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Ghosts in Run-10 200GeV

Ghosts in Run-10 200GeV. Mihael Makek WIS 30-Mar-11. Contents. DC Ghosts RICH ring sharing. I. DC Ghosts. The distributions show no visible centrality dependance Using the same cuts for all centralities. Cuts: |phi1-phi2|<0.05 AND |z1-z2|<0.5. I. DC Ghosts. Treating the DC ghosts:

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Ghosts in Run-10 200GeV

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  1. Ghosts in Run-10 200GeV MihaelMakek WIS 30-Mar-11

  2. Contents • DC Ghosts • RICH ring sharing

  3. I. DC Ghosts • The distributions show no visible centrality dependance • Using the same cuts for all centralities Cuts: |phi1-phi2|<0.05 AND |z1-z2|<0.5

  4. I. DC Ghosts • Treating the DC ghosts: • Select the pairs which fall inside the window • Randomly discard on of the tracks and remove it from the buffer • The distributions after randomly removing one of the tracks

  5. I. DC Ghosts Left: the total number of electron tracks per event vs. centrality Right: the percentage of the tracks removed by DC ghost cut

  6. I. DC Ghosts Left: the yield removed by the DC ghost cut Right: the fraction of the remaining +- background after the DC ghost cut

  7. II. RICH ring sharing Cuts: |phi1-phi2|<0.08 AND |z1-z2|<25 • The widths of the peaks show no significant centrality dependance • Using the same cuts for all centralities

  8. II. RICH ring sharing Counting the events with the RICH ghosts: Left: the percentage of the ghost events in total events Right: the percentage of the ghost events in events with ntrk>=2

  9. II. RICH ring sharing Applying HBD as ghost rejector: The mass spectra for: 40 < centrality < 100 Left: N+- with CA only Right: N+- with CA + HBD (Rejection 10)  The fraction of the ghost in the yield drops from 0.032 to 0.024 when applying HBD (for 40 < centrality < 100 )

  10. II. RICH ring sharing Proposed strategy: • Use HBD as the first step of the rejection • In the remaining cases remove the event if a pair falls inside the cut window

  11. Backup slides

  12. The data set, event cuts, eID cuts • Run-10 – 200 GeV Au+Au data • EWG files: 530/828 runs, the fraction of runs with HBD gain calibrated • Events 3.5B out of 7.0B in +/-20 cm vertex • Event cuts: • abs(bbcz) < 20 cm • Track selection: • track quality = 31, 51, 63 • eID cuts: • n0 > 2 • sqrt(emcsdphi*emcsdphi + emcsdz*emcsdz) < 3 [#] • dep > -2 [#] • chi2/npe0 < 10 • disp < 5 • prob > 0.01 • |zed| < 75 [#]EMC recalibrators for 62GeV - Deepali M. Makek - WIS

  13. Approach to ghosts • In the DC: • Select pairs with |f1-f2| < 0.05 && |zed1-zed2|< 0.5 • Randomly remove one of the tracks • In the RICH: • Most of the ring sharing pairs are formed by an electron and a hadron • Most of the electrons are coming from the HBD backplane and can be rejected by looking for a hit in the HBD (R~10) • Most of the hadrons can be rejected by the HBD (R~10) • We expect that HBD can reduce the number of ghost pairs up to a factor of ~100 • We want to use the HBD as the first step for the rejection of the ring sharing pairs M. Makek - WIS

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