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Exploring Centrality Selections in Multi-Dimensional Space at PHENIX

Delve into the intricacies of centrality definitions and selection using detectors at PHENIX, such as bbcN, zdcS, and fcalS, in different collision scenarios. Investigate how detector responses vary based on nucleon interactions, presenting insights into centrality determination in high-energy physics.

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Exploring Centrality Selections in Multi-Dimensional Space at PHENIX

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  1. More about centrality selections… bbcN, zdcS, fcalS... • Initial assumptions: • There could be different definitions for “centrality”, like “b”, Ncoll, Npart; • But experimental conditions are limited; • It’s more obvious for bbcS. • What about bbcN (deuteron side), zdcS, fcalS (Au side)? • Many things are already known... Fractal of participants, spectators, collisions, nucleons and secondary in multi-dimensional space of all PHENIX detectors ?

  2. Central arm bbcN bbcS rapidity 3 -3 0 • For d+Au system bbc are very assymmetric in kinematics. • By selecting “very peripheral” collisions (nucleon-nucleon) confirm that detector responses are similar. • Even for almost single n-n collision we get ~ 5 hits in each bbc

  3. We select events with ONLY one nucleon from D interacting, and start increase centrality by other detectors: • bbcNorth (deuteron side) changes for 10% only -> it “does not care” how many nucleons from Au interact. • We will not require “only one nucleon”, and will see how OTHER detectors centrality selections will change bbcN: • Selection by bbcS quickly saturate the signal; • there is a “plateau” for more central events with ~2x amplitude; • bbcN “cares only” how many nucleons from D interact.

  4. There is no saturation for fcal and zdc; In both detectors the signal stops raising as soon as TWO nucleons from D interact - The number of “evaporating neutrons and protons” does not depend much on centrality for (more central) dAu.

  5. Look from other dimension - central arm: • Very peripheral looks the same. - > • Very central are different: • Saturation of zdc/fcal? OR • bbcS collision fluctuations?

  6. Check by tendency in most central events: • zdc-fcal (evaporation) saturates; • bbcS - not. • How much left for fluctuation? Impact parameter? Glauber estimation shows this (from A. Milov’s presentation)

  7. bbcN vertex dependence: convolution of solid angle and particle cross sections. Linear correction for solid angle improves situation. Conclusions: • bbc North (deuteron side) does not depend on Npart or Ncoll; • bbcN could be useful for selection events with 1 to 2 (and between) participating nucleons (the same way as bbcS selects gold participants); • zdc/fcal could be useful for peripheral (60-90%) collisions, but not for central; • So far “bbc South” is the only detector for most “central” selection.

  8. Backup

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