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A Hadron Blind Detector for the PHENIX Experiment at RHIC

A Hadron Blind Detector for the PHENIX Experiment at RHIC. Craig Woody RHIC II Workshop April 30, 2005. The PHENIX HBD Collaboration. A.Dubey, Z. Fraenkel, A. Kozlov, M. Naglis, I. Ravinovich, D.Sharma, I.Tserruya Weizmann Institute of Science B.Azmoun, D.Lynch, R.Pisani, C.Woody

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A Hadron Blind Detector for the PHENIX Experiment at RHIC

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  1. A Hadron Blind Detector for the PHENIX Experiment at RHIC Craig Woody RHIC II Workshop April 30, 2005

  2. The PHENIX HBD Collaboration A.Dubey, Z. Fraenkel, A. Kozlov, M. Naglis, I. Ravinovich, D.Sharma, I.Tserruya Weizmann Institute of Science B.Azmoun, D.Lynch, R.Pisani, C.Woody Physics Dept., Brookhaven National Lab J.Harder, P.O’Connor, V.Radeka, B.Yu Instrumentation Division, Brookhaven National Lab A. Drees, J. Franz,T. Hemmick, R. Hutter, B. Jacak, M.McCumber A. Milov, A. Sickles, A.Tois Stony Brook University C.-Y. Chi Nevis Labs, Columbia University H. Hamagaki, S. Oda, K. Ozawa University of Tokyo L.Baksay, M.Hohlmann, S.Rembeczki Florida Institute of Technology D. Kawall Riken M. Grosse-Purdekamp University of Ilinois

  3. Motivation • Low mass e+e- pairs provide a sensitive probe for studying Chiral Symmetry Restoration (CSR). • Can be observed through in-medium effects of low mass vector mesons (in particular, the r, which has ct = 1.3 fm/c) • Low mass pairs are also a sensitive probe of thermal radiation qqbar  *  e+e- (QGP) +-   *  e+e- (HG) • Effects of CSR may have been seen in CERN SPS results • The same effects are predicted to occur at RHIC, but will be difficult to detect • PHENIX is the only experiment at RHIC that could perform this measurement C.Woody, RHIC II Workshop, 4/30/05

  4. Low Mass Electron Pairs at the SPS Strong enhancement of low-mass e+e- pairs in A-A collisions (wrt to expected yield from known sources) No enhancement in pp and pA collisions Enhancement factor (.25 <m<.7GeV/c2) : 2.6 ± 0.5 (stat) ± 0.6 (syst) C.Woody, RHIC II Workshop, 4/30/05

  5. Low Mass Electron Pairs at RHIC • Strong enhancement of low-mass pairs persists at RHIC • Contribution from open charm becomes significant R. Rapp nucl-th/0204003 • Possibility to observe in-medium modification of the intermediate vector mesons (r,f,w): • Dropping of r invariant mass (Rapp & Wambach) • Broadening of vector meson (r, w, f) invariant masses (Brown et.al) • Thermal radiation from hadron gas pp rg*  e+e- C.Woody, RHIC II Workshop, 4/30/05

  6.  e+ e - po   e+ e- “combinatorial pairs” total background S/B ~ 1/500 Irreducible charm background all signal charm signal Experimental Challenges at RHIC • Both members of the electron pair are needed to reconstruct the Dalitz pair or conversion. • Single electron pair members contribute to background: • Limited by: • Low pT acceptance of outer PHENIX detector: • ( pT > 200MeV) • Limited geometrical acceptanceof present PHENIX • configuration Large combinatorial pair background due to copiously produced photon conversions and Dalitz decays : Need rejection factor > 90% of  e+ e - andp0   e+ e - C.Woody, RHIC II Workshop, 4/30/05

  7. RealandMixede+e- Distribution Real-Mixede+e- Distribution e+e- from light hadron decays net e+e- e+e- pairs (real) e+e- from charm (PYTHIA) e+e- pairs (mixed) PHENIX Run 2 Results S/B ~ 1/100  ~ 1/500 depending on mass and pT cut Must improve rejection of Dalitz pairs and conversions by ~100-200 C.Woody, RHIC II Workshop, 4/30/05

