REU Physics 2003 Abstracts

Sevan Aydin James Conlon · Emily ConoverTom CummingsJason KaminDustin Kavich • Eric Lessac-Chenan • James NapolitanoAndrew NenckaChieu Nguyen Jason Pawlowski · Samantha RobertsAllison Schmitz James ScholtzKathryn Tschann-Grim

Sevan Aydin Physical Acceptability of Exact Solutions to Einstein's Equations
Sevan Aydin and James Lattimer, Department of Physics & Astronomy, Stony Brook University

The structures of neutron and quark matter stars are of current interest because new X-ray and optical observations of compact stars are being made. It is therefore of interest to construct analytical models for comparison. Because these stars are very compact it is necessary to use Einstein's equations of general relativity to describe them.
Due to the non-linearity of Einstein's field equations, exact solutions are difficult to come across and the few that are known are celebrated although they do not always describe the universe as we see it. In practice, one often must resort to numerical methods. Of the few previously known exact solutions, even fewer are suitable for describing neutron or quark matter stars. The metric of space-time is assumed to be spherically symmetric and the energy-momentum tensor to be that of an ideal perfect fluid. In this case Einstein's equations reduce to the Tolman-Oppenheimer-Volkoff (TOV) relations, which determine the mass function, pressure, and energy density given a metric.
Recently, K. Lake (gr-qc/0209104) has developed a source function that yields infinitely many exactly solvable metrics depending upon one parameter, an integer N. For the first time we derive details of these metrics to find solutions that could be used to describe a neutron star or strange quark star. The resulting pressure and energy density define the equation of state and speed of sound. Constraints are placed on the mass function, pressure, energy density, and speed of sound to obtain ranges of compactness for which the metrics are physically acceptable as a function of N.

This study was made possible by NSF Grant No. Phy-0243935.

James Conlon & Kathryn Tschann-Grim Computer Simulations of Higgs Events in Preparation for ATLAS
James Conlon, Bucknell University; Kathryn Tschann-Grimm, University of California, LA; and Michael Rijssenbeek, Department of Physics & Astronomy, Stony Brook University

In order to find the mass carrier particle under the Standard Model, more energetic particle collisions are required than are currently possible. In the most promising attempt yet to prove the existence of the Higgs Boson a Proton-Proton Collider at CERN called ATLAS (A Toroidal LHC ApparatuS) is currently under construction. As in many of the detectors currently in use, ATLAS will utilize a series of calorimeters surrounding the point of collision to detect and analyze the resulting particles that will be generated. These calorimeters require a high voltage power source that is being created and tested by the Stony Brook University group.
In preparation for data received from ATLAS at CERN, proton-proton collisions are simulated and analyzed. Simulated events are generated that mimic proton-proton collisions and are controlled by the program ATHENA. PYTHIA is used to generate particles and ATLFAST creates and fills ntuples, which carry information about the energy and momentum of electrons, photons, muons, and jets resulting from collisions, and can be analyzed with the Physics Analysis Workshop (PAW). This is used to identify what decays take place during the collision and interaction with the detector.

This study was supported by the NSF Grant No. Phy-0243935.

Emily Conover

Studies of the Measurement of Reaction Plane in Relativistic Heavy Ion Collisions
Emily M Conover, Brown University; Thomas K Hemmick, Department of Physics and Astronomy, Stony Brook University

The Phenix experiment at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory is designed with the purpose of exploring collisions of heavy ions by measuring the products of such collisions. The Phenix experiment consists of various detectors that are used for this purpose. Two such detectors are the Beam-Beam Counters (BBC), which measure the location and centrality of a collision, and the Mulitplicity Vertex Detector (MVD), which measures collision location and the distribution of charged particles. These detectors can also be used to measure the plane in which a collision took place, each with varying degrees of accuracy. My task was to compare the accuracy of these two detectors in measuring reaction plane. It has been proposed that another detector be added to the Phenix experiment with the express purpose of determining reaction plane, and my task was to test other designs for possible future detectors in order to determine the optimal shape and type of detector for defining reaction plane as accurately as possible.

