arXiv subjects

J. M. Conrad

Publications and source records attributed to J. M. Conrad.

At least 343 records · Page 19Linked to original sources

arXiv2013

Testing of Cryogenic Photomultiplier Tubes for the MicroBooNE Experiment

The MicroBooNE detector, to be located on axis in the Booster Neutrino Beamline (BNB) at the Fermi National Accelerator Laboratory (Fermilab), consists of two main components: a large liquid argon time projection chamber (LArTPC), and a light collection system. Thirty 8-inch diameter Hamamatsu R5912-02mod cryogenic photomultiplier tubes (PMTs) will detect the scintillation light generated in the liquid argon (LAr). This article first describes the MicroBooNE PMT performance test procedures, including how the light collection system functions in the detector, and the design of the PMT base. The design of the cryogenic test stand is then discussed, and finally the results of the cryogenic tests are reported.

physics.ins-det↗

arXiv2013

Improved Search for $\bar ν_μ\rightarrow \bar ν_e$ Oscillations in the MiniBooNE Experiment

The MiniBooNE experiment at Fermilab reports results from an analysis of $\bar ν_e$ appearance data from $11.27 \times 10^{20}$ protons on target in antineutrino mode, an increase of approximately a factor of two over the previously reported results. An event excess of $78.4 \pm 28.5$ events ($2.8 σ$) is observed in the energy range $200<E_ν^{QE}<1250$ MeV. If interpreted in a two-neutrino oscillation model, $\barν_μ\rightarrow\barν_e$, the best oscillation fit to the excess has a probability of 66% while the background-only fit has a $χ^2$-probability of 0.5% relative to the best fit. The data are consistent with antineutrino oscillations in the $0.01 < Δm^2 < 1.0$ eV$^2$ range and have some overlap with the evidence for antineutrino oscillations from the Liquid Scintillator Neutrino Detector (LSND). All of the major backgrounds are constrained by in-situ event measurements so non-oscillation explanations would need to invoke new anomalous background processes. The neutrino mode running also shows an excess at low energy of $162.0 \pm 47.8$ events ($3.4 σ$) but the energy distribution of the excess is marginally compatible with a simple two neutrino oscillation formalism. Expanded models with several sterile neutrinos can reduce the incompatibility by allowing for CP violating effects between neutrino and antineutrino oscillations.

hep-ex↗

arXiv2013

Measurement of the neutrino component of an anti-neutrino beam observed by a non-magnetized detector

Two independent methods are employed to measure the neutrino flux of the anti-neutrino-mode beam observed by the MiniBooNE detector. The first method compares data to simulated event rates in a high purity $\numu$ induced charged-current single $\pip$ (CC1$\pip$) sample while the second exploits the difference between the angular distributions of muons created in $\numu$ and $\numub$ charged-current quasi-elastic (CCQE) interactions. The results from both analyses indicate the prediction of the neutrino flux component of the pre-dominately anti-neutrino beam is over-estimated - the CC1$\pip$ analysis indicates the predicted $\numu$ flux should be scaled by $0.76 \pm 0.11$, while the CCQE angular fit yields $0.65 \pm 0.23$. The energy spectrum of the flux prediction is checked by repeating the analyses in bins of reconstructed neutrino energy, and the results show that the spectral shape is well modeled. These analyses are a demonstration of techniques for measuring the neutrino contamination of anti-neutrino beams observed by future non-magnetized detectors.

hep-ex↗

arXiv2013

A Prototype Detector for Directional Measurement of the Cosmogenic Neutron Flux

This paper describes a novel directional neutron detector prototype. The low pressure time projection chamber uses a mix of helium and CF4 gases. The detector reconstructs the energy and angular distribution of fast neutron recoils. This paper reports results of energy calibration using an alpha source and angular reconstruction studies using a collimated neutron source. The best performance is obtained with a 12.5% CF4 gas mixture. At low energies the target for fast neutrons transitions is primarily helium, while at higher energies, the fluorine contributes as a target. The reconstruction efficiency is both energy and target dependent. For neutrons with energies less than 20 MeV, the reconstruction efficiency is ~40% for fluorine recoils and ~60% for helium recoils.

physics.ins-det↗

arXiv2012

First Test of Lorentz Violation with a Reactor-based Antineutrino Experiment

We present a search for Lorentz violation with 8249 candidate electron antineutrino events taken by the Double Chooz experiment in 227.9 live days of running. This analysis, featuring a search for a sidereal time dependence of the events, is the first test of Lorentz invariance using a reactor-based antineutrino source. No sidereal variation is present in the data and the disappearance results are consistent with sidereal time independent oscillations. Under the Standard-Model Extension (SME), we set the first limits on fourteen Lorentz violating coefficients associated with transitions between electron and tau flavor, and set two competitive limits associated with transitions between electron and muon flavor.

hep-ex↗

arXiv2012

Proposal for an Electron Antineutrino Disappearance Search Using High-Rate 8Li Production and Decay

