Diapositive 1

Calo Calibration Meeting 29/04/2009Plamen Hopchev, LAPPCalibration from 0 with a converted photonContentsDescription of the calibration methodShort overview; more details in my presentation in the previous Calorimeter Calibration Exercise:http://indico.cern.ch/getFile.py/access?contribId=13&sessionId=3&resId=0&materialId=slides&confId=51076Preview of the selection criteriaResultsConclusion

1Aim: Calibrate ECAL for high energy photons ( > few GeV )The method: Use 0 (e+e) (one of the photons converts)Reconstruct the Converted Photon and predict the energy of the non-converted photon, using For a given pair of reconstructed Conv Photon and Non-Conv Photon we have

Build the distribution of

We expect it to be:Flat for the random CP + NCP combinationsGaussian, centered at 0 for the photon pairs from 0

2Overview of the methodAnalyzed ~ 5.4 M MinBias L0-passed events (DC06/L0-v1-lumi2)Used DaVinci v22r2

Procedure:Make all possible pairs of StdTightElectrons (2 Long or 2 Downstream tracks; get also same sign pairs for background estimation)Form Converted Photon (CP) and extrapolate it to ECALSimply sum the momenta of the electronsStart extrapolating from the mean position of the electrons before the magnetLook for a brem in a small region around the projection pointCombine the CP with the nearby Photons (Non-Converted Photon, NCP)Require that the NCP is outside the brem region and inside a larger circle around the CP projection pointThe entity of interest is the triplet of the 2 electrons and the NCPPreselect potential signal triplets and store in a Tree for analysisThe distributions shown later and called ALL correspond to these preselected triplets and not to the real spectrum List of the preselection cuts and results are shown in the Backup slides

Overview of the exercise3Signal Selection Criteria Conv Photon (1)

Shown on the plot: Invariant mass distribution for opposite sign electron pairsCuts used for the selection:Long Tracks: Minv < 15 MeVDownstream Tracks: Minv< 70 MeV4

Signal Selection Criteria Conv Photon (2)Shown on the plots: x & y distance between the two electrons before the MagnetCuts used for the selection ( used only for Downstream tracks ):

Long Tracks Downstream Tracks: |dx|< 6 mm && |dy| < 4 mm

5Shown on the plots: Correlation of the VeloCharges of the 2 electrons (LL)Cuts used for the selection ( used only for Long tracks ):VeloCharge1 > 45VeloCharge2 > 45| VeloCharge1 VeloCharge2) | < 5

Signal Selection Criteria Conv Photon (3)6Shown on the plots: projected converted photon x vs y position at ECALCuts used for the selection:abs( xEcal ) < 3000 mmabs( yEcal ) < 3000 mmExclude inner hole of 380 x 380 mm

Signal Selection Criteria Conv Photon (4)

7Shown on the plots on the right: 1-D chi2 match of Projected Conv Photon and BestRecBrem and MCBrem( for x and y )Cuts used for the selection:chi2x < 50chi2y < 20Signal Selection Criteria Brems

8Shown on the plots on the right: 1-D chi2 match of Projected Conv Photon and Non-Converted Photon CandidateCuts used for the selection:50 < chi2x < 1.e620 < chi2y < 1.e6Signal Selection Criteria Non-Conv Photon

9Signal Selection Criteria summarySelection of electron pairs2 Long Tracks:Inv Mass < 15 MeVVelo Charges > 45 && abs( VeloCharge1 VeloCharge2) < 5 2 Downstream Tracks:Inv Mass < 70 MeVx- and y- distance between electrons measured at TT less than 6 and 4 mm respectively Collect pairs with el. charges which are: opposite - possible signalsame - to estimate the background

Project Conv Photon to ECAL:abs( xEcal ) < 3000 mmabs( yEcal ) < 3000 mmExclude inner hole of 380 x 380 mmSelection of BremsLook for Neutral PP near the projected CP ( two 1-D matches ):chi2x < 50chi2y < 20Potential additional cuts:Cluster Energy < 20 GeVCluster size < 15 cellsPhotonID > X

Selection of Non-Conv Phot:50 < chi2x < 1.e620 < chi2y < 1.e6

We use exactly the same cuts to select background from same sign electron pairs

10Fitting procedureParametrize the Background with double sigmoid:

