Distributions Of Differential Cross Sections Research Articles

Isolated photon production in association with a jet pair through next-to-next-to-leading order in QCD

In this work, we provide a comprehensive set of differential cross-section distributions for photon + di-jet production in proton-proton collisions with next-to-next-to-leading order precision in massless QCD. The event selection corresponds to recent measurements by the ATLAS collaboration. We observe an improved description of data in comparison to lower-order calculations in the case of observables that are expected to be well described by perturbation theory. The results also show better agreement with data than parton-shower-matched and multi-jet-merged predictions generated for the ATLAS analysis using the Sherpa Monte Carlo. A particular highlight of our study is the use of exact five-point two-loop virtual amplitudes. This is the first calculation of a complete two-to-three hadron-collider process at next-to-next-to-leading order in QCD that does not rely on the leading-colour approximation at two loops. We demonstrate, nevertheless, that the sub-leading-colour effects present in the infraredand ultraviolet-finite double-virtual contributions are negligible in view of the remaining scale uncertainties.

Measurement of the polarisation of W bosons produced in top-quark decays using dilepton events at [formula omitted] TeV with the ATLAS experiment

A measurement of the polarisation of W bosons produced in top-quark decays is presented, using proton–proton collision data at a centre-of-mass energy of s=13 TeV. The data were collected by the ATLAS detector at the Large Hadron Collider and correspond to an integrated luminosity of 139 fb−1. The measurement is performed selecting tt¯ events decaying into final states with two charged leptons (electrons or muons) and at least two b-tagged jets. The polarisation is extracted from the differential cross-section distribution of the cos⁡θ⁎ variable, where θ⁎ is the angle between the momentum direction of the charged lepton from the W boson decay and the reversed momentum direction of the b-quark from the top-quark decay, both calculated in the W boson rest frame. Parton-level results, corrected for the detector acceptance and resolution, are presented for the cos⁡θ⁎ angle. The measured fractions of longitudinal, left- and right-handed polarisation states are found to be f0=0.684±0.005(stat.)±0.014(syst.), fL=0.318±0.003(stat.)±0.008(syst.) and fR=−0.002±0.002(stat.)±0.014(syst.), in agreement with the Standard Model prediction.

O18 -induced single-nucleon transfer reactions on Ca40 at 15.3A MeV within a multichannel analysis

Background: Nucleon transfer reactions are selective tools for nuclear physics investigations. The theoretical and computational limits affecting in the past their data analysis could be nowadays surmounted thanks to the advent of methods with refined approximations and constraints, even when heavy-ion collisions are considered. Purpose: Modern microscopic calculations of heavy-ion-induced transfer reactions combined with precise experimental data offer the chance for accurately testing different reaction models as well as the nuclear structure description of the involved nuclear states. Method: Single proton and neutron transfer reactions were measured with the MAGNEX magnetic spectrometer for the O18+Ca40 system at 15.3A MeV. Excitation energy spectra and angular differential cross section distributions were extracted. The experimental results are compared with theoretical calculations performed in distorted wave and coupled channel Born approximation. The use of a coupled channel equivalent polarization potential to effectively describe the coupling effects affecting the initial state interaction is also considered. Spectroscopic amplitudes derived from a large-scale shell model with appropriate interactions adapted for the involved nuclei are employed. Results: Our theoretical calculations are in good agreement with experimental data, without the need for any scaling factor, validating the adopted reaction and nuclear structure parameters. Moreover, under the present experimental conditions, a weak dependence of the obtained results on the choice of the reaction models was observed. Conclusions: The good agreement between experimental and theoretical results validates the reliability of the parameter sets entering the calculations. They are extracted from or tested in complementary analyses of other reaction channels under the same experimental conditions. Such a multichannel approach represents the best option to pursue a solid, comprehensive, and model-independent description of the single-nucleon transfer reactions. The successful description of the present one-nucleon transfer data is also propaedeutic to the accurate assessment, under the same theoretical description, of higher-order transfer processes, like the sequential nucleon transfer mechanisms which are in competition with the direct charge exchange reactions.Received 14 September 2021Accepted 16 November 2021DOI:https://doi.org/10.1103/PhysRevC.104.064609©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasLow & intermediate energy heavy-ion reactionsModels & methods for nuclear reactionsTransfer reactionsTechniquesOptical, coupled-channel & distorted wave modelsNuclear Physics

