abstract

The Electron–Ion Collider (EIC) will be a novel experimental facility to explore the properties of gluons in nucleons and nuclei, shedding light on their structure and dynamics. The EIC community outlined the physics program of the EIC in a White Paper, and the demanding detector requirements and potential technologies to deploy at an EIC detector were published in a comprehensive Yellow Report. The general-purpose detector resulting from these efforts, ePIC, is designed to perform a broad physics program. At the same time, the wider EIC community is strongly in favor of a second detector at the EIC. Having two general-purpose collider detectors to support the EIC science program allows us to have cross-checks and control of systematic uncertainties for potential scientific discoveries. The second detector should feature complementary technologies where possible. It can also focus on specific measurements that are less well-addressed by ePIC. The second interaction region provides potentially improved forward detector acceptance at low \(p_{\mathrm {T}}\) and a secondary beam focus that enables to enhance the exclusive, tagging, and diffractive physics program. Hereby, I will present the potential capabilities of the second detector and discuss studies related to its diffractive physics program.

abstract

The study of the production of strange \({\mit \Lambda }\)s and multistrange baryons (\({\mit \Xi },\ {\mit \Omega }\)) and antibaryons on nuclear targets at the energy region from SPS up to LHC in the framework of the Quark–Gluon String Model is presented and compared with the available experimental data. The most significant results of this analysis is the significant dependence on the centrality of the collision of the experimental \(\bar {{\mit \Xi }}^+/\bar {{\mit \Lambda }}\) and \(\bar {{\mit \Omega }}^+/\bar {{\mit \Lambda }}\) ratios in heavy-ion collisions, at SPS energies.

abstract

Though taking of the new data from the H1 and ZEUS experiments at HERA finished in 2007, their analysis is still ongoing and new results are being published. Here, we discuss the most recent results obtained from the two experiments. A new measurement of inclusive-jet cross sections in the Breit frame and the azimuthal correlation between the leading jet and the scattered lepton in NC DIS are presented. Also, the differential cross-section measurement of NC DIS events with an empty hemisphere in the Breit frame, the 1-jettiness event shape observable \(\tau ^{\rm b}_1\) and the first measurement of groomed event shape observables in DIS are discussed.

abstract

We calculate differential distributions for diffractive production of dijets in the \(ep\rightarrow e^{'}p\) jet jet reaction using off-diagonal unintegrated gluon distributions, often called GTMDs for brevity. Different models are used. We focus on the contribution to exclusive \(q\bar {q}\) dijets. The results of our calculations are compared with the H1 and ZEUS data. Except for one GTMD, our results are below the HERA data points. This is in contrast with recent results where the normalization was adjusted to some selected distributions and no agreement with other observables was checked. We conclude that the calculated cross sections are only a small part of the measured ones which probably contain also processes with Pomeron remnant, Reggeon exchange, etc. We present also azimuthal correlations between the sum and the difference of dijet transverse momenta. The cuts on transverse momenta of jets generate azimuthal correlations (in this angle) which can be easily misinterpreted as due to the so-called elliptic GTMD.

abstract

The Central Exclusive Production (CEP) processes with Double Pomeron Exchange (DPE) in proton–proton collisions are particularly intriguing as they can generate the exclusive \(h^+h^-\) pair with an even spin and positive parity. This unique characteristic makes them an ideal environment for the exploration and discovery of glueball states. In this work, we will present results on CEP of charged hadron pairs \(h^+h^-(h = \pi , K, p)\) measured with the STAR experiment at RHIC in proton–proton collisions at \(\sqrt {s} = 200\) GeV and 510 GeV. The differential fiducial cross sections at \(\sqrt {s} = \) 200 GeV will be presented and compared to the theoretical calculations from DPE models. Structures observed in the mass spectra of \(\pi ^+\pi ^-\) and \(K^+K^-\) pairs were found consistent with the DPE model, while angular distributions of pions suggested a dominant spin-0 contribution to \(\pi ^+\pi ^-\) production. We also present preliminary results on the measurement of the same physics process at the higher \(\sqrt {s} = \) 510 GeV.

