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G. Perez

Publications and source records attributed to G. Perez.

At least 19 recordsLinked to original sources
arXiv2025

Feebly Interacting Particles: FIPs at LHCb

With the establishment and maturation of the experimental programs searching for new physics with sizeable couplings at the LHC, there is an increasing interest in the broader particle and astrophysics community for exploring the physics of light and feebly-interacting particles as a paradigm complementary to a New Physics sector at the TeV scale and beyond. FIPs@LHCb continues the successful series of the FIPs workshops, FIPs 2020 and FIPs 2022. The main focus of the workshop was to explore the LHCb potential to search for FIPs thanks to the new software trigger deployed during the recent upgrade. Equally important goals of the workshop were to update the available parameter space in the commonly used FIPs benchmarks by including recent results from the high energy physics community and to discuss recent theory progress necessary for a more accurate definition of observables related to FIP benchmarks. This document presents the summary of the talks presented at the workshops and the outcome of subsequent discussions.

hep-ph↗
arXiv2024

Gemini High-resolution Optical SpecTrograph (GHOST) at Gemini-South: Instrument performance and integration, first science, and next steps

The Gemini South telescope is now equipped with a new high-resolution spectrograph called GHOST (the Gemini High-resolution Optical SpecTrograph). This instrument provides high-efficiency, high-resolution spectra covering 347-1060 nm in a single exposure of either one or two targets simultaneously, along with precision radial velocity spectroscopy utilizing an internal calibration source. It can operate at a spectral element resolving power of either 76000 or 56000, and can reach a SNR$\sim$5 in a 1hr exposure on a V$\sim$20.8 mag target in median site seeing, and dark skies (per resolution element). GHOST was installed on-site in June 2022, and we report performance after full integration to queue operations in November 2023, in addition to scientific results enabled by the integration observing runs. These results demonstrate the ability to observe a wide variety of bright and faint targets with high efficiency and precision. With GHOST, new avenues to explore high-resolution spectroscopy have opened up to the astronomical community. These are described, along with the planned and potential upgrades to the instrument.

astro-ph.IM↗
arXiv2024

Tuning the spontaneous exchange bias effect in La1.5Sr0.5CoMnO6 with sintering temperature

Here, we present a study of the influence of microstructure on the magnetic properties of polycrystalline samples of the La1.5Sr0.5CoMnO6 double perovskite, with primary attention to the spontaneous exchange bias effect, a fascinating recently discovered phenomena for which some materials exhibit unidirectional magnetic anisotropy after being cooled in zero magnetic fields. By sintering La1.5Sr0.5CoMnO6 at different temperatures, we obtained samples with distinct average grain sizes, ranging from 1.54 to 6.65 mu_m. A detailed investigation of the material's structural, morphologic, electronic, and magnetic properties using X-ray powder diffraction, powder neutron diffraction, X-ray absorption near edge structure spectroscopy, scanning electron microscopy, and AC and DC magnetometry has revealed a systematic enhancement of the exchange bias effect with increasing the average grain size. This evolution is discussed in terms of changes in the material's porosity and grain morphology and its influence on the exchange couplings at the magnetic interfaces.

cond-mat.mtrl-sci↗
arXiv2022

Star Cluster Formation and Evolution in M101: An Investigation with the Legacy Extragalactic UV Survey

