Proton Target Research Articles

Gluon Sivers function and transverse single spin asymmetries in e+p↑→γ+X

We present estimates of transverse single-spin asymmetry in prompt photon production in the scattering of low virtuality photons off a polarized proton target and discuss the possibility of using this as a probe to get information about the gluon Sivers function (GSF). Using a generalized parton model (GPM) framework, we estimate the asymmetries at electron-ion collider energy ($\sqrt{s}$ =140 GeV) taking into account both direct and resolved photon processes and find that the dominant contribution, up to $10\%$, comes from quark Sivers function (QSF) while the contribution from GSF is found to be up to $2\%$. However, upon taking into account the effects of the process-dependent initial and final state interactions through the color-gauge invariant generalized parton model approach we find that the situation is significantly changed, with near zero contributions from the QSFs and up to a $1\%$ level contribution from the \textit{f}-type GSF. Our results indicate that this process may be useful for distinguishing between GPM and color-gauge invariant generalized parton models and can be used as a good probe of \textit{f}-type GSF.

Proton RBE models: commonalities and differences

Uncertainties in the relative biological effectiveness (RBE) of protons remains a major barrier to the biological optimisation of proton therapy. While a constant value of 1.1 is widely used in treatment planning, extensive preclinical in vitro and in vivo data suggests that proton RBE is variable, depending on proton energy, target tissue, and endpoint. A number of phenomenological models have been developed to try and explain this variation, but agreement between these models is often poor. This has been attributed to both the models’ underlying assumptions and the data to which they are fit. In this brief note, we investigate the underlying trends in these models by comparing their predictions as a function of relevant biological and physical parameters, to determine where models are in conceptual agreement or disagreement. By doing this, it can be seen that the primary differences between models arise from how they handle biological parameters (i.e. and from the linear–quadratic model for photon exposures). By contrast, when specifically explored for linear energy transfer-dependence, all models show extremely good correlation. These observations suggest that there is a pressing need for more systematic exploration of biological variation in RBE across different cells in well-controlled conditions to help distinguish between these different models and identify the true behaviour.

Proton inelastic scattering in inverse kinematics as a mean for determining decay rates in continuum: The 9Be + p case

In this work we investigate whether it is feasible with proton inelastic scattering in inverse kinematics to quantify breakup decay rates, by observing the proton recoil in a full kinematics approach. Taking as example the 2.43 MeV excited state of 9Be, we perform an exclusive breakup measurement of 9Be incident on a proton target at an energy of 51 MeV. Two of the three cluster constituents (α and α) as well as the proton target recoil are recorded in a triple coincidence mode. As in other methods we have determined relative α−α and α−n, Q-value and 9Be excitation spectra, energy spectra for all fragments observed and non observed, reconstructed in a full kinematics approach. Additionally to that, we have obtained and concentrated on energy spectra of the proton recoil. The signature of the 9Be configurations were identified in bi-dimensional ΔE−E spectra (proton contour) and decay rates were determined for all three configurations He5+α, Be8+n and α+α+n. Finally a breakup cross section was deduced as σbreak=(142±20)mb. We conclude that proton inelastic excitation to continuum of Borromean light nuclei in inverse kinematics, may provide the mean for probing in the proton recoil spectra the decay rates through all cluster configurations. This involves extensive simulations with the implementation of the experimental conditions and of calculations describing the physics in continuum.

A modern Q-meter system to measure the polarization of solid polarized targets

Solid polarized targets are widely used in nuclear and particle physics experiments. Polarization measurements for these targets are normally performed using nuclear magnetic resonance (NMR). The Liverpool Q-meter was developed in the late 1970s and became the de facto standard for these NMR-based measurements. However, it has become increasingly difficult to obtain the required number of Q-meter channels, as the components have become obsolete. The Los Alamos National Laboratory (LANL) high energy nuclear physics (HENP) group has developed a new NMR-based Q-meter system, building upon the basic Liverpool design. The new Q-meter introduces several improvements, such as remote tuning and compact design, while being less costly to produce. These improvements have the potential to increase the accuracy of the polarization measurements, thereby reducing the experimental systematic uncertainties. This modern Q-meter has been successfully tested with both polarized proton and deuteron targets.

