Total Production Cross Section Research Articles

Probing hidden leptonic scalar portals using the NA64 experiment at CERN

In this study, we demonstrate the potential of the NA64 experiment at CERN SPS to search for New Physics processes involving e→μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$e\\rightarrow \\mu $$\\end{document} transitions after the collision of 100 GeV electrons with target nuclei. A new Dark Sector leptonic portal in which a scalar boson φ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varphi $$\\end{document} could be produced in the lepton-flavor-changing bremsstrahlung-like reaction, eN→μNφ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$eN\\rightarrow \\mu N\\varphi $$\\end{document}, is used as benchmark process. In this work, we develop a realistic Monte Carlo simulation of the NA64 experimental setup implementing the differential and total production cross-section computed at exact tree-level and applying the Weiszäcker–Williams phase space approximation. Using this framework, we investigate the main background sources and calculate the expected sensitivity of the experiment. The results indicate that with minor setup optimization, NA64 can probe a large fraction of the available parameter space compatible with the muon g-2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$g-2$$\\end{document} anomaly and the Dark Matter relic predictions in the context of a new Dark Sector leptonic portal with 1011\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^{11}$$\\end{document} EOT. This result paves the way to the exploration of lepton-flavour-changing transitions in NA64.

Heavy-Quark Pair Production at Lepton Colliders at NNNLO in QCD.

We compute the total cross section and invariant mass distribution for heavy-quark pair production in e^{+}e^{-} annihilation at the next-to-next-to-next-to-leading order in QCD. The obtained results are expressed as piecewise functions defined by several deeply expanded power series, facilitating a rapid numerical evaluation. Utilizing top-pair production at a collision energy of 500GeV as a benchmark, we observe a correction of approximately 0.1% for the total cross section and around 10% for the majority of the invariant mass distribution range. These results play a crucial role in significantly reducing theoretical uncertainty: the scale dependence has been diminished to 0.06% for the total cross section and to 5% for the invariant mass distribution. This reduction of uncertainty meets the stringent requirements of future lepton colliders.

Latest ALICE results on charm and beauty hadronisation in hadronic collisions

The study of heavy-flavour mesons and baryons in hadronic collisions provides unique access to the properties of heavy-quark hadronisation in the presence of large partonic densities, where new mechanisms of hadron formation beyond in-vacuum fragmentation can emerge. Performing these measurements in intervals of charged-particle multiplicities across different collision systems provides sensitivity to understand whether different hadronisation mechanisms are at play in small and large hadronic colliding systems. In this contribution, a selection of the latest charm and beauty production measurements in proton–proton (pp) collisions is presented, which can shed light on the modification of the heavy-quark hadronisation mechanisms with respect to leptonic collisions. New published results of the production of all prompt charm ground states in pp collisions at √S = 13 TeV, which allowed us to measure the charm fragmentation fractions and the total cc production cross section at midrapidity, will be shown. The new final measurement of non-prompt (i.e. originating from beauty-hadron decays) Λc+ baryons in the same collisions system will be discussed to provide a quantitative comparison between the hadronisation properties of beauty and charm hadrons. New measurements of Ξc0 production as a function of charged-particle multiplicity in pp collisions at √S = 13, and of Ξc0 production in p–Pb collisions at √SNN = 5.02 TeV, will be also presented, shedding further light on the hadronisation of charm-strange baryons in different colliding systems.

K-shell X-ray production cross sections of Ti, Cr, Ni and Zn induced by chlorine ions

In this work we report on the results of the total K-shell X-ray production cross sections of Ti, Cr, Ni and Zn induced by Cl4+ and Cl5+ ions with energies ranging from 4 MeV to 10 MeV. The experimental results were compared with Atomic Orbitals Coupled-Channels (CC) calculations based on the independent electron model. The experimental X-ray production cross sections vary from about 10−2 barns for Zn up to 102 barns for Ti. The results obtained for Ti indicate that the present CC calculations underestimate the experimental cross sections up to two orders of magnitude at 10 MeV chlorine bombarding energy. However, the discrepancy between CC calculations and experimental results decreases as both bombarding energy and the atomic number of the target species increase. The dependency of the experiment-theory agreement on the asymmetry and adiabaticity parameters α and η respectively is discussed.

