Thursday, December 17, 2015 Sky D. Rolnick UC Riverside 1 Baseline study for Chiral Symmetry Restoration using the Hadron Blind Detector in the PHENIX

Friday, April 21, 2023 Sky D. Rolnick UC Riverside 1

Baseline study for Chiral Symmetry Restoration usingthe Hadron Blind Detector in the PHENIX Experiment

SKY ROLNICK

University California Riverside

APS April Meeting


Low Mass Dilepton Pairs in Heavy Ion CollisionsLow Mass Dilepton Pairs in Heavy Ion Collisions

Electron pairs landscapeChiral 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.


PHENIX Experiment Dielectron Measurement

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.


Dilepton Pair Analysis in p+p

arxiv: 0912.0244v1 [nucl-ex]

Low mass:Dalitz decays: 0e+e-, e+e-, 0e+e-,

e+e-Direct decays:e+e-, e+e-, e+e-, J/e+e-,

’e+e-Heavy flavor:cce+e- +X, bbe+e- +XDrell-Yan:qqe+e-

Intermediate mass:

Extract charm and bottom:σcc = 518 ± 47 (stat) ± 135 (syst) ±

190 (model) μbσbb = 3.9 ± 2.4 (stat) +3/-2 (syst)

μb

Charm: integration after cocktail subtraction σcc = 544 ± 39 (stat) ± 142 (syst) ±

200 (model) μbExcellent agreement with Cocktail

Filtered in PHENIX acceptance


Dilepton Pair Analysis in Au+Au

Signal/Background 1/500 – 1/100 depending on pt 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 Npart

•pT dependency: enhancement concentrated at low pT

Intermediate mass•Agreement with PYTHIA: coincidence?

arxiv: 0912.0244v1 [nucl-ex]


The PHENIX Hadron Blind Detector

Dilepton pair

Beam Pipe

Cherenkov “blobs”

(rBLOB~3.36cm)Triple GEM

stacks(10 panels/side)

5 cm

50 cm

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


Separating Signal from BackgroundSeparating 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


Single vs Double Electron Clusters (Run 9)

Use reconstructed Dalitz pairs (Mee < 150 MeV/c) in PHENIX Central ArmsMatch 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.


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


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


Improvements in S/B with HBD in Run 10

Z.Citron

Run 4 = 0.8 x 109 MB eventsRun 7 = 5.4 x 109 MBRun 10 ~ 6.0 x 109 MB f ~ 7.5

~ 25% decrease due to scintillation in central collisions

Npe single = 22 pe

Run 4 statistics Run 4 statistics

With these numbers we can Expect an increase in effective Signal by ~70!


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

Backup Slides


Detector OccupancyDetector Occupancy

90% CentralityI.Ravinovich








Scintillation makes life Difficult!Scintillation makes life Difficult!

Curves show: Blue = DoubleRed = SingleMagenta= Scintiallation

I.Ravinovich


HBD Clustering AlgorithmsHBD 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)


SummarySummary

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.

Documents

Thursday, December 17, 2015 Sky D. Rolnick UC Riverside 1 Baseline study for Chiral Symmetry Restoration using the Hadron Blind Detector in the PHENIX