Simulation of reaction plane measurements requires creating a program which simulates events and outputs data that is consistent with data recorded from actual collisions. For each centrality, the degree of overlap between two colliding nuclei, I produced particles with an appropriate pseudorapidity and anisotropic azimuthal angle distribution. The second Fourier moment of the produced particles, v2, is used to determine the orientation of the reaction plane. This orientation as measured by a simulated detector is compared to the input value and thereby determines the resolution of the detector. This resolutions of the existing detectors can be compared to each other as well as to any proposed new detector. This study was supported by NSF Grant No. PHY02-43935

Tom Cummings


Jason Kamin

Investigating the Cronin Cartoon
Jason Kamin, Hampshire College; Thomas Hemmick, Department of Physics and Astronomy, Stony Brook University; Ralf Averbeck, Department of Physics and Astronomy, Stony Brook University; Axel Drees, Department of Physics and Astronomy, Stony Brook University; Eftychios (Felix) Matathias, Department of Physics and Astronomy, Stony Brook University

The Cronin Effect occurs when a deuteron collides with a large nucleus (such as Au at RHIC). The transverse momentum (PT) spectra of the particles that are produced in the most central collisions are different than the spectra produced in the most peripheral ones. There are more particles with higher PT and less at low PT. In addition, the degree to which this difference is observed seems to be correlated with the mass of the particles that are produced.
In deuteron-gold collisions, the most peripheral events (60 - 90 % centrality) are generally thought of as simple nucleon-nucleon interactions while the most central events (0 - 20 % centrality) are thought to consist of a cascade of deflecting collisions within the nucleus. A typical "cartoon" of the collision process envisions the deuteron getting knocked around many times as it bounces it's way through the nucleus, colliding at different angles with the Au nucleons along the way.
The goal of this project was to determine if this widely accepted "cartoon" explanation of the Cronin Effect is able to account for the particle species dependence of this phenomenon. We modeled the high centrality collisions identically to the peripheral ones except for one major difference: we treated the high centrality interactions as taking place at an angle rather than head-on. Applying the necessary relativistic transformations we were able to treat these as identical interactions taking place in different frames.
We found that when using identical primordial spectra for all species, our intuition is indeed confirmed; the purely naïve Cronin cartoon produces a species dependent effect similar to that found in the data. However, we additionally found that the strength of the effect is highly sensitive to the primordial spectrum. Several more realistic initial state distributions were tried, all of which exhibited reduced species dependence of the Cronin enhancement and did not adequately describe the data. We thus conclude that this "cartoon" description of the Cronin Effect is not able to solely account for the particle species dependence.

This Work was supported by a grant from the National Science Foundation (Phy - 0243935).

Dustin Kavich

Electron Spin Resonance of Anti-ferromagnetic Materials
Dustin Kavich, Lewis University; Laszlo Mihaly, Stony Brook University

The intent of the author is to combine the fundamental theory of electron spin resonance with experience in the proceeding research being conducted at Brookhaven National Laboratory. This research requires access to the National Synchrotron Light Source, which provides a means for observing electron spin transitions in the visible and ultraviolet region of the electromagnetic spectrum. Technical aspects of the experimentation involve the procedures for cooling the super-conducting electromagnet in order to generate a magnetic field of a suitable intensity. With the aid of a graduate student, the author observed the absorption spectrum of an anti-ferromagnetic crystal. The main classes of magnetic materials are termed diamagnetic, paramagnetic, and ferromagnetic. Diamagnetic materials are composed of atoms with zero net spin, while paramagnetic materials are composed of atoms with a net spin. While ferromagnets contain atoms with a net spin, as in the paramagnetic case, an extra exchange force exists that locks the spins into similar directions. Regions of volume in which the spins point in the same direction are termed "magnetic domains". In the case of an anti-ferromagnetic material, a domain structure is non-existent. The atoms are arranged in a crystalline structure such that the spins alternate from "up" to "down". Once the atoms are placed in a magnetic field, the z-components of angular momentum lose their degeneracy due to the interaction of the magnetic moment with the external field. Finally, spin transitions may be observed upon application of an external radiation field in the visible and ultraviolet region. Relevant data and its conclusions are available upon presentation.

