Cross Section For Production Of Photons Research Articles

Improved prompt and delayed photon heating computational methods for fast reactors

In order to accurately calculate the photon heating distribution of fast reactor, the photon cross section processing code NGAMMA has been developed. NGAMMA can process MATXS format library and generate multi-group forms of photo-atomic cross sections, prompt photon production cross sections, delayed photon production cross sections, and neutron-photon KERMA factors for neutron-photon coupled heating calculations. An improved 21-groups photon library containing both prompt and delayed photon data is generated using the NGAMMA code based on the 1968n × 94γ MATXS format database. The photon library was verified using the fast reactor benchmark problem ZPR-6/7 and MET-1000. The results of the calculations show that the use of the 21-groups photon library generated by energy group collapse using 94-groups photon fluxes results in a significant improvement in the accuracy of the prompt photon heating calculations, especially in the non-fuel region, resulting in a relative error of less than 1% between the photon heating calculations and the MCNP calculations, compared to an error of 7% using the previous photon library. For the ZPR-6/7 benchmark problem, consideration of the delayed photons results in a 30% improvement in photon heating in the fuel region. For the MET1000 benchmark problem, the total power results of the neutron-photon coupling calculations based on the improved photon library are in good agreement with the MCNP, with a maximum relative error of no more than 3% in the total power of the fuel assembly. For reflector assemblies where photon power is a major contribution to heat release, the maximum relative error in prompt photon power is only −5.96%. Considering delayed photon significantly affects the photon heating, and for the MET1000 benchmark problem, considering delayed photon results in an overall increase of more than 30% in the photon power of the fuel assembly.

The multigroup library processing method for coupled neutron and photon heating calculation of fast reactor

To accurately calculate the heating distribution of the fast reactor, a neutron-photon library in MATXS format named Knight-B7.1-1968n × 94γ was processed based on the ENDF/B-VII.1 library for ultrafine groups. The neutron cross-section processing code MGGC2.0 was used to generate few-group neutron cross sections in ISOTXS format. Additionally, the self-developed photon cross-section processing code NGAMMA was utilized to generate photon libraries for neutron-photon coupled heating calculations, including photo-atom cross sections for the ISOTXS format, prompt photon production cross sections, and kinetic energy release in materials (KERMA) factors for neutrons and photons, and the self-shielding effect from the capture and fission cross sections of neutron to photon have been taken into account when the photon source generated by neutron is calculated. The interface code GSORCAL was developed to generate the photon source distribution and interface with the DIF3D code to calculate the neutron-photon coupling heating distribution of the fast reactor core. The neutron-photon coupled heating calculation route was verified using the ZPPR-9 benchmark and the RBEC-M benchmark, and the results of the coupled heating calculations were analyzed in comparison with those obtained from the Monte Carlo code MCNP. The calculations show that the library was accurately processed, and the results of the fast reactor neutron-photon coupled heating calculations agree well with those obtained from MCNP.

NNLO photon fragmentation within antenna subtraction

We report on our recent progress towards including the photon fragmentation contribution in next-to-next-to-leading order (NNLO) QCD predictions for photon production cross sections. This extension to previous NNLO calculations requires the identification of the photon in singular parton-photon collinear limits. We discuss how these limits can be subtracted within antenna subtraction using fragmentation antenna functions and we outline their integration.

A Non-Equilibrium Approach to Photon Emission from the Late Stages of Relativistic Heavy-Ion Collisions

Cross sections for photon production in hadronic scattering processes have been calculated according to an effective chiral field theory. For π + ρ → π + γ and π + π → ρ + γ processes, these cross sections have been implemented into a novel hadronic transport approach (SMASH), which is suitable for collisions at low and intermediate energies. The implementation is verified by systematically comparing the thermal photon rate to theoretical expectations. The photon rates we obtain are compared to previous works, where scattering processes mediated by ω mesons are found to contribute significantly to the total photon production. Finally, the impact of considering the finite width of the ρ meson is investigated, and a significant enhancement of photon production in the low-energy region is observed. This work is the first step towards a consistent treatment of photon emission in hybrid hydrodynamics+transport approaches. The quantification of the importance of the hadronic stage for the resolution of the direct photon flow puzzle is a next step and can be applied to identify equilibrium and non-equilibrium effects in the hadronic afterburner.

