R. A. Rojas
A5060889870- Particle physics theoretical and experimental studies
- High-Energy Particle Collisions Research
- Particle Detector Development and Performance
- Quantum Chromodynamics and Particle Interactions
- Dark Matter and Cosmic Phenomena
- Computational Physics and Python Applications
- Neutrino Physics Research
- Cosmology and Gravitation Theories
- Radiation Detection and Scintillator Technologies
- Distributed and Parallel Computing Systems
- Medical Imaging Techniques and Applications
- Atomic and Subatomic Physics Research
- Astrophysics and Cosmic Phenomena
- Advanced Data Storage Technologies
- Advanced Optical Sensing Technologies
- Superconducting Materials and Applications
- CCD and CMOS Imaging Sensors
- Advanced X-ray and CT Imaging
- Advanced Wireless Network Optimization
- Wireless Communication Networks Research
- Control Systems and Identification
- Lung Cancer Diagnosis and Treatment
- 3D IC and TSV technologies
- Big Data Technologies and Applications
- Algorithms and Data Compression
University of Massachusetts Amherst
2023-2025
European Organization for Nuclear Research
2023-2025
Federico Santa María Technical University
2013-2024
Instituto de Física Corpuscular
2022-2024
Universitat de València
2022-2024
Tel Aviv University
2020-2024
Institute for High Energy Physics
2023-2024
Institute of Science and Technology
2023-2024
Universidad Técnica Federico Santa María
2010-2024
Atlas Scientific (United States)
2024
A search for sub-GeV dark matter production mediated by a new vector boson A^{'}, called photon, is performed the NA64 experiment in missing energy events from 100 GeV electron interactions an active beam dump at CERN SPS. From analysis of data collected years 2016, 2017, and 2018 with 2.84×10^{11} electrons on target no evidence such process has been found. The most stringent constraints A^{'} mixing strength photons parameter space scalar fermionic mass range ≲0.2 are derived, thus...
A search is performed for a new sub-GeV vector boson (${A}^{\ensuremath{'}}$) mediated production of dark matter ($\ensuremath{\chi}$) in the fixed-target experiment, NA64, at CERN SPS. The ${A}^{\ensuremath{'}}$, called photon, can be generated reaction ${e}^{\ensuremath{-}}Z\ensuremath{\rightarrow}{e}^{\ensuremath{-}}Z{A}^{\ensuremath{'}}$ 100 GeV electrons dumped against an active target followed by its prompt invisible decay...
We report the first results on a direct search for new 16.7 MeV boson (X) which could explain anomalous excess of e^{+}e^{-} pairs observed in excited ^{8}Be^{*} nucleus decays. Because its coupling to electrons, X be produced bremsstrahlung reaction e^{-}Z→e^{-}ZX by 100 GeV e^{-} beam incident an active target NA64 experiment at CERN Super Proton Synchrotron and through subsequent decay into pair. With 5.4×10^{10} electrons target, no evidence such decays was found, allowing us set limits...
The improved results on a direct search for new X(16.7 MeV) boson which could explain the anomalous excess of $e^+e^-$ pairs observed in excited 8Be nucleus decays ("Berillium anomaly") are reported. Due to its coupling electrons, X be produced bremsstrahlung reaction e-Z -> e-ZX by high-energy beam electrons incident active target NA64 experiment at CERN SPS and through subsequent decay into pair. No evidence such was found from combined analysis data samples with total statistics...
We carried out a model-independent search for light scalar ($s$) and pseudoscalar axionlike ($a$) particles that couple to two photons by using the high-energy CERN SPS H4 electron beam. The new particles, if they exist, could be produced through Primakoff effect in interactions of hard bremsstrahlung generated 100 GeV electrons NA64 active dump with virtual provided nuclei dump. $a(s)$ would penetrate downstream HCAL module, serving as shield, observed either their...
The current most stringent constraints for the existence of sub-GeV dark matter coupling to Standard Model via a massive vector boson ${A}^{\ensuremath{'}}$ were set by NA64 experiment mass region ${m}_{{A}^{\ensuremath{'}}}\ensuremath{\lesssim}250\text{ }\text{ }\mathrm{MeV}$, analyzing data from interaction $2.84\ifmmode\times\else\texttimes\fi{}{10}^{11}$ 100-GeV electrons with an active thick target and searching missing-energy events. In this work, including production secondary...
We performed a search for new generic $X$ boson, which could be scalar ($S$), pseudoscalar ($P$), vector ($V$), or an axial ($A$) particle produced in the 100 GeV electron scattering off nuclei, ${e}^{\ensuremath{-}}Z\ensuremath{\rightarrow}{e}^{\ensuremath{-}}ZX$, followed by its invisible decay NA64 experiment at CERN. No evidence such process was found full dataset of $2.84\ifmmode\times\else\texttimes\fi{}{10}^{11}$ electrons on target. place bounds $S$, $P$, $V$, $A$ coupling strengths...
The instantaneous luminosity of the Large Hadron Collider at CERN will be increased up to a factor five with respect present design value by undergoing an extensive upgrade program over coming decade. most important project for ATLAS Muon System is replacement first station in forward regions so-called New Small Wheels (NSWs). NSWs installed during LHC long shutdown 2018/19. Small-Strip Thin Gap Chamber (sTGC) detectors are designed provide fast trigger and high precision muon tracking under...
