We report a search for an invisible particle <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi></math> in the decay <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msubsup><mrow><mi>K</mi></mrow><mrow><mi>L</mi></mrow><mrow><mn>0</mn></mrow></msubsup><mo stretchy="false">→</mo><mi>γ</mi><mi>X</mi></mrow></math> (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi><mo stretchy="false">→</mo><mtext>invisible</mtext></math>), where <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi></math> can be interpreted as a massless or massive dark photon. No evidence for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi></math> was found, based on 13 candidate events consistent with a predicted background of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>12.66</mn><mo>±</mo><mn>4.4</mn><msub><mrow><mn>2</mn></mrow><mrow><mi>stat</mi></mrow></msub><mo>±</mo><mn>2.1</mn><msub><mrow><mn>3</mn></mrow><mrow><mi>syst</mi></mrow></msub></mrow></math> events. Upper limits on the branching ratio of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi>K</mi><mi>L</mi><mn>0</mn></msubsup><mo stretchy="false">→</mo><mi>γ</mi><mi>X</mi></math> were set for the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi></math> mass range <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>0</mn><mo>≤</mo><msub><mrow><mi>m</mi></mrow><mrow><mi>X</mi></mrow></msub><mo>≤</mo><mn>425</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math>. For massless <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi></math>, the upper limit was <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>3.4</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>7</mn></mrow></msup></math> at the 90% confidence level, improving the previous indirect bound by over three orders of magnitude. This result yielded a new lower bound of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>4.1</mn><mo>×</mo><msup><mn>10</mn><mn>6</mn></msup><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> on the probed effective mass scale governing flavor-changing dark-photon couplings, representing approximately two orders of magnitude improvement on existing constraints. For massive <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi></math>, the upper limits in the searched mass region ranged from <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>7</mn></mrow></msup><mo stretchy="false">)</mo></math> to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>3</mn></mrow></msup><mo stretchy="false">)</mo></math>.

China

T. Wu

Taiwan

Y.C. Tung

Y.B. Hsiung

South Korea

J.K. Ahn

Japan

M. Gonzalez

E.J. Kim

T.K. Komatsubara

K. Kotera

S.K. Lee

G.Y. Lim

C. Lin

T. Matsumura

H. Nanjo

Y. Noichi

T. Nomura

T. Nunes

K. Ono

United States

J. Redeker

N. Shimizu

S. Shinohara

K. Shiomi

R. Shiraishi

Y. Tajima

Y.W. Wah

H. Watanabe

T. Yamanaka

H.Y. Yoshida

Search for Dark Particles in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msubsup><mrow><mi>K</mi></mrow><mrow><mi>L</mi></mrow><mrow><mn>0</mn></mrow></msubsup><mo stretchy="false">→</mo><mi>γ</mi><mi>X</mi></mrow></math> at the KOTO Experiment

We perform the first high-throughput search and evaluation of materials that can serve as excellent low-mass dark matter detectors. Using properties of close to 1000 materials from the Materials Project database, we project the sensitivity in dark matter parameter space for experiments constructed from each material, including both absorption and scattering processes between dark matter and electrons. Using the anisotropic materials in the dataset, we further compute the level of daily modulation in interaction rates and the resulting directional sensitivities, highlighting materials with prospects to detect the dark matter wind. Our methods provide the basic tools for the data-driven design of dark matter detectors, and our findings lay the groundwork for the next generation of highly optimized direct searches for dark matter as light as the keV scale. This represents a major step in the application of results from condensed matter physics to dark matter search design.

Sinéad M. Griffin

Israel

Yonit Hochberg

Benjamin V. Lehmann

Rotem Ovadia

Kristin A. Persson

Bethany A. Suter

Ruo Xi Yang

Wayne Zhao

First High-Throughput Evaluation of Dark Matter Detector Materials

A search for pairs of light neutral pseudoscalar bosons (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>A</mi></mrow></math>) resulting from the decay of a Higgs boson is performed. The search is conducted using LHC proton-proton collision data at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mrow><mi>TeV</mi></mrow></mrow></math>, collected with the CMS detector in 2016–2018 and corresponding to an integrated luminosity of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>138</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>fb</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math>. The <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>A</mi></mrow></math> boson decays into a highly collimated electron-positron pair. A novel multivariate algorithm using tracks and calorimeter information is developed to identify these distinctive signatures, and events are selected with two such merged electron-positron pairs. No significant excess above the standard model background predictions is observed. Upper limits on the branching fraction for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>H</mi><mo stretchy="false">→</mo><mrow><mi>A</mi><mi>A</mi></mrow><mo stretchy="false">→</mo><mn>4</mn><mi>e</mi></mrow></math> are set at 95% confidence level, for masses between 10 and 100 MeV and proper decay lengths below <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>100</mn><mtext> </mtext><mtext> </mtext><mi mathvariant="normal">μ</mi><mrow><mi mathvariant="normal">m</mi></mrow></mrow></math>, reaching branching fraction sensitivities as low as <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>5</mn></mrow></msup></mrow></math>. This is the first search for Higgs boson decays to four electrons via light pseudoscalars at the LHC. It significantly improves the experimental sensitivity to axionlike particles with masses below 100 MeV .

