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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. - PowerPoint PPT Presentation

Text of Photons corrections

  • Photons correctionsLHCb CaloSoft meeting 25 May 2004Olivier DeschampsLPC-Clermont

    CaloSoft meeting May 2004 LHCb week

  • Remind Photon corrections (E-/S-/L-corrections) for DC04 were evaluated in February 2004 using PGUN-produced / 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* and B->-+ 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

  • Data sample Roughly mimics photon from radiative B decay Gauss v15r6 - Boole v5r8 Brunel v23r7ActiveToTotal May-DC04 7.84 (Geant4 v6r1)February-DC04 8.4 (Geant4 v6r0) January-DC04 10.5 (bad evaluation) DC03 7.5 (Geant3)

    Use samples of single photons produced with PGUNDiscrete energy & acceptance samples:K*Pgun

    CaloSoft meeting May 2004 LHCb week

  • 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

  • Energy correction3x3 measured energy versus PGUN energyLeakage at high energy was not observed with february databackward leakage

    CaloSoft meeting May 2004 LHCb week

  • Energy correction3x3 measured energy versus relative barycenter positionStrange behaviour already observed with february dataE3x3/Ebarycenter-center distance (cell size unit)Outer EcalInner Ecal

    CaloSoft meeting May 2004 LHCb week

  • Energy resolutionNo Spd hit( unconverted )Spd hit ( converted )No Spd No Ps1/E (GeV1/2)E/E (%)Spread E/Overall :Similar to february performance

    CaloSoft meeting May 2004 LHCb week

  • Energy resolution : DC04 versus DC03DC03 PGUN photonsDC04 PGUN photonsUnconverted photons (No SPD hit)

    CaloSoft meeting May 2004 LHCb week

  • Angular resolutionNo Spd hit( unconverted )Spd hit ( converted )No Spd No Ps1/E (GeV1/2)/ (%)InnerMiddleOuterSimilar to february performanceWarning : average resolutions ! Here PGUN distribution is used !1/E (GeV1/2)

    CaloSoft meeting May 2004 LHCb week

  • Angular resolutionAngular spread /Polar angle spread badly fitwith a single-gaussian function2 gaussians slightly displacedAngular resolution should be improved

    CaloSoft meeting May 2004 LHCb week

  • Resolved and merged 0sResolvedMerged Performance seems OKNeutral pions from PGUN production

    CaloSoft meeting May 2004 LHCb week

  • 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 BK* and B 3 selections (see Tuesday meeting last week)- B mass resolution and selection yield seems OK for B 3 - Galina reported a degradated B mass resolution for K* wrt TDR (however the mass peak is correctly located)

    (K*)~ 75 MeV/c (TDR 2003 : 64 MeV/c)

    Degradation more important for converted (SPD) photons

    CaloSoft meeting May 2004 LHCb week

  • Check energy resolutionPgun (single photon events) versus photon from K* (full events)PGUNK*Converted (SPD) photons onlyEnergy resolution slightly degradated in full events. No dramatic effect with converted photons.Energy spread (EMC-E)/E(E) from PGUNEnergy spread (EMC-E)/

    CaloSoft meeting May 2004 LHCb week

  • Check angular resolutionPgun (single photon events) versus photon from K* (full events)PGUNK*Converted (SPD) photons onlyAngular resolution slightly degradated in full events. No dramatic effect with converted photons.Angular spread (-MC)/(E) from PGUNAngular spread (-MC)/

    CaloSoft meeting May 2004 LHCb week

  • Inner hole effectPGUN photon well produced in Ecal acceptanceLow angle photon from K* (
  • 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 arenot adjacent !!! Small piece of code added in DaVinci to correct for that.

    More efficient fix will be done next week (thanks to Vanyas help)

    CaloSoft meeting May 2004 LHCb week

  • Photon origin spread effectThe 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* selection But not yet in B3 (Arnaud will introduce it soon in selection)Could be technically usefull to change ResolvedPi0 and MergedPi0Maker algorithmsas DaVinci tools allowing analysis dependent origin for neutral pions.

    CaloSoft meeting May 2004 LHCb week

  • 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-evaluatedthese imperfections was already present last year (can not explain degradation observed in K* by Galina)Some improvement should be possible

    CaloSoft meeting May 2004 LHCb week

  • 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 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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