abstract

ILUMI4d, an algorithm to compute the single-bunch luminosity and the space-time structure of luminosity at a collider for arbitrary beam parameter settings, is described. The performance of ILUMI4d is benchmarked for different beam settings (no crab angle), by comparing the computed luminosity for Gaussian bunches with the analytical formula (no hourglass effect) and the numerical integrator (hourglass effect) for the standard LHC settings. The results obtained with ILUMI4d show an agreement better than 1.2%. Furthermore, the vertex distribution as a function of the bunch crossing time is computed for an ideal and full compensating crab cavity.

abstract

A dip–bump structure in the squared four-momentum transfer (\(t\)) distribution of proton’s single- and double-diffractive dissociation is predicted around \(t\approx -4\) GeV\(^2\) for single-diffractive distribution at LHC energies.

abstract

The collective flow of particles produced in heavy-ion collisions offers valuable insights into the dynamics of the Quark–Gluon Plasma (QGP) medium. Flow coefficients can be measured to probe the medium as they are sensitive to its different properties. The directed flow \((v_{1})\) slope (d\(v_{1}/\)d\(y\)) of protons at mid-rapidity is expected to be sensitive to the first-order phase transition. The number of constituent quarks (NCQ) scaling of elliptic flow (\(v_{2}\)) can be regarded as a signature of the QGP formation. Triangular flow (\(v_{3}\)) typically arises from fluctuations and can offer constraints on the initial state geometry and fluctuations. The Relativistic Heavy-Ion Collider (RHIC) is a versatile facility to collide a wide range of heavy-ion systems at various beam energies. In this paper, we will discuss selected results on the collective properties of nuclear matter from the STAR and PHENIX experiments at RHIC.

abstract

The identification of gamma-ray-induced air showers with Cherenkov telescopes suffers from contamination with a specific class of cosmic-ray-induced air showers. The predictions for this background show strong discrepancies between the available event generators. In this study, we identify collision events of cosmic rays with atmospheric nuclei in which a large fraction of the original beam energy is transmitted to the electromagnetic part of the shower as the main source for this background. Consequently, we define a pseudorapidity region of interest for hadron collider experiments that corresponds to this background, taking into account the center-of-mass energy. This region of interest is compared with the available datasets and the pseudorapidity coverage of the detectors that recorded it. We find that the LHCf and RHICf detectors are the only ones covering substantial parts of this region of interest and suggest a measurement of the energy spectra of reconstructed neutral pions to be made with this data. Such results could serve as valuable constraints for future parameter tuning of the event generators to improve the background estimation uncertainties for gamma-ray-induced air shower identification.

abstract

The odderon is the \(C\)-odd amplitude that does not fall (or decrease very slowly) with energy. The expected amplitude is small and mainly real. Therefore, extracting it from the data on top of a much larger \(C\)-even contribution is challenging. The only chance is to consider the very low-\(|t|\) region of the Coulomb nuclear interference or the diffractive dip region. Here, we perform the analysis of elastic scattering \(pp\) and \(\bar pp\) data at low momentum transfer \(|t| \lt 0.1\) GeV\(^2\) within large collider energy interval \(\sqrt s = 50\) GeV–13 TeV in order to evaluate quantitatively the possible odderon contribution. We use the two-channel eikonal model, which naturally accounts for the screening of the odderon amplitude by the \(C\)-even (Pomeron) exchanges.

abstract

A short run of proton–oxygen (\(p\)O) collisions is planned at the Large Hadron Collider at CERN to improve the modeling of air showers, which are described using hadronic Monte Carlo simulations. The very forward proton and neutron detectors introduced by the ATLAS and CMS experiments could provide a unique opportunity to study elastic and diffractive interactions in \(p\)O collisions for the first time at center-of-mass energies above the TeV scale. In these proceedings, we will present the impact of proton and neutron tagging on the measurement of the diffractive components and discuss the perspectives of measuring decay products of oxygen ions after dissociation.