  8. Measuring Low Mass Electron Pairs in PHENIX • Hardware • Compensate magnetic field with an inner coil to • preserve e+e- pair opening angle (foreseen in • original design  B0 for r  50-60cm) • Compact HBDin inner region (possibly to be • complemented by a TPC or other tracking detector • in the future). • Strategy • Identify signal electrons with p > 200 MeV/c from • vector mesons in the outer PHENIX detectors • Identify low momentum electrons with p < 200 MeV/c • (mainly from Dalitz pairs and conversions) in the HBD • Reject pair if opening angle < 200 mrad • (for ~ 90% rejection). Requirements * Electron efficiency  90% * Double hit recognition  90% * Modest  rejection ~ 200 C.Woody, RHIC II Workshop, 4/30/05

  9. e+ e- q Pair Opening Angle The HBD Detector Electron pairs produce Cherenkov light, but hadrons with P < 4 GeV/c do not HBD Gas Volume: Filled with CF4 Radiator (nCF4=1.000620, LRADIATOR = 50 cm) Proximity focused Windowless Cherenkov Detector Radiator gas = Working Gas Cherenkov forms “blobs” on an image plane (Qmax = cos-1(1/n)~36 mradrBLOB~3.6cm) 55 cm 5 cm Coarse granularity readout (~ 2x2 cm2) Triple GEM detectors (8-12 panels per side) Space allocated for services Dilepton pair Beam Pipe C.Woody, RHIC II Workshop, 4/30/05

  10. Principle of the Hadron Blind Detector • Gain ~ 104 to detect few (~ 5-10) • photoelectons (multistage GEM • minimizes photon feedback and ion • backflow) • Most of the ionization in the collection • region is drifted away from the GEM • stack and is collected by the mesh • Some ionization (from a region • ~ 100 mm thickness) is collected by • the GEM stack • Additional ionization is produced in • the lower transfer regions, but receives • less gain ( ~ 10) •  not totally hadron blind, but • very highly suppressed Multistage GEM detector with CsI photocathode deposited on outer GEM foil detects Cherenkov light from electrons C.Woody, RHIC II Workshop, 4/30/05

  11. GEANT hits Reconstructed e’s Monte Carlo Simulation of the HBD Central HIJING event (2%), dNch/dy = 940 - 400 charged particles traverse the HBD - 19 reconstructed electrons: 5.7 from vertex, 13.5 not from vertex • Remove 1 pad clusters • Npe percluster > 20 C.Woody, RHIC II Workshop, 4/30/05

  12. 2 1 2 1 3 4 3 4 Improvement in Background Rejection Combinatorial background Embedded fe+e- Improved S/B Ratio 73K Central HIJING events Initial Central Arm spectrum Central Arm electron tracks matched to HBD with 3 p-dependent cuts. Reject “conversions” tracks with amplitude cut (>60 e) Reject Dalitzes with close hit cut (< 200 mrad) C.Woody, RHIC II Workshop, 4/30/05

  13. Resulting Low Mass Pair Spectrum with the HBD • Combinatorial background is • reduced by more than two • orders of magnitude • Measurement of the low • mass pair region is then • limited by combinatorial • background from open charm • A precision measurement of • charm will be carried out in • PHENIX using the Silicon • Vertex Tracking Detector. C.Woody, RHIC II Workshop, 4/30/05

  14. Rates for Vector Meson Production • Consider Run 8 (200 GeV Au x Au, 4x Design Luminosity) : • Lpeak = 30 x 1026 cm-2 s-1 • L ave store= 8 x 1026 cm-2 s-1 • 20 KHz peak min. bias rate • 5.4 KHz avg min. bias rate • 10 week dedicated HBD run (central field in  configuration) • eRHIC x ePHENIX = 0.5 x 0.5 = 0.25 • f’s produced in |h| < 0.5 • e+,e- into PHENIX central • arm acceptance • pT,e > 200 MeV/c 8.2 x 109 min. bias events produced N fe+e-= 1.5 x 10-5 / min.bias event f:w:r (e+e-PHENIX) = 1 : 0.9 : 0.7 N fe+e-= 1.2 x 105 produced in PHENIX acceptance C.Woody, RHIC II Workshop, 4/30/05

  15. Events Recorded • PHENIXarchive rate ~ 600 MB/s (possibly  ~1200 MB/s) • Event size (Au x Au ) : ~ 200 kB ( ~ 120 kB w/compression) •  5.0 KHz recording rate for Au x Au (already achieved for pp) • ~ Keeps up with average min. bias rate • Estimate ~ 70% efficiency due to peak luminosity •  8.4 x 104f’s recorded from min bias in a 10 week run • At RHIC II, Lave store 70 x 1026 cm-2 s-1 • 47 KHz avg min bias rate • Further gains in low mass pair/vector meson yields with • increased luminosity require a low mass dilepton trigger C.Woody, RHIC II Workshop, 4/30/05

