The observed fluid behavior of the matter produced in heavy ion and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mi>p</mi></mrow></math> collisions implies that the strings stretched between the constituents of the projectile and target should have a hard core giving rise to a repulsion between them. It is shown that in these collisions there are two critical string densities, one corresponding to the well-studied percolation of strings and another to the percolation of the hard core of the strings. These two critical densities are related to two critical temperatures, one <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>T</mi><mspace width="4pt"></mspace><mo>≈</mo><mspace width="4pt"></mspace><mn>160</mn></mrow></math> MeV would correspond to the restoration of chiral symmetry and partial deconfinement and a second transition <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>T</mi><mspace width="4pt"></mspace><mo>≈</mo><mspace width="4pt"></mspace><mn>220</mn></mrow></math> MeV form the fluid behavior of quantum chromodynamics matter strongly interacting to a quasi free gas of quarks and gluons. This argument is supported by the recently published results on the sudden increase in the degrees of freedom above the deconfinement temperature in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mi>p</mi></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>A</mi><mtext>−</mtext><mi>A</mi></mrow></math> collisions [Mishra et al., <a href="http://dx.doi.org/10.1016/j.nuclphysa.2024.122865">Nucl. Phys. A 1046, 122865 (2024)</a>].

Spain

C. Pajares

United States

R.P. Scharenberg

B.K. Srivastava

Existence of a second phase transition in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>A</mi><mtext>−</mtext><mi>A</mi></mrow></math> collisions at energies available at the CERN Large Hadron Collider: A physical interpretation

We study the use of higher-order resummation for transverse observables to achieve <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>NNLO</mi><mo>+</mo><mi>PS</mi></mrow></math> matching within the geneva framework. In particular, we embed <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>q</mi><mi>T</mi></msub></math> resummation for color-singlet production at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi mathvariant="normal">N</mi><mn>3</mn></msup><mi>LL</mi></math> obtained via soft-collinear effective theory and implemented in the library scetlib within geneva. We also study for the first time the use of the generalized <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>N</mi></math>-jettiness variable in parton shower matching, and achieve the resummation of the one-jettiness defined with transverse measures up to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>NLL</mi><mo>′</mo></msup></math> accuracy. As a case study, we use these resummed calculations to construct a geneva <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>NNLO</mi><mo>+</mo><mi>PS</mi></mrow></math> generator for Higgs boson production in heavy-quark annihilation (with beauty or charm quarks in the initial state). The use of transverse measures facilitates the matching to showers ordered in transverse momentum, and opens the door to possible future extensions of this approach to the production of color singlets in association with final-state jets.

Germany

Alessandro Gavardi

Rebecca von Kuk

United Kingdom

Italy

Matthew A. Lim

Resumming transverse observables for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>NNLO</mi><mo>+</mo><mi>PS</mi></mrow></math> matching in geneva

We study classical background electric fields and the Schwinger effect in de Sitter space. We show that a constant electric field in de Sitter requires the photon to have a tachyonic mass proportional to the Hubble scale. This has physical implications for the induced Schwinger current that affect its IR behaviour. To study this, we recompute the Schwinger current in de Sitter space for charged fermions and minimally coupled scalars, imposing a physically consistent renormalization condition. We find a $\textit{finite and positive}$ Schwinger current even in the massless limit. This is in contrast to previous calculations in the literature, which found a negative IR divergence. We also obtain the first result for the Schwinger current of a non-minimally coupled scalar, including the conformally coupled case, which we find exhibits behaviour very similar to that of the fermion current. Our results may have physical implications for both magnetogenesis and inflationary dark matter production.

