ghosts in run-10 200gev
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Ghosts in Run-10 200GeV
Mihael MakekWIS
30-Mar-11
Contents
I. DC GhostsII. RICH ring sharing
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
Cuts:
|phi1-phi2|<0.05
AND
|z1-z2|<0.5
•The distributions show no visible centrality dependance•Using the same cuts for all centralities
I. DC Ghosts
• The distributions after randomly removing one of the tracks
I. DC Ghosts
Left: the total number of electron tracks per event vs. centralityRight: the percentage of the tracks removed by DC ghost cut
I. DC Ghosts
Left: the +- yield removed by the DC ghost cut (foreground)Right: the fraction of the remaining +- background after the DC ghost cut (as for efficiency correction)
II. RICH ring sharing
• The peaks fitted with a double Gaussian - the widths show no significant centrality dependance
• Using the same cuts for all centralities
Cuts:
|phi1-phi2|<0.08
AND
|z1-z2|<25
II. RICH ring sharingCounting 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 > 1
II. RICH ring sharing• Use HBD as the first step of the rejection• In the remaining cases remove the event
Left: N+- with CA only
Middle: N+- with CA + HBD The fraction of the ghost yield in the total yield drops from 0.032 to 0.024 when applying HBD (for 40 < centrality < 100)
Right: N+- with CA + HBD and ghost event rejection
The mass spectra for: 40 < centrality < 100
II. RICH ring sharing
Left: the yield removed by the RICH ghost cut (foreground)Right: the fraction of the remaining +- background after the RICH ghost cut
(as for efficiency correction)
II. RICH ring sharing• Consistency check: we want see that the fraction of ghost
events obtained from the counters corresponds to the ghost yield obtained from the mass spectra:
• The numbers are in agreement (see the next slide)
event
pair
pair
ghpair
ghpair
ghevent
event
pair
spectra
pair
ghpair
counters
event
ghevent
N
N
N
N
N
N
N
N
N
N
N
N
1
II. RICH ring sharingFrom the event counters: From the mass spectra:
CA:
CA+HBD:
centrality Nevents N>1events Ngh
events
0-10% 5.09 106 1.88 106 1.85 105
40-50% 5.03 106 1.69 105 6.97 103
Npairs Npairs /
Nevents
Npairs/
N>1events
Nghpairs
Nghpairs /
Npairs
4.62 106 0.907 2.455 1.98 105 0.043
2.17 105 0.043 1.285 7.0 103 0.032
centrality Nevents N>1events Ngh
events
0-10% 6.44 106 2.58 105 1.08 104
40-50% 6.35 106 3.47 104 907
Npairs Npairs /
Nevents
Npairs/
N>1events
Nghpairs
Nghpairs /
Npairs
3.31 105 0.514 1.283 1.09 104 0.033
3.87 104 0.006 1.117 910 0.024
Electron track distributions
CA + projection cut CA + projection cut + HBD matching
• 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
The data set, event cuts, eID cuts
[#] EMC recalibrators for 62GeV - Deepali
• In the DC:• Select pairs with || < 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
Approach to ghosts
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