Search

The possibility of a Photon-Photon collider extension to the Beam dump of the 17.5 GeV European XFEL has been discussed before as the first high energy collider of its sort. It would not just be to study the concept of photon colliders but would also be a collider without competition in the region of 5 − 12 GeV for photon-photon collision. In this range, bb¯ and cc¯ resonances, tetraquarks as well as mesonic molecules can be observed. Furthermore, some BSM processes can also be reached in this range. In this paper we want to discuss the possibility of observing ALPs at such a collider. We will use a simplified description of the compton backscattering process to get a first look at cross sections and extend this to the full beam dynamics included prediction. [ABSTRACT FROM AUTHOR]

We study the finite temperature equation of state by using an effective lagrangian in which a dilaton field reproduces the breaking of scale symmetry in QCD. We start by extending a previous investigation in the pure gauge sector, where the dynamics of the gluon condensate, expressed in terms of a dilaton lagrangian, is dominated below the critical phase transition temperature, while at greater temperatures the condensate evaporates in the form of quasi-free gluons. In this context, we study the role of the inclusion of thermal fluctuations of the dilaton field and compare our results with the lattice QCD data. Moreover, we take into account of the meson sector at zero chemical potential by means of an effective lagrangian which incorporates broken scale in addition to spontaneously broken chiral symmetry. Beyond the mean-field approximation, the relevance of the thermal fluctuations of the scalar glueball, other than the contribution of the σ and π meson fields is considering by following a general technique. In this framework, we investigate the thermodynamic nature of the phase transition. [ABSTRACT FROM AUTHOR]

The X(3872) to ψ(2S) yield ratio (NX/Nψ(2S)) has been recently measured in pp, pPb and PbPb collisions by the LHCb and CMS Collaborations at the LHC. It was found that this ratio grows with the system size and this growth was attributed to the formation of quark gluon plasma and/or of a hot hadron gas. Here we focus on the effects of the hadron gas on the abundance of X(3872) and ψ(2S). The interaction of charmonium states with the light mesons in the gas can be studied with an effective Lagrangian formalism. One can calculate the relevant cross sections and use them as input in rate equations. With this formalism one can follow the time evolution of the X(3872) and ψ(2S) abundances until the final freeze-out of the gas. The initial conditions for this evolution are given by the coalescence model, which depends on the spatial configuration of the states and yields quite different numbers for compact tetraquarks and extended meson molecules. It has been found that the interactions in the hadron gas yield a suppression in most of the states and, most importantly, preserve the difference between the number of tetraquarks and the number of meson molecules, formed at the beginning of the hadronization. We discuss the predictions made for the ratio NX/Nψ(2S) in PbPb collisions at √sNN = 5.02 TeV to be measured by the ALICE Collaboration in the Run 3. The existing calculations suggest that the molecular configuration generates a ratio compatible with the CMS data, whereas the ratio obtained with the tetraquark configuration is 50 times smaller. [ABSTRACT FROM AUTHOR]

The top-quark mass is a fundamental parameter of the Standard Model, as it plays a crucial role in the electroweak precision tests, stability of the vacuum and inflation. I review the method and the main results contained in a recent ATLAS analysis which measures the top mass by using the invariant mass of the leptons coming from W and B-hadron decays. The extracted top mass turns out to be the most precise single measurement by ATLAS. [ABSTRACT FROM AUTHOR]

This work uses the connection between hadronic stability and configurational entropy to explore hadronic structures written in terms of non-quadratic dilaton (κ z)2-α. These hadronic structures are described using the relation between the parameters κ and α with the constituent mass. We test Zc, Zb, and ψ as non-qq states defined as hybrid meson, hadroquarkonium, hadronic molecule, or diquark-antidiquark pair. We find that, holographically speaking, Zc and ZB are better described as a hybrid meson and ψ as hadrocharmonium. [ABSTRACT FROM AUTHOR]

The NA62 measurement of the branching ratio and the di-photon mass spectrum of the K+ → π+γγ decay is presented, together with a preliminary result on the branching fraction of the rare decay π0 → e+e−. The first observation of the decay K±→π0π0μ±v(K00μ4) by the NA48/2 experiment at the CERN is also reported, together with the measurement of the branching ratio. [ABSTRACT FROM AUTHOR]