O18+Se76 elastic and inelastic scattering at 275 MeV

Background: An accurate description of the initial and final state interactions in the O18+Se76 collision is demanded by the NUMEN project. The study of single and double charge exchange nuclear reactions is the main purpose for NUMEN, since these can be used as tools to provide experimentally driven information about nuclear matrix elements of interest in the context of neutrinoless double-β decay. To date, the details of the optical potentials and nuclear response to isospin operators for many of the projectile-target systems proposed for the NUMEN double charge exchange studies are poorly known. The O18+Se76 case, here under study, is particularly relevant due to its connection with the Ge76 neutrinoless double-β decay. Purpose: In this work the authors want to characterize the initial-state interaction for the O18+Se76 reactions at 275 MeV incident energy determining the optical potential and evaluating the effect of couplings with the inelastic scattering on the elastic channel. Methods: The angular distributions of differential cross section were measured in the angular region between 4∘ and 22∘ in the center-of-mass reference frame. The cross sections were compared with theoretical calculations, that adopt different optical potentials. Coupling effects on the elastic channel were determined into the coupled channels formalism. Results: The excitation energy spectrum of the colliding nuclei and the cross section angular distributions were measured with satisfactory energy resolution. The elastic scattering cross section is not well reproduced in the full angular range explored when the optical model approach is adopted. A good agreement is found using coupled channel calculations. The initial state interaction for the O18+Se76 nuclear reactions at 275 MeV is determined. Conclusions: Coupled channels effects are crucial to obtain a good description of the measured elastic and inelastic channels cross sections, even at large transferred momenta where the optical model approach fails in reproducing the experimental data. The role of channel coupling could be relevant also in the analysis of other open reaction channels in the same collision and should be accounted for in double charge exchange analyses as well.Received 19 December 2020Revised 6 October 2021Accepted 10 November 2021DOI:https://doi.org/10.1103/PhysRevC.104.054610©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDirect reactionsLow & intermediate energy heavy-ion reactionsNuclear reactionsNuclear structure & decaysNucleon-nucleon interactionsTransfer reactionsProperties59 ≤ A ≤ 896 ≤ A ≤ 19TechniquesCollective modelsNuclear data analysis & compilationNuclear reaction analysisOptical, coupled-channel & distorted wave modelsSpectrometers & spectroscopic techniquesNuclear Physics

ψ(2S) and J/ψ production in pp collisions at √s = 7, 8 and 13 TeV

Proton-proton collision is an essential part of high energy physics, as it is a baseline for nucleus-nucleus and hadron-nucleus collisions. Quark-gluon plasma, an exotic state of strongly interacting QCD matter, is routinely produced in heavy nuclei high-energy collisions. Charmonium, the bound states of $c\bar{c}$ produced at the early stages of collisions, are nice probes to examine the properties of matter through which they pass. The differential cross-sections of inclusive $\psi(2S)$ in pp collisions at energies of $\sqrt{s}$ = 7, 8 and 13 TeV have been studied. PYTHIA 8.1 event generator is used for the simulation of data. The differential cross-section of inclusive $J/\psi$ is also presented in order to examine the $\psi(2S)$ to $J/\psi$ ratio at similar energies. Both charmonium states are simulated in dimuon ($\mu^{+}\mu^{-}$) decay channel. The simulated data is also compared with the ALICE and LHCb experimental data based at LHC. We have plotted the differential cross-section as a function of transverse momentum ($p_T$) and rapidity $y$. PYTHIA simulation is found to be in good agreement with ALICE data for low $p_T$ interval, y interval close to midrapidity, while PYTHIA agrees with LHCb data at low $p_T$ interval. It is observed that the LHCb differential cross-section distributions of $J/\psi$ and $\psi(2S)$ as a function of y are lower compared to the ALICE data distributions and PYTHIA simulations. The $\psi(2S)$ to $J/\psi$ ratio is also well explained by PYTHIA and shows an increase in production of inclusive $J/\psi$ as compared to inclusive $\psi(2S)$.

