1 Alexander Milov CIPANP06 June 02, 2006 Hadron Blind Detector for PHENIX experiment at RHIC Alexander Milov (for the PHENIX collaboration) Jun 02, 2006

2 Alexander Milov CIPANP06 June 02, 2006  Physics: Low mass pair measurements with di-electrons.  HBD principles of operation: Original ideas Their implementation Detector concept R&D  HBD progress Full scale prototype in PHENIX Detector under construction  SummaryOutline

3 Alexander Milov CIPANP06 June 02, 2006 Why low mass di-electrons?  A unique probe to investigate newly discovered matter: Particles built with light quarks should have different properties in created media than in vacuum: mass, width, branching ratios. Short living particles, decaying before freeze-out. Decay products leave media undisturbed by strong interactions.  Decays we are interested in: ρ (m = 770MeV τ ~ 1fm/c)  e + e - ω (m = 782MeV τ ~20fm/c)  e + e - φ (m =1020MeV τ ~40fm/c)  e + e -  Here is the signal!  With HUGE combinatorial background

4 Alexander Milov CIPANP06 June 02, 2006 Why low mass di-electrons? Signal quality we need  Here is the signal!  With HUGE combinatorial background NA60 (CERN) Lower energy  Decays we are interested in: ρ (m = 770MeV τ ~ 1fm/c)  e + e - ω (m = 782MeV τ ~20fm/c)  e + e - φ (m =1020MeV τ ~40fm/c)  e + e -  A unique probe to investigate newly discovered matter: Particles built with light quarks should have different properties in created media than in vacuum: mass, width, branching ratios. Short living particles, decaying before freeze-out. Decay products leave media undisturbed by strong interactions.

5 Alexander Milov CIPANP06 June 02, 2006 New RICH for PHENIX?  This volume is in the magnetic field  If we put mirrors inside, where do we send light to?  Let’s get rid of mirrors and put detector right in the beam  Possible, but… it still must be thin it has to detect a single UV photon and be blind to all ionizing particles passing through it!!!

6 Alexander Milov CIPANP06 June 02, 2006 The original idea  The original idea by Y.Giomataris and G.Charpak 1991 (NIMA 310) HV Cherenkov photon Ionizing particle Photocathode Mesh  Electrons from Cherenkov light are produced at the photocathode and amplified full way.  Electrons from primary ionization are produced at random and are amplified much less (exponential law).

7 Alexander Milov CIPANP06 June 02, 2006 Original idea modified  Problem: such setup requires a window. Radiator gas must be transparent. The avalanche in the gas contains as many photons as electrons What happens if photons shine back on photocathode? HV  We need to separate the radiator and detector volume by a window  And get even more problems… Windows are bulky Window is a perfect source of the Cherenkov photons from any particle!  Let’s get rid of the window!

8 Alexander Milov CIPANP06 June 02, 2006 Photocathode Original idea modified  Solution: Pull electron through!  Photomultipliers do exactly that. HV  But at a significant cost of efficiency Light conversion probability is the best at the upper surface Electron extraction probability is the best on the lower surface They work against each other resulting in small overall efficiency light conversion probability electron extraction probability overall: product of two  Much better way to get electron on the same side and then pull it through

9 Alexander Milov CIPANP06 June 02, 2006 Gas Electron Multiplier (GEM)  The original idea by F.Sauli (mid 90s) US Patent 6,011,265  The same field is sufficient to pull electrons from the surface into holes  HV creates very strong field such that the avalanche develops inside the holes  Photon feedback is not there: GEMs screen the photocathode 150μ

10 Alexander Milov CIPANP06 June 02, 2006 The concept.  Take a GEM  Put a photocathode on top  Electron from Cherenkov light goes into the hole and multiplies  Use more GEMs for larger signal  Pick up the signal on pads  What about ionizing particle?  Mesh with a reverse bias drifts ionization away from multiplication area HV  Sensitive to UV and blind to traversing ionizing particles

11 Alexander Milov CIPANP06 June 02, 2006 Photocathode and gas.  Photocathode: CsI is an obvious choice. We are using INFN built evaporator, currently at Stony Brook to do this project.  High area,  High vacuum,  In-situ Q.E. control,  Zero exposure to open air.  Gas CF 4 (well known): Transparent up to 11.5 eV, makes perfect match to CsI Is a good detector gas.

12 Alexander Milov CIPANP06 June 02, 2006 Photocathode and gas.  Photocathode: CsI is an obvious choice. We are using INFN built evaporator, currently at Stony Brook to do this project.  High area,  High vacuum,  In-situ Q.E. control,  Zero exposure to open air.  Gas CF 4 (was not really known): Has high electron extraction probability Has avalanche self quenching mechanism  Gas CF 4 (well known): Transparent up to 11.5 eV, makes perfect match to CsI Is a good detector gas.

13 Alexander Milov CIPANP06 June 02, 2006 Transmission for high purity Ar and CF 4 Gas purity.  Even CF 4 is transparent, oxygen and especially water can absorb UV light Water blocks the UV in the region of highest CsI efficiency. More water in presence of ionization can damage the detector physically. Oxygen is a good photo absorber too. Desired levels:  H 2 0 < 10 ppm  0 2 < 5 ppm.

