A search for the rare decay <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>B</mi></mrow><mrow><mo>+</mo></mrow></msup><mo stretchy="false">→</mo><mrow><mover accent="true"><mrow><mi mathvariant="normal">Λ</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover><mi>p</mi><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></mrow></math> is performed using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of <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>, corresponding to an integrated luminosity of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>5.4</mn><mtext> </mtext><mtext> </mtext><msup><mi>fb</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math>. An excess of events is found with respect to the background-only expectation, with a signal significance of 3.5 standard deviations, in the low invariant-mass region of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>m</mi><mo stretchy="false">(</mo><mover accent="true"><mrow><mi mathvariant="normal">Λ</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover><mi>p</mi><mo stretchy="false">)</mo><mo>&lt;</mo><mn>2.8</mn><mtext> </mtext><mtext> </mtext><mrow><mi>GeV</mi><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></mrow></math>. The branching fraction is measured to be <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi mathvariant="script">B</mi></mrow><mrow><mi>low</mi></mrow></msub><mo stretchy="false">(</mo><msup><mrow><mi>B</mi></mrow><mrow><mo>+</mo></mrow></msup><mo stretchy="false">→</mo><mrow><mover accent="true"><mrow><mi mathvariant="normal">Λ</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover><mi>p</mi><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow><mo stretchy="false">)</mo><mo>=</mo><mrow><mo minsize="1ex" stretchy="true">(</mo><mn>1.7</mn><msubsup><mrow><mn>0</mn></mrow><mrow><mo>−</mo><mn>0.56</mn></mrow><mrow><mo>+</mo><mn>0.65</mn></mrow></msubsup><mo stretchy="false">(</mo><mrow><mi>stat</mi></mrow><mo stretchy="false">)</mo><mo>±</mo><mn>0.17</mn><mo stretchy="false">(</mo><mrow><mi>syst</mi></mrow><mo stretchy="false">)</mo><mo>±</mo><mspace linebreak="goodbreak"></mspace><mn>0.14</mn><mo stretchy="false">(</mo><mi>ext</mi><mo stretchy="false">)</mo><mo minsize="1ex" stretchy="true">)</mo></mrow><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>8</mn></mrow></msup></mrow></math>, where the last uncertainty is due to external inputs on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="script">B</mi><mo stretchy="false">(</mo><msup><mrow><mi>B</mi></mrow><mrow><mo>+</mo></mrow></msup><mo stretchy="false">→</mo><mrow><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow><mover accent="true"><mrow><mi mathvariant="normal">Λ</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover><mi>p</mi></mrow><mo stretchy="false">)</mo><mo>×</mo><mspace linebreak="goodbreak"></mspace><mi mathvariant="script">B</mi><mo stretchy="false">(</mo><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow><mo stretchy="false">→</mo><mrow><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow><mo stretchy="false">)</mo></mrow></math>. With no significant signal observed in the high <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>m</mi><mo stretchy="false">(</mo><mover accent="true"><mi mathvariant="normal">Λ</mi><mo stretchy="false">¯</mo></mover><mi>p</mi><mo stretchy="false">)</mo></math> region above <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>2.8</mn><mtext> </mtext><mtext> </mtext><mrow><mi>GeV</mi><mo>/</mo><msup><mi>c</mi><mn>2</mn></msup></mrow></mrow></math>, an upper limit is set to be <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi mathvariant="script">B</mi></mrow><mrow><mi>high</mi></mrow></msub><mo stretchy="false">(</mo><msup><mrow><mi>B</mi></mrow><mrow><mo>+</mo></mrow></msup><mo stretchy="false">→</mo><mrow><mover accent="true"><mrow><mi mathvariant="normal">Λ</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover><mi>p</mi><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow><mo stretchy="false">)</mo><mo>&lt;</mo><mn>2.8</mn><mo stretchy="false">(</mo><mn>3.7</mn><mo stretchy="false">)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>9</mn></mrow></msup></mrow></math> at the 90% (95%) confidence level.

