30-GeV Proton Research Articles

Study of nucleon structure using hadron beam at J-PARC

Recently, 30-GeV proton beam became available at the high momentum beamline of the J-PARC Hadron Experimental Facility. A following project of beamline upgrade will make available negative and positive secondary π/K/p beam up to 20 GeV/c. We will study the nucleon partonic structure utilizing the high-momentum hadron beams. The generalized parton distributions (GPDs) of nucleon can be accessed by various single diffractive hard exclusive processes (SDHEPs): a pure hadronic process (p + p → p + π + B), a diphoton production process (π− + p → γ + γ + n), and an exclusive Drell-Yan process (π− + p → μ+ + μ− + n). Measurements of these reactions give complementary information of nucleon GPDs to one from lepton-induced exclusive reactions.

Design Study of Superconducting Transmission Line Magnet for J-PARC MR Upgrade

In order to enhance the beam efficiency of the J-PARC main ring, installation of a new ring is being considered. The new ring, which can accommodate up to 30-GeV proton beam, enables to operate the fast and slow extractions simultaneously with the maximum throughput. Use of superconducting transmission line magnets is proposed as bending magnets for the new ring. Design study of the magnets has started. This paper reports on the brief concept of the new ring, requirements to the magnets, and the status of the design study.

New results from T2K

The T2K experiment is a 295-km long-baseline neutrino experiment in Japan employing an off-axis muon neutrino beam with a ~ 0.6 GeV peak energy. The beam, produced from 30-GeV protons at the J-PARC complex on the Pacific coast, is directed to the Super-Kamiokande detector. T2K released the first long-baseline measurement of a nonzero value for the θ 13 mixing parameter through the observation of electron neutrino appearance (vµ → ve ) and produced the most precise measurement of θ 23 through the observation of muon neutrino disappearance (vµ → vµ ). T2K data, in combination with reactor experiments, also excludes at 90% C.L. a significant region of the Dirac CP phase: δ CP CP > -0.49(-0.98) for the normal (inverted) hierarchy. A full joint appearance and disappearance fit including both neutrino (7×1020 protons on target, PoT) and anti-neutrino (4 × 1020 PoT) data and, for the first time, a constraint from water target data in the near detector, is presented yielding improved sensitivity on δ CP and improved precision on sin2 2θ 23 and the atmospheric mass splitting.

Monitoring System for the Gold Target by Radiation Detectors in Hadron Experimental Facility at J-PARC

At the Hadron Experimental Facility in J-PARC, we inject a 30-GeV proton beam into a gold target to produce secondary particle beams required for various particle and nuclear physics experiments. The gold target is placed in a hermetic chamber, and helium gas is circulated in the chamber to monitor the soundness of the target. The radioactivity in helium gas is continuously monitored by gamma-ray detectors such as a germanium detector and a NaI(Tl) detector. Beam operations with those target-monitoring systems were successfully performed from April to June and October to December 2015, and from May to June 2016. In this paper, the details of the helium gas circulation system and gamma-ray detectors and the analysis results of the obtained gamma-ray spectra are reported.

Development of Lambertson Magnet and Septum Magnets for Splitting 30-GeV Proton Beam in Hadron Experimental Facility at J-PARC

We developed a Lambertson magnet and two septum magnets as the splitting devices for the new beamline at the Hadron Experimental Facility in J-PARC. This new beamline, now under construction, is called high-p/COMET beamline, and the experiments using 30- and 8-GeV proton beams are planned. The required functions of the splitting devices are as follows: to split a small fraction (around 10−4) of the 30-GeV proton beam into the high-p/COMET beamline (30-GeV mode) and to bend all of the 8-GeV proton beam into the high-p/COMET beamline (8-GeV mode). These two requirements are met by adjusting the vertical beam position at the entrance of the Lambertson magnet. In 30-GeV mode, the Lambertson magnet is used to scrape the beam halo of the proton beam and bend the beam into the high-p/COMET beamline. The beam loss at the Lambertson magnet is inevitable; thus, the magnet must be resistant to the radiation and heat caused by the beam loss. The magnet is composed of nonorganic materials only and equipped with two water pipes to remove the heat induced by the beam loss. The branched beam is bent further by two septum magnets at the downstream of the Lambertson magnet. The construction and the magnetic field measurements of these devices were completed in March 2015, and the installation into the beamline is planned for the summer of year 2017.

