Physics with ALICEPMD Basanta K Nandi IIT Bombay

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

Photon Multiplicity Detector (PMD) in ALICE PMD Ø Distance from IP : 367 cm Ø Approx. 9 sq. m. Ø η Covergae : 2. 3 to 3. 9 2

Photon Multiplicity Detector Ø Cell depth : 0. 5 cm Ø Cell cross-section : 0. 23 cm 2 Ø Total no. of cells : 220 K Ø Sensitive medium : Gas (Ar+CO 2 in the ratio 70: 30) Honeycomb chamber (48× 96 cells) 3

Principle of Photon Multiplicity Detector Energy deposition in PMD Hadron Photon Edep (a. u. ) 4 Particle CPV PRE Photon No Yes Ch Hadron Yes

Photon Multiplicity Detector v PMD measures: - Event-by-event number of photons produced in heavy-ion collisions - Spatial distribution (x, y) or ( , ) of photons v 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 ? ? ? 5

Charged Particle pseudo-rapidity Density Au + Au at mid-rapidity Ø Particle production mechanism § Soft process : Nch/γ scales with Npart 200 Ge. V 130 Ge. V 19. 6 Ge. V § Hard process : Nch/γ scales with Ncoll d. Nch/d = 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 theorist to validate their model Q. What happens at higher energy? 6

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

Pseudo-rapidity distributions of Photons 900 Ge. V p+p 7 Te. V p+p ALICE PRELIMINARY Ø At 0. 9 Te. V Phojet explains the data where as Pythia 6 D 6 T and Pythia 6 ATLAS underpredict. Ø At 7 Te. V both Pythia and Phojet under-predict the data. 8

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

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

Elliptic 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. y py x z Reaction plane: z-x plane 11 px

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

Charged particle measurement FMD 1 FMD 2 FMD 3 Outer ing Inner ring PMD Similar Eta acceptance of FMD 2 I and CPV = 2. 3 = 3. 5 FMD 2 i IP FMD 1 FMD 2 o 13 PRE CPV Beam line FMD 3 i Z-axis FMD 3 o

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