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More about centrality selections… bbcN, zdcS, fcalS...

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)?

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More about centrality selections… bbcN, zdcS, fcalS...

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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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