大俘获立体角的内靶超导螺线管表面muon源的设计研究

高通量μ子源是国际上μ子科学研究的重要条件。在中国散裂中子源的高能质子应用区中,运用蒙特卡罗工具Geant4和G4beamline软件设计了使用内靶超导螺线管俘获高通量表面μ子的束线。与传统的分离靶和基于四极磁铁的收集系统相比,大孔径超导螺线管可以将收集效率提高两个量级。通过对不同靶材的粒子产率进行分析得出石墨是最佳靶材,然后比较俘获螺线管与束流的不同偏转角度下收集的表面μ的产率,提出了合理的较高产率的俘获和输运螺线管的设计方案,并与常规磁铁方案比较,最终在衰变螺线管端口的表面μ通量高达108/s。     

The Muon Science Facility at the JKJ Project

The muon science facility is one of the experimental arenas of the JKJ project, which was recently approved for construction in a period from 2001 to 2006, as well as neutron science, particle and nuclear physics, neutrino physics and nuclear transmutation science. The muon science experimental area is planned to be located in the integrated building of the facility for the materials and life science study. One muon target will be installed upstream of the neutron target in a period of phase 1. The beam line and facility are designed to allow the later installation of a 2nd muon target in a more upstream location. The detailed design for electricity, cooling water, primary proton beam line, one muon target and secondary beam lines (a superconducting solenoid decay muon channel, a dedicated surface muon channel, and an ultra slow muon channel) is underway. In the symposium, a latest status of the muon science facility at JKJ project will be reported. This revised version was published online in August 2006 with corrections to the Cover Date.     

Advanced muon radiography with compact accelerator system

By using a well-defined mono-energetic, pencil-like, high-energy and intense muon beam, one can realize, via simultaneous measurements of energy-loss and multiple-scattering, a quick and element-selective radiography to detect e.g. a few kg of U which is shielded in a thick Fe container or hidden within 2–3 m of low-Z material. A source of such an ideal beam of muons can be realized in transportable form via truck trailers, by combining a compact 400 MeV electron accelerator for photo π/μ production, a superconducting solenoid for full-solid-angle π/μ capture and transport, a stopping in hot tungsten metal for cooling of energetic μ⁺ to sub-eV μ⁺, and finally a compact linear accelerator for rapid acceleration to 600 MeV. Principle and some details are described.     

Construction of Riken-ral muon facility at ISIS and advanced μSR

By utilizing the intense pulsed proton beam available at the ISIS facility of RAL, the new muon facility project of an advanced superconducting muon channel funded by the RIKEN is now under construction. The new facility, by adopting the superconducting solenoid system, will produce the strongest backward decay pulsed ⁺ or ^–in the momentum range from 20 MeV/c to 120 MeV/c. Also, by adopting the pulsed magnetic kicker, each one of two muon pulses will be supplied to two extraction channels simultaneously. Various important muon science experiments including advanced pulsed ^–SR andmu ⁺SR experiments will be realized.     

Study of the hybrid state of Y9Co7(2.0≲T≲ 6 K) by means of zero field muon spin relaxation

Muon spin relaxation functions were measured in the magnetic superconductor Y₉Co₇ for T ? 2.0 K and at zero applied field. In the paramagnetic region (T ? 6.0 K) the depolarization of the muon spins is due to the quasi-static ⁵⁹Co nuclear moments. The onset of the magnetic state results in a fast-relaxing signal that corresponds to dipolar fields of the order of 100 0e; this component grows steadily in amplitude as the material transists from the hybrid into the superconducting state. The data are consistent with the high degree of inhomogeneity of the (not long-range) ordering and coexisting but non-competing magnetic and superconducting properties in the “hybrid” state (2<T<5K).     

Ultra slow muons generated by laser resonant ionization of thermal muonium produced by 500‐MeV protons with hot tungsten

We report recent progress to date on the UT‐MSL/KEK “Ultra Slow Muon” project, in which thermal muonium (Mu) atoms are generated from the surface of a hot tungsten target placed at the primary 500 MeV proton beam line and resonantly ionized by intense u.v. lasers synchronized with the emission of the Mu. The positive muon ionization fragments are collected by electrostatic beam optics to form a beam of slow positive muons. This revised version was published online in August 2006 with corrections to the Cover Date.     

