The production of heavy quarks (charm and beauty) in high-energy hadronic and nuclear collisions provides an excellent testing ground for the theory of strong interactions and validates models based on quantum chromodynamics (QCD). In this work, prompt and nonprompt production of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">J</mi><mo>/</mo></mrow><mi>ψ</mi></math> in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>p</mi></math> collisions at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> are studied as a function of the transverse spherocity using pythia8. <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">J</mi><mo>/</mo></mrow><mi>ψ</mi></math> is reconstructed via its electromagnetic decay to dielectrons and dimuons, in mid- and forward rapidity, respectively. Transverse spherocity, an event-shape observable, is used to distinguish hard-QCD events from the softer, isotropic ones. In pythia8, the production of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">J</mi><mo>/</mo></mrow><mi>ψ</mi></math> can be influenced by the average number of multiple parton interactions (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">⟨</mo><msub><mi>N</mi><mrow><mi>mpi</mi></mrow></msub><mo stretchy="false">⟩</mo></math>), owing to the underlying events, which have a dominant contribution to particle production at lower transverse momentum. Since transverse spherocity is correlated to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">⟨</mo><msub><mi>N</mi><mrow><mi>mpi</mi></mrow></msub><mo stretchy="false">⟩</mo></math>, this can serve as an experimentally accessible tool for event selection to study the underlying QCD processes influencing the prompt and nonprompt <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">J</mi><mo>/</mo></mrow><mi>ψ</mi></math> production. This study reveals the correlation between heavy-flavor production dynamics and topological event selection in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>p</mi></math> collisions using pythia8, whose relevance awaits experimental validation.

India

Aswathy Menon Kavumpadikkal Radhakrishnan

Suraj Prasad

Finland

Neelkamal Mallick

Raghunath Sahoo

Topological production of charmonia with event-shape engineering in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>p</mi></math> collisions at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> using pythia8

RHIC and LHC have injected <math altimg='si2.svg'><mrow><msup><mrow /><mn>16</mn></msup><mrow><mi mathvariant='normal'>O</mi></mrow></mrow></math> nuclei in their accelerator complexes with a focus on investigating collectivity and the origin of quark-gluon plasma signatures in small collision systems. The <math altimg='si2.svg'><mrow><msup><mrow /><mn>16</mn></msup><mrow><mi mathvariant='normal'>O</mi></mrow></mrow></math> nuclei are known to possess clusters of <math altimg='si1.svg'><mi>&#945;</mi></math>-particles ( <math altimg='si19.svg'><mrow><msup><mrow /><mn>4</mn></msup><mrow><mi mathvariant='normal'>H</mi></mrow><mi>e</mi></mrow></math>) inside the nucleus. This paper attempts to study the clustered-nuclear-geometry dependence of anisotropic flow coefficients such as elliptic flow ( <math altimg='si20.svg'><msub><mi>v</mi><mn>2</mn></msub></math>) and triangular flow ( <math altimg='si21.svg'><msub><mi>v</mi><mn>3</mn></msub></math>), which are sensitive to the nuclear geometry of colliding nuclei. The study is performed in pO and OO collisions at <math altimg='si6.svg'><mrow><msqrt><msub><mi>s</mi><mrow><mrow><mi mathvariant='normal'>N</mi></mrow><mi>N</mi></mrow></msub></msqrt><mo linebreak='goodbreak'>=</mo><mn>9.61</mn></mrow></math> TeV and 7 TeV respectively, employing a hybrid model encompassing IP-Glasma + MUSIC + iSS + UrQMD. The results of the clustered nuclear geometry are compared with those of the Woods&#8211;Saxon nuclear profile. Both initial and final state anisotropies are estimated. This study is thus one of its first kind, where the study of anisotropic flow coefficients for pO and OO collisions is presented using a hybrid hydrodynamics model. While the effect of <math altimg='si1.svg'><mi>&#945;</mi></math>-clustering in pO is found to be small, it is significant for each observable studied in OO collisions. It is also observed that the magnitude of this effect has a noteworthy dependence on the size of the 4He.

