S→π+ π–,π0 π0)

227M BB

B0→K+K–K0L (B0→ Kφ 0L excluded)

227M BB

(syst. from CP-content)

B0

B0


Combined bCombined b→→ccs, bccs, b→→sss, bsss, b→→qqsqqs

Caveats:

– New Physics could affect differentmodes by different amounts, hence“average” is only meaningful in theStandard Model

– Additional suppressed contributionswith different weak phases in somechannels

– Average neglects possibleexperimental correlations betweenmodes

Many of these resultsare preliminary

Charmonium and naïves-penguin sin2βeff averagesare consistent at 2.6 levelσ


Unitarity Triangle ResultsUnitarity Triangle Results

CKMfitter Group:EPJ C41,1 (2005)and EPS 2005 update

Substantial progress inconstraining CP violationparameters since the B factoriesbegan operations


Direct CP violation in BDirect CP violation in B00→→ KK++ππ--

● Asymmetry in yields between a decay and it CP conjugate mode

– Expected to be large in B decays but previously not observed

– Requires at least two contributing decay amplitudes carrying different weak andstrong phases

– B0→ K+π- occurs via both tree and penguin processes hence direct CP violationpossible

AKπ = -0.133 ∓ 0.030 (stat) ∓ 0.009 (syst) 4.2σ

● Total of 1605∓51candidates identified in227M BB events

● It took 40 years to observedirect CP violation in kaondecays, but only 4 years inB decays!

hep-ex/0407057


Future prospects for CP studiesFuture prospects for CP studies

● Most CP asymmetry measurementsare currently statistically limited

– Expect errors of ~0.1 on SfCP and CfCPfrom individual b→sss, b→qqsmodes

– Very precise determination of b→ccs,both in individual modes andcombined average

● BABAR and PEP-II will continue data taking until 2008 followingsummer 2006 shutdown for IFR upgrade and accelerator work

– Anticipate ~4 times current dataset (~1ab-1 or >1 billion BB pairs) by end ofexperiment


Global CKM fit circa 2008Global CKM fit circa 2008

(Vσ ub)~8% ( mσ Δ s)~5% (sin2 )~0.019 ( )~6 ( )~10σ β σ α σ γ°∘ °∘


Other selected topics...Other selected topics...


More fun with penguinsMore fun with penguins

l+

l-γ, Z0

B- K-

W-

b su,c,t

u u

● As for gluonic penguins used for CV violation measurements,processes mediated by Electroweak Penguins are potentially sensitiveto New Physics contributions

– Heavy new particles in the loop could affect branching fractions, angulardistributions, direct CP asymmetries etc


Electroweak penguin modesElectroweak penguin modes

preliminaryXsγ

Kl+l–

K*l+l–

Scaled by 10


BB→→ρρ(770)(770)γγ and Band B→→ωω(782)(782)γγ● FCNC processes proceed via EM penguin processesin SM with top quark in the loop

● Rates related by spectator quark model

– SM B[B→( , )ρ ω γ] (~ 0.9 -1.8) × 10-6 but also possible New Physicscontributions

● Analysis on full BABARdataset searches formodes B+→ ρ+γ , B0→ ρ0γand B0→ωγ

B. Aubert et al., PRL 94,011801 (2005)


Unitarity triangle constraintsUnitarity triangle constraints● Ratio of b→ dγ to b→ sγ modes constrains ratio of the CKM elements

|Vtd|/|Vts| :

flavour SU(3) breakingζ2= 0.85 ± 0.10

weak annihilationcorrection ΔR = 0.1 ± 0.1

Ali et al. hep-ph/0405075

● Using B[B (→ , )ρ ω γ] and BABARmeasurement of B→K*γ , obtain limitof <0.029 (90% C.L.) on the ratio ofbranching fractions

● Neglecting theoretical uncertaintiesyields |Vtd|/|Vts| < 0.19

B. Aubert et al. , PRD 70, 112006 (2004)


Observation of Y(4260)Observation of Y(4260)→→J/J/ΨπΨπ++ππ-- in ISRin ISR

● Use initial state radiation events (similar to LEP “radiative return”) tolook for X(3872) state...

o Signal 125±23 events; >8σ statistical significanceo Mass (4258±8) MeV; just above DSDS threshold

o Total width (88±23) MeV

ψ(2S)

hep-ex/0506081

LP05

232 fb-1

Joins growing list ofpoorly understoodheavy mass states...