Netherlands

R. Aaij

United Kingdom

A.S.W. Abdelmotteleb

Switzerland

C. Abellan Beteta

F. Abudinén

T. Ackernley

United States

A.A. Adefisoye

Spain

B. Adeva

M. Adinolfi

P. Adlarson

France

C. Agapopoulou

C.A. Aidala

Z. Ajaltouni

S. Akar

K. Akiba

Poland

M. Akthar

Italy

P. Albicocco

Germany

J. Albrecht

R. Aleksiejunas

CERN

F. Alessio

P. Alvarez Cartelle

R. Amalric

Brazil

S. Amato

J.L. Amey

Y. Amhis

China

L. An

L. Anderlini

M. Andersson

P. Andreola

M. Andreotti

S. Andres Estrada

A. Anelli

D. Ao

C. Arata

F. Archilli

Z. Areg

M. Argenton

Costa Rica

S. Arguedas Cuendis

L. Arnone

A. Artamonov

M. Artuso

E. Aslanides

R. Ataíde Da Silva

M. Atzeni

B. Audurier

J.A. Authier

D. Bacher

I. Bachiller Perea

S. Bachmann

M. Bachmayer

J.J. Back

P. Baladron Rodriguez

V. Balagura

A. Balboni

W. Baldini

Z. Baldwin

L. Balzani

H. Bao

J. Baptista de Souza Leite

C. Barbero Pretel

M. Barbetti

I.R. Barbosa

R.J. Barlow

M. Barnyakov

S. Barsuk

W. Barter

J. Bartz

S. Bashir

B. Batsukh

P.B. Battista

A. Bavarchee

A. Bay

A. Beck

M. Becker

F. Bedeschi

I.B. Bediaga

N.A. Behling

S. Belin

A. Bellavista

K. Belous

I. Belov

I. Belyaev

G. Benane

G. Bencivenni

E. Ben-Haim

A. Berezhnoy

R. Bernet

S. Bernet Andres

A. Bertolin

F. Betti

J. Bex

O. Bezshyyko

S. Bhattacharya

M.S. Bieker

N.V. Biesuz

A. Biolchini

M. Birch

F.C.R. Bishop

A. Bitadze

A. Bizzeti

T. Blake

Evidence for the Rare Decay <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>B</mi></mrow><mrow><mo>+</mo></mrow></msup><mo stretchy="false">→</mo><mover accent="true"><mrow><mi mathvariant="normal">Λ</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover><mi>p</mi><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></math>

Muon-electron universality is tested in <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><mo>ℓ</mo></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mo>ℓ</mo></mrow><mrow><mo>−</mo></mrow></msup></mrow></math> decays, in the dilepton-invariant-mass region above the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ψ</mi><mrow><mo stretchy="false">(</mo><mn>2</mn><mi>S</mi><mo stretchy="false">)</mo></mrow></math> resonance. The analysis uses beauty mesons produced in proton-proton collisions recorded by the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>9</mn><mtext> </mtext><mtext> </mtext><msup><mi>fb</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math>. The ratio of branching fractions between the muon and electron channels <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>R</mi><msup><mi>K</mi><mrow><mo>*</mo><mn>0</mn></mrow></msup></msub></math> is measured to be <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msubsup><mrow><mn>1.08</mn></mrow><mrow><mo>−</mo><mn>0.12</mn></mrow><mrow><mo>+</mo><mn>0.14</mn></mrow></msubsup><mrow><mo stretchy="false">(</mo><mi>stat</mi><mo stretchy="false">)</mo></mrow><mo>±</mo><mn>0.07</mn><mrow><mo stretchy="false">(</mo><mi>syst</mi><mo stretchy="false">)</mo></mrow></mrow></math> for a dilepton-invariant-mass squared above <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>14.0</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>GeV</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>4</mn></mrow></msup></mrow></math>, consistent with the standard model prediction. This result represents the most precise measurement of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>R</mi><msup><mi>K</mi><mrow><mo>*</mo><mn>0</mn></mrow></msup></msub></math> in this region and the first such measurement performed at a hadron collider.

