Parton Hadron Research Articles

Collision energy dependence of elliptic flow of identified hadrons in heavy-ion collisions using the PHSD model

We report the first predictions of elliptic flow (v2) of identified hadrons at mid-rapidity (|y|< 1.0) in Au+Au collisions at Elab=6.7,8,11,and 25 A GeV using the Parton Hadron String Dynamics (PHSD) model. The transverse momentum (pT) dependence of identified hadron v2 in different centrality intervals (0-10%, 10-40%, and 40-80%) is shown. A clear centrality dependence of v2(pT) is observed for particles at Elab=6.7,8,11,and 25 A GeV. Within the PHSD model, the number of constituent quark (NCQ) scaling of v2 approximately follows in Au+Au collisions at all beam energies. A collision energy (sNN) dependence of π, K, and pv2 is studied in comparison with available published experimental data in the beam energy range of 6-25 A GeV. These predictions will help in interpreting the data from the forthcoming Compressed Baryonic Matter (CBM) experiment at the Facility for Antiproton and Ion Research (FAIR) and Multi-Purpose Detector (MPD) at the Nuclotron-based Ion Collider facility (NICA).

Herwig 7.3 release note

A new release of the Monte Carlo event generator Herwig (version 7.3) has been launched. This iteration encompasses several enhancements over its predecessor, version 7.2. Noteworthy upgrades include: the implementation of a process-independent electroweak angular-ordered parton shower integrated with QCD and QED radiation; a new recoil scheme for initial-state radiation improving the behaviour of the angular-ordered parton shower; the incorporation of the heavy quark effective theory to refine the hadronization and decay of excited heavy mesons and heavy baryons; a dynamic strategy to regulate the kinematic threshold of cluster splittings within the cluster hadronization model; several improvements to the structure of the cluster hadronization model allowing for refined models; the possibility to extract event-by-event hadronization corrections in a well-defined way; the possibility of using the string model, with a dedicated tune. Additionally, a new tuning of the parton shower and hadronization parameters has been executed. This article discusses the novel features introduced in version 7.3.0.

Measurement of jet substructure in boosted tt¯ events with the ATLAS detector using 140 fb−1 of 13 TeV pp collisions

Measurements of the substructure of top-quark jets are presented, using 140 fb−1 of 13 TeV pp collision data recorded with the ATLAS detector at the LHC. Top-quark jets reconstructed with the anti-kt algorithm with a radius parameter R=1.0 are selected in top-quark pair (tt¯) events where one top quark decays semileptonically and the other hadronically, or where both top quarks decay hadronically. The top-quark jets are required to have transverse momentum pT&gt;350 GeV, yielding large samples of data events with jet pT values between 350 and 600 GeV. One- and two-dimensional differential cross sections for eight substructure variables, defined using only the charged components of the jets, are measured in a particle-level phase space by correcting for the smearing and acceptance effects induced by the detector. The differential cross sections are compared with the predictions of several Monte Carlo simulations in which top-quark pair-production quantum chromodynamic matrix-element calculations at next-to-leading-order precision in the strong coupling constant αS are passed to leading-order parton shower and hadronization generators. The Monte Carlo predictions for measures of the broadness, and also the two-body structure, of the top-quark jets are found to be in good agreement with the measurements, while variables sensitive to the three-body structure of the top-quark jets exhibit some tension with the measured distributions. © 2024 CERN, for the ATLAS Collaboration 2024 CERN

Study on the sensitivity of the Higgs boson couplings in photon–photon collision at CLIC and muon collider

In a model-independent way, we explore the potential of photon-induced interactions with the process γ*γ* → ZZ to investigate CP-conserving and CP-violating dimension-six operators of Higgs-gauge boson couplings using the standard model effective field theory. The existence of anomalous H γ γ and HZZ couplings is discussed at 3 TeV compact linear collider (CLIC) and 10 TeV muon collider (MuC) with integrated luminosities of 5 and 10 ab−1, respectively. All signal and relevant background events are generated in MadGraph and passed through PYTHIA for parton showering and hadronization. The detector effects are evaluated using CLIC and MuC detector cards tuned in Delphes. We report the 95% confidence level limits on the Wilson coefficients c¯γ , c¯HB , c¯HW , c̃γ , c̃HB , and c̃HW and compare them with the experimental and phenomenological limits.

