arXiv subjects

S. R. Mishra

Publications and source records attributed to S. R. Mishra.

At least 19 recordsLinked to original sources

arXiv2025

Search for Accelerator-Produced Sub-GeV Dark Matter with the NOvA Near Detector

The NuMI facility at Fermilab produces a high-intensity beam of muon neutrinos and antineutrinos, designed to study neutrino oscillations. This beam may also be a source of dark matter particles produced through a light mediator. We search for dark matter particles with masses between 1 and 200 MeV that interact with Standard Model particles via a vector portal, producing forward-scattered single-electron events in the NOvA near detector. We set limits on the dark-visible coupling based on an exposure of 2.55x10^21 protons of 120 GeV energy on the NuMI target. For the dark matter mass range 10-20 MeV, this analysis sets the tightest constraints on the coupling to date.

hep-ex↗

arXiv2025

Spatio-temporal Monte Carlo modeling of loading and decay dynamics in an optical dipole trap

Here, we present our studies on intra-trap dynamics of an optical dipole trap (ODT) loaded from a Magneto-optical trap (MOT) of $^{87}$Rb atoms. A spatio-temporal Monte Carlo (MC) simulation approach has been employed in conjunction with the semi-classical theory based calculations for estimation of various intra-trap two-body loss parameters in the ODT. The temporal MC method based on estimated parameters from spatial MC, gives a close estimation of the experimentally observed atom-number evolution in ODT. We also find that, the decay rate of atoms in an ODT is dominated by momentum-transfer elastic collisions in the absence of MOT beams. However, in presence of MOT beams, the radiative escape process is the dominant two-body loss mechanism in the trap, which surpasses the fine-structure changing and hyperfine changing collisional losses by nearly an order of magnitude.

physics.atom-ph↗

arXiv2025

On damping of Rabi oscillations in two-photon Raman excitation in cold $^{87}$Rb atoms

Two-photon Raman excitation between the ground hyperfine states $|5 \ ^2S_{1/2}, F = 2\rangle$ and $|5 \ ^2S_{1/2}, F = 1\rangle$ of $^{87}$Rb atom has been experimentally studied. The Rabi coupling strengths of various transition involved have been calculated in presence of a weak magnetic field. A density matrix formalism has been developed to understand the experimentally observed damping of Rabi oscillations of population in a hyperfine state of $^{87}$Rb atom during interaction with the Raman laser beams. The observed damping of Rabi oscillations has been attributed to the dephasing during the light atom interaction.

physics.atom-ph↗

arXiv2024

A Novel Approach to Neutrino-Hydrogen Measurements

The limited statistics of the available (anti)neutrino-hydrogen (H) interactions has been a longstanding impediment for high-energy neutrino physics. We discuss a practical way to achieve accurate (anti)neutrino-hydrogen measurements, addressing the principal limitations of earlier experiments. Interactions on hydrogen are extracted by subtracting measurements on thin dedicated graphite (pure C) and polypropylene (CH$_2$) targets within a highly segmented low-density detector. A kinematic selection is used to increase the purities to 80-95\% before subtraction. A statistics of ${\cal O}(10^6)$ can be realistically achieved in modern neutrino beams for the various $ν(\bar ν)$-H event topologies. The availability of such samples would allow a precise determination of neutrino and antineutrino fluxes, as well as to directly constrain nuclear effects from a comparison with corresponding measurements on heavy materials within the same detector. The (anti)neutrino fluxes and the nuclear smearing are typically the leading sources of systematic uncertainties in long-baseline oscillation experiments. (Anti)neutrino-hydrogen interactions also provide an ideal tool for a wide range of precision tests of fundamental interactions.

hep-ph↗

arXiv2024

Measurement of gravitational acceleration in a single laser operated atomic fountain

We present measurements on Earth's gravitational acceleration (g) using an in-house developed cold atom gravimeter (CAG) in an atomic fountain geometry. In the setup, the laser cooled $^{87}Rb$ atoms are launched vertically up in the fountain geometry and Doppler sensitive two-photon Raman pulse atom interferometry is applied to detect the gravitational acceleration experienced by the atoms. Using our gravimeter setup, we have measured the local value of 'g' in our laboratory with sensitivity of 621 $μ$Gal for integration time of 1350 s.

physics.atom-ph↗

arXiv2024

On trapping geometry for cold atoms in a radio-frequency (rf) dressed potential

We have investigated the atom trapping geometry for trapping of $^{87}{Rb}$ atoms in a radio-frequency (rf) dressed potential generated after superposing a strong linearly polarized rf-field on a static magnetic trap. For this, laser cooled atoms in a magneto-optical trap (MOT) in an ultra-high vacuum (UHV) chamber (pressure $\sim$ 1.5 $\times$ $10^{-10}$ Torr) were trapped in a quadrupole magnetic trap and evaporatively cooled before transferring them to the rf-dressed potential. The experimentally observed hollow shell type atom trapping geometry has been explained by theoretical modelling of the trapping potential.

