Dan-Dan Cheng, Zhu-Fang Cui, Minghui Ding, Craig D. Roberts, Sebastian M. Schmidt
A symmetry preserving treatment of a vector $otimes$ vector contact interaction (SCI) is used as the basis for calculations of the two pion transverse momentum dependent parton distribution functions (TMDs); namely, that for unpolarised valence degrees-of-freedom and the analogous Boer-Mulders (BM) function. Amongst other things, the analysis enables the following themes to be addressed: the quark current mass dependence of pion TMDs; the impact of the gauge link model on the positivity constraint that bounds the BM function relative to the unpolarised TMD; the equivalence of direct diagrammatic and light-front wave function TMD calculations; and the size of the BM shift. Interpreted astutely, these SCI results enable one to draw insightful pictures of pion TMDs.
{"title":"Pion Boer-Mulders function using a contact interaction","authors":"Dan-Dan Cheng, Zhu-Fang Cui, Minghui Ding, Craig D. Roberts, Sebastian M. Schmidt","doi":"arxiv-2409.11568","DOIUrl":"https://doi.org/arxiv-2409.11568","url":null,"abstract":"A symmetry preserving treatment of a vector $otimes$ vector contact\u0000interaction (SCI) is used as the basis for calculations of the two pion\u0000transverse momentum dependent parton distribution functions (TMDs); namely,\u0000that for unpolarised valence degrees-of-freedom and the analogous Boer-Mulders\u0000(BM) function. Amongst other things, the analysis enables the following themes\u0000to be addressed: the quark current mass dependence of pion TMDs; the impact of\u0000the gauge link model on the positivity constraint that bounds the BM function\u0000relative to the unpolarised TMD; the equivalence of direct diagrammatic and\u0000light-front wave function TMD calculations; and the size of the BM shift.\u0000Interpreted astutely, these SCI results enable one to draw insightful pictures\u0000of pion TMDs.","PeriodicalId":501573,"journal":{"name":"arXiv - PHYS - Nuclear Theory","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142263262","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this work, we study the thermodynamic properties of quark-gluon plasma using Kramer's $q-potential$ method. We propose a modification in the first law of thermodynamics by including a temperature-dependent term when single particle energies themselves are temperature-dependent. With this modified first law, we derive an expression for pressure starting from Kramer's $q-potential$. We find that to maintain thermodynamic consistency, pressure receives an additional term solely due to medium-dependent dispersion relation. The energy density, by definition, remains a sum over all the single-particle energies with an appropriate weight factor. We confront this quasiparticle model with the lattice QCD data of SU(3) pure gluon plasma.
{"title":"Thermodynamic properties of gluon plasma: A q-potential approach","authors":"Guruprasad Kadam","doi":"arxiv-2409.11038","DOIUrl":"https://doi.org/arxiv-2409.11038","url":null,"abstract":"In this work, we study the thermodynamic properties of quark-gluon plasma\u0000using Kramer's $q-potential$ method. We propose a modification in the first law\u0000of thermodynamics by including a temperature-dependent term when single\u0000particle energies themselves are temperature-dependent. With this modified\u0000first law, we derive an expression for pressure starting from Kramer's\u0000$q-potential$. We find that to maintain thermodynamic consistency, pressure\u0000receives an additional term solely due to medium-dependent dispersion relation.\u0000The energy density, by definition, remains a sum over all the single-particle\u0000energies with an appropriate weight factor. We confront this quasiparticle\u0000model with the lattice QCD data of SU(3) pure gluon plasma.","PeriodicalId":501573,"journal":{"name":"arXiv - PHYS - Nuclear Theory","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142263267","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Ruotsalainen, M. Stryjczyk, M. Ramalho, T. Eronen, Z. Ge, A. Kankainen, M. Mougeot, J. Suhonen
The mass of $^{109}$Ag isotope was measured with respect to $^{110}$Cd with the phase-imaging ion-cyclotron-resonance technique using the JYFLTRAP double Penning trap at the IGISOL facility. By combining this new result with the known spectroscopic information, the $Q_beta$ value of $405(135)$ eV between the $6^+$ isomer of $^{110}$Ag and the $5^+_2$ state in $^{110}$Cd was determined. This is the lowest $Q_beta$ for any allowed transition observed to date. The nuclear shell-model results were performed with the {sc kshell} code employing the textit{jj45pnb} interaction, and combined with the state-of-the-art atomic calculations. The theoretical partial half-life, $2.23^{+5.24}_{-1.28} times 10^7$ years, and the resulting branching ratio, $3.07^{+4.16}_{-2.15} times 10^{-8}$, combined with a viable production method, thermal-neutron capture on stable $^{109}$Ag, make $^{110}$Ag$^{m}$ as a promising candidate for future antineutrino mass measurement experiments.
