Forward Cross Section Research Articles

Dynamical studies for the S+ + D2(v0 = 2, j0 = 0) → SD+ + D reaction by time-dependent wave packet

Using time-dependent wave packet method, the dynamics studies of the S+ + D2(v0 = 2, j0 = 0) → SD+ + D reaction were carried out based on the potential energy surface (PES) reported by Zhu et al., (Phys. Chem. Chem. Phys.23 4757–4767 (2021)). The isotope effect is very obvious. When the H atom is replaced by the D atom, the reaction probability at total angular momentum equal to zero has a threshold of about 0.28 eV and it decreases significantly in the collision energy range studied. The total and rovibrational state-resolved integral cross section were reported and the results indicate that the distribution of integral cross section is mainly concentrated in the ground state. The forward biased differential cross sections show that the stripping mechanism due to high total angular momentum plays a dominant role in the reaction.

Single inclusive jet production in pA collisions at NLO in the small-x regime

We present the first complete next-to-leading-order (NLO) prediction with full jet algorithm implementation for the single inclusive jet production in pA collisions at forward rapidities within the color glass condensate (CGC) effective theory. Our prediction is fully differential over the final state physical kinematics, which allows the implementation of any infra-red safe observable including the jet clustering procedure. The NLO calculation is organized with the aid of the observable originated power counting proposed in [1] which gives rise to the novel soft contributions in the CGC factorization. We achieve the fully-differential calculation by constructing suitable subtraction terms to handle the singularities in the real corrections. The subtraction contributions can be exactly integrated analytically. We present the NLO cross section with the jets constructed using the anti-kT algorithm. The NLO calculation demonstrates explicitly the validity of the CGC factorization in jet production. Furthermore, as a byproduct of the subtraction method, we also derive the fully analytic cross section for the forward jet production in the small-R limit. We show that in the small-R approximation, the forward jet cross section can be factorized into a semi-hard cross section that produces a parton and the semi-inclusive jet functions (siJFs). We argue that this feature holds for generic jet production and jet substructure observables in the CGC framework. Last, we show numerical analyses of the derived formula to validate our calculations. We justify when the small-R approximation is appropriate. Like forward hadron production, the obtained NLO result also exhibits the negativity of the cross section in the large jet transverse regime, which signals the need for the threshold resummation. A sketch of the threshold resummation in the CGC framework is presented based on the multiple emission picture and it is found to agree with the approach using the rapidity renormalization group equation developed in [2].

Study on the influence of blade on electromagnetic scattering characteristics in the open-ended cavity

The aero engine intake is the most important and strongest scattering source of the combat aircraft in the forward area. The incident electromagnetic wave will directly illuminate the fan/compressor blades which would change the forward radar cross section (RCS) distribution of the intake. The influence of the internal blade geometry parameter, including blade number, blade stages and the angle between two-stage blades on the RCS of the open-ended cavity was obtained by using the method of moment with the multi-layer fast multipole. The results show that the mean RCS of the cavity decreases with the increasing blade number in the smaller detection angle range. The mean RCS of the cavity increases with the increasing blade stage which changes the transmission path of the incident electromagnetic wave inside the cavity. And compared with the cavity with only one blade, the mean RCS with three-stage blades increases by more than 55%. With the angle between the two-stage blades increasing, the mean RCS of the cavity decreases first and then increases.

Measurement of inclusive forward neutron production cross section in proton-proton collisions at sqrt{s}=13 TeV with the LHCf Arm2 detector

In this paper, we report the measurement relative to the production of forward neutrons in proton-proton collisions at sqrt{s}=13 TeV obtained using the LHCf Arm2 detector at the Large Hadron Collider. The results for the inclusive differential production cross section are presented as a function of energy in three different pseudorapidity regions: η > 10.76, 8.99 < η < 9.22 and 8.81 < η < 8.99. The analysis was performed using a data set acquired in June 2015 that corresponds to an integrated luminosity of 0.194 nb−1. The measurements were compared with the predictions of several hadronic interaction models used to simulate air showers generated by Ultra High Energy Cosmic Rays. None of these generators showed good agreement with the data for all pseudorapidity intervals. For η > 10.76, no model is able to reproduce the observed peak structure at around 5 TeV and all models underestimate the total production cross section: among them, QGSJET II-04 shows the smallest deficit with respect to data for the whole energy range. For 8.99 < η < 9.22 and 8.81 < η < 8.99, the models having the best overall agreement with data are SIBYLL 2.3 and EPOS-LHC, respectively: in particular, in both regions SIBYLL 2.3 is able to reproduce the observed peak structure at around 1.5–2.5 TeV.

