Fall 2014

The basics of the standard model are things that we all pretty much know, but we all focus on different parts. In this talk we each gave our unique perspective on the most important parts of the model.

How do we know that there are quarks if we've never isolated one? How do we know that the up and down quarks have masses of only a few MeV? Is asymptotic freedom a real thing, or something that was just made up because it sounds cool? After years in grad school spent researching proton structure with the OLYMPUS experiment, these sorts of questions still keep me up at night. In this talk I'll attempt to get to the bottom of these questions by looking at the original experiments and papers by Hofstadter, Kendall, Friedman, and Taylor, and more recent results from high energy experiments at HERA. Bring questions and let's have a fun and interesting discussion.

The observed momentum imbalance of dijet events in PbPb collisions at the LHC, relative to corresponding proton-proton collisions, is one of the most striking results of the heavy ions jet program at CERN. Subsequent results on dijet asymmetry suggest that modification is a combination of in-cone and out-of-cone effects. Recent studies performed by CMS have, to some reasonable extent, characterized the out-of-cone modification. To explore in-cone jet modification due to the presence of a strongly coupled medium such as the quark-gluon plasma, a fledgling heavy ions jet substructure program has taken its first steps. This talk explores the potential of such a program, and the paths it might follow in the future. Both are of significant importance in understanding the produced quark-gluon plasma, and jets as probes.

Among the technologies under consideration for use in future particle physics experiments are "edgeless" silicon pixel detectors. The prototypes used for the study described in this paper were designed by VTT Technical Research Centre of Finland, whose team developed a state-of-the-art fabrication process to create sensors with a negligible guardring as a dead region at the edges. We find that the test subjects perform in accordance with expectations and fulfill the technical needs of their intended implementation. The state-of-the-art active edge technology is effective in maximizing the useful area of the sensor. Overall these devices meet the specifications of a detector for particle physics such as LHCb, but may also find a role in medical imaging or X-ray spectroscopy. However, some mysterious behavior of these devices at the edges is still not well understood.

OLYMPUS overview talk.

Discussion of the building of the MiniCLEAN detector including the challenges of constructing a high precision detector deep underground. Also describes the function of the detector components.

Part III topic: Heavy Ion Physics, with additional questions as practice.

While currently direct detection and accelerator based experiments have been headlining the search for Dark Matter, there is another potentially fruitful avenue of research, namely indirect detection. In this talk I will discuss the current limits published by the ICECUBE collaboration, which places limits by looking at the high energy neutrino spectrum and examining the possible Dark Matter decay modes that could decay into neutrinos. These results will then be compared to other indirect limits and possible signals currently review in the community. arXiv:1307.3473

Part III Topic: Dark Matter: Physics and Detection, addtitional questions were the focus of this talk due to scheduling of topic receipt.

The observation of neutrino oscillations at the opening of this century demonstrates that neutrinos have small masses, contradicting an assumption of neutrino masslessness which had been held for more than 70 years.  When compared with other fermions, neutrino masses are orders of magnitude smaller, which likely indicates a very different mass generation mechanism is at work in this sector.  Furthermore, as the most common fermion in the universe, neutrinos play an important role in cosmological structure formation, for which a non-zero neutrino mass has strong and observable consequences.  Direct kinematic measurements of the neutrino mass have coalesced around tritium beta-decay experiments which have reached their practical limits at the KATRIN experiment with a sensitivity of 200 electron-millivolts.  Should nature have conspired to make neutrino masses lighter than this sensitivity, a completely new spectroscopic technique would be necessary, motivating the development of Project 8.  Project 8 works by magnetically trapping electrons within a waveguide, into which the gyrating particles emit radiation; the weak relativistic energy dependence of the frequency of this emitted cyclotron radiation opens the door to a new type of high-precision spectroscopy, with very broad potential applications even outside of neutrino mass searches.  A prototype of the Project 8 experiment has been constructed over the last three years at University of Washington, and took data using 83mKr earlier this summer.  Analysis of these data will be presented, which demonstrate the observation of the cyclotron radiation from single conversion electrons, from which a precise energy spectrum is extracted.

The ability of photons to scattering off charged particles has long been known and studied. But it wasn’t until 1923 that a quantum description of inelastic photon-electron scattering was given by Arthur H. Compton after whom the process is named. Polarized Compton Scattering has since been worked out in QED and finds application in precision polarimetry of electron beams. Using such polarimeters, a complete QED description of Compton scattering gives us access to probe the properties of light itself, independent of physical fluctuations which might occur with beams of light or electrons such as fluctuations in beam position, beam energy and, beam polarization to name a few. This opens up the door to test Lorentz symmetry at unprecedented precision which then(curiously enough) allows for a test of spacial isometry at Plank scale and in-turn as a probe of physics beyond standard model. We will present a historic evolution of the understanding of light scattering off charged particles followed by a systematic workings of Compton Polarimeters. Finally we will present preliminary studies of such probes of fundamental symmetries and a future outlook on a dedicated experiment.

Earlier this semester, you heard about the application of V-tagging jets in heavy ion collisions. V-tagging is also useful in proton-proton collisions. In particular, I will describe the Mono-V analysis which makes up the larger Mono-X search by CMS for dark matter production at the LHC. We are working to create an improved method to identify hadronically decaying weak vector bosons that are boosted into a single jet. In the process, we are identifying correlations between variables, ranking their discrimination power, and trying to determine the total amount of useful information in the event. The development of the V-tagger done over the summer will be given in detail as well as ongoing efforts to optimize the method for currently blinded data.

Multivariate analysis techniques are increasingly used in experimental particle physics for tasks like triggering, particle ID, and event selection. Such a study (V-tagging at CMS) was the topic of last week's seminar by Daniel Abercrombie. This week, I will give a bottom-up description of the most relevant machine learning topics (decision trees, neural networks, and boosting). We will carefully go through the motivations and training algorithms behind each of these techniques. This will be followed by a brief comparison of the classifiers' performance at V-tagging at CMS. Finally, I will discuss recent developments in machine learning research, some of which are being explored by the MIT PPC group.