SciPost: SciPost Physics Proceedings: issue detail

SciPost Physics Proceedings issue 15

51st International Symposium on Multiparticle Dynamics (ISMD2022)

Event dates: from 2022-08-01 to 2022-08-05.

Updates and inquiries into the nature of the strong force, both experimental and theoretical, across high-energy particle physics, nuclear physics, heavy-ion physics, and astroparticle physics. Jointly organised in Atholl Palace Hotel, Pitlochry, Scotland by the Universities of Glasgow and Edinburgh. Contributions included a mixture of plenary presentations, short talks, and posters.

(Guest) Fellows responsible for this Issue

Prof. Andy Buckley
Dr Jennifer Smillie

Can quantized fragmentation replace colour reconnection models?

Šárka Todorova-Nová

SciPost Phys. Proc. 15, 001 (2024) · published 2 April 2024 | · pdf

A brief overview of properties of the model of quantized fragmentation of a helical QCD string is followed by the discussion of colour reconnection models and of the ways to reproduce the evolution of the average transverse momentum in hadronic events, as function of charged particle multiplicity. Reference to recent experimental data is included.
NLO finite system size corrections to $2\to2$ scattering in $\phi^4$ theory using newly derived sum of sinc functions

Jean F. Du Plessis, William A. Horowitz

SciPost Phys. Proc. 15, 002 (2024) · published 2 April 2024 | · pdf

Previously an equation of state for the relativistic hydrodynamics encountered in heavy-ion collisions at the LHC and RHIC has been calculated using lattice gauge theory methods. This leads to a prediction of very low viscosity, due to the calculated trace anomaly. Finite system corrections to this trace anomaly could challenge this calculation, since the lattice calculation was done in an effectively infinite system. In order to verify this trace anomaly it is sensible to add phenomenologically relevant finite system corrections. We investigate massive $\phi^4$ theory with periodic boundary conditions on $n$ of the 3 spatial dimensions. $2\to2$ NLO scattering is then computed. Using a newly derived formula for an arbitrary dimensional sum of sinc functions, we show that the NLO finite size corrections preserve unitarity.
Photon-photon fusion and tau g-2 measurement in ATLAS

Agnieszka Ogrodnik

SciPost Phys. Proc. 15, 003 (2024) · published 2 April 2024 | · pdf

Relativistic heavy-ion beams at the LHC are accompanied by a large flux of equivalent photons. New measurements of exclusive dilepton production (electron, muon, and tau pairs) performed by the ATLAS experiment are discussed. We present the photon-induced production of tau pairs and constraints on the tau lepton's anomalous magnetic dipole moment. In addition, measurements of photon-induced electron and muon pair production are presented, which provide strong constraints on the nuclear photon flux and its dependence on the impact parameter and photon energy. Forward neutrons are utilised to provide an experimental handle on the impact parameter range sampled in the events.
Towards the computation of inclusive decay rates using lattice QCD

Paolo Gambino, Shoji Hashimoto, Sandro Mächler, Marco Panero, Francesco Sanfilippo, Silvano Simula, Antonio Smecca, Nazario Tantalo

SciPost Phys. Proc. 15, 004 (2024) · published 2 April 2024 | · pdf

We present a non-perturbative computation of inclusive rates of semileptonic decays of heavy mesons from lattice QCD simulations. The calculation is based on the extraction of smeared spectral functions obtained from four-point Euclidean correlation functions computed on configuration ensembles of the JLQCD and ETM collaborations. We compare our results for the inclusive decay rates with analytical predictions from the operator-product expansion, finding a good agreement for the calculation of the inclusive decay rate. This opens the path to the theoretical determination of the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element $V_{cb}$ to a level of precision competitive with the present experimental uncertainty.
Implications of exclusive J/$\psi$ photoproduction in a tamed collinear factorisation approach to NLO

