Study of GEM-like detectors with resistive electrodes for RICH applications A.G. Agocs 1, A. Di Mauro 2, A. Ben David 3, B. Clark 4, P. Martinengo 2, E. Nappi 2,5, V. Peskov 2,6, 1 Eötvös University, Budapest, Hungary 2 CERN, Switzerland 3 Tel Aviv University, Israel 4 North Carolina State University, USA 5 Bari University 6 Ecole Superior des Mines, St Etienne, France 1

Recent results from RHIC as well as numerous theoretical predictions indicate that a very high momentum particle identification (VHMPID) may be needed in the future ALICE experiments. In connection to this the ALICE-HMPID collaboration is studying the possibility to make a new detector to identify charged particles with momentum p > 5÷10 GeV/c  VHMPID (Very High Momentum Particle Identification Detector). Several Cherenkov detector designs were preliminary considered and simulated by the ALICE VHMPID collaboration : a threshold type as well as a RICH type (see G. Volpe talk at this Conference). 2

One of the complication- there is a very limited space available for VHMPID So only compact and simple VHMPID designs can be considered 3

Focusing setup The focusing properties of a spherical mirror of radius R = 240 cm, are exploited. The photons emitted in the radiator are focused in a plane that is located at R/2 from the mirror center, where the photon detector is placed. (from G. Volpe talk at this Conference). 4

One of the promising photodetector element in this RICH design could be GEM-like detectors combined with CsI photocathodes Advantages : ● They are compact ● Can operate at higher gains and in badly quenched gases including inflammable gases ● Can be used in the same gas as a radiator ● Have high QE ● Have potential for higher special resolution 5

For the last several years we were focused on developing more robust GEM-like detectors for RICH application 6

First attempt-”Optimized”/Thick GEM Further development of this detector was performed by Breskin group- see R. Chechik presentation 7

Photo of one of the “ optimized ” or “ thick GEM ” developed by us earlier L. Periale et al., NIM A478,2002,377 J. Ostling et al., IEEE Nucl. Sci 50,2003,809 precisedrilling Cu etching TGEM is manufactured by standard PCB techniques of precise drilling in G-10 (+ other materials) and Cu etching. 8

We would like present today a new promising direction- resistive electrodes TGEMs 9

The main advantage of these detectors is that they are fully spark-protected 10

Thick GEM with resistive electrodes (RETGEM)- a fully spark protected detector A. Di Mauro et al, Presented at the Vienna Conf. on Instrum; to be published in NIM Geometrical and electrical characteristics: Holes diameter mm, pitch mm, thickness mm. Resitivity: kΩ/□ Kapton type: 100XC10E 30mm or 70mm Principle of operation 11

Filled symbols-single RETGEM, open symbols –double RETGEMs Stars-gain measurements with double RETGEM coated with CsI layer. 15 min continues discharge harm ether the detector or the electronics QE~30% at λ=120nm Energy resolution ~30%FWHM for 6 keV With increase of the rate the amplitude drop, but now discharges Summary of the main preliminary results obtained with kapton RETGEMs 1 mm thick Fully spark -protectedFully spark -protected Discovery: kapton can be coated with CsI and have after high QE 12

Confirmation of high QE (QE measurements at 185 nm) 13

QE calibration TMAE filled single-wire gas counter Double-step RETGEMS with CsI photocathode Monochromator Lens Hg lamp CsI Windows Q CsI =Q TMAE N CsI /N TMAE 14

Hg lamp Lens Monochromator Gas chamber with RETGEM coated with CsI Photo of the experimental set up 15

Charge sensitive or current amplifier -V dr Top RETGEM Bottom RETGEM V 1 top V 2 top Gas in Gas out HV feedthrough Drift mesh Window CsI (0.35μm) Experimental set up for studies RETGEM with CsI photocathodes UV light 16

Counting plateau TMAE detector Double RETGEM 17

Q CsI =33%N CsI /N TMAE ~ 14.5% Hg lamp spectra, measured with TMAE (a) detector and RETGEM (b) a) b) TMAE QE vs. wavelength (c) c) (assuming that TMAE is clean enough) 18

Measurements of the stability of the RETGEM, using Hg as a source, at 185nm. The light is concentrated on a small slit. About 30min without light have passed between each run. 19

Stability measurements of photosensitive RETGEM 20

Very low single photoelectron counting rate Gas gain~

Single –electron (CsI pc) counting rate at a constant threshold Gas gain~ 10 6 This behavior is similar to RPC 22

“Long –term” stability of CsI pc s measures at low counting rate 23

Unexpected problem-very difficult to get the resistive kapton from the US Dear Mr. Peshkov, I'm in charge of sales and marketing of Kapton® polyimide film in Europe. As explained in attached notes Kapton® 100XC10E5 is subject to an ITAR license to be exported from the US and this is indeed quite a complex procedure to go through. Suggest you call me at in order to discuss how we can proceed. My best regards, Giulio Cecchetelli High Performance Films DuPont de Nemours (Luxembourg) S.à r.l. Société à responsabilité limitée au capital de Euro Rue Général Patton L-2984 Luxembourg R.C.S. Luxembourg B

