BSMD calibration algo has been developed based on M-C response of BSMD & towers to single gammas.

Executive summary:

The purpose of BSMD absolute calibration summarized at this drupal page is to reconstruct integrated energy deposit (dE) in BSMD based on measured ADC.
By integrated dE in BSMD I mean sum over few strips forming EM cluster, no matter what is the cluster shape.
This calibration method accounts for the varying absorber in front of BSMD and between eta & phi planes.
This calibration will NOT help in reconstruction:  
- full energy of EM particle which gets absorbed in BEMC ( shower development after BSMD layer does not matter for this calibration).
- partial energy of hadrons passing or showering in BEMC
- correct for the incident angle of the particle passing through detector
- saturation of BSMD readout. I only state up to which  loss (DE) the formula used in reconstruction:
      dE/GeV= (rawAdc-ped) * C0 * (1 +/- C1etaBin)
- determine sampling fraction (SF) of BSMD with high accuracy 

Below you will find brief description of the algo, side by side comparison of selected plots for M-C and real data, finally PDF with many more plots.

Proposed absolute calibration coefficients are show in table 2.

 

Part 1

Description of algorithm finding isolated gammas in the Barrel.

Input events

• M-C :  single gamma per event, 6 GeV ET, flat in eta, phi covers 3 barrel modules 12,13,14, geometry=y2006
• DATA: BHT0,1,2 triggered pp 2008 events from day 47, total 100K, individual triggers: 44K, 33K, 40K, respectively
  events were privately produced w/ zero suppression.

Raw data processing based on muDst

• M-C : BSMD - take geant energy deposit  ~100 keV range, towers - take ADC*0.493 to have nominal calibration of 4070 ADC=60 GeV ET.
• Data : BSMD - use private  pedestals & status tables for day 47, use custom calibration
  use BSMD calibration dE/GeV= (rawAdc-ped) * C0 * (1 +/- C1_etaBin), where '+' is for Phi-plane and '-' for eta plane, see table below
  skip strips 4 sigma above ped or with energy below 1keV, strip to strip relative gains NOT used , data from CAPs=123,124,125 were not used
   towers- take ADC as is, no offline gains correction.

Cluster finder algo (seed is sliding fixed window), tuned on M-C gamma events

• work with 150 Eta-strips per module or 900 Phi-strips at fixed eta
• all strips are marked as 'unused'

1. sum  dE in fixed window of 4 unused strips, snap at location which maximizes the energy
2. if sum below 10 keV STOP searching for clusters in this band
3. add energy from one strip on each side, mark all 1+4+1 strips as 'used'
4. compute energy weighted  cluster position and RMS
5. goto 1

This cluster finder process full Barrel West, more details about clustering is in one cluster topology , definition of 'barrel cell' 

Isolated EM shower has been selected as follows, tuned on gamma events,

• select isolated eta-cluster in every segment of 15 eta strips.
• require cluster center is at least 3 strips away from edges  of this segment (defined by eta values of 0.0, 0.1, 0.2,....0.9, 1.0)
• require there is only one phi-cluster in the same 0.1x0.1 eta.phi cell
  • require phi-cluster center is at least 3 strips from the edges
• find hit tower matching to the cross of eta & phi cluster
• sum tower energy from 3x3 patch centered on hit tower
  • require 3x3 tower  ADC sum >150 ADC (equivalent to 2.2 GeV ET, EM)
• sum tower energy from 5x5 patch centered on hit tower
  • require 3x3 sum/ 5x5 sum >0.9  
• require RMS of Phi & Eta-cluster  is above 0.2 strips

 Below is listing of all cuts used by this algo:

  useDbPed=1; // 0= use my private peds
  par_skipSpecCAP=1; // 0 means use all BSMD caps
  par_strWinLen=4; (3)  // length of integration window, total  1+4+1, in strips
  par_strEneThr=1.e-6;  (0.5e-6) // GeV, energy threshold for strip to start cluster search
  par_cluEneThr=10.0e-6; (2.0e-6) // GeV, energy threshold for cluster in window
  par_kSigPed=4.; (3) // ADC threshold
  par_isoRms=0.2;  (0.11) // minimal smd 1D cluster RMS 
  par_isoMinT3x3adc=150; //cut off for low tower response
  par_isoTowerEneR=0.9; //  ratio of 3x3/5x4 cluster
(in red are adjusted values for MIP or ET=1GeV cluster selection)  

 Table 1 Tower cluster cut defines energy of isolated gammas.

