The presence of α clustered structures in light nuclei can enhance the initial spatial anisotropies in relativistic nuclear collisions relative to those arising from nuclei with uniform density distributions. Thus, observables that are strongly sensitive to the initial geometry can be a more efficient probe of the clustered structures than observables dominated by final state dynamics. We investigate the collisions of α clustered oxygen nuclei at √(s_NN)=7 A TeV at the LHC using the GLISSANDO initial state model along with the MUSIC event-by-event hydrodynamical framework. The tetrahedral α clustered structure of ^16 O leads to significantly larger initial triangular eccentricity ϵ _3 than collisions with uniform density distributions especially in the most central events. The spatial eccentricity ϵ _2 is found to be relatively less sensitive to the initial state clustered structure. The production of thermal photons is estimated to be only marginally influenced by clustering for both central as well as peripheral collisions. In contrast, the photon triangular flow coefficient v_3(p_T) is strongly affected by initial state clustering resulting in substantially larger values in both central and peripheral collisions. An experimental determination of photon anisotropic flow together with the ratios of flow coefficients in ^16 O+ ^16 O collisions therefore expected to provide valuable insight into the possible clustered structure in light nuclei and also to constrain parameters in theoretical modeling.

Collisions of lead nuclei at relativistic energies provide valuable insight into the properties of the quark gluon plasma formed in such collisions where the initial geometry and density profile play a crucial role in governing the subsequent evolution of the produced hot and dense fireball. The neutron skin thickness resulting from the difference between the neutron and proton density distributions in neutron rich lead nuclei plays an important role in nuclear structure studies. In this work we investigate the impact of neutron skin on the space time evolution of the fireball formed in Pb+Pb collisions at 2.76A TeV at the LHC and analyze how the presence of neutron skin affect bulk observables sensitive to the initial nuclear structure. The time evolution of initial profile along with the average p_T, particle spectra and anisotropic flow parameters are estimated to investigate the effect of neutron skin on these observables. The initial spatial anisotropy of the fireball is found to be affected by the neutron skin thickness significantly especially for the peripheral collisions. This leads to a substantial enhancement of the elliptic flow of hadrons with an even stronger effect observed for photons. In addition, the effect is found to be more pronounced for lower beam energy collisions of lead nuclei.

In relativistic nuclear collisions, initial spatial anisotropies subsequently manifest as momentum anisotropies in the final-state particles through the collective expansion of the hot and dense medium produced in such collisions. The presence of alpha clustered structures in light nuclei, such as ^7,9 Be, ^12 C, and ^16 O, induces nuclear deformities, leading to significant spatial anisotropies in the overlap region when collided at relativistic energies. In this work, we investigate the effect of α clustered structures on the photon anisotropic flow parameters using a hydrodynamical model framework and state of the art photon rates. We observe significant qualitative and quantitative differences between the photon observables from clustered and unclustered cases for 7A TeV ^16 O+ ^16 O collisions at the LHC.

Electromagnetic radiation is considered as a powerful probe for exploring the hot and dense strongly interacting matter produced in relativistic nuclear collisions. The study of photon anisotropic flow provides valuable insights into the initial state and the subsequent space time evolution of the created fireball. Additionally, recent studies have demonstrated the potential of photon anisotropic flow as an effective tool to probe the initial nucleon level geometry, α clustered structures, and nuclear deformations.

