Rutgers University Department of Physics and Astronomy

2006-07 Handbook for Physics and Astronomy Graduate Students

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Research Programs

Experimental Elementary Particle Physics

A lively area of experimental work in the department is High Energy Physics. This area includes both experiments studying particle physics at accelerators and experiments studying the new area of astroparticle physics. Eight faculty members supervise efforts involving roughly forty people (physicists, technical and clerical staff, graduate and undergraduate students) in a wide spectrum of elementary particle investigations. These efforts are well supported by the National Science Foundation, the Department of Energy and the University, and they have had considerable success in obtaining precious beam time at large accelerator facilities. At Rutgers, there are extensive resources for the construction and testing of detectors and electronics used in experiments, and dedicated computers for the analysis of the resulting data. Grants in this area provide financial support for advanced graduate students to spend full time on research, and they do not have to teach to earn an income.

Professors Eva Halkiadakis, Amit Lath, Steve Schnetzer and Sunil Somalwar

We are members of the Compact Muon Solenoid (CMS) Experiment, one of two large detector facilities being built for the Large Hadron Collider (LHC) under construction at the CERN laboratory near Geneva, Switzerland. When the LHC is completed in 2008, it will be the world's highest energy accelerator, colliding protons on protons at a center-of-mass energy of 14 TeV, seven times greater than that currently available. The LHC is a guaranteed discovery machine. Either the elusive Higgs boson particle will be discovered or, if not, other unexpected "new physics" must necessarily be found. The Higgs particle is a remnant of the Higgs Mechanism, the process that is believed to be the source of all mass. Its discovery would be a major breakthrough in our understanding of one of the fundamental properties of nature. Supersymmetry, the ultimate symmetry that relates fermions and bosons, is also likely to be found at the LHC. Supersymmetry is an elegant theory that is favored by many theorists and that may point the way toward a quantum theory of gravity. It is also a necessary ingredient of all string theories. More speculatively, evidence for large extra dimensions and for strong gravity manifested by a prolific production of mini black holes might also be seen. Clearly, the LHC will usher in an exciting new era in fundamental particle physics research.

Our group at Rutgers is well positioned to be active and leading participants in this forefront physics program. We plan to build on the expertise that we have gained in our work on the CDF detector at Fermilab to play a leading role in most if not all of the prominent physics studies mentioned above. In particular, we plan, initially, to concentrate on a search for the Higgs particle via its decay to a pair of tau leptons, the most sensitive decay mode in many supersymmetric Higgs scenarios. The ability to identify tau leptons will also be important in many supersymmetric particle searches and measurements providing a wealth of thesis opportunities. Identification of tau leptons in the large background of QCD jets at the LHC will be challenging. The expertise that our group has gained in developing these techniques in the "real world" environment of the CDF detector at the Fermilab Collider should prove invaluable.

In the area of detector hardware and construction, our group has played a leading role in designing custom, radiation-hard, deep sub micron electronics for the readout of the CMS pixel detector. We are currently working on an exciting new proposal that we recently made for building a luminosity monitor for CMS based on diamond pixel telescopes. This device will measure the bunch-by-bunch luminosity, intensity of the collisions, to a precision of about 1% while also monitoring the location of the collision point. Both of these are important inputs needed for many of the physics measurements. The luminosity monitor utilizes two advanced detector developments that our group has extensive expertise in, pixels and radiation-hard diamond sensors. We plan to construct the luminosity monitor at Rutgers during 2006 and 2007 and deliver the device to CERN for installation at CMS in time for the first physics running in 2008. This would be an excellent project for a graduate student to work on. It is a small scale device that a student could really "get their hands on" while, at the same time, learning state-of-the-art detector technology and electronics and participating in the large CMS Collaboration.

Professors Douglas Bergman and Gordon Thomson

We are working on the High Resolution Fly's Eye Experiment (HiRes), which has the aim of studying the highest energy cosmic rays. In the energy range of our experiment there are several important physics and astrophysics topics to study.

The transition between cosmic rays of galactic origin to extragalactic occurs here. We observe this transition through composition change: the highest energy galactic cosmic rays should be heavy nuclei (e.g., iron) and extragalactic cosmic rays should be almost all protons.

Interactions between cosmic ray particles and photons of the cosmic microwave background radiation form two energy-loss mechanisms for cosmic rays. Pion production limits protons which have traveled more than 50 Megaparsecs across intergalactic space to an energy lower than about 6*10**19 electron Volts. This produces the so-called GZK cutoff above this energy. Electron-positron pair production is a somewhat weaker energy loss mechanism. It nevertheless produces a dip in the cosmic ray spectrum. Our experiment sees both of these features.