The electronics, online trigger system and data acquisition system of the J-PARC E16 experiment

The J-PARC E16 experiment was proposed to investigate the restoration of chiral symmetry at the normal nuclear density. E16 will systematically measure in-medium mass of vector mesons at J-PARC Hadron Experimental Facility using a 30-GeV proton beam with an intensity of 2 x 1010 protons per pulse. The E16 spectrometer was designed to detect e+e- from slowly moving vector meson, particularly the ϕ meson. The detector system consists of GEM tracker, Gas Cerenkov detector based on GEM and electromagnetic calorimeter made of lead-glass, whose number of channels reaches about 100,000 in total. The readout electronics, trigger system and data acquisition system for the detectors have been developed, for which level-1 trigger rate of 1-2 kHz is required under several 10 MHz interaction rate. The preparation is underway for the first beam time in 2017.

Summary of the Latest Results and Future Prospects from the T2K Experiment

The T2K long-baseline experiment is located in Japan and is designed to study oscillations of muon neutrinos. T2K obtains a beam of muon neutrinos peaked at 0.6 GeV that are produced at J-PARC accelerator complex by converting a beam of 30-GeV protons hitting a graphite target. Upon traveling 295 km, neutrinos are detected by the Super-Kamiokande (SK) water Cherenkov detector. Located at 280 m from the target, the near detector complex (ND280) provides information about un-oscillated neutrino flux, beam stability and interaction cross-sections. The T2K experiment observed electron neutrino appearance at SK with the significance of 7.3σ and measured the associated oscillation parameter θ13 for both normal and inverted mass hierarchies. In addition, by looking at muon neutrino disappearance T2K provided improved measurements of the θ23 and Δm232 parameters. The results of these measurements are presented as well as a brief summary of the selected neutrino cross-section measurements. Future prospects of the T2K experiment are discussed.

Optical transition radiation monitor for the T2K experiment

An optical transition radiation monitor has been developed for the proton beam-line of the T2K long baseline neutrino oscillation experiment. The monitor operates in the highly radioactive environment in proximity to the T2K target. It uses optical transition radiation, the light emitted from a thin metallic foil when the charged beam passes through it, to form a two-dimensional image of the 30GeV proton beam profile in the transverse plane. One of its key features is an optical system capable of transporting the light over a large distance out of the harsh environment near the target to a lower radiation area where it is possible to operate a camera to capture this light. The monitor measures the proton beam position and width with an accuracy better than 0.5mm, meeting the physics requirements of the T2K experiment.

Particle production for a muon storage ring II. Radiation loads

Efficient production and collection of a large number of muons is needed to make a neutrino factory based on a muon storage ring viable. Results of extensive MARS simulations for 2–30GeV protons on various targets in a 20T hybrid solenoid followed by a matching section and decay channel are reported. Part II describes radiation loads on targets, capturing system and shielding.

Particle production for a muon storage ring I. Targetry and π/μ yield

Efficient production and collection of a large number of muons is needed to make a neutrino factory based on a muon storage ring viable. Results of extensive MARS simulations for 2–30GeV protons on various targets in a 20T hybrid solenoid followed by a matching section and decay channel are reported. Part I describes pion and muon yields, targetry issues, and beam energy and power considerations. Part II describes radiation loads on targets, the capturing system and shielding.

Acoustic signals of nonthermal origin from high energy protons in water

Acoustic pulses generated by the passage of 30-GeV protons through water show evidence for the presence of a nonthermal source. In addition to the bipolar leading-compression signal expected from thermal shock, a tripolar leading-rarefaction component is observed. The component is dominant at 4°C, where the thermal signal should vanish. A space-charge effect may be the source of this component, since other proposed mechanisms leading to tripolar pulses should give a leading-compression signal.

Low-temperature 30 GeV-proton effects on critical properties of type-II superconducting filamentary conductors

The highlights of the results of four irradiation runs at 4.2 K using 30-GeV protons on six specimens each run are reported. In situ critical-current measurements were made as a function of fluence and various annealing procedures in applied fields up to 40 kG. Filamentary wire specimens of NbTi, Nb 3Sn and V 3Ga were investigated. Reductions of I c in NbTi up to 18% were observed with tecovery of 50–60% observed upon annealing to room temperature. The suppression mechanism is proposed to be “magnetic” in nature rather than microstructural and is coupled to changes in the normal-state resistivity. Nb 3Sn exhibits up to 98% reduction in I c for 1.6 × 10 18 p/ cm 2 with recovery that is dependent upon the fluence. More relative recovery is observed for low fluences than for higher ones. This is interpreted to be due to the higher ratio of Frenkel pair defects available for recovery at low fluences to antisite defects produced directly in the initial damage events. At all fluences, however, the recovery of I c in Nb 3Sn is small when compared with that of NbTi.

