1 / 14

Reconstruction of converted photons E. Tournefier LAPP meeting Feb. 2,2012

Reconstruction of converted photons E. Tournefier LAPP meeting Feb. 2,2012. Algorithm for the reconstruction of converted photons Performances studies: B s  and D 0 *  D 0  MC First look at real data: D 0 *  D 0 . Converted photons in LHCb.

blaineb
Download Presentation

Reconstruction of converted photons E. Tournefier LAPP meeting Feb. 2,2012

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Reconstruction of converted photonsE. TournefierLAPP meetingFeb. 2,2012 • Algorithm for the reconstruction of converted photons • Performances studies: Bs and D0*  D0  MC • First look at real data: D0*  D0 

  2. Converted photons in LHCb • 40% of the photons convert before the calorimeter (MC truth) • Out of which: • ~ 40% convertafter the magnet (z>8m) • 50% convertbefore the end of TT (z<3m)  we are trying to reconstructthoseones

  3. Reconstruction of converted photons 1/ Bremstrahlung recovery: Start from StdAllLoosePhotons with PhotonID> -0.25 Add photons which satisfy: (X and Y refer to position measured or extrapolated to CALO) - |Ye-Y| 3Y (the magnetic field is oriented along Y) - |X - Xtr|  3X : the photon should match the track extrapolation - Ptr<Ee+ E or Ptr  Ee + E - 2E :to make sure the track momentum was measured before brem 2/ Converted photon reconstruction: - select electrons with CALO information and CombDLLe  0. - make electron pairs which satisfy: |Ye--Ye+ |3 Y - do brem recovery making sure each photon is added only to e- OR to e+ - define converted photon CL as CL= CombDLLe1 x CombDLLe2 - combine the 2 electrons to make the photon * if one electron track has double charge in VELO (>1.5): redefine the photon direction with this track - select pairs with Mee  200 MeV and CL>10

  4. Performances studies with Bs: energy resolution • Bs MC11a (100k evts used here) Look only at events with E(MC electron)>2GeV so that it has a chance to reach ECAL Reconstructed inv mass Long tracks Down tracks MeV Z of  decay: Conv photon reconstructed Conv photon not reconstructed • Converted photon reconstructedwithM<200MeV: 43% • + with|Erec-EMC|/EMC<0.1: 30%

  5. Performances studies with Bs: angular resolution • Angular resolution: • 25% of the events with converted photons have 1 electron track with double VELO charge (>1.5): define photon direction with this track => Angular resolution improved by a factor 1.6 for these events • New algo • Old algo d = rec- MC

  6. Performances studies with Bs: efficiency • Reconstruction efficiency of converted photons drops at low Pt: the electrons don’t reach the ECAL Efficiency • Efficiency for all events • Efficiency for events with 1 electron E>2GeV Pt of photon Pt of electronfrom Pt • Not a bigproblem for Bs since the photons are quite energetic

  7. Performance studies: D0*  D0  • The aim is to check the performances on data on a channel with high statistics • Try with prompt D0*  D0  Problem: the photon has very low energy => efficiency drops: only few % at Pt ~500 MeV • Efficiency for all events • Efficiency for events with 1 electron E>2GeV Pt photon (MeV)

  8. First look at 2011 data: D0*  D0  1/ Try to reconstruct D0*  D0  with non converted photons (many thanks to Vincent for his code!!) 2/ with converted photons (10 times more data) dM=M (D0*)-M (D0) dM=M (D0*)-M (D0) Converted  Non converted  dM (MeV) dM (MeV) • In both cases I used photons with Pt>600 MeV • Given the (low) efficiency the number of eventswithconverted photons are as expectedfrom the non-converted case • =>Need to run on more data (I usedonly 1% of total sample)

  9. First look at 2011 data: D0*  D0  • Can roughly measure the efficiency on data: ~ok with MC • Efficiency from MC • Efficiency measured on data Pt photon (MeV) • Otheridea: look atB- D0* - as Vincent is doing • Thought the photon would be more energetic but this is not the case....

  10. Summary • Converted photons reconstruction: • some improvements for tracks with double VELO charge (angular resolution /1.6) • Studies with D0*  D0  : • Very low efficiency due to low energy photons • No mass peak seen for converted photons… need to run on larger data sample • Efficiency measured on Data seems ok with MC • Next: try to use low energy electrons (with RICH ID) Pb: most of these tracks are not reconstructed

  11. Converted photons with ‘RICH electrons’ • Try to reconstruct converted photons with 1 CALO electron and 1 non-CALO electron • Stastitics increased by 15% if one includes these events for Bs Minimum energy of the 2 electrons (MC)

  12. END

  13. Non-reconstructed photons • Many of the non-reconstructed events have at least 1 low energy electron • Many have large brem => the electron does not reach the ECAL => Upstream track sharing a VELO segment with other electron: not reconstructed • Try to reconstruct the Upstream tracks sharing the VELO segment with another track? • Need to use tracks without calorimetric information but with RICH1 PID Minimum energy of the 2 electrons (MC) • Converted photon not reconstructed • Converted photon reconstructed

  14. Track types • Conversion into VELO (z<80cm): • 2 Downstream tracks: 53% of events • 2 Long tracks: 24% most (75%) share the same VELO segment • 1 Long + 1 Downstream: 23% • The VELO segment is often lost in the reconstruction (likely due to bremstrahlung) VELO charge: case of 2 Long tracks

More Related