<p>Millicharged particles, proposed by various extensions of the standard model, can be created in pairs by high-energy photons within nuclear reactors and can interact electromagnetically with electrons in matter. Recently, the existence of a plasmon peak in the interaction cross section with silicon in the eV range was highlighted as a promising approach to enhance low-energy sensitivities. The CONNIE and Atucha-II reactor neutrino experiments utilize Skipper-CCD sensors, which enable the detection of interactions in the eV range. We present world-leading limits on the charge of millicharged particles within a mass range spanning 6 orders of magnitude, derived through a comprehensive analysis and the combination of data from both experiments.</p>

Mexico

Alexis A. Aguilar-Arevalo

Juan Carlos D’Olivo

Youssef Sarkis

Argentina

Nicolas Avalos

Xavier Bertou

Pablo Bellino

Brazil

Carla Bonifazi

United States

Ana Botti

Gustavo Cancelo

Juan Estrada

Richard Ford

Kevin Kuk

Andrew Lathrop

Javier Tiffenberg

Austria

Mariano Cababié

Brenda A. Cervantes-Vergara

Paraguay

Claudio Chavez

Fernando Chierchie

David Delgado

Eliana Depaoli

João dos Anjos

Herman P. Lima

Guillermo Fernandez Moroni

Aldo R. Fernandes Neto

Switzerland

Ben Kilminster

Patrick Lemos

Katherine Maslova

Irina Nasteva

Ana Carolina Oliveira

Pedro Ventura

Martin Makler

Agustina Magnoni

Franciole Marinho

Jorge Molina

Diego Stalder

Santiago Perez

Dario Rodrigues

Laura Paulucci

Ivan Sidelnik

Miguel Sofo Haro

Search for Reactor-Produced Millicharged Particles with Skipper-CCDs at the CONNIE and Atucha-II Experiments

Millicharged particles appear in several extensions of the standard model, but have not yet been detected. These hypothetical particles could be produced by an intense proton beam striking a fixed target. We use data collected in 2020 by the SENSEI experiment in the MINOS cavern at the Fermi National Accelerator Laboratory to search for ultrarelativistic millicharged particles produced in collisions of protons in the NuMI beam with a fixed graphite target. The absence of any ionization events with 3 to 6 electrons in the SENSEI data allow us to place world-leading constraints on millicharged particles for masses between 30 to 380 MeV. This work also demonstrates the potential of utilizing low-threshold detectors to investigate new particles in beam-dump experiments, and motivates a future experiment designed specifically for this purpose.

Israel

Liron Barak

Itay M. Bloch

Ana M. Botti

Mariano Cababie

Luke Chaplinsky

Michael Crisler

Alex Drlica-Wagner

Rouven Essig

Erez Etzion

Stephen E. Holland

Yaron Korn

Canada

Ian Lawson

Steffon Luoma

Sravan Munagavalasa

Aviv Orly

Santiago E. Perez

Nathan A. Saffold

France

Silvia Scorza

Aman Singal

Leandro Stefanazzi

Kelly Stifter

Sho Uemura

Tomer Volansky

Tien-Tien Yu

Roni Harnik

Zhen Liu

Ryan Plestid

Search by the SENSEI Experiment for Millicharged Particles Produced in the NuMI Beam

Oscura is a planned light-dark matter search experiment using Skipper-CCDs with a total active mass of 10 kg. As part of the detector development, the collaboration plans to build the Oscura Integration Test (OIT), an engineering test with 10% of the total mass. Here we discuss the early science opportunities with the OIT to search for millicharged particles (mCPs) using the NuMI beam at Fermilab. mCPs would be produced at low energies through photon-mediated processes from decays of scalar, pseudoscalar, and vector mesons, or direct Drell-Yan productions. Estimates show that the OIT would be a world-leading probe for mCPs in the ∼MeV mass range.

Brenda Cervantes-Vergara

Juan D’Olivo

Alexis Aguilar-Arevalo

Fabricio Alcalde-Bessia

Nicolás Avalos

Oscar Baez

Daniel Baxter

Spain

Nuria Castelló-Mor

Alvaro Chavarria

Juan Egea

Cyrus Dreyer

Ezequiel Estrada

Paul Grylls

Guillermo Fernandez-Moroni

Marivi Fernández-Serra

Santiago Ferreyra

Stephen Holland

Agustín Barreda

Ben Loer

Edgar Villalpando

Mauricio Montero

Kellie McGuire

Danielle Norcini

Alexander Piers

Paolo Privitera

Nathan Saffold

Richard Saldanha

Radomir Smida

Miguel Sofo-Haro

Michelangelo Traina

Yu-Dai Tsai

Rocío Cortabitarte

Rachana Yajur

Searching for millicharged particles with 1 kg of Skipper-CCDs using the NuMI beam at Fermilab

The Coherent Neutrino-Nucleus Interaction Experiment (CONNIE) is taking data at the Angra 2 nuclear reactor with the aim of detecting the coherent elastic scattering of reactor antineutrinos with silicon nuclei using charge-coupled devices (CCDs). In 2019 the experiment operated with a hardware binning applied to the readout stage, leading to lower levels of readout noise and improving the detection threshold down to 50 eV. The results of the analysis of 2019 data are reported here, corresponding to the detector array of 8 CCDs with a fiducial mass of 36.2 g and a total exposure of 2.2 kg-days. The difference between the reactor-on and reactor-off spectra shows no excess at low energies and yields upper limits at 95% confidence level for the neutrino interaction rates. In the lowest-energy range, 50 − 180 eV, the expected limit stands at 34 (39) times the standard model prediction, while the observed limit is 66 (75) times the standard model prediction with Sarkis (Chavarria) quenching factors.

