1. 1 Alexander Milov Goldhaber Mini-Symposium Jan 26, 2006 Hadron Blind Detector for PHENIX experiment at RHIC Alexander M. Milov Jan 26, 2006

2. 2 Alexander Milov Goldhaber Mini-Symposium Jan 26, 2006  Physics: What are the signals we are look at? Where the background comes from? How to deal with it?  HBD principles of operation: Original ideas Their implementation Detector concept  HBD in construction Some more technical details What the HBD looks like What the event looks like  SummaryOutline

3. 3 Alexander Milov Goldhaber Mini-Symposium Jan 26, 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!

4. 4 Alexander Milov Goldhaber Mini-Symposium Jan 26, 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

5. 5 Alexander Milov Goldhaber Mini-Symposium Jan 26, 2006 What are we looking at?  Now we know what we want: We need a short-living particle (life-time about a time of sQGP) Which decays into electrons and positrons because they do not interact with quarks and gluons as strong as other hadrons do.  Here are example of particle 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!  But here is a problem too: The background is HUGE! Main source of it is from π 0 : π 0  γe + e - π 0  γγ  γe + e -

6. 6 Alexander Milov Goldhaber Mini-Symposium Jan 26, 2006 What are we looking at?  Now we know what we want: We need a short-living particle (life-time about a time of sQGP) Which decays into electrons and positrons because they do not interact with quarks and gluons as strong as other hadrons do.  Here are example of particle 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!  But here is a problem too: The background is HUGE! Main source of it is from π 0 : π 0  γe + e - π 0  γγ  γe + e - NA60 (CERN) Lower energy

7. 7 Alexander Milov Goldhaber Mini-Symposium Jan 26, 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:

8. 8 Alexander Milov Goldhaber Mini-Symposium Jan 26, 2006 What to do with background? ~12 m  But life is not that easy, many particles are lost… some of them miss the detector sensitive area. Some of them curl up in the magnetic field and never come out.  To cut the background we need a new detector such that: It sees only electrons It sits at the origin It does not make its own background (is thin) …

9. 9 Alexander Milov Goldhaber Mini-Symposium Jan 26, 2006 “Classic” Cherenkov Detector  Classic RICH (Ring Imaging Cherenkov Counter) has following parts gaseous radiator (n ~ 1.0004 – 1.0006) VUV mirror window CaF 2 (cheaper) LiF (better) photo-detector (gaseous or PMT) gas with n~1.0006 mirror primary particle Cherenkov light ring detector unit window HADES @ GSI 1m+

10. 10 Alexander Milov Goldhaber Mini-Symposium Jan 26, 2006 Let’s put it in 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!!!

11. 11 Alexander Milov Goldhaber Mini-Symposium Jan 26, 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).

12. 12 Alexander Milov Goldhaber Mini-Symposium Jan 26, 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!

13. 13 Alexander Milov Goldhaber Mini-Symposium Jan 26, 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

14. 14 Alexander Milov Goldhaber Mini-Symposium Jan 26, 2006 Gas Electron Multiplier (GEM)  The original idea by F.Sauli (mid 90s) US Patent 6,011,265  Two copper layers separated by insulating film with regular pitch of holes  Just add the photocathode  HV creates very strong field such that the avalanche develops inside the holes  By the way: no shine back onto photocathode 150μ

15. 15 Alexander Milov Goldhaber Mini-Symposium Jan 26, 2006 The concept.  Get 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?  We need a mesh with a reverse voltage on it to blow electrons away!!! HV  We have a detector sensitive to UV and blind to ionizing particles!

16. 16 Alexander Milov Goldhaber Mini-Symposium Jan 26, 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 2 0 + 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

17. 17 Alexander Milov Goldhaber Mini-Symposium Jan 26, 2006 HBD design. 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 36 72

18. 18 Alexander Milov Goldhaber Mini-Symposium Jan 26, 2006 Event display (simulation)

19. 19 Alexander Milov Goldhaber Mini-Symposium Jan 26, 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 detector is now in construction. The prototype of the detector is at BNL and will be installed in PHENIX during this upcoming run.  New physics results may become available during this year.Summary:

20. 20 Alexander Milov Goldhaber Mini-Symposium Jan 26, 2006 BACKUPS

21. 21 Alexander Milov Goldhaber Mini-Symposium Jan 26, 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 2006. What does it look like

22. 22 Alexander Milov Goldhaber Mini-Symposium Jan 26, 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

23. 23 Alexander Milov Goldhaber Mini-Symposium Jan 26, 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

24. 24 Alexander Milov Goldhaber Mini-Symposium Jan 26, 2006 Back to prototype?  With “unexpected” return of Run6 we need to make sure the full scale prototype can go in and work to have something better. 1R, Bertan (4100V), I~330  A1R, LeCroy (2400V), I~194  A 2R, Bertan (4100V), I~165  A2R, LeCroy (4100V), I~165  A Bob checked that the LeCroy power supply can be used. It requires divider resistance to be doubled. No extra noise detected.