3x3 tower ET (GeV), trigger used	MIP, BHT0,1,2	1.0, BHT0,1,2	3.4, BHT0	4.7, BHT1	5.5, BHT2	7, BHT2
3x3 tower ADC sum range	15-30 ADC	50-75 ADC	170-250 ADC	250-300 ADC	300-380 ADC	400-500 ADC
3x3 energy &  RMS (GeV) @ eta=[0.1,0.2]	0.34 +/- 0.06	0.92 +/- 0.11	3.1 +/- 0.3	4.1 +/- 0.2	5.1 +/- 0.3	6.6 +/- 0.4
3x3 energy &  RMS (GeV) @ eta=[0.4,0.5]	0.37 +/- 0.07	1.0 +/- 0.11	3.4 +/- 0.4	4.6 +/- 0.3	5.6 +/- 0.4	7.3 +/- 0.5
3x3 energy &  RMS (GeV) @ eta=[0.8,0.9]	0.47 +/- 0.09	1.3 +/- 0.16	4.3 +/- 0.4	5.7 +/- 0.3	7.1 +/- 0.5	9.3 +/- 0.6

  

Table 2 shows assumed calibration.   

Contains relative calibration  of eta vs. phi plane, different for M-C vs. data,
and single absolute DATA normalization of the ratio of SMD (Eta+Phi) cluster energy vs. 3x3 tower cluster at eta=0.5 .

Table 3 shows what comes from data & M-C analysis using calibration from table 2.

 

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Part 2

Side by side comparison of M-C and real data. 

Fig 2.1 BSMD "Any cluster" properties

TOP : RMS vs. energy, only Eta-plane shown, Phi-plane looks similar
BOTTOM: eta -phi distribution of found clusters. Left is M-C - only 3 modules were 'populated'. Right is data, white bands are masked modules or whole BSMD crate 4

 

 

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Fig 2.2  Crucial  cuts after coincidence & isolation was required for a pair BSMD Eta & Phi clusters 

TOP :  3x3 tower energy (black), hit-tower energy (green) , if 3x3 energy below 150 ADC cluster is discarded
BOTTOM: eta dependence of 3x3 cluster energy. M-C has 'funny' calibration - there is no reason for U-shape, Y-value at eta=0.5 is correct by construction.

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Fig 2.3  None-essential cuts, left by inertia 

TOP :  ratio of 3x3 tower energy to 5x5 tower energy ,  rejected if below 0.9 
BOTTOM:  RMS of Eta & Phi cluster must be above 0.2, to exclude single strip clusters

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Part 3

Examples of relative response of BSMD Eta vs. Phi AFTER  calibration above is applied. 

I'm showing examples for 3 eta slices of 0.15, 0.55, 0.85 -  plots for all eta bins  are available as PDF, posted in Table 2 at the end.

The red vertical line marks the target calibration, first 2 columns are aligned by definition, 3rd column is independent measurement confirming calibration for data holds for ~40% lower gamma energy.

Fig 3.1 Phi-cluster vs. Eta cluster for eta range [0.1,0.2]. M-C on the left, data in the middle, right.

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Fig 3.2 Phi-cluster vs. Eta cluster for eta range [0.4,0.5]. M-C on the left, data in the middle, right.

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Fig 3.3 Phi-cluster vs. Eta cluster for eta range [0.8,0.9]. M-C on the left, data in the middle, right.

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Fig 3.4 Phi-cluster vs. Eta cluster for eta range [0.9,1.0]. M-C on the left, data in remaining columns.