{"title":"Ultra-low $Q_β$ value for the allowed decay of $^{110}$Ag$^m$ confirmed via mass measurements","authors":"J. Ruotsalainen, M. Stryjczyk, M. Ramalho, T. Eronen, Z. Ge, A. Kankainen, M. Mougeot, J. Suhonen","doi":"arxiv-2409.11203","DOIUrl":"https://doi.org/arxiv-2409.11203","url":null,"abstract":"The mass of $^{109}$Ag isotope was measured with respect to $^{110}$Cd with\u0000the phase-imaging ion-cyclotron-resonance technique using the JYFLTRAP double\u0000Penning trap at the IGISOL facility. By combining this new result with the\u0000known spectroscopic information, the $Q_beta$ value of $405(135)$ eV between\u0000the $6^+$ isomer of $^{110}$Ag and the $5^+_2$ state in $^{110}$Cd was\u0000determined. This is the lowest $Q_beta$ for any allowed transition observed to\u0000date. The nuclear shell-model results were performed with the {sc kshell} code\u0000employing the textit{jj45pnb} interaction, and combined with the\u0000state-of-the-art atomic calculations. The theoretical partial half-life,\u0000$2.23^{+5.24}_{-1.28} times 10^7$ years, and the resulting branching ratio,\u0000$3.07^{+4.16}_{-2.15} times 10^{-8}$, combined with a viable production\u0000method, thermal-neutron capture on stable $^{109}$Ag, make $^{110}$Ag$^{m}$ as\u0000a promising candidate for future antineutrino mass measurement experiments.","PeriodicalId":501573,"journal":{"name":"arXiv - PHYS - Nuclear Theory","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142263264","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The process of L'evy walk, i.e., movement patterns described by heavy-tailed random walks, play a role in many different phenomena, from chemical and microbiological systems through marine predators to climate change. Recent experiments have suggested that this phenomenon also appears in heavy-ion collisions. However, the theoretical background is not yet well understood. In high-energy collisions of heavy nuclei, the strongly interacting Quark Gluon Plasma is created, which, similarly to the early Universe, undergoes a rapid expansion and transition back to normal hadronic matter. In the subsequent expanding hadron gas, particles interact until kinetic freeze-out, when their momenta become fixed, and they freely transition toward the detectors. Measuring spatial freeze-out distributions is a crucial tool in understanding the dynamics of the created matter as well as the interactions among its constituents. In this paper, we present a novel three-dimensional analysis of the spatial freeze-out distribution of pions (the most abundant particles in such collisions). Utilizing Monte-Carlo simulations of high-energy collisions, we show that the chain of processes ending in a final state pion has a step length distribution leading to L'evy-stable distributions. Subsequently, we show that pion freeze-out distributions indeed exhibit heavy tails and can be described by a three-dimensional elliptically contoured symmetric L'evy-stable distribution.