Hungary

Gergely Gábor Barnaföldi

Probing the sensitivity of anisotropic flow coefficients to the initial nuclear structure in pO and OO collisions at the LHC

Anisotropic flow and fluctuations are sensitive observables of the initial state effects in heavy ion collisions and are characterized by the medium properties and final state interactions. Using event-shape observables, one can constrain the probability distributions of anisotropic flow coefficients, thus reducing the linear and nonlinear contributions in the measured higher-order harmonics. In this paper, we use transverse spherocity as an event shape observable to study the flow coefficients and elliptic flow fluctuations. Transverse spherocity is found to have a strong correlation with elliptic flow and its fluctuations. We exploit this feature of transverse spherocity to remove the contribution to elliptic flow from higher-order harmonics. The study is performed in Pb–Pb collisions at <math altimg='si1.svg'><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi mathvariant='normal'>NN</mi></mrow></msub></mrow></msqrt><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mn>5.02</mn></math> TeV using a multi-phase transport model. The multi-particle Q-cumulant method estimates the anisotropic flow coefficients, which reduces the non-flow contributions. We observe a stronger system response to the flow coefficients for the events with smaller values of elliptic flow.

Higher order flow coefficients – a messenger of QCD medium formed in heavy-ion collisions at the Large Hadron Collider

In relativistic heavy-ion collisions, the formation of a deconfined and thermalized state of partons, known as quark-gluon plasma (QGP), leads to enhanced production of strange hadrons in contrast to proton-proton (<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mi>p</mi></mrow></math>) collisions, which are taken as baseline. This observation is known as strangeness enhancement in heavy-ion collisions and is considered one of the important signatures that can signify the formation of QGP. However, in addition to strangeness enhancement, recent measurements hint at observing several heavy-ion-like features in high multiplicity <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mi>p</mi></mrow></math> collisions at energies available at the CERN Large Hadron Collider. Alternatively, event shape observables, such as transverse spherocity, transverse sphericity, charged particle flattenicity, and relative transverse activity classifiers, can fundamentally separate hard interaction-dominated jetty events from soft isotropic events. These features of event shape observables can probe the observed heavy-ion-like features in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mi>p</mi></mrow></math> collisions with significantly reduced selection bias and can bring all collision systems on equal footing. In this article, we present an extensive summary of the strange particle ratios to pions as a function of different event classifiers using the PYTHIA 8 model with color reconnection and rope hadronization mechanisms to understand the microscopic origin of strangeness enhancement in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mi>p</mi></mrow></math> collisions and also prescribe the applicability of these event classifiers in the context of strangeness enhancement. Charged-particle flattenicity is found to be most suited for the study of strangeness enhancement, and it shows a quantitative enhancement similar to that seen for the analysis based on the number of multiparton interactions.

Bhagyarathi Sahoo

CERN

Sushanta Tripathy

Probing strangeness with event topology classifiers in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mi>p</mi></mrow></math> collisions at energies available at the CERN Large Hadron Collider with the rope hadronization mechanism in PYTHIA

Nuclei having 4n number of nucleons are theorized to possess clusters of α particles ($^{4}$He nucleus). The Oxygen nucleus ($^{16}$O) is a doubly magic nucleus, where the presence of an α-clustered nuclear structure grants additional nuclear stability. In this study, we exploit the anisotropic flow coefficients to discern the effects of an α-clustered nuclear geometry with respect to a Woods-Saxon nuclear distribution in O–O collisions at <math><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>NN</mi></mrow></msub></mrow></msqrt><mo>=</mo><mn>7</mn></math> TeV using a hybrid of IP-Glasma + MUSIC + iSS + UrQMD models. In addition, we use the multi-particle cumulants method to measure anisotropic flow coefficients, such as elliptic flow (<math><msub><mrow><mi>v</mi></mrow><mrow><mn>2</mn></mrow></msub></math>) and triangular flow (<math><msub><mrow><mi>v</mi></mrow><mrow><mn>3</mn></mrow></msub></math>), as a function of multiplicity class. Anisotropic flow fluctuations, which are expected to be larger in small collision systems, are also studied for the first time in O–O collisions. It is found that an α-clustered nuclear distribution gives rise to an enhanced value of <math><msub><mrow><mi>v</mi></mrow><mrow><mn>2</mn></mrow></msub></math> and <math><msub><mrow><mi>v</mi></mrow><mrow><mn>3</mn></mrow></msub></math> for the low-multiplicity events. Consequently, a rise in <math><msub><mrow><mi>v</mi></mrow><mrow><mn>3</mn></mrow></msub><mo>/</mo><msub><mrow><mi>v</mi></mrow><mrow><mn>2</mn></mrow></msub></math> is also observed for the 0–10% multiplicity class. Further, for α-clustered O–O collisions, fluctuations of <math><msub><mrow><mi>v</mi></mrow><mrow><mn>2</mn></mrow></msub></math> are larger for the highest multiplicity events, which decrease as the final-state multiplicity decreases. In contrast, for a Woods-Saxon $^{16}$O nucleus, <math><msub><mrow><mi>v</mi></mrow><mrow><mn>2</mn></mrow></msub></math> fluctuations show an opposite behavior with decreasing multiplicity. When confronted with experimental data, this study may reveal the importance of the nuclear density profile on the discussed observables and provide physics validation for the hybrid model discussed in this work.

