1. Thursday, December 17, 2015 Sky D. Rolnick UC Riverside 1 Baseline study for Chiral Symmetry Restoration using the Hadron Blind Detector in the PHENIX Experiment SKY ROLNICK University California Riverside APS April Meeting

2. Thursday, December 17, 2015 Sky D. Rolnick UC Riverside 2 Low Mass Dilepton Pairs in Heavy Ion Collisions Electron pairs landscape Chiral symmetry is a symmetry of QCD which is expected to be restored at high temperatures achievable at RHIC Dileptons are our best probe to study chiral symmetry restoration and medium modification of vector mesons. Ideal EM probes, no strong interaction, long mean free path, carry information about the medium. Produced throughout the history of the collision.

3. Thursday, December 17, 2015 Sky D. Rolnick UC Riverside 3 PHENIX Experiment Dielectron Measurement e+e+ ee   Experimental challenge: huge combinatorial background arising from e + e - pairs from copiously produced from  0 Dalitz decay and  conversions. Currently, electrons are tracked by drift chamber and pad chamber The Ring Imaging Cherenkov Counter is primary electron ID device Electromagnetic calorimeters measure electron energy Typically, in normal magnetic field configuration, only 1 electron from a pair falls within the PHENIX acceptance. Both members of the pair are needed to reconstruct a Dalitz decay or a  conversion.

4. Thursday, December 17, 2015 Sky D. Rolnick UC Riverside 4 Dilepton Pair Analysis in p+p arxiv: 0912.0244v1 [nucl-ex] Low mass: Dalitz decays:  0   e+e-,    e+e-,    0 e+e-,    e+e- Direct decays:   e+e-,   e+e-,   e+e-, J/   e+e-,  ’  e+e- Heavy flavor: cc  e+e- +X, bb  e+e- +X Drell-Yan: qq  e+e- Intermediate mass: Extract charm and bottom: σ cc = 518 ± 47 (stat) ± 135 (syst) ± 190 (model) μb σ bb = 3.9 ± 2.4 (stat) +3/-2 (syst) μb Charm: integration after cocktail subtraction σ cc = 544 ± 39 (stat) ± 142 (syst) ± 200 (model) μb Excellent agreement with Cocktail Filtered in PHENIX acceptance

5. Thursday, December 17, 2015 Sky D. Rolnick UC Riverside 5 Dilepton Pair Analysis in Au+Au Signal/Background  1/500 – 1/100 depending on p t cut and mass. Au+Au Low mass Enhancement above the cocktail expectations: 3.4±0.2(stat.) ±1.3(syst.)±0.7(model) Centrality dependency: increase faster than N part p T dependency: enhancement concentrated at low p T Intermediate mass Agreement with PYTHIA: coincidence? arxiv: 0912.0244v1 [nucl-ex]

6. Thursday, December 17, 2015 Sky D. Rolnick UC Riverside 6 The PHENIX Hadron Blind Detector Dilepton pair Beam Pipe Cherenkov “blobs” (r BLOB ~3.36cm) Triple GEM stacks (10 panels/side) 5 cm 50 cm e-e- e+e+ Opening angle can be used to cut out photon conversion and Dalitz decays MUST BE ABLE TO DISTINGUISH SINGLE AND DOUBLE HITS Create a field free region close to the vertex to preserve opening angle of close pairs. Identify electrons in the field free region reject close pairs. HBD concept: Windowless Cherenkov detector (L=50cm) CF4 as radiator and detector gas Proximity focus: detect circular blob not ring CF4 Gas

7. Thursday, December 17, 2015 Sky D. Rolnick UC Riverside 7 Separating Signal from Background Opening angle can be used to cut out photon conversion and Dalitz decays Identify electrons with p > 200 MeV/c in Central Arms, project back and match to HBD. Reject if there is another electron within θ < 200 mrad

8. Thursday, December 17, 2015 Sky D. Rolnick UC Riverside 8 Single vs Double Electron Clusters (Run 9) Use reconstructed Dalitz pairs (M ee < 150 MeV/c) in PHENIX Central Arms Match to single or double clusters in HBD ~ 40 p.e. per two electron track I.Ravinovich ~ 22 p.e. per single electron track Agrees with our expected yield taking into account p.e. collection efficiency and transmission loss in the gas.