Scattering of two mesons is considered in the framework of twodimensional QCD in the large-Nc limit with four different quark flavors. The scattering takes place through two coupled channels, corresponding to direct and quark-exchange processes, which are of order O(Nc-2) and O(Nc-1), respectively. Finiteness of the scattering amplitudes to order Nc-2 is pointed out. The theory reduces, at low energies, to an effective theory of mesons, interacting by a quark-exchange process, by means of a contact term. The unitarization of the scattering amplitudes leads to the emergence of a tetraquark bound state, located very close to the lowest two-meson elastic threshold. [ABSTRACT FROM AUTHOR]

Constituting the largest subset of multiquark states so far observed by experiment, tetraquark mesons carrying overall quark flavour quantum numbers identical to those of the (conventional) quark–antiquark mesons necessitate their particularly deliberate phenomenological analyses. A collection of (more or less recent) insights specific to the latter subclass of exotic hadrons bears the promise to enable even significant improvement in the understanding of these hadrons by theoretical approaches such as, among others, the framework of QCD sum rules. [ABSTRACT FROM AUTHOR]

We study the rare decays of the Bc meson induced by the flavour changing neutral current c → uγ transition. In the Standard Model they are strongly suppressed by the Glashow-Iliopoulos-Maiani mechanism, therefore they are sensitive to new physics. The difficulty is to get rid of long-distance contributions. We study such effects in radiative Bc transitions both to B* and to the axial-vector B′1 meson. [ABSTRACT FROM AUTHOR]

We perform a model-independent study of c → sµν mediated transitions to analyze the new physics effects in the presence of right-handed neutrinos. We have adopted the effective field theory approach and write the lowenergy effective Hamiltonian including all possible dimension-six operators. The Wilson coefficients introduced through low energy effective Hamiltonian encode all New Physics that can enter in c → s transition at the dimension-six operator level. These Wilson coefficients are determined through a χ2 fit by using the Miniut package to available experimental data of leptonic Ds+ → µ+νµ and semileptonic decays D0 → K−µ+νµ, D+ → K¯0µ+νµ and D0 → K∗−µ+νµ, D+ → K¯∗0µ+νµ, Ds+ → φµ+νµ. The differential decay width of Bc+ → Bsµ+νµ is derived to investigate the role of right-handed neutrinos in the search for new physics through the three-body decay process. We also make the predictions of q2 spectra for the mode Bc+ → Bsμ+νμ to inspect the effect of the allowed new physics in c → s sector through right-handed neutrinos to motivate the future measurements. [ABSTRACT FROM AUTHOR]

The Belle and Belle II experiments have collected a 1.1 ab−1 sample of e+e−BB¯ collisions at the ϒ(4S) resonance. These data, with low particle multiplicity, constrained initial state kinematics and excellent lepton identification, are an ideal environment to study lepton-flavour universality in semileptonic decays of the B meson. We present measurements of branching-fraction ratios that test the universality of τ and light leptons, using both exclusive and inclusive B semileptonic decays. We also report measurements of angular observables that probe universality between electrons and muons. [ABSTRACT FROM AUTHOR]

Observations of flavor anomalies in the b-sector, particularly the deviations in the measurements of the lepton flavor universality ratios in the b → cτντ transitions from the standard model (SM) predictions, suggest the existence of possible new physics beyond the SM. In the pursuit of new physics in similar decays involving b → cℓνℓ transitions, we scrutinize the decay modes Λb Λc*(2595, 2625)τ−ν¯τ beyond the SM. In particular, we examine the impact of the presence of leptoquarks in these decay modes, within the framework of the vector leptoquark U1 model. We employ form factors obtained from lattice QCD (LQCD) calculations to predict various q2-dependent observables. Some of these observables include the differential branching fraction, the ratio of branching fractions and the forward-backward asymmetry of the charged lepton. The new couplings are constrained using current b → cℓνℓ experimental data. [ABSTRACT FROM AUTHOR]

The precise measurement of the CP-violating phase ϕs, the average decay width Γs and the difference between the widths of the light and heavy mass eigenstates ΔΓs is presented in the B s 0 → J/ψϕ decay channel. Data of pp collisions at √s = 13 TeV are used, corresponding to 80.5 fb−1 of integrated lu-minosity collected by the ATLAS detector at the Large Hadron Collider in years 2015–2017. Results are statistically combined with the previous measurement with 19.2 fb−1 data with 7 and 8 TeV energy. The measured values are: ϕs = −0.087 ± 0.036 (stat.) ± 0.021 (syst.) Γs = 0.6703 ± 0.0014 (stat.) ± 0.0018 (syst.) ΔΓs = 0.0657 ± 0.0043 (stat.) ± 0.0037 (syst.). Moreover, a study estimating the ATLAS detector performance in measuring the CP-violating phase ϕs after the HL-LHC upgrade is presented. [ABSTRACT FROM AUTHOR]