  16. Use of HBD at Higher Luminosities • The HBD Front End electronics is being designed to provide a Level 1 Trigger • There are plans to develop algorithms for a low mass pair/ vector meson trigger • - supplements the current RICH/EMCAL trigger • - can provide additional rejection power ~ 4-6 in pp (reference) running • The HBD can also provide a trigger • for high pT charged hadrons in pp • The HBD will provide electron id • outside the present PHENIX • acceptance which could increase • sensitivity to J/Y, DY, U’s etc when • used along with the VTX Silicon Tracker • After the initial measurements of low • mass pairs in sNN = 200 GeV/c2 Au x Au collisions, one would hope to carry out a systematic study of the energy and species dependence of the any effect observed Low pT electrons High pT hadrons Look for tracks with small curvature using the HBD, RICH and PC3 C.Woody, RHIC II Workshop, 4/30/05

  17. PHENIX Inner RegionHBD Retracted Position C.Woody, RHIC II Workshop, 4/30/05

  18. Tests with a Prototype HBD • Triple GEM detector • CsI photocathode deposited on • top surface of uppermost GEM • foil • Operate in pure CF4 • Gain < 104 • Hg lamp to study photocathode • 55Fe source to monitor gas gain Prototype HBD detector at the WIS (similar prototype at BNL) C.Woody, RHIC II Workshop, 4/30/05

  19. Hadron Blindness: UV photons vs Charged particles At slightly negative Ed, photoelectron detection efficiency is preserved whereas charge collection is largely suppressed. C.Woody, RHIC II Workshop, 4/30/05

  20. Landau fit Hadron Rejection KEK Beam Test Simulated e and p signals Hadron rejection vs charge threshold C.Woody, RHIC II Workshop, 4/30/05

  21. Test of a Triple GEM Detector in PHENIX • Triple GEM detector performed smoothly within the PHENIX IR using both Ar/CO2 (70/30) and CF4 - exhibited no sparking or excessive gain instabilities. • In close proximity to the beam pipe (50cm), the detector was sensitive to some soft beam related background - low signal (< 50 e’s) - depended strongly on beam conditions. - mostly out of time with beam-beam collisions Conclusion: • There appears to be no fundamental problem with operating a GEM detector close to the beam pipe at RHIC 55Fe spectrum with Ar/CO2 in Lab Additional background 55Fe spectrum with full luminosity Au-Au collisions at RHIC C.Woody, RHIC II Workshop, 4/30/05

  22. Full Scale Prototype Presently under construction at the Weizmann Institute C.Woody, RHIC II Workshop, 4/30/05

  23. Final HBD Design • Same design as full-scale • prototype but: • larger acceptance • || ≤0.36 || ≤0.45 • =110o=135o • smaller pad size • a =16.7  15.6 mm • Number of channels • 1368  2304 • Number of detector modules • 16  24 • GEM size • 26 x 24  23 x 27 cm2 C.Woody, RHIC II Workshop, 4/30/05

  24. Schedule • Full Scale prototype under construction at WIS • Full detector will be constructed by end of 2005 • Engineering/physics run during Run 6 PHENIX Beam Use Proposal C.Woody, RHIC II Workshop, 4/30/05

  25. The PHENIX HBD will provide a unique opportunity for measuring low mass electrons pairs at RHIC, and will provide an important tool for the study of Chiral Symmetry Restoration in relativistic heavy ion collisions. • This will require a high statistics measurement of electron pairs in the the mass region from 0.2 – 1.0 GeV/c2, including the low mass vector mesons and their Dalitz decays, as well as a high precision measurement of the open charm pair contribution in this same mass region. • The HBD would be used to study low mass pairs in not only central Au x Au collisions at the highest energies, but could also be used to study the energy and species dependence of any effects which are observed. Such measurements, along with the implementation of a Level-1 low mass pair trigger, would benefit significantly from higher luminosity. • The HBD can also provide a high pT hadron trigger and increased hadron rejection in high luminosity pp running. • When used in conjunction with the VTX, the HBD could provide additional coverage for measuring high pT electrons, which would increase the sensitivity for measuring quarkonia and Drell-Yan in heavy ion collisions at high luminosity Conclusions C.Woody, RHIC II Workshop, 4/30/05

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