Mar Bastero-Gil

Portugal

Paulo B. Ferraz

António Torres Manso

Slovenia

Lorenzo Ubaldi

Roberto Vega-Morales

Schwinger current in de Sitter space * This work has been partially supported by Junta de Andalucía Projects P21-00199 and A-FQM-472-UGR20 (FEDER funds); SRA (10.13039/501100011033) and ERDF (PID2022-139466NB-C21) (R.V.M.); PID2022-140831NB-I00, funded by MICIU/AEI/10.13039/501100011033 and FEDER, UE (M.B.G., A.T.M.); by FCT CERN (10.54499/2024.00252.CERN) (M.B.G., A.T.M., P.F.); FCT Grant No. SFRH/BD/151475/2021 and 10.54499/SFRH/BD/151475/2021 (P.F.). LU is supported by the Slovenian Research Agency under research core funding No. P1-0035 and by research grants J1-60026 and J1-4389. This article is based upon work from COST Action COSMIC WISPers CA21106, supported by COST (European Cooperation in Science and Technology). R.V.M. thanks the Mainz Institute for Theoretical Physics (MITP) of the Cluster of Excellence PRISMA$^{+}$ (Project ID 390831469) for its hospitality and partial support during the completion of this work

The production of <math xmlns="http://www.w3.org/1998/Math/MathML"><msubsup><mi mathvariant="normal">Λ</mi><mi>c</mi><mo>+</mo></msubsup></math> baryons in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Pb</mi><mo>+</mo><mi>Pb</mi></mrow></math> collisions at <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>=</mo><mn>5.02</mn></mrow></math> TeV is investigated within the quark recombination framework, including the energy loss of light and charm quarks inside the hot and dense medium. The model simultaneously describes the transverse momentum (<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mi>T</mi></msub></math>) spectra of <math xmlns="http://www.w3.org/1998/Math/MathML"><msubsup><mi mathvariant="normal">Λ</mi><mi>c</mi><mo>+</mo></msubsup></math> baryons, <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msubsup><mi mathvariant="normal">Λ</mi><mi>c</mi><mo>+</mo></msubsup><mo>/</mo><msup><mi>D</mi><mn>0</mn></msup></mrow></math> yield ratio, which is attributed to the dominance of the quark recombination mechanism in the quark-gluon plasma), and the second harmonic coefficient of <math xmlns="http://www.w3.org/1998/Math/MathML"><msubsup><mi mathvariant="normal">Λ</mi><mi>c</mi><mo>+</mo></msubsup></math> baryons with emphasis on the effects of minijets on the azimuthal anisotropy. Furthermore, we extend the theoretical calculation to <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Pb</mi><mo>+</mo><mi>Pb</mi></mrow></math> collisions at <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>=</mo><mn>2.76</mn></mrow></math> TeV and make predictions for <math xmlns="http://www.w3.org/1998/Math/MathML"><msubsup><mi mathvariant="normal">Λ</mi><mi>c</mi><mo>+</mo></msubsup></math> baryons and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msubsup><mi mathvariant="normal">Λ</mi><mi>c</mi><mo>+</mo></msubsup><mo>/</mo><msup><mi>D</mi><mn>0</mn></msup></mrow></math> yield ratio. The simultaneous description of the yield, baryon-to-meson ratio, and azimuthal anisotropy further validates that the recombination model is an effective hadronization mechanism in heavy-ion collisions.

China

Jing-Zong Zhang

Hua Zheng

Lilin Zhu

Hadronization of <math xmlns="http://www.w3.org/1998/Math/MathML"><msubsup><mi mathvariant="normal">Λ</mi><mrow><mi>c</mi></mrow><mo>+</mo></msubsup></math> baryons from a recombination model in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Pb</mi><mo>+</mo><mi>Pb</mi></mrow></math> collisions at energies available at the CERN Large Hadron Collider

We analyze how NA64$\textit{μ}$ can contribute to the global SMEFT program demonstrating that it can probe two effective four-lepton operators completely unbounded so far and break one of the current flat directions. Furthermore, we also study an extension of SMEFT that includes fermion singlets of the SM gauge group in the low energy field content. This effective field theory, usually dubbed $\textit{ν}$SMEFT, is well motivated by the observation of light neutrino masses and leptonic mixing. We find that NA64$\textit{μ}$ can constrain three unbounded four-fermion operators of the $\textit{ν}$SMEFT. We derive the current bounds on these operators and compute the future sensitivity.