We present Hubble Space Telescope WFC3/UVIS (F275W, F336W) and ACS/WFC optical (F435W, F555W, and F814W) observations of the nearby grand-design spiral galaxy M101 as part of the Legacy Extragalactic UV Survey (LEGUS). Compact sources detected in at least four bands were classified by both human experts and the convolutional neural network StarcNet. Human experts classified the 2,351 brightest sources, retrieving $N_{c} = 965$ star clusters. StarcNet, trained on LEGUS data not including M101, classified all 4,725 sources detected in four bands, retrieving $N_{c} = 2,270$ star clusters. The combined catalog represents the most complete census to date of compact star clusters in M101. We find that for the 2,351 sources with both a visual- and ML-classification StarcNet is able to reproduce the human classifications at high levels of accuracy ($\sim 80-90\%$), which is equivalent to the level of agreement between human classifiers in LEGUS. The derived cluster age distribution implies a disruption rate of $dN/dτ\propto τ^{-0.45 \pm 0.14}$ over $10^{7} < τ< 10^{8.5}$yr for cluster masses $\geq 10^{3.55} M_{\odot}$ for the central region of M101 and $dN/dτ\propto τ^{-0.02 \pm 0.15}$ for cluster masses $\geq 10^{3.38} M_{\odot}$ in the northwest region of the galaxy. The trends we recover are weaker than those of other nearby spirals (e.g. M51) and starbursts, consistent with the M101 environment having a lower-density interstellar medium, and providing evidence in favor of environmentally-dependent cluster disruption in the central, southeast, and northwest regions of M101.

astro-ph.GA↗
arXiv2022

New Horizons: Scalar and Vector Ultralight Dark Matter

The last decade has seen unprecedented effort in dark matter model building at all mass scales coupled with the design of numerous new detection strategies. Transformative advances in quantum technologies have led to a plethora of new high-precision quantum sensors and dark matter detection strategies for ultralight ($<10\,$eV) bosonic dark matter that can be described by an oscillating classical, largely coherent field. This white paper focuses on searches for wavelike scalar and vector dark matter candidates.

hep-ex↗
arXiv2021

Search for oscillations of fundamental constants using molecular spectroscopy

A possible implication of an ultralight dark matter (UDM) field interacting wibeginth the Standard Model (SM) degrees of freedom is oscillations of fundamental constants. Here, we establish direct experimental bounds on the coupling of an oscillating UDM field to the up, down, and strange quarks and to the gluons, for oscillation frequencies between 10 Hz and 10^8 Hz. We employ spectroscopic experiments that take advantage of the dependence of molecular transition frequencies on the nuclear masses. Our results apply to previously unexplored frequency bands, and improve on existing bounds at frequencies > 5 MHz. We identify a sector of UDM - SM coupling space where the bounds from Equivalence Principle tests may be challenged by next-generation experiments of the present kind.

hep-ph↗
arXiv2021

NuSTAR reveals the hidden nature of SS433

SS433 is the only Galactic binary system known to persistently accrete at highly super-critical (or hyper-critical) rates, similar to those in tidal disruption events, and likely needed to explain the rapid growth of those very high redshift quasars containing massive SMBHs. Probing the inner regions of SS433 in the X-rays is crucial to understanding this system, and super-critical accretion in general, but is highly challenging due to obscuration by the surrounding wind, driven from the accretion flow. NuSTAR observed SS433 in the hard X-ray band across multiple phases of its 162 day super-orbital precession period. Spectral-timing tools allow us to infer that the hard X-ray emission from the inner regions is likely being scattered towards us by the walls of the wind-cone. By comparing to numerical models, we determine an intrinsic X-ray luminosity of $\ge$ 2$\times$10$^{37}$ erg/s and that, if viewed face on, we would infer an apparent luminosity of $>$ 1$\times$10$^{39}$ erg/s, confirming SS433's long-suspected nature as an ultraluminous X-ray source (ULX). We present the discovery of a narrow, $\sim 100$s lag due to atomic processes occurring in outflowing material travelling at least 0.14-0.29c, which matches absorption lines seen in ULXs and -- in the future -- will allow us to map a super-critical outflow for the first time.

astro-ph.HE↗
arXiv2020

Status of the Beryllium Tile Bonding Qualification activities for the Manufacturing of the ITER First Wall