Chris A. Flett, Alan D. Martin, Misha G. Ryskin, Thomas Teubner

SciPost Phys. Proc. 15, 005 (2024) · published 2 April 2024 | · pdf

We discuss exclusive J/$\psi$ photoproduction, initially in conventional collinear factorisation at NLO and then subsequently in a refined approach with a programme of low x resummation and implementation of a crucial low $Q_0$ subtraction included. We compare and contrast predictions in both frameworks and remark about the possibility to constrain and ultimately determine the low x and low scale gluon PDF, emphasising the significance of this for future global PDF analyses.
Towards better discrimination and improved modelling of dark-sector showers

Andy Buckley, Deepak Kar, Sukanya Sinha

SciPost Phys. Proc. 15, 006 (2024) · published 2 April 2024 | · pdf

As no evidence for classic WIMP-based signatures of dark matter have been found at the LHC, several phenomenological studies have raised the possibility of accessing a strongly-interacting dark sector through new collider-event topologies. If dark mesons exist, their evolution and hadronization procedure are currently little constrained. They could decay promptly and result in QCD-like jet structures, even though the original decaying particles are dark sector ones; they could behave as semi-visible jets; or they could behave as completely detector-stable hadrons, in which case the final state is just the missing transverse momentum. In this contribution we will introduce a study performed to explore use of jet substructure methods to distinguish dark-sector from QCD jets in the first two scenarios, using observables in a IRC-safe linear basis, and discuss ways forward for this approach to dark-matter at the LHC.
Amplitude and colour evolution

Simon Plätzer

SciPost Phys. Proc. 15, 007 (2024) · published 2 April 2024 | · pdf

Colour evolution and parton branching at the amplitude level have become important theoretical frameworks to improve parton showers, and are algorithms in their own right: They complement shower development by resummation algorithms capable of including interference effects and subleading colour contributions at an unprecedented level. I summarize recent development in the field, focusing on soft gluon evolution, hadronization, and the CVolver framework.
Forward proton measurements with ATLAS

Mustafa Schmidt

SciPost Phys. Proc. 15, 008 (2024) · published 2 April 2024 | · pdf

The ALFA subdetector is designed to measure elastic proton-proton scattering from which the total cross section and $\rho$-parameter are determined. In 2016, special runs at a center-of-mass energy of $\sqrt{s}$ = 13 TeV and with $\beta^\star$ = 2.5 km were recorded.
Recent LHCb results on forward physics and diffraction

Luke McConnell

SciPost Phys. Proc. 15, 009 (2024) · published 2 April 2024 | · pdf

The LHCb detector at the LHC offers unique coverage of forward rapidities for studies of Central Exclusive Production (CEP) and soft QCD. CEP measurements allow the investigation of the nature of pomerons, and provide constraints on low-x gluon phenomenology, probing potential saturation effects. Moreover LHCb can test phenomenological models of soft QCD processes, by measuring the production of forward hadrons in pp collisions. In this talk the latest results from the LHCb experiment will be presented.
Intermittency analysis of charged particles generated in Xe-Xe~collisions at $\sqrt{s_{\rm{NN}}}$ = 5.44 TeV using the AMPT model

Zarina Banoo, Ramni Gupta

SciPost Phys. Proc. 15, 010 (2024) · published 2 April 2024 | · pdf

The multiplicity fluctuations are sensitive to QCD phase transition and to the presence of critical point in QCD phase diagram. At critical point a system undergoing phase transition is characterized by large fluctuations in the observables which is an important tool to understand the dynamics of particle production in heavy-ion interactions and phase changes. Multiplicity fluctuations of produced particles is an important observable to characterize the evolving system. Using scaling exponent obtained from the normalized factorial moments of the number of charged hadrons in the two dimensional ($\eta,\phi$) phase space, one can learn about the dynamics of system created in these collisions. Events generated using Xe-Xe collisions at $\sqrt{s_{\rm{NN}}} = 5.44 $ TeV with string-melting (SM) version of the AMPT model are analyzed and the scaling exponent $(\nu)$ for various $p_T$ intervals is determined. It is observed that the calculated value of $\nu$ is larger than the universal value 1.304, as is obtained from Ginzburg-Landau theory for second order phase transition. Here we will also present the results of the dependence of the scaling exponent on the transverse momentum bin width.
Recent ATLAS results on forward physics and diffraction