Compilation of isomeric ratios of light particle induced nuclear reactions

Experimental isomeric ratios of light (A ≤ 4) particle-induced nuclear reactions were compiled for the product nuclides having metastable states with half-lives longer than 0.1 s. The experimental isomeric ratio data were taken from the EXFOR library and reviewed. When an experiment reports isomer production cross sections instead of isomeric ratios, the cross sections taken from the EXFOR library were converted to the isomeric ratios by us. During compilation, questionable data (e.g., preliminary data compiled in EXFOR in parallel with their final data, sum of isomer production cross sections larger than the total production cross sections) were excluded. As an application of the new compilation, goodness-of-fit was studied for the isomeric ratios predicted by the reaction model code TALYS-1.96. A text file and plots of the compiled isomer production cross sections and isomeric ratios are provided as supplemental materials.

Quark and gluon two-loop beam functions for leading-jet pT and slicing at NNLO

We compute the complete set of two-loop beam functions for the transverse momentum distribution of the leading jet produced in association with an arbitrary colour-singlet system. Our results constitute the last missing ingredient for the calculation of the jet-vetoed cross section at small veto scales at the next-to-next-to-leading order, as well as an important ingredient for its resummation to next-to-next-to-next-to-leading logarithmic order. Our calculation is performed in the soft-collinear effective theory framework with a suitable regularisation of the rapidity divergences occurring in the phase-space integrals. We discuss the occurrence of soft-collinear mixing terms that might violate the factorisation theorem, and demonstrate that they are naturally absorbed into the beam functions at two loops in the exponential rapidity regularisation scheme when performing a multipole expansion of the measurement function. As in our recent computation of the two-loop soft function, we present the results as a Laurent expansion in the jet radius R. We provide analytic expressions for all flavour channels in x space with the exception of a set of R-independent non-logarithmic terms that are given as numerical grids. We also perform a fully numerical calculation with exact R dependence, and find that it agrees with our analytic expansion at the permyriad level or better. Our calculation allows us to define a next-to-next-to-leading order slicing method using the leading-jet pT as a slicing variable. As a check of our results, we carry out a calculation of the Higgs and Z boson total production cross sections at the next-to-next-to-leading order in QCD.

Precision predictions for exotic lepton production at the Large Hadron Collider

We calculate total and differential cross sections for the pair production, at the Large Hadron Collider, of exotic leptons that could emerge from models with vectorlike leptons and in type-III seesaw scenarios. Our predictions include next-to-leading-order QCD corrections, and we subsequently match them with either parton showers, or threshold resummation at the next-to-next-to-leading logarithmic accuracy. Our results show an important increase of the cross sections relative to the leading-order predictions, exhibit a distortion of the shapes for various differential distributions, and feature a significant reduction of the scale uncertainties. Our predictions have been obtained from new feynrules model implementations and associated Universal FeynRules Output (UFO) model libraries. This completes the set of next-to-leading-order implementations of new physics models featuring extra leptons that are publicly available on the feynrules model database.

Threshold enhanced cross sections for colorless productions

We study the threshold effect for neutral and charged Drell-Yan productions, associated production of Higgs boson with a massive vector boson and Higgs production in bottom quark annihilation at LHC to the third order in QCD. Using the third order soft-virtual results for these processes and exploiting the universality of the threshold logarithms, we extract the process-dependent coefficients for these processes and resum large threshold logarithms to next-to-next-to-next-to leading logarithmic (N$^3$LL) accuracy. By matching our results to the recently available N$^3$LO results, we provide the most precise theoretical predictions for these processes. We present numerical results for invariant mass distribution and total production cross-sections. We find the conventional scale uncertainties of about $0.4\%$ at N$^3$LO level in the fixed order results get reduced to as small as less than $0.1\%$ at N$^3$LO+N$^3$LL level in the high invariant mass region.

Charge Transfer and Electron Production in Proton Collisions with Uracil: A Classical and Semiclassical Study.

Cross sections for charge transfer and ionization in proton-uracil collisions are studied, for collision energies 0.05<E<2500 keV, using two computational models. At low energies, below 20 keV, the charge transfer total cross section is calculated employing a semiclassical close-coupling expansion in terms of the electronic functions of the supermolecule (H-uracil)+. At energies above 20 keV, a classical-trajectory Monte Carlo method is employed. The cross sections for charge transfer at low energies have not been previously reported and have high values of the order of 40 Å2, and, at the highest energies of the present calculation, they show good agreement with the previous results. The classical-trajectory Monte Carlo calculation provides a charge transfer and electron production cross section in reasonable agreement with the available experiments. The individual molecular orbital contributions to the total electron production and charge transfer cross sections are analyzed in terms of their energies; this permits the extension of the results to other molecular targets, provided the values of the corresponding orbital energies are known.

