We report an experimental investigation of the reactions <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mover accent="true"><mrow><mi>n</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover><mi>p</mi><mo stretchy="false">→</mo><mn>2</mn><msup><mrow><mi>π</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mover accent="true"><mrow><mi>n</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover><mi>p</mi><mo stretchy="false">→</mo><mn>2</mn><msup><mrow><mi>π</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup></mrow></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mover accent="true"><mrow><mi>n</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover><mi>p</mi><mo stretchy="false">→</mo><mn>2</mn><msup><mrow><mi>π</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup><mn>2</mn><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup></mrow></math> using <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">(</mo><mn>10.087</mn><mo>±</mo><mn>0.044</mn><mo stretchy="false">)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>9</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> events collected with the BESIII detector at the BEPCII storage ring. The antineutron (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mover accent="true"><mi>n</mi><mo stretchy="false">¯</mo></mover></math>) is produced in the decay <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi><mo stretchy="false">→</mo><mi>p</mi><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup><mover accent="true"><mrow><mi>n</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover></mrow></math> with studied momentum from 200 to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>1174</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mo>/</mo><mi>c</mi></mrow></math>, while the target proton originates from the hydrogen nuclei in the cooling oil of the beam pipe. This novel method pioneers the study of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mover accent="true"><mi>n</mi><mo stretchy="false">¯</mo></mover></math>-nucleon interactions at an <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> collider, providing the first experimental data for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mover accent="true"><mrow><mi>n</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover></mrow></math> momenta exceeding <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>800</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mo>/</mo><mi>c</mi></mrow></math>.

China

M. Ablikim

Russia

M.N. Achasov

Sweden

P. Adlarson

X.C. Ai

Germany

R. Aliberti

Italy

A. Amoroso

Q. An

Y. Bai

JINR

O. Bakina

Y. Ban

H.R. Bao

X.L. Bao

Poland

V. Batozskaya

Mongolia

K. Begzsuren

N. Berger

M. Berlowski

M.B. Bertani

D. Bettoni

F. Bianchi

E. Bianco

A. Bortone

I. Boyko

United States

R.A. Briere

A. Brueggemann

H. Cai

M.H. Cai

X. Cai

A. Calcaterra

G.F. Cao

N. Cao

Türkiye

S.A. Cetin

X.Y. Chai

J.F. Chang

T.T. Chang

G.R. Che

Y.Z. Che

C.H. Chen

Chao Chen

G. Chen

H.S. Chen

H.Y. Chen

M.L. Chen

S.J. Chen

S.M. Chen

T. Chen

W. Chen

X.R. Chen

X.T. Chen

X.Y. Chen

Y.B. Chen

Y.Q. Chen

Z.K. Chen

J. Cheng

L.N. Cheng

South Korea

S.K. Choi

X. Chu

G. Cibinetto

F. Cossio

United Kingdom

J. Cottee-Meldrum

H.L. Dai

J.P. Dai

X.C. Dai

A. Dbeyssi

R.E. de Boer

D. Dedovich

C.Q. Deng

Z.Y. Deng

A. Denig

I. Denisenko

M. Destefanis

F. De Mori

X.X. Ding

Y. Ding

Y.X. Ding

J. Dong

L.Y. Dong

M.Y. Dong

X. Dong

M.C. Du

S.X. Du

X.L. Du

Y.Y. Duan

Z.H. Duan

P. Egorov

G.F. Fan

J.J. Fan

Y.H. Fan

J. Fang

S.S. Fang

W.X. Fang

Y.Q. Fang

L. Fava

F. Feldbauer

G. Felici

C.Q. Feng

J.H. Feng

L. Feng

Q.X. Feng

Study of the Reactions <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mover accent="true"><mrow><mi>n</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover><mi>p</mi><mo stretchy="false">→</mo><mn>2</mn><msup><mrow><mi>π</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>2</mn><msup><mrow><mi>π</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup></mrow></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>2</mn><msup><mrow><mi>π</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup><mn>2</mn><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup></mrow></math> Using <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi><mo stretchy="false">→</mo><mi>p</mi><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup><mover accent="true"><mrow><mi>n</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover></mrow></math>

We have performed hyperfine spectroscopy of two transitions in ground-state deuterium and searched for violations of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>C</mi><mi>P</mi><mi>T</mi></mrow></math> and Lorentz symmetry that would manifest as sidereal variations of the observed transition frequencies. Several nonrelativistic proton coefficients of the Standard-Model extension framework have been addressed. The spin-independent coefficients with momentum power <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>k</mi><mo>=</mo><mn>2</mn></math>, 4 are constrained for the first time. Bounds on spin-dependent coefficients are improved by exploiting a sensitivity enhancement originating from the relative momenta of the nucleons in the deuteron. The best previous constraints by hydrogen maser measurements are surpassed by 4 and 14 orders of magnitude for coefficients with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>k</mi><mo>=</mo><mn>2</mn></math> and 4, respectively.

