arXiv subjects

E. Santos

Publications and source records attributed to E. Santos.

At least 37 records · Page 2Linked to original sources

arXiv2015

First Measurement of Neutrino and Antineutrino Coherent Charged Pion Production on Argon

We report on the first cross section measurements for charged current coherent pion production by neutrinos and antineutrinos on argon. These measurements are performed using the ArgoNeuT detector exposed to the NuMI beam at Fermilab. The cross sections are measured to be $2.6^{+1.2}_{-1.0}(stat)^{+0.3}_{-0.4}(syst) \times 10^{-38} \textrm{cm}^{2}/\textrm{Ar}$ for neutrinos at a mean energy of $9.6$ GeV and $5.5^{+2.6}_{-2.1}(stat)^{+0.6}_{-0.7}(syst) \times 10^{-39} \textrm{cm}^{2}/\textrm{Ar}$ for antineutrinos at a mean energy of $3.6$ GeV.

hep-ex↗

arXiv2015

Molecular dissociation in presence of catalysts: Interpreting bond breaking as a quantum dynamical phase transition

In this work we show that the molecular chemical bond formation and dissociation in presence of the d-band of a metal catalyst can be described as a Quantum Dynamical Phase Transition (QDPT). This agree with DFT calculations that predict sudden jumps in some observables as the molecule breaks. According to our model this phenomenon emerges because the catalyst provides for a non- Hermitian Hamiltonian. We show that when the molecule approaches the surface, as occurs in the Heyrovsky reaction of H 2, the bonding H 2 orbital has a smooth crossover into a bonding molecular orbital built with the closest H orbital and the surface metal d-states. The same occurs for the antibonding state. Meanwhile, two resonances appear within the continuous spectrum of the d- band which are associated with bonding and antibonding orbitals between the furthest H atom and the d-states at the second metallic layer. These move towards the band center where they collapse into a pure metallic resonance and an almost isolated H orbital. This phenomenon constitutes a striking example of the non-trivial physics enabled when one deals with non-Hermitian Hamiltonian beyond the usual wide band approximation.

physics.chem-ph↗

arXiv2014

Light sterile neutrino sensitivity at the nuSTORM facility

A facility that can deliver beams of electron and muon neutrinos from the decay of a stored muon beam has the potential to unambiguously resolve the issue of the evidence for light sterile neutrinos that arises in short-baseline neutrino oscillation experiments and from estimates of the effective number of neutrino flavors from fits to cosmological data. In this paper, we show that the nuSTORM facility, with stored muons of 3.8 GeV/c $\pm$ 10%, will be able to carry out a conclusive muon neutrino appearance search for sterile neutrinos and test the LSND and MiniBooNE experimental signals with 10$σ$ sensitivity, even assuming conservative estimates for the systematic uncertainties. This experiment would add greatly to our knowledge of the contribution of light sterile neutrinos to the number of effective neutrino flavors from the abundance of primordial helium production and from constraints on neutrino energy density from the cosmic microwave background. The appearance search is complemented by a simultaneous muon neutrino disappearance analysis that will facilitate tests of various sterile neutrino models.

hep-ex↗

arXiv2013

The HAWC Gamma-Ray Observatory: Sensitivity to Steady and Transient Sources of Gamma Rays

The High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory is designed to record air showers produced by cosmic rays and gamma rays between 100 GeV and 100 TeV. Because of its large field of view and high livetime, HAWC is well-suited to measure gamma rays from extended sources, diffuse emission, and transient sources. We describe the sensitivity of HAWC to emission from the extended Cygnus region as well as other types of galactic diffuse emission; searches for flares from gamma-ray bursts and active galactic nuclei; and the first measurement of the Crab Nebula with HAWC-30.

astro-ph.HE↗

arXiv2013

The HAWC Gamma-Ray Observatory: Observations of Cosmic Rays

We describe measurements of GeV and TeV cosmic rays with the High-Altitude Water Cherenkov Gamma-Ray Observatory, or HAWC. The measurements include the observation of the shadow of the moon; the observation of small-scale and large-scale angular clustering of the TeV cosmic rays; the prospects for measurement of transient solar events with HAWC; and the observation of Forbush decreases with the HAWC engineering array and HAWC-30.