Antikaon-induced K1(1270)+ meson production on nuclei near threshold

We study the inclusive strange axial-vector meson K1(1270)+ production in K−A reactions at near-threshold laboratory incident antikaon momenta within a nuclear spectral function approach, which describes incoherent direct K1(1270)+ meson production in K− meson–proton K−p→K1(1270)+Ξ− production processes and accounts for three different options for its in-medium mass shift (or for its effective scalar potential) at central density ρ0. We calculate the absolute differential and total cross sections for the production of K1(1270)+ mesons on 12C and 184W target nuclei at laboratory angles of 0∘–45∘ by K− mesons with momenta of 2.5, 2.8 and 3.5 GeV/c, which are close to the threshold momentum (≈ 2.95 GeV/c) for K1(1270)+ meson production off the free target proton at rest. The intrinsic properties of carbon and tungsten target nuclei have been described in terms of their spectral functions, which take into account the momenta of target protons and the energies of their separation from the considered nuclei. We show that the differential and total (absolute and relative) K1(1270)+ antikaon-induced production cross sections at initial momenta not far from threshold – at momenta ∼ 2.8–3.5 GeV/c, at which there is yet no strong drop in their strength, reveal a distinct sensitivity to changes in the in-medium shift of the K1(1270)+ mass, studied in the paper, both in the K1(1270)+ meson low-momentum (0.1–1.0 GeV/c) and in its full-momentum ranges. This would permit evaluating this shift. Experimental data necessary for this aim can be obtained in a dedicated experiment at the J-PARC Hadron Experimental Facility.

Inclusive prompt photon-jet correlations as a probe of gluon saturation in electron-nucleus scattering at small x

We compute the differential cross-section for inclusive prompt photon+quark production in deeply inelastic scattering of electrons off nuclei at small x (e + A DIS) in the framework of the Color Glass Condensate effective field theory. The result is expressed as a convolution of the leading order (in the strong coupling αs) impact factor for the process and universal dipole matrix elements, in the limit of hard photon transverse momentum relative to the nuclear saturation scale Qs,A(x). We perform a numerical study of this process for the kinematics of the Electron-Ion Collider (EIC), exploring in particular the azimuthal angle correlations between the final state photon and quark. We observe a systematic suppression and broadening pattern of the back-to-back peak in the relative azimuthal angle distribution, as the saturation scale is increased by replacing proton targets with gold nuclei. Our results suggest that photon+jet final states in inclusive e + A DIS at high energies are in general a promising channel for exploring gluon saturation that is complementary to inclusive and diffractive dijet production. They also provide a sensitive empirical test of the universality of dipole matrix elements when compared to identical measurements in proton-nucleus collisions. However because photon+jet correlations at small x in EIC kinematics require jet reconstruction at small k⊥, it will be important to study their feasibility relative to photon-hadron correlations.

Global study of Be9 + p at 2.72A MeV

Background: In our recent experiment, $^9$Be+p at 5.67A MeV, the breakup decay rates to the 3 configurations, $\alpha$+$\alpha$+n, $^8$Be$^*$+n and $^5$He+$^4$He of $^9$Be, were observed and quantified, in a full kinematics approach. Unfolding step by step the accessibility to the above configurations, it will require similar studies at lower and higher energies as well as the interpretation of the data in a theoretical framework. Purpose: Investigate the breakup decay rate of $^9$Be+p at 2.72A MeV, where the $\alpha$+$\alpha$+n configuration is mainly accessible. Compare and interpret data at 2.72A MeV and 5.67A MeV into a 4-body CDCC formalism; Point out and discuss couplings to continuum. Methods: Our experimental method includes an exclusive breakup measurement in a full kinematic approach of $^9$Be incident on a proton target at 2.72A MeV, together with elastic scattering and other reaction channels measurements under the same experimental conditions. The interpretation of the data at 2.72A MeV and 5.67A MeV is considered in a 4-body CDCC approach, using the Transformed Harmonic Oscillator method for the 3-body projectile. Results: An elastic scattering angular distribution at 2.72A MeV is measured, which compares very well with CDCC calculations, indicating a strong coupling to continuum. At the same energy, the measured breakup and total reaction cross sections present good agreement with the calculated values. Further on, the elastic scattering and breakup cross section data at 5.67A MeV are found in very good agreement with the CDCC calculations. The present results support further our 3-body model for the structure of $^9$Be, validating relevant radiative reaction rates obtained previously.