M. Abdelfatah

Z.B. Bai

F. Blanc

J.E. Blank

S. Blusk

Test of Lepton Flavor Universality with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>B</mi><mn>0</mn></msup><mo stretchy="false">→</mo><msup><mi>K</mi><mrow><mo>*</mo><mn>0</mn></mrow></msup><msup><mo>ℓ</mo><mo>+</mo></msup><msup><mo>ℓ</mo><mo>−</mo></msup></math> Decays at Large Dilepton Invariant Mass

A first-order phase transition could occur in the late Universe when vacuum energy begins dominating the energy density (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>z</mi><mo>≲</mo><mn>0.3</mn></mrow></math>) and convert some latent heat into other forms such as invisible radiation. This generic possibility also has concrete motivation in particle physics models, which invoke a multitude of vacua to address theoretical puzzles. The naïve constraint on such an event comes from measurements of the Hubble expansion rate, but this can only probe transitions involving <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><mn>10</mn><mo stretchy="false">)</mo><mo>%</mo></mrow></math> of the dark energy. In this Letter, we show that significantly tighter constraints appear when accounting for phase transition fluctuations affecting CMB photon propagation anisotropically. For instance, if a completed phase transition has <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>β</mi><mo>/</mo><msub><mrow><mi>H</mi></mrow><mrow><mo>⋆</mo></mrow></msub><mo>≲</mo><mn>25</mn></mrow></math>, current CMB data limit the associated vacuum energy released to less than 1% of the dark energy. A transition to negative vacuum energy (quasi-anti–de Sitter) is allowed only for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>β</mi><mo>/</mo><msub><mrow><mi>H</mi></mrow><mrow><mo>⋆</mo></mrow></msub><mo>≳</mo><mn>300</mn></mrow></math>. For <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>β</mi><mo>/</mo><msub><mrow><mi>H</mi></mrow><mrow><mo>⋆</mo></mrow></msub><mo>≲</mo><mn>500</mn></mrow></math>, the Universe will not crunch for at least 14 Gyr.

Seth Koren

Yuhsin Tsai

Runqing Wang

Boiling After the Dust Settles: Constraining First-Order Phase Transitions During Dark Energy Domination

In this Letter, we study pole skipping in nonmaximally quantum chaotic systems. Using Rindler conformal field theories and the large-<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>q</mi></math> Sachdev-Ye-Kitaev chain as illustrative examples, we argue that the pole skipping points of few-body operators organize into trajectories in the complex frequency-momentum plane, with the leading trajectory encoding the quantum Lyapunov exponent. We further propose that these trajectories admit a natural interpretation as Regge trajectories of stringy excitations in a dual stringy black-hole geometry. From this perspective, pole skipping for an individual operator can be viewed as tracking the stringy horizon through the response of a single excitation. Our results suggest that pole skipping reflects intrinsic properties of quantum chaotic systems and may be deeply connected to the structure of horizons in the stringy regime.

Ping Gao

Hong Liu

Probing Stringy Horizons with Pole Skipping in Nonmaximal Chaotic Systems

In this Letter, we consider constraints on the low-energy spectrum of scalar amplitudes with higher-spin exchanges. Assuming unitarity, crossing symmetry, and superconvergent high energy behavior, we demonstrate that the spectrum that maximizes the leading higher spin couplings of the second and third resonances is consistently given by a linear trajectory. We work strictly in ten dimensions although we expect analysis in other dimensions to be similar. For gravitational theories, the optimal spectrum is the linear trajectory defined by the mass and spin of the graviton and the lightest spin-4 resonance.

