<p>Axions, originally proposed to resolve the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>C</mi><mi>P</mi></mrow></math> problem in the strong interaction, remain a leading dark matter candidate. While cavity haloscopes offer the most sensitive technique for detecting axions, searches have largely been limited to masses below <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>10</mn><mtext> </mtext><mtext> </mtext><mi>μeV</mi></mrow></math>. We report a sensitive search for axion dark matter with masses around <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>21</mn><mtext> </mtext><mtext> </mtext><mi>μeV</mi></mrow></math>, utilizing the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>TM</mi></mrow><mrow><mn>020</mn></mrow></msub></mrow></math> mode of a cylindrical cavity equipped with an innovative tuning mechanism. Our search achieved a sensitivity of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>1.7</mn><mo>×</mo></math> the Kim-Shifman-Vainshtein-Zakharov benchmark over a 100-MHz range, representing a significant advance in this mass range. These results demonstrate that higher-order modes provide a viable strategy for extending haloscope searches into previously unexplored higher-mass regions.</p>

South Korea

Sungjae Bae

Sweden

Junu Jeong

Germany

Younggeun Kim

SungWoo Youn

Jinsu Kim

Japan

Arjan F. van Loo

Yasunobu Nakamura

Seonjeong Oh

Taehyeon Seong

Sergey Uchaikin

Jihn E. Kim

Yannis K. Semertzidis

Axion Dark Matter Search with Sensitivity near the Kim-Shifman-Vainshtein-Zakharov Benchmark Using the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>TM</mi></mrow><mrow><mn>020</mn></mrow></msub></mrow></math> Mode

It has been known for some time that the cosmological bound on the invisible axion scale can be avoided by an early phase of strong QCD. While most approaches rely on theories where the strong coupling constant is determined through the expectation value of some scalar field, we show that this mechanism can also be implemented into the benchmark Kim-Shifman-Vainshtein-Zakharov and Dine-Fischler-Srednicki-Zhitnitsky models when the early phase of strong QCD emerges by the modification of the running coupling during inflation. For both models the physics that are responsible for making QCD strong do not displace the axions minimum by too much, so that the efficiency of the relaxation is controlled by parameters of the theory and the number of inflationary <math><mi>e</mi></math>-folds. In particular, we consider the case of very efficient relaxation where the axion abundance is dominated by inflationary quantum and postinflationary thermal fluctuations. Within this situation we identify the parameter space compatible with all cosmological constrains and derive conditions on the reheating temperature and the QCD scale during inflation that result in the axion making up all the dark matter. Because of duality below the Peccei-Quinn scale and a minor influence of the Kim-Shifman-Vainshtein-Zakharov and Dine-Fischler-Srednicki-Zhitnitsky fields on the running, our findings also apply to a minimal two-form implementation of the axion.

Emmanouil Koutsangelas

Removing the cosmological bound on the axion scale in the Kim-Shifman-Vainshtein-Zakharov and Dine-Fischler-Srednicki-Zhitnitsky models

A search for the neutrinoless quadruple beta decay of $^{136}$Xe was conducted with the liquid-xenon detector XMASS-I using 327 kg ×800.0 days of the exposure. The pulse shape discrimination based on the scintillation decay time constant which distinguishes γ-rays including the signal and β-rays was used to enhance the search sensitivity. No significant signal excess was observed from the energy spectrum fitting with precise background evaluation, and we set a lower limit of the half life of 3.7 × 10$^{24}$ years at 90% confidence level. This is the first experimental constraint of the neutrinoless quadruple beta decay of $^{136}$Xe.