Switzerland

Paolo Crivelli

Josu Hernández-García

Jacobo López-Pavón

Víctor Martín Lozano

Laura Molina Bueno

First bounds on effective muon interactions using the NA64$\textit{μ}$ experiment at CERN

The recently developed “imaging-by-smashing” technique has emerged as a powerful approach to connect final-state collective flow phenomena in ultra-relativistic nuclear collisions with the intrinsic structure of the colliding nuclei. While most efforts have focused on constraining nuclear shape properties such as deformation and triaxiality, less attention has been given to the neutron skin, primarily in heavy nuclei such as $$^{208}$$ Pb. In this work, a novel study of the neutron-skin thickness in $$^{48}$$ Ca is presented, based on comparative analyses of $$^{48}$$ Ca+ $$^{48}$$ Ca and $$^{40}$$ Ca+ $$^{40}$$ Ca collisions at $$\sqrt{s_\textrm{NN}}=5.02$$ TeV. Simulations within the AMPT framework are employed to investigate the impact of varying neutron-skin thicknesses $$\Delta r_{np}$$ for $$^{48}$$ Ca on collective flow observables, including anisotropic flow coefficients and mean transverse momentum ( $$[p_\textrm{T}]$$ ) fluctuations. The triangular flow $$v_3$$ , quadrangular flow $$v_4$$ , as well as the variance and skewness of $$[p_\textrm{T}]$$ fluctuations, display notable sensitivity to $$\Delta r_{np}$$ . These findings indicate that calcium-isotope runs at the LHC could provide an independent and complementary approach to constraining $$\Delta r_{np}$$ , with the potential to help resolve the current tension between PREX and CREX measurements.

Denmark

Andreas Vitsos

Leonora Soranzo

Emil Nielsen

You Zhou

Characterizing the neutron skin of $$^{48}$$ Ca through collective flow at the CERN large hadron collider

Single-field freeze-in dark matter barely leaves observable footprints in dark matter direct detection, collider, or fixed-target experiments, which can be altered in the two-field context. In this work, we consider sequential freeze-in dark matter through signals of a dark photon mediator with a mass range of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>m</mi></mrow><mrow><msup><mrow><mi>A</mi></mrow><mrow><mo>′</mo></mrow></msup></mrow></msub><mo>∼</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msup><mi>–</mi><mn>10</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math> covered by the proposed SHiP experiment. We show that the dark charge is fixed to be <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>′</mo></msup><mo>∼</mo><mn>1.3</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>12</mn></mrow></msup></math> and the mixing parameter is restricted to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>11</mn></mrow></msup><mo>≤</mo><mi>ε</mi><mo>&lt;</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>8</mn></mrow></msup><mi>–</mi><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>7.5</mn></mrow></msup></mrow></math>, as a result of the out-of-equilibrium condition of dark photon and the observed relic abundance of dark matter. Within this <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ε</mi></math> region, the 5-yr (15-yr) data of the proton bremsstrahlung process for the dark photon, assuming vector meson (dipole) dominance, excludes <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ε</mi><mo>≥</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>8.5</mn></mrow></msup><mo stretchy="false">(</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>7.9</mn></mrow></msup><mo stretchy="false">)</mo></math> at 90% confidence level, implying only a narrow region of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ε</mi></math> close to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo>∼</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>11</mn></mrow></msup></math> left for alternative tests.

