Background subtraction

1
Background subtraction

• Start with tracks that survive best cuts
• 2 sigma matching cut at brz,naz,brphi,naphi.
• Quality31Quality63,nx1gt2nx2gt2,
  abs(zed)lt40
• look at brphi distribution and subtract remaining
  background statistically
• conversion estimation based on n0gt4/n0gt0.
• Conversion e-, 46.5 independent on pt and
  centrality
• high pt pion, lt5 below 8GeV/c, lt10 below
  10GeV/c
• conversion e- therefore is n0gt4/0.465
• decay
• mostly low momentum(lt1.5GeV/c), have large
  residual bend.
• Rbg(lt2 sigma)/bg(gt3sigma), assume it doesnt
  depend on pt.
• From Rptgt12GeV/c, we can estimate bg for 4-10GeV/c

tracks tracks(n0gt0) tracks(n0lt0)
2
bg subtraction in brf, 4-4.5GeV/c

• all
• conversions
• decay
• conversiondecay

bg subtracted
negtive
positive
3
4.5-5GeV/c
4
5-5.5GeV/c
5
5.5-6GeV/c
6
6-6.5GeV/c
7
6.5-7GeV/c
8
7-7.5GeV/c
9
7.5-8GeV/c
10
8-8.5GeV/c
11
8.5-9GeV/c
12
9-10GeV/c
13
Corrections

• Combined pi and pi-.
• 5 Million 0-10GeV/c, 10 Million 4-20GeV/c single
  MC
• estimation
• geometrical acceptance
• f 0.5p/2p 25
• normalize from -0.35 to 1 unit in h 70
• fabs(zed)lt40cm 51
• live detector area
• DC,pc1 live areas 70
• pc2,pc3 91
• pc2,pc3 2 sigma matching
• 9595
• dc efficiency 100
• total correction factor 20
• multiplicity dependence correction
• no pt dependence
• need more statistics

14
Corrections
15
Pt spectra
16
Ratio (0-10/60-92)
17
Ratio to NN
18
Pt spectra
19
Pt spectra
20
Spectra shape

• Local inverse slope is exponential fit to 4
  neighboring bins
• ltpTtruncgt ltpTgt - pTlow above some pT threshold

21
Ratio to UA1
22
To do

• Higher statistics multiplicity dependence
  correction
• check momentum resolution correction(iterate)
• Estimate systematic errors
• check UA1 parameterization.
• Check number of events.

23
Background
24
Background