Triple GEM Beam Test within PHENIX DC Upgrades Meeting 4/14/04 B. Azmoun PHENIX Brookhaven National Lab

4/14/04B. Azmoun2 Outline Basic format of presentation: Timeline of tests performed with triple GEM detector in and out of close proximity to A-A beam in PHENIX. –Simple Survival test ( trips, sparks ) –Performance Evaluation ( Gain, Stability, Response to beam-beam collisions ) Data acquired with GEM detector mounted in various orientations within central region of PHENIX. –Self Triggered Fe-55 Spectra –Beam-Beam Triggered Data ( Correlation between Beam collisions and GEM hits ) Comparison of: Fe-55 Peak Position, abs. Signal Gain, %Res.( FWHM ), and Background: –Lab Vs. PHENIX Data –Beam ON Vs. Beam OFF Data –Magnet (Inner/Cent.) ON Vs. Magnet OFF Data Objective: Objective: To monitor the behavior of a triple GEM detector within the PHENIX interaction region, and to compare these results with in-lab tests.

4/14/04B. Azmoun3 Layout of Triple GEM Detector Gases Used Ar/CO 2 (70/30) > Volt Configuration: DG: 0.5kV/cm TG1:2.5kV/cm TG2: 3.0kV/cm IG: 3.5kV/cm > Nominal Operating Gain:~6.5x10 Foil Pot. = 360V CF 4 > Volt. Configuration: DG: 0.5kV/cm TG1:2.5kV/cm TG2: 3.5kV/cm IG: 5.0kV/cm > Nominal Operating Gain:~3.2x10 Foil Pot. = 495V Std. Conical, Segmented CERN Foils Active area of pads ~1.0x1.5cm

Photos of detector in place within PHENIX Det. Mounted near N. Cent. Mag. Det. on MVD lifting table, Mylar window Facing Upright

4/14/04B. Azmoun5 Lab Test Data Data taken in the lab provides a baseline measurement. Timeline Start: Gas: Ar/CO 2 (70/30) HV: ON Data Run Parameters Fe-55 Spectrum

4/14/04B. Azmoun6 GEM Det. Mounted in inner central region of PHENIX Orientation #1: Gas: Ar/CO 2 (70/30) Beam: OFF, Mags: OFF HV: ON Isolation Trans. Mounted onto Det. Spect. ~ identical to lab data, but inc. peak width Pedestal Calib. Pulse

4/14/04B. Azmoun7 Variation in position of main peak is within normal limits (<+/-10%) Beam Dumped Beam: ON, Mags: ON ~ Consistent Response 13 days later HV: ON Beam: OFF, Mags: OFF END of Fill #1 320 V (This was the only spectrum measured during fill #1, before the beam dump.) Survival Test: Passed (GEM exhibits normal behavior near beam)

4/14/04B. Azmoun8 Orientation #2: Gas: Ar/CO 2 (70/30) HV: ON Beam: OFF, Mags: OFF Isolation Transformer moved outside of PHENIX field boundaries, to DAQ in PHENIX rack room for orient. 2, 3, and 4. Similar Spect. Compared to Orient. #1

4/14/04B. Azmoun9 Variation in position of main peak is within normal limits (<+/-10%) Magnets ON do not affect data ! Mags: ON Inc. in backgnd. Beam: ON, Mags: OFF>>ON HV OFF>>ON Fill #2 END of Fill #2 Fract. of events above ped. (~ch.70) = 4.4% Beam-Beam Triggered Data Ped.

4/14/04B. Azmoun10 Gas: Ar/CO 2 (70/30), CF 4 Orientation #3: Large Inc. in background (as well as Dec. Gain) 4.6% Fill #3 Ar/CO 2 (70/30) Beam: ON, Mags: ON

4/14/04B. Azmoun11 Switch to CF 4 HV OFF>>ON Bkgnd. Persists during CF4 Runs, but is relatively smaller Smaller Number of Counts compared with Ar/CO2 Dec. in Bckgnd. Beam: OFF, Mags: ON (HV Remains ON) 2.7% Mags /HV Trip END of Fill #3

4/14/04B. Azmoun12 (Overflow count rate inc.) Large Inc. in Backgnd. HV: OFF>>ON Mags. OFF>>ON (Beam Remains OFF) Inc. in number of counts above ped. Beam ON Peak lost in Backgnd... Beam related ?? 5.1% Fill #4

4/14/04B. Azmoun13 Other than some anomalies (e.g. run 16), possibly related to inc.’d background, the variation in the position of the main peak is within normal limits (< +/-10%). Peak Recovered after HV OFF/ON, (Mag OFF, Beam still ON) HV: OFF>>ON Mags: OFF Dec in Backgnd. Beam Dumped END of Fill #4

4/14/04B. Azmoun14 Gas: CF 4 Orientation #4: Similar to Orient. 3, with beam OFF, Mags ON Beam: OFF, Mags: ON

4/14/04B. Azmoun15 Variation in the position of the main peak is within normal limits (< +/-10%). Lower backgrnd. Compared to Orient. #3 Beam: ON Dec. in number of counts above ped. 0.22% Fill #5 END of Fill #5

4/14/04B. Azmoun16 Gain Stability The following plot depicts the variation in gain at a constant field potential within Ar/CO 2 and CF 4 during the series of measurements presented in the previous slides. Gain variations are mainly due to two factors: 1. Fluctuations in physical parameters like temperature, pressure, etc. 2. Before arriving at a steady state value, the gain initially continues to grow due to a charging effect within the Kapton foil, after the HV is applied (see the example to the right).

4/14/04B. Azmoun17 % Res. Vs. Data Run

4/14/04B. Azmoun18 Scaler Rates near PHENIX: 3/19/04 Anomalous Behavior of Det. (Run )

4/14/04B. Azmoun19 Summary The GEM detector performed smoothly within the central region of PHENIX using both Ar/CO 2 (70/30) and CF 4 –trouble free operation at reasonable gains in both gases –no sparking or excessive gain instabilities with beam ON, or during a beam dump No observed effect in detector operation due to magnetic field Detector sees low energy, beam related background when positioned close to the beam (primary signal < 100 e’s) –possibly less sensitive with CF 4 The detector appeared to be sensitive to beam conditions –large increase in low energy background seen during one fill with CF 4, but decreased dramatically at other times (so far cannot correlate this with scalers of background counters--see slide #18)