14 Alexander Milov CIPANP06 June 02, 2006 Made of 2 units with R~60cm, the volume is filled with CF 4 magnetic field is turned off Electrons emit Cherenkov light Cherenkov light is registered by 12 photo-detectors in each unit Signal is read out by 94 pads in each unit, pad size ~ size of a circle Accumulating ~36 photoelectrons from each primary electron, while most other operational RICHes have ~15 or less. High statistics allows to separate 2 close electrons even if their signals overlay! Number of photoelectrons The design.

15 Alexander Milov CIPANP06 June 02, 2006 Outer (copper) side Inner side Final detector construction Detector panels glued on a jig  Final HBD under construction. Mechanical parts for the cage and GEM on frames are being produced at the Weizmann Institute in Israel. First GEMs were shipped from WIS to SUNYSB on Sunday for CsI coating. Final electronics (Nevis Columbia) is waiting test results. McPherson gas transparency monitor to arrive at BNL this month. ~1.2m

16 Alexander Milov CIPANP06 June 02, 2006 The full scale prototype.  Full scale prototype was moved into PHENIX last Wednesday. 1 instrumented GEM sector. Final electronics. Integrated into PHENIX DAQ.  We expect first results very soon.

17 Alexander Milov CIPANP06 June 02, 2006  PHENIX detector at RHIC can investigate a new class of probes to study newly invented sQGP.  It requires to built a revolutionary detector based on novel ideas and techniques. Figure of merit for such detector is 6 times more than any detector built so far.  The concept of a new detector has been developed over last several years backed up by extensive R&D and simulations.  The final detector is now in construction. The prototype installed in PHENIX right now and is taking data.  Full HBD will be installed during next physics run.Summary:

18 Alexander Milov CIPANP06 June 02, 2006  CsI quantum efficiency and CF 4 transparency make a perfect match.  Amplification field is sufficient to pull all electrons from GEM surface into holes.  GEM acts as a semitransparent photocathode providing high Q.E.  GEM geometry eliminates photon feed back from amplification region onto the photocathode.  Self quenching mechanism works for GEMs operating in pure CF 4  High electron extraction efficiency is measured into pure CF 4  Given optical purity is observed CF 4 chemical activity is not an issueHighlights:

19 Alexander Milov CIPANP06 June 02, 2006 BACKUPS

20 Alexander Milov CIPANP06 June 02, 2006 Event display (simulation).

21 Alexander Milov CIPANP06 June 02, 2006 Background sources? ~12 m  In the decays contributing to the background: π 0  e + e - γ π 0  γ γ  e + e - γ  Only one electron is detected in PHENIX and another is lost  To cut the background we need a new detector such that: It sees only electrons Located at the origin It does not produce its own background (is thin) …

22 Alexander Milov CIPANP06 June 02, 2006 “Classic” Cherenkov Detector  Classic RICH (Ring Imaging Cherenkov Counter) has following parts gaseous radiator (n ~ – ) VUV mirror window CaF 2 (cheaper) LiF (better) photo-detector (gaseous or PMT) gas with n~ mirror primary particle Cherenkov light ring detector unit window GSI 1m+

23 Alexander Milov CIPANP06 June 02, 2006 Some technical details. λ (n-1) 2 /λ 2 Number of photons  Gas: As transparent in UV as possible. As high refraction index as possible. But still usable as a detector working gas.  The best possible choice is CF 4  Photocathode choice: There are no many options for solid photocathode. CsI evaporated onto surface is pretty much the only choice  Chemists in the room should throw a flag! What if moisture gets in the detector? H CF 4 + e -  HF + X?   Physicists in the room may stay calm… Moisture in the detector kills UV transparency and CsI much before it kills the detector Monitoring gas transparency and humidity on PPM level is required

24 Alexander Milov CIPANP06 June 02, 2006 What to do with background?  Main difference between the signal and background is due to the mass of the primary particle.  Here is a solution: we need to eliminate close e + e - pairs which are due to background and use the rest for the analysis. π 0 135MeV φ 1020MeV Same Momentum  Compare these two:

25 Alexander Milov CIPANP06 June 02, 2006  We want to distinguish between two different states of matter: Normal nuclear matter where quarks are confined in triplets sQGP where quark interact “freely” with other quarks around What are we looking at?  OK, we need a probe! Probe interacts in a differently way with different media  Oops! If probe leaves the media it’s no different as if it never been there. We need another probe  Better now! But we still need to catch up what is left from the probe!

26 Alexander Milov CIPANP06 June 02, 2006 What are we looking at?  Let’s look at the probe closer. We are interested what happens to the daughter particles of our probe  Decays shall leave the media. If during their journey the interaction continues we loose the information!  So we need a probe, whose decay products go out without interacting with a media

27 Alexander Milov CIPANP06 June 02, 2006 All raw materials (FR4 sheets, honeycomb, HV resistors, HV connectors) ordered and most of them in house Detector box design fully completed Jig design underway Small parts (insert, pins, screws, HV holders..) in the shops Detector construction to start Nov. 1st PCB design almost complete Detailed construction schedule foresees shipment of boxes to SUNY in January What does it look like

28 Alexander Milov CIPANP06 June 02, 2006 Mechanical parts and PCB. PCB final design. Quick MC shows no difference with standard cells Entrance window frames are ready, the window itself to be tight between them

29 Alexander Milov CIPANP06 June 02, 2006 Gas monitoring system. Input and two outputs measured by moving mirror. More expensive but clearly better Input and two outputs measured by switching gas