But important questions remain. The origin of the highest energy cosmic rays is a mystery. Known sources should produce cosmic rays no higher in energy than about 10**19 eV, whereas events over 10**20 eV have been seen.

The nature of the sources is not known. Active galactic nuclei, quasistellar objects, and gamma ray bursts are possibilities, and much work is being done searching for anisotropy (both point sources and extended sources) in the cosmic rays.

The HiRes experiment is located atop two desert mountains in west central Utah and consists of large mirrors which collect fluorescence light from cosmic ray showers and focus it onto an array of photomultiplier tubes. As the shower propagates down through the atmosphere its image moves across the photomultiplier tubes and by recording the time the tubes fire and their pulse heights we can completely reconstruct the characteristics of the cosmic ray that initiated the shower.

Our group consists of two faculty, three postdoctoral research fellows, three graduate students and several undergraduates, and we are collaborating with several other universities in the U.S. and Australia. We travel to Utah to work on the experiment and collect data, then analyze it using the excellent computer system we have here at Rutgers. We think of our experiment as one where high energy physics techniques are being employed to solve problems in astrophysics.

We are planning a future experiment that will have much greater capabilities than HiRes. This is called the Telescope Array Experiment (TA). It will also be located in Utah, and have five fluorescence detectors that watch cosmic ray showers propagate through the atmosphere, and two arrays of scintillation counters deployed to measure the particles that hit the ground.

Professors Thomas Devlin, Eva Halkiadakis, Amit Lath, Sunil Somalwar, and Terence Watts

Rutgers is a collaborator in the construction and operation of CDF (Collider Detector at Fermilab), a $100-million-plus facility which detects the particles resulting from 2-TeV proton-antiproton collisions produced by the Tevatron collider. The Tevatron is, and will remain until 2009, the premier facility on the planet for studying fundamental interactions at highest possible energy. High energy interactions are the key to exploring the smallest units of matter and exploring phenomena that dominated the evolution of the early universe.

The Tevatron is poised to collect enough data to either find the mechanism that breaks electroweak symmetry -- which makes the W and Z bosons heavy while leaving the photon massless -- or severely constrain most models of this phenomenon. Most such models invoke one or more "Higgs bosons" as well as supersymmetric (SUSY) particles that are heavier partners of known quarks, leptons and bosons. These phenomena have yet to be verified by experiment.

The Rutgers CDF group is deeply involved in searches for such new phenomena, including those for SUSY particles and Higgs bosons. Our group has implemented or improved analysis techniques for many of these searches. Members of our group have worked on identification of tau leptons and b-quark decays for Higgs searches. We have studied low energy electrons and muons that can arise from decays of possible supersymmetric particles. We work closely with theorists to refine our searches and create new analyses as understanding of models of new physics grows.

The CDF experiment offers many other fascinating research topics. Although the top quark has been discovered, its properties (such as mass and couplings to other particles) remain poorly understood. CDF will collect thousands of top quarks and detailed study may well find this heaviest of Standard Model particles is affected by new physics. CDF is also poised to collect a large sample of particles containing b-quarks. In addition to searches for new phenomena, these particles can be used to study b-quark couplings, which may reveal new physics. Several other topics, such as precision measurements of W and Z boson masses and asymmetries, searches for quark substructure in jet events, and many others are available to students willing to work with the CDF Rutgers group.

Students, both undergraduate and graduate, have always been a key part of the high energy physics effort at Rutgers. The data coming from the CDF experiment offer an extraordinarily wide range of choices for learning experimental and analytical techniques and for thesis topics at the frontier of physics.

Prof. Devlin is analyzing data from CDF to understand the mechanism responsible for polarization of Lambda hyperons. When this is complete, his research efforts will be devoted to astrophysics.

Professors Mohan Kalelkar and Richard Plano

We are nearly finished with the analysis of data from an experiment called SLD at the Stanford Linear Collider, studying electron-positron interactions at 91 GeV, the mass of the neutral weak boson Z. A unique feature of our experiment is longitudinal polarization of the electron beam. We have published the world's best measurement of the weak mixing angle, a crucial parameter of the Standard Model, as well as the world's best measurement of the parity-violating coupling of the Z to the s-quark. Our graduate students have written PhD theses on hadron production in Z decays into quarks of different flavors, observing large flavor dependencies that permitted sensitive tests of QCD fragmentation models.

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Revised September, 2006