the phenix detection and analysis of electron signals

Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

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The PHENIX The PHENIX detectiondetection andand analysisanalysis of electron signalsof electron signals

Marco Leite (USP)Marco Leite (USP)For the PHENIX collaborationFor the PHENIX collaboration

II Latin American Workshop on High Energy PhenomenologyII Latin American Workshop on High Energy Phenomenology

São Miguel das Missões – RSSão Miguel das Missões – RS03 – 07 December 200703 – 07 December 2007


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OutlineOutline

• MotivationMotivation• The Relativistic Heavy Ion Collider The Relativistic Heavy Ion Collider • Detector overviewDetector overview• Measuring electrons in PHENIXMeasuring electrons in PHENIX• Efficiency considerationsEfficiency considerations• Single (heavy quarks) and di-electron (quarkonia) Single (heavy quarks) and di-electron (quarkonia)

signals signals • Accounting for other electron sources (background)Accounting for other electron sources (background)• Nuclear modification factor RNuclear modification factor RAAAA

• Shadowing and absorption: cold nuclear matter effects Shadowing and absorption: cold nuclear matter effects • Prospects and conclusionsProspects and conclusions


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MotivationMotivation• cc production is a hard process (gluon fusion) happening at cc production is a hard process (gluon fusion) happening at

early stages of collisionearly stages of collision• They may bound to a light quark and leave the system as a D They may bound to a light quark and leave the system as a D

meson.meson.• Occasionally, they may form a bound state – the J/Occasionally, they may form a bound state – the J/ • If this is formed inside a QGP, they may be screened (Debye If this is formed inside a QGP, they may be screened (Debye

screening) by the free color charges in the medium, and once screening) by the free color charges in the medium, and once more leave the system as D meson after bounding to a light more leave the system as D meson after bounding to a light quark (Matsui and Satz*quark (Matsui and Satz*))

**Phys. Lett. B178, 416 (1986)Phys. Lett. B178, 416 (1986)

Perturbative Vacuum

cc

Color Screening

cc

• The J/The J/ will decay into e will decay into e++ee-- or or ++-- (we will focus on the former only) (we will focus on the former only)• If this suppression can be measured, it will be an indication of QGP If this suppression can be measured, it will be an indication of QGP

formationformation• There is also feed down from other states (There is also feed down from other states (’,’,cc) decays that will ) decays that will

enhance the production of J/enhance the production of J/


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RHIC complexRHIC complex


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RHIC: some numbersRHIC: some numbersSpeciesSpecies SSNN NN [GeV][GeV] L L [1/cm[1/cm22s]s] PolarizationPolarization # #

BunchesBunches

Au + AuAu + Au 62 ~ 20062 ~ 200 8 108 102626 -- 111111

Cu + CuCu + Cu 62 ~ 20062 ~ 200 80 1080 102626 -- 3737

p+pp+p 62~200*62~200* 60 1060 103030 70%70% 111111

d+Ad+A 200200 2 102 102828 -- 5555

*500 GeV under machine development.


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Detector Overview Detector Overview • We can “divide” the system in We can “divide” the system in

• Global DetectorsGlobal Detectors• Central ArmCentral Arm• Muon ArmsMuon Arms

• Plus the magnetsPlus the magnets• Central MagnetCentral Magnet• Muon MagnetsMuon Magnets

• Electrons are detected in the Electrons are detected in the Central ArmCentral Arm


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Beam-Beam CounterBeam-Beam Counter

• Quartz Cherenkov Quartz Cherenkov radiator and PM radiator and PM readoutreadout• ~ 1.5 m form the ~ 1.5 m form the

centercenter• Vertex determinationVertex determination• Timing (t0) for the Timing (t0) for the

eventevent• Minimum Bias trigger Minimum Bias trigger

– or get-almost-– or get-almost-everythingeverything

• Centrality (together Centrality (together with ZDC) with ZDC)

• Reaction plane Reaction plane determinationdetermination

(ZDC&BBLL1) Au+Au (Run4) d+Au (Run3)


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Zero Degree CalorimeterZero Degree Calorimeter

• Measures forward neutrons

• Tungsten-scintilattor sampling calorimeter

• Collision Centrality• Timing and vertex (z)• 6 , non-

compensating hadronic calorimeter

• Trigger

BBC


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Phenix Central ArmPhenix Central Arm

• Divided in two sides Divided in two sides (instrumented (instrumented somewhat differently)somewhat differently) = = /2/2 = 0.35= 0.35

• Tracking and electron Tracking and electron identification usingidentification using• Drift chamberDrift chamber• Pad ChamberPad Chamber• Ring Image Cherenkov Ring Image Cherenkov