Rafał Staszewski

SciPost Phys. Proc. 15, 011 (2024) · published 2 April 2024 | · pdf

The ATLAS detector at the LHC is equipped with dedicated systems designed for the detection of forward protons produced in diffractive and photon-induced processes. These detectors significantly extend the ATLAS physics reach. Recent measurements performed using these forward proton detectors: elastic proton-proton scattering, exclusive charged pion-pair production, and two-photon production of lepton pairs are presented.
Intermittency analysis of charged hadrons generated in Pb-Pb collisions at $\sqrt{s_{NN}}$= 2.76 TeV and 5.02 TeV

Salman Khurshid Malik, Ramni Gupta

SciPost Phys. Proc. 15, 012 (2024) · published 2 April 2024 | · pdf

Local density fluctuations are expected to scale as a universal power-law when the system approaches critical point. Such power-law fluctuations are studied within the framework of intermittency through the measurement of normalized factorial moments in ($\eta$, $\phi$) phase space. Observations and results from the intermittency analysis performed for charged particles in Pb-Pb collisions using PYTHIA8/Angantyr at 2.76 TeV and 5.02 TeV are reported. We observe no scaling behaviour in the particle generation for any of the centrality studied in narrow p$_T$ bins. The scaling exponent $\nu$ shows no dependence on the centrality ranges.
ATLAS results on exotic hadronic resonances

Yue Xu

SciPost Phys. Proc. 15, 013 (2024) · published 2 April 2024 | · pdf

Recent results from the proton-proton collision data taken by the ATLAS experiment on exotic resonances are presented. A search for $J/\psi p$ resonances in $\Lambda_{b}→ J/\psi p K$ decays with large $p K$ invariant masses is reported. A search for exotic resonances in the four-muon final state is shown.
The role of the underlying event in the charm-baryon enhancement observed in pp collisions at LHC energies

Zoltán Varga, Anett Misák, Róbert Vértesi

SciPost Phys. Proc. 15, 014 (2024) · published 2 April 2024 | · pdf

We study the enhanced production of $\Lambda_c$ charmed baryons relative to that of charmed $D^0$ mesons in proton–proton collisions at LHC energies. We simulated collision events with the enhanced color-reconnection model in PYTHIA 8 MC generator and propose measurements based on the comparative use of different event-activity classifiers to identify the source of the charmed-baryon enhancement. We demonstrate that in this enhanced color-reconnection scenario the excess production is primarily linked to the underlying event and not to the production of high-momentum jets.
Sub-TeV hadronic interaction model differences and their impact on air showers

Michael Schmelling, Álvaro Pastor-Gutiérrez, Harm Schorlemmer, Robert Daniel Parsons

SciPost Phys. Proc. 15, 015 (2024) · published 2 April 2024 | · pdf

In the sub-TeV regime, the most widely used hadronic interaction models disagree significantly in their predictions of particle spectra from cosmic ray induced air showers. We investigate the nature and impact of model uncertainties, focussing on air shower primaries with energies around the transition between high and low energy hadronic interaction models, where the dissimilarities are largest and which constitute the bulk of the interactions in air showers.
Precision measurements of jet and photon production at the ATLAS experiment

Giuseppe Callea

SciPost Phys. Proc. 15, 016 (2024) · published 3 April 2024 | · pdf

The production of jets and prompt isolated photons at hadron colliders provides stringent tests of perturbative QCD. We present the latest measurements of photon+jets and diphoton production using proton-proton collision data collected by the ATLAS experiment at the LHC. The measurements are compared to state-of-the-art NLO and NNLO predictions.
Study of charmonium(-like) spectroscopy and decay at BESIII

