Test of the GEM Front Tracker for the SBS Spectrometer at Jefferson Lab F. Mammoliti, V. Bellini, M. Capogni, E. Cisbani, E. Jensen, P. Musico, F. Noto, G. Ruscica, M.C. Sutera, B. Wojtsekhowski

OUTLINE -JLab facility -Super BigBite Spectrometer -GEM Tracker -Mainz Test Beam Facility -Experimental Data

The Continuous Electron Beam Accelerator Facility The high resolution and high luminosity (polarized) CEBAF electron beam: -Current: up to 200 µA -Energy: up to 6 GeV -Energy resolution : 2.5* Duty factor: 100% (continuous beam) -3 Experimental halls: A, B and C JLab, Newport News (VA)

CEBAF UPGRADE Two superconducting linear accelerators (LINACs) Arches with Magnets that form a circuit of 1.4 Km Electrons Energy of 10.9 GeV for Hall A, B, C and 12 GeV for new Hall D Currents Sum: 5 μA for Hall D and 85 μA for the others Searching for exotic Mesons Proton and Neutron structure Nucleus Structure Parity Violation Research fields

SUPER BIGBITE SPECTROMETER 1/3 -High Luminosity: 8 x cm -2 s -1 -Forward angle (down to 6°) -Large Momentum Range (2-10 GeV/c) -Moderate angular acceptance (64 mrad) -High rate capability (1 MHz/cm 2 ) Flexibility: use the same detectors in different experimental setup

SUPER BIGBITE SPECTROMETER 2/3 1st tracker2nd tracker 3rd tracker Tracking Detector Configuration HCAL (X,Y) x2 (U,V) x2 Number of LayersArea (cm 2 ) First Tracker640*150 Second Tracker450*200 Third Tracker450*200 HCAL280*300

Silicon tracker 10 x 20 cm 2 Dipole Two GEM planes 40 x 150 cm 2 CH 4 polarimeter Second GEM tracker Second CH 4 polarimeter Third GEM tracker Calorimeter Resistant to shock Rate > 5 ∙10 5 Hz/mm 2 Nominal spatial resolution of 60 μm Readout flexibility Low Cost Why GEM detector? SUPER BIGBITE SPECTROMETER 3/3

GEM FOIL Gas Electron Multiplier GEM foil: 50 μm Kapton + few μm copper on both sides with 70 μm holes, 140 μm pitch Strong electrostatic field in the GEM holes V GEM = 500 V → E ≈ 100 kV/cm P = 140 μm D = 70 μm d = 50 μm

Multi-GEM Detectors Cathode Drift Region (3 mm) GEM Foil Induction Region (1 mm) Anode (readout plane) Maximum Gain 10 3 Cathode Drift Region (3 mm) GEM Foil Transfer Region (2 mm) Induction Region (1 mm) Anode (readout plane) Maximum Gain 10 6 Single-GEM Triple-GEM

GEM Prototype GEM Prototype (10x10 cm 2 ) built and tested at I.S.S. Roma Assembling the GEM chambers parts requires a careful quality control at several check points and specific tools for gluing, heating, testing, cleaning

Assembling the first 40x50 cm2 module 11 Stretching Gluing the next frame with spacers Tendigem made in Catania

12 FULLY equipped GEM module 18 front-end cards 2304 channels (front end cards on the othe side) 7 independente HV levels

-Three GEM Chambers: 10x10 cm 2 -Electron Beam energy 400 – 800 MeV -Strip distance 0.4 mm -Chamber distance 50 cm -Carbon Target -Lead glass and Plastic Scintillators Beam MAINZ 1/2 Electron beam produced at MAMI (MAinz MIkrotron) at the Nuclear Physics Institute of Mainz MAMI is a continuous wave accelerator

Beam MAINZ 2/2 By using APV 25 chips, it is possible to register different parts of the signal (every 25 ns), event by event. -Different run performed: with beam without beam (pedestal) -Different angles between the electron beam and the plane of the GEM chambers -Different HV settings -Different Chamber positions

DATA ANALYSIS -More than 50 beam run analyzed -Study of the Pedestal -Study of the Signal -Study of the Clusters -Beam Profile reconsctruction -Tracking and Efficiency evaluation

SIGNAL OBTAINED BY USING A 90 Sr SOURCE ID RUNHVID CHAMBER V0 (FRONT) V1 (MIDDLE) V2 (BACK) FRONT CHAMBER MIDDLE CHAMBER

PEDESTAL RUN STUDY ADC mean value obtained each 100 events in a single pedestal run: values change in different samples! IDEA: we decide to create a pedestal for each beam run by using the adc mean values of 200 events for all samples (1200 values).

signal New pedestal Beam run before the pedestal suppression Beam run after pedestal suppression SIGNAL signal ADC(A.U.) Strips 1 strip = 0,4 mm

SIGNAL IN DIFFERENT SAMPLES SAMPLE 1 SAMPLE 2SAMPLE 3 SAMPLE 4 SAMPLE 5SAMPLE 6

SIGNAL SHAPE Signal shape: - τ 1 and τ 2 are the slope and falling time of the signal, respectively; - t 0 is the stop time; - A is the Amplitude ; Signal Amplitude for different strips. Peak around strip # 200 (ok!) and more or less 0 in all the others.

STUDY OF THE CLUSTERS 1/2 A tree is filled, event by event, with different informations for each beam run: -Number of clusters; -Number of strips for each cluster; -Index of the first strip of each cluster; -ADC sum of each cluster; -Centroid of each cluster; CLUSTERS NUMBERSTRIPS NUMBER OF EACH CLUSTER RUN #446 – 300 EVENTS – SAMPLE 2: from 0.25 to 0.50 ns

Centroids plot Adc sums of single cluster vs strip VERY LOW PILE-UP! STUDY OF THE CLUSTERS 2/2

Examples of CENTROID EVALUATION for 2 RUN with different Energy ABOUT 4-6 mm400 MeV800 MeV Beam Profile

TRACKING AND EFFICIENCY1/2 Z X -POSSIBLE EVENT IF THERE IS A CLUSTER IN ALL CHAMBERS -HIT POSITION WITH σ FOR EACH CHAMBER -WE CONSIDER X = a*Z + b with a and b obtained by linear fit -BY USING P 0 (x 0, y 0 ) and P 1 (x 1,y 1 ) WE OBTAIN a AND b -WE CONSIDER P 3 (x 3,y 3 ) and if lx 3 -az 3 –bl<σ 3 THAN THE SIGNAL OF THE 3 CHAMBERS BELONGS TO THE SAME PARTICLE OTHERWISE IT IS REJECTED

TRACKING AND EFFICIENCY 2/2 EFFICIENCY= NUMBER OF EVENTS IN TRAJECTORY NUMBER OF EVENTS (TRIGGER) RESULTS FOR A RUN WITH HV = 3950 V ID CHAMBERPOSITIONEFFICIENCY 0Z=095% 1Z=50 CM85% 2Z=100 CM85%

CONCLUSIONS: -GEM Tracker operated stably during the test at Mainz -Study of pedestal and signal -Study of clusters -Beam Profile was reconsctructed -Preliminary Efficiency was evaluated -GEM Tracker is a complex detector and improvement is still in progress

THANKS FOR YOUR ATTENTION