We provide an updated assessment of the power of the Cherenkov Telescope Array (CTA) to search for thermally produced dark matter at the TeV scale, via the associated gamma-ray signal from ...pair-annihilating dark matter particles in the region around the Galactic centre. We find that CTA will open a new window of discovery potential, significantly extending the range of robustly testable models given a standard cuspy profile of the dark matter density distribution. Importantly, even for a cored profile, the projected sensitivity of CTA will be sufficient to probe various well-motivated models of thermally produced dark matter at the TeV scale. This is due to CTA's unprecedented sensitivity, angular and energy resolutions, and the planned observational strategy. The survey of the inner Galaxy will cover a much larger region than corresponding previous observational campaigns with imaging atmospheric Cherenkov telescopes. CTA will map with unprecedented precision the large-scale diffuse emission in high-energy gamma rays, constituting a background for dark matter searches for which we adopt state-of-the-art models based on current data. Throughout our analysis, we use up-to-date event reconstruction Monte Carlo tools developed by the CTA consortium, and pay special attention to quantifying the level of instrumental systematic uncertainties, as well as background template systematic errors, required to probe thermally produced dark matter at these energies. "Full likelihood tables complementing our analysis are provided here https://doi.org/10.5281/zenodo.4057987 "
We report on the lowest-frequency detection to date of three bursts from the fast radio burst FRB 180916, observed at 328 MHz with the Sardinia Radio Telescope (SRT). The SRT observed the periodic ...repeater FRB 180916 for five days from 2020 February 20 to 24 during a time interval of active radio bursting, and detected the three bursts during the first hour of observations; no more bursts were detected during the remaining ~ 30 hours. Simultaneous SRT observations at 1548 MHz did not detect any bursts. Burst fluences are in the range 37 to 13 Jy ms. No relevant scattering is observed for these bursts. We also present the results of the multi-wavelength campaign we performed on FRB 180916, during the five days of the active window. Simultaneously with the SRT observations, others with different time spans were performed with the Northern Cross at 408 MHz, with XMM-Newton, NICER, INTEGRAL, AGILE, and with the TNG and two optical telescopes in Asiago, which are equipped with fast photometers. XMM-Newton obtained data simultaneously with the three bursts detected by the SRT, and determined a luminosity upper limit in the 0.3-10 keV energy range of ~\(10^{45}\) erg/s for the burst emission. AGILE obtained data simultaneously with the first burst and determined a fluence upper limit in the MeV range for millisecond timescales of \( 10^{-8}\) erg cm\(^{-2}\).Our results show that absorption from the circumburst medium does not significantly affect the emission from FRB 180916, thus limiting the possible presence of a superluminous supernova around the source, and indicate that a cutoff for the bursting mechanism, if present, must be at lower frequencies. Our multi-wavelength campaign sensitively constrains the broadband emission from FRB 180916, and provides the best limits so far for the electromagnetic response to the radio bursting of this remarkable source of fast radio bursts.
We examine properties of $t\overline{t}$ candidate events in lepton + jets final states to establish the helicities of W bosons in $t\rightarrow$W+b$ decays. Our analysis is based on a direct ...calculation of a probability density for each event to correspond to a $t\overline{t}$ final state, as a function of the helicity of the $W$ boson. Using the 125 events/pb of data collected by the D0 experiment at the Fermilab Tevatron $p\overline{p}$ Collider at $\sqrt{s}$=1.8 TeV, we obtain a longitudinal helicity fraction $F_0$=0.56$\pm$0.31, consistent with the prediction of $F_0$=0.70 from the standard model.
A search for narrow resonances that decay into t-tbar pairs has been performed using 130 pb^{-1} of data in the lepton+jets channel collected in p-pbar collisions at \sqrt{s} = 1.8 TeV. There is no ...significant deviation observed from the standard model, and upper limits at the 95 % confidence level on the product of the production cross section and branching fraction to t-tbar are presented for narrow resonances as a function of the resonance mass M_X. These limits are used to exclude the existence of a leptophobic topcolor particle with mass M_X < 560 GeV/c^2 and width \Gamma_X = 0.012 M_X.
Using 85.2 +/- 3.6 pb^-1 of p-pbar collisions collected at sqrt(s)=1.8 TeV with the D0 detector at Fermilab's Tevatron Collider, we present the results of a search for direct pair production of ...scalar top quarks ~t, the supersymmetric partners of the top quark. We examined events containing two or more jets and missing transverse energy, the signature of light scalar top quark decays to charm quarks and neutralinos. After selections, we observe 27 events while expecting 31.1 +/- 6.4 events from known standard model processes. Comparing these results to next-to-leading-order production cross sections, we exclude a significant region of ~t and neutralino phase space. In particular, we exclude the ~t mass m_~t < 122 GeV/c^2 for a neutralino mass of 45 GeV/c^2.
Trans-Neptunian objects (TNOs) and Centaurs are remnants of our planetary system formation, and their physical properties have invaluable information for evolutionary theories. Stellar occultation is ...a ground-based method for studying these small bodies and has presented exciting results. These observations can provide precise profiles of the involved body, allowing an accurate determination of its size and shape. The goal is to show that even single-chord detections of TNOs allow us to measure their milliarcsecond astrometric positions in the reference frame of the Gaia second data release (DR2). Accurated ephemerides can then be generated, allowing predictions of stellar occultations with much higher reliability. We analyzed data from stellar occultations to obtain astrometric positions of the involved bodies. The events published before the Gaia era were updated so that the Gaia DR2 catalog is the reference. Previously determined sizes were used to calculate the position of the object center and its corresponding error with respect to the detected chord and the International Celestial Reference System (ICRS) propagated Gaia DR2 star position. We derive 37 precise astrometric positions for 19 TNOs and 4 Centaurs. Twenty-one of these events are presented here for the first time. Although about 68\% of our results are based on single-chord detection, most have intrinsic precision at the submilliarcsecond level. Lower limits on the diameter and shape constraints for a few bodies are also presented as valuable byproducts. Using the Gaia DR2 catalog, we show that even a single detection of a stellar occultation allows improving the object ephemeris significantly, which in turn enables predicting a future stellar occultation with high accuracy. Observational campaigns can be efficiently organized with this help, and may provide a full physical characterization of the involved object.
We have searched for the signature of 3- and 4-body decays of pair-produced scalar top quarks (stop) in the inclusive final state containing an electron, a muon, and significant missing transverse ...energy using a sample of p p ̄ events corresponding to 108.3 pb −1 of data collected with the DØ detector at Fermilab. The search is done in the framework of the minimal supersymmetric standard model assuming that the neutralino ( χ ̃ 0 1 ) is the lightest supersymmetric particle and is stable. No evidence for a signal is found and we derive cross-section upper limits as a function of stop ( t̃ ) and neutralino masses in different decay scenarios leading to the bℓν χ ̃ 0 1 final state. (Elsevier)
Using the DØ detector, we have observed events produced in p̄p collisions that contain W or Z bosons in conjunction with very little energy deposition (“rapidity gaps”) in large forward regions of ...the detector. The fraction of W boson events with a rapidity gap (a signature for diffraction) is 0.89±0.190.17%, and the probability that the non-diffractive background fluctuated to yield the observed diffractive signal is 3×10−14, corresponding to a significance of 7.5σ. The Z boson sample has a gap fraction of 1.44±0.610.52%, with a significance of 4.4σ. The diffractive events have very similar properties to the more common non-diffractive component.
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