Photoproduction of the J/ψ-pair at the LHC with Forward Detector Acceptances

LHC provides a chance to study the physical processes of γγ collision and γ p collision mode by adding a forward detector. In this paper, we investigate J/ψ-pair photoproduction in NRQCD framework at the LHC with γγ collision mode. We calculate the contributions from ${~}^{3}S_{1}^{1}$ , ${~}^{3}S_{1}^{(8)}$ , ${{~}^{1}}S_{0}^{(8)}$ , ${~}^{3}P_{J}^{(8)}$ Fock states, and find that contribution from the colour octet ${{~}^{1}}{S_{0}^{8}}$ ${~}^{3}P_{J}^{(8)}$ and ${~}^{3} P_{J}^{(8)}{~}^{3}P_{J}^{(8)}$ channels dominates this process with forward detector acceptance 0.0015 < ξ < 0.5. We present the differential cross section distributions of transverse momentum $p_{t}^{J/\psi }$ and rapidity yJ/ψ with forward detector acceptances 0.0015 < ξ < 0.5, analyse the signal for J/ψ decaying to a opposite-sign (OS) muon pair. The results show that this process has the potential to be detected at the 13 TeV LHC with forward detector acceptance 0.0015 < ξ < 0.5.

Mechanisms of Modulation Formation in Elastic Diffraction Scattering of Charged Particles

In this work, the authors describe experimental data on the angular distributions of alpha particles on light alpha-cluster nuclei. The angular distributions of elastic scattering of alpha particles are analyzed under the assumption of complete absorption inside the sphere of the cluster structure and the sphere of the interaction core. These assumptions made it possible to decompose the scattering amplitude into components—scattering on the nucleus itself and on different cluster structures. The calculations result in the following. The amplitude for describing diffraction elastic scattering by 4n ± 1 light nuclei in the framework of the theory of diffraction scattering is a superposition of wave functions in the scattering approximation on a completely black core and on its absolutely black substructures. The nucleon association modes, as well as the scattering modes on the correlated motion of nucleons and spatially separated nucleons, make a significant contribution to the total scattering amplitude. This manifests itself as an increase in angular distributions due to the interference of modes of various cluster structures and nucleons. Owing to these effects, not only an uneven rise in the angular distributions of differential cross sections over the Rutherford section is possible, but also a rise at rear angles.

Optical model analysis of alpha particle scattering

The angular distributions of differential cross sections for $$\alpha$$ + $$^{36}$$ Ar elastic and inelastic scattering at $$E_{\text {lab}}$$ = 40, 48, and 54 MeV have been examined in terms of the current theoretical approaches. Therefore, the elastic scattering data have been obtained by using three different theoretical approaches, namely the single-folding cluster model, the double-folding model with CDM3Y6 effective interaction, and the phenomenological Woods–Saxon model. The inelastic scattering data have been obtained from coupled-channel calculations with the fitted parameters for elastic scattering. Both elastic and inelastic results have provided a successful description of the experimental data. Finally, the deformation lengths obtained from coupled-channel calculations are found to be consistent with the values determined from electromagnetic measurements and those reported in the previous studies. Also, the potential parameters, cross sections, volume integrals, and $$\chi ^{2}$$ values have been given for each theoretical approach.

An analysis of cross-sections of 9Be+28Si interaction in the framework of the double-folding model

In this paper the experimental data on the differential cross sections for elastic scattering of 9 Be ions on 28 Si nucleus at the energies of the incident nucleus ranging from 12 to 201.6 MeV were analyzed in the framework of the double folding model using the Paris NN-potential CDM3Y. A good agreement with the experimental angular distributions of differential cross sections for elastic scattering was obtained and the values of the total reaction cross sections were calculated. When the double folding potential was used as real and imaginary parts, no manifestation of the threshold anomaly was detected. The reason for such a behavior of the potential can be explained by the presence of break up and/or transfer channels at low energies.

