Performance Studies of Serial and Parallel Gas Distribution Systems in Monitored Drift Tube Chambers for the ATLAS detector at LHC, CERN

Click here for a .pdf copy of the actual paper

My Division II gave me a well-rounded education in both physics and astronomy.  To close out the Division II, I participated in an REU (Research Experience for Undergraduates) program at the State University of New York at Stony Brook funded by the NSF.  After having spent the summer working at Stony Brook and nearby Brookhaven National Laboratory, I have found that I am very interested in high-energy particle physics.  Within this REU program I got to work closely with scientists collaborating on experiments involving the PHENIX (Pioneering High Energy Nuclear Interaction eXperiment) detector at RHIC (Relativistic Heavy-Ion Collider). 

Since this work was primarily theoretical, getting involved in some experimental research became an important goal for me.  Therefore, for my Division III, I would like to participate with the ATLAS-Frascati group at Laboratori Nazionali di Frascati (LNF).  I will spend 10 weeks with the group in Frascati from late August through early November, 2003.  This group is helping to build the ATLAS (A Toriodal LHC ApparatuS) detector, which will be operating at the Large Hadron Collider (LHC) at the CERN Laboratory in Switzerland.  The experiments involving the LHC make up the largest collaborative effort ever attempted in the physical sciences, involving 2000 physicists from more than 150 universities from over 30 countries.  The Frascati group has the responsibility of building Monitored Drift Tube (MDT) chambers which will be mounted in the Barrell Middle Large (BML) stations of the ATLAS muon spectrometer. 

In the 2003 test beam setup, the BML station is split into two sections (BML1 & BML2) and each section is split into two multi-layers, resulting in four distinct multi-layers.  Each multi-layer is made of three rows of 56 drift tubes filled with gas.  When a muon passes through a drift tube it ionizes the molecules in the gas and leaves a trail of electrons.  The electrons then drift onto a wire that runs through the middle of the tube and produces a measurable current.  It is possible to reconstruct the path of the muon by tracking which tubes produce a signal and when they produce a signal.  Therefore, an important quantity to understand is the drift time, defined as the time that it takes an electron to drift to the wire, because it tells us the position of a muon track with respect to a given wire. 

One of the goals of this recent test beam is to examine the difference between a parallel gas distribution system and a serial gas distribution system and what effect each has on the drift time.  A parallel gas system is one in which every tube has its own fresh input of gas.  Conversely, the serial system (designed at LNF), pumps the gas through three tubes in series before flushing and refreshing the gas.  The MDT’s of multi-layer 2 in the BML1 station use a parallel system while the remaining three multi-layers of BML1 use a serial distribution system. 

Previous results from serial systems suggested that the drift time of the MDTs varied depending on whether the tube was a gas input tube, a middle tube, or a gas output tube.  This analysis was initiated in order to discover whether there is a dependence and, if a dependence exists, to understand the cause.  It has been hypothesized that water could be leaking into the system through the hoses that connect the input, middle, and output tubes. 

My involvement with the group will begin with analyzing data taken from the 2003 test beam.  I will work to create a series of macros in ROOT, an object oriented data analysis framework developed at CERN, that will analyze the test beam data.  Once we are sure that we are observing this tube dependant effect of the drift time, we can begin to explore the hypothesis.  This will involve running simulations with GARFIELD, a program designed for drift chamber simulations.  Through these simulations, we will investigate what effect humidity levels could have on the drift times.  In addition, we will try to develop a humidity correction factor from the simulated data.  Applying this correction to the test beam data, we will try to determine whether this humidity correction can account for the difference in drift times. 

The ATLAS-Frascati group has given me an account that grants access to the vast array of computers available at LNF.  This is the main tool that I will need complete my project.  With this account, I can pipe into the LNF computers from anywhere in the world that has internet access.  In addition, members of the ATLAS-Frascati group have committed to helping me through this task.  In particular, I will be working closely with Maura Barone, Mario Antonelli, and Bellisario Esposito.  Piotr Decowski of Smith College, who also works for SLAC at Stanford doing high-energy particle physics (and is familiar with ROOT), is another resource for me throughout this project. 

This is a great opportunity for me to have a complete project that has a definitive beginning and ending.  It also differs from my previous experience in that it is very experimental.  I will have the opportunity to work directly with raw 2003 test beam data and be able to build a framework through ROOT that organizes, cuts, analyzes, tests, and even evaluates real scientific data. 

This project should result in an analysis note.  In addition to the note, I plan to write a paper outlining what modern particle physics is and how it is carried out.  Assuming a knowledge of basic introductory college physics, the paper will give general explanations of things such as calorimeters, colliders, bremsstrahlung, cherenkov radiation, and particle cross-sections.  Additional processes and physics, including the specifics of what is involved in my project, will be described as well. 

My first Advanced Educational Activity will be an upper-level course during the Spring 2004 semester at Mt. Holyoke College, Analytical Mechanics – Physics 315.  My second Advanced Educational Activity will be a teaching assistant position with Fred Wirth, NS102 – Musical Acoustics. 


J. Kamin