Austria

A. Nanda

France

D. Comparat

O. Dulieu

S. Lahs

Canada

C. Malbrunot

L. Nowak

M.C. Simon

E. Widmann

Demonstration of Deuterium’s Enhanced Sensitivity to Symmetry Violations Governed by the Standard-Model Extension

Custodial naturalness is a recently introduced idea that combines conformal and scalar sector custodial symmetry to address the electroweak (EW) scale hierarchy problem of the standard model (SM). We introduce a new model that realizes custodial naturalness without extension of the SM gauge group. The number of new dynamical degrees of freedom is minimized, and the custodial symmetry is reduced to SO(5). This requires a new scalar singlet field that automatically is a good dark matter (DM) candidate, produced via freeze-in with moderate couplings. The most minimal scenario allows the quantum critical generation of the EW scale in a phenomenologically viable way requiring a UV completion at around <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mn>10</mn></mrow><mrow><mn>11</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math>. Including ingredients for neutrino mass generation can push this scale to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>M</mi><mi>Pl</mi></msub></math>.

Thede de Boer

Manfred Lindner

Portugal

Andreas Trautner

Hidden Sector Custodial Naturalness

We investigate the charge-charge correlation (QQC) in electron-positron annihilation as a probe of charge dynamics in quantum chromodynamics. While generally divergent beyond leading order, we show that the QQC is infrared and collinear safe in the back-to-back limit, a property that we dub leading-power safety. This enables an analytic perturbative treatment that bypasses the reliance on nonperturbative track or fragmentation functions. Using soft-collinear effective field theory, we derive a factorization theorem and determine its logarithmic behavior analytically up to four loops in QCD, uncovering remarkable connections with the energy-energy correlation (EEC). Prior to this Letter, the behavior of the QQC beyond leading order was entirely unknown; we now establish its resummation to next-to-next-to-next-to-next-to-leading logarithmic (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi mathvariant="normal">N</mi></mrow><mrow><mn>4</mn></mrow></msup><mi>LL</mi></mrow></math>) accuracy, placing it among the observables with the highest perturbative precision alongside the EEC. Our results are validated through a numerical analysis using event2, exhibiting excellent agreement with the predicted singular terms. This Letter establishes the QQC as a novel, calculable probe of charge dynamics and unveils a new window into the inner workings of non-Abelian gauge theories.

CERN

Pier Francesco Monni

Gherardo Vita

Zhen Xu

Hua Xing Zhu

Edge of Safety: Charge-Charge Correlation in the Back-to-Back Limit

We report a follow-up axion haloscope search near 1.036 GHz that completes and extends our previous work [Ahn et al. <a href="http://dx.doi.org/10.1103/PhysRevX.14.031023">Phys. Rev. X 14, 031023 (2024)</a>], in which a portion of the HEMT-based data could not be analyzed due to unrecorded experimental information. While recovering this dataset, we identified an excess near 1.036 GHz that satisfied our candidate-selection criteria, motivating dedicated validation studies, including independent cross-checks and reexamination with the original apparatus. The excess did not persist under these investigations and was not confirmed as an axion dark-matter signal. We subsequently extended the search over a 20-MHz band surrounding the candidate using a quantum-noise-limited amplifier, achieving sensitivity close to the Dine-Fischler-Srednicki-Zhitnitsky benchmark. In the absence of a confirmed signal, we set improved 90% confidence-level upper limits on the axion-photon coupling over the frequency range 1.026–1.045 GHz. This Letter highlights the importance of robust candidate-validation strategies as haloscope searches approach discovery-level sensitivity.

