The Gas Electron Multiplier (GEM), a type of position-sensitive gaseous ionization detector, is a powerful innovation in experimental Particle Physics used to track scattered particle position and beam trajectories with precision of 50-60 microns. GEM detectors used at the European Organization for Nuclear Research (CERN), the Italian National Institute of Nuclear Physics (INFN), and Thomas Jefferson National Accelerator Facility require further development and analysis for future applications in Particle Physics experiments. This study presents the results of a systematic investigation of GEM detector data collected at CERN in December 2012. The analysis consists of the determination of electron/pion particle beam trajectory and position using 2-dimensional histograms generated in the object-oriented data analysis program, ROOT. Results from our software development and analysis will be used to examine detector efficiency and will enable high precision measurement of the contributions of elementary particles such as the strange quark to the proton.

Claire N. Saunders, Andrew J. Witchger Supervisor: Fatiha Benmokhtar

Duquesne University, Jefferson Lab

The detectors consists of insulating capton foil with a copper layer on both sides. The foil is perforated with holes, etched in a photolithic-graphic process. The diameter of each hole is 70 µm. A low-pressure gas mixture comprised of 70 % argon and 30 % carbon dioxide flows through the chamber.

A high potential is applied across the copper (~400 V), forming an electric field inside the holes. Electrons entering the holes are accelerated by the electric field. The high electric field in the holes excites these charged particles causing a Coulomb interaction with the gas, which results in the formation or an electron-ion pair.

The primary electrons further ionize the gas creating secondary electrons. This causes an avalanche effect resulting in an exponential increase in the number of electrons. The x and y coordinates are recorded using a grid of tightly packed wires that are sensitive to the electric field of the group of electrons. Data from these wires is analyzed using ROOT.

Experimental Hall B- CEBAF Large Acceptance Spectrometer (CLAS)

Experimental Hall C- Detector Setup

Event with discernible peaks are fit with a Gaussian function.

The pedestal was identified and fit with a Gaussian function so that it could be subtracted from the run data.

Events without discernible peaks are not fit.

Proton

Neutron The proton

consists of three quarks: 2 up, 1 down

The analyzer uses a peak search algorithm based on the TSpectrum root class. Identified peaks are fit with a Gaussian to obtain a better estimation of the position.

•  The pedestal run is a data collection taken while using a false trigger, which means that no charged particles are being sent through the GEMs.

•  This establishes that the noise in the data is in a reasonable range.

•  The pedestal run is used as a baseline that is subtracted from the data runs.

References •  Mirazita, Marco. “GEM tracking and

data quality.” •  https://www.jlab.org