Very new (preliminary) results: RETGEMs manufactured by screen printing technology For more details see: B. Clark et al., Preprint/Physics/ , Aug

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Screen printing is widely used in microelectronics to produce patterns of different shape and resistivity. Therefore, RETGEM technology produced with screen printing techniques offers a convenient and widely available alternative to RETGEMs made of Kapton. Offers cost-effectiveness, convenience, and easy optimization RETGEMs resistivity and geometry. It is also important to mention that large -area RETGEMs can be produced by this technology. Advantages of the screen printing technology: 27

Consequent steps in RETGEM manufacturing in by screen printing technique (Oliveira Workshop): a) b) c) DE-156, an Isola product, is used as the base material. Excess copper is removed from the top and bottom, thereby creating a copper border. A resistive paste ( Encre MINICO ) is applied to the top and bottom surfaces using screen printing techniques and technology. The paste is cured in air at 200 C for one hour. After the curing process is complete, the resistive layer is 15μm thick. d) Drill consistently sized holes at even intervals in the region enclosed by the copper border. 28

RETGEM type- 1 Geometrical and Resistive Characteristics Thickness = 1mm Hole Diameter = 0.5mm Pitch = 0.8mm Active Area = 30mm x 30mm Resistive Layer Thickness = 15μm Resistivity = 1 MΩ/□ or 0.5 MΩ/□ RETGEM type -2 Geometrical and Resistive Characteristics Thickness = 0.5mm Hole Diameter = 0.3mm Pitch = 0.7mm Active Area = 30mm x 30mm Resistive Layer Thickness = 15μm Resistivity = 0.5 MΩ/□ Two types of RETGEM were manufactured by screen printing technology and tested 29

a) medium magnification Photo of holes at various magnifications: b) higher magnification 30

Charge sensitive amplifier -V dr RETGEM Gas in Gas out HV feedthrough Drift mesh Radioactive sourceWindow Experimental set up for studies RETGEM manufactured by screen printing technology 31

Charge sensitive amplifier -V dr Top RETGEM Bottom RETGEM V 1 top V 2 top Gas in Gas out HV feedthrough Drift mesh Radioactive sourceWindow Experimental set up for studies RETGEM manufactured by screen printing technology 32

Results of measurements in Ne (SP-RETGEM type 1) Gain curve measured with double SP-RETGEM operating in Ne ( 55 Fe). Gain curve measured with single SP-RETGEM ( 55 Fe). Alpha particles 33

Results obtained in Ar (SP-RETGEM type1) Single step SP-RETGEM Double SP-RETGEM 34

Results obtained in Ar+CO 2 (type1) Single step Double SP-RETGEM 35

“Low resistivity”(0.5MΩ/□) 1mm thick double step in Ne (preliminary!) 36

The maximum achievable gain with a 0.5 mm thick SP- RETGEM was the same as in the case of the 1 mm thick, however there voltages were considerably smaller Some samples had excess of high amplitude spurious pulses 37

Preliminary tests of photosensitive RETGEM manufactured by a screen printing technology 38

Charge sensitive amplifier -V dr Top RETGEM Bottom RETGEM V 1 top V 2 top Gas in Gas out HV feedthrough Drift mesh Window CsI Experimental set up for studies RETGEM with CsI photocathodes manufactured by screen printing technology Hg lamp Filter Monochromator 39

Q CsI =33%N CsI /N TMAE ~ 12.2% - for SP-RETGEM Hg lamp spectra, measured with TMAE (a) detector and RETGEM (b) a) b) TMAE QE vs. wavelength (c) c) Gas gain 3x

“Long-term” stability 41

Can ~12-14% QE be sufficient for VHMPID? Volpe talk at this Conference 185 nm 12% Yes, it looks O’K (40%-are holes) 42

Preliminary comparison of K- RETGEMs with SP-RETGEMs ▪ In all gases tested K-RETGEMs allow to achieve at least 10 times higher gains than SP-RETGEMs ▪ Some samples of SP-RETGEM exhibit high amplitude spurious pulses (it is not the case for K-TGEMs!) ▪ Both detectors are spark-protected, however after 10 min of continuous glow discharge a low resistivity SP-RETGEM can be damage (it is not the case of K-RETGEM!)-the counting rate of spurious pulses increased ▪ Energy resolution in the case of SP-TGEM was worse ▪ Photosensitive K-RETGEMS and SP RETGEMS have almost the same QE at 185 nm: % at 185 nm -and these values remained stable at least in a month scale 43

Conclusions: ●RETGEM detectors are fully spark protected (the energy released in sparks is at least 100 times less than in the case of metallic TGEMs) ● At low rate they behave like GEM ( and the gas gain is stable with time) and at high rates and high gains RETGEMs are more resembling RPCs ( gain reduces with rate) ● Being coated by a CsI layer RETGEMs operate stable at high gains and low rates and their QE is % at 185nm ●“Long term “ (few months) stability of RETGEMs with CsI pc was demonstrated ● We believe that RETGEMs can be good candidates for the VHPMID and some other RICH detectors 44

Future tasks: In contrast to K-TGEMs, the SP-RETGEMs require more tuning up: ●optimization its resistivity and geometry, ● understanding some detail in operation, ● tests in C 5 H 12 gas Final evaluation and conclusions can be drowned only after a beam test 45

Pad plain RETGEMs CsI Drift mesh Should be manufactured New, exists Old, exist Should be modified 40 mm Old, exist Proto-4 Plans for future beam test Liquid radiator 46

The photodetectors to be tested : GEM TGEM RETGEM The beam test will allow to select the best one 47

Spairs

Wire chamber with CaF 2 window approach is not excluded yet!