Gamma-UPC: automated generation of exclusive photon-photon processes in ultraperipheral proton and nuclear collisions with varying form factors

The automated generation of arbitrary exclusive final states produced via photon fusion in ultraperipheral high-energy collisions of protons and/or nuclei, A B overset{upgamma upgamma}{to } A X B, is implemented in the MadGraph5_aMC@NLO and HELAC-Onia Monte Carlo codes. Cross sections are calculated in the equivalent photon approximation using γ fluxes derived from electric dipole and charge form factors, and incorporating hadronic survival probabilities. Multiple examples of γγ cross sections computed with this setup, named gamma-UPC, are presented for proton-proton, proton- nucleus, and nucleus-nucleus ultraperipheral collisions (UPCs) at the Large Hadron Collider and Future Circular Collider. Total photon-fusion cross sections for the exclusive production of spin-0, 2 resonances (quarkonia, ditauonium, and Higgs boson; as well as axions and gravitons), and for pairs of particles (J/ψJ/ψ, WW, ZZ, Zγ, toverline{t} , HH) are presented. Differential cross sections for exclusive dileptons and light-by-light scattering are compared to LHC data. This development paves the way for the upcoming automatic event generation of any UPC final state with electroweak corrections at next-to-leading-order accuracy and beyond.

Neutrino-induced single pion production and the reanalyzed bubble chamber data

In this work we report the calculation of the charged current total and differential cross sections for weak pion production with neutrinos and antineutrinos, with the final pion-nucleon pair invariant mass ${W}_{\ensuremath{\pi}N}\ensuremath{\lesssim}2\text{ }\text{ }\mathrm{GeV}$. Our results are compared with the recent reanalyzed data from the old bubble chamber experiments, that solved the discrepancy between the Argonne National Laboratory and Brookhaven National Laboratory data. We implement a model previously tested for the cuts ${W}_{\ensuremath{\pi}N}&lt;1.4$, 1.6 GeV, which explicitly includes resonances in the first and second resonance regions within different approaches for the resonances self-energy and $\frac{3}{2}$ vertexes and propagators, a fact not usually analyzed. Our model leans on consistently effective Lagrangians that generate resonant amplitudes together with nonresonant and resonant backgrounds. Effects of hadrons' finite extension and more energetic resonances correspond to the emitted pion-nucleon invariant mass in the $1.6&lt;{W}_{\ensuremath{\pi}N}&lt;2\text{ }\text{ }\mathrm{GeV}$ region are taking into account using appropriate form factors in consistency with previous results on neutral current pion production calculations. Our results reproduce well the reanalyzed data without cuts and are compared with other models.

Measurement of the inclusive and differential WZ production cross sections, polarization angles, and triple gauge couplings in pp collisions at sqrt{s} = 13 TeV

The associated production of a W and a Z boson is studied in final states with multiple leptons produced in proton-proton (pp) collisions at a centre-of-mass energy of 13 TeV using 137 fb−1 of data collected with the CMS detector at the LHC. A measurement of the total inclusive production cross section yields σtot(pp → WZ) = 50.6 ± 0.8 (stat) ± 1.5 (syst) ± 1.1 (lumi) ± 0.5 (theo) pb. Measurements of the fiducial and differential cross sections for several key observables are also performed in all the final-state lepton flavour and charge compositions with a total of three charged leptons, which can be electrons or muons. All results are compared with theoretical predictions computed up to next-to-next-to-leading order in quantum chromodynamics plus next-to-leading or- der in electroweak theory and for various sets of parton distribution functions. The results include direct measurements of the charge asymmetry and the W and Z vector boson polarization. The first observation of longitudinally polarized W bosons in WZ production is reported. Anomalous gauge couplings are searched for, leading to new constraints on beyond-the-standard-model contributions to the WZ triple gauge coupling.