Abstract The presence of $$\alpha $$ α clustered structures in light nuclei can enhance the initial spatial anisotropies in relativistic nuclear collisions relative to those arising from nuclei with uniform density distributions. Thus, observables that are strongly sensitive to the initial geometry can be a more efficient probe of the clustered structures than observables dominated by final state dynamics. We investigate the collisions of $$\alpha $$ α clustered oxygen nuclei at $$\sqrt{s_{NN}}=7$$ s NN = 7 A TeV at the LHC using the GLISSANDO initial state model along with the MUSIC event-by-event hydrodynamical framework. The tetrahedral $$\alpha $$ α clustered structure of $$^{16}$$ 16 O leads to significantly larger initial triangular eccentricity $$\epsilon _3$$ ϵ 3 than collisions with uniform density distributions especially in the most central events. The spatial eccentricity $$\epsilon _2$$ ϵ 2 is found to be relatively less sensitive to the initial state clustered structure. The production of thermal photons is estimated to be only marginally influenced by clustering for both central as well as peripheral collisions. In contrast, the photon triangular flow coefficient $$v_3(p_T)$$ v 3 ( p T ) is strongly affected by initial state clustering resulting in substantially larger values in both central and peripheral collisions. An experimental determination of photon anisotropic flow together with the ratios of flow coefficients in $$^{16}$$ 16 O+ $$^{16}$$ 16 O collisions therefore expected to provide valuable insight into the possible clustered structure in light nuclei and also to constrain parameters in theoretical modeling.

Electromagnetic probes, such as photons and dileptons, play a key role in diagnosing the initial temperature of the hot and dense quark-gluon plasma (QGP) matter created in relativistic nuclear collisions at very high energies. This is due to their large mean free path λ, which allows them to escape the medium without significant interactions. Unlike hadronic particles, which experience multiple scatterings and are affected by the evolving medium, electromagnetic probes carry undistorted information from the initial stages of the expanding system. In this work an attempt has been made to revisit the estimation of mean free paths of photons in QGP phase for a temperature range predicted by hydrodynamics for heavy ion collisions at √(s_NN)=200 GeV at RHIC and √(s_NN)=2.76 TeV at the LHC. The mean free paths have been estimated for a plasma expanding via (1+1)D and (2+1)D hydrodynamical expansions. For the (1+1)D case, photons with low energy (E_γ< 0.2 GeV) coming from a high temperature (>250 MeV) source are found to have shorter mean free path compared to the expansion scale of the system; while the high energy photons have always larger mean free paths. A similar qualitative nature of the mean free path has also been observed for a more realistic (2+1)D hydrodynamic model calculations although the λ values are found to be larger on a quantitative scale compared to the (1+1)D case.

The presence of cluster structures in light nuclei, such as 8Be, 12C and 16O induces significant spatial anisotropies in the overlap region when collided at relativistic energies which subsequently manifest as momentum anisotropies in the final-state particles through the collective expansion of the QGP medium. In this work we have investigated the effect of cluster structure on photon flow in O+O collisions at 7A TeV.

Isobaric collisions provide a unique opportunity to investigate how variations in the charge to mass ratio affect the final state observables produced in relativistic heavy ion collisions. Most importantly, isobaric systems that differ in their nuclear structure offer valuable insights into the underlying nuclear geometries, making them powerful tools to probe the role of nuclear structure using heavy ion collisions. We study the initial state and evolution of the hot and dense medium formed in Ru+Ru and Zr+Zr collisions at 200A GeV at RHIC using a relativistic hydrodynamical model. The initial geometry of the two isobaric collisions is found to influence the evolution of the hot and dense medium produced. The sensitivity of photon production, charged particle spectra and anisotropic flow coefficients (v_n) to the initial geometry, including different orientations of the isobaric set have been studied in detail. Significant variations in anisotropic flow of photons and hadrons are observed, highlighting the role of nuclear deformation in shaping final state observables. Moreover, photon anisotropic flow is found to be considerably more sensitive to the initial state than charged particle anisotropic flow, indicating that photon measurements in isobaric collisions have strong potential to constrain initial state modeling and improve our understanding of QGP properties in such systems.

