arXiv subjects

N. Mishra

Publications and source records attributed to N. Mishra.

11 recordsLinked to original sources

arXiv2024

Implications of first neutrino-induced nuclear recoil measurements in direct detection experiments

PandaX-4T and XENONnT have recently reported the first measurement of nuclear recoils induced by the $^8$B solar neutrino flux, through the coherent elastic neutrino-nucleus scattering (CE$\nu$NS) channel. As long anticipated, this is an important milestone for dark matter searches as well as for neutrino physics. This measurement means that these detectors have reached exposures such that searches for low mass, $\lesssim 10$ GeV dark matter cannot be analyzed using the background-free paradigm going forward. It also opens a new era for these detectors to be used as neutrino observatories. In this paper we assess the sensitivity of these new measurements to new physics in the neutrino sector. We focus on neutrino non-standard interactions (NSI) and show that -- despite the still moderately low statistical significance of the signals -- these data already provide valuable information. We find that limits on NSI from PandaX-4T and XENONnT measurements are comparable to those derived using combined COHERENT CsI and LAr data, as well as those including the latest Ge measurement. Furthermore, they provide sensitivity to pure $\tau$ flavor parameters that are not accessible using stopped-pion or reactor sources. With further improvements of statistical uncertainties as well as larger exposures, forthcoming data from these experiments will provide important, novel results for CE$\nu$NS-related physics.

hep-ph↗

arXiv2024

Reactor-based Search for Axion-Like Particles using CsI(Tl) Detector

The absence of conclusive signals in weakly interacting massive particle (WIMP) searches has motivated increased interest in alternative dark matter candidates such as axions and axion-like particles (ALPs), which also provide a solution to the strong CP problem. In this work, we employ a $\sim100~\mathrm{kg}$ scale CsI(Tl)-based detector operated in proximity to a nuclear reactor to achieve a sub-100 DRU (differential rate unit, expressed in counts/keV/kg/day) background level in the MeV energy range through a combination of active veto and passive shielding techniques. Such a low-background environment enables sensitivity to ALPs with axion--photon coupling $g_{a\gamma\gamma} \gtrsim 10^{-6}$ and axion--electron coupling in the range $10^{-8} < g_{aee} < 10^{-4}$ for ALP masses between 1~keV and 10~MeV. These results demonstrate that the experiment has the potential to probe previously unexplored regions of parameter space, including the so-called cosmological triangle in the ALP--photon coupling for MeV-scale ALPs.

hep-ex↗

arXiv2023

Prospects for detecting axionlike particles at the Coherent CAPTAIN-Mills experiment

We show results from the Coherent CAPTAIN Mills (CCM) 2019 engineering run which begin to constrain regions of parameter space for axion-like particles (ALPs) produced in electromagnetic particle showers in an 800 MeV proton beam dump, and further investigate the sensitivity of ongoing data-taking campaigns for the CCM200 upgraded detector. Based on beam-on background estimates from the engineering run, we make realistic extrapolations for background reduction based on expected shielding improvements, reduced beam width, and analysis-based techniques for background rejection. We obtain reach projections for two classes of signatures; ALPs coupled primarily to photons can be produced in the tungsten target via the Primakoff process, and then produce a gamma-ray signal in the Liquid Argon (LAr) CCM detector either via inverse Primakoff scattering or decay to a photon pair. ALPs with significant electron couplings have several additional production mechanisms (Compton scattering, $e^+e^-$ annihilation, ALP-bremsstrahlung) and detection modes (inverse Compton scattering, external $e^+e^-$ pair conversion, and decay to $e^+e^-$). In some regions, the constraint is marginally better than both astrophysical and terrestrial constraints. With the beginning of a three year run, CCM will be more sensitive to this parameter space by up to an order of magnitude for both ALP-photon and ALP-electron couplings. The CCM experiment will also have sensitivity to well-motivated parameter space of QCD axion models. It is only a recent realization that accelerator-based large volume liquid argon detectors designed for low energy coherent neutrino and dark matter scattering searches are also ideal for probing ALPs in the unexplored $\sim$MeV mass scale.

