arXiv subjects

T. Le

Publications and source records attributed to T. Le.

53 records · Page 3Linked to original sources

arXiv2016

Evidence for neutral-current diffractive neutral pion production from hydrogen in neutrino interactions on hydrocarbon

The MINERvA experiment observes an excess of events containing electromagnetic showers relative to the expectation from Monte Carlo simulations in neutral-current neutrino interactions with mean beam energy of 4.5 GeV on a hydrocarbon target. The excess is characterized and found to be consistent with neutral-current neutral pion production with a broad energy distribution peaking at 7 GeV and a total cross section of 0.26 +- 0.02 (stat) +- 0.08 (sys) x 10^{-39} cm^{2}. The angular distribution, electromagnetic shower energy, and spatial distribution of the energy depositions of the excess are consistent with expectations from neutrino neutral-current diffractive neutral pion production from hydrogen in the hydrocarbon target. These data comprise the first direct experimental observation and constraint for a reaction that poses an important background process in neutrino oscillation experiments searching for muon neutrino to electron neutrino oscillations.

hep-ex↗

arXiv2016

Measurement of $K^{+}$ production in charged-current $ν_μ$ interactions

Production of K^{+} mesons in charged-current ν_μ interactions on plastic scintillator (CH) is measured using MINERvA exposed to the low-energy NuMI beam at Fermilab. Timing information is used to isolate a sample of 885 charged-current events containing a stopping K^{+} which decays at rest. The differential cross section in K^{+} kinetic energy, dσ/dT_{K}, is observed to be relatively flat between 0 and 500 MeV. Its shape is in good agreement with the prediction by the \textsc{genie} neutrino event generator when final-state interactions are included, however the data rate is lower than the prediction by 15\%.

hep-ex↗

arXiv2016

First evidence of coherent $K^{+}$ meson production in neutrino-nucleus scattering

Neutrino-induced charged-current coherent kaon production, $ν_μA\rightarrowμ^{-}K^{+}A$, is a rare, inelastic electroweak process that brings a $K^+$ on shell and leaves the target nucleus intact in its ground state. This process is significantly lower in rate than neutrino-induced charged-current coherent pion production, because of Cabibbo suppression and a kinematic suppression due to the larger kaon mass. We search for such events in the scintillator tracker of MINERvA by observing the final state $K^+$, $μ^-$ and no other detector activity, and by using the kinematics of the final state particles to reconstruct the small momentum transfer to the nucleus, which is a model-independent characteristic of coherent scattering. We find the first experimental evidence for the process at $3σ$ significance.

hep-ex↗

arXiv2016

Neutrino Flux Predictions for the NuMI Beam

Knowledge of the neutrino flux produced by the Neutrinos at the Main Injector (NuMI) beamline is essential to the neutrino oscillation and neutrino interaction measurements of the MINERvA, MINOS+, NOvA and MicroBooNE experiments at Fermi National Accelerator Laboratory. We have produced a flux prediction which uses all available and relevant hadron production data, incorporating measurements of particle production off of thin targets as well as measurements of particle yields from a spare NuMI target exposed to a 120 GeV proton beam. The result is the most precise flux prediction achieved for a neutrino beam in the one to tens of GeV energy region. We have also compared the prediction to in situ measurements of the neutrino flux and find good agreement.

hep-ex↗

arXiv2016

Measurement of Neutrino Flux from Neutrino-Electron Elastic Scattering

Muon-neutrino elastic scattering on electrons is an observable neutrino process whose cross section is precisely known. Consequently a measurement of this process in an accelerator-based $ν_μ$ beam can improve the knowledge of the absolute neutrino flux impinging upon the detector; typically this knowledge is limited to $\sim$ 10% due to uncertainties in hadron production and focusing. We have isolated a sample of 135 $\pm$ 17 neutrino-electron elastic scattering candidates in the segmented scintillator detector of MINERvA, after subtracting backgrounds and correcting for efficiency. We show how this sample can be used to reduce the total uncertainty on the NuMI $ν_μ$ flux from 9% to 6%. Our measurement provides a flux constraint that is useful to other experiments using the NuMI beam, and this technique is applicable to future neutrino beams operating at multi-GeV energies.

