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Photons corrections

LHCb CaloSoft meeting – 25 May 2004. Photons corrections. Olivier Deschamps LPC-Clermont. Remind. Photon corrections (E-/S-/L-corrections) for DC04 were evaluated in February 2004 using PGUN-produced γ / π ° samples (Gauss v14r1 - Geant4 bugged - v6r0) and introduced in Brunel v23r3.

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Photons corrections

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  1. LHCb CaloSoft meeting – 25 May 2004 Photons corrections Olivier Deschamps LPC-Clermont CaloSoft meeting May 2004 LHCb week

  2. Remind • Photon corrections (E-/S-/L-corrections) for DC04 were evaluated in February 2004 using PGUN-produced γ/π° samples (Gauss v14r1 - Geant4 bugged - v6r0) and introduced in Brunel v23r3. • Study of pre-produced DC04 data (Geant4 v6r1) shows a bad behaviour for neutrals -> Miscalibration reported in B->K*γ and B->π-π+π° selections -> bad electron identification • Patrick reports a 7.2% Ecal energy shift between Geant4 v6r0 and v6r1 (origin unknown) Photon corrections re-evaluated using PGUN sample (G4 v6r1). CaloSoft meeting May 2004 LHCb week

  3. Outer Energy : 5.0 10.0 16.8 33.8 50.0 100.0 168.0 GeV Middle Inner Data sample Use samples of single photons produced with PGUN Discrete energy & acceptance samples: • Roughly mimics photon from radiative B decay • Gauss v15r6 - Boole v5r8 – Brunel v23r7 • ActiveToTotal • May-DC04 7.84 (Geant4 v6r1) • February-DC04 8.4 (Geant4 v6r0) • January-DC04 10.5 (bad evaluation) • DC03 7.5 (Geant3) K*γ Pgun γ CaloSoft meeting May 2004 LHCb week

  4. E/S/L corrections • New correction parameters not drastically different from february one. • With february data the transversal shower shape was found to be smaller by 10-15% wrt DC03 value. • S-shape parameter now slightly re-increases (but not at the level of DC03) • Rough feeling : new corrections are in between February and DC03 corrections • Main effect is the 7.2% energy miscalibration CaloSoft meeting May 2004 LHCb week

  5. Energy correction 3x3 measured energy versus PGUN energy backward leakage Leakage at high energy was not observed with february data CaloSoft meeting May 2004 LHCb week

  6. Energy correction 3x3 measured energy versus relative barycenter position Outer Ecal Inner Ecal E3x3/Eγ barycenter-center distance (cell size unit) Strange behaviour already observed with february data CaloSoft meeting May 2004 LHCb week

  7. Energy resolution Spd hit (« converted ») σE/E (%) No Spd hit (« unconverted ») No Spd No Ps Spread ΔE/σ 1/√E (GeV1/2) Overall : Similar to february performance CaloSoft meeting May 2004 LHCb week

  8. Energy resolution : DC04 versus DC03 Unconverted photons (No SPD hit) DC04 PGUN photons DC03 PGUN photons CaloSoft meeting May 2004 LHCb week

  9. Overall : Angular resolution σΘ/Θ(%) Spd hit (« converted ») No Spd hit (« unconverted ») Outer Inner Middle No Spd No Ps 1/√E (GeV1/2) 1/√E (GeV1/2) Warning : average resolutions ! Here PGUN distribution is used ! Similar to february performance CaloSoft meeting May 2004 LHCb week

  10. Angular resolution Polar angle spread badly fit with a single-gaussian function 2 gaussians slightly displaced Angular resolution should be improved Angular spread ΔΘ/σ CaloSoft meeting May 2004 LHCb week

  11. Resolved and merged π0s Neutral pions from PGUN production Resolved Merged Performance seems OK CaloSoft meeting May 2004 LHCb week

