arXiv subjects

Ran Budnik

Publications and source records attributed to Ran Budnik.

7 recordsLinked to original sources

arXiv2025

Atmospheric muon flux suppression at potential new low-radiation underground physics laboratory in Israel

The residual atmospheric muon flux was measured at a candidate site for a new underground, low-radiation physics laboratory beneath the Kokhav HaYarden national park in Israel. Located inside the tunnels of a hydroelectric pumped-storage facility operating since 2024, the proposed site benefits from a vertical rock overburden of 361 meters, large potential floorspace, and easy access by road. A muon hodoscope of vertically stacked wide-area $144 \times 60 \times 1.2 $ cm$^3$ plastic scintillator plates was employed to measure the suppression in the integrated muon flux at the site as compared with above ground at sea level. Data-taking took place in mid-August of 2024 for several days and was split into South-North and West-East orientations to account for the directional acceptances due to the geometry of the detector. The suppression factor is reported at $4456 \pm 77$, expressed as $3.75 \pm 0.06 \times 10^{-6}$ cm$^{-2}$ s$^{-1}$ in absolute terms, corresponding to an effective overburden of roughly $873$ m.w.e.. A deeper location at the site may also be available, but it could not be reached at this time. Furthermore, the asymmetric topography of the mountain above and its muon shadow are clearly visible in the angular data. Finally, auxiliary environmental measurements recorded low background radon activity at $28.3 \pm 14.0$ Bq m$^{-3}$. The experimental campaign thus succeeded in demonstrating the viability of the site's working conditions for future scientific research.

physics.ins-det↗

arXiv2016

Dark Sectors 2016 Workshop: Community Report

This report, based on the Dark Sectors workshop at SLAC in April 2016, summarizes the scientific importance of searches for dark sector dark matter and forces at masses beneath the weak-scale, the status of this broad international field, the important milestones motivating future exploration, and promising experimental opportunities to reach these milestones over the next 5-10 years.

hep-ph↗

arXiv2012

Performance of a cryogenic system prototype for the XENON1T Detector

We have developed an efficient cryogenic system with heat exchange and associated gas purification system, as a prototype for the XENON1T experiment. The XENON1T detector will use about 3 ton of liquid xenon (LXe) at a temperature of 175K as target and detection medium for a dark matter search. In this paper we report results on the cryogenic system performance focusing on the dynamics of the gas circulation-purification through a heated getter, at flow rates above 50 Standard Liter per Minute (SLPM). A maximum flow of 114 SLPM has been achieved, and using two heat exchangers in parallel, a heat exchange efficiency better than 96% has been measured.

physics.ins-det↗

arXiv2010

Fast radiation mediated shocks and supernova shock breakouts

We present a simple analytic model for the structure of non-relativistic and relativistic radiation mediated shocks. At shock velocities β_s\equiv v_s/c\gtrsim 0.1, the shock transition region is far from thermal equilibrium, since the transition crossing time is too short for the production of a black-body photon density (by Bremsstrahlung emission). In this region, electrons and photons (and positrons) are in Compton (pair) equilibrium at temperatures T_s significantly exceeding the far downstream temperature, T_s\gg T_d\approx 2(\varepsilon n_u \hbar^3c^3)^{1/4}. T_s\gtrsim 10 keV is reached at shock velocities β_s\approx 0.2. At higher velocities, β_s\gtrsim0.6, the plasma is dominated in the transition region by e^\pm pairs and 60 keV\lesssim T_s \lesssim 200 keV. We argue that the spectrum emitted during the breaking out of supernova shocks from the stellar envelopes (or the surrounding winds) of Blue Super Giants and Wolf-Rayet stars, which reach β_s>0.1 for reasonable stellar parameters, may include a hard component with photon energies reaching tens or even hundreds of keV. This may account for the X-ray outburst associated with SN2008D, and possibly for other SN-associated outbursts with spectra not extending beyond few 100 keV (e.g. XRF060218/SN2006aj).

