<p>By analyzing <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">(</mo><mn>2712.4</mn><mo>±</mo><mn>14.3</mn><mo stretchy="false">)</mo><mo>×</mo><msup><mn>10</mn><mn>6</mn></msup><mtext> </mtext><mtext> </mtext><mi>ψ</mi><mo stretchy="false">(</mo><mn>3686</mn><mo stretchy="false">)</mo></math> events collected with the BESIII detector operating at the BEPCII collider, the decays <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mrow><mi>c</mi><mi>J</mi></mrow></msub><mo stretchy="false">→</mo><mi>p</mi><msup><mi>K</mi><mo>−</mo></msup><mover accent="true"><mi mathvariant="normal">Λ</mi><mo stretchy="false">¯</mo></mover><mi>η</mi><mo>+</mo><mi mathvariant="normal">c</mi><mo>.</mo><mi mathvariant="normal">c</mi></math>. (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>J</mi><mo>=</mo><mn>0</mn></math>, 1, 2) are observed for the first time, with statistical significances exceeding <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>5</mn><mi>σ</mi></math> for all three <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mrow><mi>c</mi><mi>J</mi></mrow></msub></math> states. The measured branching fractions are <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">B</mi><mo stretchy="false">(</mo><msub><mi>χ</mi><mrow><mi>c</mi><mn>0</mn></mrow></msub><mo stretchy="false">→</mo><mi>p</mi><msup><mi>K</mi><mo>−</mo></msup><mover accent="true"><mi mathvariant="normal">Λ</mi><mo stretchy="false">¯</mo></mover><mi>η</mi><mo>+</mo><mi mathvariant="normal">c</mi><mo>.</mo><mi mathvariant="normal">c</mi><mo>.</mo><mo stretchy="false">)</mo><mo>=</mo><mo stretchy="false">(</mo><mn>5.3</mn><mo>±</mo><mn>0.7</mn><mo>±</mo><mn>0.5</mn><mo stretchy="false">)</mo><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>5</mn></mrow></msup></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">B</mi><mo stretchy="false">(</mo><msub><mi>χ</mi><mrow><mi>c</mi><mn>1</mn></mrow></msub><mo stretchy="false">→</mo><mi>p</mi><msup><mi>K</mi><mo>−</mo></msup><mover accent="true"><mi mathvariant="normal">Λ</mi><mo stretchy="false">¯</mo></mover><mi>η</mi><mo>+</mo><mi mathvariant="normal">c</mi><mo>.</mo><mi mathvariant="normal">c</mi><mo>.</mo><mo stretchy="false">)</mo><mo>=</mo><mo stretchy="false">(</mo><mn>9.8</mn><mo>±</mo><mn>0.6</mn><mo>±</mo><mn>0.6</mn><mo stretchy="false">)</mo><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>5</mn></mrow></msup></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">B</mi><mo stretchy="false">(</mo><msub><mi>χ</mi><mrow><mi>c</mi><mn>2</mn></mrow></msub><mo stretchy="false">→</mo><mi>p</mi><msup><mi>K</mi><mo>−</mo></msup><mover accent="true"><mi mathvariant="normal">Λ</mi><mo stretchy="false">¯</mo></mover><mi>η</mi><mo>+</mo><mi mathvariant="normal">c</mi><mo>.</mo><mi mathvariant="normal">c</mi><mo>.</mo><mo stretchy="false">)</mo><mo>=</mo><mo stretchy="false">(</mo><mn>9.3</mn><mo>±</mo><mn>0.6</mn><mo>±</mo><mn>0.6</mn><mo stretchy="false">)</mo><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>5</mn></mrow></msup></math>, where the first uncertainties are statistical and the second are systematic. Structures consistent with the known hyperon resonances <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">Λ</mi><mo stretchy="false">(</mo><mn>1520</mn><mo stretchy="false">)</mo></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mover accent="true"><mi mathvariant="normal">Λ</mi><mo stretchy="false">¯</mo></mover><mo stretchy="false">(</mo><mn>1690</mn><mo stretchy="false">)</mo></math> are seen in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><msup><mi>K</mi><mo>−</mo></msup></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mover accent="true"><mi mathvariant="normal">Λ</mi><mo stretchy="false">¯</mo></mover><mi>η</mi></math> invariant mass spectra, respectively. The reported branching fractions include both resonant and nonresonant contributions. These results provide new experimental information on hadronic decays of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>P</mi></math>-wave charmonium states and contribute to the understanding of baryon production and hadronization dynamics in the nonperturbative QCD regime.</p>

