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.

China

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

Germany

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.

Italy

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

In 2022, the collider detector at Fermilab (CDF) collaboration reported the $\textit{W}$-boson mass ( $ M_W= $ $ 80.4335\pm0.0094\; \text{GeV} $ ), which deviates from the standard model (SM) prediction ( $ M_W^{\rm SM}=80.357\pm0.006\; \text{GeV} $ ) by ~ $ 7\sigma $ . In contrast, the CMS collaboration obtained $ M_W=80.3602\pm0.0099\; \text{GeV} $ , which was very close to the SM global electroweak fit value of $ \sim80.357\; \text{GeV} $ . Motivated by this situation, we reassess the $\textit{W}$-boson mass within the lepton-specific two Higgs doublet model (LS-2HDM). To this end, we perform random scans (generated with SARAH 4.13.0 and evaluated with SPheno 4.0.3) and confront the results with up-to-date theoretical and experimental constraints. The scan enforces vacuum stability, perturbative unitarity, and perturbativity; electroweak precision observables via the oblique parameters $ (S,T,U) $ ; LEP bounds on $ H^\pm $ ; rare $\textit{B}$-meson decays; lepton flavor universality (LFU) in $\textit{Z}$ and $\textit{τ}$ decays; and 13 TeV LHC searches for additional Higgs bosons. Viable points are further tested with HiggsTools (HiggsSignals + HiggsBounds). In the LS-2HDM, if $ h_1 $ is the SM-like Higgs at $ m_{h_1}\simeq125 $ GeV with $ |\cos(\beta-\alpha)|\lesssim0.06 $ , $ 17\lesssim\tan\beta\lesssim39 $ , $ 144\lesssim m_{h_2}\lesssim414 $ GeV, and $ 435\lesssim m_{A,H^{\pm}}\lesssim685 $ GeV, the model reproduces the 2024 CMS $\textit{W}$-boson mass within $ 3\sigma $ . Solutions near the 2022 CDF value ( $ M_W=80.4335\pm0.0094\; \text{GeV} $ ) survive; however, after applying all constraints, including HiggsTools, they approach it at best within $ \lesssim2\sigma $ . Our findings emphasize that LS-2HDM favors the CMS results consistently with the current experimental results. Although one can theoretically accommodate the CDF results in this model, up-to-date electroweak precision bounds on oblique parameters $ (S,T,U) $ with the SM-like Higgs and LFU constraints exclude these solutions. Our results for $ W $ -boson mass can only be as close as about $ 2\sigma $ to $_{the CDF results}$.

Ali Çiçi

Hüseyin Dağ

Resolving the $\textit{W}$ boson mass in the lepton specific two Higgs doublet model * This work was supported in part by the Turkish Energy, Nuclear and Mineral Research Agency under project number 2022TENMAK(CERN)A5.H3.F2-02

Hadronic resonances, with lifetimes of a few <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>fm</mi><mo>/</mo><mi>c</mi></mrow></math> are key tools for studying the hadronic phase in high-energy collisions. This work investigates resonance production in pp collisions at <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13.6</mn><mspace width="0.28em"></mspace><mi>TeV</mi></mrow></math> and in Pb-Pb 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>5.36</mn><mspace width="0.28em"></mspace><mi>TeV</mi></mrow></math> using the EPOS4 model. The EPOS4 model provides the capability of switching the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) ON or OFF, allowing the study of final-state hadronic interactions in the hadronic phase. Although this study is primarily focused on understanding the production of hadronic resonances, we also investigate the production of strange and nonstrange hadrons in relation to rescattering, regeneration, baryon-to-meson production, and strangeness enhancement, using transverse momentum (<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mi mathvariant="normal">T</mi></msub></math>) spectra and particle ratios. Rescattering effects and strangeness enhancement play an important role in the low-<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mi mathvariant="normal">T</mi></msub></math> region, where soft, nonperturbative processes dominate particle production. At intermediate <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mi mathvariant="normal">T</mi></msub></math>, the baryon-to-meson yield ratios show an enhancement, and the strong mass-dependent radial flow observed for baryons in the most central Pb-Pb collisions reflects the interplay between hadronization dynamics and collective effects. The average <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mi mathvariant="normal">T</mi></msub></math> scaled with the reduced hadron mass (i.e., the mass divided by the number of valence quarks) is examined, revealing a deviation from a linear trend for short-lived resonances, attributed to hadronic phase effects. By analyzing the yield ratios of short-lived resonances to stable hadrons in pp and Pb-Pb collisions, the time duration (<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>τ</mi></math>) of the hadronic phase as a function of average charged multiplicity is estimated. The results show that <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>τ</mi></math> increases with increasing multiplicity and system size, also exhibiting a nonzero value for high-multiplicity pp collisions. It is found that the production of baryons such as nonstrange (<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>p</mi></math>), strange (<math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">Λ</mi></math>), and multistrange (<math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">Ξ</mi></math>, <math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">Ω</mi></math>) in the most central Pb-Pb collisions is influenced by competing processes of strangeness enhancement and baryon-antibaryon annihilation. Comparing these findings with measurements at energies available at the CERN Large Hadron Collider offers valuable insights into the underlying dynamics of the hadronic phase and their production dynamics.

