Update on Energy Resolution of

Transcription

1 Update on Energy Resolution of the EMC Using µµγ Sample David Hopkins Royal Holloway, University of London EMC Reconstruction Workshop, December 5 th, 2004

2 Outline Study of photon energy resolution Compare measured (BtaCandidate) photon energy with the true photon energy implied by a kinematic fit. Using µµγ sample taken from 184 fb -1 of data (Runs 1-4), produced in release 14. Sample is produced by the Inclusive Hadronic Particle Spectra AWG Currently have two sets of SP5 MC One set of MC has cut at Eγ* = 3.0 GeV Now have sample with 500 MeV cut, but this is less plentiful, with a low number of entries in higher energy bins December 5 th, 2004 EMC Reconstruction Workshop 2

3 Photon Energy Spectrum My cuts: Two good measured tracks One good measured photon One of the charged particles identified as a muon (using loose PidMuonMicroSelector) Convergent kinematic fit χ 2 probability > 0.05 Cuts leave around 700,000 events from data. However, there were also pre-selection cuts applied (see BAD 558 and 831). December 5 th, 2004 EMC Reconstruction Workshop 3

4 Fitted Energy as Estimator for True Energy Cuts are as on the previous slide Kinematically fitted photon energies are closer to MC true energies than measured photon energies Energy from kinematic fit is good estimator for true energy Fit overestimates photon energy more often than it underestimates it Caused by energy loss, especially in forwards direction outside the EMC angular acceptance Eγ meas Eγ true Eγ fit Eγ true December 5 th, 2004 EMC Reconstruction Workshop 4

5 Data Vs MC comparison Data Eγ meas /Eγ fit MC Eγ meas /Eγ fit MC Eγ meas /Eγ true Plot shows energy response functions Eγ meas /Eγ fit Data seems to have more events with measured energy higher than fitted energy than MC Seen in most plots of Eγ meas /Eγ fit, irrespective of polar angle or energy range. Are non-uniformities in crystals not simulated in MC causing this? December 5 th, 2004 EMC Reconstruction Workshop 5

6 Example of comparison of Eγ response in data and MC (forwards barrel) Data Eγ meas /Eγ fit fit MC Eγ meas /Eγ fit fit MC Eγ meas /Eγ true December 5 th, 2004 EMC Reconstruction Workshop 6

7 Comparison of Eγ response in data and MC in the endcap Data Eγ meas /Eγ fit MC Eγ meas /Eγ fit MC Eγ meas /Eγ true Data Eγ meas /Eγ fit MC Eγ meas /Eγ fit MC Eγ meas /Eγ true December 5 th, 2004 EMC Reconstruction Workshop 7

8 Eγ meas /Eγ fit examples from forwards barrel Running Gaussian fit σ= σ 0 for x > µ, σ= σ 0 r(x µ) for x < µ December 5 th, 2004 EMC Reconstruction Workshop 8

9 Variation of µ for Eγ meas meas /Eγ fit < cosθ (b/w barrel) < cosθ 0.0 (b/w barrel) 0.0 < cosθ (f/w barrel) µ < cosθ (f/w barrel) < cosθ 0.94 (endcap) Eγ (GeV) December 5 th, 2004 EMC Reconstruction Workshop 9

10 Variation of FWHM for Eγ meas meas /Eγ fit < cosθ (b/w barrel) < cosθ 0.0 (b/w barrel) 0.0 < cosθ (f/w barrel) < cosθ (f/w barrel) < cosθ 0.94 (endcap) FWHM / Eγ (GeV) December 5 th, 2004 EMC Reconstruction Workshop 10

11 2-D D Plots of µ and FWHM for Eγ meas /Eγ fit µ Mean usually close to 1 Mean in endcap consistently higher than 1 Caused by poor fits to unusual energy response functions FWHM / FWHM initially decreases with energy, and then levels out December 5 th, 2004 EMC Reconstruction Workshop 11

12 Eγ fit /Eγ true examples from forwards barrel Gaussian fit December 5 th, 2004 EMC Reconstruction Workshop 12

13 2-D D Plots of µ and FWHM for Eγ fit /Eγ true µ Mean usually close to 1 However, tendency for fit to slightly overestimate true energy is clearly seen FWHM / FWHM usually around 10 times smaller than those for Eγ meas /Eγ fit December 5 th, 2004 EMC Reconstruction Workshop 13

14 To be continued Will use MC that has lower photon energy cut in CM frame Will give better idea of how well fit works in different energy bins Have some of this, but will probably need more! Need to look at cuts again, to increase efficiency Will use smaller bins in terms of cosθ Should offer better understanding of EMC over entire angular range Quantify energy resolution as it varies with photon energy and with cosθ Maybe look at how data and MC compare in terms of Eγ response See: er/software/calib_mtg/photon.html for more plots and talks December 5 th, 2004 EMC Reconstruction Workshop 14

15 Supplemental slides

16 Eγ meas /Eγ fit in range < cosθ (backwards barrel) December 5 th, 2004 EMC Reconstruction Workshop 16

17 Eγ meas /Eγ fit in range < cosθ 0.0 (backwards barrel) I December 5 th, 2004 EMC Reconstruction Workshop 17

18 Eγ meas /Eγ fit in range < cosθ 0.0 (backwards barrel) II December 5 th, 2004 EMC Reconstruction Workshop 18

19 Eγ meas /Eγ fit in range 0.0 < cosθ (forwards barrel) I December 5 th, 2004 EMC Reconstruction Workshop 19

20 Eγ meas /Eγ fit in range 0.0 < cosθ (forwards barrel) II December 5 th, 2004 EMC Reconstruction Workshop 20

21 Eγ meas /Eγ fit in range < cosθ (forwards barrel) I December 5 th, 2004 EMC Reconstruction Workshop 21

22 Eγ meas /Eγ fit in range < cosθ (forwards barrel) II December 5 th, 2004 EMC Reconstruction Workshop 22

23 Eγ meas /Eγ fit in range < cosθ 0.94 (endcap)) I December 5 th, 2004 EMC Reconstruction Workshop 23

24 Eγ meas /Eγ fit in range < cosθ 0.94 (endcap)) II December 5 th, 2004 EMC Reconstruction Workshop 24