abstract

The potential effects of absorptive corrections in high-energy forward elastic proton–proton scattering were investigated. The analysis revealed that a hypothetical systematic bias in the experimentally measured values of the real-to-imaginary ratio, \(\rho \), improves the Regge fit for the proton–proton \(\rho \) and \(\sigma _{\mathrm {tot}}\). However, such a bias worsens the discrepancy between \(\sigma ^{\mathrm {meas}}_{\mathrm {tot}}\) and \(\rho ^{\mathrm {meas}}\) reported in the TOTEM measurements at \(\sqrt {s} = 13\) TeV. Additionally, assuming a logarithmic dependence of the hadronic slope on \(t\), \(B(t) = \beta _0 (1 + \beta ' \ln {t})\), may influence the interpretation of the TOTEM result for \(\rho \).

abstract

We discuss scaling properties of the elastic \(pp\) cross section both at the ISR and the LHC. We observe that the ratio of bump-to-dip positions of the differential cross section d\(\sigma _{\rm el}/\)d\(t\) is constant over a wide energy range. We next study the consequences of this property, including geometric scaling at the ISR and new scaling laws at the LHC.

abstract

The diffractive cross sections constitute a significant fraction of the total hadronic cross section in proton–proton collisions. However, due to its non-perturbative nature, the understanding of the fundamental properties of these processes highly relies on experimental studies. In these proceedings, we report on the measurements of the inclusive and identified charged-hadron spectra produced via a single diffraction process in proton–proton collisions at \(\sqrt {s} = 200\) GeV. In particular, we compare particle ratios of \(\bar {p}/p\) and \(K/\pi \) to theoretical models’ calculations. In addition, the first measurement of the proton–proton elastic cross section at \(\sqrt {s} = 510\) GeV is presented. The dependences of the elastic cross section on the collision energy and the four-momentum transfer \(t\) are discussed and compared to model calculations for the relevant physics implications.

abstract

The LHCb detector, with its unique forward rapidity coverage, is able to probe kinematic regions at Bjorken-\(x\) as low as \(10^{-6}\). This unique capability, combined with excellent momentum resolution, vertex reconstruction, and particle identification, enables precision measurements at low transverse momentum and forward rapidity. In this paper, we discuss the latest results of vector-meson exclusive production in \(pp\) and PbPb collisions and the production of light neutral mesons and \(D^0\) mesons in lead–lead collisions, shedding light on partonic and nuclear dynamics at unprecedented small-\(x\) scales.

abstract

The ALICE detector at the LHC has undergone a major upgrade in the long shutdown 2019–2021 to be able to take data at much-increased rates in Runs 3 and 4. The upgrades of the detector systems used for analysing double-gap events are described, and the improvement in data taking capability for such double-gap events is presented.

abstract

Over many years of operation, the ATLAS detector at the LHC has proved its capabilities in studies of diffractive processes. The paper presents an overview of the measurements performed.

abstract

Experimental results from the CMS and TOTEM collaborations on diffractive processes, namely nonresonant continuum central exclusive production of pion pairs, hard color-singlet exchange in dijet events, and single-diffractive dijet production in proton–proton collisions, are presented.

abstract

The Lévy \(\alpha \)-stable generalization of the ReBB model of elastic proton–proton and proton–antiproton scattering is presented. The motivation for the future use of this model in describing experimental data is discussed.

abstract

We demonstrate the breakdown of collinear factorisation for the exclusive photoproduction at leading twist of a \(\pi ^0 \gamma \) pair, sensitive to both quark and gluon GPD channels. For the very first time in the case of an exclusive process, we demonstrate the breakdown of collinear factorisation through soft-to-collinear Glauber exchanges. We show that the amplitude fails to factorise due to the presence of a Glauber pinch, which has the same power counting as the standard collinear pinch. The Glauber pinch that occurs here is peculiar, since the mechanism that produces it involves two-loop integrals. This is corroborated by an explicit calculation of the gluon GPD channel to pair photoproduction, which leads to a divergent amplitude already at leading twist-2 and at leading order in \(\alpha _\mathrm {s}\). On the other hand, for processes where the gluon GPD channel is forbidden, for example when the outgoing meson is a charged pion or a rho meson, collinear factorisation works without any issues.