Probing the electromagnetic properties of the neutrinos at future lepton colliders

In this study, we explore the non-standard νν¯γγ couplings parametrized by dimension-seven operators via e+e−→νν¯γ process at the FCC-ee/CEPC and μ+μ−→νν¯γ process at the Muon Colliders. For the detailed Monte Carlo simulation, all signal and relevant background events are produced within the framework of Madgraph where non-standard νν¯γγ couplings are implemented. After passing through Pythia for parton showering and hadronization, detector effects are included via tuned corresponding detector cards for each collider in Delphes. Projected sensitivities on νν¯γγ couplings are obtained at a 5σ confidence level without and with 5% systematic uncertainties for the FCC-ee/CEPC and the Muon Colliders, showcasing the complementarity between lepton colliders. Our best limit on the anomalous νν¯γγ couplings even with 5% systematic uncertainties for muon collider with s=10 TeV and Lint=10 ab−1 are found to be fourteen orders of magnitude stronger than the upper bound obtained from rare decay Z→γγνν¯ analysis using LEP data.

Elliptic flow of inclusive charged hadrons in Au+Au collisions at E lab = 35 A GeV using the PHSD model

Elliptic flow (v 2) of inclusive charged hadrons at mid-rapidity (∣η∣ < 1.0) in Au+Au collisions at E lab = 35 A GeV using the parton hadron string dynamics (PHSD) model are presented as a function of centrality, transverse momentum (p T) and pseudo-rapidity (η). The v 2 results are obtained using the η-sub event plane method with respect to the event plane angle (ψ 2) and participant plane angle (). p T-integrated charged hadron v 2 shows a strong centrality dependence in Au+Au collisions at E lab = 35 A GeV. The eccentricity-scaled elliptic flow (v 2/ε 2) also shows centrality dependence. The higher values of v 2/ε 2 in central collisions suggest the development of stronger collectivity. The calculations are compared with the results from Au+Au collisions at published by the STAR experiment at RHIC. We also compare the results of HSD and PHSD modes to investigate the contribution of hadronic and partonic phases of the medium on the calculated v 2. The current results serve as a prediction of the collective behavior of the matter produced in baryon-rich and moderate temperature conditions for the upcoming multi-purpose detector at the nuclotron-based Ion collider facility (NICA) and compressed baryonic matter experiment at the facility for antiproton and ion research. These predictions are also useful for interpreting data measured at relativistic heavy ion collider (RHIC) beam energy scan program.

Dead cone effect in charm and bottom quark jets

The evolution of a heavy quark initiated jet is mainly ruled by gluon bremsstrahlung. As a consequence of the dead-cone effect, this radiation is suppressed in the forward direction at angles smaller than that proportional to the heavy quark mass MQ, i.e. Θ0=MQ/EQ at energy EQ of the primary quark. In this paper, we unveil this effect in charm and bottom quark jets using DELPHI and OPAL data from Z0 boson decays in e+e− annihilation at center of mass energy 91.2 GeV. The analysis of the reconstructed heavy quark fragmentation function in momentum space shows the strong suppression of hadrons at high momenta in such events compared to light quark fragmentation by a factor ≲1/10. The amount of this suppression is well reproduced by perturbative QCD (pQCD) within the Modified Leading Logarithmic Aproximation and the compact scheme of Local Parton Hadron Duality (MLLA-LPHD). As a new result, we obtain an almost perfect agreement between the light quark fragmentation functions expected at W0∝MQ from DELPHI and OPAL data with Pythia8 and shed light on the reasons for the existence of the ultra-soft gluon excess at small momentum fraction in comparison with pQCD predictions.

Measurement of the Prompt D^{0} Nuclear Modification Factor in p-Pb Collisions at sqrt[s_{NN}]=8.16 TeV.