Prompt photon measurements in relativistic nuclear collisions serve as an essential comparative basis for heavy ion studies enabling the separation of medium induced effects. However, the identification of prompt photons is experimentally challenging due to substantial backgrounds from photons produced in hadron decays and jet fragmentation. Appropriate isolation criteria are applied to suppress these background contributions. We analyze prompt photon spectra using the JETPHOX framework to quantify the relative contributions of fragmentation and direct production mechanisms to the total photon yield. We perform a systematic study of the impact of isolation criteria on prompt photon production in relativistic nuclear collisions with emphasis on their dependence on beam energy and photon transverse momentum. The fragmentation contribution is found to be substantially large particularly for p_T < 15 GeV and the isolation criterion plays a crucial role in the analysis of prompt photons in that p_T region. A dynamical isolation criterion suppresses the fragmentation component more effectively than a fixed one in this region. Furthermore, the isolation criterion shows a stronger dependence on beam energy and photon p_T than on system size. These observations emphasize the importance of employing carefully selected and consistent isolation criteria when comparing experimental data with theoretical calculations especially for observables sensitive to fragmentation.

The presence of α clustered structures in light nuclei can enhance the initial spatial anisotropies in relativistic nuclear collisions relative to those arising from nuclei with uniform density distributions. Thus, observables that are strongly sensitive to the initial geometry can be a more efficient probe of the clustered structures than observables dominated by final state dynamics. We investigate the collisions of α clustered oxygen nuclei at √(s_NN)=7A TeV at the LHC using the GLISSANDO initial state model along with the MUSIC event-by-event hydrodynamical framework. The tetrahedral α clustered structure of ^16O leads to significantly larger initial triangular eccentricity ε_3 than collisions with uniform density distributions especially in the most central events. The spatial eccentricity ε_2 is found to be relatively less sensitive to the initial state clustered structure. The production of thermal photons is estimated to be only marginally influenced by clustering for both central as well as peripheral collisions. In contrast, the photon triangular flow coefficient v_3(p_T) is strongly affected by initial state clustering resulting in substantially larger values in both central and peripheral collisions. An experimental determination of photon anisotropic flow together with the ratios of flow coefficients in ^16O+^16O collisions therefore expected to provide valuable insight into the possible clustered structure in light nuclei and also to constrain parameters in theoretical modeling.

The second Hot QCD Matter 2024 conference at IIT Mandi focused on various ongoing topics in high-energy heavy-ion collisions, encompassing theoretical and experimental perspectives. This proceedings volume includes 19 contributions that collectively explore diverse aspects of the bulk properties of hot QCD matter. The topics encompass the dynamics of electromagnetic fields, transport properties, hadronic matter, spin hydrodynamics, and the role of conserved charges in high-energy environments. These studies significantly enhance our understanding of the complex dynamics of hot QCD matter, the quark-gluon plasma (QGP) formed in high-energy nuclear collisions. Advances in theoretical frameworks, including hydrodynamics, spin dynamics, and fluctuation studies, aim to improve theoretical calculations and refine our knowledge of the thermodynamic properties of strongly interacting matter. Experimental efforts, such as those conducted by the ALICE and STAR collaborations, play a vital role in validating these theoretical predictions and deepening our insight into the QCD phase diagram, collectivity in small systems, and the early-stage behavior of strongly interacting matter. Combining theoretical models with experimental observations offers a comprehensive understanding of the extreme conditions encountered in relativistic heavy-ion and proton-proton collisions.

The anisotropic flow of photons produced in relativistic nuclear collisions is known as a promising observable for studying the initial state and the subsequent evolution of the hot and dense medium formed in such collisions. The investigation of photon anisotropic flow coefficients, vn, has attracted high interest over the last decade, involving both theory and experiment. The thermal emission of photons and their anisotropic flow are found to be highly sensitive to the initial state of the fireball, where even slight modifications can lead to significant variations in the final state results. In contrast, the ratio of photon anisotropic flow stands out as a robust observable, exhibiting minimal sensitivity to the initial conditions. Here, we briefly review the studies of the individual elliptic and triangular flow parameters of photons as well as their ratios and how these parameters serve as valuable probes for investigating the intricacies of the initial state and addressing the challenges posed by the direct photon puzzle.