astro-ph.HE↗

arXiv2013

The HAWC Gamma-Ray Observatory: Dark Matter, Cosmology, and Fundamental Physics

The High-Altitude Water Cherenkov Gamma Ray Observatory (HAWC) is designed to perform a synoptic survey of the TeV sky. The high energy coverage of the experiment will enable studies of fundamental physics beyond the Standard Model, and the large field of view of the detector will enable detailed studies of cosmologically significant backgrounds and magnetic fields. We describe the sensitivity of the full HAWC array to these phenomena in five contributions shown at the 33rd International Cosmic Ray Conference in Rio de Janeiro, Brazil (July 2013).

astro-ph.HE↗

arXiv2013

The HAWC Gamma-Ray Observatory: Design, Calibration, and Operation

The High-Altitude Water Cherenkov Gamma Ray Observatory (HAWC) is under construction 4100 meters above sea level at Sierra Negra, Mexico. We describe the design and cabling of the detector, the characterization of the photomultipliers, and the timing calibration system. We also outline a next-generation detector based on the water Cherenkov technique.

astro-ph.IM↗

arXiv2013

nuSTORM - Neutrinos from STORed Muons: Proposal to the Fermilab PAC

The nuSTORM facility has been designed to deliver beams of electron neutrinos and muon neutrinos (and their anti-particles) from the decay of a stored muon beam with a central momentum of 3.8 GeV/c and a momentum acceptance of 10%. The facility is unique in that it will: 1. Allow searches for sterile neutrinos of exquisite sensitivity to be carried out; 2. Serve future long- and short-baseline neutrino-oscillation programs by providing definitive measurements of electron neutrino and muon neutrino scattering cross sections off nuclei with percent-level precision; and 3. Constitutes the crucial first step in the development of muon accelerators as a powerful new technique for particle physics. The document describes the facility in detail and demonstrates its physics capabilities. This document was submitted to the Fermilab Physics Advisory Committee in consideration for Stage I approval.

physics.acc-ph↗

arXiv2013

Sensitivity of the High Altitude Water Cherenkov Detector to Sources of Multi-TeV Gamma Rays

The High Altitude Water Cherenkov (HAWC) observatory is an array of large water Cherenkov detectors sensitive to gamma rays and hadronic cosmic rays in the energy band between 100 GeV and 100 TeV. The observatory will be used to measure high-energy protons and cosmic rays via detection of the energetic secondary particles reaching the ground when one of these particles interacts in the atmosphere above the detector. HAWC is under construction at a site 4100 meters above sea level on the northern slope of the volcano Sierra Negra, which is located in central Mexico at 19 degrees N latitude. It is scheduled for completion in 2014. In this paper we estimate the sensitivity of the HAWC instrument to point-like and extended sources of gamma rays. The source fluxes are modeled using both unbroken power laws and power laws with exponential cutoffs. HAWC, in one year, is sensitive to point sources with integral power-law spectra as low as 5x10^-13 cm^-2 sec^-1 above 2 TeV (approximately 50 mCrab) over 5 sr of the sky. This is a conservative estimate based on simple event parameters and is expected to improve as the data analysis techniques are refined. We discuss known TeV sources and the scientific contributions that HAWC can make to our understanding of particle acceleration in these sources.

astro-ph.HE↗

arXiv2013

Neutrinos from Stored Muons nuSTORM: Expression of Interest

The nuSTORM facility has been designed to deliver beams of electron and muon neutrinos from the decay of a stored muon beam with a central momentum of 3.8 GeV/c and a momentum spread of 10%. The facility is unique in that it will: serve the future long- and short-baseline neutrino-oscillation programmes by providing definitive measurements of electron-neutrino- and muon-neutrino-nucleus cross sections with percent-level precision; allow searches for sterile neutrinos of exquisite sensitivity to be carried out; and constitute the essential first step in the incremental development of muon accelerators as a powerful new technique for particle physics. Of the world's proton-accelerator laboratories, only CERN and FNAL have the infrastructure required to mount nuSTORM. Since no siting decision has yet been taken, the purpose of this Expression of Interest (EoI) is to request the resources required to: investigate in detail how nuSTORM could be implemented at CERN; and develop options for decisive European contributions to the nuSTORM facility and experimental programme wherever the facility is sited. The EoI defines a two-year programme culminating in the delivery of a Technical Design Report.