The production of prompt D^{0} mesons in proton-lead collisions in both the forward and backward rapidity regions at a center-of-mass energy per nucleon pair of sqrt[s_{NN}]=8.16 TeV is measured by the LHCb experiment. The nuclear modification factor of prompt D^{0} mesons is determined as a function of the transverse momentum p_{T}, and the rapidity in the nucleon-nucleon center-of-mass frame y^{*}. In the forward rapidity region, significantly suppressed production with respect to pp collisions is measured, which provides significant constraints on models of nuclear parton distributions and hadron production down to the very low Bjorken-x region of ∼10^{-5}. In the backward rapidity region, a suppression with a significance of 2.0-3.8 standard deviations compared to parton distribution functions in a nuclear environment expectations is found in the kinematic region of p_{T}>6 GeV/c and -3.25<y^{*}<-2.5, corresponding to x∼0.01.

Measurements of jet multiplicity and jet transverse momentum in multijet events in proton–proton collisions at {sqrt{s}=13, text {TeV}}

Multijet events at large transverse momentum (p_{textrm{T}}) are measured at sqrt{s}=13,text {TeV} using data recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 36.3{,text {fb}^{-1}} . The multiplicity of jets with p_{textrm{T}} >50,text {GeV} that are produced in association with a high-p_{textrm{T}} dijet system is measured in various ranges of the p_{textrm{T}} of the jet with the highest transverse momentum and as a function of the azimuthal angle difference varDelta phi _{1,2} between the two highest p_{textrm{T}} jets in the dijet system. The differential production cross sections are measured as a function of the transverse momenta of the four highest p_{textrm{T}} jets. The measurements are compared with leading and next-to-leading order matrix element calculations supplemented with simulations of parton shower, hadronization, and multiparton interactions. In addition, the measurements are compared with next-to-leading order matrix element calculations combined with transverse-momentum dependent parton densities and transverse-momentum dependent parton shower.

Elliptic flow of identified hadrons in Au+Au collisions at E_{lab} = 35~text {A}~text {GeV} using the PHSD model

We present predictions of elliptic flow (v_2) of identified hadrons at mid-rapidity (|y| < 1.0) in Au+Au collisions at E_{lab} = 35~text {A}~text {GeV} using the Parton Hadron String Dynamics (PHSD) model. The transverse momentum (p_{textrm{T}}) dependence of identified hadron v_2 in minimum bias (0–80%) and three different centrality intervals (0–10%, 10–40%, and 40–80%) are presented. A clear centrality dependence of v_2(p_{textrm{T}}) is observed for particles and anti-particles. We also present the p_{textrm{T}} dependence of v_2 difference ({Delta } v_2) between particles and corresponding anti-particles. A significant difference in v_2 values for baryons and anti-baryons is observed. Constituent quark scaling (NCQ) of v_{2} is investigated in Au+Au collisions. We also present a v_2(p_{textrm{T}}) ratio between the HSD and PHSD modes to explore the effect of hadronic and partonic interactions in the medium. These predictions are useful for interpreting the data measured in the Beam Energy Scan (BES) program at RHIC. They will also be useful for the future Compressed Baryonic Matter (CBM) experiment at the Facility for Antiproton and Ion Research (FAIR) and Multi-Purpose Detector (MPD) at the Nuclotron-based Ion Collider facility (NICA).