L'evy walk 过程，即重尾随机漫步所描述的运动模式，在许多不同的现象中发挥作用，从化学和微生物系统到海洋捕食者再到气候变化。最近的实验表明，这种现象也出现在重离子碰撞中。然而，人们对其理论背景还不甚了解。在重核的高能碰撞中，强相互作用的夸克胶子等离子体（Quark GluonPlasma）被创造出来，与早期宇宙类似，它经历了急剧膨胀，并过渡回正常的强子物质。在随后膨胀的强子气体中，粒子相互作用，直到动能冻结，此时它们的动量变得固定，并自由地过渡到探测器。在本文中，我们对粒子（碰撞中最多的粒子）的空间凝固分布进行了新颖的三维分析。通过对高能碰撞的蒙特卡洛模拟，我们证明了以最终态先锋为结局的过程链具有导致 L'evy-stable 分布的阶长分布。随后，我们证明了先驱凝固分布确实表现出重尾，并且可以用三维椭圆轮廓对称的 L'evy-stabled 分布来描述。
{"title":"Lévy walk of pions in heavy-ion collisions","authors":"Dániel Kincses, Márton Nagy, Máté Csanád","doi":"arxiv-2409.10373","DOIUrl":"https://doi.org/arxiv-2409.10373","url":null,"abstract":"The process of L'evy walk, i.e., movement patterns described by heavy-tailed\u0000random walks, play a role in many different phenomena, from chemical and\u0000microbiological systems through marine predators to climate change. Recent\u0000experiments have suggested that this phenomenon also appears in heavy-ion\u0000collisions. However, the theoretical background is not yet well understood. In\u0000high-energy collisions of heavy nuclei, the strongly interacting Quark Gluon\u0000Plasma is created, which, similarly to the early Universe, undergoes a rapid\u0000expansion and transition back to normal hadronic matter. In the subsequent\u0000expanding hadron gas, particles interact until kinetic freeze-out, when their\u0000momenta become fixed, and they freely transition toward the detectors.\u0000Measuring spatial freeze-out distributions is a crucial tool in understanding\u0000the dynamics of the created matter as well as the interactions among its\u0000constituents. In this paper, we present a novel three-dimensional analysis of\u0000the spatial freeze-out distribution of pions (the most abundant particles in\u0000such collisions). Utilizing Monte-Carlo simulations of high-energy collisions,\u0000we show that the chain of processes ending in a final state pion has a step\u0000length distribution leading to L'evy-stable distributions. Subsequently, we\u0000show that pion freeze-out distributions indeed exhibit heavy tails and can be\u0000described by a three-dimensional elliptically contoured symmetric L'evy-stable\u0000distribution.","PeriodicalId":501573,"journal":{"name":"arXiv - PHYS - Nuclear Theory","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142263014","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The interaction of a proton with a deuteron is the simplest nuclear reaction. However, it allows the study of precursors of nuclear medium effects such as initial-state/final-state interactions (ISI/FSI). In case of hard proton knockout, the deviation of ISI/FSI from the 'standard' values may carry a signal of color transparency. In this regard, it is important to define the 'standard' as precisely as possible. This work continues previous studies within the framework of the Generalized Eikonal Approximation (GEA). The focus is on processes where the participating protons experience multiple soft rescattering on the spectator neutron. It is shown that correct treatment of deviations of the trajectories of outgoing protons from the longitudinal direction leads to a significant modification of partial amplitudes with soft rescattering of two outgoing protons and non-vanishing amplitudes with rescattering of incoming and outgoing protons. The new treatment of multiple rescattering is important in kinematics with a forward spectator neutron.
{"title":"Multiple rescattering effects in the hard knockout reaction $mathbf{^2mbox{H}(p,2p)n}$","authors":"A. B. Larionov","doi":"arxiv-2409.10260","DOIUrl":"https://doi.org/arxiv-2409.10260","url":null,"abstract":"The interaction of a proton with a deuteron is the simplest nuclear reaction.\u0000However, it allows the study of precursors of nuclear medium effects such as\u0000initial-state/final-state interactions (ISI/FSI). In case of hard proton\u0000knockout, the deviation of ISI/FSI from the 'standard' values may carry a\u0000signal of color transparency. In this regard, it is important to define the\u0000'standard' as precisely as possible. This work continues previous studies\u0000within the framework of the Generalized Eikonal Approximation (GEA). The focus\u0000is on processes where the participating protons experience multiple soft\u0000rescattering on the spectator neutron. It is shown that correct treatment of\u0000deviations of the trajectories of outgoing protons from the longitudinal\u0000direction leads to a significant modification of partial amplitudes with soft\u0000rescattering of two outgoing protons and non-vanishing amplitudes with\u0000rescattering of incoming and outgoing protons. The new treatment of multiple\u0000rescattering is important in kinematics with a forward spectator neutron.","PeriodicalId":501573,"journal":{"name":"arXiv - PHYS - Nuclear Theory","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142263018","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
T. M. ShneidmanJoint Institute for Nuclear Research, Dubna, Russia, A. RahmatinejadJoint Institute for Nuclear Research, Dubna, Russia, G. G. AdamianJoint Institute for Nuclear Research, Dubna, Russia, N. V. AntonenkoJoint Institute for Nuclear Research, Dubna, Russia
The quantum-mechanical description of the collective angular motion in a system of two touching fission fragments is proposed. The main peculiarities of excitation spectrum and the structure of the wave functions are investigated. As found, the angular motion approximately corresponds to independent vibrations of fragments around the pole-to-pole configuration. The model allows us to explain the experimentally observed lack of correlation between the angular momenta of fission fragments. Additionally the correlation between angular momentum and fragment mass is primarily linked to the change of fragments deformation. The saw-tooth behavior of angular momentum distribution with respect to the fragment mass is well explained.