CounterCounter• Time Expansion Time Expansion

Chamber/ Transition Chamber/ Transition Radiation DetectorRadiation Detector

• EM CalorimeterEM Calorimeter


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Drift ChambersDrift Chambers• Operated in proportional Operated in proportional

regionregion• Charged particle’s Charged particle’s

momentum determinationmomentum determination• Immersed in the magnetic Immersed in the magnetic

fieldfield• Part of global tracking in Part of global tracking in

PHENIXPHENIX• 120120m of spatial resolution m of spatial resolution

and track reconstruction uses and track reconstruction uses Hough transform methodHough transform method


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Ring Image Cherenkov Counter (RICH)Ring Image Cherenkov Counter (RICH)• Provides Provides

discrimination discrimination between charged between charged hadrons and electrons hadrons and electrons up to 4.9 GeV (8GeV up to 4.9 GeV (8GeV with extended cuts)with extended cuts)

• The light cone will be The light cone will be focused in the PM focused in the PM photocathode by photocathode by spherical mirrors, so spherical mirrors, so the ring shape image the ring shape image


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Pad ChambersPad Chambers• Wire chambers operating in

proportional region, with cathode pad readout

• Tracking information and verification

• Track resolving using points in 3D space

• Veto of charged particle in front of EmCal

• Entrance/exit points (RICH,EmCal) for Lvl2 trigger


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Time Expansion Chamber/Transition Radiation Detector Time Expansion Chamber/Transition Radiation Detector (TEC/TRD)(TEC/TRD)

• Gas Mixture of 45%Xe+45%He+10%CHGas Mixture of 45%Xe+45%He+10%CH4 4 at 760 mmHgat 760 mmHg

• Separate drift and multiplication regionSeparate drift and multiplication region• Proportional regimeProportional regime• Transition Radiation (TR) can be used for Transition Radiation (TR) can be used for

particle discrimination:particle discrimination:• TR production (TR production ( > 1000) > 1000)

• ee--,e,e++: p > 0.5GeV/c: p > 0.5GeV/c : p > 140GeV/c: p > 140GeV/c

• TR (few keV x-rays) provides a large TR (few keV x-rays) provides a large ionization signal (compared to dE/dx)ionization signal (compared to dE/dx)

track

+HV

-HV

GND

GND

charge clusters

e- track

E

rr

z

RadiatorRadiator


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Electromagnetic CalorimeterElectromagnetic Calorimeter• Set of sampling and homogeneous Set of sampling and homogeneous

calorimeters calorimeters • PbSc: sampling calorimeter, layers PbSc: sampling calorimeter, layers

of lead and scintillating material of lead and scintillating material (18 (18 XX00) )

• PbGl: homogeneous, lead-glass PbGl: homogeneous, lead-glass volume, Cherenkov radiator (14.4 volume, Cherenkov radiator (14.4 XX00) )

• GranularityGranularity• EnergyEnergy• TimingTiming• Position Position


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Electron IdentificationElectron Identification• Select events identified as Select events identified as

electrons using the electrons using the criteria:criteria: =Energy(EmCal)/p=Energy(EmCal)/p• Electrons:Electrons:

• 0.8<0.8<<1.2<1.2• Other:Other:

• 0.2<0.2<<0.4<0.4• Electron tracks will have Electron tracks will have

associated to it a associated to it a Cerenkov ring (RICH) and Cerenkov ring (RICH) and a shower in the EM a shower in the EM calorimetercalorimeter

photon

EM Calorimeter RICH

electron

pion

(p by B and DC tracking)


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Efficiency determinationEfficiency determination

• Simulation aided (e.g. J/Simulation aided (e.g. J/))• Generate J/Generate J/ using an using an

uniform pT and rapidity uniform pT and rapidity distributiondistribution

• Reconstruct the decay eReconstruct the decay e--

ee++ pairs based on the pairs based on the detector geometry and detector geometry and blind areasblind areas

• It’s a both way operation, It’s a both way operation, as the reconstruction as the reconstruction needs input from needs input from calibration, tuning etc.calibration, tuning etc.

• This will give us a figure of This will give us a figure of how much we can detect how much we can detect in a (perfect) real situationin a (perfect) real situation

• Eval this in function of pT Eval this in function of pT (binned)(binned)

• Use pT distribution of J/Use pT distribution of J/ as weighting functionas weighting function

correctiondata

• During data taking, the detector During data taking, the detector performance fluctuates (relative efficiency) performance fluctuates (relative efficiency) and this needs to be taken into account and this needs to be taken into account (run by run)(run by run)

• There is also a centrality dependent effect, There is also a centrality dependent effect, which can be inferred by embedding which can be inferred by embedding simulation data into real data, divided in simulation data into real data, divided in centrality regions, and see how many of centrality regions, and see how many of the artificial inserted simulation data the artificial inserted simulation data events can be reconstructedevents can be reconstructed


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Identifying the sourcesIdentifying the sources