Fast neutron inelastic scattering from 7Li

The inelastic scattering of fast neutrons from 7Li nuclei was investigated at the nELBE neutron-time-of-flight facility. The photon production cross section of 478 keV γ-rays from the first excited state of 7Li was determined by irradiating a disc of LiF with neutrons of energies ranging from 100 keV to about 10 MeV. The target position was surounded by a setup of 7 LaBr3 scintillation detectors and 7 high-purity germanium detectors to detect the de-excitation γ-rays. A 235U fission chamber was used to determine the incoming neutron flux. The number of detected photons was corrected for the detection efficiency, multiple scattering and the time-of-flight dependent data acquisition dead time. The preliminary results show reasonable agreement with some previous measurments but are about 15 % below the recent data taken at the GELINA facility.

Measurement of the inclusive isolated photon production cross section in text{ p }text{ p } collisions at sqrt{s}=7 TeV

The production cross section of inclusive isolated photons has been measured by the ALICE experiment at the CERN LHC in pp collisions at a centre-of-momentum energy of sqrt{s}= 7 TeV. The measurement is performed with the electromagnetic calorimeter EMCal and the central tracking detectors, covering a range of |eta |<0.27 in pseudorapidity and a transverse momentum range of 10< p_mathrm {T}^{gamma }< 60~mathrm {GeV}/c. The result extends the p_mathrm {T} coverage of previously published results of the ATLAS and CMS experiments at the same collision energy to smaller p_mathrm {T}. The measurement is compared to next-to-leading order perturbative QCD calculations and to the results from the ATLAS and CMS experiments. All measurements and theory predictions are in agreement with each other.

Benchmarking a nonequilibrium approach to photon emission in relativistic heavy-ion collisions

In this work, the production of photons through binary scattering processes is investigated for equilibrated hadronic systems. More precisely, a non-equilibrium hadronic transport approach to describe relativistic heavy-ion collisions is benchmarked with respect to photon emission. Cross sections for photon production in $\pi + \rho \to \pi + \gamma$ and $\pi + \pi \to \rho + \gamma$ scattering processes are derived from an effective chiral field theory and implemented into the hadronic transport approach, SMASH (Simulating Many Accelerated Strongly-interacting Hadrons). The implementation is verified by systematically comparing the thermal photon rate to theoretical expectations. Further, the impact of form factors is discussed, scattering processes mediated by $\omega$ mesons are found to contribute significantly to the total photon production. Several comparisons of the yielded photon rates are performed: to parametrizations of the very same rates, as used in hydrodynamic simulations, to previous works relying on different cross sections for the production of direct photons from the hadronic stage, and to partonic rates. Finally, the impact of considering the finite width of the $\rho$ meson is investigated, where a significant enhancement of photon production in the low-energy region is observed. This benchmark is the first step towards a consistent treatment of photon emission in hybrid hydrodynamics+transport approaches and a genuine dynamical description.

Diffractive incoherent vector meson production off protons: a quark model approach to gluon fluctuation effects

Fluctuations play an important role in diffractive production of vector mesons. It was in particular recently suggested, based on the Impact-Parameter dependent Saturation model (IPSat), that geometrical fluctuations triggered by the motion of the constituent quarks within the protons could explain incoherent diffractive processes observed at HERA. We propose a variant of the IPSat model which includes spatial and symmetry correlations between constituent quarks, thereby reducing the number of parameters needed to describe diffractive vector meson production to a single one, the size of the gluon cloud around each valence quark. The application to J/varPsi , rho and phi diffractive electron and photon production cross sections reveal the important role of geometrical fluctuations in incoherent channels, while other sources of fluctuations are needed to fully account for electroproduction of light mesons, as well as photo production of J/varPsi mesons at small momentum transfer.