physics.acc-ph↗

arXiv2012

A model for the transport of muons in extensive air showers

In this article we identify the key elements that govern the propagation of muons from the production in extensive air showers to ground. We describe a model based on simple assumptions that propagates the muons starting from the few relevant distributions at production. We compare the results to the ground distributions given by a full air shower Monte Carlo. This study is motivated by the need of modeling the muon component in extensive air showers with the goal of experimentally reconstructing their distributions at production, which act as a footprint of the hadronic cascade.

astro-ph.HE↗

arXiv2012

nuSTORM: Neutrinos from STORed Muons

The results of LSND and MiniBooNE, along with the recent papers on a possible reactor neutrino flux anomaly give tantalizing hints of new physics. Models beyond the neutrino-SM have been developed to explain these results and involve one or more additional neutrinos that are non-interacting or "sterile." Neutrino beams produced from the decay of muons in a racetrack-like decay ring provide a powerful way to study this potential new physics. In this Letter of Intent, we describe a facility, nuSTORM, "Neutrinos from STORed Muons," and an appropriate far detector for neutrino oscillation searches at short baseline. We present sensitivity plots that indicated that this experimental approach can provide over 10 sigma confirmation or rejection of the LSND/MinBooNE results. In addition we indicate how the facility can be used to make precision neutrino interaction cross section measurements important to the next generation of long-baseline neutrino oscillation experiments.

hep-ex↗

arXiv2011

Single electron emission in two-phase xenon with application to the detection of coherent neutrino-nucleus scattering

We present an experimental study of single electron emission in ZEPLIN-III, a two-phase xenon experiment built to search for dark matter WIMPs, and discuss applications enabled by the excellent signal-to-noise ratio achieved in detecting this signature. Firstly, we demonstrate a practical method for precise measurement of the free electron lifetime in liquid xenon during normal operation of these detectors. Then, using a realistic detector response model and backgrounds, we assess the feasibility of deploying such an instrument for measuring coherent neutrino-nucleus elastic scattering using the ionisation channel in the few-electron regime. We conclude that it should be possible to measure this elusive neutrino signature above an ionisation threshold of $\sim$3 electrons both at a stopped pion source and at a nuclear reactor. Detectable signal rates are larger in the reactor case, but the triggered measurement and harder recoil energy spectrum afforded by the accelerator source enable lower overall background and fiducialisation of the active volume.

physics.ins-det↗

arXiv2011

Search for the Rare Decays KL->pi0pi0mu+mu- and KL->pi0pi0X0->pi0pi0mu+mu-

The KTeV E799 experiment has conducted a search for the rare decays KL->pi0pi0mu+mu- and KL->pi0pi0X0->pi0pi0mu+mu-, where the X0 is a possible new neutral boson that was reported by the HyperCP experiment with a mass of (214.3 pm 0.5) MeV/c^{2}. We find no evidence for either decay. We obtain upper limits of Br(KL->pi0pi0X0->pi0pi0mu+mu-) < 1.0 x 10^{-10} and Br(KL->pi0pi0mu+mu-) < 9.2 x 10^{-11} at the 90% confidence level. This result rules out the pseudoscalar X0 as an explanation of the HyperCP result under the scenario that the \bar{d}sX0 coupling is completely real.

hep-ex↗

arXiv2011

The ALPS project release 2.0: Open source software for strongly correlated systems