Armenia

A. Hayrapetyan

V. Makarenko

A. Tumasyan

Austria

W. Adam

J.W. Andrejkovic

L. Benato

T. Bergauer

M. Dragicevic

C. Giordano

P.S. Hussain

M. Jeitler

N. Krammer

A. Li

D. Liko

M. Matthewman

I. Mikulec

J. Schieck

R. Schöfbeck

D. Schwarz

M. Shooshtari

M. Sonawane

W. Waltenberger

C.E. Wulz

Belgium

T. Janssen

H. Kwon

D. Ocampo Henao

T. Van Laer

P. Van Mechelen

J. Bierkens

N. Breugelmans

J. D’Hondt

S. Dansana

A. De Moor

M. Delcourt

F. Heyen

Y. Hong

P. Kashko

S. Lowette

I. Makarenko

D. Müller

J. Song

S. Tavernier

M. Tytgat

G.P. Van Onsem

S. Van Putte

D. Vannerom

B. Bilin

B. Clerbaux

A.K. Das

I. De Bruyn

G. De Lentdecker

H. Evard

L. Favart

P. Gianneios

A. Khalilzadeh

F.A. Khan

A. Malara

M.A. Shahzad

L. Thomas

M. Vanden Bemden

C. Vander Velde

P. Vanlaer

F. Zhang

M. De Coen

D. Dobur

G. Gokbulut

J. Knolle

D. Marckx

K. Skovpen

A.M. Tomaru

N. Van Den Bossche

J. van der Linden

J. Vandenbroeck

L. Wezenbeek

S. Bein

A. Benecke

A. Bethani

G. Bruno

A. Cappati

J. De Favereau De Jeneret

C. Delaere

F. Gameiro Casalinho

A. Giammanco

A.O. Guzel

V. Lemaitre

J. Lidrych

P. Malek

P. Mastrapasqua

S. Turkcapar

Brazil

G.A. Alves

M. Barroso Ferreira Filho

E. Coelho

C. Hensel

T. Menezes De Oliveira

C. Mora Herrera

P. Rebello Teles

M. Soeiro

E.J. Tonelli Manganote

A. Vilela Pereira

W.L. Aldá Júnior

Search for Light Pseudoscalar Bosons, Pair-Produced in Higgs Boson Decays in the Four-Electron Final State in Proton-Proton Collisions at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></mrow></math>

We present an inclusive search for anomalous production of single-photon events from neutrino interactions in the MicroBooNE experiment. The search and its signal definition are motivated by the previous observation of a low-energy excess of electromagnetic shower events from the MiniBooNE experiment. We use the Wire-Cell reconstruction framework to select a sample of inclusive single-photon final-state interactions with a final efficiency and purity of 7.0% and 40.2%, respectively. We leverage simultaneous measurements of sidebands of charged current <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ν</mi><mi>μ</mi></msub></math> interactions and neutral current interactions producing <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>π</mi><mn>0</mn></msup></math> mesons to constrain signal and background predictions and reduce uncertainties. We perform a blind analysis using a dataset collected from February 2016 to July 2018, corresponding to an exposure of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>6.34</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>20</mn></mrow></msup></mrow></math> protons on target from the Booster Neutrino Beam at Fermilab. In the full signal region, we observe agreement between the data and the prediction, with a goodness-of-fit <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi></math> value of 0.11. We then isolate a subsample of these events containing no visible protons, and observe <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>93</mn><mo>±</mo><mn>22</mn><mrow><mo stretchy="false">(</mo><mi>stat</mi><mo stretchy="false">)</mo></mrow><mo>±</mo><mn>35</mn><mrow><mo stretchy="false">(</mo><mi>syst</mi><mo stretchy="false">)</mo></mrow></mrow></math> data events above prediction, corresponding to just above <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>2</mn><mi>σ</mi></math> local significance, concentrated at shower energies below 600 MeV.