Energy dependent ratios of level-density parameters in superheavy nuclei

The nuclear level densities and level-density parameters in fissioning nuclei at their saddle points of fission barriers, ${a}_{f}$, as well as those for neutron, ${a}_{n}$, proton, ${a}_{p}$, and $\ensuremath{\alpha}$-particle, ${a}_{\ensuremath{\alpha}}$, emission residues at the ground states are calculated for isotopic chains of superheavy nuclei with $Z$ = 112--120. The calculations are performed with the superfluid formalism using the single-particle energies obtained from the diagonalization of the deformed Woods-Saxon potential. Spectra were generated at global minima of the adiabatic potential energy surfaces, found by the multidimensional minimization method, and at the proper saddle points, found by the ``immersion water flow'' technique on multidimensional energy grids, with allowed reflection and axial symmetry breaking. The influence of shell effects on the energy dependence of the ratios of level-density parameters corresponding to residues of the considered decay modes to those of neutron emission is studied. As shown, in contrast to the ${a}_{f}/{a}_{n}$ ratio, the ${a}_{p}/{a}_{n}$ and ${a}_{\ensuremath{\alpha}}/{a}_{n}$ ratios do not show characteristic maxima depending on the excitation energy of the compound nucleus being formed. In the case of $\ensuremath{\alpha}$ decay, we identified the collective enhancement caused by cluster degrees of freedom as playing quite an important role. The energetic course of the variability of the level-density parameters before reaching the asymptotic value, not taken into account so far, is of great importance for the estimation of the probabilities of de-excitation cascades via light particles emission in competition with fission and, thus, for the determination of the survival probabilities and finally for the total production cross sections of superheavy nuclei.

Validation of e+e−Pair Production Total Cross Sections for Monte Carlo Particle Transport

Several sources of total cross sections for e$^+$e$^-$ pair production by photon interaction with matter, used by major Monte Carlo codes for particle transport, are quantitatively evaluated with respect to experimental measurements collected from the literature. They include data libraries deriving from theoretical calculations and analytical formulae representing empirical fits to tabulations. Although most of these sources of cross sections are based on one theoretical reference, the statistical data analysis documented in the paper highlights differences in their compatibility with experiment. The cross sections collected in the 1997 version of the Evaluated Photon Data Library (EPDL) exhibit the lowest incompatibility with experiment; the paper details the validation results for all the examined cross section sources. The scarcity of experimental data does not allow the validation process to discern pair production in the field of the nucleus and in the field of atomic electrons; nevertheless, the paper documents relevant clues regarding the contribution of the latter to reproduce experimental measurements.

Quark and gluon contents of a lepton at high energies

In high-energy leptonic collisions, such as at a multi-TeV muon collider, the collinear splittings of the electroweak (EW) gauge bosons and leptons are the dominant phenomena, and the scattering processes should thus be formulated in terms of the EW parton distribution functions (EW PDFs). We complete this formalism in the Standard Model to include the QCD sector and evaluate the quark and gluon PDFs inside a lepton at the double-log accuracy. The splittings of the photon and subsequently the quarks and gluons control the quark/gluon PDFs below the EW scale. The massive gauge bosons lead to substantial contributions at high scales. The jet production cross section can reach the order of a few nb (50 pb) in e+e−(μ+μ−) collisions, at the TeV c.m. energies with a moderate acceptance cut, that governs the overall event shape up to about {p}_T^j ∼ 60 GeV. To complete the picture, we also provide an estimation of the total cross section for the photon-induced hadronic production at low partonic energies, which can reach the level of one hundred or a few tens of nb in high-energy electron or muon collisions.

On-shell Z boson production at hadron colliders through \U0001d4aa(ααs)

The analytical expressions of the mixed QCD-EW corrections to on-shell Z boson inclusive production cross section at hadron colliders are presented, together with computational details. The results are given in terms of polylogarithmic functions and elliptic integrals. The impact on the prediction of the Z boson production total cross section is discussed, comparing different proton parton density sets.