Example double sigmoids We use only part of the curve

Also tried Argus function (defined in RooFit), but its drop-off is not steep enoughCompare 2 different ways of fitting:Directly fit the Signal + Background distributionUse double sigmoid + gaussianAll 5 + 3 parameters are variable (not fixed)The parameters of the gaussian are of primary interestAlternative approach :Fit the background obtained from same sign electron pairs with a double sigmoid Fix all but one of the parameters of the sigmoid leave parameter C variableFit the signal + background distribution with gaussian + the double sigmoid Results in comparison with the direct fit:sensibly worse 2 of the fitin some of the cases the fitted gaussians have sensibly different parameters

11Long Tracks && No Brem - plots 1GREEN direct fit

RED fit same sign el. bkg and fit sig+bkg

12

c = 534 = 9.5 % = 12.7 %c = 565 = 8.9 % = 14.0 %Long Tracks && No Brem - plots 2

13Long Tracks && Yes Brem - plots 1GREEN direct fit

RED fit same sign el. bkg and fit sig+bkg

14

c = 96 = 4.4 % = 13.0 %c = 103.6 = 4.1 % = 14.9 %Long Tracks && Yes Brem - plots 2

15

GREEN direct fit

Downstream Tracks && No Brem - plots 1RED fit same sign el. bkg and fit sig+bkg

16

c = 1.9 e3 = 3.1 % = 17.4 %c = 1.9 e3 = 2.8 % = 16.9 %Downstream Tracks && No Brem - plots 217

Downstream Tracks && Yes Brem - plots 1

GREEN direct fit

RED fit same sign el. bkg and fit sig+bkg

18

c = 223.5 = 2.4 % = 22.4 %c = 230.1 = 0.6 % = 16.6 %

Downstream Tracks && Yes Brem - plots 219For the fit results:The upper line describes the direct fitThe lower line describes the 2-step fitTo be added:A column with a info about the energy resolution on the Conv Phot

20Type of tracksYes/NoBrem N of Sig + Bkg EventsFit 2 / ndf Gauss Mean [%]Gauss Sigma [%]LongNo Brem31 960109.0 / 72380.2 / 798.9 0.4 9.5 0.4 14.0 0.4 12.7 0.4 Yes Brem7 88496.6 / 72159.1 / 794.1 1.1 4.4 1.1 14.9 1.3 13.0 1.1 DownstreamNo Brem112 446148.6 / 72261.8 / 792.8 0.2 3.1 0.3 16.9 0.317.4 0.3Yes Brem13 844123.0 / 72209.2 / 790.6 0.82.4 0.716.6 0.9 22.4 1.1Summary of the FitsRate of preselected triplets: 10.5/event (1.34x10-3 / event are MCConf )The preselection is described in the backup slidesRate of triplets passing final cuts: 3x10-3/event (0.4x10-3 / event are MCConf) Eff 34 % Bkg Retention 3x10-4

Distribution of signal events over CALO Zones:Inner : Middle : Outer = 5.1 : 2.2 : 1.021Expected RatesType of tracksYes/NoBrem N of Sig + Bkg EventsN of MCConf as signalLongNo Brem31 9603 598 (11.3%)Yes Brem7 884989 (12.5%)DownstreamNo Brem112 44615 239 (13.5%)Yes Brem13 8442 245 (16.2%)TOTAL166 13422 071 (13.3%)The results keep improving

Conclusion BAKUP SLIDES

Preselection cuts for tripletsTriplet = 2 electrons and a photonElectron pair:Track Types: Long/Long or Downstream/DownstreamMinv < 120 MeVDistance between projected Conv Photon and the Non-Converted Photon < 1200 mmOther sanity cuts:e.g. for long electrons we require existence of State at BegRich1RESULTS OF THE PRESELECTIONNumber of preselected electronsopposite el charge: 2.0/event ( 0.19/event are MCConf )same el charge: 2.5/event ( 2x10-4/event are MCConf )Number of preselected triplets: 10.5/event (1.34x10-3 / event are MCConf )

More Plots to be done:DELTA as function of the ECAL zoneDELTA as function of the NCP energy

To Fix:The x/y distance of the electrons before the magnet: only for opposite sign electrons !!!

For LL try distance cut like DD, instead of VeloCharge