Session F2: High Energy/Nuclear Accelerators and Plasma Physics

Development of Mirrors for the CLAS12 High Threshold Cerenkov Counter

The Thomas Jefferson National Accelerator Facility (JLab) has begun an ambitious program to upgrade its beam energy from 6~GeV to 12~GeV. CLAS, one of the detectors at JLab, is being upgraded (to ``CLAS12'') to accommodate the higher energy. The existing \v{C}erenkov counter in CLAS will be unable to distinguish electrons from pions at the higher beam energy, which necessitates the construction of a new, High-Threshold \v{C}erenkov Counter (HTCC). An important part of the HTCC is the light collection system, which utilizes high-quality, extremely lightweight mirrors to reflect the \v{C}erenkov light to a set of photomultiplier tubes located at the back of the detector. To ensure uniformity in performance, it is important to simplify as much as possible the construction of these mirrors. This talk will discuss the properties of CLAS12 and the HTCC, and will describe the technique to be used in the construction of the mirrors.   

LHC Status and Upgrade Challenges

The Large Hadron Collider has had a trying start-up and a challenging operational future lays ahead. Critical to the machine's performance is controlling a beam of particles whose stored energy is equivalent to 80 kg of TNT. Unavoidable beam losses result in energy deposition throughout the machine and without adequate protection this power would result in quenching of the superconducting magnets. A brief overview of the machine layout and principles of operation will be reviewed including a summary of the September 2008 accident. The current status of the LHC, startup schedule and upgrade options to achieve the target luminosity will be presented.   

Identifying non-photonic electrons in Pb+Pb collisions with ALICE at the LHC

One useful method for probing a quark-gluon plasma is through analysis of partonic energy loss, which is a direct indicator of the color charge density of the plasma medium. Electrons coming from the decays of heavy quarks, the so-called ``non- photonic'' electrons, should be sensitive to the differences in partonic energy loss for heavy and light quarks, and yet observations at RHIC suggest that they are as suppressed as light hadrons. This talk will overview the capabilities of the ALICE Experiment at CERN to detect non-photonic electrons, particularly emphasizing the performance of the Electromagnetic Calorimeter (EMCal), which will be used to investigate the flavor-dependence of partonic energy loss in Pb+Pb collisions at the LHC.   

Identification of bottom quark jets in Pb+Pb collisions in ALICE at the LHC

Partonic energy loss of high transverse momentum (pT) quarks and gluons in the Quark-Gluon Plasma has been inferred from the suppression of high pT hadrons observed in heavy ion collisions at RHIC. In order to learn more about the details of this energy loss, one would like to separately measure the effects on quarks and gluons. One way to do this is by identifying heavy quark jets through the semileptonic decay to electrons of bottom hadrons produced in the jet. This talk will show how results from the ALICE tracking system and electromagnetic calorimeter (EMCAL) can be used to identify heavy quark jets by identifying candidates containing electrons that satisfy a displaced vertex cut or those with large transverse impact parameter significance.   

Charged hadron spectra for Cu+Cu collisions at $\sqrt{S}=22.4 GeV$ with the STAR detector at RHIC

Identified charged particle spectra of $\pi\pm$, $K\pm$, $p$ and $\bar{p}$ measured using energy loss in the STAR TPC are reported for $|y|<0.1$ for Cu+Cu collisions at $\sqrt{S} = 22.4 GeV$. Total particle production, particle ratios, and average transverse momenta, are presented for different collision centralities. These results are compared with previously published results from collisions of different systems at similar collision energies.   

STAR as a fixed target experiment?

Collisions between gold or copper ions in the RHIC beam with aluminum nuclei in the beam pipe allow us to analyze fixed target interactions with the STAR detector at RHIC. These lower energy fixed target collisions may allow us to extend the low energy reach of the RHIC beam energy scan and possibly improve the chance of finding the critical point of the hadronic to quark matter phase boundary. In this talk, we will present preliminary results of spectra analysis for the fixed target collisions from various low energy test runs. Moreover, the viability of doing fixed target experiments with a collider detector will be discussed.   