Two-dimensional mapping of hydrogen and other elements in materials with microbeam-based transmission ERDA and PIXE

We report on the preliminary studies for two-dimensional (2D) mapping of hydrogen and other elements in materials with transmission ERDA and PIXE using a microbeam of 8 MeV 4He. The extremely enhanced forward recoil cross section of hydrogen in the non-Rutherford scattering allows 2D mapping of hydrogen in the sample. The mapping by PIXE, which provides complementary information to the mapping by ERDA, was obtained simultaneously. The present work probably leads to 3D mapping of hydrogen in bulk materials, i.e., the present spatial 2D plus depth as an additional dimension, since the energy of the outgoing hydrogen corresponds to the depth where the hydrogen is originally located.

First measurement of coherent ϕ -meson photoproduction from He4 near threshold

The differential cross sections and decay angular distributions for coherent ϕ-meson photoproduction from helium-4 are measured for the first time at forward angles with linearly polarized photons in the energy range Eγ=1.685–2.385GeV. Thanks to the target with spin-parity JP=0+, unnatural-parity exchanges are absent, and thus natural-parity exchanges can be investigated clearly. The decay asymmetry with respect to photon polarization is shown to be very close to the maximal value. This ensures the strong dominance (>94%) of natural-parity exchanges in this reaction. To evaluate the contribution from natural-parity exchanges to the forward cross section (θ=0∘) for the γp→ϕp reaction near threshold, the energy dependence of the forward cross section (θ=0∘) for the γHe4→ϕHe4 reaction is analyzed. The comparison to γp→ϕp data suggests that enhancement of the forward cross section arising from natural-parity exchanges and/or destructive interference between natural-parity and unnatural-parity exchanges is needed in the γp→ϕp reaction near threshold.Received 3 November 2017Revised 21 January 2018DOI:https://doi.org/10.1103/PhysRevC.97.035208©2018 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasParticle interactionsParticle productionPhotonuclear reactionsParticles & FieldsNuclear Physics

Forward Physics at CMS

Recent forward physics measurements performed with the CMS detector at the LHC are reviewed. The measurements of the pseudorapidity dependence of the energy and transverse energy density, inclusive energy spectrum in the very forward direction, and the very forward inclusive jet cross sections are presented. The results are also compared to the predictions of various models used to describe high energy hadronic interactions.

Anomalous Light Scattering by Topological PT-symmetric Particle Arrays.

Robust topological edge modes may evolve into complex-frequency modes when a physical system becomes non-Hermitian. We show that, while having negligible forward optical extinction cross section, a conjugate pair of such complex topological edge modes in a non-Hermitian -symmetric system can give rise to an anomalous sideway scattering when they are simultaneously excited by a plane wave. We propose a realization of such scattering state in a linear array of subwavelength resonators coated with gain media. The prediction is based on an analytical two-band model and verified by rigorous numerical simulation using multiple-multipole scattering theory. The result suggests an extreme situation where leakage of classical information is unnoticeable to the transmitter and the receiver when such a -symmetric unit is inserted into the communication channel.

Scattering of individual particles from cytometry: tests on phytoplankton cultures.

