1. HBD studies in Run9 200GeV p+p collisions Jiayin Sun 1

2. Two kinds of HBD responses single electron clusters (SINGLES): – One electron per cluster – Smaller HBD signal double electron clusters (DOUBLES): – two electrons per cluster – Larger HBD signal 2

3. 4 types of electrons in HBD SINGLE Signal non-phot FAKE SINGLE Type 2 Background : One-legged doubles SINGLE type 0 Background : open pairs DOUBLE type1 background One electron is not detected. They appear to be singles but are in fact doubles. Both electrons are detected by PHENIX 3

4. What I did Search an event for an electron track (normal electron cut) – Get 1 st electron – Then look for its HBD cluster ID, charge, size etc. Search the event again for another electron track (loose cut) – No 2 nd electron  single (signal + type2) – Find 2 nd electron: Look for its HBD cluster. Share same HBD cluster with 1 st e  double (type1) Different HBD cluster  single (signal + type0 + type2) Real singles and Type 2 are indistinguishable (both appear to be singles: 1 electron/cluster) 4

5. Basic HBD cuts Distance btw track projection & cluster < 4cm HBD cluster size > 2 pads Default HBD clusterizer: LBS clusterizer by Ermias. Ermias’s cut on minimum cluster charge: 15p.e. – To cut out scintillations 5

6. Single electron clusters are composed of:  signals  background: one legged doubles (type2)  background: open pairs (type0) SINGLES HBD charge distribution 0<pT<11<pT<22<pT<3 3<pT<44<pT<5 6

7. Double electron clusters are composed of: background: doubles / type 1 clean background. DOUBLES HBD charge distribution 0<pT<11<pT<22<pT<3 3<pT<4 4<pT<5 7

8. Background: one-legged doubles Can be constructed from 2-legged doubles (type1), Define: R 12 = To get a clean sample of doubles, choose clusters with large charge – Use arbitrary cut at charge > 60 p.e. (justified later) – Assume all clusters > 60 p.e. to be real doubles. Type 2Two-legged doubles (type1) one-legged doubles (type2) 8

9. Background: one-legged doubles singles Type 1 single && charge >60 Type 1 && charge >60 Singles: (Type 2 dominant) Type 1 type charge 9

10. Construct one-legged doubles type 2 = type1 x (R 12 ) -1 0<pT<11<pT<22<pT<3 3<pT<44<pT<5 HBD charge inclusive singles type2 type1 10

11. Signal after subtraction 0<pT<11<pT<22<pT<3 3<pT<44<pT<5 HBD charge inclusive singles type2 open pairs (type0) (type1) 11

12. Signal ( 1 < pT < 2) Charge (p.e.) 12

13. Results from WIS clusterizer 0<pT<11<pT<22<pT<3 3<pT<44<pT<5 HBD charge inclusive singles type2 open pairs (type0) (type1) 13

14. Signal ( 1 < pT < 2) (WIS) Charge (p.e.) 14

15. 15

16. HBD charge Cut Design a cut on HBD cluster charge – Reject electrons with HBD charge > cut value. Ideally, this cut should: – cut out as many double clusters (photonic electrons) as possible. – Keep as many signal as possible – Keep S/B ratio as high as possible S/B ratio is a function of the cut. – S/B = signal / (type0+type1+type2) 16

17. S/B vs. charge cut 0<pT<11<pT<22<pT<3 3<pT<44<pT<5 17 S/B decline with cut lower cut: Cut out a lot of signals higher cut: Lower S/B ratio

18. Efficiency vs. charge cut 0<pT<11<pT<22<pT<3 3<pT<44<pT<5 18 Efficiency = Signals left after cut Total signals

19. R 12 vs. pT (charge > 60 p.e.) 19

20. R 12 vs. cut at cluster charge 0<pT<11<pT<22<pT<3 3<pT<44<pT<5 R 12 flat from 45 p.e. to 65 p.e. insensitive to the cut after 45 p.e. Stat. fluctuation at higher pT 20

21. Background: open pairs (type0) Distance between clusters – All – 0 < Mee < 0.14GeV – Mee > 0.14GeV Cut: dist < 10 cm SINGLE type 0 Background: open pairs dist 21

22. Background: open pairs (type0) A look at open pairs SINGLE type 0 Background: open pairs dist mis-associated doubles 22