physics.atom-ph↗

arXiv2024

Pulsed loading of a magneto-optical trap on atom chip for fast pressure recovery in ultrahigh vacuum environment

This study presents investigations on pulsed loading of a magneto-optical trap (MOT) on an atom chip in an UHV environment. Using three parallel resistively heated Rb-metal dispensers activated by pulsed current supply, approximately 3.0 $\times$ $10^{7}$ cold $^{87}Rb$ atoms were loaded into the MOT. A current pulse of $\sim$ 24 A with duration of $\sim$ 10 s raised the pressure in the chamber from 2.0 $\times$ $10^{-10}$ Torr to 3.3 $\times$ $10^{-10}$ Torr. Remarkably, the pressure recovery time after switching off the dispensers current was found to be $\sim$ 600 ms, making a significant advancement in achieving fast recovery of UHV environment surrounding the MOT region. This study is very useful for laser cooling and magnetic trapping / evaporative cooling of atoms on atom chip in the same UHV chamber.

physics.atom-ph↗

arXiv2023

Development of a pyramidal magneto-optical trap for pressure sensing application

Here, we report the development and working of a compact rubidium (Rb) atom magneto-optical trap (MOT) operated with a hollow pyramidal mirror and a single laser beam. This type of compact MOT is suitable for developing portable atom-optic devices, as it works with less number of optical components as compared to conventional MOT setup. The application of this compact MOT setup for pressure sensing has been demonstrated.

physics.atom-ph↗

arXiv2023

Ultra-high vacuum pressure measurement using cold atoms

In this work, we have measured the background pressure in an ultra-high vacuum (UHV) chamber by measuring the collisional loss rates in a Rb atom magneto-optical trap (MOT) on an atom chip. The loss rate due to non-Rb gases in the background has been estimated by measuring the MOT loss rate in low Rb pressure regime. These results can be useful for development of cold-atoms based UHV pressure standards.

physics.atom-ph↗

arXiv2022

A compact setup for loading magneto-optical trap in ultrahigh vacuum environment

We have developed a compact setup which enables loading a magneto-optical trap (MOT) in ultra-high vacuum (UHV) environment. Nearly $1 \times 10^{8}$ atoms of $^{87}Rb$ are trapped in the MOT at $\sim 2 \times 10^{-10}$ Torr base pressure in the chamber. After the MOT loading, we have successfully demonstrated working of quadrupole magnetic trap in this chamber with a lifetime of $\sim 8 $ s

physics.atom-ph↗

arXiv2022

Efficient quantum state preparation using Stern-Gerlach effect on cold atoms

The Zeeman hyperfine state dependent force in a Stern-Gerlach (SG) experiment has been exploited to separate and detect atoms having different Zeeman hyperfine states in a cold atom cloud. Utilizing this SG technique, we have made the quantitative estimate of atoms in different Zeeman hyperfine states in an atom cloud, which has been helpful in optimizing the optical pumping of atoms for efficient preparation of atomic state. Employing an optimized optical pumping, nearly $92 \% $ of cold $^{87}Rb$ atoms from a grey magneto-optical trap (G-MOT) on atom-chip have been optically pumped to the trappable Zeeman hyperfine state $\ket{F=2, \, m_{F} = +2}$. These optically pumped atoms have been trapped in an Ioffe-Pritchard magnetic trap near the atom-chip surface.

physics.atom-ph↗

arXiv2021

Different atom trapping geometries with time averaged adiabatic potentials

In this article, we have theoretically studied the time averaged adiabatic potential (TAAP) scheme for realizing different atom trapping geometries. It is shown that by varying time orbiting potential (TOP) fields and radio frequency (rf) fields parameters, controlled manipulation of trapping potentials, and conversion from one trapping geometry to another, is possible. The proposed trapping geometries can be useful for studying various atom-optic phenomena such as Bose-Einstein condensation (BEC) in low dimensions, super-fluidity, tunnelling, atom interferometry, etc.

physics.atom-ph↗

arXiv2020

Search for sterile neutrinos in MINOS and MINOS+ using a two-detector fit

A search for mixing between active neutrinos and light sterile neutrinos has been performed by looking for muon neutrino disappearance in two detectors at baselines of 1.04 km and 735 km, using a combined MINOS and MINOS+ exposure of $16.36\times10^{20}$ protons-on-target. A simultaneous fit to the charged-current muon neutrino and neutral-current neutrino energy spectra in the two detectors yields no evidence for sterile neutrino mixing using a 3+1 model. The most stringent limit to date is set on the mixing parameter $\sin^2θ_{24}$ for most values of the sterile neutrino mass-splitting $Δm^2_{41} > 10^{-4}$ eV$^2$.

hep-ex↗

arXiv2019

On continuous loading of a U-magneto-optical trap (U-MOT) on atom-chip in ultra high vacuum