Exact treatment of confinement in the semirelativistic Faddeev approach to three-quark problems

The spin=1/2 elementary particles, the baryons, are mostly described as three-quark configurations. The quarks obey relativistic quantum mechanics. Their mutual interaction is modeled by infinitely rising potentials whose short-range nature is mediated by the exchange of Goldstone bosons. We solve the relativistic three-quark problem by using the Faddeev method. In the Faddeev method we break the wave function into components, and the components satisfies somewhat better integral equations. Nevertheless, the solution was not possible without approximating and violating the asymptotically rising potential. In this work we overcome this problem. We devised an approximation method, which allows the exact calculation of the Green's operator of an asymptotically rising potential with semirelativistic kinetic energy operator by using matrix continued fractions.   

Semi-Analytical Approach to the Gravitational Wave Signal From the Electroweak Phase Transition in General Standard Model-like Effective Potentials

Upcoming gravitational wave (GW) detectors might detect a stochastic background of GWs possibly arising from bubble collisions and turbulence from a strongly first-order electroweak phase transition (EWPT). We investigate whether it is possible to connect, via a semi-analytical approximation to the tunneling rate of scalar fields with quartic potentials, the GW signal with the parameters entering the potential that drives the EWPT. We consider a finite temperature effective potential similar to the Higgs potential in the Standard Model (SM). In the context of a semi-analytic approximation to the three dimensional Euclidean action, we derive a general approximate form for the tunneling temperature and the relevant GW parameters. We explore the GW signal across the parameter space of the potential. We comment on the potential detectability of a GW signal with future experiments, and physical relevance of the associated potential parameters from extensions to the SM. In particular we consider singlet, triplet, higher dimensional operators, and top-flavor extensions to the Higgs sector of the SM. We find that the addition of a temperature independent cubic term in the potential, arising from a gauge singlet for instance, can greatly enhance the GW power. The other parameters have milder, but potentially noticeable, effects.   

CUORE: Cryogenic Maintenance

CUORE (Cryogenic Underground Observatory for Rare Events) will be the largest detector used to investigate neutrinoless double beta decay in tellurium-130 (Te-130). Neutrinoless double beta decay has never been observed in nature. If detected, it would be a major scientific discovery indicating that the neutrino is its own antiparticle; this breakthrough would signal a fundamental revision to the Standard Model of physics. Located in Assergi, Italy at the Gran Sasso National Laboratory (LNGS), CUORE will be a cryogenic bolometer composed of 988 tellurium dioxide (Te02) crystals with a total mass of 750 kg. Over the summer of 2009, we traveled to the LNGS to assist the CUORE Collaboration by performing standard shifts for the Three Towers Test, a diagnostic experiment used to determine optimal hardware cleaning methods. This involved refilling the cryogenics system with liquid helium coolant to keep the crystal bolometers at an operating temperature of approximately 10 mK, and other routine tasks. This work was supported in part by the NSF RUI grant PHY-0653284.   

New results from ADMX -- an ultra sensitive axion detection experiment

Axions are hypothetical pseudoscalar particles that exist as a consequence of the Peccei-Quinn solution to the strong-CP problem. Light axions (ueV-meV) are also a natural cold dark matter candidate. One important detection technique is via resonant conversion to microwave photons in a high-Q cavity immersed in a strong magnetic field. In this class of experiment, the signal from the cavity is amplified by an ultralow noise amplifier, and mixed down to the audio frequency range using a double-heterodyne receiver. The power spectrum results by a Fast Fourier Transform, with the putative axion appearing as a narrow line at a frequency corresponding to its rest mass. This detection strategy provides the basis for the Axion Dark Matter eXperiment (ADMX) which has been taking data at Lawrence Livermore National Laboratory (LLNL) since 1996. ADMX has established limits in two distinct data channels - a medium resolution channel configured to search for ``thermalized'' axions and a high resolution channel for detecting axions that have recently fallen into the gravitational well of our galaxy. This talk will present an overview of the newly reconfigured experiment featuring an ultralow-noise first stage cryogenic SQUID amplifiers and present latest results from the two data channels.   