{"title":"Quantum-mechanical description of angular motion of fission fragments at scission","authors":"T. M. ShneidmanJoint Institute for Nuclear Research, Dubna, Russia, A. RahmatinejadJoint Institute for Nuclear Research, Dubna, Russia, G. G. AdamianJoint Institute for Nuclear Research, Dubna, Russia, N. V. AntonenkoJoint Institute for Nuclear Research, Dubna, Russia","doi":"arxiv-2409.10114","DOIUrl":"https://doi.org/arxiv-2409.10114","url":null,"abstract":"The quantum-mechanical description of the collective angular motion in a\u0000system of two touching fission fragments is proposed. The main peculiarities of\u0000excitation spectrum and the structure of the wave functions are investigated.\u0000As found, the angular motion approximately corresponds to independent\u0000vibrations of fragments around the pole-to-pole configuration. The model allows\u0000us to explain the experimentally observed lack of correlation between the\u0000angular momenta of fission fragments. Additionally the correlation between\u0000angular momentum and fragment mass is primarily linked to the change of\u0000fragments deformation. The saw-tooth behavior of angular momentum distribution\u0000with respect to the fragment mass is well explained.","PeriodicalId":501573,"journal":{"name":"arXiv - PHYS - Nuclear Theory","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142263016","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We study a generalised version of Gross-Neveu model in 2+1 dimensions. The model is inspired from graphene which shows a linear dispersion relation near the Dirac points. The phase structure and the thermodynamic properties in the mean field approximation have been studied before. Here we go beyond the mean field level by deriving a Beth-Uhlenbeck equation for Gaussian fluctuations, solutions of which we explore numerically, for the first time including their momentum dependence. We discuss the excitonic mass, fluctuation pressure and phase shifts. We also perform a comparison with the NJL model in 3+1 dimension and discuss its implication for graphene.
{"title":"Beth-Uhlenbeck equation for the thermodynamics of fluctuations in a generalised 2+1D Gross-Neveu model","authors":"Biplab Mahato, David Blaschke, Dietmar Ebert","doi":"arxiv-2409.10507","DOIUrl":"https://doi.org/arxiv-2409.10507","url":null,"abstract":"We study a generalised version of Gross-Neveu model in 2+1 dimensions. The\u0000model is inspired from graphene which shows a linear dispersion relation near\u0000the Dirac points. The phase structure and the thermodynamic properties in the\u0000mean field approximation have been studied before. Here we go beyond the mean\u0000field level by deriving a Beth-Uhlenbeck equation for Gaussian fluctuations,\u0000solutions of which we explore numerically, for the first time including their\u0000momentum dependence. We discuss the excitonic mass, fluctuation pressure and\u0000phase shifts. We also perform a comparison with the NJL model in 3+1 dimension\u0000and discuss its implication for graphene.","PeriodicalId":501573,"journal":{"name":"arXiv - PHYS - Nuclear Theory","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142263021","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We performed textit{ab initio} valence-space in-medium similarity renormalization group (VS-IMSRG) calculations based on chiral two-nucleon and three-nucleon interactions to investigate the anomalous seniority breaking in the neutron number $N=50$ isotones: $^{92}$Mo, $^{94}$Ru, $^{96}$Pd, and $^{98}$Cd. Our calculations well reproduced the measured low-lying spectra and electromagnetic $E2$ transitions in these nuclei, supporting partial seniority conservation in the first $pi g_{9/2}$ shell. Recent experiments have revealed that, compared to the symmetric patterns predicted under the conserved seniority symmetry, the $4^+_1to2^+_1$ $E2$ transition strength in $^{94}$Ru is significantly enhanced and that in $^{96}$Pd is suppressed. In contrast, the $6^+_1to 4^+_1$ and $8^+_1to6^+_1$ transitions exhibit the opposite trend. We found that this anomalous asymmetry is sensitive to subtle seniority breaking effects, providing a stringent test for state-of-the-art nucleon-nucleon interactions and nuclear models. We analyzed the anomalous asymmetry using VS-IMSRG calculations across various valence spaces. Our textit{ab initio} results suggest that core excitations of both proton and neutron across the $Z=50$ shell are ascribed to the observed anomalous seniority breaking in the $N=50$ isotones.