Magnetic field effects on photon emission in intermediate energy heavy-ion collisions

Photon production cross section in heavy-ion collisions is estimated by employing the elementary process of proton-neutron bremsstrahlung in a Boltzmann-Uehling-Uhlenbeck model. With taking the electromagnetic field into account for simulating the reactions, the magnetic effects are considered in different impact parameter regions for the collisions of 14N + 208Pb at incident energy of 40 MeV/nucleon in the laboratory system. We investigated the energy spectra, production rates, and the polar angular distributions of photons. In particular, the directed flow $ v_{1}$ and elliptic flow $ v_{2}$ are extracted for both photons and free nucleons. In contrast with unaffected nucleon flows by the magnetic field, photon flows do display magnetic field effect.

Soft-Collinear Effects in Threshold and Joint Resummation

Large perturbative corrections, which appear in perturbative expressions for many QCD observables, either at small \(Q_T\) or at partonic threshold, can be organized by way of all order resummation. Joint resummation allows simultaneous resummation of threshold and recoil effects and its impact has been assessed upto leading log, next-to-leading log (NLL) and in some cases up to NNLL accuracy. We discuss another class of terms, called soft-collinear effects, which give rise to corrections of the form \(\frac{\ln ^jN}{N}\) and their impact on the joint resummed calculations of prompt photon production cross section.

Measurement of forward photon production cross-section in proton–proton collisions at [formula omitted] with the LHCf detector

In this paper, we report the production cross-section of forward photons in the pseudorapidity regions of η>10.94 and 8.99>η>8.81, measured by the LHCf experiment with proton–proton collisions at s=13TeV. The results from the analysis of 0.191nb−1 of data obtained in June 2015 are compared to the predictions of several hadronic interaction models that are used in air-shower simulations for ultra-high-energy cosmic rays. Although none of the models agree perfectly with the data, EPOS-LHC shows the best agreement with the experimental data among the models.

Measurement of photon production cross sections also in association with jets with the ATLAS detector

The production of prompt isolated photons at hadron colliders provides a stringent test of perturbative QCD and can be used to probe the proton structure. The production of prompt photons in association with jets provides an additional testing ground for perturbative QCD with a hard colourless probe less affected by hadronisation effects than jet production. At the LHC, the ATLAS collaboration has performed precise measurements of the inclusive production of isolated prompt photons at a centre-of-mass energy of 13 TeV. The dynamics of isolated-photon plus jet production in pp collisions at a centre-of-mass energy of 8 TeV have also been measured. In addition, the integrated and differential cross sections for isolated photon pairs at a centre-of-mass energy of 8 TeV have been measured. The results are compared with state-of-the art theory predictions at next-to-leading order in perturbative QCD.

Direct Photon Production in Pion-Proton Collisions

In this article we calculate the contribution of the higher-twist Feynman diagrams to the large-pT inclusive single direct photon production cross section in πp collisions in case of the running coupling and frozen coupling approaches within holographic QCD. We determined the structure of infrared renormalon singularities of the higher-twist subprocess cross section. Also compared and analyzed the resummed higher-twist cross sections with the ones obtained in the framework of the frozen coupling approach.