abstract

In the Standard Model, the axial current is not conserved due to fermion masses and the axial anomaly. In this work, we employ perturbative quantum chromodynamics to evaluate the matrix elements of the local and non-local axial currents for a gluon target, providing insights into their relation with the axial anomaly. Our analysis revisits well-established results related to the nucleon spin sum rule, along with recent developments in off-forward kinematics. A significant aspect of our approach is the use of an infrared regulator, with a particular focus on the non-zero quark mass. We observe important cancellations between the contributions from the axial anomaly and the quark mass term, and we discuss how these cancellations are linked to the conservation of angular momentum.

abstract

We report progress on the Heavy-Flavor Non-Relativistic Evolution (HF-NRevo) setup, a novel methodology to address quarkonium formation within the fragmentation approximation. Our study sheds light on the moderate-to-large transverse-momentum sector, where the leading-twist collinear fragmentation of a single parton prevails over the higher-twist fragmentation from a constituent heavy-quark pair produced in the hard scattering. As for the initial energy-scale inputs, we rely on nonrelativistic next-to-leading calculations for all the parton-to-quarkonia fragmentation channels. Preliminary sets of Variable-Flavor Number-Scheme (VFNS) fragmentation functions, named NRFF1.0, are built via an evolution-threshold enhanced DGLAP scheme. Taking NRFF1.0 as a starting point, we use HF-NRevo to address the collinear fragmentation of quarkonia inside jets.

abstract

According to perturbative quantum chromodynamic calculations, in \(pp\) collisions at \(\sqrt {s} = 200\) and 510 GeV studied at RHIC, jet production in mid-pseudorapidity, \(|\eta | \lt 1\), is dominated by quark–gluon and gluon–gluon scattering processes. Therefore, jets at RHIC are direct probes of the gluon parton distribution functions (PDFs) for momentum fractions \(0.01 \lt x\lt 0.5\). Moreover, \(W\) boson cross-section ratio, \(\sigma (W^+)/\sigma (W^-)\), in \(pp\) collisions at \(\sqrt {s} = 510\) GeV, is an effective tool to explore anti-quark PDFs, \(\bar {d}/\bar {u}\). Last but not least, di-\(\pi ^{0}\) correlation in forward pseudorapidity, \(2.6 \lt \eta \lt 4.0\), is an important indication of the non-linear gluon dynamics at low \(x\) where the gluon density is high in protons and nuclei. In this contribution, we present recent STAR results of mid-pseudorapidity inclusive jet cross sections at \(\sqrt {s} =\) 200 and 510 GeV in \(pp\) collisions, \(W\) boson cross-section ratio at \(\sqrt {s} = 510\) GeV in \(pp\) collisions, and forward di-\(\pi ^0\) correlations in \(pp\), \(p\)Al, and \(p\)Au collisions at \(\sqrt {s_{NN}} = 200\) GeV.

abstract

We review the recent developments in the use of the homotopy method for solving the non-linear evolution equation for the diffractive production in deep-inelastic scattering. We introduce part of the non-linear corrections in the linear term. This simplified non-linear evolution equation is solved analytically taking into account the initial and boundary conditions for the process. It turns out that these corrections are rather small and can be estimated in the regular iterative procedure.

abstract

We provide the most general description of the exclusive leptoproduction of a light vector meson at high center-of-mass energy, within the CGC/shockwave formalism. We keep a twist-3 accuracy in the \(s\) channel, thus being able to describe all possible helicity amplitudes, including the ones for the production of a transversally polarized meson. In this latter case, we overcome the well-known issue of endpoint singularities by promoting the GPD to a GTMD given by matrix elements of dipole and double-dipole operators. The all-twist treatment of the proton (nucleon) target allows to safely twist-expand the general vacuum-to-meson matrix elements. Therefore, unlike previous attempts in the modified perturbative approach, our final results are expressed in terms of the twist-3 collinear distribution amplitudes, introduced in the context of the higher-twist collinear formalism.