Rare decays are suppressed in the Standard Model, making them intriguing avenues for exploring new physics beyond the current theoretical framework. Many new physics models could potentially emerge from the study of these decays, providing the insights how the Standard Model could be extended. This proceeding presents the latest studies on rare B meson and τ lepton decays, specifically B s 0 → µ+µ− and τ → 3µ, using data collected by the CMS experiment. Additionally, recent observations of η 4µ and J/ψ 4µ decays are discussed. [ABSTRACT FROM AUTHOR]

The rare decays of B mesons offer a prime opportunity to test predictions of the Standard Model and to search for effects beyond the Standard Model. The coherent production of B mesons at e+e− colliders provides a clean experimental setup for these studies. In this paper, we discuss the recent results of rare B decays from the Belle and Belle II experiments. [ABSTRACT FROM AUTHOR]

In this proceeding we will review the current theoretical status of rare hadronic decays, with a particular focus on decays of the B meson. These decays are indeed excellent indirect probes while searching for New Physics. Given the current experimental situation at colliders, where no new particles have been directly produced, rare decays provide a fundamental and alternative approach in the search for Physics beyond the Standard Model. In particular, the following classes of decays will be here reviewed: Bq → τν, Bq → µµ, B → K(∗)νν¯, B → K(∗)ℓℓ, Bs → ϕℓℓ and b → sγ. We will provide the most updated Standard Model predictions, highlight which are the main sources of uncertainty, and give the current status of New Physics searches in these channels when confronting the theory predictions to current experimental results. [ABSTRACT FROM AUTHOR]

Differential cross section of the deuteron breakup reaction 1H(d,pp)n exhibits sensitivity to interaction dynamics components like three-nucleon force and/or Coulomb force. This sensitivity facilitates comprehensive testing of theoretical potential models that describe interactions within three-nucleon systems. An analysis of experimental data of the breakup reaction, conducted at a beam energy of 100 MeV, has been performed. The presented cross section results for selected configurations agree well with calculations based on meson exchange model potentials and on state-of-the-art results within the Chiral Effective Field Theory framework. [ABSTRACT FROM AUTHOR]

We discuss results of a simultaneous fit to the K−p reactions and πΣ photoproduction data employing an approach that combines tree level photoproduction amplitudes with πΣ − KN coupled channel model describing the meson-baryon rescattering in the final state. The achieved reproduction of the photoproduction mass distributions represents a significant improvement when compared with the parameter free predictions made earlier but remains inferior to more comprehensive models that employ much larger sets of adjustable parameters. [ABSTRACT FROM AUTHOR]

Hard Exclusive Meson Production (HEMP) and Deeply Virtual Compton Scattering (DVCS) are very promising reactions to access Generalized Parton Distributions (GPDs). Such exclusive measurements were performed at COMPASS in 2016 and 2017 at the M2 beamline of the CERN SPS using the 160 GeV muon beam scattering off a 2.5 m long liquid hydrogen target surrounded by a barrel-shaped time-of-flight system to detect the recoiling target proton. The scattered muons and the produced real photons were detected by the COMPASS spectrometer, which was supplemented by an additional electromagnetic calorimeter for the detection of large-angle photons. Exclusive π0 production is the main source of background for the DVCS measurement, while it provides complementary information for the parametrization of GPDs. We will report on preliminary results of the exclusive π0 production cross section and its dependence on the squared four-momentum transfer |t| and on the azimuthal angle ϕ between the scattering plane and the π0 production plane. The COMPASS data will provide further input to constrain GPDs, in particular chiral-odd ("transversity") GPDs. [ABSTRACT FROM AUTHOR]

This talk focuses on a recent work aiming at determining the composition of certain N* and Δ resonances, i.e. whether they are compact states formed directly by quarks and gluons, or composite generated from the mesonbaryon interaction. The information of the resonance poles is provided by a comprehensive coupled-channel approach, the Jülich-Bonn model. Thirteen states that are significant in this approach are studied. Two criteria for each state are adopted in this paper, the comparison thereof roughly indicates the model uncertainties. It is found that the conclusions for eight resonances are relatively certain: N(1535)1/2−,N(1440)1/2+,N(1710)1/2+, and N(1520)3/2− tend to be composite; whereas N(1650)1/2−, N(1900)3/2+, N(1680)5/2+, and Δ(1600)3/2+ tend to be compact. [ABSTRACT FROM AUTHOR]