Weimin Song, Honghong Zhang

SciPost Phys. Proc. 15, 017 (2024) · published 3 April 2024 | · pdf

The recent results on Charmonium and Charmonium-like states at BESIII are reviewed, including the observation of $\rm Z_{cs}(3985)$ state, the study of the new decay modes of $\psi_2(3823)$ state, observation of resonance structure in $\rm e^+e^- \to \pi^+\pi^-\psi_2(3823)$ process, the study of the $\rm e^+e^- \to K^+K^-J/\psi$ process, cross section measurement of $\rm e^+e^- \to \omega\pi^0$ and $\omega\eta$ process, branching fraction measurement of $\psi(3686)\to\bar{\Sigma}^0\Lambda + c.c.$ process. Decay channels for $\chi_{cJ} \to \Lambda\bar{\Lambda}$, $\chi_{cJ} \to \Lambda\bar{\Lambda}\eta$, $\psi(3686) \to \Lambda\bar{\Lambda}\omega$ and $\eta_c(2S)\to3(\pi^+\pi^-)$ are also discussed. The property of the spin singlet P wave Charmonium state, $\rm h_c$ is also reported.
Multiplicity dependence of charged-particle jet production in pp collisions at 13 TeV with ALICE

Debjani Banerjee

SciPost Phys. Proc. 15, 018 (2024) · published 3 April 2024 | · pdf

Measurements of jet production and jet properties in pp collisions provide a test of perturbative quantum chromodynamics (pQCD) and form a baseline for similar measurements in heavy ion (A-A) collisions. In this contribution, we report recent ALICE measurements of charged-particle jet production and intra-jet properties, including mean charged-constituent multiplicity and fragmentation distribution for leading jets, in minimum bias pp collisions at $\sqrt{s}$ = 13 TeV. In addition, the event multiplicity dependence of jet production and jet properties in pp collisions at $\sqrt{s}$ = 13 TeV will be presented. Results will be compared with theoretical model predictions.
Air showers and hadronic interactions with CORSIKA 8

Maximilian Reininghaus

SciPost Phys. Proc. 15, 019 (2024) · published 3 April 2024 | · pdf

The CORSIKA 8 project is a collaborative effort aiming to develop a versatile C++ framework for the simulation of extensive air showers, intended to eventually succeed the long-standing FORTRAN version. I present an overview of its current capabilities, focusing on aspects concerning the hadronic and muonic shower components. In particular, I demonstrate the "cascade lineage" feature and its application to quantify the importance of certain phase-space regions in hadronic interactions for muon production. Additionally, I show first results using Pythia 8.3, which as of late is usable as interaction model in cosmic-ray applications and is currently being integrated into CORSIKA 8.
Muon measurements at the Pierre Auger Observatory

Dariusz Góra

SciPost Phys. Proc. 15, 020 (2024) · published 3 April 2024 | · pdf

The Pierre Auger Observatory is the world's largest detector for observation of ultra-high-energy cosmic rays (UHECRs) (above the energy of $10^{17}$ eV). It consists of a Fluorescence Detector (FD) and an array of particle detectors known as the Surface Detector (SD). Observations of extensive air showers by the Observatory can be used to probe hadronic interactions at high energy, in a kinematic and energy region inaccessible to experiments at man-made accelerators and to measure the muon component of the shower. Air showers induced by different primaries have different muon contents. With increasing mass of the primary cosmic ray particle, it is expected that the muon content in the corresponding air showers should also increase. Therefore, the determination of the muon component in the air shower is crucial to infer the mass of the primary particle. This is a key ingredient in the searches conducted to pinpoint the sources of UHECRs. Recent results obtained from the Pierre Auger Observatory and other experiments indicate that all the shower simulations underestimate the number of muons in the showers compared to the data. This is the so-called muon deficit. In this paper we briefly review the muon measurements, and present in more detail recent results on fluctuations in the muon number. These results provide new insights into the origin of the muon deficit in air shower simulations and constrain the models of hadronic interactions at ultrahigh energies. With the current design of the surface detectors it is also difficult to reliably separate the contributions of muons to the SD signal from the contributions of photons, electrons, and positrons. Therefore, we also present a new method to extract the muon component of the signal time traces recorded by each SD station using recurrent neural networks. The combination of such algorithms, with the future data collected by the upgraded Pierre Auger Observatory, will be a major step forward, as we are likely to achieve an unprecedented resolution in mass estimation on an event-by-event basis.
All about the neutron from lattice QCD