Towards constraining dark matter at the LHC: higher order QCD predictions for t overline{t} + Z (Z → νℓ overline{v} ℓ)

Triggered by ongoing dark matter searches in the top quark sector at the Large Hadron Collider we report on the calculation of the next-to-leading order QCD corrections to the Standard Model process pp → t overline{t} + Z (Z → νℓ overline{v} ℓ). This calculation is based on matrix elements for {e}^{+}{nu}_e{mu}^{-}{overline{nu}}_{mu }boverline{b}kern0.33em {nu}_{tau }{overline{nu}}_{tau } production and includes all non-resonant diagrams, interferences, and off-shell effects of the top quarks. Non-resonant and off-shell effects due to the finite W -boson width are also consistently taken into account. As it is common for such studies, we present results for both integrated and differential cross sections for a few renormalisation and factorisation scale choices and three different parton distribution functions. Already with the fairly inclusive cut selection and independently of the scale choice and the parton distribution function non-flat differential mathcal{K} -factors are obtained for {p}_T^{miss} , ∆\U0001d719ℓℓ, ∆\U0001d4b4ℓℓ, cos θℓℓ, HT, {H}_T^{prime } observables that are relevant for new physics searches. Good theoretical control over the Standard Model background is a fundamental prerequisite for a correct interpretation of possible signals of new physics that may arise in this channel. Thus, these observables need to be carefully reexamined in the presence of more exclusive cuts before any realistic strategies for the detection of new physics signal can be further developed. Since from the experimental point of view both t overline{t} and t overline{t} + Z (Z → νℓ overline{v} ℓ) comprise the same final states, we additionally study the impact of the enlarged missing transverse momentum on various differential cross section distributions. To this end normalised differential distributions for pp → {e}^{+}{nu}_e{mu}^{-}{overline{nu}}_{mu }boverline{b}kern0.33em {nu}_{tau }{overline{nu}}_{tau } and pp → {e}^{+}{nu}_e{mu}^{-}{overline{nu}}_{mu }boverline{b} are compared.

W Boson Pair Production in Association with the Photon in Proton - Proton Collisions at LHC Energies

The vector bosons production at the Large Hadron Collider makes it possible to investigate in detail the basic structure of electroweak interactions. Besides the LHC with a good accuracy will be measure production of weak bosons (pp → W+W−). The production of weak bosons with photon (pp → W+W−γ) provides an increasingly powerful handle at higher center-of-mass energies. We present phenomenological results for WWγ production in proton-proton interaction at the Large Hadron Collider. In this paper, we calculate the total and differential cross sections. We consider the dependence of differential cross section distributions on transverse momentum and rapidity particles, which are produced in the final state (W+ and W−). We consider several important distributions, which are included in the search for new physics at the Large Hadron Collider. The results for transverse momentum distributions, rapidity distributions and total cross section are presented.

Модуляция угловых распределений рассеянных ионов 12с на ядрах 16о и кластерных его подструктурах

In this paper, the authors considered the question of the experimental study of the 16-O cluster structure by decomposing the experimental angular distributions of differential cross sections into cluster diffraction modes in elastic scattering of charged particles on cluster nuclei. Experimental data on the reaction of elastic scattering 16О(12С, 12С)16О, taken from the international database EXFOR (M.P. Nicoli, F. Haas, R.M. Freeman, S. Szilner, Z. Basrak, A. Morsad, G.R. Satchler, M.E. Brandan. Universety of Hassan II), for incident particle energies of 62 MeV, 75 MeV, 80 MeV, 94.8 MeV, 100 MeV, 115.9 MeV, 124 MeV are described. &nbsp;The results of decomposition of experimental angular distributions of differential cross sections into cluster diffraction modes of elastic scattering of 12-C ions on 16-O nuclei, as well as using classical wave optics, calculated the angles in which the corresponding cluster structures should appear. Peaks of scattering amplitudes on various clusters were determined depending on the energy of the incident particles. At the angles corresponding to the peaks of optical scattering on alpha clusters at energies of 62 MeV, 75 MeV, 80 MeV, 94.8 MeV, 100 MeV, 115.9 MeV satisfactory agreement of the experimental data with theoretical curves was revealed. The sizes of the target nucleus and cluster substructures are determined. As a result of the fittings, it was found that the best experimental data of the differential cross sections for the angular distributions of 12-C to 16-O elastic scattering were described by theoretical curves in the concept of the 12-C and 16-O alpha-cluster structure. The resulting abnormally small radii of intranuclear alpha clusters with respect to the classical radius of free alpha particles are most likely explained by the fact that alpha clusters are in a bound state and are surrounded by nuclear matter, which leads to an increased density of matter. In addition, it is possible that the radii of intranuclear alpha clusters are reduced due to the so-called EMC effect.