Neural-Network-Based Quark–Gluon Plasma Trigger for the CBM Experiment at FAIR

Algorithms optimized for high-performance computing, which ensure both speed and accuracy, are crucial for real-time data analysis in heavy-ion physics experiments. The application of neural networks and other machine learning methodologies, which are fast and have high accuracy, in physics experiments has become increasingly popular over recent years. This paper introduces a fast neural network package named ANN4FLES developed in C++, which has been optimized for use on a high-performance computing cluster for the future Compressed Baryonic Matter (CBM) experiment at the Facility for Antiproton and Ion Research (FAIR, Darmstadt, Germany). The use of neural networks for classifying events during heavy-ion collisions in the CBM experiment is under investigation. This paper provides a detailed description of the application of ANN4FLES in identifying collisions where a quark–gluon plasma (QGP) was produced. The methodology detailed here will be used in the development of a QGP trigger for event selection within the First Level Event Selection (FLES) package for the CBM experiment. Fully-connected and convolutional neural networks have been created for the identification of events containing QGP, which are simulated with the Parton–Hadron–String Dynamics (PHSD) microscopic off-shell transport approach, for central Au + Au collisions at an energy of 31.2 A GeV. The results show that the convolutional neural network outperforms the fully-connected networks and achieves over 95% accuracy on the testing dataset.

Model-independent study on the anomalous $$ZZ\gamma $$ and $$Z\gamma \gamma $$ couplings at the future muon collider

In this study, we investigate the potential of $$\mu ^{-} \mu ^{+}\rightarrow Z\gamma \rightarrow \nu \bar{\nu }\gamma $$ process at the future muon collider with a center-of-mass energy of 3 TeV to examine the anomalous ZZ $$\gamma $$ and $$Z\gamma \gamma $$ neutral triple gauge couplings defining CP-conserving $$C_{\widetilde{B}W}/{\Lambda ^4}$$ coupling and three CP-violating $$C_{\mathrm{BB}}/{\Lambda ^4}$$ , $$C_{\mathrm{BW}}/{\Lambda ^4}$$ , $$C_{\mathrm{WW}}/{\Lambda ^4}$$ couplings. All signal and relevant background events are generated in MadGraph and passed through Pythia for parton showering and hadronization. Detector effects are also considered via tuned muon detector cards in Delphes. The effects of systematic uncertainties of $$0\%$$ , $$3\%$$ and $$5\%$$ on the sensitivities are studied. The best sensitivities obtained from the process $$\mu ^{-} \mu ^{+}\rightarrow Z\gamma \rightarrow \nu \bar{\nu }\gamma $$ are $$[-6.53;6.64]\times 10^{-2}$$ TeV $$^{-4}$$ on CP-conserving $$C_{\widetilde{B}W}/{\Lambda ^4}$$ coupling and $$[-2.47;2.47]\times 10^{-2}$$ TeV $$^{-4}$$ , $$[-8.46;8.46]\times 10^{-2}$$ TeV $$^{-4}$$ and $$[-2.20;2.20]\times 10^{-1}$$ TeV $$^{-4}$$ on CP-conserving $$C_{\mathrm{BB}}/{\Lambda ^4}$$ , $$C_{\mathrm{BW}}/{\Lambda ^4}$$ , $$C_{\mathrm{WW}}/{\Lambda ^4}$$ couplings , respectively. Our obtained results on the anomalous neutral gauge couplings set more stringent sensitivity, ranging between 5 and 15 times than the current experimental results while slightly better than the phenomenological studies at future pp colliders such as the HL-LHC, the HE-LHC and the FCC-hh, respectively. On the other hand, we can see that the bounds on the anomalous neutral gauge couplings expected to be obtained for the future $$e^{-}e^{+}$$ colliders such as the CLIC are roughly 2 times better than our results.

Recent Jet Measurements in ALICE

The precise measurement of jets in pp collisions plays a critical role in the study of quantum chromodynamics (QCD). Measurements of jets in relativistic heavy-ion collisions are additionally useful for probing QCD matter in the regime of high densities and temperatures since the partons in the jet evolution interact strongly with the medium. This phenomenon is called jet quenching and is characterized by both jet energy loss and modification of the internal structure of the jet. The ALICE experiment is well suited for studies of jets and their corresponding internal structure due to the high precision tracking system. These proceedings report on an overview of recent ALICE jet results in both pp and Pb–Pb collisions. Results in pp collisions include measurements of generalized angularities of groomed and inclusive jets, a measurement of the Lund jet plane, and a measurement of jet axis differences. Results from Pb–Pb collisions include measurements of jet splittings, studies of subjet fragmentation, as well as a measurement of the jet nuclear modification factor made with machine learning techniques. These new results, when combined with the corresponding theoretical comparisons, provide information regarding the QCD processes of the parton shower and hadronization, as well as the underlying physics of jet quenching.

