<p>Super-Kamiokande (SK) has observed <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mmultiscripts><mrow><mi mathvariant="normal">B</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>8</mn></mrow></mmultiscripts></mrow></math> solar neutrino elastic scattering at recoil electron kinetic energies (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>E</mi><mi>kin</mi></msub></math>) as low as 3.49 MeV to study neutrino flavor conversion within the Sun. At SK-observable energies, these conversions are dominated by the Mikheyev-Smirnov-Wolfenstein effect. An upturn in the electron neutrino survival probability in which vacuum neutrino oscillations become dominant is predicted to occur at lower energies, but radioactive background increases exponentially with decreasing energy. New machine learning approaches provide substantial background reduction below 3.49 MeV such that statistical extraction of solar neutrino interactions becomes feasible. This article presents an analysis of the solar neutrino interaction rate at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>E</mi><mi>kin</mi></msub><mo>&lt;</mo><mn>3.49</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi></math> with the full SK-IV period, using data from a wideband intelligent trigger when available and with a boosted decision tree for event selection. A solar neutrino signal is observed between <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>2.99</mn><mtext> </mtext><mtext> </mtext><mrow><mi>MeV</mi></mrow><mo>&lt;</mo><msub><mi>E</mi><mi>kin</mi></msub><mo>&lt;</mo><mn>3.49</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi></math> with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>2.76</mn><mi>σ</mi></math> significance and a data to unoscillated Monte Carlo ratio of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mn>0.307</mn><mrow><mo>−</mo><mn>0.111</mn></mrow><mrow><mo>+</mo><mn>0.112</mn></mrow></msubsup></math>. These additional low-energy data have a negligible effect on the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>1</mn><mi>σ</mi></math> intervals of the fits to the solar neutrino energy spectrum but have a noticeable effect on the best fit when using the exponential parametrization.</p>

United States

A. Yankelevich

Japan

K. Abe

Y. Asaoka

M. Harada

Y. Hayato

K. Hiraide

T.H. Hung

K. Hosokawa

K. Ieki

M. Ikeda

J. Kameda

Y. Kanemura

Y. Kataoka

S. Miki

S. Mine

M. Miura

S. Moriyama

K. Nakagiri

M. Nakahata

S. Nakayama

Y. Noguchi

G. Pronost

K. Sato

H. Sekiya

R. Shinoda

M. Shiozawa

Y. Suzuki

A. Takeda

Y. Takemoto

H. Tanaka

T. Yano

S. Chen

Y. Itow

T. Kajita

R. Nishijima

K. Okumura

T. Tashiro

T. Tomiya

X. Wang

Spain

F.J. de Garay Arcones

P. Fernandez

L. Labarga

D. Samudio

B. Zaldivar

C. Yanagisawa

B. Jargowsky

E. Kearns

J. Mirabito

L. Wan

T. Wester

Canada

B.W. Pointon

J. Bian

B. Cortez

N.J. Griskevich

Y. Jiang

M.B. Smy

H.W. Sobel

V. Takhistov

J. Hill

South Korea

M.C. Jang

S.H. Lee

D.H. Moon

R.G. Park

B.S. Yang

B. Bodur

K. Scholberg

C.W. Walter

France

A. Beauchêne

O. Drapier

A. Ershova

M. Ferey

E. Le Blévec

Th. A. Mueller

P. Paganini

C. Quach

R. Rogly

T. Nakamura

J.S. Jang

United Kingdom

R.P. Litchfield

L.N. Machado

F.J.P. Soler

J.G. Learned

K. Choi

Vietnam

S. Cao

L.H.V. Anthony

N.W. Prouse

M. Scott

Y. Uchida

Italy

V. Berardi

N.F. Calabria

M.G. Catanesi

N. Ospina

E. Radicioni

A. Langella

G. De Rosa

G. Collazuol

M. Feltre

M. Mattiazzi

L. Ludovici

M. Gonin

Measurement of the solar neutrino interaction rate below 3.49 MeV in Super-Kamiokande-IV

A search is presented for massive long-lived particles in events featuring at least one displaced vertex and at least one displaced muon, using proton–proton collision data collected by the ATLAS detector at the Large Hadron Collider from 2022 to 2024 at a centre-of-mass energy of 13.6 TeV. The data sample corresponds to an integrated luminosity of 164 fb <math altimg='si22.svg'><msup><mrow /><mrow><mo>&#8722;</mo><mn>1</mn></mrow></msup></math>. The analysis targets scenarios in which long-lived particles decay inside the ATLAS inner detector, resulting in a topology of at least one massive, displaced vertex (DV) with multiple associated tracks, and at least one muon with a large transverse impact parameter relative to the primary interaction point. The muon is not required to be associated with the DV. Two signal regions are defined by the transverse distance of the reconstructed DV from the interaction point. Background contributions are estimated by using fully data-driven techniques. No significant excess above the expected background is observed. Upper limits at 95% confidence level are set on the visible cross-section and on the production cross-sections of several benchmark models of <italic>R</italic>-parity-violating supersymmetry.

G. Aad

Norway

E. Aakvaag

B. Abbott

United Arab Emirates

S. Abdelhameed

Germany

K. Abeling

N.J. Abicht

S.H. Abidi

M. Aboelela

Morocco

A. Aboulhorma

Israel

H. Abramowicz

B.S. Acharya

A. Ackermann

C. Adam Bourdarios

Poland

L. Adamczyk

S.V. Addepalli

M.J. Addison

J. Adelman

Türkiye

A. Adiguzel

T. Adye

A.A. Affolder

Y. Afik

M.N. Agaras

A. Aggarwal

Romania

C. Agheorghiesei

A. Ahmad

F. Ahmadov

S. Ahuja

China

X. Ai

G. Aielli

A. Aikot

M. Ait Tamlihat

Sweden

T.P.A. Åkesson

D. Akiyama

N.N. Akolkar

S. Aktas

G.L. Alberghi

J. Albert

Switzerland

U. Alberti

P. Albicocco

S. Alderweireldt

Z.L. Alegria

M. Aleksa

I.N. Aleksandrov

C. Alexa

Greece

T. Alexopoulos

F. Alfonsi

M. Algren

M. Alhroob

Czechia

B. Ali

H.M.J. Ali

S. Ali

S.W. Alibocus

South Africa

M. Aliev

G. Alimonti

C. Allaire

B.M.M. Allbrooke

D.R. Allen

J.S. Allen

J.F. Allen

Australia

C.S. Alley

E.R. Almazan

A. Aloisio

Argentina

F. Alonso

C. Alpigiani

A. Alvarez Fernandez

M. Alves Cardoso

M.G. Alviggi

M. Aly

Brazil

Y. Amaral Coutinho

A. Ambler

C. Amelung

M. Amerl

Search for massive, long-lived particles in events with displaced vertices and displaced muons in <italic>pp</italic> collisions at <math altimg='si21.svg'><mrow><msqrt><mi>s</mi></msqrt><mo linebreak='goodbreak'>=</mo><mn>13.6</mn></mrow></math> TeV with the ATLAS experiment