• Quarkonia • J/ψ, ψ’→ e+e-

• Heavy Quark decays• D,B→ e + X

• Dalitz decay of light neutral mesons

• π0→γe+e-• η, η’→γe+e-

• Conversion of photons in material• γ→e+e-

• Weak kaon decays• (e.g.: K± → π0e±νe-)

• dielectron decays of vector mesons

• conversion of direct photons in material

• Thermal radiation• The analysis should isolate the

signal we are looking from the rest


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Electrons pair analysis (J/Electrons pair analysis (J/))

• Reconstruct the invariant mass by looking at e+e- pairsReconstruct the invariant mass by looking at e+e- pairs• The combinatorial background is determined by using The combinatorial background is determined by using

ee++ and e and e-- from different events from different events


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J/J/ Production Production

• J/J/ invariant mass and invariant yield reconstructed as a function of pT invariant mass and invariant yield reconstructed as a function of pT • Forward rapidity data (muons) is also shownForward rapidity data (muons) is also shown

PRL 98, 232002 (2007)

PRL 98, 232301(2007)


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Nuclear modification factorNuclear modification factor• Relation of the invariant Relation of the invariant

yield of J/yield of J/ in A+A collisions in A+A collisions and the binary scaled and the binary scaled invariant yield of p+pinvariant yield of p+p


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Effect of cold nuclear matter Effect of cold nuclear matter • J/J/ production for d+Au ( production for d+Au (√S√SNNNN = 200 GeV) = 200 GeV)

• Shadowing effect predictions not well constrainedShadowing effect predictions not well constrained

• Also need more data (on the way …)Also need more data (on the way …)

arXiv:0711.3917v1 (2007)


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Single electrons Single electrons

PRL 94, 232301 (2005)

Get the e+e- the by using a decay Monte

Carlo generator

PHENIX has measured direct photons

• Heavy flavour decay signaturesHeavy flavour decay signatures• Unlike eUnlike e++ee-- correlation, now we need to account for correlation, now we need to account for

each sourceeach source• The “cocktail” methodThe “cocktail” method• Start the cocktail with direct gamma sourcesStart the cocktail with direct gamma sources


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Single Electron contribution sources (I)Single Electron contribution sources (I)• Add other ingredients:Add other ingredients:


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All sources together …All sources together …

A. Toia - QM 2005


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Electron contribution sources (II)Electron contribution sources (II)• The converter methodThe converter method

• Uses (around beam pipe) a 1.7XUses (around beam pipe) a 1.7X00 brass foil brass foil • Background Photonic source : Dalitz decays

conversions• Background non-photonic: K, vector mesons

• Non-photonic sources : mainly from heavy quarks.

• The converter will increase the background by a known factor

• Compare the yield with/without the converter• Reasonable agreement between cocktail and

converter methods

PRL 97, 252002 (2007)


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Invariant yield and RAA Invariant yield and RAA

PRL 97, 252002 (2007)

• Single electrons from Single electrons from heavy flavor decaysheavy flavor decays

PRL 98, 172301 (2007)

0 1 2 3 4 5 6 7

8 9


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Prospects and ConclusionsProspects and Conclusions

PHENIX has been providing electron data at mid rapidity PHENIX has been providing electron data at mid rapidity range and prange and pTT < 8GeV for quarkonia and heavy quark < 8GeV for quarkonia and heavy quark production studies production studies

A suitable methodology is in established to remove unwanted A suitable methodology is in established to remove unwanted electron contributionselectron contributions

RRAA AA from single electrons datafrom single electrons data shows a high suppression in shows a high suppression in high phigh pTT for heavy quarks, indicating a high density and for heavy quarks, indicating a high density and interacting matter being formed at RHICinteracting matter being formed at RHIC

The J/The J/ suppression is consistent with lower energy data, suppression is consistent with lower energy data, with indications of coalescence inside the plasmawith indications of coalescence inside the plasma

Run 8 (on going) should provide d+Au data to increase the Run 8 (on going) should provide d+Au data to increase the number of J/ number of J/ by a factor ~ 20. Shadowing parameterization by a factor ~ 20. Shadowing parameterization still needs better understanding still needs better understanding

TRD information can be used for detection of very high TRD information can be used for detection of very high momentum electrons beyond the RICH limitmomentum electrons beyond the RICH limit

PHENIX detector upgrades (HBD) will provide low background PHENIX detector upgrades (HBD) will provide low background measurements (Dalitz rejection) to probe for low mass measurements (Dalitz rejection) to probe for low mass dileptons decays.dileptons decays.

In the mid and long term future, RHIC II and eRHIC will In the mid and long term future, RHIC II and eRHIC will provide substantial upgrades/facilities/increased luminosityprovide substantial upgrades/facilities/increased luminosity


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the phenix detection and analysis of electron signals

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