The preparation of the manufacturing of the ITER first wall involves a qualification stage. The qualification aims at demonstrating that manufacturers can deliver the needed reliability and quality for the beryllium to copper bond, before the manufacturing can commence. The qualification is done on semi-prototype, containing relevant features relative to the beryllium armour (about 1/6 of the panel size). The qualification is done by the participating parties, firstly by a manufacturing semi-prototype and then by testing it under heat flux. One semi-prototype is manufactured and is being tested, and further from other manufacturers are still to come. The qualification program is accompanied by bond defect investigations, which aim at defining defect acceptance criteria. Qualification and defect acceptance program are supported by thermal and stress analyses, with good agreement regarding the thermal results, and some insights about the governing factors to bond damage. ITER, First Wall, Qualification, prototypes, high heat flux tests.

physics.ins-det↗
arXiv2020

Probing the strange Higgs coupling at lepton colliders using light-jet flavor tagging

We propose a method to probe the coupling of the Higgs to strange quarks by tagging strange jets at future lepton colliders. For this purpose we describe a jet-flavor observable, $J_F$, that is correlated with the flavor of the quark associated with the hard part of the jet. Using this variable, we set up a strangeness tagger aimed at studying the decay $h\to s\bar{s}$. We determine the sensitivity of our method to the strange Yukawa coupling, and find it to be of the order of the standard-model expectation.

hep-ph↗
arXiv2019

Letter of Intent for the LUXE Experiment

This Letter of Intent describes LUXE (Laser Und XFEL Experiment), an experiment that aims to use the high-quality and high-energy electron beam of the European XFEL and a powerful laser. The scientific objective of the experiment is to study quantum electrodynamics processes in the regime of strong fields. High-energy electrons, accelerated by the European XFEL linear accelerator, and high-energy photons, produced via Bremsstrahlung of those beam electrons, colliding with a laser beam shall experience an electric field up to three times larger than the Schwinger critical field (the field at which the vacuum itself is expected to become unstable and spark with spontaneous creation of electron-positron pairs) and access a new regime of quantum physics. The processes to be investigated, which include nonlinear Compton scattering and nonlinear Breit-Wheeler pair production, are relevant to a variety of phenomena in Nature, e.g. in the areas of astrophysics and collider physics and complement recent results in atomic physics. The setup requires in particular the extraction of a minute fraction of the electron bunches from the European XFEL accelerator, the installation of a powerful laser with sophisticated diagnostics, and an array of precision detectors optimised to measure electrons, positrons and photons. Physics sensitivity projections based on simulations are also provided.

physics.ins-det↗
arXiv2019

Scalar dark matter in the radio-frequency band: atomic-spectroscopy search results

Among the prominent candidates for dark matter are bosonic fields with small scalar couplings to the Standard-Model particles. Several techniques are employed to search for such couplings and the current best constraints are derived from tests of gravity or atomic probes. In experiments employing atoms, observables would arise from expected dark-matter-induced oscillations in the fundamental constants of nature. These studies are primarily sensitive to underlying particle masses below $10^{-14}$ eV. We present a method to search for fast oscillations of fundamental constants using atomic spectroscopy in cesium vapor. We demonstrate sensitivity to scalar interactions of dark matter associated with a particle mass in the range $8\cdot10^{-11}$ to $4\cdot 10^{-7}$ eV. In this range our experiment yields constraints on such interactions, which within the framework of an astronomical-size dark matter structure, are comparable with, or better than, those provided by experiments probing deviations from the law of gravity.

physics.atom-ph↗
arXiv2019

The CLIC Potential for New Physics

The Compact Linear Collider (CLIC) is a mature option for the future of high energy physics. It combines the benefits of the clean environment of $e^+e^-$ colliders with operation at high centre-of-mass energies, allowing to probe scales beyond the reach of the Large Hadron Collider (LHC) for many scenarios of new physics. This places the CLIC project at a privileged spot in between the precision and energy frontiers, with capabilities that will significantly extend knowledge on both fronts at the end of the LHC era. In this report we review and revisit the potential of CLIC to search, directly and indirectly, for physics beyond the Standard Model.