Here, we report our studies on the continuous loading of a U-magneto-optical trap (U-MOT) on atom-chip from background rubidium (Rb) vapor generated using a dispenser source in ultra high vacuum (UHV) environment. Using the U-MOT loading curves, the partial pressure due to Rb vapor and pressure due to background gas have been estimated near the MOT cloud position. The estimated pressure due to Rb vapor increased from $\sim \; 1.4 \times 10^{-10}$ Torr to $ \sim \; 4.1 \times 10^{-9} $ Torr as Rb-dispenser current was increased from 2.8 to 3.4 A. The increase in dispenser current also resulted in decrease in loading as well as lifetime of the MOT cloud. This study is useful for magnetic trapping experiments where accurate information of pressure in chamber is important for the lifetime of the magnetic trap.

physics.atom-ph↗

arXiv2019

A Precise Determination of (Anti)neutrino Fluxes with (Anti)neutrino-Hydrogen Interactions

We present a novel method to accurately determine the flux of neutrinos and antineutrinos, one of the dominant systematic uncertainty affecting current and future long-baseline neutrino experiments, as well as precision neutrino scattering experiment. Using exclusive topologies in $ν(\bar ν)$-hydrogen interactions, $ν_μp \to μ^- p π^+$, $\bar ν_μp \to μ^+ p π^-$, and $\bar ν_μp \to μ^+ n$ with small hadronic energy, we achieve an overall accuracy on the relative fluxes better than 1\% in the energy range covering most of the available flux. Since we cannot rely on simulations nor model corrections at this level of precision, we present techniques to constrain all relevant systematic uncertainties using data themselves. The method can be implemented using the approach we recently proposed to collect high statistics samples of $ν(\bar ν)$-hydrogen interactions in a low-density and high-resolution detector, which could serve as part of the near detector complex in a long-baseline neutrino experiment, as well as a dedicated beam monitoring detector.

hep-ph↗

arXiv2019

Observation of dual electromagnetically induced transparencies in cold $^{87}Rb$ atoms

We have observed two dual electromagnetically induced transparency (EIT) spectra in probe transmission through cold $^{87}Rb$ atoms trapped in a magneto-optical trap (MOT). These dual EIT peaks are generated in two different N-systems formed by probe, coupling and control beams interacting with different levels in $D_{2}$ line transitions of $^{87}Rb$ atom. The dependence of spectral features of two N-systems on driving beams (\textit{i.e.} coupling and control beams) strength and detuning has been investigated. The results show that the dual EIT spectral features in both the N-systems can be manipulated by varying the strength and detuning of both the driving beams. The two N-systems have been modelled theoretically using a density matrix formalism and results have shown a reasonable agreement with the experimental observations.

physics.atom-ph↗

arXiv2018

Spectral characteristics of a modified inverted-Y system beyond rotating wave approximation

The spectral properties of a multilevel atomic system interacting with multiple electromagnetic fields, a modified inverted-Y system, have been theoretically investigated. In this study, a numerical matrix propagation method has been employed to study the spectral characteristics beyond the validity regime of the rotating wave approximations. The studied atomic system, comprising of several basic sub-systems i.e. lambda, ladder, vee, N and inverted-Y, is useful to study the interdependence among these basic sub-systems. The key features of the obtained probe spectra as a function of coupling strength and detuning of the associated electromagnetic fields show inter-conversion, splitting and shifting of the transparency and absorption peaks. The dressed and doubly dressed state formalism have been utilized to explain the numerically obtained results. This study has application in design of novel optical devices capable of multi-channel optical communication along with switching.

physics.atom-ph↗

arXiv2018

New constraints on oscillation parameters from $ν_e$ appearance and $ν_μ$ disappearance in the NOvA experiment

We present updated results from the NOvA experiment for $ν_μ\rightarrowν_μ$ and $ν_μ\rightarrowν_e$ oscillations from an exposure of $8.85\times10^{20}$ protons on target, which represents an increase of 46% compared to our previous publication. The results utilize significant improvements in both the simulations and analysis of the data. A joint fit to the data for $ν_μ$ disappearance and $ν_e$ appearance gives the best fit point as normal mass hierarchy, $Δm^2_{32} = 2.44\times 10^{-3}{{\rm eV}^2}/c^4$, $\sin^2θ_{23} = 0.56$, and $δ_{CP} = 1.21π$. The 68.3% confidence intervals in the normal mass hierarchy are $Δm^2_{32} \in [2.37,2.52]\times 10^{-3}{{\rm eV}^2}/c^4$, $\sin^2θ_{23} \in [0.43,0.51] \cup [0.52,0.60]$, and $δ_{CP} \in [0,0.12π] \cup [0.91π,2π]$. The inverted mass hierarchy is disfavored at the 95% confidence level for all choices of the other oscillation parameters.

hep-ex↗