{"title":"Ab initio calculations of anomalous seniority breaking in the $π g_{9/2}$ shell for the $N=50$ isotones","authors":"Q. Yuan, B. S. Hu","doi":"arxiv-2409.10342","DOIUrl":"https://doi.org/arxiv-2409.10342","url":null,"abstract":"We performed textit{ab initio} valence-space in-medium similarity\u0000renormalization group (VS-IMSRG) calculations based on chiral two-nucleon and\u0000three-nucleon interactions to investigate the anomalous seniority breaking in\u0000the neutron number $N=50$ isotones: $^{92}$Mo, $^{94}$Ru, $^{96}$Pd, and\u0000$^{98}$Cd. Our calculations well reproduced the measured low-lying spectra and\u0000electromagnetic $E2$ transitions in these nuclei, supporting partial seniority\u0000conservation in the first $pi g_{9/2}$ shell. Recent experiments have revealed\u0000that, compared to the symmetric patterns predicted under the conserved\u0000seniority symmetry, the $4^+_1to2^+_1$ $E2$ transition strength in $^{94}$Ru\u0000is significantly enhanced and that in $^{96}$Pd is suppressed. In contrast, the\u0000$6^+_1to 4^+_1$ and $8^+_1to6^+_1$ transitions exhibit the opposite trend. We\u0000found that this anomalous asymmetry is sensitive to subtle seniority breaking\u0000effects, providing a stringent test for state-of-the-art nucleon-nucleon\u0000interactions and nuclear models. We analyzed the anomalous asymmetry using\u0000VS-IMSRG calculations across various valence spaces. Our textit{ab initio}\u0000results suggest that core excitations of both proton and neutron across the\u0000$Z=50$ shell are ascribed to the observed anomalous seniority breaking in the\u0000$N=50$ isotones.","PeriodicalId":501573,"journal":{"name":"arXiv - PHYS - Nuclear Theory","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142263015","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Atif Sultan, Jiayin Kang, Adnan Bashir, Lei Chang
Based upon a combined formalism of Schwinger-Dyson and Bethe-Salpeter equations in quantum chromodynamics (QCD), we propose a QCD kindred algebraic model for the dressed quark propagator, for the Bethe-Salpeter amplitude of the pion and the electromagnetic quark-photon interaction vertex. We then compute the $gamma^{*}pi^0gamma$ transition form factor $G^{gamma^{*}pi^0gamma}(Q^2)$ for a wide range of photon momentum transfer squared $Q^2$. The quark propagator is expanded out in its perturbative functional form but with dynamically generated dressed quark mass. It has complex conjugate pole singularities in the complex-momentum plane which is motivated by the solution of the quark gap equation with rainbow-ladder truncation of the infinite set of Schwinger-Dyson equations. This complex pole singularity structure of the quark propagator can be associated with a signal of confinement which prevents quarks to become stable asymptotic states. The Bethe-Salpeter amplitude is expressed without a spectral density function, which encapsulate its low and large momentum behaviour. The QCD evolution of the distribution amplitude is also incorporated into our model through the direct implementation of Efremov-Radyushkin-Brodsky-Lepage evolution equations. We include the effects of the quark anomalous magnetic moment in the description of the quark-photon vertex whose infrared enhancement is known to dictate hadronic properties. Once the QCD kindred model is constructed, we calculate the form factor $G^{gamma^{*}pi^0gamma}(Q^2)$ and find it consistent with direct QCD-based studies as well as most available experimental data. It slightly exceeds the conformal limit for large $Q^2$ which might be attributed to the scaling violations in QCD. The associated interaction radius and neutral pion decay width turn out to be compatible with experimental data.