Quantum interference among heavy NMSSM Higgs bosons

In the Next-to-Minimal Supersymmetric Standard Model (NMSSM), it is possible to have strong mass degeneracies between the new singlet-like scalar and the heavy doublet-like scalar, as well as between the singlet-like and doublet-like pseudoscalar Higgs states. When the difference in the masses of such states is comparable with the sum of their widths, the quantum mechanical interference between their propagators can become significant. We study these effects by taking into account the full Higgs boson propagator matrix in the calculation of the production process of $\tau^+\tau^-$ pairs in gluon fusion at the Large Hadron Collider (LHC). We find that, while these interference effects are sizeable, they are not resolvable in terms of the distributions of differential cross sections, owing to the poor detector resolution of the $\tau^+\tau^-$ invariant mass. They are, however, identifiable via the inclusive cross sections, which are subject to significant variations with respect to the standard approaches, wherein the propagating Higgs bosons are treated independently from one another. We quantify these effects for several representative benchmark points, extracted from a large set of points, obtained by numerical scanning of the NMSSM parameter space, that satisfy the most important experimental constraints currently available.

NEUT/NuWro cross-section modelling at low three-momentum transfer

The MINERvA collaboration has reported a Charged-Current inclusive (CCinc) cross-section measurement on a CH target. This was performed by looking at both the muon and hadronic final state particles to create a double differential cross-section distribution that provides additional insight into the different regions of the phase-space where nuclear effects are present. We show early comparisons of the NEUT and NuWro generators in an attempt to estimate which parts of the models are in agreement with this data.

Repulsive three-body force and channel-coupling effects via C12+C12 scattering at 100A MeV

The angular distributions of differential cross sections of $^{12}\mathrm{C}+^{12}\mathrm{C}$ elastic and inelastic scattering populating the ground and excited states in $^{12}\mathrm{C}$ up to 15 MeV excitation energy are precisely measured for the first time at an incident energy of $100A$ MeV to study the effect of repulsive three-body forces. Using the high-resolution spectrometer Grand Raiden at the Research Center for Nuclear Physics (RCNP), Osaka University, we have obtained the differential cross sections for the ground state (${0}_{1}^{+}$) and 4.44 MeV (${2}_{1}^{+}$) excited state, as well as the summed differential cross sections for the states between 4.44 and 15 MeV in the angular range of $1.{0}^{\ensuremath{\circ}}--7.{5}^{\ensuremath{\circ}}$. The results are compared with microscopic coupled-channel calculations. The potential between the colliding nuclei is determined by the double folding method with three different complex $G$-matrix interactions, the ESC, CEG07b, and MPa interactions. The CEG07b and MPa interactions, which include repulsive three-body forces, describe the data well, whereas the ESC interaction, which does not include repulsive three-body forces, fails to reproduce the data. The results provide evidence of repulsive three-body forces in $^{12}\mathrm{C}$ and demonstrate the possible sensitivity of elastic scattering to three-body forces.

Differential cross-sections measurements for hadrontherapy: 50 MeV/A12C reactions on H, C, O, Al andnatTi targets

In order to keep the benefits of a carbon treatment, the dose and biological effects induced by secondary fragments must be taken into account when simulating the treatment plan. These Monte-Carlo simulations codes are done using nuclear models that are constrained by experimental data. It is hence necessary to have precise measurements of the production rates of these fragments all along the beam path and for its whole energy range. In this context, a series of experiments aiming to measure the double differential fragmentation cross-sections of carbon on thin targets of medical interest has been started by our collaboration. In March 2015, an experiment was performed with a 50 MeV/nucleon 12 C beam at GANIL. During this experiment, energy and angular differential cross-section distributions on H, C, O, Al and nat Ti have been measured. In the following, the experimental set-up and analysis process are briefly described and some experimental results are presented. Comparisons between several exit channel models from Phits and Geant4 show great discrepancies with the experimental data. Finally, the homemade Sliipie model is briefly presented and preliminary results are compared to the data with a promising outcome.