JPC = 1--


Pentaquark searchesPentaquark searches● Recent pentaquark frenzy triggered by paper by D.Diakonok, V.Petrov and M. Polyakov Z.Phys. A 359 (1997) 305., and evidence forΘ+(1540) from several experimental groups

– Chiral soliton model with N+(1710) as input, and mass splitting of ~180MeV

– “Exotic” Θ+(1540) would have to have minimal quark content of ududs

● BABAR preliminary results presentedat ICHEP 04 (hep-ex/0408064; BABAR-CONF-04/36)

– Search for Θ+(1540), Ξ--(1860), Ξ0(1860) aswell as other members of the antidecuplet andcorresponding octet

● Results recently submitted to PRL


ΘΘ(1540)(1540)++,, ΞΞ55(1860)(1860)---- andand ΞΞ55(1860)(1860)00

● Search for Θ+→ p K0s (K0s→ π+π-)

– Use all events accepted by trigger (>99%efficient for ee→ qq)

– Reconstructed invariant mass resolutionranges from 2 – 8 MeV/c depending onmode and momentum.

● Ξ5--→ Ξ- π- and Ξ50→ Ξ- π+ with Ξ-→ Λ0π- , Λ0 p→ π-

– observe 290000 Ξ- candidates withS:B of 23:1 in Λ0π- mass

– signal efficiency of 6.5% (low p*)to12% (high p*)

98000 Λc+→pK0s decayspeak s<6 MeV/c2

BABARPreliminary!

Ξ50

Ξ5--


Pentaquark resultsPentaquark results● BABAR sees no evidence for either theΘ(1540)+ or Ξ5(1860)

● Unfortunately, since the production mechanismis not known:

– model-independent limits derived on inclusiveproduction rates by fitting mass spectra in bins ofp*

– signal width varied from 1 MeV/c2 up to naturalwidths of 8(18) MeV/c2 for (1540)Θ + (Ξ(1860)--)reported by other experiments

– yields quoted relative to total number of both ee→qq and Y(4S) events Pentaquark Cross-section e+e-→qq yield

state UL (fb) UL (10-5/event)Θ+ + Θ- 171 (363) 5 (11)Ξ5-- + Ξ5++ 25 (36) 0.74 (1.1)

= 1 MeV/cΓ 2 ( =natural width)ΓBased on 123 fb-1 of BABAR datahep-ex/0502004 (submitted to PRL)

BABARPreliminary!

● If Θ(1540)+ or Ξ5(1860)--pentaquarks exist, they aresubstantially suppressed ine+e-→ qq relative to ordinarybaryons of similar mass


ConclusionConclusion● Asymmetry B Factories have been extremely successfully sincebeginning operations in 1999

● KM picture of CP violation in the Standard Model has been very clearlyconfirmed via precise sin2β determinations from charmonium modes

● Independent verification of sin2β in b→ sss penguin modes constrainsNew Physics contributions

– Many additional constraints from triangle sides, and angles andα γ (notdiscussed here!)

● First observation of direct CP violation in B0→ K+π- by BABAR in 2004● Very robust program of non-CP studies, particularly searches for rareand exotic states

– Electroweak penguins (b s/d→ γ)– Pentaquarks (non-confirmation of claimed signal)

– Observation of the Y(4260)

● Anticipate exciting new results with ~4X current data sample by 2008


PEP-II Asymmetric B FactoryPEP-II Asymmetric B Factory

Collide 9.0 GeV electrons with3.1 GeV positrons

CM Energy = 10.58 GeVDesign luminosity 3.0 x 1033 cm-2 s-1

Ring circumference: 2219.3 mNumber of bunches: 1658Particles per bunch: (HER) 2.73x1010