Anisotropic flow fluctuation as a possible signature of clustered nuclear geometry in O–O collisions at the Large Hadron Collider

In proton-proton and heavy-ion collisions, the study of charm hadrons plays a pivotal role in understanding the QCD medium and provides an undisputed testing ground for the theory of strong interaction, as they are mostly produced in the early stages of collisions via hard partonic interactions. The lightest open charm, <math><msup><mi>D</mi><mn>0</mn></msup></math> meson (<math><mrow><mi>c</mi><mover><mrow><mi>u</mi></mrow><mrow><mo>¯</mo></mrow></mover></mrow></math>), can originate from two separate sources. The prompt <math><msup><mi>D</mi><mn>0</mn></msup></math> originates from either direct charm production or the decay of excited open charm states, while the nonprompt stems from the decay of beauty hadrons. In this paper, using different machine learning (ML) algorithms such as XGBoost, CatBoost, and Random Forest, an attempt has been made to segregate the prompt and nonprompt production modes of the <math><msup><mi>D</mi><mn>0</mn></msup></math> meson signal from its background. The ML models are trained using the invariant mass through its hadronic decay channel, i.e., <math><msup><mi>D</mi><mn>0</mn></msup><mo>→</mo><msup><mi>π</mi><mo>+</mo></msup><msup><mi>K</mi><mo>−</mo></msup></math>, pseudoproper time, pseudoproper decay length, and distance of closest approach of <math><msup><mi>D</mi><mn>0</mn></msup></math> meson, using pythia8 simulated <math><mi>p</mi><mi>p</mi></math> collisions at <math><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math>. The ML models used in this analysis are found to retain the pseudorapidity, transverse momentum, and collision energy dependence. In addition, we report the ratio of nonprompt to prompt <math><msup><mi>D</mi><mn>0</mn></msup></math> yield, the self-normalized yield of prompt and nonprompt <math><msup><mi>D</mi><mn>0</mn></msup></math>, and explore the charmonium, <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> to open charm, <math><msup><mi>D</mi><mn>0</mn></msup></math> yield ratio as a function of transverse momenta and normalized multiplicity. The observables studied in this paper are well predicted by all the ML models compared to the simulation.

Kangkan Goswami

Gagan B. Mohanty

Machine learning-based study of open-charm hadrons in proton-proton collisions at the Large Hadron Collider

