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Journal of Physics G: Nuclear and Particle Physics - latest papers
Latest articles for Journal of Physics G: Nuclear and Particle Physics
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Sensitivity of transverse momentum correlations to early-stage and thermal fluctuations
Transverse momentum correlations were recently measured by the ALICE collaboration at the LHC [Acharya etal (2020 Phys. Lett. B804 135375)]. A long-range structure in terms of relative pseudorapidity of particle pairs is observed. This may imply some signal of the initial state owing to the sheer spread of the correlation. However, the fluctuations inside a thermally equilibrated medium have to be taken into account, serving as motivation for this paper. Using lattice Quantum Chromodynamics constraints, we predicted the development and spread of balancing correlations caused by energy-momentum conservation. At the same time, we propagated the Gaussian-shaped initial correlation using hydrodynamics to estimate its effects. Our findings suggest that the resulting correlation, known as ‘the ridge,’ is sensitive both to flucutations seeded in the pre-equilibrium stage and to those seeded in the equilibrated medium. This can provide important insight into the early stages of the collision.
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Summary of the trigger systems of the Large Hadron Collider experiments ALICE, ATLAS, CMS and LHCb
In modern high energy physics (HEP) experiments, triggers perform the important task of selecting, in real time, the data to be recorded and saved for physics analyses. As a result, trigger strategies play a key role in extracting relevant information from the vast streams of data produced at facilities like the large hadron collider (LHC). As the energy and luminosity of the collisions increase, these strategies must be upgraded and maintained to suit the experimental needs. This whitepaper presents a high-level overview and reviews recent developments of triggering practices employed at the LHC. The general trigger principles applied at modern HEP experiments are highlighted, with specific reference to the current trigger state-of-the-art within the ALICE, ATLAS, CMS and LHCb collaborations. Furthermore, a brief synopsis of the new trigger paradigm required by the upcoming high-luminosity upgrade of the LHC is provided. This whitepaper, compiled by Early Stage Researchers of the SMARTHEP network, is not meant to provide an exhaustive review or substitute documentation and papers from the collaborations themselves, but rather offer general considerations and examples from the literature that are relevant to the SMARTHEP network.
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Detection of reactor neutrinos using gadolinium-doped plastic scintillators enhanced by machine learning techniques
In this study, we present a detailed approach for detecting reactor neutrinos by employing gadolinium-doped plastic scintillators combined with machine learning techniques. The proposed detector design was simulated using the Geant4 framework, featuring segmented modules of plastic scintillators doped with gadolinium to enhance neutron capture efficiency. Inverse beta decay (IBD) events generated by ERNIE and background events produced by cosmic ray simulations were used to train and test an Extreme Gradient Boosting (XGBoost) model for signal-background discrimination. The model demonstrated high discrimination accuracy for prompt IBD events but encountered challenges with delayed neutron background discrimination due to similarities in neutron capture. Performance comparisons with traditional cut-based analyses highlighted the improved accuracy achieved through machine learning, particularly when utilizing additional event features. This work establishes the potential of gadolinium-doped plastic scintillators and machine learning in enhancing neutrino detection and lays the groundwork for future experimental validation and detector optimization.
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Time-dependent gamma-ray emission from quasi-spherical explosions: the case of novae
We consider a general model for a quasi-spherical explosion in which a part of the explosion energy is thermalized, forming an expanding photosphere around a compact object, and the second part of energy is taken by the expanding shell of material which forms a shock wave in the surrounding medium. Different types of particles (electrons, hadrons) can, in principle, be accelerated at the shock. They interact with the thermal radiation from the photosphere and also with the material at the shell. We determine the equilibrium spectra of particles in the shell as a function of time after explosion and calculate the time-dependent γ-ray spectra by taking into account the effects which are due to the anisotropy of the photo-spheric radiation field on the Inverse Compton (IC) process; we also include the absorption of IC γ-rays in the photosphere radiation. We conclude that, in principle, both leptonic and hadronic models can explain the GeV-TeV gamma-ray emission recently detected from the Nova RS Oph. However, the hadronic model, in comparison to the leptonic model, is more energetically demanding and requires much stronger magnetization of the nova shell.
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Toward the first gluon parton distribution from the LaMET
We present progress towards the first unpolarized gluon quasi-parton distribution function (PDF) from lattice quantum chromodynamics using high-statistics measurements for hadrons at two valence pion masses Mπ ≈ 310 and 690 MeV computed on an a ≈ 0.12 fm ensemble with 2 + 1 + 1-flavors of highly improved staggered quark generated by the MILC collaboration. In this study, we consider two gluon operators for which the hybrid-ratio renormalization matching kernels have been recently derived and a third operator that has been used in prior pseudo-PDF studies of the gluon PDFs. We compare the matrix elements for each operator for both the nucleon and pion, at both pion masses, and using two gauge-smearing techniques. Focusing on the more phenomenologically studied nucleon gluon PDF, we compare the ratio and hybrid-ratio renormalized matrix elements at both pion masses and both smearings to those reconstructed from the nucleon gluon PDF from the CT18 global analysis. We identify the best choice of operator to study the gluon PDF and present the first gluon quasi-PDF under some caveats. Additionally, we explore the recent idea of Coulomb gauge fixing to improve signal at large Wilson-line displacement and find it could be a major help in improving the signal in the gluon matrix elements. This work helps identify the best operator for studying the gluon quasi-PDF, shows higher hadron boost momentum is needed to implement hybrid-ratio renormalization reliably, and suggests the need to study more diverse set of operators with their corresponding perturbative calculations for hybrid-ratio renormalization to further gluon quasi-PDF study.