The presence of alpha-clustered structure in the light nuclei produces different exotic shapes in nuclear structure studies at low energies. Recent phenomenological studies suggest that collision of heavy nuclei with alpha-clustered carbon (12C) at relativistic energies can lead to large initial state anisotropies. This is expected to impact the final momentum anisotropies of the produced particles significantly. The emission of electromagnetic radiations is considered to be more sensitive to the initial state compared to hadronic observables and thus photon observables are expected to be affected by the initial clustered structure profoundly. In this work we estimate the production and anisotropic flow of photons from most-central collisions of triangular alpha-clustered carbon and gold at root sNN = 200 GeV using an event-by-event hydrodynamic framework and compare the results with those obtained from unclustered carbon and gold collisions. We show that the thermal photon v3 for most central collisions is significantly large for the clustered case compared to the case with unclustered carbon, whereas the elliptic flow parameter does not show much difference for the two cases. In addition, the ratio of anisotropic flow coefficients is found to be a potential observable to constrain the initial state produced in relativistic heavy-ion collisions and also to know more about the alpha-clustered structure in carbon nucleus.

BACKGROUND: The ChAdOx1 nCoV-19 vaccine against COVID-19 is a two-dose vaccine spread 3 to 4 weeks apart. This study aims to ascertain the antibody response to each dose with respect to age, previous infection status etc. METHODS: Baseline total COVID-19 antibody level was ascertained using Siemens SARS‑CoV‑2 Total Antibody assay in consenting health care workers before the first dose of vaccination. Adverse effects were noted in each individual and were monitored weekly for the total antibody titre following both doses. Descriptive statistical tests were used to analyse the changes in antibodies levels weekly after both doses. Association of previous COVID infection and age with antibody levels was assessed. RESULTS: Median (range) of age of the 30 study participants was 31.5 years.23% of the participants had a history of previous COVID-19 infection. Mild adverse events following immunisation were reported by 87% participants after first dose whereas only in 7% after second dose. Median baseline antibody titres were significantly higher among those with previous COVID infection as compared to previously uninfected individuals. Antibody titres increased consistently after first dose and showed a declining trend following the second dose in all participants and showed no significant association with previous COVID-19 infection or age. CONCLUSIONS: Antibody titre response was similar amongst the various age groups. Higher response in the previously infected individuals following first dose may make them ideal candidates for a single dose vaccine regimen. Individuals showing lower levels of neutralising antibodies can be ideal candidates for a booster dose.

Background: Pleomorphic adenomas are benign salivary gland tumors predominantly arising from the superficial lobe of the parotid gland and rarely from the small salivary glands located at various locations including parotid, lacrimal duct, lip, floor of the mouth etc. Surgical excision of the tumor mass is the treatment of choice with utmost care taken to preserve the facial nerve in cases involving the parotid gland. Case details: This case series highlights three consecutive cases of pleomorphic adenoma arising from three different locations. Conclusion: Pleomorphic adenoma is the commonest salivary gland tumor characterized by diverse histomorphological features and can occur at any site where salivary tissue is present. Careful histopathological analysis should be done in all tumors arising especially in the head and neck region.

Different orientations of $$\alpha $$ -clustered carbon nuclei colliding with heavy ions can result in a large variation in the value of anisotropic flow. Thus, photon flow observables from clustered $${\mathrm{^{12}C}}$$ and $${\mathrm{^{197}Au}}$$ collisions could be a potential probe to study the ‘direct photon puzzle’. We calculate the transverse momentum spectra and anisotropic flow coefficients ( $$v_n$$ ) of thermal photons from collisions of triangular $$\alpha $$ -clustered carbon and gold at $$\sqrt{s_{\mathrm{NN}}}=200$$ GeV at RHIC using a hydrodynamic model framework and compare the results with those obtained from unclustered carbon and gold collisions. The slope of the thermal photon spectra is found to vary moderately for different orientations of collisions. However, we find that the elliptic ( $$v_2$$ ) and triangular flow ( $$v_3$$ ) coefficients of direct photons for specific configurations are significantly larger and predominantly formed by the QGP radiation. A strong anti-correlation between initial spatial ellipticity and triangularity is observed in an event-by-event framework of $$\alpha $$ -clustered $${\mathrm{C+Au}}$$ collisions. These special features provide us an opportunity to detect the exotic nature of cluster structure inside carbon nucleus using the photon probe in the future experiments.