hep-ph↗

arXiv2022

Large-mass, low-threshold sapphire detector for rare event searches

Low mass nuclear recoil dark matter and coherent-elastic-neutrino-nucleus-scattering (CENNS) searches confront similar challenges in choosing ultra-low threshold and large-mass detectors. We report experimental results from the first-of-its-kind 100 g single-crystal sapphire detector design with a diameter of 76 mm and thickness of 4 mm. The detector is designed to be sensitive for low-energy rare interactions with an intention to investigate the low mass region of dark matter phase-space and search for CENNS at the reactor site. Sapphire is a crystal of aluminum oxide (Al2O3) and has been found to be a good candidate for light mass spin-dependent dark matter search experiments due to its lower atomic mass compared to other detector materials such as germanium and silicon. Using the data collected from the test facility at Texas A&M University, we were able to resolve low energy lines from calibration sources and estimated that our newly developed sapphire detector has a baseline recoil energy resolution of 18 eV. These detectors are operated at 0 V with the phonon-assisted detection providing a quenching-free low-threshold operation.

physics.ins-det↗

arXiv2022

A novel active veto prototype detector with an inner target for improved rare event searches

We report the fabrication and performance of an annular, cryogenic, phonon-mediated veto detector that can host an inner target detector, allowing substantial reduction in radiogenic backgrounds for rare event search experiments. A germanium veto detector of mass $\sim$500 g with an outer diameter of 76 mm and an inner diameter of 28 mm was produced. A 25 mm diameter germanium inner target detector of mass $\sim$10 g was mounted inside the veto detector. The detector was designed using inputs from a GEANT4 based simulation, where it was modeled to be sandwiched between two germanium detectors. The simulation showed that the background rates (dominantly gamma interactions) could be reduced by $>$ 90$\%$, and that such an arrangement is sufficient for aggressive background reduction needed for neutrino and dark matter search experiments. During testing at the experimental site the veto detector prototype achieved a baseline resolution of 1.24 $\pm$ 0.02 keV while hosting a functional inner target detector. The baseline resolution of the inner target detector was 147 $\pm$ 2 eV. The detectors were operated at mK temperatures. The experimental results of an identical detector arrangement are in excellent agreement with the simulation.

physics.ins-det↗

arXiv2021

Design and Characterization of a Phonon-Mediated Cryogenic Particle Detector with an eV-Scale Threshold and 100 keV-Scale Dynamic Range

We present the design and characterization of a cryogenic phonon-sensitive 1-gram Si detector exploiting the Neganov-Trofimov-Luke effect to detect single-charge excitations. This device achieved 2.65(2)~eV phonon energy resolution when operated without a voltage bias across the crystal and a corresponding charge resolution of 0.03 electron-hole pairs at 100~V bias. With a continuous-readout data acquisition system and an offline optimum-filter trigger, we obtain a 9.2~eV threshold with a trigger rate of the order of 20~Hz. The detector's energy scale is calibrated up to 120~keV using an energy estimator based on the pulse area. The high performance of this device allows its application to different fields where excellent energy resolution, low threshold, and large dynamic range are required, including dark matter searches, precision measurements of coherent neutrino-nucleus scattering, and ionization yield measurements.

physics.ins-det↗

arXiv2020

2D MoSe2 as a Promising Chemo-resistive Sensor for N2O Detection: A DFT Approach

We have investigated the impact of toxic N2O gas upon structural and electronic properties of 2D MoSe2 monolayer using DFT approach. In this work, as a result of N2O gas absorption, charge transfer, band gap and density of states (DOS) are changed and these parameters are extracted as electronic properties of 2D MoSe2 monolayer nano-gas sensor. Moreover, the band gap is tunable upon the N2O gas absorption for pristine and adsorbed MoSe2 in both Top Mo (Top Se) structures. Also, the spin up and down states in the DOS results considerable magnetic moment altering the magnetic property of the 2D MoSe2 monolayer. Later, the desorption property of the 2D MoSe2 monolayer towards the target N2O gas molecule at three different temperature are calculated. Thus, the paper concludes with outcomes of the structural and electronic properties aligning its behavior as a chemo-resistive nano-gas sensor and showing it as a potential applicant for sensing of toxic N2O gas molecule. The nature of toxic N2O gas molecule is not explored till date using 2D monolayer, thus, in this work it is estimated through simulated results and the experimental verification is awaited.

cond-mat.mtrl-sci↗

arXiv2020

Graphene promotes axon elongation through local stall of Nerve Growth Factor signaling endosomes