physics.ins-det↗

arXiv2015

Single neutral pion production by charged-current $\barν_μ$ interactions on hydrocarbon at $\langle E_ν\rangle = $ 3.6 GeV

Single neutral pion production via muon antineutrino charged-current interactions in plastic scintillator (CH) is studied using the \minerva detector exposed to the NuMI low-energy, wideband antineutrino beam at Fermilab. Measurement of this process constrains models of neutral pion production in nuclei, which is important because the neutral-current analog is a background for $\barν_e$ appearance oscillation experiments. The differential cross sections for $π^0$ momentum and production angle, for events with a single observed $π^0$ and no charged pions, are presented and compared to model predictions. These results comprise the first measurement of the $π^0$ kinematics for this process.

hep-ex↗

arXiv2015

Charged Pion Production in $ν_μ$ Interactions on Hydrocarbon at $\langle E_ν\rangle$= 4.0 GeV

Charged pion production via charged current $ν_μ$ interactions on plastic (CH) is studied using the MINERvA detector exposed to the NuMI wideband neutrino beam at Fermilab. Events with hadronic invariant mass W $<$ 1.4 GeV are selected to isolate single pion production, which is expected to occur primarily through the $Δ(1232)$ resonance. Cross sections as functions of pion production angle and kinetic energy are reported and compared to predictions from different theoretical calculations and generator-based models, for neutrinos ranging in energy from 1.5 GeV to 10 GeV. The data are best described by calculations which include significant contributions from pion intranuclear rescattering. These measurements constrain the primary interaction rate and the role of final state interactions in pion production, both of which need to be well understood by neutrino oscillation experiments.

hep-ex↗

arXiv2015

MINERvA neutrino detector response measured with test beam data

The MINERvA collaboration operated a scaled-down replica of the solid scintillator tracking and sampling calorimeter regions of the MINERvA detector in a hadron test beam at the Fermilab Test Beam Facility. This article reports measurements with samples of protons, pions, and electrons from 0.35 to 2.0 GeV/c momentum. The calorimetric response to protons, pions, and electrons are obtained from these data. A measurement of the parameter in Birks' law and an estimate of the tracking efficiency are extracted from the proton sample. Overall the data are well described by a Geant4-based Monte Carlo simulation of the detector and particle interactions with agreements better than 4%, though some features of the data are not precisely modeled. These measurements are used to tune the MINERvA detector simulation and evaluate systematic uncertainties in support of the MINERvA neutrino cross section measurement program.

physics.ins-det↗

arXiv2015

Measurement of muon plus proton final states in $ν_μ$ Interactions on Hydrocarbon at $\langle$$E_ν$$\rangle$ = 4.2 GeV

A study of charged-current muon neutrino scattering on hydrocarbon in which the final state includes a muon and a proton and no pions is presented. Although this signature has the topology of neutrino quasielastic scattering from neutrons, the event sample contains contributions from both quasielastic and inelastic processes where pions are absorbed in the nucleus. The analysis accepts events with muon production angles up to 70$^{\circ}$ and proton kinetic energies greater than 110 MeV. The extracted cross section, when based completely on hadronic kinematics, is well-described by a simple relativistic Fermi gas nuclear model including the neutrino event generator modeling for inelastic processes and particle transportation through the nucleus. This is in contrast to the quasielastic cross section based on muon kinematics, which is best described by an extended model that incorporates multi-nucleon correlations. This measurement guides the formulation of a complete description of neutrino-nucleus interactions that encompasses the hadronic as well as the leptonic aspects of this process.

