Calo Calibration Meeting 29/04/2009 Plamen Hopchev, LAPP Calibration from 0 with a converted...

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Aim: Calibrate ECAL for high energy photons ( > few GeV ) The method: Use π 0 → γ (e + e – ) γ (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 combinations Gaussian, centered at 0 for the photon pairs from π 0 Aim: Calibrate ECAL for high energy photons ( > few GeV ) The method: Use π 0 → γ (e + e – ) γ (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 combinations Gaussian, centered at 0 for the photon pairs from π 0 2 Overview of the method

Transcript of Calo Calibration Meeting 29/04/2009 Plamen Hopchev, LAPP Calibration from 0 with a converted...

Calo Calibration Meeting 29/04/2009 Plamen Hopchev, LAPP Calibration from 0 with a converted photon Contents Description of the calibration method Short overview; more details in my presentation in the previous Calorimeter Calibration Exercise:=slides&confId=51076 Preview of the selection criteria Results Conclusion 1 Aim: 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 combinations Gaussian, centered at 0 for the photon pairs from 0 Aim: 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 combinations Gaussian, centered at 0 for the photon pairs from 0 2 Overview of the method Analyzed ~ 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 ECAL Simply sum the momenta of the electrons Start extrapolating from the mean position of the electrons before the magnet Look for a brem in a small region around the projection point Combine 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 point The entity of interest is the triplet of the 2 electrons and the NCP Preselect potential signal triplets and store in a Tree for analysis The 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 exercise 3 Signal Selection Criteria Conv Photon (1) Shown on the plot: Invariant mass distribution for opposite sign electron pairs Cuts used for the selection: Long Tracks: M inv < 15 MeV Downstream Tracks: M inv < 70 MeV 4 Signal Selection Criteria Conv Photon (2) Shown on the plots: x & y distance between the two electrons before the Magnet Cuts used for the selection ( used only for Downstream tracks ) : Long Tracks Downstream Tracks: |dx|< 6 mm && |dy| < 4 mm 5 Shown on the plots: Correlation of the VeloCharges of the 2 electrons (LL) Cuts used for the selection ( used only for Long tracks ) : VeloCharge1 > 45 VeloCharge2 > 45 | VeloCharge1 VeloCharge2) | < 5 Signal Selection Criteria Conv Photon (3) 6 Shown on the plots: projected converted photon x vs y position at ECAL Cuts used for the selection: abs( xEcal ) < 3000 mm abs( yEcal ) < 3000 mm Exclude inner hole of 380 x 380 mm Signal Selection Criteria Conv Photon (4) 7 Shown 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 < 50 chi2y < 20 Signal Selection Criteria Brems 8 Shown on the plots on the right: 1-D chi2 match of Projected Conv Photon and Non-Converted Photon Candidate Cuts used for the selection: 50 < chi2x < 1.e6 20 < chi2y < 1.e6 Signal Selection Criteria Non-Conv Photon 9 Signal Selection Criteria summary Selection of electron pairs 2 Long Tracks: Inv Mass < 15 MeV Velo Charges > 45 && abs( VeloCharge1 VeloCharge2) < 5 2 Downstream Tracks: Inv Mass < 70 MeV x- and y- distance between electrons measured at TT less than 6 and 4 mm respectively Collect pairs with el. charges which are: opposite - possible signal same - to estimate the background Project Conv Photon to ECAL: abs( xEcal ) < 3000 mm abs( yEcal ) < 3000 mm Exclude inner hole of 380 x 380 mm Selection of Brems Look for Neutral PP near the projected CP ( two 1-D matches ): chi2x < 50 chi2y < 20 Potential additional cuts: Cluster Energy < 20 GeV Cluster size < 15 cells PhotonID > X Selection of Non-Conv Phot: 50 < chi2x < 1.e6 20 < chi2y < 1.e6 We use exactly the same cuts to select background from same sign electron pairs 10 Fitting procedure Parametrize 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 enough Compare 2 different ways of fitting: Directly fit the Signal + Background distribution Use double sigmoid + gaussian All parameters are variable (not fixed) The parameters of the gaussian are of primary interest Alternative 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 variable Fit the signal + background distribution with gaussian + the double sigmoid Results in comparison with the direct fit: sensibly worse 2 of the fit in some of the cases the fitted gaussians have sensibly different parameters 11 Long Tracks && No Brem - plots 1 GREEN 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 13 Long Tracks && Yes Brem - plots 1 GREEN direct fit RED fit same sign el. bkg and fit sig+bkg 14 c = 96 = 4.4 % = 13.0 % c = = 4.1 % = 14.9 % Long Tracks && Yes Brem - plots 2 15 GREEN direct fit Downstream Tracks && No Brem - plots 1 RED 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 2 17 Downstream Tracks && Yes Brem - plots 1 GREEN direct fit RED fit same sign el. bkg and fit sig+bkg 18 c = = 2.4 % = 22.4 % c = = 0.6 % = 16.6 % Downstream Tracks && Yes Brem - plots 2 19 For the fit results: The upper line describes the direct fit The lower line describes the 2-step fit To be added: A column with a info about the energy resolution on the Conv Phot 20 Type of tracks Yes/No Brem N of Sig + Bkg EventsFit 2 / ndf Gauss Mean [%] Gauss Sigma [%] Long No Brem / / 0.4 Yes Brem / / 1.1 Downstream No Brem / / 0.3 Yes Brem / / 1.1 Summary of the Fits Rate of preselected triplets: 10.5/event (1.34x10 -3 / event are MCConf ) The preselection is described in the backup slides Rate 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 : Expected Rates Type of tracksYes/No Brem N of Sig + Bkg Events N of MCConf as signal Long No Brem (11.3%) Yes Brem (12.5%) Downstream No Brem (13.5%) Yes Brem (16.2%) TOTAL (13.3%) The results keep improving Conclusion BAKUP SLIDES Preselection cuts for triplets Triplet = 2 electrons and a photon Electron pair: Track Types: Long/Long or Downstream/Downstream M inv < 120 MeV Distance between projected Conv Photon and the Non-Converted Photon < 1200 mm Other sanity cuts: e.g. for long electrons we require existence of State at BegRich1 RESULTS OF THE PRESELECTION Number of preselected electrons opposite 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 zone DELTA 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