K. Abe

K. Hiraide

K. Ichimura

N. Kato

Y. Kishimoto

K. Kobayashi

M. Kobayashi

S. Moriyama

M. Nakahata

K. Sato

H. Sekiya

T. Suzuki

A. Takeda

S. Tasaka

M. Yamashita

B.S. Yang

N.Y. Kim

Y.D. Kim

Y.H. Kim

R. Ishii

Y. Itow

K. Kanzawa

K. Masuda

K. Martens

A. Mason

Y. Suzuki

K. Miuchi

Y. Takeuchi

K.B. Lee

M.K. Lee

Y. Fukuda

H. Ogawa

K. Nishijima

K. Fushimi

China

B.D. Xu

S. Nakamura

Search for neutrinoless quadruple beta decay of Xe in XMASS-I

We have searched for exotic neutrino-electron interactions that could be produced by a neutrino millicharge, by a neutrino magnetic moment, or by dark photons using solar neutrinos in the XMASS-I liquid xenon detector. We observed no significant signals in 711 days of data. We obtain an upper limit for neutrino millicharge of <math><mn>5.4</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>12</mn></mrow></msup><mi>e</mi></math> at 90% confidence level assuming all three species of neutrino have common millicharge. We also set flavor-dependent limits assuming the respective neutrino flavor is the only one carrying a millicharge, <math><mn>7.3</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>12</mn></mrow></msup><mi>e</mi></math> for <math><msub><mrow><mi>ν</mi></mrow><mrow><mi>e</mi></mrow></msub></math>, <math><mn>1.1</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>11</mn></mrow></msup><mi>e</mi></math> for <math><msub><mrow><mi>ν</mi></mrow><mrow><mi>μ</mi></mrow></msub></math>, and <math><mn>1.1</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>11</mn></mrow></msup><mi>e</mi></math> for <math><msub><mrow><mi>ν</mi></mrow><mrow><mi>τ</mi></mrow></msub></math>. These limits are the most stringent yet obtained from direct measurements. We also obtain an upper limit for the neutrino magnetic moment of <math><mn>1.8</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>10</mn></mrow></msup></math> Bohr magnetons. In addition, we obtain upper limits for the coupling constant of dark photons in the <math><mi>U</mi><msub><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow><mrow><mi>B</mi><mo>−</mo><mi>L</mi></mrow></msub></math> model of <math><mn>1.3</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>6</mn></mrow></msup></math> if the dark photon mass is <math><mn>1</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>3</mn></mrow></msup></math> MeV<math><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></math>, and <math><mn>8.8</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>5</mn></mrow></msup></math> if it is 10 MeV<math><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></math>.

Y. Chen

S. Imaizumi

Search for exotic neutrino-electron interactions using solar neutrinos in XMASS-I

A search for dark matter (DM) with mass in the sub-GeV region (0.32–1 GeV) was conducted by looking for an annual modulation signal in XMASS, a single-phase liquid xenon detector. Inelastic nuclear scattering accompanied by bremsstrahlung emission was used to search down to an electron equivalent energy of 1 keV. The data used had a live time of 2.8 years (3.5 years in calendar time), resulting in a total exposure of 2.38 ton-years. No significant modulation signal was observed and 90% confidence level upper limits of <math><mn>1.6</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>33</mn></mrow></msup></math> cm$^{2}$ at 0.5 GeV was set for the DM-nucleon cross section. This is the first experimental result of a search for DM mediated by the bremsstrahlung effect. In addition, a search for DM with mass in the multi-GeV region (4–20 GeV) was conducted with a lower energy threshold than previous analysis of XMASS. Elastic nuclear scattering was used to search down to a nuclear recoil equivalent energy of 2.3 keV, and upper limits of 2.9 ×<math><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>42</mn></mrow></msup></math> cm$^{2}$ at 8 GeV was obtained.

N. Oka

M. Miyasaka

G. Kanzaki

Search for sub-GeV dark matter by annual modulation using XMASS-I detector

A search for dark matter using an underground single-phase liquid xenon detector was conducted at the Kamioka Observatory in Japan, particularly for Weakly Interacting Massive Particles (WIMPs). We have used 705.9 live days of data in a fiducial volume containing <math><mn>97</mn><mspace width="0.2em"></mspace><mtext>kg</mtext></math> of liquid xenon at the center of the detector. The event rate in the fiducial volume after the data reduction was <math><mo>(</mo><mn>4.2</mn><mo>±</mo><mn>0.2</mn><mo>)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>3</mn></mrow></msup><mspace width="0.2em"></mspace><msup><mrow><mtext>day</mtext></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup><mspace width="0.2em"></mspace><msup><mrow><mtext>kg</mtext></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup><mspace width="0.2em"></mspace><mrow><mi>ke</mi><msubsup><mrow><mi>V</mi></mrow><mrow><mi>ee</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msubsup></mrow></math> at <math><mn>5</mn><mspace width="0.2em"></mspace><mrow><mi>ke</mi><msub><mrow><mi>V</mi></mrow><mrow><mi>ee</mi></mrow></msub></mrow></math>, with a signal efficiency of 20%. All the remaining events are consistent with our background evaluation, mostly of the “mis-reconstructed events” originated from $^{210}$Pb in the copper plates lining the detector's inner surface. The obtained upper limit on a spin-independent WIMP-nucleon cross section was <math><mn>2.2</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>44</mn></mrow></msup><mspace width="0.2em"></mspace><msup><mrow><mtext>cm</mtext></mrow><mrow><mn>2</mn></mrow></msup></math> for a WIMP mass of <math><mn>60</mn><mspace width="0.2em"></mspace><msup><mrow><mtext>GeV/c</mtext></mrow><mrow><mn>2</mn></mrow></msup></math> at the 90% confidence level, which was the most stringent limit among results from single-phase liquid xenon detectors.