The KLOE/KLOE-2 Collaboration ended its data taking in 2018, about 20 years after the detector was turned on. In two different periods of datataking about 8 fb−1 at the peak of the ϕ(1020) resonance have been collected. During the years many results of the study of the light mesons have been published. The analysis of this unique data sample continues and the results of the latest measurements concerning kaons, and vector and pseudoscalar mesons are presented in this paper. [ABSTRACT FROM AUTHOR]

Recent lattice QCD calculations predict a multiplet of hybrid mesons, which are mesons with gluonic degrees of freedom. By mapping out the hybrid meson spectrum, we can gain insight into how the gluon contributes to the properties of bound states in QCD. The π1(1600) is a candidate for the lightest hybrid meson. This state has exotic quantum numbers of JPC = 1−+, which are forbidden for conventional mesons. The GlueX experiment has collected high statistics photoproduction data, which we are using to search for the π1(1600). These proceedings will summarize the search strategy for the π1(1600) at GlueX, including the most recent results in the ωππ, ηπ, and η′π final states. [ABSTRACT FROM AUTHOR]

In the domain of hadron spectroscopy, the investigation of meson resonances plays a pivotal role. This study focuses on the significance of twopion photoproduction as a prominent avenue for studying meson resonances in the ππ system. By employing the Regge formalism, our model incorporates the background contribution from the well-known "Deck Mechanism" and emphasizes the significant ρ(770) resonance, representing the P-wave contribution arising from pomeron and f2 exchanges. The model is extended by accounting for scalar mesons, namely σ, f0(980) and f0(1370), contributing to the S-wave behavior, as well as the tensor meson f2(1270) corresponding to the D-wave contributions, while also considering non-resonant P- and S-wave components. The model contains a number of free parameters, which are constrained from a global fit of the available experimental data for angular moments up to L = 2 for M = 0, ..., 2. The fitted angular moments are compared with experimental data obtained from CLAS. The key physical insights gained from the model are summarized. Furthermore, we extract the t-dependence of the Regge amplitude residue function for the subdominant exchanges, shedding light on their contribution to the overall dynamics. [ABSTRACT FROM AUTHOR]

The BGOOD photoproduction experiment accesses forward meson angles and low momentum exchange kinematics in the uds sector, which may be sensitive to molecular-like hadron structure. Recent results are presented, including strangeness photoproduction at forward meson angles, and π0π0 coherent photoproduction off the deuteron. [ABSTRACT FROM AUTHOR]

In this analysis, the production of pseudoscalar η′ mesons via two virtual spacelike photons is studied (γ*γ* → η′). Double-tagged measurements are conducted at the BESIII experiment in Beijing, China, in which both virtual photons possess nonzero virtualities Q12 and Q22. The Monte Carlo generator Ekhara 3.0 is used to simulate the expected signal event distribution. By measuring the double differential cross section at BESIII, the transition form factor (TFF) can be determined for Q12, Q22 < 2 GeV2. The TFF of pseudoscalar mesons serves as essential input for calculating the hadronic light-by-light contribution to the theoretical Standard Model prediction of the anomalous magnetic moment of the muon aμ = (gμ − 2)/2. [ABSTRACT FROM AUTHOR]

NA66/AMBER has been approved by CERN in 2020 as a new multipurpose facility for experiments in meson and baryon physics. In a first beamtime in 2023, data have been taken for the determination of antiproton production cross-sections in proton-helium collisions, needed for the interpretation of cosmic antimatter observations. Preparations are ongoing for a measurement of the proton charge radius in high-energy muon-proton scattering. This measurement will feature substantially different systematics than other approaches and aims at clarifying the present discrepancies. Further, experiments to study the partonic structure of mesons in Drell-Yan processes and strange-meson spectroscopy are on the menu of AMBER. [ABSTRACT FROM AUTHOR]