Eric Lessac-Chenan

James Napolitano

MD Simulations of MgO Nanoclusters using the Aspherical Ion Model
J. A. Napolitano, Rensselaer Polytechnic Institute; P. B. Allen and Y.-R. Chen, Department of Physics and Astronomy, Stony Brook University

Modeling physical systems on the nanoscale presents an interesting problem in contemporary physics. Systems consisting of hundreds or even thousands of atoms are beyond the reach of quantum mechanical computational methods yet are too small for statistical approaches. Shell models simplify the situation by approximating the quantum mechanical problem with a classical one. They introduce a classical potential for the energy of interaction between any two ions that is intended to mimic the important quantum mechanical effects.

A major difficulty in modeling O2- ions is that their properties depend on their environment. Prof. P. Madden of Oxford University has developed the Aspherial Ion Model (AIM), a shell model which takes into account Coulomb repulsion, induced dipole and quadrupole moments, dispersion forces, ion "breathing", repulsion due to wave function overlap, and distortion of the shape of the ion cloud. We expect that the AIM potential for O2- ions will be transferable to different environments. The test will be whether the results agree with electronic structure calculations and experiment.
This project is to code a molecular dynamical simulation of a magnesium oxide cluster using the AIM. Various cluster sizes will be simulated to analyze the effects of the cluster surface. In particular, we will compare the contributions of the surface and bulk ions to the vibrational density of states of the cluster. While much of the computer code has been completed, the simulation is not yet ready to run. This study was supported by NSF Grant No. DMR00-89492.

Andrew Nencka

Photometric Observation of KH 15D: February 3 to March 6, 2003
Andrew Nencka, Marquette University; Michal Simon and Vincent Lore,
Department of Physics & Astronomy, Stony Brook University

To continue to monitor the dynamic eclipses of the pre-main-sequence star KH 15D, we have observed its eclipse which was centered around 19 February 2003. The observations of this eclipse were made through Stony Brook University's involvement in the Small and Medium Aperture Research Telescope System (SMARTS). Observations consisted of two five second exposures in the I, V, and B bands (these filters are centered on wavelengths of 9700, 5500, and 4400 angstroms, respectively, and have widths of approximately 1000 angstroms), taken nightly near the ingress and egress of the eclipse and about every other night during the bottom of the eclipse. These observations were made through service observing from the Cerro Tololo Inter-American Observatory's 1.3 meter ex-2MASS telescope with the ANDICAM CCD camera from 3 February to 6 March 2003. We performed relative photometry with KH 15D and FMS 105, a known reference star in the field. The duration of the eclipse has increased to 21 days, and its depth has remained relatively constant at 3.2 magnitudes in the I band, 3 magnitudes in the V band, and over 0.7 magnitudes in the B band. Thus, there appears to be an evolution in the structure or orientation of the eclipsing object. Fluctuations from .3 to 3.5 magnitudes have been observed in the bottom of KH 15D's previous eclipses. Probably because of low signal to noise ratios in the observations made at the bottom of the eclipse, no fluctuations were resolved. However, fluctuations of over .4 magnitude in the V band and 2 magnitudes in the I band can be excluded. V-I colors have shown that the eclipse is wavelength independent, or gray. Therefore, the eclipses are being caused by material which is larger than typical interstellar dust. Stony Brook's participation in the SMARTS consortium is made possible with support from the offices of the Vice President for Research and the Dean of Arts and Sciences, and the Jet Propulsion Laboratory. This work was supported by a grant from the National Science Foundation (Phy--0243935).