Studies related to <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> meson, a bound state of charm and anticharm quarks (<math><mi>c</mi><mover><mi>c</mi><mo>¯</mo></mover></math>), in heavy-ion collisions, provide genuine testing grounds for the theory of strong interaction, quantum chromodynamics. To better understand the underlying production mechanism, cold nuclear matter effects, and influence from the quark-gluon plasma, baseline measurements are also performed in proton-proton (<math><mi>p</mi><mi>p</mi></math>) and proton-nucleus (<math><mi>p</mi></math>-A) collisions. The inclusive <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> measurement has contributions from both prompt and nonprompt productions. The prompt <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> is produced directly from the hadronic interactions or via feed down from directly produced higher charmonium states, whereas nonprompt <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> comes from the decay of beauty hadrons. In experiments, <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> is reconstructed through its electromagnetic decays to lepton pairs, in either <math><msup><mi>e</mi><mo>+</mo></msup><mo>+</mo><msup><mi>e</mi><mo>−</mo></msup></math> or <math><msup><mi>μ</mi><mo>+</mo></msup><mo>+</mo><msup><mi>μ</mi><mo>−</mo></msup></math> decay channels. In this work, for the first time, machine learning techniques are implemented to separate the prompt and nonprompt dimuon pairs from the background to obtain a better identification of the <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> signal for different production modes. The study has been performed in <math><mi>p</mi><mi>p</mi></math> collisions at <math><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>7</mn></math> and 13 TeV simulated using pythia8. Machine learning models such as XGBoost and LightGBM are explored. The models could achieve up to 99% prediction accuracy. The transverse momentum (<math><msub><mi>p</mi><mi>T</mi></msub></math>) and rapidity (<math><mi>y</mi></math>) differential measurements of inclusive, prompt, and nonprompt <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math>, its multiplicity dependence, and the <math><msub><mi>p</mi><mi>T</mi></msub></math> dependence of fraction of nonprompt <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> (<math><msub><mi>f</mi><mi>B</mi></msub></math>) are shown. These results are compared to experimental findings wherever possible.

Inclusive, prompt and nonprompt <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> identification in proton-proton collisions at the Large Hadron Collider using machine learning

To understand the true origin of flowlike signatures and applicability of hydrodynamics in small collision systems, effects of soft QCD dynamics, the sensitivity of jetlike correlations, and nonequilibrium effects, efforts are being made to perform <math><mrow><mi>p</mi></mrow></math>-O and O-O collisions at the LHC and RHIC energies. It is equally interesting to look into the possible signatures of an <math><mi>α</mi></math>-clustered nuclear geometry in <math><mrow><mrow><mmultiscripts><mrow><mi>O</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>16</mn></mrow></mmultiscripts></mrow><mtext>−</mtext><mrow><mmultiscripts><mrow><mi>O</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>16</mn></mrow></mmultiscripts></mrow></mrow></math> collisions by studying the initial-state effects on the final-state observables. In this work, within a multiphase transport model, we implement an <math><mi>α</mi></math>-cluster tetrahedral density profile in the oxygen nucleus along with the default Woods-Saxon density profile. We study the eccentricity (<math><msub><mi>ε</mi><mn>2</mn></msub></math>), triangularity (<math><msub><mi>ε</mi><mn>3</mn></msub></math>), normalized symmetric cumulants [NSC(2,3)], elliptic flow (<math><msub><mi>v</mi><mn>2</mn></msub></math>), and triangular flow (<math><msub><mi>v</mi><mn>3</mn></msub></math>) in <math><mrow><mrow><mmultiscripts><mrow><mi>O</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>16</mn></mrow></mmultiscripts></mrow><mtext>−</mtext><mrow><mmultiscripts><mrow><mi>O</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>16</mn></mrow></mmultiscripts></mrow></mrow></math> collisions at <math><msqrt><msub><mi>s</mi><mrow><mi>NN</mi></mrow></msub></msqrt><mo>=</mo><mn>7</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math>. The constituent quark number scaling of the elliptic flow is also reported. For the most central collisions, enhanced effects in <math><mo>⟨</mo><msub><mi>ε</mi><mn>3</mn></msub><mo>⟩</mo><mo>/</mo><mo>⟨</mo><msub><mi>ε</mi><mn>2</mn></msub><mo>⟩</mo></math> and <math><mo>⟨</mo><msub><mi>v</mi><mn>3</mn></msub><mo>⟩</mo><mo>/</mo><mo>⟨</mo><msub><mi>v</mi><mn>2</mn></msub><mo>⟩</mo></math> with a negative value of NSC(2,3), and an away-side broadening in the two-particle azimuthal correlation function [<math><mi>C</mi><mo>(</mo><mi>Δ</mi><mi>ϕ</mi><mo>)</mo></math>] of the identified particles are observed in the presence of an <math><mi>α</mi></math>-clustered geometry.