 

Part 4

Absolute response of BSMD (Eta + Phi) vs. 3x3 tower cluster,  AFTER  calibration above is applied. 

I'm showing eta slices [0.4,0.5] used to set absolute scale. The red vertical line marks the target calibration, first 2 columns are aligned by definition, 3rd column is independent measurement  for gammas with ~40% lower --> BSMD response is NOT proportional to gamma energy.

Fig 4.1 Phi-cluster vs. Eta cluster for eta range [0.4,0.5]. Only data are shown.

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Fig 4.2 Absolute BSMD calibration for eta range [0.0,0.1] (top) and eta range [0.1,0.2] (bottom) . Only data are shown.
Left: Y-axis is BSMD(E+P) cluster energy, y-error is error of the mean; X-axis 3x3 tower cluster energy, x-error is RMS of distribution . Fit (magenta thick) is using only to 4 middle points - I trust them more. The MIP point is too high due to necessary SMD cluster threshold, the 7GeV point has very low stat. There is no artificial point at 0,0. Dashed line is extrapolation of the fit.
Right: only slope param (P1) from the left is used to compute full BSMD Phi & Eta-plane calibration using formulas:

slope P1_Eta=P1/2./(1-C1[xCell])/C0
slope P1_Phi=P1/2./(1+C1[xCell])/C0

Using C1[xCell],C0 from table 2.

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Fig 4.3 Absolute BSMD calibration for eta range [0.2,0.3] (top) and eta range [0.3,0.4] (bottom) . Only data are shown, description as above.

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Fig 4.4 Absolute BSMD calibration for eta range [0.4,0.5] (top) and eta range [0.5,0.6] (bottom) . Only data are shown, description as above.

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Fig 4.5 Absolute BSMD calibration for eta range [0.6,0.7] (top) and eta range [0.7,0.8] (bottom) . Only data are shown, description as above.

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Fig 4.6 Absolute BSMD calibration for eta range [0.8,0.9] (top) and eta range [0.9,0.95] (bottom) . Only data are shown, description as above.

I'm showing the last eta bin because it is completely different - I do not understand it at all. It was different on all plots above - just reporting here.

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Fig 4.7 Expected BSMD gain dependence on HV, from  Oleg document The 2008 working HV=1430 V (same for eta & phi planes) - in the middle of the measured gain curve.

 Part 5

Possible extensions of this algo.

1. cover also East barrel (for the cross check)
2. include vertex correction in projecting SMD cluster to tower (perhaps)
3. study energy resolution of eta & phi plane - now I just compensated relative gains but the total BSMD energy is simply sum of both planes
4. last eta bin [0.9,1.0] is completely different, e.g. there is no MIP peak in the 2D fig 2.2 - BTOW gain (HV) is factor 2 or more way too high in this 2 bins 
   Justification: Inspect right plot on figures 4.2,...,4.6, in particular note at what gamma energy the blue line reaches ADC of 1000 counts. Look at this pattern vs. eta bin. On the last plot it should happen at gamma energy of ~5 GeV but in reality it is at ~10 GeV.    
5. crate 4 (unmodified) would have different gains - excluded in this analysis
6. Speculation: those multiple peaks in raws BSMD spectra (seen by others) could be correlated with BHT0,1,2 triggers
7. Scott suggestion: more detailed study of BSMD saturation could use BSMD cluster location for fiducial cut forcing gamma to be in the tower center and use just the hit tower. This needs more stats. This analysis uses 1 day of data and ends up with just ~100 entries per energy point.
8. non-linear BSMD response does not mean we can reco cluster position with accuracy better than 1 strip.

 

 

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Fig 5.1 BSMD cluster energy vs. eta of the cluster.

 

 

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Fig 5.2 hit tower to 3x3 cluster energy for accepted clusters. DATA, trigger BHT2, gamma ET~5.5 GeV.

 

 

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Fig 5.3 hit tower to 3x3 cluster energy for accepted clusters. M-C, single gamma ET=6 GeV, flat in eta .