astro-ph.HE↗

arXiv2010

Relativistic Radiation Mediated Shocks

The structure of relativistic radiation mediated shocks (RRMS) propagating into a cold electron-proton plasma is calculated and analyzed. A qualitative discussion of the physics of relativistic and non relativistic shocks, including order of magnitude estimates for the relevant temperature and length scales, is presented. Detailed numerical solutions are derived for shock Lorentz factors $Γ_u$ in the range $6\leΓ_u\le30$, using a novel iteration technique solving the hydrodynamics and radiation transport equations (the protons, electrons and positrons are argued to be coupled by collective plasma processes and are treated as a fluid). The shock transition (deceleration) region, where the Lorentz factor $ Γ$ drops from $ Γ_u $ to $ \sim 1 $, is characterized by high plasma temperatures $ T\sim Γm_ec^2 $ and highly anisotropic radiation, with characteristic shock-frame energy of upstream and downstream going photons of a few~$\times\, m_ec^2$ and $\sim Γ^2 m_ec^2$, respectively.Photon scattering is dominated by e$^\pm$ pairs, with pair to proton density ratio reaching $\approx10^2Γ_u$. The width of the deceleration region, in terms of Thomson optical depths for upstream going photons, is large, $Δτ\simΓ_u^2$ ($Δτ\sim1$ neglecting the contribution of pairs) due to Klein Nishina suppression of the scattering cross section. A high energy photon component, narrowly beamed in the downstream direction, with a nearly flat power-law like spectrum, $νI_ν\proptoν^0$, and an energy cutoff at $ \sim Γ_u^2 m_ec^2 $ carries a fair fraction of the energy flux at the end of the deceleration region. An approximate analytic model of RRMS, reproducing the main features of the numerical results, is provided.

astro-ph.HE↗

arXiv2009

The energy production rate & the generation spectrum of UHECRs

We derive simple analytic expressions for the flux and spectrum of ultra-high energy cosmic-rays (UHECRs) predicted in models where the CRs are protons produced by extra-Galactic sources. For a power-law scaling of the CR production rate with redshift and energy, d\dot{n} /dE\propto E^-α(1+z)^m, our results are accurate at high energy, E>10^18.7 eV, to better than 15%, providing a simple and straightforward method for inferring d\dot{n}/dE from the observed flux at E. We show that current measurements of the UHECR spectrum, including the latest Auger data, imply E^2d\dot{n}/dE(z=0)=(0.45\pm0.15)(α-1) 10^44 erg Mpc^-3 yr^-1 at E<10^19.5 eV with αroughly confined to 2\lesseqα<2.7. The uncertainty is dominated by the systematic and statistic errors in the experimental determination of individual CR event energy, (ΔE/E)_{sys} (ΔE/E)_{stat} ~20%. At lower energy, d\dot{n}/dE is uncertain due to the unknown Galactic contribution. Simple models in which α\simeq 2 and the transition from Galactic to extra-Galactic sources takes place at the "ankle", E ~10^19 eV, are consistent with the data. Models in which the transition occurs at lower energies require a high degree of fine tuning and a steep spectrum, α\simeq 2.7, which is disfavored by the data. We point out that in the absence of accurate composition measurements, the (all particle) energy spectrum alone cannot be used to infer the detailed spectral shapes of the Galactic and extra-Galactic contributions.

astro-ph↗

arXiv2004

Low Energy Singlets in the Heisenberg Kagome Antiferromagnet

The spin half Heisenberg antiferromagnet on the Kagome lattice, is mapped by Contractor Renormalization to a Spin-Pseudospin Hamiltonian on the triangular superlattice. Variationally, we find a ground state with columnar dimer order. Dimer orientation fluctuations are described by an effective O(2) model at energies above an exponentially suppressed clock mass scale. Our results explain the large density of low energy singlets observed numerically, and the non magnetic T-squared specific heat observed experimentally.

cond-mat.str-el↗