1 A Study On Photonic Electrons In The Endcap EMC  Purity of electrons from MC simulation & real data  Reconstructed photonic electrons Naresh Subba,KSU November 5, 2007 Data analysed : 1.Purity ppTrans, runs 2.Reco. photonic electrons ppTrans, runs (~1.25M events)

2 Real Data ppTrans, 2006, 103 runs (no trigger selection)

3 Definition: Purity = S/(S+B) S+B ~ 149 B ~ 5 Purity ~ 96.8% However,purity ~ 6% from MC simulation Q. Why such a huge discrepancy? hadron electron

4 Endcap view of gamma converting to e+e- global e+ global e-  dist (1 st point) reco glob trak Conversion  vertex  DCA(2 helices ) SVT cone material  prim vertex OFC  IFC  TPC Gamma momentum  TPC hit Deflection exaggerated One track Enters Endcap (thanks Jan for this figure)

5 Invariant mass distribution of e+e- pairs before any cuts It is different for OS and SS e- pairs It peaks at ~0 for OS e- pairs

6 DCA distribution is different for OS and SS e- pairs The difference is most pronounced below 0.6 cm

7 The azimuthal angle between the e- pairs has different distributions for the OS and SS The difference is most pronounced below 0.10 radians Photonic e- SSOSCut

Photonic e- SSOSCut The polar angle between the e- pairs has different distributions for the OS and SS The difference is most pronounced below 0.02 radians

9 The open angle between the e- pairs has different distributions for the OS and SS The difference is most pronounced below 0.05 radians Photonic e- SSOSCut

10 The OS and SS e- pairs have different invariant mass distributions The difference is most pronounced below 0.10 GeV Reconstructed photonic electrons is the difference of OS and SS histograms Photonic electron is the reconstructed photonic electron/efficiency The efficiency is unknown yet Will need to look at embedding data for photonic reconstruction efficiency OS - SS Cuts: 1.DCA cut < 0.6 cm 2.ΔΦ < 0.10 rad 3.ΔΘ < 0.02 rad 4.3D Opening Angle < 0.05 rad 5.Invariant Mass < 100 MeV

11 Assuming Xiaoyun’s result for inclusive/background ~1.25 We get 6710 inclusive electrons, and 3472 reco. photonic electrons,hence,the rough estimation for the photonic electron reconstruction efficiency ~ 40%. (thanks Gang & Xiaoyan for this figure)

12 Summary  Purity of electron ID from MC simulation and real data do not agree with each together. Need to investigate why.  Yield of non-photonic electrons in the endcap EMC from pp2006 (no trigger selection) ~20 K~11 Kprojection for ppLong, 200 runs ~30 K~16 Kprojection for ppTrans, 300 runs ppTrans, 66 runs # non-photonic e- (assume 40% eff) # reco. photonic e-data type Next to do: Calculate photonic electron reconstruction efficiency using embedded data.

13 Backup Slides

14 electronID summary, tune 2 cuts: ~20%6%33%~60%PYTHIA: non-photonic e+,e- ~16%81%27%~60%PYTHIA: any e+,e- 42%95%54%80%e+ from one B0-meson 37%100%46%80%One electron Efficiency overall Purity eleID Efficiency eleID only efficiency TPC track M-C sample Yield of electrons reconstructed in the Endcap from pp2006 (no trigger selection) 30K (90K) 24K (75K) Accepted e+,e- 1.8K (5K) ppLong, 63 runs (projection for 200 runs) 1.4K (4K) ppTrans 103 runs, (projection for 300 runs) non-photonic e+,e- (assume 6% purity) Data type Efficiency & Purity averaged over reco eta [1,1.5] (trigger simu not accounted for)

15 Effect of various cuts on dE/dx distribution electrons hadrons

16 Cuts DCA cut < 0.6 cm ΔΦ < 0.10 rad ΔΘ < 0.02 rad 3D Opening Angle < 0.05 rad Invariant Mass < 100 MeV 2-D Invariant Mass < 100 MeV The no. of photonic electrons is different for OS and SS e- pairs Clearly,it is much enhanced for OS than SS e- pairs for the same cut

17 Initially tried w/ this global-global first point distance of the e- pairs cut Later on realized that DCA cut between the e- pairs was more powerful to discriminate between photonic electrons coming from OS and SS e- pairs

18 Gamma DCA to the vertex Rv prim vertex Rc Conversion point Beam line e+ momentum e - momentum P =gamma momentum D=DCA(P,V) 90   *U Gamma track UU (thanks Jan for this figure)

19 Rxy at secondary vertex point (i.e gamma conversion point) Its distribution is clearly different for OS and SS e- pairs It is most pronounced between 15 and 35 cm Since it is clustered around low mass region, it is automatically taken care of when invariant mass cut is applied

20 Rxy distribution ( between ~15-35 cm) is clustered at low invariant mass region for OS e- pairs Rxy distribution (in and around the origin) is clustered towards higher invariant mass region for SS e- pairs