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Physics with ALICE PMD: Photon Multiplicity Detector in Heavy-Ion Collisions

This study delves into the detailed workings and capabilities of the Photon Multiplicity Detector (PMD) within the ALICE experiment, examining energy deposition, spatial distributions of photons, pseudo-rapidity density, and fragmentation limitations. The PMD measures event-by-event photon production, aiding in azimuthal anisotropy determination and charged particle multiplicity analysis. Investigating varying beam energies, the study evaluates photon behaviors, elliptic flow phenomena, event plane determination, and primary charged particle tracking methods. Additionally, it explores jet studies, K* measurement, and anti-nuclei searches, providing insights for theoretical validations and further physics studies.

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Physics with ALICE PMD: Photon Multiplicity Detector in Heavy-Ion Collisions

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  1. Physics with ALICE-PMD Basanta K. Nandi IIT Bombay For PMD collaboration

  2. Photon Multiplicity Detector (PMD) in ALICE PMD • Distance from IP : 367 cm • Approx. 9 sq.m. • η Covergae : 2.3 to 3.9

  3. Photon Multiplicity Detector • Cell depth : 0.5 cm • Cell cross-section : 0.23 cm2 • Total no. of cells : 220 K • Sensitive medium : Gas • (Ar+CO2 in the ratio 70:30) Honeycomb chamber (48×96 cells)

  4. Principle of Photon Multiplicity Detector Energy deposition in PMD Hadron Photon Edep (a.u.)

  5. Photon Multiplicity Detector • PMD measures: • - Event-by-event number of photons produced • in heavy-ion collisions    •   - Spatial distribution (x,y) or (,) of photons • Physics Capabilities: • - Pseudo-rapidity density • - Limiting Fragmentation • - Fluctuation in the ratio of N/Nch in the common • coverage of PMD & FMD • - Azimuthal anisotropy and event plane determination • - Charged particle multiplicity • - Jet ???

  6. Charged Particle pseudo-rapidity Density Au + Au at mid-rapidity 200 GeV • Particle production mechanism 130 GeV • Soft process : Nch/γscales with Npart 19.6 GeV • Hard process : Nch/γscales with Ncoll dNch/dh = A x Npart + B x Ncoll • Hard processes contribution increases with centrality from ~30% to 50% in the mid-rapidity • Rapidity distribution of charged particles and photons gives the input • to the theorist to validate their model Q. What happens at higher energy?

  7. Charged Particle pseudo-rapidity Density Q. What happens in the forward rapidity for photons?

  8. Pseudo-rapidity distributions of Photons 900 GeV p+p 7 TeV p+p ALICE PRELIMINARY • At 0.9 TeV Phojet explains the data where as Pythia6D6T and Pythia6ATLAS underpredict. • At 7 TeV both Pythia and Phojet under-predict the data.

  9. Limiting Fragmentation • Particle production is independent of beam energy near beam rapidity Q. Is the limiting fragmentation scenario valid for photons?

  10. Limiting fragmentation (LF) behavior of photons • Limiting fragmentation behavior of photons seems to be inline with the • earlier measurement.

  11. y py px x y z x Reaction plane: z-x plane Elliptic Flow Flow is a phenomenon seen in nucleus-nucleus collisions, which correlates the momentum distributions of the produced particles with the spatial eccentricity of the overlap region. azimuthal dependence of the pressure gradient.

  12. Event Plane Determination from PMD • PMD event plane determination codes are in the repository for global use

  13. FMD 1 FMD 3 FMD 2 Outer ing Inner ring  = 2.3 FMD2i  = 3.5 Beam line FMD3i FMD1 Similar Eta acceptance of FMD2I and CPV FMD2o FMD3o IP Z-axis Charged particle measurement PMD CPV PRE

  14. Method to determine primary Charged Particles I.P. @ z = 0 CPV FMD X-Y plane @ z = 0 • Principle – Three point straight line tracking • Necessity – Magnetic Field OFF data

  15. Method to determine primary Charged Particles Y X R = √(x2 + y2)

  16. Charged particle measurement using CPV

  17. p p Jet Study using PMD ? TPC PMD

  18. Physics studies other than PMD • Fluctuation in mid-rapidity • K* measurement • Anti-Nuclei search

  19. Centrality Dependence of νdyn 10% Centrality Bins 5% Centrality Bins

  20. Measurement of K*

  21. Anti-Nuclei Search in ALICE pp @ 7 TeV • Approximately 350 M events are analyzed • Various nuclei are nicely identified in ALICE

  22. Summary:

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