The extension of Standard Model made by inclusion additional $U(1)$ gauge ${L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}$ symmetry can explain the difference between measured and predicted value muon magnetic moment solve tension in $B$ meson decays. This model predicts existence a new, light ${Z}^{\ensuremath{'}}$ vector boson, predominantly coupled to second third generation leptons, whose interaction with electrons is due loop mechanism involving muons taus. In this work, we...
We report the results of a search for light pseudoscalar particle $a$ that couples to electrons and decays ${e}^{+}{e}^{\ensuremath{-}}$ performed using high-energy CERN SPS H4 electron beam. If such exists, it could explain ATOMKI anomaly (an excess pairs in nuclear transitions $^{8}\mathrm{Be}$ $^{4}\mathrm{He}$ nuclei at invariant mass $\ensuremath{\simeq}17\text{ }\text{ }\mathrm{MeV}$ observed by experiment 5 MV Van de Graaff accelerator ATOMKI, Hungary). used NA64 data collected...
Abstract We report the results of a search for new vector boson ( $$ A'$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>A</mml:mi> <mml:mo>′</mml:mo> </mml:msup> </mml:math> ) decaying into two dark matter particles $$\chi _1 \chi _2$$ <mml:mrow> <mml:msub> <mml:mi>χ</mml:mi> <mml:mn>1</mml:mn> </mml:msub> <mml:mn>2</mml:mn> </mml:mrow> different mass. The heavier particle subsequently decays to _1$$ and an off-shell Dark Photon A'^* \rightarrow e^+e^-$$...
Abstract Recently, the ATOMKI experiment has reported new evidence for excess of $$e^+e^-$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mo>-</mml:mo> </mml:mrow> </mml:math> events with a mass $$\sim $$ <mml:mo>∼</mml:mo> 17 MeV in nuclear transitions $$^4$$ <mml:mrow/> <mml:mn>4</mml:mn> He, that they previously observed measurements $$^8$$ <mml:mn>8</mml:mn> Be. These observations could be explained...
We present the measurement of intrinsic hadronic contamination at CERN SPS H4 beamline configured to transport electrons and positrons 100 GeV/c. The analysis, performed using data collected by NA64-e experiment in 2022, is based on calorimetric measurements, exploiting different interaction mechanisms hadrons NA64 detector. determined comparing results obtained nominal electron/positron configuration with those from a dedicated setup, which only impinged also an estimate relative protons,...
Abstract The MDT Trigger Processor (MDTTP) is a key ATLAS Level-0 Muon trigger upgrade component designed to meet High-Luminosity LHC requirements. MDTTP will use hits in the hardware level for first time improve momentum resolution of muon candidates provided by RPC and TGC detectors reduce fake rate. based on Apollo ATCA platform. prototype includes VU13P-FPGA, high-speed FireFly optical transceivers, peripherals, other improvements learned from using previous demonstrator. We present...
The Muon Spectrometer of the ATLAS Experiment at CERN is composed Thin Gap Chambers (TGC) and Monitoring Drift Tubes (MDT) technologies. TGCs are arranged in 6 Big Wheels 2 Small Wheels. Gain stability efficiency required to be monitored during Large Hadron Collider (LHC) operation (runs). A Charge monitoring board identified as a solution measure gain runs for forthcoming High Luminosity upgrade. Specifications topology proposed with preliminary results demonstration feasibility.
Recently, the ATOMKI experiment has reported new evidence for excess of $e^+ e^-$ events with a mass $\sim$17 MeV in nuclear transitions $^4$He, that they previously observed measurements $^8$Be. These observations could be explained by existence vector $X17$ boson. So far, search decay $X17 \rightarrow e^+ NA64 at CERN SPS gave negative results. Here, we present technique implemented aiming to improve sensitivity and cover remaining parameter space. If signal-like event is detected, an...
The novel Hamamatsu Multi Pixel Photon Counter Array S12045(X) is an array of 16 individual MPPCs (3×3 [mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ]) (further in the article MPPC channel) each with 3600 G-APD (Geiger-mode Avalanche Photodiode) pixels (50×50 [μ m ]). Each works its reverse bias voltage around 70[V]. We studied main features channel for 2800 arrays at different temperatures. Two measurement systems were built to...
Abstract The Versatile Data AcQuisition (VerDAQ) system is a modular and flexible data acquisition platform designed to be used in wide range of high-energy physics experiments, from small desktop detectors large experiments accelerators. main characteristic VerDAQ its flexibility that stems design, separating the front-end electronics mezzanine board back-end on motherboard. latter includes programmable System-on-Chip (SoC) provides preprocessing communication capabilities. hardware...
The LSCR method (Leave-out-Sign-dominant-Correlation-Regions) provides confidence regions for the parameters of a system by evaluating set correlation functions calculated available data. To do approximation whole region, procedure must be repeated each value parameter vector. main attributes are its validity finite data and scarce asumptions on noise. However, needs much computational effort, which limitates application to very simple cases. In this work some theoretical aspects improved...