Potential higher radial excitations in the light pseudoscalar meson family

Inspired by the event accumulation around 2.6 GeV in the $\eta^\prime\pi^+\pi^-$ invariant mass spectrum of $J/\psi\to \gamma \eta^\prime\pi^+\pi^-$, which was reported by the BESIII Collaboration, we carry out the study of the mass spectrum and decay behavior of four radial excitations in the pseudoscalar meson family, which include $\eta^{(\prime)}(6S)$ and $\eta^{(\prime)}(7S)$. Combining with these analysis, we present the calculation of the reactions induced by a pion or kaon on the proton target which are relevant to these four discussed states. According to this information, we give concrete experimental suggestion of searching for them, which will become a new task for future experiments.

Benchmarking Faddeev and transfer-to-the-continuum calculations for ( p,pN ) reactions

Nucleon-knockout reactions on proton targets (p, pN ) have experienced a renewed interest due to the availability of inverse-kinematics experiment with exotic nuclei. Various theoretical descriptions have been used to describe these reactions, such as the Distorted-Wave Impulse Approximation (DWIA), the Faddeev-type formalism and the Transfer to the Continuum method. Our goal is to benchmark the observables computed with the Faddeev and Transfer to the Continuum formalisms in the intermediate energy regime relevant for the experimental (p, pn) and (p, 2p) studies. In this paper, we analyze the 11 Be(p,pn)10Be reaction for different beam energies, binding energies and orbital quantum numbers with both formalisms to assess their agreement for different observables. We obtain a good agreement in all cases considered, within 10%, when the input potentials are taken consistently and realistically.

A clear signature of the breakup modes for 9Be on a proton target at 5.6 MeV/nucleon

The breakup of 9Be is studied via an inelastic scattering experiment on a proton target at 5.6 A MeV in inverse kinematics. Two of the three cluster constituents (α and α) as well as the proton target recoil were recorded in a triple coincidence mode allowing a full kinematics approach analysis. In this respect relative α - α and α - n, Q-value and 9Be excitation spectra, energy spectra for all fragments as well as the energy spectrum of the recoil proton were reconstructed. A clear signature of the two breakup sequential modes (5He + 4He and 8Be + n) was identified via the recoiling proton reconstructed spectra together with the direct breakup decay. A strong 5He + 4He mode was observed compatible with previous beta decay experiments.

Measurements of total reaction cross sections for 17Ne using a solid hydrogen target

We measured the energy dependence of the total reaction cross sections (σR) for the proton-drip-line nucleus,17Ne, using a solid hydrogen target. We compared the experimental data with theoretical calculations using the Glauber model. We found that the theoretical cross sections overestimate the experimental ones in the low-energy region (∼100A MeV), whereas they significantly underestimate the experimental data in the intermediate-energy region (∼300-500A MeV). These trends are the same as those for σR for carbon-proton collisions, which were measured previously. We discuss several possibilities for resolving this discrepancy. This work demonstrates the necessity of additional careful investigations of the energy dependence of σR for various nuclei on proton targets in order to determine nuclear size properties precisely.

Double polarisation observables G and E and helicity dependent cross section for single π 0 photoproduction off proton and neutron at MAMI

Meson photoproduction, like other photon-induced reactions, allow to study the excitation spectra of the nucleons and, in combination with the use of polarised beam and/or target, allow to determine the properties of the nucleon resonances by accessing many different polarisation observables with great accuracy. The A2 Collaboration, located at the MAMI facility in Mainz, used elliptically polarised photons on longitudinally polarised proton and deuteron targets, for energies up to 1.6 GeV. From the experimental data, it was possible to extract the double polarisation observables E and G on single π 0 photoproduction off the proton and the neutron. New precise results on the helicity-dependent total and differential cross sections on the deuteron were collected too.