T. Norita

O. Takachio

R. Kegasa

H. Takiya

R. Fujita

K. Hosokawa

A direct dark matter search in XMASS-I

Hidden photons and axion-like particles are candidates for cold dark matter if they were produced non-thermally in the early universe. We conducted a search for both of these bosons using 800 live-days of data from the XMASS detector with 327 kg of liquid xenon in the fiducial volume. No significant signal was observed, and thus we set constraints on the <math><msup><mrow><mi>α</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>/</mo><mi>α</mi></math> parameter related to kinetic mixing of hidden photons and the coupling constant <math><msub><mrow><mi>g</mi></mrow><mrow><mi>A</mi><mi>e</mi></mrow></msub></math> of axion-like particles in the mass range from 40 to 120 keV/<math><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></math>, resulting in <math><msup><mrow><mi>α</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>/</mo><mi>α</mi><mo>&lt;</mo><mn>6</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>26</mn></mrow></msup></math> and <math><msub><mrow><mi>g</mi></mrow><mrow><mi>A</mi><mi>e</mi></mrow></msub><mo>&lt;</mo><mn>4</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>13</mn></mrow></msup></math>. These limits are the most stringent over this mass range derived from both direct and indirect searches to date.

Search for dark matter in the form of hidden photons and axion-like particles in the XMASS detector

COSINE is a dark matter search experiment based on an array of low background NaI(Tl) crystals located at the Yangyang underground laboratory. The assembly of COSINE-100 was completed in the summer of 2016 and the detector is currently collecting physics quality data aimed at reproducing the DAMA/LIBRA experiment that reported an annual modulation signal. Stable operation has been achieved and will continue for at least 2Â years. Here, we describe the design of COSINE-100, including the shielding arrangement, the configuration of the NaI(Tl) crystal detection elements, the veto systems, and the associated operational systems, and we show the current performance of the experiment.

G. Adhikari

P. Adhikari

United States

E. Barbosa de Souza

Brazil

N. Carlin

S. Choi

W.Q. Choi

Indonesia

M. Djamal

United Kingdom

A.C. Ezeribe

C. Ha

I.S. Hahn

A.J.F. Hubbard

E.J. Jeon

J.H. Jo

H.W. Joo

W.G. Kang

W. Kang

M. Kauer

B.H. Kim

H. Kim

H.J. Kim

K.W. Kim

M.C. Kim

S.K. Kim

V.A. Kudryavtsev

H.S. Lee

J. Lee

J.Y. Lee

M.H. Lee

D.S. Leonard

K.E. Lim

W.A. Lynch

R.H. Maruyama

F. Mouton

S.L. Olsen

H.K. Park

H.S. Park

J.S. Park

K.S. Park

W. Pettus

Z.P. Pierpoint

H. Prihtiadi

S. Ra

F.R. Rogers

C. Rott

Canada

A. Scarff

N.J.C. Spooner

W.G. Thompson

L. Yang

S.H. Yong

Initial performance of the COSINE-100 experiment

We have developed ultra-low-background NaI(Tl) crystals to reproduce the DAMA results with the ultimate goal of achieving purity levels that are comparable to or better than those of the DAMA/LIBRA crystals. Even though the achieved background level does not approach that of DAMA/LIBRA, it is crucial to have a quantitative understanding of the backgrounds. We have studied background simulations toward a deeper understanding of the backgrounds and developed background models for a 9.16-kg NaI(Tl) crystal used in the test arrangement. In this paper we describe the contributions of background sources quantitatively by performing Geant4 Monte Carlo simulations that are fitted to the measured data to quantify the unknown fractions of the background compositions. In the fitted results, the overall simulated background spectrum well describes the measured data with a 9.16-kg NaI(Tl) crystal and shows that the background sources are dominated by surface 210 Pb and internal 40 K in the 2â6-keV energy interval, which produce 2.4Â counts/day/keV/kg (dru) and 0.5Â dru, respectively.

S.Y. Kong

S.Y. Oh

Understanding NaI(Tl) crystal background for dark matter searches

A search for dark matter was conducted by looking for an annual modulation signal due to the Earth's rotation around the Sun using XMASS, a single phase liquid xenon detector. The data used for this analysis was 359.2 live days times 832 kg of exposure accumulated between November 2013 and March 2015. When we assume Weakly Interacting Massive Particle (WIMP) dark matter elastically scattering on the target nuclei, the exclusion upper limit of the WIMP–nucleon cross section <math><mn>4.3</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>41</mn></mrow></msup><msup><mrow><mtext> cm</mtext></mrow><mrow><mn>2</mn></mrow></msup></math> at 8 GeV/c$^{2}$ was obtained and we exclude almost all the DAMA/LIBRA allowed region in the 6 to 16 GeV/c$^{2}$ range at ∼10$^{−40}$ cm$^{2}$. The result of a simple modulation analysis, without assuming any specific dark matter model but including electron/γ events, showed a slight negative amplitude. The p-values obtained with two independent analyses are 0.014 and 0.068 for null hypothesis, respectively. We obtained 90% C.L. upper bounds that can be used to test various models. This is the first extensive annual modulation search probing this region with an exposure comparable to DAMA/LIBRA.

J. Liu

Y. Onishi

J.S. Lee

Direct dark matter search by annual modulation in XMASS-I