{"title":"Neutral pion to two-photons transition form factor revisited","authors":"M. Atif Sultan, Jiayin Kang, Adnan Bashir, Lei Chang","doi":"arxiv-2409.09595","DOIUrl":"https://doi.org/arxiv-2409.09595","url":null,"abstract":"Based upon a combined formalism of Schwinger-Dyson and Bethe-Salpeter\u0000equations in quantum chromodynamics (QCD), we propose a QCD kindred algebraic\u0000model for the dressed quark propagator, for the Bethe-Salpeter amplitude of the\u0000pion and the electromagnetic quark-photon interaction vertex. We then compute\u0000the $gamma^{*}pi^0gamma$ transition form factor\u0000$G^{gamma^{*}pi^0gamma}(Q^2)$ for a wide range of photon momentum transfer\u0000squared $Q^2$. The quark propagator is expanded out in its perturbative\u0000functional form but with dynamically generated dressed quark mass. It has\u0000complex conjugate pole singularities in the complex-momentum plane which is\u0000motivated by the solution of the quark gap equation with rainbow-ladder\u0000truncation of the infinite set of Schwinger-Dyson equations. This complex pole\u0000singularity structure of the quark propagator can be associated with a signal\u0000of confinement which prevents quarks to become stable asymptotic states. The\u0000Bethe-Salpeter amplitude is expressed without a spectral density function,\u0000which encapsulate its low and large momentum behaviour. The QCD evolution of\u0000the distribution amplitude is also incorporated into our model through the\u0000direct implementation of Efremov-Radyushkin-Brodsky-Lepage evolution equations.\u0000We include the effects of the quark anomalous magnetic moment in the\u0000description of the quark-photon vertex whose infrared enhancement is known to\u0000dictate hadronic properties. Once the QCD kindred model is constructed, we\u0000calculate the form factor $G^{gamma^{*}pi^0gamma}(Q^2)$ and find it\u0000consistent with direct QCD-based studies as well as most available experimental\u0000data. It slightly exceeds the conformal limit for large $Q^2$ which might be\u0000attributed to the scaling violations in QCD. The associated interaction radius\u0000and neutral pion decay width turn out to be compatible with experimental data.","PeriodicalId":501573,"journal":{"name":"arXiv - PHYS - Nuclear Theory","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142263022","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mu2e and COMET will search for electrons produced via the neutrinoless conversion of stopped muons bound in 1s atomic orbits of $^{27}$Al, improving existing limits on charged lepton flavor violation (CLFV) by roughly four orders of magnitude. Conventionally, $murightarrow e$ conversion experiments are optimized to detect electrons originating from transitions where the nucleus remains in the ground state, thereby maximizing the energy of the outgoing electron. Clearly, detection of a positive signal in forthcoming experiments would stimulate additional work $-$ including subsequent conversion experiments using complementary nuclear targets $-$ to further constrain the new physics responsible for CLFV. Here we argue that additional information can be extracted without the need for additional experiments, by considering inelastic conversion in $^{27}$Al. Transitions to low-lying nuclear excited states can modify the near-endpoint spectrum of conversion electrons, with the ratio of the elastic and inelastic responses being sensitive to the underlying CLFV operator. We extend the nuclear effective theory of $murightarrow e$ conversion to the inelastic case, which adds five new response functions to the six that arise for the elastic process. We evaluate these nuclear response functions in $^{27}$Al and calculate the resulting conversion-electron signal, taking into account the resolution anticipated in Mu2e/COMET. We find that $^{27}$Al is an excellent target choice from the perspective of the new information that can be obtained from inelastic $mu rightarrow e$ conversion.
{"title":"Nuclear-level effective theory of $μrightarrow e$ conversion: Inelastic process","authors":"W. C. Haxton, Evan Rule","doi":"arxiv-2409.10581","DOIUrl":"https://doi.org/arxiv-2409.10581","url":null,"abstract":"Mu2e and COMET will search for electrons produced via the neutrinoless\u0000conversion of stopped muons bound in 1s atomic orbits of $^{27}$Al, improving\u0000existing limits on charged lepton flavor violation (CLFV) by roughly four\u0000orders of magnitude. Conventionally, $murightarrow e$ conversion experiments\u0000are optimized to detect electrons originating from transitions where the\u0000nucleus remains in the ground state, thereby maximizing the energy of the\u0000outgoing electron. Clearly, detection of a positive signal in forthcoming\u0000experiments would stimulate additional work $-$ including subsequent conversion\u0000experiments using complementary nuclear targets $-$ to further constrain the\u0000new physics responsible for CLFV. Here we argue that additional information can\u0000be extracted without the need for additional experiments, by considering\u0000inelastic conversion in $^{27}$Al. Transitions to low-lying nuclear excited\u0000states can modify the near-endpoint spectrum of conversion electrons, with the\u0000ratio of the elastic and inelastic responses being sensitive to the underlying\u0000CLFV operator. We extend the nuclear effective theory of $murightarrow e$\u0000conversion to the inelastic case, which adds five new response functions to the\u0000six that arise for the elastic process. We evaluate these nuclear response\u0000functions in $^{27}$Al and calculate the resulting conversion-electron signal,\u0000taking into account the resolution anticipated in Mu2e/COMET. We find that\u0000$^{27}$Al is an excellent target choice from the perspective of the new\u0000information that can be obtained from inelastic $mu rightarrow e$ conversion.","PeriodicalId":501573,"journal":{"name":"arXiv - PHYS - Nuclear Theory","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142263011","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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