Measurement of single-spin asymmetry for charged pions in the SPASCHARM experiment at U70 accelerator

The SPASCHARM experiment at U70 aims an exploration of a fundamental problem in modern particle physics, the role of spin in strong interactions. At present, the first physics data have been accumulated at a negative 28 GeV beam, interacting with a frozen polarized proton target. The SPASCHARM wide-aperture spectrometer can detect both charged and neutral particles in the large solid angle with 2π azimuthal coverage in the fragmentation region of beam-particles. It covers the kinematic region of non-perturbative quantum chromodynamics (QCD), where the theoretical predictions are difficult and unreliable due to the full strength quark confinement at low and medium momentum transfers. In this report, the current status of the experiment is presented. The algorithm for reconstructing charged tracks is discussed along with its results on real data and the comparison with the Monte Carlo (MC) simulations. Based on a real track reconstruction, the statistical errors for the measurements of single-spin asymmetries in inclusive charged pion production are estimated. The data analysis is in progress.

Production of pulsed high-energy neutron bursts from beam–target interaction using a 15 MeV HERMES III ion beam

Intense pulsed neutron fluences are generated by a high-energy (>10 MeV) proton beam using the beam-target method on the HERMES III facility at Sandia National Laboratories [J. J. Ramirez et al., in Proceedings of the 7th International Conference on High Power Particle Beams (Kernforschungszentrum, Karlsruhe GmbH, Karlsruhe, Germany, 1988), p. 148]. In order to generate the high-energy proton beam, a radial ion diode previously developed and fielded at the 6-MeV level in negative polarity was extended in performance to the 15-MeV level. This performance increase is described along with the development of a more durable hardware set to withstand the much more potent 15-MeV proton beam. An extensive series of simulations is developed to characterize the neutrons produced by the proton–target interaction. Particle-in-cell simulations describe the electron and ion dynamics, while Monte Carlo simulations characterize the neutron output. Due to differing estimates of proton beam voltage and current between the respective simulations, we make an approximate estimate of 13.5-MeV to 15-MeV and 120-kA ion beams at peak power in a 40 ns FWHM pulse. Simulations indicate that a total of 1.7 × 1013 neutrons are generated into 4π. Comparison of the neutron output predictions with a limited set of neutron flux measurements suggests a flux level of ∼1 × 1010 neutrons/cm2 to 10 × 1010 neutrons/cm2 over an approximately few tens of cm2 area at the relevant application location. This effort also contributes to physics understanding of the use of inductive voltage adder platforms to drive ion-beam diode loads.

New COMPASS results on kaon multiplicities from SIDIS

Preliminary COMPASS results on kaon multiplicities produced in semi-inclusive deep inelastic scattering of 160 GeV muons off a pure proton target are presented. The results constitute a data set of more than 600 data points, covering a large x, Q 2 and z domain in a fine binning with W > 5GeV/c2. The results from the sum of the z-integrated multiplicities M(K+)+M(K−) are presented versus x and compared to earlier COMPASS results on a deuteron target and to other experiments.In addition, we show the K−/K+ as well as /p multiplicity ratios measured for hadrons carrying a large fraction z of the virtual-photon energy, 0.5 < z < 1. The data were obtained using a 160 GeV muon beam and an isoscalar 6LiD target. For values of z larger than 0.8, the results contradict expectations obtained using the formalism of (next-to-) leading order perturbative quantum chromodynamics. In particular the data show a strong dependence upon the missing mass Mx , not expected from the calculations. The results suggest that additional corrections to the formalism may be required to take into account the phase space available for hadronization.

Feasibility studies for the measurement of single-spin asymmetry in inclusive K0 s production at pion beam at U-70

In the Spring 2018, the first physics data was accumulated in the new SPASCHARM experiment at U-70 accelerator of IHEP, Protvino. The first stage of SPASCHARM’s physics programs prursues the goal of studying spin effects in the beam fragmentation region at an unpolarized negative 28 GeV beam, interacting with a frozen polarized proton target. In this resport, the feasibility of measuring the single spin asymmetry AN in the reaction: π − + p↑→K 0 S + X is evaluated by Monte-Carlo simulations. We present estimates of the detection efficiency as well as for expected event statistics. It is shown that, in the process of interest above, the attainable statistical errors for AN would be at the scale of a few percents.