This paper introduces a novel, high-intensity source of electron antineutrinos from the production and subsequent decay of 8Li. When paired with an existing ~1 kton scintillator-based detector, this =6.4 MeV source opens a wide range of possible searches for beyond standard model physics via studies of the inverse beta decay interaction. In particular, the experimental design described here has unprecedented sensitivity to electron antineutrino disappearance at $Δm^2\sim$ 1 eV$^2$ and features the ability to distinguish between the existence of zero, one, and two sterile neutrinos.

hep-ex↗

arXiv2012

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 (BP). 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.

physics.ins-det↗

arXiv2012

Dual baseline search for muon antineutrino disappearance at 0.1 eV^2 < Δm^2 < 100 eV^2

The MiniBooNE and SciBooNE collaborations report the results of a joint search for short baseline disappearance of \bar{ν_μ} at Fermilab's Booster Neutrino Beamline. The MiniBooNE Cherenkov detector and the SciBooNE tracking detector observe antineutrinos from the same beam, therefore the combined analysis of their datasets serves to partially constrain some of the flux and cross section uncertainties. Uncertainties in the ν_μ background were constrained by neutrino flux and cross section measurements performed in both detectors. A likelihood ratio method was used to set a 90% confidence level upper limit on \bar{ν_μ} disappearance that dramatically improves upon prior limits in the Δm^2=0.1-100 eV^2 region.

hep-ex↗

arXiv2012

Direct Measurement of Backgrounds using Reactor-Off Data in Double Chooz

Double Chooz is unique among modern reactor-based neutrino experiments studying $\bar ν_e$ disappearance in that data can be collected with all reactors off. In this paper, we present data from 7.53 days of reactor-off running. Applying the same selection criteria as used in the Double Chooz reactor-on oscillation analysis, a measured background rate of 1.0$\pm$0.4 events/day is obtained. The background model for accidentals, cosmogenic $β$-$n$-emitting isotopes, fast neutrons from cosmic muons, and stopped-$μ$ decays used in the oscillation analysis is demonstrated to be correct within the uncertainties. Kinematic distributions of the events, which are dominantly cosmic-ray-produced correlated-background events, are provided. The background rates are scaled to the shielding depths of two other reactor-based oscillation experiments, Daya Bay and RENO.

hep-ex↗

arXiv2012

Cost-effective Design Options for IsoDAR

This whitepaper reviews design options for the IsoDAR electron antineutrino source. IsoDAR is designed to produce $2.6 \times 10^{22}$ electron antineutrinos per year with an average energy of 6.4 MeV, using isotope decay-at-rest. Aspects which must be balanced for cost-effectiveness include: overall cost; rate and energy distribution of the electron antineutrino flux and backgrounds; low technical risk; compactness; simplicity of underground construction and operation; reliability; value to future neutrino physics programs; and value to industry. We show that the baseline design outlined here is the most cost effective.

physics.acc-ph↗

arXiv2012

Letter of Intent: A new investigation of numu to nue oscillations with improved sensitivity in an enhanced MiniBooNE experiment

We propose adding 300 mg/l PPO to the existing MiniBooNE detector mineral oil to increase the scintillation response. This will allow the detection of associated neutrons and increase sensitivity to final-state nucleons in neutrino interactions. This increased capability will enable an independent test of whether the current excess seen in the MiniBooNE oscillation search is signal or background. In addition it will enable other neutrino interaction measurements to be made including a search for the strange-quark contribution to the nucleon spin Delta s and a low-energy measurement of charged-current quasielastic scattering.

hep-ex↗

arXiv2012

Beam Dynamics Simulation for the High Intensity DAEδALUS Cyclotrons

In the DAEδALUS (Decay-At-rest Experiment for δCP studies At the Laboratory for Underground Science) project, high power H+2 cyclotron chains are proposed to efficiently provide proton beams with a kinetic energy of 800 MeV and an average power in the MW range. Space charge plays a pivotal role in both the injector and the ring cyclotrons. Large-scale particle simulations show that the injector cyclotron is a space charge dominated cyclotron and that a 5mA beam current can be extracted with tolerable beam losses on the septum. In contrast, in the ring cyclotron, no space charge induced beam loss is observed during acceleration and extraction.

physics.acc-ph↗

arXiv2012

Reactor electron antineutrino disappearance in the Double Chooz experiment

The Double Chooz experiment has observed 8,249 candidate electron antineutrino events in 227.93 live days with 33.71 GW-ton-years (reactor power x detector mass x livetime) exposure using a 10.3 cubic meter fiducial volume detector located at 1050 m from the reactor cores of the Chooz nuclear power plant in France. The expectation in case of theta13 = 0 is 8,937 events. The deficit is interpreted as evidence of electron antineutrino disappearance. From a rate plus spectral shape analysis we find sin^2 2θ13 = 0.109 \pm 0.030(stat) \pm 0.025(syst). The data exclude the no-oscillation hypothesis at 99.8% CL (2.9σ).