Rajan Gupta

SciPost Phys. Proc. 15, 021 (2024) · published 3 April 2024 | · pdf

I describe how simulations of lattice QCD using the path integral formulation provide the two basic quantum mechanical properties of QCD, its ground state in which correlation functions are calculated, and Fock state wavefunctions between which matrix elements of operators are calculated. Both constructs are stochastic, so unfortunately one gets no intuitive picture or even qualitative understanding of what they look like, nevertheless they contain and display all the subtleties of the quantum field theory. Today, these simulations provide many quantities that are impacting phenomenology and experiments. I illustrate the methods and the steps in the analysis using, as examples, three observables: the isovector charges of the nucleon, the contribution of the quark's intrinsic spin to the nucleon spin, and the pion-nucleon sigma term.
All order merging of high energy and soft collinear resummation

Jeppe R. Andersen, Hitham Hassan, Sebastian Jaskiewicz

SciPost Phys. Proc. 15, 022 (2024) · published 3 April 2024 | · pdf

We present a method of merging the exclusive LO-matched high energy resummation of High Energy Jets (HEJ) with the parton shower of PYTHIA which preserves the accuracy of the LO cross sections and the logarithmic accuracy of both resummation schemes across all of phase space. Predictions produced with this merging prescription are presented with comparisons to data from experimental studies and suggestions are made for further observables and experimental cuts which highlight the importance of both high energy and soft-collinear effects.
Helix string fragmentation and charged particle correlations with ATLAS

Šárka Todorova-Nová

SciPost Phys. Proc. 15, 023 (2024) · published 3 April 2024 | · pdf

Correlations between charged particles provide important insight into the hadronization process. The analysis of the momentum difference between charged hadrons in pp, p-lead, and lead-lead collisions at LHC is performed by the ATLAS Collaboration in order to study the dynamics of hadron formation. The spectra of correlated hadron chains are explored and compared to the predictions based on the quantized fragmentation of a three dimensional QCD helix string. This provides an alternative view of the two-particle correlation phenomenon typically attributed to the Bose-Einstein interference.
Centrality dependence of multistrange baryon production in high-energy heavy-ion collisions

Gevorg H. Arakelyan, Carlos Merino, Yuli M. Shabelski

SciPost Phys. Proc. 15, 024 (2024) · published 3 April 2024 | · pdf

We consider the experimental data on the production of strange $\Lambda^{\prime}$s, and multistrange baryons ($\Xi$, $\Omega$), and antibaryons, on nuclear targets, at the energy region from SPS up to LHC, in the framework of the Quark-Gluon String Model. One remarkable result of this analysis is the significant dependence on the centrality of the collision of the experimental $\overline{\Xi}^+/\overline{\Lambda}$ and $\overline{\Omega}^+/\overline{\Lambda}$ ratios in heavy-ion collisions, at SPS energies.
How the blast-wave model describes PID hadron spectra from 5 TeV p-Pb collisions