Javier Bernal

Victor Carvalho

Gustavo Corrêa

João Anjos

Aldo Fernandes Neto

Ana Foguel

Julián Gasanego Barbuscio

Juan Gonzalez Cuevas

Susana Hernandez

Federico Izraelevitch

Herman Lima

Mauricio Martinez Montero

Larissa Mendes

Philipe Mota

Eduardo Paolini

Y. Sarkis

Search for coherent elastic neutrino-nucleus scattering at a nuclear reactor with CONNIE 2019 data

The CONNIE experiment is located at a distance of 30 m from the core of a commercial nuclear reactor, and has collected a 3.7 kg-day exposure using a CCD detector array sensitive to an ∼1 keV threshold for the study of coherent neutrino-nucleus elastic scattering. Here we demonstrate the potential of this low-energy neutrino experiment as a probe for physics Beyond the Standard Model, by using the recently published results to constrain two simplified extensions of the Standard Model with light mediators. We compare the new limits with those obtained for the same models using neutrinos from the Spallation Neutron Source. Our new constraints represent the best limits for these simplified models among the experiments searching for CEνNS for a light vector mediator with mass     <math> <msub> <mi>M</mi> <msup> <mi>Z</mi> <mo>′</mo> </msup> </msub> </math> $$ {M}_{Z^{\prime }} $$  &lt; 10 MeV, and for a light scalar mediator with mass Mϕ &lt; 30 MeV. These results constitute the first use of the CONNIE data as a probe for physics Beyond the Standard Model.

H. Lima

Carlos Romero

Miguel Haro

Christian Torres

Search for light mediators in the low-energy data of the CONNIE reactor neutrino experiment

The CONNIE experiment is located at a distance of 30 m from the core of a commercial nuclear reactor, and has collected a 3.7 kg-day exposure using a CCD detector array sensitive to an 1 keV threshold for the study of coherent neutrino-nucleus elastic scattering. Here we demonstrate the potential of this low-energy neutrino experiment as a probe for physics Beyond the Standard Model, by using the recently published results to constrain two simplified extensions of the Standard Model with light mediators. We compare the new limits with those obtained for the same models using neutrinos from the Spallation Neutron Source. Our new constraints represent the best limits for these simplified models among the experiments searching for CE NS for a light vector mediator with mass $$ {M}_{Z^{\prime }} $$ 10 MeV, and for a light scalar mediator with mass 30 MeV. These results constitute the first use of the CONNIE data as a probe for physics Beyond the Standard Model.

We present new direct-detection constraints on eV-to-GeV dark matter interacting with electrons using a prototype detector of the Sub-Electron-Noise Skipper-CCD Experimental Instrument. The results are based on data taken in the MINOS cavern at the Fermi National Accelerator Laboratory. We focus on data obtained with two distinct readout strategies. For the first strategy, we read out the Skipper CCD continuously, accumulating an exposure of 0.177 g day. While we observe no events containing three or more electrons, we find a large one- and two-electron background event rate, which we attribute to spurious events induced by the amplifier in the Skipper-CCD readout stage. For the second strategy, we take five sets of data in which we switch off all amplifiers while exposing the Skipper CCD for 120 ks, and then read out the data through the best prototype amplifier. We find a one-electron event rate of <math><mrow><mo>(</mo><mn>3.51</mn><mo>±</mo><mn>0.10</mn><mo>)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>3</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>events</mi><mo>/</mo><mi>pixel</mi><mo>/</mo><mi>day</mi></mrow></math>, which is almost 2 orders of magnitude lower than the one-electron event rate observed in the continuous-readout data, and a two-electron event rate of <math><mrow><mo>(</mo><msubsup><mrow><mn>3.18</mn></mrow><mrow><mo>−</mo><mn>0.55</mn></mrow><mrow><mo>+</mo><mn>0.86</mn></mrow></msubsup><mo>)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>5</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>events</mi><mo>/</mo><mi>pixel</mi><mo>/</mo><mi>day</mi></mrow></math>. We again observe no events containing three or more electrons, for an exposure of 0.069 g day. We use these data to derive world-leading constraints on dark matter-electron scattering for masses between 500 keV and 5 MeV, and on dark-photon dark matter being absorbed by electrons for a range of masses below 12.4 eV.

Orr Abramoff

 Dawa

Guillermo Fernandez

Daniel Gift

Joseph Taenzer

SENSEI: Direct-Detection Constraints on Sub-GeV Dark Matter from a Shallow Underground Run Using a Prototype Skipper CCD

The Sub-Electron-Noise Skipper CCD Experimental Instrument (SENSEI) uses the recently developed Skipper-CCD technology to search for electron recoils from the interaction of sub-GeV dark matter particles with electrons in silicon. We report first results from a prototype SENSEI detector, which collected 0.019 g day of commissioning data above ground at Fermi National Accelerator Laboratory. These commissioning data are sufficient to set new direct-detection constraints for dark matter particles with masses between <math><mrow><mo>∼</mo><mn>500</mn><mtext> </mtext><mtext> </mtext><mi>keV</mi></mrow></math> and 4 MeV. Moreover, since these data were taken on the surface, they disfavor previously allowed strongly interacting dark matter particles with masses between <math><mo>∼</mo><mn>500</mn><mtext> </mtext><mtext> </mtext><mi>keV</mi></math> and a few hundred MeV. We discuss the implications of these data for several dark matter candidates, including one model proposed to explain the anomalously large 21-cm signal observed by the EDGES Collaboration. SENSEI is the first experiment dedicated to the search for electron recoils from dark matter, and these results demonstrate the power of the Skipper-CCD technology for dark matter searches.

CERN

SENSEI: First Direct-Detection Constraints on Sub-GeV Dark Matter from a Surface Run