abstract

Using the leading twist approach (LTA) to nuclear shadowing (NS), we calculate the ratio of the diffractive-to-total DIS cross sections, \(R_{\mathrm {diff/tot}}\), for a heavy nucleus and proton and confirm that \(R_{\mathrm {diff/tot}} \approx 0.5\)–1 in contrast to \(R_{\mathrm {diff/tot}} \approx 1.5\)–2 in the dipole model. We show that the magnitude of \(R_{\mathrm {diff/tot}}\) is controlled by an effective dipole cross section so that \(R_{\mathrm {diff/tot}} \!\to \! 1\) in the black disk limit. We also argue that the strong leading twist NS as well as the dilute nuclear density deplete nuclear enhancement of the saturation scale leading to \(Q_{\mathrm {s}A}^2(b=0)/Q_{\mathrm {s}p}^2(b=0) \sim 1\).

abstract

We present a comprehensive analysis of reduced cross-section data from HERA used to determine diffractive parton distribution functions (DPDFs) using the fracture function formalism. A novel neural network-based methodology is employed, providing an independent determination of DPDFs that is broadly compatible with the previous extractions. This approach improves the flexibility of the QCD analysis, minimizing model-dependent biases, and allowing for a more accurate characterization of diffractive processes.

abstract

We present recent results from the ALICE Collaboration on the study of coherent and incoherent \(J/\psi \) photoproduction in ultra-peripheral Pb–Pb collisions, including results from exclusive and dissociate \(J/\psi \) mesons in ultra-peripheral \(p\)–Pb interactions. These measurements provide unique insights into the initial state of protons and ions, with great sensitivity for both gluon saturation and shadowing. Furthermore, we will discuss the prospects for these measurements using the Run 3 and Run 4 data.

abstract

We present the transverse single-spin asymmetry, \(A_{N}\), for the electromagnetic jets (EM-jets) at forward rapidity in inclusive and diffractive processes in transversely polarized \(p^{\uparrow } + p\) collisions at \(\sqrt {s} = 200\) GeV at STAR. The inclusive EM-jet \(A_{N}\) is studied as functions of EM-jet transverse momentum and longitudinal momentum fraction, in different ranges of EM-jet energy and photon multiplicity. The \(A_{N}\) for single diffractive process and rapidity gap event, with a focus on photon multiplicity dependence, is also examined. A direct comparison of \(A_{N}\) from inclusive process, single diffractive process, and rapidity gap events shows consistency within uncertainties. Furthermore, a non-zero \(A_{N}\) from the semi-exclusive process is observed. These findings suggest that diffractive EM-jets do not contribute to the large \(A_{N}\) observed in the inclusive process at 200 GeV. Finally, we discuss the opportunities for the EM-jet \(A_{N}\) in inclusive and diffractive processes at \(\sqrt {s} = 510\) GeV.

abstract

The proton–proton collisions at the LHC generate high-intensity collimated beams of forward neutrinos up to TeV energies. Their recent observations and the initiation of a novel LHC neutrino program motivate investigations of this previously unexploited beam. The kinematic region for neutrino deep-inelastic scattering measurements at the LHC overlaps with the Electron–Ion Collider. The effect of the LHC \(\nu \)DIS data on parton distribution functions (PDFs) is assessed by generating projections for the Run 3 LHC experiments and for selected proposed detectors at the HL-LHC. Estimating their impact in global (n)PDF analyses reveals a significant reduction of PDF uncertainties, particularly for strange and valence quarks. Furthermore, the effect of neutrino flux uncertainties is examined by parametrizing the correlations between a broad selection of neutrino production predictions in forward hadron decays. This allows determination of the highest achievable precision for neutrino observations, and constraining physics within and beyond the Standard Model, demonstrated by setting bounds on effective theory operators and projections for an experimental confirmation of the enhanced strangeness scenario proposed to resolve the cosmic ray muon puzzle, using LHC data. There is also promise for a first measurement of neutrino tridents with a statistical significance beyond 5\(\sigma \).

abstract

We identify a new way of pinpointing the presence of saturation effects in the LHC data by looking at incoherent \(J/\psi \) production at large \(|t|\). We use an energy-dependent hot spot model to show that saturation effects are manifested through a fall-off of the incoherent vector-meson production cross section. This fall-off comes from the reduced variance of possible target configurations due to parton overlap at Mandelstam-\(t\) scales, where individual hot spots become important.