We present release 2.0 of the ALPS (Algorithms and Libraries for Physics Simulations) project, an open source software project to develop libraries and application programs for the simulation of strongly correlated quantum lattice models such as quantum magnets, lattice bosons, and strongly correlated fermion systems. The code development is centered on common XML and HDF5 data formats, libraries to simplify and speed up code development, common evaluation and plotting tools, and simulation programs. The programs enable non-experts to start carrying out serial or parallel numerical simulations by providing basic implementations of the important algorithms for quantum lattice models: classical and quantum Monte Carlo (QMC) using non-local updates, extended ensemble simulations, exact and full diagonalization (ED), the density matrix renormalization group (DMRG) both in a static version and a dynamic time-evolving block decimation (TEBD) code, and quantum Monte Carlo solvers for dynamical mean field theory (DMFT). The ALPS libraries provide a powerful framework for programers to develop their own applications, which, for instance, greatly simplify the steps of porting a serial code onto a parallel, distributed memory machine. Major changes in release 2.0 include the use of HDF5 for binary data, evaluation tools in Python, support for the Windows operating system, the use of CMake as build system and binary installation packages for Mac OS X and Windows, and integration with the VisTrails workflow provenance tool. The software is available from our web server at http://alps.comp-phys.org/.

cond-mat.str-el↗

arXiv2010

Precise Measurements of Direct CP Violation, CPT Symmetry, and Other Parameters in the Neutral Kaon System

We present precise tests of CP and CPT symmetry based on the full dataset of K to pipi decays collected by the KTeV experiment at Fermi National Accelerator Laboratory during 1996, 1997, and 1999. This dataset contains 16 million K to 2pi0 and 69 million K to pi+pi- decays. We measure the direct CP violation parameter Re(epsilon'/epsilon) = (19.2 pm 2.1)x10-4. We find the KL-KS mass difference Deltam = (5270 pm 12)x10^6 hbar/s and the KS lifetime tauS = (89.62 pm 0.05)x10-12 s. We also measure several parameters that test CPT invariance. We find the difference between the phase of the indirect CP violation parameter, epsilon, and the superweak phase, phi_epsilon - phi_SW = (0.40 pm 0.56) degrees. We measure the difference of the relative phases between the CP violating and CP conserving decay amplitudes for K to pi+pi- (phi+-) and for K to 2pi0 (phi00), Delta phi = (0.30 pm 0.35) degrees. From these phase measurements, we place a limit on the mass difference between K0 and K0bar, DeltaM < 4.8 x 10-19 GeV/c^2 at 95% C.L. These results are consistent with those of other experiments, our own earlier measurements, and CPT symmetry.

hep-ex↗

arXiv2008

Search for the Rare Decay K_{L}\toπ^{0}π^{0}γ

The KTeV E799 experiment has conducted a search for the rare decay $K_{L}\toπ^{0}π^{0}γ$ via the topology $K_{L}\toπ^{0}π^{0}_Dγ$ (where $π^0_D\toγe^+e^-$). Due to Bose statistics of the $π^0$ pair and the real nature of the photon, the $K_{L}\toπ^{0}π^{0}γ$ decay is restricted to proceed at lowest order by the CP conserving direct emission (DE) of an E2 electric quadrupole photon. The rate of this decay is interesting theoretically since chiral perturbation theory predicts that this process vanishes at level $O(p^4)$. Therefore, this mode probes chiral perturbation theory at $O(p^6)$. In this paper we report a determination of an upper limit of $2.43\times 10^{-7}$ (90% CL) for $K_{L}\toπ^{0}π^{0}γ$. This is approximately a factor of 20 lower than previous results.

hep-ex↗

arXiv2008

Observation of the Decay Xi^0 --> Sigma^+ mu^- nu(bar)

The Xi^0 muon semi-leptonic decay has been observed for the first time with nine identified events using the KTeV beam line and detector at Fermilab. The decay is normalized to the Xi^0 beta decay mode and yields a value for the ratio of decay rates of $(1.8^{+0.7}_{-0.5}(stat.)\pm0.2(syst.))\times 10^{-2}$. This is in agreement with the SU(3) flavor symmetric quark model.

hep-ex↗