hep-ph↗
arXiv2016

On the challenge of estimating diphoton backgrounds at large invariant mass

Diphoton searches at high invariant mass are an integral part of the experimental high energy frontier. Using the analyses of the 750\,GeV diphoton resonance as a case study, we examine the methodology currently employed by the experimental analyses in estimating the dominant standard model backgrounds. We assess the dependence of the significance associated with the excess on the background modeling. In particular, we show that close to the high energy tails of the distributions, estimates of the jet faking backgrounds relying on functional extrapolations or Monte Carlo estimates of the challenging photon-jet contributions introduce a large uncertainty. Analyses with loose photon cuts, low photon $p_T$ cuts and those susceptible to high photon rapidity regions are especially affected. Given that diphoton-based searches beyond 1\,TeV are highly motivated as discovery modes, these considerations are relevant and applicable in the future. We first consider a physics-driven deformation of the shape of the diphoton faking photon-jet spectrum by next-to-leading order effects combined with a rapidity and transverse momentum dependent fake rate. We show that the resulting local significance of the excess is reduced due to such a deformation. Then using a simple, but more general, ansatz to modify the contribution of the jet faking backgrounds at high invariant masses but keeping the inclusive and differential sample purities within experimental uncertainty estimates, we demonstrate that the originally reported local 750\,GeV excess significances could have been overestimated by more than one standard deviation. We furthermore cross-check our analysis by comparing fit results based on the smaller 2015 and the larger 2016 LHC datasets. Finally we employ our methodology on the complete 13\,TeV LHC dataset to asses the systematics involved in the current diphoton searches beyond the TeV region.

hep-ph↗
arXiv2016

Proceedings of the 2013 European School of High-Energy Physics (ESHEP 2013), Paradfurdo, Hungary, 5-18 Jun 2013

The European School of High-Energy Physics is intended to give young physicists an introduction to the theoretical aspects of recent advances in elementary particle physics. These proceedings contain lecture notes on the Standard Model of electroweak interactions, quantum chromodynamics, Higgs physics, physics beyond the Standard Model, flavour physics, and practical statistics for particle physicists.

hep-th↗
arXiv2016

The Latin American Giant Observatory: Contributions to the 34th International Cosmic Ray Conference (ICRC 2015)

The Latin American Giant Observatory (LAGO) is an extended cosmic ray observatory composed by a network of water-Cherenkov detectors spanning over different sites located at significantly different altitudes (from sea level up to more than $5000$\,m a.s.l.) and latitudes across Latin America, covering a huge range of geomagnetic rigidity cut-offs and atmospheric absorption/reaction levels. This detection network is designed to measure the temporal evolution of the radiation flux at ground level with extreme detail. The LAGO project is mainly oriented to perform basic research in three branches: high energy phenomena, space weather and atmospheric radiation at ground level. LAGO is built and operated by the LAGO Collaboration, a non-centralized collaborative union of more than 30 institutions from ten countries. These are the contributions of the LAGO Collaboration to the 34th International Cosmic Ray Conference, 30 July - 6 August 2015, The Hague, The Netherlands

astro-ph.IM↗
arXiv2016

Proceedings of the 2013 CERN - Latin-American School of High-Energy Physics (CLASHEP 2013), Arequipa, Peru, 6-19 Mar 2013

The CERN - Latin-American School of High-Energy Physics is intended to give young physicists an introduction to the theoretical aspects of recent advances in elementary particle physics. These proceedings contain lecture notes on the Standard Model of electroweak interactions, quantum chromodynamics, flavour physics, quantum chromodynamics under extreme conditions, cosmic-ray physics, cosmology, recent highlights of LHC results, practical statistics for particle physicists and a short introduction to the principles of particle physics instrumentation.

hep-ph↗
arXiv2013

Report of the Quark Flavor Physics Working Group

This report represents the response of the Intensity Frontier Quark Flavor Physics Working Group to the Snowmass charge. We summarize the current status of quark flavor physics and identify many exciting future opportunities for studying the properties of strange, charm, and bottom quarks. The ability of these studies to reveal the effects of new physics at high mass scales make them an essential ingredient in a well-balanced experimental particle physics program.

hep-ex↗