117090989
Statistical analysis of detection of, and upper limits on, dark matter lines
In this note we present calculations of coverage and power for three different methods which could be used to calculate upper limits and/or claim discovery in a GLAST‐LAT search for a dark matter line. The methods considered are Profile Likelihood, Bayesian factors and likelihood ratio confidence intervals and the calculations are done considering a simple benchmark model of two uncorrelated Poissonian measurements. Profile likelihood has the best coverage properties, the standard χ2 test the worst. For the power, the situation is vice‐versa. In choosing a method one has to consider the false detection rate (1 ‐ coverage) and counterweigh it to the possible achievable power.
18437847
Fluctuation studies and energy reconstruction in a segmented calorimeter
In order to better understand energy estimation of electromagnetic showers in segmented calorimeters, detailed Geant4 simulation studies of electromagnetic showers in the energy range 1-100 GeV in CsI have been performed. When sampled in layers of 1.99 cm thickness, corresponding to 1.08 radiation lengths, the energy fluctuations in the samples show distributions that vary significantly with depth. The energy distributions are similar for incident electrons and photons and were found to change systematically along the shower, varying little with the initial energy. Three probability distributions have been fitted to the data: negative binomial, log-normal and Gaussian distributions, none of which gives a good fit over the full shower length. The obtained parameterizations might be useful in the use of the maximum likelihood method for estimating the energy. Two methods for estimating the energy have also been studied. One method is based on fitting individual longitudinal shower profiles with a Gamma-function, the other one corrects the measured energy for leakage by utilizing the energy deposited in the last layer. Our simulations indicate that the last-layer correction method applied to photons and electrons of 1 and 10 GeV gives about a factor of 2 improvement in the energy resolution.
15563733
Applying rule ensembles to the search for super-symmetry at the large hadron collider
In this note we give an example application of a recently presented predictive learning method called Rule Ensembles. The application we present is the search for super-symmetric particles at the Large Hadron Collider. In particular, we consider the problem of separating the background coming from top quark production from the signal of super-symmetric particles. The method is based on an expansion of base learners, each learner being a rule, i.e. a combination of cuts in the variable space describing signal and background. These rules are generated from an ensemble of decision trees. One of the results of the method is a set of rules (cuts) ordered according to their importance, which gives useful tools for diagnosis of the model. We also compare the method to a number of other multivariate methods, in particular Artificial Neural Networks, the likelihood method and the recently presented boosted decision tree method. We find better performance of Rule Ensembles in all cases. For example for a given significance the amount of data needed to claim SUSY discovery could be reduced by 15% using Rule Ensembles as compared to using a likelihood method.
17385602
On sensitivity calculations for neutrino oscillation experiments
Calculations of sensitivities of future experiments are a necessary ingredient in experimental high energy physics. Especially in the context of measurements of the neutrino oscillation parameters extensive studies are performed to arrive at the optimal configuration. In this note we clarify the definition of sensitivity as often applied in these studies. In addition, we examine two of the most common methods to calculate sensitivity from a statistical perspective using a toy model. The importance of inclusion of uncertainties in nuisance parameters for the interpretation of sensitivity calculations is pointed out.
15402465
Coverage of Confidence Intervals for Poisson Statistics in Presence of Systematic Uncertainties
Coverage of Confidence Intervals for Poisson Statistics in Presence of Systematic Uncertainties
118516643
Anisotropies in the diffuse gamma-ray background from dark matter with Fermi LAT: a closer look
This thesis addresses the isotropic diffuse gamma-ray background, as measured by the Fermi gamma ray space telescope, and its implications for indirect detection of dark matter. We describe the measurement of the isotropic background, including also an alternative analysis method besides the one published by the Fermi-LAT collaboration. The measured isotropic diffuse background is compatible with a power law differential energy spectrum with a spectral index of -2.41 ± 0.05 and -2.39 ± 0.08, for the two analysis methods respectively. This is a softer spectrum than previously reported by the EGRET experiment. This rules out any dominant contribution with a significantly different shape, e.g. from dark matter, in the energy range 20 MeV to 102.4 GeV. Instead we present upper limits on a signal originating from annihilating dark matter of extragalactic origin. The uncertainty in the dark matter signal is primarily dependent on the cosmological evolution of the dark matter distribution. We use recent N-body simulations of structure formation, as well as a semi-analytical calculation, to assess this uncertainty. We investigate three main annihilation channels and find that in some, but not in all, of our scenarios we can start to probe, and sometimes rule out, interesting parameter spaces of particle physics models beyond the standard model.We also investigate the possibility to use the angular anisotropies of the annihilation signal to separate it from a background originating from conventional sources, e.g. from active galactic nuclei. By carefully modelling the performance of the Fermi gamma-ray space telescope and galactic foregrounds we find that this method could be as sensitive as using information from the energy spectrum only.