hep-ex↗

arXiv2015

Measurement of Ratios of $ν_μ$ Charged-Current Cross Sections on C, Fe, and Pb to CH at Neutrino Energies 2-20 GeV

We present measurements of $ν_μ$ charged-current cross section ratios on carbon, iron, and lead relative to a scintillator (CH) using the fine-grained MINERvA detector exposed to the NuMI neutrino beam at Fermilab. The measurements utilize events of energies $2 =8~GeV$, which have a reconstructed $μ^{-}$ scattering angle less than $17^\circ$ to extract ratios of inclusive total cross sections as a function of neutrino energy $E_ν$ and flux-integrated differential cross sections with respect to the Bjorken scaling variable $x$. These results provide the first high-statistics direct measurements of nuclear effects in neutrino scattering using different targets in the same neutrino beam. Measured cross section ratios exhibit a relative depletion at low $x$ and enhancement at large $x$. Both become more pronounced as the nucleon number of the target nucleus increases. The data are not reproduced by GENIE, a conventional neutrino-nucleus scattering simulation, or by the alternative models for the nuclear dependence of inelastic scattering that are considered.

hep-ex↗

arXiv2014

Measurement of Coherent Production of $π^\pm$ in Neutrino and Anti-Neutrino Beams on Carbon from $E_ν$ of $1.5$ to $20$ GeV

Neutrino-induced coherent charged pion production on nuclei, $\stackrel{(-)}ν_μA\toμ^\pmπ^\mp A$ is a rare, inelastic interaction in which a small squared four-momentum $| t|$ is transferred to the recoil nucleus leaving it intact in the reaction. In the scintillator tracker of MINERvA, we remove events with evidence of particles from nuclear breakup and reconstruct $| t|$ from the final state pion and muon. We select low $| t|$ events to isolate a sample rich in coherent candidates. By selecting low $| t|$ events we produce a model-independent measurement of the differential cross section for coherent scattering of neutrinos and anti-neutrinos on carbon. We find poor agreement with the predicted kinematics in neutrino generators used by current oscillation experiments.

hep-ex↗

arXiv2014

Measurement of Muon Antineutrino Quasi-Elastic Scattering on a Hydrocarbon Target at E_ν ~ 3.5 GeV

We have isolated muon anti-neutrino charged-current quasi-elastic interactions occurring in the segmented scintillator tracking region of the MINERvA detector running in the NuMI neutrino beam at Fermilab. We measure the flux-averaged differential cross-section, dσ/dQ^2, and compare to several theoretical models of quasi-elastic scattering. Good agreement is obtained with a model where the nucleon axial mass, M_A, is set to 0.99 GeV/c^2 but the nucleon vector form factors are modified to account for the observed enhancement, relative to the free nucleon case, of the cross-section for the exchange of transversely polarized photons in electron-nucleus scattering. Our data at higher Q^2 favor this interpretation over an alternative in which the axial mass is increased.

hep-ex↗

arXiv2014

Measurement of Muon Neutrino Quasi-Elastic Scattering on a Hydrocarbon Target at E_ν ~ 3.5 GeV

We report a study of muon neutrino charged-current quasi-elastic events in the segmented scintillator inner tracker of the MINERvA experiment running in the NuMI neutrino beam at Fermilab. The events were selected by requiring a μ^- and low calorimetric recoil energy separated from the interaction vertex. We measure the flux-averaged differential cross-section, dσ/dQ^2, and study the low energy particle content of the final state. Deviations are found between the measured dσ/dQ^2 and the expectations of a model of independent nucleons in a relativistic Fermi gas. We also observe an excess of energy near the vertex consistent with multiple protons in the final state.

hep-ex↗

arXiv2012

Demonstration of Communication using Neutrinos

Beams of neutrinos have been proposed as a vehicle for communications under unusual circumstances, such as direct point-to-point global communication, communication with submarines, secure communications and interstellar communication. We report on the performance of a low-rate communications link established using the NuMI beam line and the MINERvA detector at Fermilab. The link achieved a decoded data rate of 0.1 bits/sec with a bit error rate of 1% over a distance of 1.035 km, including 240 m of earth.