Chieu Nguyen Energy Loss of Charged Low-Momentum Particles Produced in Relativistic Heavy Ion Collisions
Chieu Nguyen, University of North Texas; Ralf Averbeck, Thomas K. Hemmick, Department of Physics and Astronomy, State University of New York at Stony Brook

The Pioneering High Energy Nuclear Interaction eXperiment (PHENIX) at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory attempts to understand the very early stages of the universe following the Big Bang. Among the many measurements that PHENIX makes are measurements of the spectra of identified charged hadrons. The momentum as measured by the PHENIX drift chambers and the velocity as measured by the PHENIX Time-of-Flight (TOF) wall are used to calculate the mass and thereby identity of each hadron. The present momentum reconstruction algorithm ignores the energy loss of particles as they pass through material prior to reaching the drift chamber. Although this is valid for high-momentum particles, it is not valid for low-momentum particles. Thus far, PHENIX has only published the momentum spectra of high-momentum particles.

My project was to determine and correct for the energy loss of low-momentum particles in PHENIX. There are four steps in this determination: particle production, particle propagation, reconstruction, and analysis. Propagation and reconstruction are accomplished using the standard PHENIX tools and are no different in my work than in most other detailed simulation tasks. The unique aspect here is to generate particle input spectra of fixed momenta and analyze them by comparing the reconstructed momentum to the input momentum. I configured the program Exodus to produce electrons, positrons, protons, antiprotons, positive and negative kaons, and positive and negative pions having varying momenta from 0.2 to 5 GeV. Following the propagation and reconstruction steps, I analyzed the momenta of the particles as detected by the PHENIX drift chambers and compared them to input momenta to determine correction functions for each particle. These correction functions enable the PHENIX experiment to acquire valid data from low-momentum particles. This study was supported by NSF Grant No. Phy 02-43935.

Jason Pawlowski Are Progenies of Thermalized Systems Always Thermal?
Jason Pawlowski and Madappa Prakash, Department of Physics & Astronomy
, Stony Brook University

We examine the extent to which the products of in-medium reactions in a thermalized system can be regarded as either thermally or chemically equilibrated. Our results can be used to advantage at the decoupling stages of observable particles in cosmology, astrophysics, and relativistic heavy-ion collisions. The basic idea is to compare the various moments of the energy spectrum of the products to those of an ideal thermal system of the products characterized by the appropriate temperature T and chemical potential µ. Under arbitrary conditions of degeneracy and relativity, a reliable calculation of all the moments of even ideal fermions or bosons is cumbersome, unless special numerical techniques are employed. We therefore focus on the first and second moments, and take suitable ratios to characterize the degree of non-thermality. Much physical insight can be gained even at this level.. .

See attached PDF File for more information.

Sam Roberts Simulations of the . . . decay process in PHENIX.
S. P. Roberts, M. A. Nguyen, T. K. Hemmick, A. Milov, R.Averbeck; Department of Physics and Astronomy, Stony Brook University

The principal goal of heavy ion collisions at high energies is to observe the phase transition where normally bound sets of quarks become unbound. Matter in the unbound phase has been dubbed with the name 'quark-gluon plasma'. One method to observe properties of this plasma is to look at particles with known properties that have lifetimes such that they decay before the medium has time to cool. Only by decaying within the medium do these particles allow us to measure the fact that they have been altered by the medium of quark-gluon plasma. The omega has a lifetime of 20 fm/c which is on the same order of the collision zone at ~10 fm/c.

At the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratories (BNL) beam energies of 200 GeV are used in p-p, du-Au and Au-Au Collisions. We intend to measure the . . . decay channel by measuring the invariant mass of sets of three gamma from the same event. Necessarily this measurement has a large combinatorial background in addition to the signal. Though the Au-Au collisions are of the most interest because it is only these that produce the quark-gluon plasma, they also produce so many particles that the combinatorial background is very large. Consequently we begin our search for the omega in p-p collisions. The principal tool in separating signal from background is advance knowledge of the mass resolution. Towards this end, simulations are made of particle production, decay, and detection by the PHENIX electro-magnetic calorimeter. Simulated information gives accurate predictions concerning the expected signal and background yields as a function of transverse momentum and reconstructed mass within the data set.

This study was supported by NSF Grant No. Phy02-43935

Allison Schmitz See
James Scholtz See





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