Total reaction cross section on a deuteron target and the eclipse effect of the constituent neutron and proton

Background: Eclipse effect of the neutron and proton in a deuteron target is essential to correctly describe high-energy deuteron scattering. The nucleus-deuteron scattering needs information not only on the nucleus-proton but also the nucleus-neutron interaction, for which no direct measurement of the nucleus-neutron cross sections is available for unstable nuclei. Purpose: We systematically evaluated the total reaction cross sections by a deuteron target to explore the feasibility of extracting the nucleus-neutron interaction from measurable cross sections. Methods: High-energy nucleus-deuteron collision is described by the Glauber model, in which the proton and neutron configuration of the deuteron is explicitly taken into account. Results: Our calculation reproduces available experimental total reaction cross section data on the nucleus-deuteron scattering. The possibility of extracting the nucleus-neutron total reaction cross section from nucleus-deuteron and nucleus-proton total reaction cross sections is explored. The total reaction cross sections of a nucleus by proton, neutron, and deuteron targets can be expressed, to good accuracy, in terms of the nuclear matter radius and neutron skin thickness. Incident-energy dependence of the total reaction cross sections is examined. Conclusions: The total reaction cross section on a deuteron target includes information on both the nucleus-neutron and nucleus-proton profile functions. Measuring the cross sections by deuteron and proton targets is a promising tool to extract the nuclear size properties.

Pion-induced production with baryon off proton target

In this work, the reaction is investigated with an effective Lagrangian approach. The contributions from the Born terms, including the s, t, and u channel, are considered, and the Regge model and the Feynman model are applied to treat the t-channel contribution. The existing experimental data can be reproduced with the best-fitted χ 2 being 2.38 and 1.54 for the Feynman and Regge models, respectively. Moreover, it is found that the contribution from the t channel is dominant in the cross-section. The contribution of the u channel is mainly distributed at backward angles, and the contribution from the s channel is small and negligible. In the Feynman model, the contribution of the t-channel K exchange is much larger than the contribution of the exchange, while in the Regge model the contribution of the t-channel K exchange is comparable to that of the exchange. Prediction about the differential cross-section of the reaction is also presented, which is helpful for clarifying the role of the Regge treatment. The current results suggest high-precision experimental measurements which can be performed at J-PARC and COMPASS.

The FOOT experiment

The main goal of the FOOT (FragmentatiOn Of Target) experiment is the measurement of the differential cross sections with respect to the energy and angle of the produced fragments in nuclear interactions between an ion beam, such as proton, Helium, Carbon, and different targets (proton, Carbon, Oxygen). Two important fields can benefit from these kind of measurements: firstly, in the 150 — 400MeV/u beam energy range, the data will be used to evaluate the nuclear fragmentation occurring in a standard hadrontherapy treatment and thus potential side effects. Secondly, in the 700 — 1000MeV/u beam energy range, the FOOT experiment aims at studying novel shields for spacecrafts involved in long term missions within the Solar System. The experiment has been funded by INFN since September 2017 and it is currently in its construction phase while the first data taking is scheduled by the end of 2020. A description of the experiment and a overview of expected performances and test beam results will be presented.

Relativistic corrections to the vector meson light front wave function

We compute a light front wave function for heavy vector mesons based on long distance matrix elements constrained by decay width analyses in the Non Relativistic QCD framework. Our approach provides a systematic expansion of the wave function in quark velocity. The first relativistic correction included in our calculation is found to be significant, and crucial for a good description of the HERA exclusive $\mathrm{J}/\psi$ production data. When looking at cross section ratios between nuclear and proton targets, the wave function dependence does not cancel out exactly. In particular the fully non-relativistic limit is found not to be a reliable approximation even in this ratio. The important role of the Melosh rotation to express the rest frame wave function on the light front is illustrated.