hep-ex↗

arXiv2012

A Combined $ν_μ\to ν_e$ and $\barν_μ\to \barν_e$ Oscillation Analysis of the MiniBooNE Excesses

The MiniBooNE experiment at Fermilab reports results from an analysis of the combined $ν_e$ and $\bar ν_e$ appearance data from $6.46 \times 10^{20}$ protons on target in neutrino mode and $11.27 \times 10^{20}$ protons on target in antineutrino mode. A total excess of $240.3 \pm 34.5 \pm 52.6$ events ($3.8 σ$) is observed from combining the two data sets in the energy range $200<E_ν^{QE}<1250$ MeV. In a combined fit for CP-conserving $ν_μ\rightarrow ν_e$ and $\barν_μ\rightarrow\barν_e$ oscillations via a two-neutrino model, the background-only fit has a $χ^2$-probability of 0.03% relative to the best oscillation fit. The data are consistent with neutrino oscillations in the $0.01 < Δm^2 < 1.0$ eV$^2$ range and with the evidence for antineutrino oscillations from the Liquid Scintillator Neutrino Detector (LSND).

hep-ex↗

arXiv2012

Multimegawatt DAE$δ$ALUS Cyclotrons for Neutrino Physics

DAE$δ$ALUS (Decay-At-rest Experiment for $δ_{CP}$ studies At the Laboratory for Underground Science) provides a new approach to the search for CP violation in the neutrino sector. High-power continuous-wave proton cyclotrons efficiently provide the necessary proton beams with an energy of up to 800 MeV to create neutrinos from pion and muon decay-at-rest. The experiment searches for $\barν_μ \rightarrow \barν_e$ at short baselines corresponding to the atmospheric $Δm^2$ region. The $\barν_e$ will be detected via inverse beta decay. Thus, the cyclotrons will be employed at a future ultra-large gadolinium-doped water or scintillator detector. In this paper we address the most challenging questions regarding a cyclotron-based high-power proton driver in the megawatt range with a kinetic energy of 800 MeV. Aspects of important subsystems like the ion source and injection chain, the magnet design and radio frequency system will be addressed. Precise beam dynamics simulations, including space charge and the $\text{H}_2^+$ stripping process, are the base for the characterization and quantification of the beam halo -- one of the most limiting processes in high-power particle accelerators.

physics.acc-ph↗

arXiv2012

Sterile Neutrino Fits to Short Baseline Neutrino Oscillation Measurements

This paper reviews short baseline oscillation experiments as interpreted within the context of one, two, and three sterile neutrino models associated with additional neutrino mass states in the ~1 eV range. Appearance and disappearance signals and limits are considered. We show that fitting short baseline data sets to a (3+3) model, defined by three active and three sterile neutrinos, results in an overall goodness of fit of 67%, and a compatibility of 90% among all data sets -- to be compared to the compatibility of 0.043% and 13% for a (3+1) and a (3+2) model, respectively. While the (3+3) fit yields the highest quality overall, it still finds inconsistencies with the MiniBooNE appearance data sets; in particular, the global fit fails to account for the observed MiniBooNE low-energy excess. Given the overall improvement, we recommend using the results of (3+2) and (3+3) fits, rather than (3+1) fits, for future neutrino oscillation phenomenology. These results motivate the pursuit of further short baseline experiments, such as those reviewed in this paper.

hep-ex↗

arXiv2012

Test of Lorentz and CPT violation with Short Baseline Neutrino Oscillation Excesses

The sidereal time dependence of MiniBooNE electron neutrino and anti-electron neutrino appearance data are analyzed to search for evidence of Lorentz and CPT violation. An unbinned Kolmogorov-Smirnov test shows both the electron neutrino and anti-electron neutrino appearance data are compatible with the null sidereal variation hypothesis to more than 5%. Using an unbinned likelihood fit with a Lorentz-violating oscillation model derived from the Standard Model Extension (SME) to describe any excess events over background, we find that the electron neutrino appearance data prefer a sidereal time-independent solution, and the anti-electron neutrino appearance data slightly prefer a sidereal time-dependent solution. Limits of order 10E-20 GeV are placed on combinations of SME coefficients. These limits give the best limits on certain SME coefficients for muon neutrino to electron neutrino and anti-muon neutrino to anti-electron neutrino oscillations. The fit values and limits of combinations of SME coefficients are provided.

hep-ex↗

arXiv2012

Reactor Simulation for Antineutrino Experiments using DRAGON and MURE

Rising interest in nuclear reactors as a source of antineutrinos for experiments motivates validated, fast, and accessible simulations to predict reactor fission rates. Here we present results from the DRAGON and MURE simulation codes and compare them to other industry standards for reactor core modeling. We use published data from the Takahama-3 reactor to evaluate the quality of these simulations against the independently measured fuel isotopic composition. The propagation of the uncertainty in the reactor operating parameters to the resulting antineutrino flux predictions is also discussed.

nucl-ex↗