dealing with central events in run 10 au+au collisions mihael makek weizmann institute of science...
TRANSCRIPT
Clustering algorithm („Weizmann clusterizer“)
• loop through all fired pads (“CellList”):• find pads with 3 pe < charge < 100 pe seed pads • build clusters around seed pads by summing the first neighbour pads with charge > 1 pe
• loop through the clusters („BlobList“) and merge clusters if they have overlaping pads
Matching of the CA tracks to HBD:• loop through the clusters again and find the one that is the closest to the track projection point
Subtraction of pedestals• Method 1, define the average charge per pad:
• Method 2, define the average charge per fired pad:
where a[pad] normalizes pad area • Look at the <ch>pp as a function of centrality (nCentral) • Derive this dependence module by module• Subtract charge from each pad according to nCentral
pads of no. Total
]charge[pad a[pad] ch pp
pads fired of No.
]charge[pad a[pad] ch fp
Subtraction of pedestals 1• Correction functions:
example: WN2all modulesPossible causes of variations:• zero suppression + gain difference• reverse bias voltage
After subtraction of pedestals 1 • Run WIS clusterizer on subtracted data
• Electron tracks
• Matching distribu-tions for different nCentral bins
• 3 cuts on hbdd and hbddz (mom. corrected)
• Select only clusters with size > 1 pad
• Subtracted random background gene-rated by projecting tracks to different module
Summary • After subtraction of pedestals we do see electron signal in the most central events!
• Even after subtraction we are still picking additional charge (need to subtract more?!)
• Needs to optimized:• S/B ratio is dropping for the most central events• Electron „efficiency“ decreasing for the most central events
Outlook• Ideas to proceed:
• Optimize subtraction empirically monitoring the electron efficiency and validating results with the Accumulator
• Optimize lower threshold of the seed pad (e.g. 35 pe) expected effect: low charge background reduction
• Optimize upper threshold of the seed pad (e.g. 10050 pe): expected effect: reduction of the high charge clusters
• Optimize lower threshold for the neighbouring pads according to centrality (e.g. 1 0.06 * nCentral). Expected effects:
• reduction of the cluster size according to centrality• reduction of the cluster charge to centrality
BACKUP slide: electron ID cuts
Using central arms:• quality = 31, 51, 63• n0 > 2• abs(emcdz+1.0) < 10.0, abs(emcdphi-0.00023) < 0.030• ecore/mom > 0.6• chi2/npe0 < 10• disp < 5• prob > 0.01• ecore > 0.15
Using HBD:• abs(phbdz) < 27.0• remove tracks projecting to EN2• 3 sigma matching in hbddz and hbddphi• HBD clustersize > 1