Saebyeok Ahn

Boris I. Ivanov

Ohjoon Kwon

HeeSu Byun

Japan

Arjan F. van Loo

SeongTae Park

JinMyeong Kim

Junu Jeong

Soohyung Lee

Jinsu Kim

Çağlar Kutlu

Andrew K. Yi

Yasunobu Nakamura

Seonjeong Oh

Danho Ahn

SungJae Bae

Hyoungsoon Choi

Jihoon Choi

Yonuk Chong

Woohyun Chung

Violeta Gkika

Jihn E. Kim

Younggeun Kim

Byeong Rok Ko

Lino Miceli

Doyu Lee

Jiwon Lee

Ki Woong Lee

MyeongJae Lee

Andrei Matlashov

Pallavi Parashar

Taehyeon Seong

Yun Chang Shin

Sergey V. Uchaikin

Yannis K. Semertzidis

SungWoo Youn

Extended Haloscope Search and Exclusion of a Candidate Signal near 1.036 GHz

We introduce accelerated sequential posterior inference via reuse (ASPIRE), a broadly applicable framework that transforms existing posterior samples and Bayesian evidence estimates into unbiased results under alternative models without rerunning the original analysis. ASPIRE combines normalizing flows with a generalized sequential Monte Carlo (SMC) scheme, enabling efficient updates of existing results and reducing total likelihood evaluations and wall times by factors of up to 5.8 and 5.5, respectively, with larger gains per posterior sample. This addresses a growing problem in gravitational-wave astronomy, where events must be repeatedly reanalyzed under different models or physical hypotheses. We show that ASPIRE reproduces full Bayesian results when switching waveform models or adding physical effects such as spin precession and orbital eccentricity. With this statistical robustness, ASPIRE turns repeated reanalyses into fast, reliable updates—paving the way for systematic studies of waveform systematics, scalable reanalyses across large event catalogs, and broadly applicable Bayesian reanalysis across other scientific domains.

Michael J. Williams

Accelerated Sequential Posterior Inference via Reuse for Gravitational-Wave Analyses

A terrestrial population of room-temperature millicharged particles can arise if they make up a dark matter subcomponent or if they are light enough to be produced in cosmic ray air showers. In a companion paper, we showed that a simple electrified shell acts as an efficient accumulator for such particles, parametrically enhancing their local density by many orders of magnitude. Here we demonstrate that Cavendish tests of Coulomb’s Law, performed since the late 18th century, function as both quasistatic accumulators and detectors for this overdensity. Reinterpretations of these past Cavendish tests thus provide some of the strongest bounds on a terrestrial millicharge population. We also propose surrounding a Cavendish test with an additional charged shell, which significantly improves the sensitivity and can even enable detection of the irreducible density of millicharged particles generated from cosmic rays. Using decades-old technology, this can outperform future accelerator searches for sub-GeV masses.

Asher Berlin

Zachary Bogorad

Peter W. Graham

Harikrishnan Ramani

Cavendish Tests of Millicharged Particles

We propose a quantum-error-correction-inspired noise mitigation protocol for enhancing the sensitivity of wavelike dark matter searches with quantum sensors. Our protocol uses multiple sensors to mitigate the noise affecting each sensor individually, allowing for the suppression of excitation noise that is parallel to the dark matter signal. We demonstrate that our protocol can improve the sensitivity to dark matter signals by a factor of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msqrt><mrow><mi>N</mi></mrow></msqrt></mrow></math>, where <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>N</mi></math> is the number of sensors used, for small <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>N</mi></math>. Furthermore, for sufficiently large <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>N</mi></math>, we find that our protocol achieves the same performance as the standard quantum limit by the ideal measurement, which nonentangled sensors with parallel noise cannot reach due to the unknown phase of the dark matter field. Our Letter can be widely applied to various types of signals with unknown phases and has the potential to enhance the sensitivity of quantum sensors such as arrays of resonant cavities.

Hajime Fukuda

Takeo Moroi

Thanaporn Sichanugrist

Quantum-Error-Correction-Inspired Noise Mitigation for Wavelike Dark Matter Searches with Quantum Sensors

An analysis of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>B</mi></mrow><mrow><mn>0</mn></mrow></msup><mo stretchy="false">→</mo><msup><mrow><mi>K</mi></mrow><mrow><mo>*</mo><mn>0</mn></mrow></msup><mo stretchy="false">(</mo><mo stretchy="false">→</mo><msup><mrow><mi>K</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup><mo stretchy="false">)</mo><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></math> decay is presented using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>8.4</mn><mtext> </mtext><mtext> </mtext><msup><mi>fb</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math>. The full set of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math>-averaged and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math>-asymmetric angular observables is determined in bins of the invariant mass squared of the dimuon system, as well as the branching fraction relative to the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>B</mi></mrow><mrow><mn>0</mn></mrow></msup><mo stretchy="false">→</mo><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow><mo stretchy="false">(</mo><mo stretchy="false">→</mo><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>−</mo></mrow></msup><mo stretchy="false">)</mo><msup><mrow><mi>K</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></math> decay. For the first time, the full set of observables pertaining to the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>K</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup></math> S-wave contribution to the final state are presented and consideration is given to effects arising from the mass of the muons. The extracted <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math>-asymmetry observables show no significant deviations from zero. The measurements of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math>-averaged observables and the branching fractions continue to exhibit the pattern of tensions with the standard model predictions that have been seen in previous analyses that use part of the dataset considered in this Letter.

Netherlands

R. Aaij

A.S.W. Abdelmotteleb

Switzerland

C. Abellan Beteta

F. Abudinén

T. Ackernley

A.A. Adefisoye

Spain

B. Adeva

Comprehensive Analysis of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>B</mi></mrow><mrow><mn>0</mn></mrow></msup><mo stretchy="false">→</mo><msup><mrow><mi>K</mi></mrow><mrow><mo>*</mo><mn>0</mn></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></math> Decay