Low energy protons as probes of hadronization dynamics

Energetic quarks liberated from hadrons in nuclear deep-inelastic scattering propagate through the nuclear medium, interacting with it via several processes. These include quark energy loss and nuclear interactions of forming hadrons. One manifestation of these interactions is the enhanced emission of low-energy charged particles, referred to as grey tracks. We use the theoretical components of the BeAGLE event generator to interpret grey track signatures of parton transport and hadron formation by comparing its predictions to E665 data. We extend the base version of BeAGLE by adding four different options for describing parton energy loss. The E665 data we used consists of multiplicity ratios for fixed-target scattering of 490 GeV muons on Xe normalized to deuterium as a function of the number of grey tracks. We compare multiplicity ratios for E665 grey tracks to the predictions of BeAGLE, varying the options and parameters to determine which physics phenomena can be identified by these data. We find that grey tracks are unaffected by modifications of the forward production. Thus their production must be dominated by interactions with hadrons in the backward region. This offers the advantage that selecting certain particles in the forward region is unlikely to bias a centrality selection. We see a strong correlation between the number of grey tracks and the in-medium path length. Our energy loss model does not reproduce the suppression observed in the projectile region. We see an underprediction of the proton production rate in backward kinematics, suggesting that a stronger source of interaction with the nuclear medium is needed for accurate modeling. These results lay an important foundation for future spectator tagging studies at both Jefferson Lab and at the Electron-Ion Collider, where neutron and proton grey track studies will be feasible down to very small momenta.

Prerequisites for heavy quark coalescence in heavy-ion collisions

The coalescence model assumes instant formation of a bound state from unbound particles based on the overlapping of two states in spatial and momentum spaces and quantum numbers. Therefore, applied to the hadronization of partons, it provides a snapshot of a Quark-Gluon Plasma (QGP) just before hadronization. We use the coalescence model for the formation of the ground state of open heavy flavor and the statistical model for heavier states. Assuming that all heavy flavors in thermal equilibrium hadronize through the coalescence, we find that the QGP just before hadronization is not composed of completely randomized partons but must have strong correlations in color charges as well as in momentum and/or coordinate spaces between heavy quark and light (anti-)quark.

One-loop hybrid renormalization matching kernels for quasiparton distributions

Large-momentum effective theory allows extraction of hadron parton distribution functions in lattice QCD by matching them to quark bilinear matrix elements of hadrons with large momenta. We calculate the matching kernels for the unpolarized, helicity, and transversity-isovector parton distribution functions and skewless generalized parton distributions of all hadrons in the hybrid-regularization-invariant momentum subtraction (RI/MOM) scheme. This renormalization scheme uses RI/MOM when the Wilson line length is less than ${z}_{s}$, otherwise a mass subtraction scheme is used. By design, the nonhybrid scheme is recovered as ${z}_{s}\ensuremath{\rightarrow}\ensuremath{\infty}$. In the opposite limit, ${z}_{s}\ensuremath{\rightarrow}0$, the self-renormalization scheme is obtained. When the parameters ${p}_{z}^{R}=0$ and ${\ensuremath{\mu}}^{R}{z}_{s}\ensuremath{\ll}1$, the hybrid-RI/MOM scheme coincides with the hybrid-ratio scheme times the charge of the PDF. We also discuss the subtlety related to the commutativity of Fourier transform and $\ensuremath{\epsilon}$ expansion in the $\overline{\mathrm{MS}}$ scheme.

Taming modeling uncertainties with mass unspecific supervised tagging

We address the modeling dependence of jet taggers built using the method of mass unspecific supervised tagging, by using two different parton showering and hadronisation schemes. We find that the modeling dependence of the results – estimated by using different schemes in the design of the taggers and applying them to the same type of data – is rather small, even if the jet substructure varies significantly between the two schemes. These results add great value to the use of generic supervised taggers for new physics searches.