  12. Software implementation • Because DC04 production being started, new corrections to be applied at the DaVinci level (as done in 2003 for TDR data) • Will be available with the next DaVinci release (v11r8) • Preliminary checks performed on B→K*γ and B→ 3π selections (see Tuesday meeting last week) • - B mass resolution and selection yield seems OK for B → 3π • - Galina reported a degradated B mass • resolution for K*γwrt TDR(however the mass peak • is correctly located) • σ(K*γ)~ 75 MeV/c² (TDR 2003 : 64 MeV/c²) • Degradation more important for converted (SPD) • photons CaloSoft meeting May 2004 LHCb week

  13. Check energy resolution Pgun (single photon events) versus photon from K*γ (full events) Converted (SPD) photons only PGUN K*γ Energy spread (EMC-E)/σ Energy spread (EMC-E)/σ σE(E) from PGUN Energy resolution slightly degradated in full events. No dramatic effect with converted photons. CaloSoft meeting May 2004 LHCb week

  14. Check angular resolution Pgun (single photon events) versus photon from K*γ (full events) Converted (SPD) photons only PGUN K*γ Angular spread (Θ-ΘMC)/σ Angular spread (Θ-ΘMC)/σ σΘ(E) from PGUN Angular resolution slightly degradated in full events. No dramatic effect with converted photons. CaloSoft meeting May 2004 LHCb week

  15. Inner hole effect PGUN photon well produced in Ecal acceptance Low angle photon from K*γ(Θ<40 mrad) versus larger acceptance PGUN K*γ Energy spread (EMC-E)/σ Angular spread (Θ -ΘMC)/σ σΘ(E) from PGUN Large systematic effect on photon direction near inner hole. Low angle photons represent ~ 15% of total. Inner hole acceptance changed this year. May (partially) explain Galina’s results ? CaloSoft meeting May 2004 LHCb week

  16. Middle Ecal Inner Ecal Boundary effect • Strange behaviour detected near Ecal boundaries : 3x3 cluster use more than • 9 cells to compute energy and barycenter !!! • Due to the use of the cell size to define neighbourhood. • Some large cells are defined as neighboor of smaller size seed even if they are • not adjacent !!! • Small piece of code added in DaVinci to correct for that. • More efficient fix will be done next week (thanks to Vanya’s help) CaloSoft meeting May 2004 LHCb week

  17. Photon origin spread effect The spread of the photon origin (IP is 5 cm width gaussian) is NOT a negligible effect. Has to be taken into account to compare PGUN (originating from (0,0,0)) and collision events. Impact of barycenter resolution : Impact of IP spread (5cm) : • PhotonParticleMaker compute photon momentum as originating from (0,0,0) • MergedPhoton originates from first found primary vertex • Photon direction re-evaluated according to B vertex position in K*γ selection • But not yet in B→3π (Arnaud will introduce it soon in selection) Could be technically usefull to change ResolvedPi0 and MergedPi0Maker algorithms as DaVinci tools allowing analysis dependent origin for neutral pions. CaloSoft meeting May 2004 LHCb week

  18. Conclusions • New photon corrections ready for DC04 production (to be applied on stripping). • Available with the next DaVinci release. • Performance similar to february corrections (and parameters almost). • Performance degradated wrt DC03 using Geant3 (new Calo non-uniformities ?) • Some imperfections remain : • - Ecal boundary effects (being fix) • - Inner hole border • - Limitation due to use of PGUN versus full events • - Partially overlap clusters reconstruction not re-evaluated • these imperfections was already present last year (can not explain degradation observed in K*γ by Galina) • Some improvement should be possible CaloSoft meeting May 2004 LHCb week

  19. Perspective • On another hand MC-truth is used to correct for quite tiny effects • - Use of MC 4-momentum as reference • - Use of cleaned photon sample (cluster-photon associator) • Need to trust Monte-Carlo !! • Are the correction performance achievable ?(although currently non perfect !) • Could we extract refined E-correction from data ? S-shape ? L-correction ? • - Using neutral pion fit procedure à la Hera-B • - Using tracked electrons • Try to develop new Ecal correction procedure for DC05 ... CaloSoft meeting May 2004 LHCb week

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