Predictions for the Isolated Prompt Photon Production at the LHC ats= 13 TeV

The prompt photon production in hadronic collisions has a long history of providing information on the substructure of hadrons and testing the perturbative techniques of QCD. Some valuable information about the parton densities in the nucleon and nuclei, especially of the gluon, can also be achieved by analysing the measurements of the prompt photon production cross section whether inclusively or in association with heavy quarks or jets. In this work, we present predictions for the inclusive isolated prompt photon production in pp collisions at center-of-mass energy of 13 TeV using various modern PDF sets. The calculations are presented as a function of both photon transverse energyETγand pseudorapidityηγfor the ATLAS kinematic coverage. We also study in detail the theoretical uncertainty in the cross sections due to the variation of the renormalization, factorization, and fragmentation scales. Moreover, we introduce and calculate the ratios of photon momenta for different rapidity regions and study the impact of various input PDFs on such quantity.

Precision QCD measurements in DIS at HERA

New and recent results on QCD measurements from the H1 and ZEUS experiments at the HERA ep collider are reviewed. The final results on the combined deep-inelastic neutral and charged current cross-sections are presented and their role in the extractions of parton distribution functions (PDFs) is studied. The PDF fits give insight into the compatibility of QCD evolution and heavy flavor schemes with the data as a function of kinematic variables such as the scale Q2. Measurements of jet production cross-sections in ep collisions provide direct proves of QCD and extractions of the strong coupling constants are performed. Charm and beauty cross-section measurements are used for the determination of the heavy quark masses. Their role in PDF fits is investigated. In the regime of diffractive DIS and photoproduction, dijet and prompt photon production cross-sections provide insights into the process of factorization and the nature of the diffractive exchange.

Fast-neutron Induced Reactions at the nELBE Time-of-flight Facility

The compact neutron-time-of-flight facility nELBE at the superconducting electron accelerator ELBE of Helmholtz-Zentrum Dresden-Rossendorf is being rebuilt and extended with a low-background experimental hall. The neutron radiator consists of a liquid lead circuit without additional neutron moderators. The useful neutron spectrum extends from some tens of keV to about 10 MeV. nELBE is intended to deliver cross section data of fast-neutron nuclear interactions e.g. for the transmutation of nuclear waste and improvement of neutron physical simulations of innovative nuclear systems. Before the extension of the facility, the photon production cross section of 56Fe was measured with an HPGe detector and the inelastic neutron scattering cross section to the first few excited states in 56Fe was determined. The neutron total cross sections of Au and Ta were determined in the energy from 200 keV to 7 MeV in a transmission experiment.

Measurement of inclusive top pair plus photon production cross-section

Measurement of inclusive top pair plus photon production cross-section

Coulomb corrections to photon and dilepton production in high-energypAcollisions

We consider particle production in high energy pA collisions. In addition to the coherent interactions with the nuclear color field, we take into account coherent interactions with the nuclear electromagnetic Coulomb field. Employing the dipole model, we sum up the leading multiple color and electromagnetic interactions and derive inclusive cross sections for photon and dilepton production. We found that the Coulomb corrections are up to $10\%$ at $\sqrt{s}=200$~GeV per nucleon.

Higher-twist effects in the direct photon production and the role of infrared renormalons

We calculate the contribution of the higher-twist effects to the large-${p}_{T}$ inclusive single direct photon production cross section in $\ensuremath{\pi}p$ collisions in the running coupling and frozen coupling approaches within holographic QCD. We obtain the structure of infrared renormalon singularities of the higher-twist subprocess cross section. For a full analysis we compare the resummed higher-twist cross sections with the ones obtained in the framework of the frozen coupling approach and leading-twist cross section.

A direct probe of the in-medium pn scattering cross section

Hard photon production from neutron–proton bremsstrahlung in intermediate energy heavy-ion reactions is examined as a probe of the in-medium pn scattering cross section within a transport model. Uncertainty of photon production probability pn→pnγ is cancelled out by using the ratio of hard photon spectra RC12+C12/p+n(γ) from two reactions. The in medium pn scattering cross section is constrained by using the ratio of hard photon production cross sections of proton-induced reactions p+C12 and p+H2. A reduction factor σpnmedium/σpnfree of about 0.5–0.7 around saturation density is obtained by comparing with the existing experimental data.