Taiwan

Yu-tin Huang

Sara Ricossa

Francesco Riva

Jie-Da Tsai

Rise of Linear Regge Trajectories

We consider the Polyakov loop correlator in the confining phase of large <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>N</mi></math> Yang-Mills theory in three and four dimensions. It can be computed by summing over the exchange of closed flux tubes winding around the thermal cycle. At short separations, the leading divergence is controlled by perturbation theory. Combining these two facts allows us to determine the asymptotic spectral density of string states contributing to the correlator. This sharply relates the weakly coupled UV of the gauge theory to the dynamics of highly energetic flux tubes. Then, in a toy integrable setting, we explore how this can bound the scattering data of the Goldstone modes on top of a long string. We derive a bound on the asymptotic behavior of the reflection amplitude of Goldstones against the flux tube boundary sourced by the Polyakov line, and rule out an asymptotically linear phase shift for the S matrix.

Jan Albert

Alexandre Homrich

Imprints of Asymptotic Freedom on Confining Strings

We construct a simple two-dimensional holographic model of a closed “baby” universe. The baby universe spacetime originates from the black hole interior in Jackiw-Teitelboim gravity. The holographic description is a low-temperature thermal pure state of two Sachdev-Ye-Kitaev (SYK) models. The construction of the state relies on the insertion of a heavy matter operator, which supports the baby universe, together with a first-order thermal phase transition between a black hole phase and an empty anti–de Sitter phase. For the transition, we employ a version of the Maldacena-Qi phase transition of two coupled SYK systems. The bulk entanglement between the anti–de Sitter region and the baby universe remains <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>O</mi><mo stretchy="false">(</mo><mi>N</mi><mo stretchy="false">)</mo></mrow></math> below the transition, owing to the large number of light bulk fields. This entanglement admits a definition through coarse-graining over SYK couplings.

Martin Sasieta

Brian Swingle

Canada

Alejandro Vilar López

Baby Universes from Thermal Pure States in the Sachdev-Ye-Kitaev Model

Using <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">(</mo><mn>10087</mn><mo>±</mo><mn>44</mn><mo stretchy="false">)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>6</mn></mrow></msup><mtext> </mtext></mrow></math> <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> events collected with the BESIII detector at the BEPCII collider at the center-of-mass energy of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>3.097</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math>, we report the first search for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>η</mi><mo stretchy="false">→</mo><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup><mi>S</mi><mo stretchy="false">→</mo><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup><mi>χ</mi><mover accent="true"><mrow><mi>χ</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover></mrow></math> with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi></math> denoting an on-shell dark scalar boson and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>χ</mi></math> an invisible dark matter particle. No significant signals are observed with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi></math> mass ranging from 0 to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>400</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math>. The upper limits on the branching fractions and the new physics coupling strengths between <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi></math> and quarks are set to be <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">(</mo><mn>1.8</mn><mi>–</mi><mn>5.5</mn><mo stretchy="false">)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>5</mn></mrow></msup></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">(</mo><mn>1.3</mn><mi>–</mi><mn>3.2</mn><mo stretchy="false">)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>5</mn></mrow></msup></mrow></math> at the 90% confidence level, respectively. The constraints on the dark-matter-nucleon scattering cross section is improved by approximately five orders of magnitude over previous dark-matter-nucleon scattering experiments, providing unique insights into sub-GeV dark matter.

M. Ablikim

Russia

M.N. Achasov

Sweden

X.C. Ai

R. Aliberti

A. Amoroso

Q. An

Y. Bai

JINR

O. Bakina

Y. Ban

H.R. Bao

V. Batozskaya

Mongolia

K. Begzsuren

N. Berger

M. Berlowski

M.B. Bertani

D. Bettoni

F. Bianchi

E. Bianco

A. Bortone

I. Boyko

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

X.R. Chen

X.T. Chen

X.Y. Chen

Y.B. Chen

Search for Sub-GeV Dark Particles in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>η</mi><mo stretchy="false">→</mo><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup><mo>+</mo><mtext>Invisible</mtext></mrow></math> Decay