This study presents an application of the Cytosense flow cytometer (CytoBuoy b.v., NL) for the analysis of the optical properties of phytoplankton cells. For the first time, the forward, sideward and backward cross sections (σFSC, σSSC and σbb ) were derived for two species morphologically different (Chlamydomonas concordia and Thalassiosira pseudonana). The objective of this work is to check the validity of the estimates before any applications in the frame of marine optics studies. Thus, estimates of σFSC and σSSC are tested with radiative transfer computations as no in situ measurements are available. A synthetic database is built considering homogeneous, multi-layered spheres, aggregates and cylinders. Scanning electron micrographs were performed to investigate the cell morphology to simulate particles as close as possible to the real cells. This set of numerical results represents a valuable database for many kinds of applications dealing with marine optics. Comparisons showed that the Cytosense estimates for the cultures are consistent with values predicted by the theory. In average, more than 92% of the Cytosense estimates were encompassed by predicted values. The backscattering cross section and the backscattering efficiency were compared with in situ measurements found in the literature wherever possible. Results showed that σbb and Qbb estimations fall within the range of the referenced values.

Analysis on Target Detection and Classification in LTE Based Passive Forward Scattering Radar.

The passive bistatic radar (PBR) system can utilize the illuminator of opportunity to enhance radar capability. By utilizing the forward scattering technique and procedure into the specific mode of PBR can provide an improvement in target detection and classification. The system is known as passive Forward Scattering Radar (FSR). The passive FSR system can exploit the peculiar advantage of the enhancement in forward scatter radar cross section (FSRCS) for target detection. Thus, the aim of this paper is to show the feasibility of passive FSR for moving target detection and classification by experimental analysis and results. The signal source is coming from the latest technology of 4G Long-Term Evolution (LTE) base station. A detailed explanation on the passive FSR receiver circuit, the detection scheme and the classification algorithm are given. In addition, the proposed passive FSR circuit employs the self-mixing technique at the receiver; hence the synchronization signal from the transmitter is not required. The experimental results confirm the passive FSR system’s capability for ground target detection and classification. Furthermore, this paper illustrates the first classification result in the passive FSR system. The great potential in the passive FSR system provides a new research area in passive radar that can be used for diverse remote monitoring applications.

THREE-DIMENSIONAL GEOMETRY OF A CURRENT SHEET IN THE HIGH SOLAR CORONA: EVIDENCE FOR RECONNECTION IN THE LATE STAGE OF THE CORONAL MASS EJECTIONS

ABSTRACT Motivated by the standard flare model, ray-like structures in the wake of coronal mass ejections (CMEs) have been often interpreted as proxies of the reconnecting current sheet connecting the CME with the postflare arcade. We present the three-dimensional properties of a post-CME ray derived from white light images taken from three different viewing perspectives on 2013 September 21. By using a forward modeling method, the direction, cross section, and electron density are determined within the heliocentric distance range of 5–9 R ⊙. The width and depth of the ray are 0.42 ± 0.08 R ⊙ and 1.24 ± 0.35 R ⊙, respectively, and the electron density is (2.0 ± 0.5) × 104 cm−3, which seems to be constant with height. Successive blobs moving outward along the ray are observed around 13 hr after the parent CME onset. We model the three-dimensional geometry of the parent CME with the Gradual Cylindrical Shell model and find that the CME and ray are coaxial. We suggest that coaxial post-CME rays, seen in coronagraph images, with successive formation of blobs could be associated with current sheets undergoing magnetic reconnection in the late stage of CMEs.

Λc+/Λc−andΛb0/Λ¯b0production asymmetry at the LHC from heavy quark recombination

The asymmetries in the forward region production cross section of Lambda_c^+/Lambda_c^- and Lambda_b^0/\bar{Lambda}_b^0 are predicted using the heavy quark recombination mechanism for pp collisions at 7 TeV and 14 TeV. Using non-perturbative parameters determined from various previous experiments, we find that A_p(Lambda_c^+/Lambda_c^-) ~ 1-2% and A_p(Lambda_b^0/\bar{Lambda}_b^0) ~ 1-3% in the forward region covered by the LHCb experiment.

Recent CMS results on diffraction

Recent CMS results on diffraction are presented. These include the measurements of the soft diffractive cross sections, of the forward rapidity gap cross section, of the diffractive dijet cross section, the measurement of a large rapidity gap in W and Z boson events and the measurement of the pseudorapidity distribution of charged particles in a single diffractive enhanced sample. This last measurement is the first common result of the CMS and TOTEM collaborations. Some prospects of common CMS-TOTEM data taking are also discussed.