14263651
SIMULATIONS OF PION PRODUCTION IN THE DAEDALUS TARGET
DAEDALUS, the Decay At-rest Experiment for DCP at a 
Laboratory for Underground Science will look for evidence 
of CP-violation in the neutrino sector, an ingredient in theories 
that seek to explain the matter/antimatter asymmetry 
in our universe. It will make a precision measurement of 
the oscillations of muon antineutrinos to electron antineutrinos 
using multiple neutrino sources created by low-cost 
compact cyclotrons. The experiment utilizes decay-at-rest 
neutrino beams produced by 800 MeV protons impinging 
a beam target of graphite and copper. Two well established 
Monte Carlo codes, MARS and GEANT4, have been used 
to optimise the design and the performance of the target. A 
study of the results obtained with these two codes is presented 
in this paper.
561638
Coherent neutrino scattering in dark matter detectors
Coherent elastic neutrino- and WIMP-nucleus interaction signatures are expected to be quite similar. This paper discusses how a next generation ton-scale dark matter detector could discover neutrino-nucleus coherent scattering, a precisely-predicted Standard Model process. A high intensity pion- and muon- decay-at-rest neutrino source recently proposed for oscillation physics at underground laboratories would provide the neutrinos for these measurements. In this paper, we calculate raw rates for various target materials commonly used in dark matter detectors and show that discovery of this interaction is possible with a 2 ton$\cdot$year GEODM exposure in an optimistic energy threshold and efficiency scenario. We also study the effects of the neutrino source on WIMP sensitivity and discuss the modulated neutrino signal as a sensitivity/consistency check between different dark matter experiments at DUSEL. Furthermore, we consider the possibility of coherent neutrino physics with a GEODM module placed within tens of meters of the neutrino source.
117938363
Searches for new physics at NuTeV
The NuTeV Experiment at Fermilab has searched for indications of physics beyond the standard model using indirect and direct search methods. The indirect method compares the NuTeV measurement of sin2 θW to the world measurement for this parameter. The direct measurement searches for decays of exotic neutral particles in a light mass, instrumented region upstream of the NuTeV calorimeter. No evidence for new physics has been observed. Therefore, NuTeV has placed constraints on extensions to the Standard Model which include certain Z′’s, neutral heavy leptons and the particle responsible for the Karmen Timing Anomaly.
122729879
Bringing the SciBar detector to the booster neutrino beam
This document presents the physics case for bringing SciBar, the fully active, finely segmented tracking detector at KEK, to the FNAL Booster Neutrino Beam (BNB) line. This unique opportunity arose with the termination of K2K beam operations in 2005. At that time, the SciBar detector became available for use in other neutrino beam lines, including the BNB, which has been providing neutrinos to the MiniBooNE experiment since late 2002. The physics that can be done with SciBar/BNB can be put into three categories, each involving several measurements. First are neutrino cross section measurements which are interesting in their own right, including analyses of multi-particle final states, with unprecedented statistics. Second are measurements of processes that represent the signal and primary background channels for the upcoming T2K experiment. Third are measurements which improve existing or planned MiniBooNE analyses and the understanding of the BNB, both in neutrino and antineutrino mode. For each of these proposed measurements, the SciBar/BNB combination presents a unique opportunity or will significantly improve upon current or near-future experiments for several reasons. First, the fine granularity of SciBar allows detailed reconstruction of final states not possible with the MiniBooNE detector. Additionally, the BNB neutrino energy spectrum is amore » close match to the expected T2K energy spectrum in a region where cross sections are expected to vary dramatically with energy. As a result, the SciBar/BNB combination will provide cross-section measurements in an energy range complementary to MINERvA and complete the knowledge of neutrino cross sections over the entire energy range of interest to the upcoming off-axis experiments.« less
20950520
Photodegradation mechanisms of tetraphenyl butadiene coatings for liquid argon detectors
We report on studies of degradation mechanisms of tetraphenyl butadiene (TPB) coatings of the type used in neutrino and dark matter liquid argon experiments. Using gas chromatography coupled to mass spectrometry we have detected the ultraviolet-blocking impurity benzophenone. We monitored the drop in performance and increase of benzophenone concentration in TPB plates with exposure to ultraviolet (UV) light, and demonstrate the correlation between these two variables. Based on the presence and initially exponential increase in the concentration of benzophenone observed, we propose that TPB degradation is a free radical-mediated photooxidation reaction, which is subsequently confirmed by displaying delayed degradation using a free radical inhibitor. Finally we show that the performance of wavelength-shifting coatings of the type envisioned for the LBNE experiment can be improved by 10-20%, with significantly delayed UV degradation, by using a 20% admixture of 4-tert-Butylcatechol.