India

Vikash Sumberia

Dukhishyam Mallick

Sanjeev Singh Sambyal

Nasir Mehdi Malik

Examining hadronic resonance dynamics at energies available at the CERN Large Hadron Collider: Insights from EPOS4

We present the implementation of next-to-next-to-leading order (NNLO) QCD fully-differential corrections within the G framework, for both colour-singlet and colour-singlet+jet processes at hadron colliders, by employing a nonlocal subtraction approach. In particular, we discuss the implementation details and the challenges that arise when utilizing a dynamical infrared cutoff parameter. Additionally, we combine the subtraction with the projection-to-Born method in order to include fiducial power corrections. As a test case, we provide predictions for Drell-Yan and $\textit{Z}$+jet production at the LHC, using $\textit{N}$-jettiness as resolution variable. We validate the NNLO corrections of G against finding excellent agreement. Finally, we discuss how to extend our method to calculate the N LO QCD fully-differential corrections to colour-singlet production at hadron colliders.

Simone Alioli

Switzerland

Georgios Billis

Austria

Alessandro Broggio

Giovanni Stagnitto

NNLO predictions with nonlocal subtractions and fiducial power corrections in GENEVA

A generalization of the phenomenological blast-wave-Tsallis-power model, recently proposed by the author for the hadrons' transverse momentum (<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mtext>T</mtext></msub></math>) spectra measured at the CERN Large Hadron Collider (LHC), is developed to also describe the hadrons' <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mtext>T</mtext></msub></math>-differential elliptic flow coefficients <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>v</mi><mn>2</mn></msub></math> in identical nuclei collisions of different centralities. The model describes well the available data on <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mtext>T</mtext></msub></math> spectra and <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>v</mi><mn>2</mn></msub></math> for any <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mtext>T</mtext></msub></math> of various particles, from pions to charmonia, in Pb-Pb 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></mrow></math> 2.76 and 5.02 TeV and in Xe-Xe 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></mrow></math> 5.44 TeV. Also, predictions for OO 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></mrow></math> 5.36 TeV are given. While the model is mainly targeting the energies available at the LHC, it also works at much lower energies available at the BNL Relativistic Heavy Ion Collider.

JINR

Smbat Grigoryan

Blast-wave-Tsallis-power model for <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mi>T</mi></msub></math> spectra and elliptic flow <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>v</mi><mn>2</mn></msub></math> of hadrons in collisions of identical nuclei at energies available at the CERN Large Hadron Collider

In this manuscript we examine the high energy channeling radiation datasets from the CERN-NA63 experiment using ultrarelativistic synchrotron emission. To incorporate recoil, we examine the standard quasiclassical formalism as well as develop a formalism that includes the Unruh effect by utilizing a hyperbolic recoil acceleration, based on conservation of momentum, in the classical synchrotron trajectory. We also perform an asymptotic radiation timescale analysis that predicts a photon energy threshold, beyond which the Unruh effect dominates. We then compare the classical, quasiclassical, and Unruh synchrotron theories to the data. We find that above threshold, the Unruh effect saturates the spectrum of all datasets.

Morgan H. Lynch

Hyperbolic recoil and the Unruh effect at CERN-NA63