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The PHENIX detection and analysis of electron signals

Marco Leite (USP) For the PHENIX collaboration. The PHENIX detection and analysis of electron signals. II Latin American Workshop on High Energy Phenomenology São Miguel das Missões – RS 03 – 07 December 2007. Outline. Motivation The Relativistic Heavy Ion Collider Detector overview

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The PHENIX detection and analysis of electron signals

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  1. Marco Leite (USP) For the PHENIX collaboration The PHENIX detectionandanalysis of electron signals II Latin American Workshop on High Energy Phenomenology São Miguel das Missões – RS 03 – 07 December 2007 Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

  2. Outline • Motivation • The Relativistic Heavy Ion Collider • Detector overview • Measuring electrons in PHENIX • Efficiency considerations • Single (heavy quarks) and di-electron (quarkonia) signals • Accounting for other electron sources (background) • Nuclear modification factor RAA • Shadowing and absorption: cold nuclear matter effects • Prospects and conclusions Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

  3. Motivation • cc production is a hard process (gluon fusion) happening at early stages of collision • They may bound to a light quark and leave the system as a D meson. • Occasionally, they may form a bound state – the J/ • If this is formed inside a QGP, they may be screened (Debye screening) by the free color charges in the medium, and once more leave the system as D meson after bounding to a light quark (Matsui and Satz*) • The J/ will decay into e+e- or +- (we will focus on the former only) • If this suppression can be measured, it will be an indication of QGP formation • There is also feed down from other states (’,c) decays that will enhance the production of J/ *Phys. Lett. B178, 416 (1986) Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

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

  5. RHIC: some numbers *500 GeV under machine development. Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

  6. Detector Overview • We can “divide” the system in • Global Detectors • Central Arm • Muon Arms • Plus the magnets • Central Magnet • Muon Magnets • Electrons are detected in the Central Arm Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

  7. d+Au (Run3) Au+Au (Run4) (ZDC&BBLL1) Beam-Beam Counter • Quartz Cherenkov radiator and PM readout • ~ 1.5 m form the center • Vertex determination • Timing (t0) for the event • Minimum Bias trigger – or get-almost-everything • Centrality (together with ZDC) • Reaction plane determination Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

  8. BBC Zero Degree Calorimeter • Measures forward neutrons • Tungsten-scintilattor sampling calorimeter • Collision Centrality • Timing and vertex (z) • 6 , non-compensating hadronic calorimeter • Trigger Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

  9. Phenix Central Arm • Divided in two sides (instrumented somewhat differently) •  = /2 •  = 0.35 • Tracking and electron identification using • Drift chamber • Pad Chamber • Ring Image Cherenkov Counter • Time Expansion Chamber/ Transition Radiation Detector • EM Calorimeter Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

  10. Drift Chambers • Operated in proportional region • Charged particle’s momentum determination • Immersed in the magnetic field • Part of global tracking in PHENIX • 120m of spatial resolution and track reconstruction uses Hough transform method Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

  11. Ring Image Cherenkov Counter (RICH) • Provides discrimination between charged hadrons and electrons up to 4.9 GeV (8GeV with extended cuts) • The light cone will be focused in the PM photocathode by spherical mirrors, so the ring shape image Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

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

  13. GND +HV GND e- track E charge clusters  track -HV Radiator r z r Time Expansion Chamber/Transition Radiation Detector (TEC/TRD) • Gas Mixture of 45%Xe+45%He+10%CH4 at 760 mmHg • Separate drift and multiplication region • Proportional regime • Transition Radiation (TR) can be used for particle discrimination: • TR production ( > 1000) • e-,e+: p > 0.5GeV/c • : p > 140GeV/c • TR (few keV x-rays) provides a large ionization signal (compared to dE/dx) Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

  14. Electromagnetic Calorimeter • Set of sampling and homogeneous calorimeters • PbSc: sampling calorimeter, layers of lead and scintillating material (18 X0) • PbGl: homogeneous, lead-glass volume, Cherenkov radiator (14.4 X0) • Granularity • Energy • Timing • Position Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

  15. Electron Identification • Select events identified as electrons using the criteria: • =Energy(EmCal)/p • Electrons: • 0.8<<1.2 • Other: • 0.2<<0.4 • Electron tracks will have associated to it a Cerenkov ring (RICH) and a shower in the EM calorimeter pion electron photon RICH EM Calorimeter (p by B and DC tracking) Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

  16. Efficiency determination data correction • Simulation aided (e.g. J/) • Generate J/ using an uniform pT and rapidity distribution • Reconstruct the decay e-e+ pairs based on the detector geometry and blind areas • It’s a both way operation, as the reconstruction needs input from calibration, tuning etc. • This will give us a figure of how much we can detect in a (perfect) real situation • Eval this in function of pT (binned) • Use pT distribution of J/ as weighting function • During data taking, the detector performance fluctuates (relative efficiency) and this needs to be taken into account (run by run) • There is also a centrality dependent effect, which can be inferred by embedding simulation data into real data, divided in centrality regions, and see how many of the artificial inserted simulation data events can be reconstructed Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

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

  18. Electrons pair analysis (J/) • Reconstruct the invariant mass by looking at e+e- pairs • The combinatorial background is determined by using e+ and e- from different events Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

  19. J/ Production • J/ invariant mass and invariant yield reconstructed as a function of pT • Forward rapidity data (muons) is also shown PRL 98, 232002 (2007) PRL 98, 232301(2007) Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

  20. Nuclear modification factor • Relation of the invariant yield of J/ in A+A collisions and the binary scaled invariant yield of p+p Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

  21. Effect of cold nuclear matter • J/ production for d+Au (√SNN = 200 GeV) • Shadowing effect predictions not well constrained • Also need more data (on the way …) arXiv:0711.3917v1 (2007) Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

  22. Single electrons • Heavy flavour decay signatures • Unlike e+e- correlation, now we need to account for each source • The “cocktail” method • Start the cocktail with direct gamma sources Get the e+e- the by using a decay Monte Carlo generator PHENIX has measured direct photons PRL 94, 232301 (2005) Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

  23. Single Electron contribution sources (I) • Add other ingredients: Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

  24. All sources together … A. Toia - QM 2005 Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

  25. Electron contribution sources (II) • The converter method • Uses (around beam pipe) a 1.7X0 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) Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

  26. Invariant yield and RAA • Single electrons from heavy flavor decays 0 1 2 3 4 5 6 7 8 9 PRL 97, 252002 (2007) PRL 98, 172301 (2007) Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

  27. Prospects and Conclusions • PHENIX has been providing electron data at mid rapidity range and pT < 8GeV for quarkonia and heavy quark production studies • A suitable methodology is in established to remove unwanted electron contributions • RAA from single electrons data shows a high suppression in high pT for heavy quarks, indicating a high density and interacting matter being formed at RHIC • The J/ suppression is consistent with lower energy data, with indications of coalescence inside the plasma • Run 8 (on going) should provide d+Au data to increase the number of J/  by a factor ~ 20. Shadowing parameterization still needs better understanding • TRD information can be used for detection of very high momentum electrons beyond the RICH limit • PHENIX detector upgrades (HBD) will provide low background measurements (Dalitz rejection) to probe for low mass dileptons decays. • In the mid and long term future, RHIC II and eRHIC will provide substantial upgrades/facilities/increased luminosity Marco Leite II LAWHEP – S. Miguel das Missões – RS Dec. 2007

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

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