9. Thursday, December 17, 2015 Sky D. Rolnick UC Riverside 9 Electron Efficiency (Run 9) Measured using well identified electrons in low mass region (0.025 < m < 0.050 GeV) measured in the PHENIX Central Arms and matched with hits in the HBD Single electron efficiency > 90% Pair efficiency ~ 80%. I.Ravinovich Opening angle Meets requirements for achieving 90 % rejection of photon conversions and Dalitz decays

10. Thursday, December 17, 2015 Sky D. Rolnick UC Riverside 10 First look at Run9 p+p 200 GeV dielectron data **Very** preliminary rejection numbers: matching to HBD ~2 - 7 double hit cut ~6.5 single pad cluster cut ~2 Total Rejection Factor ~26 I.Ravinovich

11. Thursday, December 17, 2015 Sky D. Rolnick UC Riverside 11 Improvements in S/B with HBD in Run 10 Z.Citron Run 4 = 0.8 x 10 9 MB events Run 7 = 5.4 x 10 9 MB Run 10  ~ 6.0 x 10 9 MB f ~ 7.5 ~ 25% decrease due to scintillation in central collisions Npe single = 22 pe Run 4 statistics With these numbers we can Expect an increase in effective Signal by ~70!

12. Thursday, December 17, 2015 Sky D. Rolnick UC Riverside 12 Collaboration  Brookhaven National Lab: B. Azmoun, A.Milov, R. Pisani, T. Sakaguchi, A. Sickles, C. Woody  Columbia University: C.-Y. Chi  UC Riverside: Rich Seto, Sky D. Rolnick  Stony Brook University: W. Anderson, Z. Citron, J. M. Durham, T.Hemmick, J. Kamin, V. Pantuyev, J. Sun, B. Lewis  Weizmann Institute of Science: A. Dubey, Z. Fraenkel, A. Kozlov, A. Milov, M. Naglis, I. Ravinovich, D. Sharma, I. Tserruya

13. Backup Slides

14. Thursday, December 17, 2015 Sky D. Rolnick UC Riverside 14 Detector Occupancy 90% Centrality I.Ravinovich

15. Thursday, December 17, 2015 Sky D. Rolnick UC Riverside 15 Detector Occupancy 30% Centrality I.Ravinovich

16. Thursday, December 17, 2015 Sky D. Rolnick UC Riverside 16 Detector Occupancy 10% Centrality I.Ravinovich

17. Thursday, December 17, 2015 Sky D. Rolnick UC Riverside 17 Scintillation makes life Difficult! Curves show: Blue = Double Red = Single Magenta= Scintiallation I.Ravinovich

18. Thursday, December 17, 2015 Sky D. Rolnick UC Riverside 18 HBD Clustering Algorithms Finds clusters using neighbor pads and associates clusters to nearest track. Scintillation in pp identified easily by single pad clusters with low charge response. Higher multiplicities often cause problems. Wis Clusterizer (pad seeded) Searches around region of track for cluster. Uses a three-tuples as primitive cluster object. In AuAu has the advantage that it is much less sensitive to scintillation. HnS Clusterizer (track seeded)

19. Thursday, December 17, 2015 Sky D. Rolnick UC Riverside 19 Summary o The HBD is a first of its kind, very high performance Cherenkov counter that has been very challenging to build an operate. o The detector performed well in Run 9 in p-p and gave the expected level of performance in terms of p.e. yield, electron efficiency and hadron rejection o It seems to be performing well again in Run 10 and should give the required level of efficiency and rejection in Au+Au collisions o Given this level of performance and the added benefit of the HBD in terms of suppressing Dalitz pairs and photon conversions, it should enable a much more sensitive and precise measurement of low mass dilepton pairs in heavy ion collisions at RHIC.