abstract

These proceedings summarise the results of three major studies of nuclear parton distribution functions (nPDFs) from high-energy collisions at the CERN LHC. The first study examines top-quark-pair production in \( p \)+Pb collisions, investigating nPDF modifications at high Bjorken-\( x \). The second study analyses the centrality dependence of dijet yields in \( p \)+Pb collisions at \( \sqrt {s_{NN}} = 8.16~\text {TeV} \), revealing scaling behaviour with Bjorken-\( x \). The final study presents photon–nuclear production of dijets in ultraperipheral Pb+Pb collisions at \( \sqrt {s_{NN}} = 5.02~\text {TeV} \), providing insights into low-\( x \) gluon distributions. Collectively, these results enhance the understanding of nPDFs and lay a foundation for future investigations into photonuclear interactions and gluon saturation phenomena.

abstract

We discuss the role of \(c \bar c g\)-Fock states in the diffractive photoproduction of \(J/\psi \)-mesons as probed in ultraperipheral nuclear collisions. We build on our earlier description of the process in the color–dipole approach, where we took into account the rescattering of \(c \bar c\) pairs using a Glauber–Gribov form of the dipole–nucleus amplitude. We compare the results of our calculations to recent data on the photoproduction of \(J/\psi \) by the ALICE, CMS, and LHCb collaborations. We also comment on the possible relation to gluon shadowing and compare to data on the ratio \(R_g = \sqrt {\sigma (\gamma A \to J/\psi A)/\sigma _\mathrm {IA}}\), where \(\sigma _\mathrm {IA}\) is the result in impulse approximation.

abstract

High-energy (or small-\(x\)) logarithms are enhanced in proton scattering processes when the collider centre-of-mass energy is much larger than the hard scattering scale. In the picture of collinear factorisation, their resummation affects QCD cross sections and DGLAP evolution kernels. In recent years, it was shown that small-\(x\) resummed theory can be used to improve predictions for the Parton Distribution Function (PDF) fitting as well as parton level cross section studied at the LHC, namely the single-Higgs and heavy-quark pair production.

abstract

We consider the on-shell production of a pair of \(Z\)-bosons via quark–antiquark annihilation and perform threshold resummation of the large logarithms up to Next-to-Next-to-Leading Logarithmic (NNLL) accuracy. The presence of the two-loop contributions makes the numerical computation a non-trivial task. We present the invariant mass distribution up to NNLO+NNLL accuracy in QCD for the current LHC energies. We observe that the scale uncertainties in the fixed-order results get reduced from \(4.56\%\) at NNLO to about \(3.19\%\) at NNLO+NNLL for \(Q=1.3\) TeV.

abstract

We compute the tree-level current for triple soft-gluon emission from both massless and massive hard partons. The three-gluon current is expressed in terms of the maximally non-Abelian irreducible correlations. We compute the soft behaviour of squared amplitudes and the colour correlations produced by the squared current. The radiation of one and two soft gluons leads to colour dipole correlations. Triple soft-gluon radiation produces, in addition, colour quadrupole correlations between the hard partons. We examine the soft and collinear singularities of the squared current in various energy-ordered and angular-ordered regions. Considering triple soft-gluon radiation from three hard partons, colour quadrupole interactions break the Casimir scaling symmetry between quarks and gluons. We also present some results on the radiation of four soft gluons from two hard partons, and we discuss the colour monster contribution and its relation with the violation (and generalization) of Casimir scaling. We also compute the first correction of \((1/N_c^2)\) to the eikonal formula for multiple soft-gluon radiation with strong energy ordering from two hard gluons. Finally, we compute also the tree-level current and its squared modulus for emission of soft quark–antiquark–gluon states.

abstract

This work presents the computation of real corrections to the impact factor for forward Higgs-boson production, preserving the full dependence on the top-quark mass. The results are shown to align with the BFKL factorization framework, particularly in reproducing the expected rapidity divergence. Additionally, the subtraction of this divergence has been demonstrated using the appropriate counterterm within the BFKL scheme. In the infinite-top-mass limit, our findings reproduce the previously established result.