Lattice QCD (LQCD) has proven to be an important tool in understanding the tension between the experimental value for the anomalous magnetic moment of the muon (g − 2)μ and its prediction from the standard model. The lattice provides a non-perturbative method for evaluating the hadronic contributions to (g − 2)μ, which contributes the largest amount to the uncertainty of the theoretical prediction. Among these the hadronic vacuum polarization aμHVP is the dominant contribution. In order to match the uncertainty of the experiment, lattice QCD needs to reach sub-percent precision. This requires the calculation of QED corrections to aμHVP, which are represented by additional Feynman diagrams. We present a lattice calculation of the UV-finite (2+2) diagram at the SU(3) flavor symmetric point and compare this to the pseudoscalar meson exchange model with a vector-meson dominance parametrization of the transition form factor. [ABSTRACT FROM AUTHOR]

In order to investigate few-particle hypernuclei within the framework of the Hyperspherical Function Method, it is necessary to obtain full wave functions that are anti-symmetric under particle interchange. These wave functions must include not only hyperspherical, but also spin-isospin parts. According to the Parentage Scheme of Symmetrization, N-particle hyperspherical functions (N=3,4,5,6...) symmetrized with respect to (N-1)-particles, can be obtained from the N-particle hyperspherical functions with arbitrary quantum numbers by the use of the transformation coefficients related with the permutations of the last two particles. This article explains how to obtain fully antisymmetrized wave functions consisting of spin-isospin and hyperspherical parts. It is demonstrated that there are sixteen possible combinations in (3+1) configuration and 12 possible combinations in (2+2) configuration when spin and isospin functions are represented by [4], [31], and [22] representations of the four-particle permutation group S4. A complete set of the fully antisymmetrized four-particle wave functions is obtained. It is demonstrated that proposed mathematical formalism can be easily generalized to obtain fully antisymmetrized wave functions for the systems of five and more particles. [ABSTRACT FROM AUTHOR]

The method and results of the first theory description of 4He Compton scattering at nuclear energies is presented, with a focus on figures. An upcoming publication [1] contains details and a comprehensive list of references. [ABSTRACT FROM AUTHOR]

The EM polarizabilities characterize a fundamental property of the proton that involves the system's response to an external electromagnetic (EM) field. They describe how easily the charge and magnetization distributions inside the system are distorted by the EM field, such as during the Compton scattering with a real photon. When the polarizabilities are generalized to finite momentum transfer by replacing the incoming real photon of the Compton scattering process with a space-like virtual photon, they map out the deformation of the quark densities in a proton subject to an EM field. Recent experimental measurements at Jefferson Lab have provided high precision data, that offer guidance and present significant challenges to nuclear theory. Future experiments aim to improve further these measurements, both by extending their kinematic range as well as by improving the level of the experimental precision. [ABSTRACT FROM AUTHOR]

We present results for the electromagnetic form factors of the proton and neutron computed on the (2 + 1)-flavor Coordinated Lattice Simulations (CLS) ensembles including both quark-connected and -disconnected contributions. The Q2-, pion-mass, lattice-spacing, and finite-volume dependence of our form factor data is fitted simultaneously to the expressions resulting from covariant chiral perturbation theory including vector mesons amended by models for lattice artefacts. From these fits, we determine the electric and magnetic radii and the magnetic moments of the proton and neutron, as well as the Zemach radius of the proton. To assess the influence of systematic effects, we average over various cuts in the pion mass and the momentum transfer, as well as over different models for the lattice-spacing and finite-volume dependence, using weights derived from the Akaike Information Criterion (AIC). [ABSTRACT FROM AUTHOR]

The 10 billion J/ψ decays collected with the BESIII experiment offer a unique opportunity to investigate the decays of η and η′ mesons produced in the radiative J/ψ → γη(′) transitions. Using this clean production mechanism, the BESIII experiment is making important contributions to precision studies of the strong and electromagnetic interactions in η(′) decays. Three papers are presented in which the decays η → π+π−π0, η → π0π0π0, η′ → ηπ0π0π0, and η′ → π+π−e+e− are studied to test C and CP symmetry, as well as the predictions of different effective field theories. [ABSTRACT FROM AUTHOR]

In electron-positron annihilations, the process of e+e− → χc1 can occur via the production of two virtual photons or through neutral current, therefore being suppressed with respect to the normal annihilation process via one virtual photon. Using a dedicated scan sample around the χc1 mass, the direct production of χc1 has been established for the first time in experiments. This provides a new approach for the study of the internal nature of hadrons. [ABSTRACT FROM AUTHOR]