arXiv subjects

C. Pepe

Publications and source records attributed to C. Pepe.

7 recordsLinked to original sources

arXiv2026

Towards Low-Energy Electron High-Resolution Spectroscopy with Transition-Edge Sensors

We present a study of the energy resolution of transition-edge sensors (TESs) for the detection of electrons in the 100 eV kinetic energy range. The TES is a Ti-Au bilayer with an active area of $(60 \times 60)$ $\mu \text{m}^2$ and a critical temperature of $\sim$ 80 mK. The electron source is based on vertically-aligned multiwall carbon nanotubes located inside the cryostat, with electrons generated via field emission. For electrons in the (92 - 99) eV kinetic energy range, we obtain a Gaussian energy resolution for fully-absorbed electrons of (0.479 $\pm$ 0.041 $\pm$ 0.055) eV. When considering the full-width at half-maximum of the peak, the corresponding resolution is of (1.44 $\pm$ 0.17 $\pm$ 0.27) eV. The former represents an improvement of (46 - 60)% with respect to previous results, and is mainly attributed to the reduction in the TES active area. The latter is instead an improvement of over a factor of 20, and is mainly due to the reduction in the emitting area of the electron source, which significantly suppresses electron back-scattering in proximity of the TES. These results represent a major milestone toward high-precision spectroscopy on low-energy electrons, which is a key objective for the PTOLEMY experiment.

physics.ins-det↗

arXiv2025

Ultra-high precision high voltage system for PTOLEMY

The PTOLEMY project is prototyping a novel electromagnetic filter for high-precision $\beta$ spectroscopy, with the ultimate and ambitious long-term goal of detecting the cosmic neutrino background through electron capture on tritium bound to graphene. Intermediate small-scale prototypes can achieve competitive sensitivity to the effective neutrino mass, even with reduced energy resolution. To reach an energy resolution better than \SI{500}{meV} at the tritium $\beta$-spectrum endpoint of \SI{18.6}{keV}, and accounting for all uncertainties in the filtering chain, the electrode voltage must be controlled at the level of a few parts per million and monitored in real time. In this work, we present the first results obtained in this effort, using a chain of commercial ultra-high-precision voltage references, read out by precision multimeters and a \emph{field mill} device. The currently available precision on high voltage is, in the conservative case, as low as \SI{0.2}{ppm} per \SI{1}{kV} single board and $\lesssim$ \SI{50}{mV} over the \SI{10}{kV} series, presently limited by field mill read-out noise. However, assuming uncorrelated Gaussian noise extrapolation, the real precision could in principle be as low as \SI{0.05}{ppm} over \SI{20}{kV}.

physics.ins-det↗

arXiv2025

A Demonstration of Slowed Electron ${\bf E} \times {\bf B}$ Drift for PTOLEMY

To resolve the effective neutrino mass $m_\beta$ with an energy resolution of 50~meV, the PTOLEMY experiment has proposed a novel transverse electromagnetic filtering process. Substantially reducing the kinetic energy of tritium $\beta$-decay electrons by counteracting motion from ${\bf E}$ $\times$ ${\bf B}$ and $\nabla{\rm B}$ drift, the PTOLEMY filter requires an input of emitted electron kinematic information to generate a tailored, suitable electric field for each candidate. The collaboration proposes to extract these quantities by using antennae to observe the relativistic frequency shift of emitted cyclotron radiation as an electron transits by ${\bf E}$ $\times$ ${\bf B}$ drift through a uniform magnetic field region preceding the filter. Electrons must be contained within this region long enough such that an adequate integrated radiated power signal is received to accurately estimate these kinematics. This necessitates a controlled, slowed drift speed. This paper presents the experimental design to vary ${\bf E}$ $\times$ ${\bf B}$ drift speed of carbon-14 $\beta$-decay electrons using a custom electrode field cage situated between the pole faces of an electromagnet. Matching our results with high-fidelity simulation, we deduce a capacity to increase particle time of flight by a factor of 5 in the field cage's slow drift region. Limited only by the dimensions of our system, we assert drift speed can be arbitrarily slowed to meet the needs of PTOLEMY's future detector. Actualizing such a system is a crucial milestone in developing the detector, enabling future cyclotron radiation measurements, filter implementation, and source injection.

physics.ins-det↗

arXiv2022

Heisenberg's uncertainty principle in the PTOLEMY project: a theory update

We discuss the consequences of the quantum uncertainty on the spectrum of the electron emitted by the $\beta$-processes of a tritium atom bound to a graphene sheet. We analyze quantitatively the issue recently raised in [Cheipesh et al., Phys. Rev. D 104, 116004 (2021)], and discuss the relevant time scales and the degrees of freedom that can contribute to the intrinsic spread in the electron energy. We perform careful calculations of the potential between tritium and graphene with different coverages and geometries. With this at hand, we propose possible avenues to mitigate the effect of the quantum uncertainty.

hep-ph↗

arXiv2016

Synthetic extinction maps around intermediate-mass black holes in Galactic globular clusters

During the last decades, much effort has been devoted to explain the discrepancy between the amount of intracluster medium (ICM) estimated from stellar evolution theories and that emerging from observations in globular clusters (GCs). One possible scenario is the accretion of this medium by an intermediate-mass black hole (IMBH) at the centre of the cluster. In this work, we aim at modelling the cluster colour-excess profile as a tracer of the ICM density, both with and without an IMBH. Comparing the profiles with observations allows us to test the existence of IMBHs and their possible role in the cleansing of the ICM. We derive the intracluster density profiles from hydrodynamical models of accretion onto a central IMBH in a GC and we determine the corresponding dust density. This model is applied to a list of 25 Galactic GCs. We find that central IMBHs decrease the ICM by several orders of magnitude. In a subset of 9 clusters, the absence of the black hole combined with a low intracluster medium temperature would be at odds with present gas mass content estimations. As a result, we conclude that IMBHs are an effective cleansing mechanism of the ICM of GCs. We construct synthetic extinction maps for M 62 and ω Cen, two clusters in the small subset of 9 with observed 2D extinction maps. We find that under reasonable assumptions regarding the model parameters, if the gas temperature in M 62 is close to 8000 K, an IMBH needs to be invoked. Further ICM observations regarding both the gas and dust in GCs could help to settle this issue.

astro-ph.GA↗

arXiv2015

Spectral energy distribution, polarization, and synthetic radio maps of Cygnus X-1: a lepto-hadronic jet model

In this work we combine SEDs, radio maps and polarization observations to understand the emission mechanisms in Cygnus X-1. Our radiative model indicates that the MeV emission originates in the jet and that all the very high-energy emission is from hadronic origin. We also performed a synthetic radio map that suggests that our description of the magnetic field should be improved, since it leads to a very compact emission region. In order to choose the most suitable magnetic field geometry, we investigated the polarization in X-rays and we found that very simple geometries can explain the high levels of polarization reported by other authors.

astro-ph.HE↗

arXiv2012

Dark matter and dark energy accretion onto intermediate-mass black holes

In this work we investigate the accretion of cosmological fluids onto an intermediate-mass black hole at the centre of a globular cluster, focusing on the influence of the parent stellar system on the accretion flow. We show that the accretion of cosmic background radiation and the so-called dark energy onto an intermediate-mass black hole is negligible. On the other hand, if cold dark matter has a nonvanishing pressure, the accretion of dark matter is large enough to increase the black hole mass well beyond the present observed upper limits. We conclude that either intermediate-mass black holes do not exist, or dark matter does not exist, or it is not strictly collisionless. In the latter case, we set a lower limit for the parameter of the cold dark matter equation of state.

astro-ph.HE↗