Session B14: SPS Undergraduate Research I

Directional Dark Matter Detector Prototype (Time Projection Chamber)

The time projection chamber is a mature technology that has emerged as a promising candidate for the directional detection of the WIMP particle. In order to utilize this technology in WIMP detection, the operational parameters must be chosen in the non-ideal regime. A prototype WIMP detector with a 10cm field cage, double GEM amplification, and ATLAS FEI3 pixel chip readout was constructed for the purpose of investigating effects of varying gas pressure in different gas mixtures. The rms radii of ionization clusters of photoelectrons caused by X-rays from a Fe-55 source were measured for several gas pressures between 760torr and 99torr in Ar(70)/ CO$_{\mathrm{2}}$(30), CF$_{\mathrm{4}}$, He(80)/Isobutane(20), and He(80)/CF$_{\mathrm{4}}$(20) mixtures. Average radii were determined from distributions of the data for each gas mixture and pressure, and revealed a negative correlation between pressure and radius in Ar(70)/CO$_{\mathrm{2}}$(30) and He(80)/Isobutane(20) mixtures. Investigation of the pressure-radius measurements are in progress using distributions of photoelectron and auger electron practical ranges (Univ. of Pisa) and diffusion, using the Garfield Monte Carlo program.   

Minimum-Bias Studies Using the Energy Scan Data from Fermilab's Tevatron Collider

We report on an analysis of the minimum-bias event data (that is, events recorded with the least selective trigger criteria) taken at the Tevatron collider at Fermilab, in particular an energy scan recording collisions at $\sqrt{s}$ = 0.3, 0.9, and 1.96 TeV. This data set represents a rare chance to analyze the energy dependence of several minimum-bias observables: the pseudorapidity ($dN/d\eta$) and transverse momentum ($dN/dP_{T}$) distributions; the distribution of charged-particle multiplicities; and the average transverse momentum vs. charged-particle multiplicity. We present the results of a comparison of these observables with the PYTHIA Monte Carlo simulation.   

Beam Test Results of the GlueX Forward Calorimeter

GlueX is an experiment to begin running in the near future at Jefferson Lab. Our research group is responsible for the forward calorimeter (FCAL) that is designed to measure the energy of photons produced from the decays of mesons. Recently, we conducted a beam test at Jefferson Lab using a prototype of the FCAL. Its goal was to experimentally verify the energy resolution of the FCAL as a function of beam energy. The prototype was tested with recoil electrons ranging in energy from 113MeV to 277MeV. We obtained the resolution by comparing the reconstructed energy to the known energy. In addition, we corrected our measured resolution for multiple scattering and energy loss based on a GEANT4 simulation of the prototype. Another important goal of the beam test was to measure the timing resolution of the channels on our flash analog to digital converters (fADCs). For GlueX, we need to require the timing resolution to be much less than the bunch spacing (2ns). The results of our studies indicate that the energy resolution of the FCAL is consistent with our predictions. We also found the timing resolution as a function of signal size and the results agreed with a similar study. For signals of about at least 75mV, the timing resolution achieved was significantly lower than 2ns.   

Development of Solid State Electronics for a Spark Chamber

Spark chambers have been used to detect charged particles in physics since the early part of the 20$^{\mathrm{th}}$ century. This very crude method can still be very useful in a classroom, museum, or outreach setting to show evidence of such particles. Older electronics such as vacuum tubes and spark gaps have been still used in recent designs, but they are resource-consuming to maintain and are becoming difficult to procure. These designs also used obsolescent electronics for the discriminators in the trigger circuit. A new design will be presented that uses a fast high voltage transistor switch along with modern comparators and programmable logic. Lower trigger latency has been achieved than in the traditional design. The muon imaging efficiency will be presented.   

Investigation of Avalanche Photodiodes and Multipixel Photon Counters as Light Detectors for Cosmic Rays

Through the Research Scholars Institute, students of Hartnell Community College experimented with the application of avalanche photodiodes (APDs) as cosmic ray detectors during the summer of 2012. An APD detector was coupled with a 10 meter long wavelength shifting fiber (WSF) wrapped around a cylindrical plastic scintillator to maximize signal detection. A photomultiplier tube (PMT) was used in conjunction to detect the same scintillation light caused by incoming cosmic rays. Two APD detectors were evaluated to confirm the viability of the setup. In addition, a similar setup was recently utilized to implement multi-pixel photon counters (MPPCs) as readout detectors. Under this configuration, a high gain preamplifier was used to amplify the signals for both the MPPC and APD detectors. We report on our results characterizing the MPPC and discuss its overall performance. Compared to the APD, our findings suggest that the MPPC detector has greater sensitivity in detecting weak light signals, and can be used in place of the PMT for certain counting applications.   

Low-temperature thermal conductivity measurements of Al$_2$O$_3$ ceramic for use in bolometric particle detector

Bolometric particle detectors for rare weak processes operate at temperatures as low as 10mK and are background-dependent, so radiopure structural materials such as alumina ceramic (Al$_2$O$_3$) are of interest, and their thermal properties in the very low temperature regime must be understood. Our experiments are conducted in a dilution refrigerator, with heaters being used to create temperature gradients across elongated alumina samples of different cross-sectional geometries mounted in copper clamps, with one end thermalized on the 10mK plate of the cryostat. Temperatures of both ends are measured with RuO$_2$ resistance thermometers, and thermal conductivity k(T) can be determined using the relationship $ \frac{dQ}{dt} =\frac{A}{l}{\int{k(T)dT}}$, where $\frac{dQ}{dt}$ is heating power, $A$ is cross-sectional area of the sample, $l$ is its length, and $T$ is temperature. Absolute values and temperature dependence of thermal conductivity of the alumina samples were measured and compared to well-investigated single-crystal sapphire properties. Thermal conductivity of other materials of interest was also investigated; the results will be presented.