D±production asymmetry at the LHC from heavy quark recombination

The asymmetry in the forward region production cross section of D^\pm is calculated using the heavy-quark recombination mechanism for pp collisions at 7 TeV. By suitable choices of four non-perturbative parameters, our calculated results can reproduce those obtained at LHCb. We find A_p ~ -1% when integrated over 2.0 GeV < p_T < 18 GeV and 2.2< eta <4.75, which agrees with A_p=-0.96\pm0.26\pm0.18% as measured by LHCb. Furthermore, the calculated distributions in eta and p_T agree reasonably well with those obtained at LHCb.

Anomaly in the [formula omitted] photoproduction cross section off the proton at the [formula omitted] threshold

The γ+p→K0+Σ+ photoproduction reaction is investigated in the energy region from threshold to Eγ=2250 MeV. The differential cross section exhibits increasing forward-peaking with energy, but only up to the K⁎ threshold. Beyond, it suddenly returns to a flat distribution with the forward cross section dropping by a factor of four. In the total cross section a pronounced structure is observed between the K⁎Λ and K⁎Σ thresholds.

Measurements of forward energy flow and forward jet production with CMS

We present measurements of the forward (3 < |η| < 5) energy flow in minimum bias events and in events with either hard jets or W and Z bosons produced at central rapidities, as well as measurements of the inclusive forward jet cross section and of associated production of forward and central jets. Results are compared to MC models with different parameter tunes for the description of the underlying event and to perturbative QCD calculations, the PYTHIA and HERWIG parton shower event generators, as well as to the CASCADE Monte Carlo.

Fraunhofer diffraction by arbitrary-shaped obstacles

We consider Fraunhofer diffraction by an ensemble of large arbitrary-shaped screens that are randomly oriented in the plane of a wavefront and have edges of arbitrary shape. It is shown that far outside the main diffraction peak the differential scattering cross section behaves asymptotically as theta(-3), where theta is the diffraction angle. Moreover, the differential scattering cross section depends only on the length of the contours bordering the screens and does not depend on the shape of the obstacles. As both strictly forward and total diffraction cross sections are specified by obstacle area only, the differential cross section of size-distributed obstacles is expected to be nearly independent of obstacle shape over the entire region of the diffraction angles.

Measuring reversible photomechanical switching rates for a molecule at a surface

We have used single-molecule-resolved scanning tunneling microscopy to measure the photomechanical switching rates of azobenzene-derived molecules at a gold surface during exposure to UV and visible light. This enables the direct determination of both the forward and reverse photoswitching cross sections for surface-mounted molecules at different wavelengths. In a dramatic departure from molecular behavior in solution-based environments, visible light does not efficiently reverse the reaction for azobenzene-derived molecules at a gold surface.

Energy dependence of forward 1S0 diproton production in the [formula omitted] reaction

The pp→{pp}sπ0 differential cross section has been measured with the ANKE spectrometer at COSY-Jülich for seven proton beam energies Tp between 0.51 and 1.97 GeV. By selecting proton pairs with an excitation energy of less than 3 MeV it is ensured that the final {pp}s system is in the S01 state. In the measured region of θppcm≲18°, the data reveal a forward dip for Tp⩽1.4 GeV whereas a forward peaking is seen at 1.97 GeV. The energy dependence of the forward cross section shows a broad peak in the 0.6–0.8 GeV region, probably associated with Δ(1232) excitation, and a minimum at 1.4 GeV. Some of these features are similar to those observed for the spin–isospin partner reaction, pp→dπ+. However, the ratio of the forward differential cross sections of the two reactions shows a significant suppression of single pion production associated with a spin-singlet final nucleon pair.

Forward-jet production in deep inelastic ep scattering at HERA

Forward jet cross sections have been measured in neutral current deep inelastic scattering at low Bjorken-x with the ZEUS detector at HERA using an integrated luminosity of ${81.8 \rm pb}^{-1}$. Measurements are presented for inclusive forward jets as well as for forward jets accompanied by a dijet system. The explored phase space, with jet pseudorapidity up to 4.3 is expected to be particularly sensitive to the dynamics of QCD parton evolution at low x. The measurements are compared to fixed-order QCD calculations and to leading-order parton-shower Monte Carlo models.