abstract

It is known that the proton is overpopulated by gluons and is characterized as a highly dense medium at high collision energies. From this, the formation of a new state of matter called Color Glass Condensate (CGC) is expected, and an open question is whether the non-linear effects predicted by this state are identifiable at the LHC. The multiplicity of particles produced in a hadronic collision presents as a means to adequately investigate this problem. Currently, the description of the available data for different multiplicity regimes remains a challenge. Even though different experimental collaborations have identified that the production of certain final states, in \(pp\) collisions, present a modification in the behavior of high-multiplicity events in relation to the case of minimum bias, we still lack a way to identify the nature of those high-multiplicity events: are they driven by initial-state effects, final-state effects or a mix of both? We argue that an analyzing different particle production process that can be described CGC framework, in particular, isolated photon production which is not sensitive to final-state effects, may provide a path forward in answering this question.

abstract

The LHCb detector, recognized as a general-purpose detector in the forward rapidity region (\(2 \lt \eta \lt 5\)) is capable of exploring quantum interference effects at high rapidities and low transverse momenta. This summary presents measurements of Bose–Einstein correlations of the same-sign charged pions studied in proton–proton collisions at \(\sqrt {s}=7\) TeV and proton–lead collisions at \(\sqrt {s_{NN}}=5.02\) TeV, marking the first such measurements in the forward region at LHC energies. Correlation parameters were analyzed across various charged-particle multiplicity ranges, showing consistency with central rapidity region observations from other LHC experiments. The correlation radii scale linearly with the cube root of charged-particle multiplicity, aligning with hydrodynamic model predictions, and there are also some indications of a dependence on pseudorapidity. The preliminary considerations of the studies on Bose–Einstein correlations for the triplets of the same-sign pions in proton–proton collisions, interpreted within the core-halo model, are also presented.

abstract

Vector-boson production in association with jets is among the Standard Model processes leaving the clearest signatures in high-energy physics experiments. The latest results on \(W/Z\)+jets measurements from the ATLAS and CMS experiments at the LHC are presented. Particular attention is given to how these measurements can be used to extract relevant electroweak and QCD parameters, and also be re-interpreted to set limits on exotic models.

abstract

Jets and their substructure in \(pp\) collisions offer a unique opportunity for probing various aspects of quantum chromodynamics (QCD), ranging from perturbative QCD (pQCD) tests to studies of non-perturbative phenomena such as hadronization. They also probe the transition between perturbative and non-perturbative regimes. In heavy-ion collisions, jets serve as a novel tool to investigate the microscopic properties of the deconfined quark–gluon plasma (QGP). Recently, significant progress has been made in developing jet substructure observables to explore these properties. The ALICE experiment is particularly well-suited for jet measurements due to its high-precision tracking system, which is especially beneficial for detecting low transverse momentum jets. This contribution will highlight recent ALICE measurements of inclusive and semi-inclusive jets, along with various jet substructure observables in \(pp\), \(p\)–Pb, and Pb–Pb collisions. The comparisons between data and predictions from Monte Carlo (MC) models as well as analytical calculations will be discussed.

abstract

We revisit a minijet model to examine the behavior of the total cross section, \(\sigma _{\mathrm {tot}}\), and the ratio of the real-to-imaginary parts of the scattering amplitude, \(\rho \), at high energies. In this framework, the growth of \(\sigma _{\mathrm {tot}}\) in \(pp\) and \(\bar {p}p\) channels is driven by semihard partonic processes dominated by gluon interactions. The QCD contribution to \(\sigma _{\mathrm {tot}}\) for the jet production is computed in the next-to-leading order. We analyze data separately from the TOTEM and ATLAS/ALFA collaborations, and find evidence in both cases suggesting the necessity of an odd semihard component that becomes asymptotically significant at high energies.

abstract

Spin physics and the 3D structure of nucleons and nuclei is a cornerstone of the science program of the EIC, which will be the world’s only polarized collider. These proceedings summarize the capabilities of the EIC in the context of spin physics, outline a few key measurements envisioned for the ePIC detector, and briefly discuss additional opportunities that could be provided by a \(2^\mathrm {nd}\) detector.