Effects of 30-GeV-proton irradiation on the critical currents of NbTi multifilament wire

Multifilamentary wires of NbTi have been irradiated at 4.2 K with 30-GeV protons and the changes in critical current Ic measured in situ in fields up to 4 T. Reductions of Ic of 20% were found for a fluence of 1.5×1018 p/cm2. Annealing to room temperature recovers 60–70% of the Ic degradation. The decrease in Ic is attributed to an increase in the Ginzburg-Landau parameter κ of cell cores relative to the dislocation cell walls, thereby lowering the pinning strength of the cell walls. This increase in κ is directly related to an increasing radiation-induced normal-state resistivity. A saturation of the decreases in Ic is indicated for low-temperature proton irradiation in keeping with an observed saturation following high-fluence ambient-temperature neutron irradiation. Evidence is presented indicating that multiple annealing over the fluence life of a NbTi magnet operating in a radiation field will minimize the accumulated reduction in Ic.

Search for MoreJParticles

We report here on an experiment done at the 30-GeV proton synchrotron at Brookhaven National Laboratory using a large-acceptance ($delta$m=1 GeV) pair spectrometer with a mass resolution of plus-or-minus5 MeV, to search for additional long-lived particles which decay into K$sup -$$pi$$sup +$, K$sup +$$pi$$sup -$, pp, K$sup +$K$sup -$, $pi$$sup +$$pi$$sup -$, K$sup -$p, $pi$$sup - $p, K$sup +$p, or $pi$$sup +$p. The result, based on 2times10$sup 7$ events, shows that, to a sensitivity comparable to or lower than the production of J particles (production) times (decay branching ratio) approx. =10$sup -34$ cm$sup 2$, no additional states were found.

Observation of Muon Pairs in High-Energy Hadron Collisions

Muon pairs with effective masses between 1 GeV/c/sup 2/ and 6.5 GeV/c/ sup 2/ have been observed in the collisions of 30-GeV protons with a uramium target. The production cross section was seen to vary smoothly with mass exhibiting no resonant strtucture. Data were taken at incident proton emergies of 22, 25, 28.5, and 29.5 GeV. Within the experimental aperture the total cross section increased with energy by a factor of 5. The experimental results are compared with the predictions of several theoretical models. Limits are presented for the contributions to the signal from both massive muon-pair resonances and antiproton-proton annihilation. Implications are presented for higher-energy accelerators, using current ideas involving scaling. (auth)

Half-lives of 83Y and 83Sr

Yttrium-83 was produced by the spallation of silver with 30-GeV protons and also by the 84Sr( p, 2n) 83Y reaction with 39-MeV protons. The half-life of 83Y was determined by means of successive 83Sr daughter separations, and a value of 7·4 ± 0·1 min was obtained. In these experiments the half-life of 83Sr has been re-determined as 32·4 ± 0·2 hr.

Production of Tritons, Deuterons, Nucleons, and Mesons by 30-GeV Protons on A1, Be, and Fe Targets

The momentum spectra of particles emerging at 30\ifmmode^\circ\else\textdegree\fi{} to a 30-GeV proton beam impinging upon various targets were measured using time-of-flight techniques. Intensities of protons, antiprotons, $\ensuremath{\pi}$ mesons, $K$ mesons, deuterons, and tritons in the range 1 to 3 GeV/c are given. Particular attention is given to the tritons and deuterons emitted from the different targets. Possible mechanisms for their production are discussed.

Energy Dependence of Product Yields in Copper Spallation by Protons between 3 and 30 GeV

Careful comparisons of cross sections for formation of 19 products of copper spallation by 3- and 30-GeV protons indicate only a small energy dependence in this energy range. As the energy is increased from 3 to 30 GeV, products of $A>40$ decrease in yield by 15% or less, except for some highly neutron-deficient species, while low-mass products increase in yield by 10 to 50%. These findings are somewhat at variance with earlier reports from CERN.