Student Perspectives

In their own words, here are the accomplishments of a few BU/CERN/UniGe students:

Adding new functionality to the High Level Trigger for CMS – Elim Cheung

“My project involved modifying the macro that is used for the High Level Trigger (HLT) timing for CMS.  While selecting interesting data for the physics, a trigger system needs to be quick and efficient. Therefore, to monitor the time spent by the trigger, my version of the HLT Timing Summary macro is the main tool that provides plots and summaries.  The outputs from the original timing macro did not show straight-forwardly the important information the researchers needed. So, my job was to become familiar with the macro and add new functions to it.  During the semester, I successfully added 8 new functions to the macro, two of which greatly speed up the timing studies. Moreover, I developed a twiki page which explains how one uses the new functions and in what situations the functions are important.  The modified macro has since been added to a new software release and is now used by researchers.”

Assessing the power of a possible detector for T2K in Korea- Chelsea Bartram

“Neutrinos are electrically neutral elementary particles which, traveling near the speed of light, are able to pass through materials unimpeded.  Until recently, they were thought to be massless, an assumption which was included in the Standard Model.  With the advent of the large Super-K detector, in Japan, BU researchers helped confirm that the neutrino possesses mass.  Neutrinos can be described in two ways, akin to describing a vector with two different coordinate systems.  These are the mass eigenstates and flavor eigenstates.

The flavor of a neutrino is a property defined by its interactions with other particles. As a result of its mass eigenstates, a neutrino changes flavor or oscillates as it propagates through space. This enabled physicists to assert that it is a massive particle. We describe the transformation of the mass eigenstates into the flavor eigenstates using the PMNS matrix.  Not all the elements in the PMNS matrix are known.  If certain parameters are zero, it becomes impossible to know if CP symmetry is preserved. C or charge conjugation is an operator which demands that particles and antiparticles are described by the same laws of physics. The P or parity operator requires that the physics stays the same under spatial inversion. Information on CP symmetry is crucial to formulating an extension to the Standard Model.

“I created contour plots which showed the sensitivity of our detector to various values of the parameters contained in the PMNS matrix. By investigating different experimental configurations, I could optimize the sensitivity to CP violation. I verified past evaluations of a proposed experiment, T2KK, involving another detector in Korea in conjunction with Super-K.  I became familiar with the powerful software package GLoBES.  Upon returning to the States, I am demonstrating the capabilities of GLoBES to the research group at BU using the tools I acquired from working at CERN and UniGE.”

Evaluating the Level 1 trigger of CMS- Ashley Rubinstein

“Every 25 nanoseconds an average of 17 events will soon occur in the CMS detector. This is an input rate of 109 Hz.  The goal of CMS Level 1 (L1) triggering system is to throw away all the data that doesn’t contain useful physics.  There is a lot of useless data and the L1 triggering system reduces the input rate to 100 kHz, so the input rate is reduced by a factor of 105.  The L1 triggering system is based on custom electronics that I helped to test for CERN.  The High Level Trigger then uses computer processors to reduce the input rate to 100 Hz.  The L1 trigger identifies muons, electrons, photons, jets, and missing transverse energy to throw away events that aren’t useful.  During the spring semester I calculated the efficiencies of different triggers.  By the end of the semester, I was able to compare the different efficiencies for different runs taken at the LHC, a facility now used by almost all those analyzing the CMS data.”

Finding bad wires in the drift tube muon detectors of ATLAS – Andrea Welsh

“One of my main tasks was calibration of the monitored drift tube (MDT) chambers for ATLAS.  I worked on analyzing both collision and cosmic ray muons that passed through the MDT chambers, looking for inconsistencies in the analog to digital converter (ADC) count.  While the histograms of the ADC data in the chambers should have looked like Gaussians, a few showed very noisy chambers.  Because of this, my research group found the fault with one of the chambers, and went down 100m underground to fix a cable which was not connected correctly.  This could have caused a major problem, such as a fire.  I also worked on aligning the MDT chambers.  I searched for various bugs which were unable to be seen the way the code was currently written.  I found and fixed parts of the code that were causing the unforeseen problems so that ATLAS could now use the alignment code more broadly than they could use it before.”

Developing the novel silicon photomultipliers for a CMS upgrade-Mike Lloyd

“During my semester at CERN I worked on computer simulations with Dr. Iouri Musienko, of ITEP, Moscow.  I focused on Silicon Photo Multipliers (SiPM’s), destined to be the upgrade of the CMS detector elements that are not functioning properly now.  These small devices detect light from particles created in a collision at the LHC.  I wrote a program using statistical methods to recreate event signals with a controlled input.  With the data I took from the devices, I reconstructed the events that caused the light signals.  In the real experiment, this is very important because the initial input is unknown; the simulation supplies an accurate model of what to expect for a large range of possible events.”

Aligning the wires in the ATLAS muon chambers- Max Yellen

“My project focused on ADC monitoring of the MDT chamber of ATLAS.  I wrote a ROOT macro that analyzed and graphed data for different runs.  It helped to identify chambers with faulty wiring that were repaired while I was in Switzerland.  At the end of the internship, I also started working on muon alignment.  I wrote code to streamline the process of reconstruction, creating the muon tracks, and alignment, comparing the tracks to the positions of the raw data and adjusting the calibration constants to improve accuracy using centralized ATLAS software.”


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