Debadatta Behera

Effects of clustered nuclear geometry on the anisotropic flow in O-O collisions at the LHC within a multiphase transport model framework

Recent developments of a deep learning feed-forward network for estimating elliptic flow (<math><msub><mi>v</mi><mn>2</mn></msub></math>) coefficients in heavy-ion collisions have shown the prediction power of this technique. The success of the model is mainly the estimation of <math><msub><mi>v</mi><mn>2</mn></msub></math> from final-state particle kinematic information and learning the centrality and transverse momentum (<math><msub><mi>p</mi><mi>T</mi></msub></math>) dependence of <math><msub><mi>v</mi><mn>2</mn></msub></math>. The deep learning model is trained with Pb-Pb collisions at <math><msqrt><msub><mi>s</mi><mrow><mi>NN</mi></mrow></msub></msqrt><mo>=</mo><mn>5.02</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> minimum bias events simulated with a multiphase transport model. We extend this work to estimate <math><msub><mi>v</mi><mn>2</mn></msub></math> for light-flavor identified particles such as <math><msup><mi>π</mi><mo>±</mo></msup></math>, <math><msup><mi>K</mi><mo>±</mo></msup></math>, and <math><mi>p</mi><mo>+</mo><mover><mi>p</mi><mo>¯</mo></mover></math> in heavy-ion collisions at RHIC and LHC energies. The number-of-constituent-quark scaling is also shown. The evolution of the <math><msub><mi>p</mi><mi>T</mi></msub></math>-crossing point of <math><msub><mi>v</mi><mn>2</mn></msub><mo>(</mo><msub><mi>p</mi><mi>T</mi></msub><mo>)</mo></math>, depicting a change in baryon-meson elliptic flow at intermediate <math><msub><mi>p</mi><mi>T</mi></msub></math>, is studied for various collision systems and energies. The model is further evaluated by training it for different <math><msub><mi>p</mi><mi>T</mi></msub></math> regions. These results are compared with the available experimental data wherever possible.

Aditya Nath Mishra

Deep learning predicted elliptic flow of identified particles in heavy-ion collisions at the RHIC and LHC energies

Anisotropic flow is accredited to have effects from the initial state geometry and fluctuations in the nuclear overlap region. The elliptic flow (<math><msub><mi>v</mi><mn>2</mn></msub></math>) and triangular flow (<math><msub><mi>v</mi><mn>3</mn></msub></math>) coefficients of the final state particles are expected to have influenced by eccentricity (<math><msub><mi>ϵ</mi><mn>2</mn></msub></math>) and triangularity (<math><msub><mi>ϵ</mi><mn>3</mn></msub></math>) of the participants, respectively. In this work, we study <math><msub><mi>v</mi><mn>2</mn></msub></math>, <math><msub><mi>v</mi><mn>3</mn></msub></math>, <math><msub><mi>ϵ</mi><mn>2</mn></msub></math>, <math><msub><mi>ϵ</mi><mn>3</mn></msub></math>, and the correlations among them with respect to event topology in the framework of a multiphase transport model (AMPT). We use transverse spherocity and reduced flow vector as event shape classifiers in this study. Transverse spherocity has the unique ability to separate events based on geometrical shapes, i.e., jetty and isotropic, which pertain to pQCD and non-pQCD domains of particle production in high-energy physics, respectively. We use the two-particle correlation method to study different anisotropic flow coefficients. We confront transverse spherocity with a more widely used event shape classifier–reduced flow vector (<math><msub><mi>q</mi><mi>n</mi></msub></math>) and they are found to have significant (anti)correlations among them. We observe significant spherocity dependence on <math><msub><mi>v</mi><mn>2</mn></msub></math>, <math><msub><mi>v</mi><mn>3</mn></msub></math>, and <math><msub><mi>ϵ</mi><mn>2</mn></msub></math>. This work also addresses transverse momentum dependent crossing points between <math><msub><mi>v</mi><mn>2</mn></msub></math> and <math><msub><mi>v</mi><mn>3</mn></msub></math>, which varies for different centrality and spherocity percentiles.

Italy

Probing initial geometrical anisotropy and final azimuthal anisotropy in heavy-ion collisions at Large Hadron Collider energies through event-shape engineering