hep-ex↗

arXiv2007

Correlation of Photon and Neutrino Fluxes in Blazars and Gamma Ray Bursts

Relativistic black-hole jet sources are leading candidates for high energy (>> TeV) neutrino production. The relations defining (a) efficient photopion losses of cosmic-ray protons on target photons and (b) gamma-gamma opacity of gamma rays through that same target photon field imply clear multiwavelength predictions for when and at what energies blazars and GRBs should be most neutrino bright and gamma-ray dim. The use of multiwavelength observations to test the standard relativistic jet model for these source is illustrated.

astro-ph↗

arXiv2006

Time-Dependent Stochastic Particle Acceleration in Astrophysical Plasmas: Exact Solutions Including Momentum-Dependent Escape

Stochastic acceleration of charged particles due to interactions with magnetohydrodynamic (MHD) plasma waves is the dominant process leading to the formation of the high-energy electron and ion distributions in a variety of astrophysical systems. Collisions with the waves influence both the energization and the spatial transport of the particles, and therefore it is important to treat these two aspects of the problem in a self-consistent manner. We solve the representative Fokker-Planck equation to obtain a new, closed-form solution for the time-dependent Green's function describing the acceleration and escape of relativistic ions interacting with Alfven or fast-mode waves characterized by momentum diffusion coefficient $D(p)\propto p^q$ and mean particle escape timescale $t_esc(p) \propto p^{q-2}$, where $p$ is the particle momentum and $q$ is the power-law index of the MHD wave spectrum. In particular, we obtain solutions for the momentum distribution of the ions in the plasma and also for the momentum distribution of the escaping particles, which may form an energetic outflow. The general features of the solutions are illustrated via examples based on either a Kolmogorov or Kraichnan wave spectrum. The new expressions complement the results obtained by Park and Petrosian, who presented exact solutions for the hard-sphere scattering case ($q=2$) in addition to other scenarios in which the escape timescale has a power-law dependence on the momentum. Our results have direct relevance for models of high-energy radiation and cosmic-ray production in astrophysical environments such as $γ$-ray bursts, active galaxies, and magnetized coronae around black holes.

astro-ph↗

arXiv2000

The Origin of the X-ray and Ultraviolet Emission in NGC 7469

We present a spectral analysis of a 30d, near-continuous observation of the Seyfert 1 galaxy NGC 7469 with RXTE. Daily integrations show strong spectral changes during the observation. Ourmain result is that we find the X-ray spectral index to be correlated with the UV flux. Furthermore, the broad-band X-ray photon flux is also correlated with the UV continuum. These correlations point towards a model in which the X-rays originate via thermal Comptonization of UV seed photons. Furthermore, the UV is also correlated with the extrapolation of the X-ray power law into the soft X-ray/EUV region. Our data analysis therefore re-opens the possibility the the UV photons and their variability arise from reprocessing, as long as the primary source of heating is photo-electric absorption in the reprocessor, rather than Compton downscattering, A coherent picture of the X-ray/UV variability can therefore be constructed whereby absorption and reprocessing of EUV/soft X-rays in a standard accretion disk produce a variable seed photon distribution which are in turn up-scattered into the X-ray band. We also find a significant correlation between the 2-10 keV flux and the 6.4 keV iron K-line suggesting that at least some portion of the line originates within ~1 lt day of the X-ray continuum source. Neither the power law photon index nor the Compton reflection component are correlated with the 2-10 keV flux. The latter is not correlated with the iron K line flux either. We do find an apparent correlation between the X-ray spectral index and the strength of the Compton reflection component. In an Appendix we show, however, that this can be produced by a combination of statistical and systematic errors. We conclude the apparent variations in the Compton reflection component may be an artifact of these effects.

astro-ph↗