(LER) 5.91x1010Beam current: (HER) 0.75 A

(LER) 2.14 A


NeutrinolessNeutrinoless tt decays (LFV)decays (LFV)

● t+ →m+ g– 232 fb-1 (on and off peak data) corresponding to2.07×108 e+e- → t+t- events

– Divide events into “signal” and “tag”hemispheres (based on thrust axis)

– Look for m-g combination consistent with a tparent in events with 1-1 or 1-3 topologies

– Include additional tag modes: e, m, h and 3h

● Lepton flavour violation in t decays among the most theoreticallyclean signatures of New Physics

– Occurs at level of ~10-54 in the SM (with non-zero neutrino mass)

– NP models predict enhancements up to current experimental limits andenhancements in t decays relative tom decays (very model specific!)

e+e-

t+

t-

nt

m-

g

p+

Signal hemisphere

Tag hemisphere

Eg > 200 MeV


tt++ →→ mm++ gg resultsresults● Define signal region as 2s ellipse in:

– DE = Emg - √s/2

– mEC = invariant mass resulting frommgkinematic fit with Emg constrained to √s/2

● Additional bg rejection from neural net(mmiss, p

Tmiss , p

tagmax, cosθH, mn

2 )

● Total of 4 events observed in all tag modes(expect 6.2 ± 0.5 background)

– signal efficiency ~7.4%

– Dominant backgrounds are e+e-→m+m- (66%)and e+e-→ t+t- (27%)

– Limits extracted from extended ML fit to mEC

● Also BABAR limits on t→ lll & lhh

Based on 232 fb-1 :B(t+→m+g) < 6.8 × 10-8

at 90% C.L.hep-ex/0502032(submitted to PRL)

PRL 92:121801, 2004 and hep-ex/0409036

BABARPreliminary!


Combined bCombined b→→ccs, bccs, b→→sss, bsss, b→→qqsqqs

sin2βeff

CfCP = 0no direct CP violation,as expected in SM

(if only a single weak phasecontributing)

AfCP = -CfCP cos (Δmt)+ SfCP sin (Δmt)

HFAG Summer 2005:taken from PDG2005 reviewby D Kirkby & Y Nir

Plot assumes no correlationbetween sine and cosinecoefficients


The treeThe tree●


PEP-IIPEP-II


Vertex Detector (SVT)Vertex Detector (SVT)

Nov 29, 2005 52Steven Robertson, IPP, McGill Beauty and the BeastNovember 29, 2005 Steven H. Robertson Stanford Linear Accelerator Center 52

Drift Chamber (DCH)Drift Chamber (DCH)Momentum resolution (SVT+DCH):

σ(pT)/pT= 0.13 % pT + 0.45 %

s(z0) = 65µm at 1 GeV/c

(1.5T solenoid field)


DIRCDIRC (Detector of Internally Reflecting Cherenkov)(Detector of Internally Reflecting Cherenkov)


K –K – ππ separationseparation

>3>3σσ KK –– ππ separationseparationup to ~4 GeVup to ~4 GeV

pions

kaons


Calorimeter (EMC)Calorimeter (EMC)● 5760 (barrel) + 820 (endcap) CsI(Tl) crystals● Energy resolution:

σE/E = 2.3% E-1/4 + 1.9 % (~5% at 500 MeV)

π0 mass =135.1 MeV/c2

π0 width = 6.9 MeV/c2

π0 γγ


Lepton identificationLepton identification

Electron IDElectron ID Muon IDMuon ID

• electrons identified with EMCelectrons identified with EMC• high efficiency (high efficiency (>>90%)90%)• lowlow ππ mis-id (mis-id (~~1010-3-3))

• muons identified with IFRmuons identified with IFR• efficiencyefficiency ~~ 70%70%• ππ mis-idmis-id ~~2.5%2.5%• efficiencies improved inefficiencies improved inreqions with LSTsreqions with LSTs

beauty and the beast - mcgill university

Documents