abstract

I give a brief overview of our current understanding of the internal partonic 3D structure of nucleons in momentum space. I discuss some recent extractions of transverse-momentum-dependent distributions for quarks, whose analyses are reaching a theoretical precision comparable to collinear parton distribution functions. On the contrary, gluon transverse-momentum distributions are poorly known from a phenomenological point of view. I briefly review their general properties and sketch a recent model calculation covering all (un)polarized combinations at leading twist.

abstract

LHCb is the only experiment at the LHC able to reconstruct simultaneously events from beam–beam and beam–gas collisions taking place in a gas storage cell. The aim of the LHCspin project is to bring spin physics at the LHC for the first time by injecting polarised hydrogen and deuterium. This would enable the high-energy LHC beam and the peculiar forward geometry of LHCb to explore the 3D structure of matter in a unique kinematic regime and by means of probes that are not accessible in other facilities.

abstract

In this contribution, we present the experimental techniques developed to select good photo-nuclear events in ultraperipheral heavy-ion collisions (UPCs) with the CMS detector at the Large Hadron Collider (LHC). The CMS Collaboration has recently designed and implemented a new trigger strategy to maximize the number of collected photo-nuclear events in Pb+Pb UPCs. This goal was achieved by integrating the Zero Degree Calorimeters (ZDCs) in the Level-1 trigger system of CMS and by triggering on events based on the presence of forward neutrons in the ZDCs. Therefore, we could select events where only one of the colliding nuclei breaks up while the other one stays intact. A rapidity gap selection, based on the information provided by the hadron forward calorimeters (HFs) was also applied in the direction of the outgoing photon. The presented techniques were used in the first measurement of the \(D^0\) production in Pb+Pb UPC collisions at \(\sqrt {s_{NN}}=5.36\) TeV.

abstract

Ultra-peripheral collisions (UPC) are events characterised by large impact parameters between the two projectiles, larger than the sum of their radii. In UPCs, the protons and ions accelerated by the LHC do not interact via strong interaction and can be regarded as sources of quasi-real photons. Using the Run 2 data, the ALICE Collaboration has carried out various measurements of different final-state systems, such as exclusive four-pion photoproduction as well as photoproduction of \(K^+K^-\) pairs, measured for the first time in ultra-peripheral collisions. In addition, vector-meson production in Pb–Pb provides the unique opportunity to carry out an analogy of the double-slit experiment at femtometre scales, owing to the interference between the production sources of the two lead nuclei. These results and prospects for UPC measurements using Run 3 data will be presented.

abstract

We first describe the possible observation of saturation effects in the measurement of ultra-peripheral vector meson production (\(J/{\mit \Psi }\) and \({\mit \Upsilon }\)) in PbPb collisions at the LHC. We then give the predictions of the jet production cross section in dedicated detectors in the very forward region, such as the FOCAL detector of ALICE, as another probe of low-\(x\) dynamics and saturation.

abstract

We review recent theoretical progress in describing collective effects in photon\(+\)nucleus collisions. The approaches considered range from the color glass condensate, where correlations are encoded in the initial state, to hydrodynamic frameworks, where a strong final-state response to the initial geometry of the collision is the key ingredient to generate momentum-space correlations.

abstract

A key focus of the physics program at the LHC is the study of head-on proton–proton collisions. However, an important class of physics can be studied for cases where the protons narrowly miss one another and remain intact. In such cases, the electromagnetic fields surrounding the protons can interact producing high-energy photon–photon collisions. Alternatively, interactions mediated by the strong force can also result in intact forward scattered protons, providing probes of quantum chromodynamics (QCD). In order to aid identification and provide unique information about these rare interactions, instrumentation to detect and measure protons scattered through very small angles is installed in the beam pipe far downstream of the interaction point. We review photoproduction results from data collected with the ATLAS Forward Proton (AFP) and Absolute Luminosity For ATLAS (ALFA) detectors in proton–proton and heavy-ion collisions.