China

M. Ablikim

Russia

M.N. Achasov

Sweden

P. Adlarson

X.C. Ai

Italy

C.S. Akondi

Germany

R. Aliberti

A. Amoroso

Q. An

Y.H. An

M.S. Anderson

Y. Bai

JINR

O. Bakina

H.R. Bao

X.L. Bao

M. Barbagiovanni

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

D. Cabiati

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

E. Di Fiore

X.X. Ding

Y. Ding

Y.X. Ding

J. Dong

L.Y. Dong

M.Y. Dong

X. Dong

Z.J. Dong

M.C. Du

S.X. Du

Shaoxu Du

X.L. Du

Y.Q. Du

Y.Y. Duan

Z.H. Duan

P. Egorov

G.F. Fan

J.J. Fan

K.X. Fan

Y.H. Fan

J. Fang

Jin Fang

S.S. Fang

W.X. Fang

Observation of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mrow><mi>c</mi><mi>J</mi></mrow></msub></math> decays into <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><msup><mi>K</mi><mo>−</mo></msup><mover accent="true"><mi mathvariant="normal">Λ</mi><mo stretchy="false">¯</mo></mover><mi>η</mi><mo>+</mo><mrow><mi mathvariant="normal">c</mi><mo>.</mo><mi mathvariant="normal">c</mi><mo>.</mo></mrow></math>

<p>Dense nuclear matter can modify the effective potential of axions, displacing them from their vacuum minimum and sourcing large external field gradients (“axion hair”). In the case of neutron stars, axion hair directly modifies the electrodynamic processes operating on the open field-line region, strongly enhancing or suppressing the acceleration experienced by ambient charges. As a result, the point in the neutron star lifetime at which pair cascades cease—known as pulsar “death”—can be dramatically altered, allowing for much older pulsars to emit observable radio emission. We study the pair discharge process in the presence of axion hair using semianalytic techniques and particle-in-cell simulations and use these results alongside pulsar demographics to derive new constraints on light QCD axions with non-negligible axion-photon coupling and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math>-violating axion-nucleon interactions. We also illustrate how nearly orthogonal rotators, where emission is observed from both poles (such as in the case of PSR <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">J</mi><mn>1906</mn><mo>+</mo><mn>0746</mn></mrow></math>), provide a complementary probe of axion hair.</p>

Samuel J. Witte

Israel

CERN

Andrea Caputo

Switzerland

Spain

Stefan Stelzl

Alexander Chernoglazov

Alexander A. Philippov

Surjeet Rajendran

Constraints on light QCD and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math>-violating axions from the death line of rotation-powered pulsars

This paper presents the measurement of $$\pi ^{\pm }$$ , $$\text {K}^{\pm }$$ , and p( $$\bar{\text {p}}$$ ) production in high-multiplicity proton–proton collisions at $$\sqrt{s}=13$$ TeV at midrapidity ( $$|y| < 0.5$$ ) using the ALICE detector at the LHC. The transverse-momentum ( $$p_\textrm{T} $$ ) spectra of these particles are reported for three high-multiplicity classes. The results show a mass- and multiplicity-dependent hardening of the $$p_\textrm{T} $$ spectra and an enhancement of the p/ $$\pi $$ ratio at intermediate $$p_\textrm{T} $$ . These features are similar to those observed in heavy-ion collisions, where quark–gluon plasma formation is expected. The new measurements have extended the highest average charged-particle multiplicity density per unit of pseudorapidity achieved in pp collisions, roughly a factor five higher than that in average inelastic pp collisions, thereby reducing the multiplicity gap between small and large collision systems. In addition, the results are further compared with previously published measurements and with model calculations obtained using distinct tunes of the PYTHIA 8 Monte Carlo generator, as well as with predictions from the EPOS4. The comparison of the $$p_\textrm{T}$$ -integrated K/ $$\pi $$ and p/ $$\pi $$ ratios across different collision systems and energies suggests that particle production scales with charged-particle multiplicity, rather than with collision energy or system size. While the PYTHIA 8 tunes and the EPOS4 model are able to reproduce some of these measurements, either quantitatively or qualitatively, none of them consistently describes all observed features of the data.

D. Abdallah

I. Abualrob

S. Acharya

G. Rinella

L. Aglietta

N. Agrawal

India

Z. Ahammed

S. Ahmad

Slovakia

I. Ahuja

Indonesia

Z. Akbar

V. Akishina

M. Al-Turany

B. Alessandro

Mexico

R. Molina

B. Ali

A. Alici

Norway

J. Alme

G. Alocco

T. Alt

I. Altsybeev

Romania

C. Andrei

N. Andreou

A. Andronic

M. Angeletti

V. Anguelov

F. Antinori

P. Antonioli

N. Apadula

H. Appelshäuser

S. Arcelli

R. Arnaldi

I. Arsene

M. Arslandok

A. Augustinus

R. Averbeck

M. Azmi

Japan

H. Baba

A. Babu

A. Badalà

J. Bae

Y. Bae

Y. Baek

X. Bai

R. Bailhache

France

Y. Bailung

R. Bala

A. Baldisseri

B. Balis

S. Bangalia

Z. Banoo

V. Barbasova

F. Barile

L. Barioglio

M. Barlou

B. Barman

Hungary

G. Barnaföldi

L. Barnby

E. Barreau

V. Barret

Brazil

L. Barreto

K. Barth

E. Bartsch

N. Bastid

G. Batigne

$$\pi $$ , K, and p production in high-multiplicity pp collisions at $$\mathbf {\sqrt{ s} = 13}$$ TeV