Development of a Compact Neutron Generator to be Used For Associated Particle Imaging Utilizing a RF-Driven Ion Source

The development of a prototype compact neutron generator for the application of associated particle imaging (API) to be used for explosive and contraband detection will be presented. The API technique makes use of the 3.5 MeV alpha particles that are produced simultaneously with the 14 MeV neutrons in the deuterium-tritium ($^{2}$D($^{3}$T,n)$^{4}\alpha )$ fusion reaction to determine the direction of the neutrons and reduce background noise. This method determines the spatial position of each neutron interaction and requires the neutrons to be generated from a small spot in order to achieve high spatial resolution. In this work an axial type neutron generator was designed and built with a predicted neutron yield of 10$^{8}$ n/s for a 50 $\mu $A D/T ion beam current accelerated to 80 kV. It was shown that the measured yield for a D/D gas filled generator was 2x10$^{5}$n/s, which scales to 2x10$^{7}$ n/s if a D/T gas fill is used. The generator utilizes an RF planar spiral antenna at 13.56 MHz to create a highly efficient inductively coupled plasma at the ion source. Experimental results show that beams with an atomic ion fraction of $>$ 80{\%} can be obtained with only 100 watts of RF power in the ion source. A single acceleration gap with a secondary electron suppression electrode is used in the acceleration column, to suppress secondary backscattered electrons produced at the target. Initial measurements of the neutron generator performance including the beam spot size and neutron yield under sealed operation will be discussed, along with suggestions for future improvements.   

Bound-Compton profiles for inelastic x-ray scattering in warm, dense matter

Inelastic x-ray scattering has recently been developed as a powerful diagnostic method for determining the densities and temperatures of warm dense matter. Accurate measurements require determination of the spectral bound-free Compton profile. Thus, improved models of bound-free transitions are of great interest to correctly infer the inelastic scattering component from bound and free electrons, particularly in mid-Z systems. We present inelastic scattering spectra taken from un-shocked samples of Boron at the Advanced Photon Source (APS) synchrotron and laser-driven samples at LLNL's Titan laser. These spectra are compared with profiles calculated within the impulse approximation. These measured profiles provide an important tool for analyzing scattering in warm, dense systems. Additionally, they will be used as a benchmark for an improved self-consistent-field model of bound-free transitions currently in development.   

Spectrally Resolved X-ray Scattering from Implosion Targets

Spectrally resolved x-ray Thomson scattering has been applied at the Omega Laser Facility to investigate the capsule adiabat of cone-in-shell targets. The technique of scattering from implosion targets was developed and tested for use as a diagnostic at the National Ignition Facility (NIF), LLNL. Measurement of the adiabat is applied to test low-adiabat pulse shaping methods, designed for optimum compressibility and stability. Theoretical equation of state models (EOS) can also be studied for conditions encountered during implosion. In these experiments, the noncollective, or microscopic behavior of the plasma, was probed with a Zn He-alpha x-ray source at a scattering angle of 113$^{\circ}$. For these degenerate plasmas, the width of the inelastic scattering peak is proportional to the Fermi energy, and thus the electron density. The electron temperature is obtained from the measured intensities of the elastic and inelastic features. In-flight scattering measurements yielded electron densities of $\sim $ 1.2x10$^{24}$cm$^{-3}$, temperatures of $\sim $10 eV, and an ionization state of C(+4)H(+1). This work was performed under the auspices of the DOE by LLNL under Contract No. DE-AC52-07NA27344, LDRD 08-ERI-003, and the Nat. Lab. User Fac. Prog.   

Evolution of Elastic X-ray Scattering in Laser-Shocked Warm Dense Li

Li foils were heated and compressed using shock waves driven by 4 ns long laser pulses. Separate 1 ns long laser pulses were used to generate a bright source of 2.96 keV Cl Ly-$\alpha$ photons for near-elastic x-ray scattering. Comparison with radiation hydrodynamics simulations shows that the plasma is highly coupled during the first several nanoseconds, then relaxes to a moderate coupling state at later times. Our main finding is that the near-elastic scattering amplitudes are quite sensitive to the mean ionization state $\overline{Z}$, and by extension to the choice of ionization model in the radiation-hydrodynamics simulations used to predict plasma properties within the shocked Li.   

The Search for Neutron Oscillations at Super-Kamiokande

Neutron oscillations are predicted by theories that attempt to unify the fundamental forces of nature. This knowledge along with the enhanced sensitivity of the detectors used to observe neutron oscillations has increased interest in a search for this phenomenon. I, Mark Gregg, will be presenting research that is being conducted at California State University, Dominguez Hills involving the Super-Kamiokande nucleon decay detector and neutrino observatory and collaboration under the supervision of Dr. Kenneth Ganezer. This research consists of the work I have conducted along with my colleagues on the Monte Carlo program that simulates the physical events expected to be seen in the detector as a result of neutron oscillations. I will also describe the overall experiment and the latest results obtained by this experiment for lifespan and oscillation time lower limits of neutrons bound in oxygen nuclei and free neutrons, respectively.