Xinyue Yin

Sibo Zheng

Illuminating sequential freeze-in dark matter with dark photon signal at the CERN SHiP experiment

We employ the Zubarev approach of the statistical operator to investigate the enhancement of the low-<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mi>T</mi></msub></math> region of pion spectra, introducing an effective pion chemical potential, to describe the overpopulation of low-energy pion states. We test a corresponding freeze-out approach by analyzing the transverse-momentum spectra of identified particles measured recently with high precision by the ALICE Collaboration in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Pb</mi><mo>+</mo><mi>Pb</mi></mrow></math> collisions at CERN LHC. A blast-wave model and a blast-wave-based particle generator, coupled to a hadronic transport model, are utilized. Bayesian inference methods are applied to extract the most probable sets of thermodynamic parameters at the chemical freeze-out hypersurface. Both models for the overpopulated pion states, the hadronic transport model and the thermal model with a nonzero pion chemical potential, provide a satisfactory description of the observed pion spectra. However, both approaches contain approximations which can be improved within a systematic nonequilibrium approach. We demonstrate that the introduction of a nonequilibrium pion chemical potential offers an efficient alternative to the conventional explanation of the low-<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mi>T</mi></msub></math> enhancement, typically attributed to resonance decays with subsequent thermalization. A similar discussion also holds for the kaon spectra.

Poland

Oleksandr Vitiuk

David Blaschke

Benjamin Dönigus

Gerd Röpke

Nonequilibrium phenomenology of identified particle spectra in heavy-ion collisions at energies available at the CERN Large Hadron Collider

Dark sector models present a rich phenomenology that requires high-intensity beams and precision detectors for thorough exploration. The NA62 experiment has already published several constraints on dark sector models, leveraging proton beam dump and meson decay techniques. This proposal aims to demonstrate the NA62 detector discovery potential for dark sector candidates by using the positron-on-target technique. High-intensity secondary positron beams, reaching up to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo>∼</mo><mn>150</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math> energy, have already been produced at the North Area extracted beam lines. If a positron beam with an intensity in the range of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>2</mn><mo>×</mo><msup><mn>10</mn><mn>14</mn></msup></math> positrons on target per year is delivered, the NA62 detector would be ideal for searches of dark sector particles in both visible and invisible decay channels. Additionally, positron on target collisions would enable precision measurements of key standard model observables, including a detailed scan of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>σ</mi><mo stretchy="false">(</mo><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup><mo stretchy="false">→</mo><msup><mrow><mi>π</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup><mo stretchy="false">)</mo></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>σ</mi><mo stretchy="false">(</mo><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</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><mo stretchy="false">)</mo></mrow></math> at the di-pion and di-muon production threshold, with discovery potential for the True Muonium <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><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></mrow></math> bound state.

F. Arias-Aragón

France

L. Darmé

R. Gargiulo

G. Grilli di Cortona

Bulgaria

V. Kozhuharov

Estonia

E. Nardi

CERN

M. Raggi

T. Spadaro

P. Valente

Dark sector searches with high-intensity positron beams in the CERN North Area

The energy-dependent hotspot model is used to predict cross sections for vector-meson diffractive photonuclear production off oxygen (<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>γ</mi><mi mathvariant="normal">O</mi></mrow></math>) and neon (<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>γ</mi><mi>Ne</mi></mrow></math>) that can be extracted from ultraperipheral O-O and Ne-Ne collisions, recently recorded at the CERN Large Hadron Collider. In both cases, two models are used to describe the nuclear shapes. Woods-Saxon prescriptions for O and Ne as well as an alpha-cluster description of O and a bowling-pin-like shape for Ne, according to the projected generator coordinate method (PGCM) formalism. Predictions are presented for the dependence on the center-of-mass energy of the photon-nucleus system, as well as on Mandelstam <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>t</mi></math>, of the cross sections for the coherent and the incoherent photonuclear production of <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>ρ</mi><mn>0</mn></msup></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> vector mesons. Furthermore, the rapidity dependence of the ultraperipheral cross section is reported for all cases. It is found that the incoherent process provides a measurable signature for the approach to the gluon-saturation regime, and that the simultaneous determination of <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>ρ</mi><mn>0</mn></msup></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> coherent and incoherent production provides a strong constraint on nuclear models for both O and Ne.

Czechia

J. Cepila

J.G. Contreras

M. Matas

A. Ridzikova

Diffractive vector meson photoproduction in oxygen-oxygen and neon-neon ultraperipheral collisions at energies available at the CERN Large Hadron Collider