Electroweak probes are potential tool to study the properties of the hot and dense strongly interacting matter produced in relativistic nuclear collisions due to their unique nature. A selection of the new experimental analysis and results from theory calculations on electromagnetic and weak probes presented at the Hard Probes 2020 are discussed in this contribution.

Fluctuations in the initial QCD matter density distribution are found to enhance the production of thermal photons significantly in the range 2 ≤ pT ≤ 4 GeV/c compared to a smooth initial state averaged profile in ideal hydrodynamic calculation for 200 AGeV Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC) and 2.76 ATeV Pb+Pb collisions at the Large Hadron Collider (LHC). The thermal emission of photons is strongly dependent on the initial temperature of the system where the presence of ’hotspots’ in the initial state translates into enhanced production of photons compared to a smooth profile. The effect of fluctuations in the initial state is found to be stronger for peripheral collisions and for lower beam energies. The pT spectra are found to be quite sensitive to the value of the initial formation time of the plasma which is not known unambiguously and which may vary with collision centralities at a particular beam energy. Increase in the value of the formation time lowers the production of thermal photons compared to the results from a shorter formation time. However, the relative enhancement from fluctuating initial states (compared to a smooth initial state) is found to be stronger for the larger values of formation time. The pT spectra alone are found to be insufficient to quantify the fluctuations in the initial density distribution due to the uncertainties in the initial conditions. A suitably normalized ratio of central-to-peripheral yield as a function of collision centrality and pT can be a useful measure of the fluctuation size scale.

The particle momentum anisotropy ($v_n$) produced in relativistic nuclear collisions is considered to be a response of the initial geometry or the spatial anisotropy $\epsilon_n$ of the system formed in these collisions. The linear correlation between $\epsilon_n$ and $v_n$ quantifies the efficiency at which the initial spatial eccentricity is converted to final momentum anisotropy in heavy ion collisions. We study the transverse momentum, collision centrality, and beam energy dependence of this correlation for different charged particles using a hydrodynamical model framework. The ($\epsilon_n -v_n$) correlation is found to be stronger for central collisions and also for n=2 compared to that for n=3 as expected. However, the transverse momentum ($p_T$) dependent correlation coefficient shows interesting features which strongly depends on the mass as well as $p_T$ of the emitted particle. The correlation strength is found to be larger for lighter particles in the lower $p_T$ region. We see that the relative fluctuation in anisotropic flow depends strongly in the value of $\eta/s$ specially in the region $p_T <1$ GeV unlike the correlation coefficient which does not show significant dependence on $\eta/s$.

Electromagnetic radiations are one of the potential probes to study the initial state of the hot and dense quark-gluon plasma (QGP) produced during the collision of heavy nuclei at relativistic energies. Photons are emitted throughout the lifetime of the evolving system and carry undistorted information from the production point to the detector. The observation of large anisotropic flow of charged particles provides a strong confirmation of QGP formation and collective behaviour of the produced matter in these collisions. However, the theoretical model calculations which explain the hadronic spectra and anisotropic flow successfully, underpredict the experimental data of elliptic as well as triangular flow of photons by a large margin. This discrepancy between data and theory results is known as direct photon puzzle. In this article, we review the anisotropic flow of photons calculated using hydrodynamical model framework for different collision systems and beam energies. In addition, we propose some new ideas which can be valuable for understanding direct photon puzzle.