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*10-5

-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 1038 cm-2s-1

-Forward angle (down to 6°)-Large Momentum Range (2-10 GeV/c)-Moderate angular acceptance (64 mrad) -High rate capability (1 MHz/cm2)

Flexibility:use the same detectors indifferent experimental setup

SUPER BIGBITE SPECTROMETER 2/3

1st tracker 2nd tracker 3rd tracker

Tracking Detector Configuration

HCAL

(X,Y) x2 (X,Y) x2

(X,Y) x2 (X,Y) x2

(U,V) x2

(U,V) x2(U,V) x2

Number of Layers

Area (cm2)

First Tracker 6 40*150

Second Tracker 4 50*200

Third Tracker 4 50*200

HCAL 2 80*300

Silicon tracker 10 x 20 cm2

Dipole

Two GEM planes 40 x 150

cm2

CH4 polarimeter

Second GEM tracker

Second CH4 polarimeter

Third GEM tracker

Calorimeter

Resistant to shock

Rate > 5 ∙105 Hz/mm2

Nominal spatial resolution of 60 μm

Readout flexibility

Low Cost

Why GEM detector?

SUPER BIGBITE SPECTROMETER 3/3

GEM FOILGas Electron Multiplier

GEM foil: 50 μm Kapton + few μm copper on both sides with70 μm holes, 140 μm pitch

Strong electrostaticfield in the GEM holes

VGEM

= 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 103

Cathode

Drift Region (3 mm)

GEM Foil

Transfer Region (2 mm)

Induction Region (1 mm)

Anode (readout plane)

Maximum Gain 106

Single-GEM Triple-GEM

GEM Prototype

GEM Prototype (10x10 cm2) 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 nextframe 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 cm2

-Electron Beam energy 400 – 800 MeV

-Strip distance 0.4 mm

-Chamber distance 50 cm

-Carbon Target

-Lead glass and Plastic Scintillators

Beam test @ MAINZ 1/2Electron beam produced at MAMI (MAinz MIkrotron) at the Nuclear Physics Institute of Mainz

MAMI is a continuous wave accelerator

Beam test @ 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 90Sr SOURCE

ID RUN HV ID CHAMBER

218 2750 V 0 (FRONT)

233 3950 V 1 (MIDDLE)

240 3950 V 2 (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 2 SAMPLE 3

SAMPLE 4 SAMPLE 5 SAMPLE 6

SIGNAL SHAPE

Signal shape:

- τ1 and τ2 are the slope and falling time of the signal, respectively;- t0 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.

2

0

1

0

1 tttt

eeA

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 NUMBER STRIPS 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 MeV 800 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 P0 (x0, y0) and P1 (x1,y1) WE OBTAIN a AND b

-WE CONSIDER P3 (x3,y3) and if lx3 -az3 –bl<σ3 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 CHAMBER POSITION EFFICIENCY

0 Z=0 95%

1 Z=50 CM 85%

2 Z=100 CM 85%

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