Several works reported increased differentiation of neuronal cells grown on graphene; however, the molecular mechanism driving axon elongation on this material has remained elusive. Here, we study the axonal transport of nerve growth factor (NGF), the neurotrophin supporting development of peripheral neurons, as a key player in the time course of axonal elongation of dorsal root ganglion neurons on graphene. We find that graphene drastically reduces the number of retrogradely transported NGF vesicles in favor of a stalled population in the first two days of culture, in which the boost of axon elongation is observed. This correlates with a mutual charge redistribution, observed via Raman spectroscopy and electrophysiological recordings. Furthermore, ultrastructural analysis indicates a reduced microtubule distance and an elongated axonal topology. Thus, both electrophysiological and structural effects can account for graphene action on neuron development. Unraveling the molecular players underneath this interplay may open new avenues for axon regeneration applications.

physics.bio-ph↗

arXiv2019

Going beyond copper: wafer-scale synthesis of graphene on sapphire

The adoption of graphene in electronics, optoelectronics and photonics is hindered by the difficulty in obtaining high quality material on technologically-relevant substrates, over wafer-scale sizes and with metal contamination levels compatible with industrial requirements. To date, the direct growth of graphene on insulating substrates has proved to be challenging, usually requiring metal-catalysts or yielding defective graphene. In this work, we demonstrate a metal-free approach implemented in commercially available reactors to obtain high-quality monolayer graphene on c-plane sapphire substrates via chemical vapour deposition (CVD). We identify via low energy electron diffraction (LEED), low energy electron microscopy (LEEM) and scanning tunneling microscopy (STM) measurements the Al-rich reconstruction root31R9 of sapphire to be crucial for obtaining epitaxial graphene. Raman spectroscopy and electrical transport measurements reveal high-quality graphene with mobilities consistently above 2000 cm2/Vs. We scale up the process to 4-inch and 6-inch wafer sizes and demonstrate that metal contamination levels are within the limits for back-end-of-line (BEOL) integration. The growth process introduced here establishes a method for the synthesis of wafer-scale graphene films on a technologically viable basis.

physics.app-ph↗

arXiv2018

Linear conduction in N-type organic field effect transistors with nanometric channel lengths and graphene as electrodes

In this work we test graphene electrodes in nano-metric channel n-type Organic Field EffectTransistors (OFETs) based on thermally evaporated thin films of perylene-3,4,9,10-tetracarboxylic acid diimide derivative (PDIF-CN2). By a thorough comparison with short channel transistors made with reference gold electrodes, we found that the output characteristics of the graphene-based devices respond linearly to the applied biases, in contrast with the supra-linear trend of gold-based transistors. Moreover, short channel effects are considerably suppressed in graphene electrodes devices. More specifically, current on/off ratios independent of the channel length (L) and enhanced response for high longitudinal biases are demonstrated for L down to ~140 nm. These results are rationalized taking into account the morphological and electronic characteristics of graphene, showing that the use of graphene electrodes may help to overcome the problem of Space Charge Limited Current (SCLC) in short channel OFETs.

physics.app-ph↗

arXiv2016

Radio follow-up of gravitational wave triggers during Advanced LIGO O1

We present radio follow-up observations carried out with the Karl G. Jansky Very Large Array during the first observing run (O1) of the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO). A total of three gravitational wave triggers were followed up during the ~4 months of O1, from September 2015 to January 2016. Two of these triggers, GW150914 and GW151226, are binary black hole merger events of high significance. A third trigger, G194575, was subsequently declared as an event of no interest (i.e., a false alarm). Our observations targeted selected optical transients identified by the intermediate Palomar Transient Factory (iPTF) in the Advanced LIGO error regions of the three triggers, and a limited region of the gravitational wave localization area of G194575 not accessible to optical telescopes due to Sun constraints, where a possible high-energy transient was identified. No plausible radio counterparts to GW150914 and GW151226 were found, in agreement with expectations for binary black hole mergers. We show that combining optical and radio observations is key to identifying contaminating radio sources that may be found in the follow-up of gravitational wave triggers, such as emission associated to star formation and AGN. We discuss our results in the context of the theoretical predictions for radio counterparts to gravitational wave transients, and describe our future plans for the radio follow-up of Advanced LIGO (and Virgo) triggers.

astro-ph.HE↗