Measurement of charged-pion production in deep-inelastic scattering off nuclei with the CLAS detector

Background: Energetic quarks in nuclear deep-inelastic scattering propagate through the nuclear medium. Processes that are believed to occur inside nuclei include quark energy loss through medium-stimulated gluon bremsstrahlung and intranuclear interactions of forming hadrons. More data are required to gain a more complete understanding of these effects. Purpose: To test the theoretical models of parton transport and hadron formation, we compared their predictions for the nuclear and kinematic dependence of pion production in nuclei. Methods: We have measured charged-pion production in semi-inclusive deep-inelastic scattering off D, C, Fe, and Pb using the CLAS detector and the CEBAF 5.014-GeV electron beam. We report results on the nuclear-to-deuterium multiplicity ratio for π+ and π− as a function of energy transfer, four-momentum transfer, and pion energy fraction or transverse momentum—the first three-dimensional study of its kind. Results: The π+ multiplicity ratio is found to depend strongly on the pion fractional energy z and reaches minimum values of 0.67±0.03, 0.43±0.02, and 0.27±0.01 for the C, Fe, and Pb targets, respectively. The z dependencies of the multiplicity ratios for π+ and π− are equal within uncertainties for C and Fe targets but show differences at the level of 10% for the Pb-target data. The results are qualitatively described by the GiBUU transport model, as well as with a model based on hadron absorption, but are in tension with calculations based on nuclear fragmentation functions. Conclusions: These precise results will strongly constrain the kinematic and flavor dependence of nuclear effects in hadron production, probing an unexplored kinematic region. They will help to reveal how the nucleus reacts to a fast quark, thereby shedding light on its color structure and transport properties and on the mechanisms of the hadronization process.Received 25 September 2021Accepted 23 December 2021DOI:https://doi.org/10.1103/PhysRevC.105.015201©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasColor confinementDeep inelastic scatteringLepton induced nuclear reactionsParticle interactionsParticle productionQuantum chromodynamicsStrong interactionNuclear PhysicsParticles & Fields

Measurement of b-quark fragmentation properties in jets using the decay B\xb1\u2192 J/\u03c8K\xb1 in pp collisions at sqrt{s} = 13 TeV with the ATLAS detector

The fragmentation properties of jets containing b-hadrons are studied using charged B mesons in 139 fb−1 of pp collisions at sqrt{s} = 13 TeV, recorded with the ATLAS detector at the LHC during the period from 2015 to 2018. The B mesons are reconstructed using the decay of B± into J/ψK±, with the J/ψ decaying into a pair of muons. Jets are reconstructed using the anti-kt algorithm with radius parameter R = 0.4. The measurement determines the longitudinal and transverse momentum profiles of the reconstructed B hadrons with respect to the axes of the jets to which they are geometrically associated. These distributions are measured in intervals of the jet transverse momentum, ranging from 50 GeV to above 100 GeV. The results are corrected for detector effects and compared with several Monte Carlo predictions using different parton shower and hadronisation models. The results for the longitudinal and transverse profiles provide useful inputs to improve the description of heavy-flavour fragmentation in jets.

Probing FCNC couplings in single top-quark production associated with a neutral gauge boson in future lepton colliders

In this paper, we consider a single top-quark production in association with a neutral gauge boson (Z boson or photon) in the future electron–positron colliders. We utilize these channels to probe the top-quark flavor changing neutral current (FCNC) interactions in tqZ and tqγ vertices. We perform two separate analyses for top-Z-jet and top-γ-jet channels. The standard model effective field theory approach is employed to search for these anomalous couplings. We consider parton showering, hadronization and fast detector simulation in our study and use a cut-and-count technique to separate the signal from the standard model background processes. The upper limits on the FCNC couplings at 95% confidence level for different integrated luminosities are obtained. It is shown that the future lepton collider would be able to probe the FCNC branching fractions to Br(t → qγ) < 10−4 and Br(t → qZ) < 10−4 with 3 ab−1 of integrated luminosity of data at a center of mass energy of 350 GeV.