Thomas A. Trainor

SciPost Phys. Proc. 15, 025 (2024) · published 3 April 2024 | · pdf

The blast-wave (BW) spectrum model has been applied extensively to nucleus-nucleus collision data with the intention to demonstrate formation of a quark-gluon plasma (QGP) in more-central A-A collisions. More recently the BW model has been applied to p-p, d-Au and p-Pb collisions. Such results are interpreted to indicate that "collectivity" (flows) and QGP appear in smaller systems. In this talk I review BW analysis of identified-hadron spectra from 5 TeV p-Pb collisions and examine the shape evolution of model spectra with collision centrality. I evaluate data-model fit quality using conventional statistical measures. I conclude that the BW model is not a valid data model.
Hyperon physics at BESIII

Viktor Thorén

SciPost Phys. Proc. 15, 026 (2024) · published 3 April 2024 | · pdf

Spin polarization and entanglement are utilized by the BESIII experiment to learn more about the production and decay properties of hyperon-antihyperon pairs in a series of recent analyses of its unprecedented datasets at the $J/\psi$ and $\psi'$ resonances. This has lead to the observation of significant transverse polarisation in decays of $J/\psi$ or $\psi'$ into $\Lambda \bar{\Lambda}$, $\Sigma \bar{\Sigma}$, $\Xi \bar{\Xi}$, and $\Omega \bar{\Omega}$. Because of the non-zero polarization, the decay parameters for the most common hadronic weak decays of both hyperons and antihyperons could be determined independently for the first time. Comparing these to each other yields precise tests of direct, $\Delta S = 1$ CP-violation that complement measurements of kaon decays.
Λ(1520) resonance production with respect to transverse spherocity using EPOS3+UrQMD

Nasir Mehdi Malik, Sanjeev Singh Sambyal

SciPost Phys. Proc. 15, 027 (2024) · published 3 April 2024 | · pdf

Resonances are sensitive to the properties of the medium created in heavy ion collision. They also provide insight into the properties of the hadronic phase. Studying the dependence of the yield of resonances on transverse spherocity and multiplicity allows us to understand the resonance production mechanism with event topology and system size, respectively. The results reported pertain to $\Lambda(1520)$, using predictions from EPOS3+UrQMD event generator.
An overview of lattice results for parton distribution functions

Luigi Del Debbio

SciPost Phys. Proc. 15, 028 (2024) · published 3 April 2024 | · pdf

Following a ground-breaking proposal by Ji [Phys. Rev. Lett. 110, 262002 (2013)], numerical simulations of Quantum Chromo Dynamics (QCD) on a Euclidean lattice have provided new, valuable information on the structure of hadrons. In this talk, we briefly review the lattice approach to the reconstruction of parton densities, highlighting the connection between lattice observables and parton densities, with a focus on theoretical issues. Since parton distributions are extracted from lattice data by solving an inverse problem, we discuss some of the difficulties that affect these determinations and how they can be formulated in a Bayesian framework.
Anomalous coupling studies with intact protons at the LHC

Cristophe Royon

SciPost Phys. Proc. 15, 029 (2024) · published 3 April 2024 | · pdf

We describe the reaches on quartic $\gamma \gamma \gamma \gamma$, $\gamma \gamma WW$, $\gamma \gamma ZZ$, $\gamma \gamma \gamma Z$, $\gamma \gamma t \bar{t}$ anomalous couplings at the LHC using intact protons in the final state measured in AFP in ATLAS or PPS in CMS-TOTEM.
Precision physics with the proton spectrometer and diffractive physics measurements from CMS

Cristophe Royon

SciPost Phys. Proc. 15, 030 (2024) · published 3 April 2024 | · pdf

We describe recent results from CMS and TOTEM on hard diffraction, diffractive jets and jet gap jet events. We also give the first sensitivities and limits on quartic anomalous couplings and axion-like particles at high mass using the LHC as a $\gamma \gamma$ collider. The predicted sensitivities with 300 fb$^{-1}$ are better by two or three orders of magnitude compared to the more standard methods at the LHC without measuring intact protons after collision.