W L-shell X-ray emission induced by C&lt;sup&gt;6+&lt;/sup&gt;ions in the energy range of several hundred MeV/u

The L-shell X-ray emissions of tungsten has been investigated under the bombardment of C&lt;sup&gt;6+&lt;/sup&gt; ions in the high energy region of 154 - 424 MeV/u. Compared to the atomic data, the energy of the X-ray is enlarged, and the relative intensity ratios of Lı, Lβ&lt;sub&gt;1, 3, 4&lt;/sub&gt; and Lβ&lt;sub&gt;2, 15&lt;/sub&gt; to Lα&lt;sub&gt;1, 2&lt;/sub&gt; X-rays are enhanced. The L-subshell and the total X-ray production cross sections were calculated by a well corrected thick target formula and compared with the theoretical estimation of BEA, PWBA and ECPSSR. On the whole, the experimental cross sections are all smaller than the prediction of PWBA and ECPSSR, but in agreement roughly with that of BEA. It is indicated that the inner-shell ionization of W can be considered to be a binary process between the high energy C&lt;sup&gt;6+&lt;/sup&gt; ions acting as a point charge and the independent target electrons. With the L-shell ionization, the outer-shells are multiply ionized. The multi-ionization degree is regard to be almost constant in the present work. This results in the X-ray energy blue shift and the enhancement of the relative intensity ratios of Lı and Lβ to Lα X-ray. Using the atomic parameters corrected by multi-ionization, the X-ray production cross section can be estimated by the BEA model.

W L-shell X-ray emission induced by C&lt;sup&gt;6+ &lt;/sup&gt;ions with several hundred MeV/u

The L-shell X-ray emission of tungsten is investigated under the bombardment of C&lt;sup&gt;6+&lt;/sup&gt; ions in a high energy range of 154—424 MeV/u. Compared with the atomic data, the energy of the X-ray is enlarged, and the relative intensity ratio of Lι, Lβ&lt;sub&gt;1,3,4&lt;/sub&gt; and Lβ&lt;sub&gt;2,15&lt;/sub&gt; to Lα&lt;sub&gt;1,2&lt;/sub&gt; X-rays are enhanced. The L-subshell and the total X-ray production cross section are calculated from a well corrected thick target formula and compared with the theoretical estimation of binary encounter approximation (BEA), plane-wave Born approximation (PWBA) and ECPSSR (PWBA theory modified with Energy-loss, Coulomb-repulsion, Perturbed-Stationary-State and Relativistic corrections). On the whole, the experimental cross sections are all smaller than the prediction of PWBA and ECPSSR, but in rough agreement with that of BEA. It is indicated that the inner-shell ionization of W can be considered as a binary process between the high energy C&lt;sup&gt;6+&lt;/sup&gt; ions acting as a point charge and the independent target electrons. With the L-shell ionization, the outer-shells are multiply ionized. The multi-ionization degree is approximately regard as a constant in the present work. This leads the X-ray energy to be blueshifted and the relative intensity ratios of Lι and Lβ to Lα X-ray to be enhanced. Using the atomic parameters corrected by multi-ionization, the X-ray production cross section can be estimated by the BEA model.

Investigation of the Σ0 hyperon production in p(3.5GeV)+p collisions

The production mechanism of the Σ0 was investigated via the exclusive reaction pp → pK+Σ0 at a beam energy 3.5 GeV with the HADES detector. The preliminary value of the extracted total production cross section is found to be σ(pK+Σ0)[μb] = 17.7 ± 1.7(stat) ± 1.6(syst). The dynamics of the reaction pp → pK+Σ0 was investigated by studying the angular distributions in the center-of-mass, Gottfried-Jackson and helicity frames. The angular distributions in the center-of-mass frame supports the pion exchange mechanism. Furthermore, the helicity angular distributions are highly non-isotropic, which is a clear indication of resonant production component.

Probing hidden sectors with a muon beam: Total and differential cross sections for vector boson production in muon bremsstrahlung

Vector bosons, such as Dark Photon $A'$ or $Z'$, can couple to muons and be produced in the bremsstrahlung reaction $\mu^- + N \rightarrow \mu^- + N + A'(Z')$. Their possible subsequent invisible decay can be detected in fixed target experiments through missing energy/momentum signature. In such experiments, not only is the energy transfer to $A'(Z')$ important, but also the recoil muon angle $\psi_{\mu'}$. In this paper, we derive the total and the double differential cross-sections involved in this process using the phase space Weisz\"acker-Williams and improved Weisz\"acker-Williams approximations, as well as using exact-tree-level calculations. As an example, we compare the derived cross-sections and resulting signal yields in the NA64$\mu$ experiment that uses a 160 GeV muon beam at the CERN Super Proton Synchrotron accelerator. We also discuss its impact on the NA64$\mu$ expected sensitivity to explore the $(g-2)_\mu$ anomaly favoured region with a $Z'$ boson considering $10^{12}$ muons accumulated on target.