Optimization of the RPC electrodes resistivity for high rate applications P. Fonte et al., NIM A413,1999,154

TMAE detector cross checks

Counting rate measurements from TMAE detector as function of radius

Ionization chamber check (with a 185 nm filter)

Charge sensitive amplifier -V RETGEM Gas in Gas out HV feedthrough Drift mesh Window Current measurements: CsI Hg lamp Filter A

Ionization chamber check (with a 185 nm filter)

Backdiffusion

Active area r R Π(1+3)r 2 /πR 2 = =0.25/0.64=40%

Giacomo related slides

Gas Cherenkov detectors for high momentum charged particle identification in the ALICE experiment at LHC G. Volpe, D. Di Bari, E. Garcia, A. Di Mauro, E. Nappi, P. Martinengo, V. Peskov, G. Paic, K. A. Shileev, N. Smirnov 6th International Workshop on Ring Imaging Cherenkov Counters October, Trieste A talk presented by G. Volpe yesterday

pioni HMPID RICH, high p T HMPID RICH, high p T ITS Vertexing, low p t tracking and PID with dE/dx ITS Vertexing, low p t tracking and PID with dE/dx TPC Main Tracking, PID with dE/dx TPC Main Tracking, PID with dE/dx TRD Electron ID, Tracking TRD Electron ID, Tracking TOF intermediate p T TOF intermediate p T PHOS ,  0 - ID PHOS ,  0 - ID MUON  -ID MUON  -ID + T0,V0, PMD,FMD and ZDC Forward rapidity region + T0,V0, PMD,FMD and ZDC Forward rapidity region L3 Magnet B= T L3 Magnet B= T ALICE experiment EMCal ALICE is designed to study the physics of strongly interacting matter and the quark- gluon plasma (QGP) in nucleus-nucleus collisions at the LHC. The p-p physics will be study as well as reference data for the nucleus-nucleus analysis. High energy 

How it was designedHow it is looked just before the installation ALICE RICH is installed inside the magnet and is in a commissioning phase now. We are looking forward for the first physics results! ALICE RICH

~ 2m ALICE Club - May 2, 2005 Paolo Martinengo

Example of a single radiator threshold imaging Cherenkov A. Braem, C.W. Fabjan et al., NIM A409, 1998, 426

Nikolai Smirnov, Yale University Y Z X 50 cm AeroGel, 10cm UV Mirror, spherical shape in ZY Double sided read-out plane: planar detectors with CsI CaF 2 Window C 4 F 10 gas CF 4 gas Particle track & UV photons R position: 500 cm. Bz: 0.5 T Another idea…

Blob diameter for C 4 F 10, pad size = 0.8x0.8 cm 2

VHMPID volumes

VHMPID Radiator gas options: CF 4 ( n ≈ ,  th ≈ 31.6) has the drawback to produce scintillation photons (N ph ≈ 1200/MeV), that increase the background. C 4 F 10 (n ≈ ,  th ≈ 18.9) is no more commercially available. C 5 F 12 (n ≈ 1.002,  th ≈ 15.84) has been chosen. Photon detector options: Pad-segmented CsI photocathode is combined with a MWPC with the same structure and characteristic of that used in the HMPID detector. The gas used is CH 4, the pads size is 0.8×0.84 cm 2 (wire pitch 4.2 mm), and the single electron pulse height is of 34 ADC channels. The chamber is separated from the radiator by a CaF 2 window (4 mm of thickness). The other option for the photon detector could be a GEM-like detector combined with a CsI photocathode (higher gain, photons feedback suppression). (see G. Volpe talk at this Conference)

Photodetector Charged particle Mirror 120 cm Radiator vessel In the case of focusing setup the determination of emission Cherenkov angle is possible. Pattern recognition algorithm is needed to retrieve the emission angle. A back-tracing algorithm has been implemented to retrieve the Cherenkov emission angle. It calculates the angle starting from the photon hit point coordinates, on the photon detector. Study of the detector response for the focusing setup (from G. Volpe talk at this Conference).

K  p  K p p115 < p < 30 GeV/c p0  K 1 K, p0  12.5< p < 8 GeV/c ?0< 2.5 GeV/c Particle Id.C 5 F 12 8 < p < 15 GeV/c 2.5 < p < 8 GeV/c 8 < p < 15 GeV/c Momentum Simulation results: Cherenkov angle from G. Volpe talk at this Conference The points and the bars in the plot correspond to mean and RMS of a sample of 100 events, respectively