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