Development of an intranuclear-cascade code CBIM applicable to the nuclear reaction with incident particle energy above 45 MeV

The Monte Carlo intra-nuclear cascade program CBIM has been developed for describing spallation reactions involving protons, neutrons and pions on complex nuclei. In order to describe cascade process, several simplifications and assumptions are made in the following:firstly, neither reaction, nor reflection, nor refraction, nor ionization will be taken into account before the incident particle enters into the target nucleus; secondly, target nucleus is regarded as being spherical and the atom number should be greater than 2; thirdly, the knocked nucleon is determined by cross section sampling; finally, in the center-of-mass frame, the scattering angle is sampled based on differential cross section distribution. The basis physics model is based on the above assumptions and Bertini intra-nuclear cascade model; meanwhile, nucleon-nucleon angle differential distributions of INCL in the center-of-mass frame are introduced to overcome the shortage of Bertini model. The interactions between nucleon and nucleon or between nucleon and pion, such as elastic scattering, pion production and charge exchange, are included in the code. In the particles collision, the nucleon density changes with the target nucleus radius; and the interaction cross sections refer to 22 kinds of experimental cross sections in Bertini model. The intra-nuclear cascades induced by 45-3500 MeV neutron, proton or pion below 2500 MeV can be simulated by this code. Finally, comparisons between experimental reaction cross section over the energy range 60-378 MeV, and some simulation results by MCNPX, GEANT4 and PHITS over the energy range 65-3000 MeV show that they are in reasonable agreement with the CBIM results over the broad energy range considered.

Phenomenon of the diffraction rise of cross sections in the forward angular hemisphere as an effect of nuclear and cluster interference

Angular distributions of differential cross sections for scattering of alpha-particles on 24Mg nuclei are described as scattering on a black absorbing nucleus and its alpha-cluster components using first-order Bessel functions. The dependence of the interaction radius of alpha-clusters in a nucleus on the energy of incident particles is found. The radius varies because scattering at low energies can occur upon the correlated motion of two or three alpha-clusters. Scattering at average energies occurs mainly on separated alpha-cluster structures. As the energy increases, the contribution from the alpha-particle mode falls while the contribution from the modes of scattering on nucleons rises; this can manifest itself as growth of the interaction radius due to the interference between the alpha-cluster mode and those of smaller cluster structures and nucleons. A contribution to the nonuniform rise of angular distributions of differential cross sections is thus also possible due to these effects.

Exclusive vector meson production at high energies and gluon saturation

We systematically study exclusiv2 diffractive (photo)production of vector mesons ($J/\ensuremath{\psi}$, $\ensuremath{\psi}(2s)$, $\ensuremath{\phi}$, and $\ensuremath{\rho}$) off protons in high-energy collisions and investigate whether the production is a sensitive probe of gluon saturation. We confront saturation-based results for diffractive $\ensuremath{\psi}(2s)$ and $\ensuremath{\rho}$ production at HERA and $J/\ensuremath{\psi}$ photoproduction with all available data, including recent work from HERA, ALICE, and LHCb, finding good agreement. In particular, we show that the $t$ distribution of differential cross sections of photoproduction of vector mesons offers a unique opportunity to discriminate among saturation and nonsaturation models. This is due to the emergence of a pronounced dip (or multiple dips) in the $t$ distribution of diffractive photoproduction of vector mesons at relatively large, but potentially accessible $|t|$ that can be traced back to the unitarity features of color dipole amplitude in the saturation regime. We show that in saturation models the dips in $t$ distribution recede towards lower $|t|$ with decreasing mass of the vector meson, increasing energy or decreasing Bjorken-$x$, and decreasing virtuality $Q$. We provide various predictions for exclusive (photo)production of different vector mesons including the ratio of $\ensuremath{\psi}(2s)/J/\ensuremath{\psi}$ at HERA, the LHC, and future colliders.

Notch Test for Radial Sensitivity on Neutron Density Distribution in 48Ca Probed by α-Particle Elastic Scattering

Notch tests are made to study the sensitive regions in the neutron density distribution in the ground state of 48Ca probed by the angular distributions of differential cross sections of α-particle elastic scattering at 104MeV with optical model potentials calculated by using a systematic single-folding model. An improved notch scheme is proposed, which perturbs the neutron density distribution of the target nucleus locally. Results of the notch tests show that the angular distribution of differential cross sections for α particle elastic scattering at 104MeV only probe the surface of the neutron density distribution in 48Ca.