Upgrading the RIKEN-RAL Muon Facility

We report a major upgrading work currently underway at the RIKEN-RAL Muon Facility. A slow muon beam line has been constructed at Port 3 experimental area in order to generate a low-energy, low-emittance positive muon beam, which will open many new possibilities for use of the muon beam. Meanwhile, a new experimental port is under construction to accommodate new experimental programs such as measurement of muonic X-rays from ions implanted to deuterium layer. This revised version was published online in August 2006 with corrections to the Cover Date.     

Angular distributions of muon pairs produced by negative pions on deuterium and tungsten

We present the angular distributions of high-mass muon pairs produced in a high-statistics experiment by 140 and 194 GeV/c π^? beams impinging on a tungsten target, and by 286 GeV/c π^? beam on deuterium and tungsten targets. We find no evidence for a center-of-mass energy dependence or a nuclear dependence of the angular distribution parameters. The two parameters λ and μ are found to be essentially independent of any kinematical variable. In contrast, the parameterv increase with the dimuon transverse momentumP _T , at variance with recent perturbative QCD predictions. Our statistics at largex ₁ are insufficient to substantiate the highertwist prediction.     

A New High-intensity, Low-momentum Muon Beam for the Generation of Low-energy Muons at PSI

At the Paul Scherrer Institute (PSI, Villigen, Switzerland) a new high-intensity muon beam line with momentum p < 40 MeV/c is currently being commissioned. The beam line is especially designed to serve the needs of the low-energy, polarized positive muon source (LE-μ⁺) and LE-μ SR spectrometer at PSI. The beam line replaces the existing μ E4 muon decay channel. A large acceptance is accomplished by installing two solenoidal magnetic lenses close to the muon production target E that is hit by the 590-MeV PSI proton beam. The muons are then transported by standard large aperture quadrupoles and bending magnets to the experiment. Several slit systems and an electrostatic separator allow the control of beam shape, momentum spread, and to reduce the background due to beam positrons or electrons. Particle intensities of up to 3.5 × 10⁸ μ⁺/s and 10⁷ μ⁻/s are expected at 28 MeV/c beam momentum and 1.8 mA proton beam current. This will translate into a LE-μ⁺ rate of 7,000/s being available at the LE-μ SR spectrometer, thus achieving μ⁺ fluxes, that are comparable to standard μ SR facilities.     

Data-driven performance evaluation method for CMS RPC trigger system using 2011 data at LHC

The compact muon solenoid (CMS) is one of the four experiments which is getting and analysing the results of the collision of protons at LHC. The CMS trigger system is divided into two stages, the level-1 trigger and high-level triggers, to handle the large stream of data produced in collision. The information transmitted from the three muon subsystems (DT, CSC and RPC) are collected by the Global Muon Trigger (GMT) Board and merged. A method for evaluating the RPC system trigger efficiency with data from pp collision was developed using the features of GMT. The results of the study with the real data of 2011 are shown and discussed here along with the comparison of Monte Carlo results.     

Excitation of the T> components of the giant dipole states in N > Z nuclei by muon capture

Muon capture on N > Z nuclei is proposed as a means of studying the T_> isospin component of giant dipole states. Calculations for nickel isotopes (except ⁵⁶Ni) indicate that these states are strongly excited by muon capture. Possible experiments to detect these states are discussed.     

Muon spin resonance by strong pulsed r.f. field with pulsed muons

Muon spin resonance experiments have been performed for the ⁺ in H₂O and for some other cases, and the first observation has been made of the time-differential pattern of muon spin resonance, namely, spin precession around the r.f. field vector under various resonance conditions. In the present experiment, a high-power pulsed r.f. field was effectively applied to the pulsed muon beam in our laboratory of the KEK-Booster Meson Facility (BOOM). Potential uses of muon spin resonance, particularly for research in the border regions of solid state and nuclear physics, are discussed in comparison with the conventional spin rotation method.     

Japanese hadron facility plans and future μSR

The proposed next major science project in Japan, the high intensity 1 GeV proton accelerator with unique beam characteristics, is described here. It will supply a proton beam of more than 100 μA in either de mode or sharply pulsed mode (down to 10 ns), using a specially designed time structure conversion ring. The beam will be used for keV μ⁺ generation at the production target, MeV surface μ⁺ production and 10 MeV decay μ⁺ and μ⁻ production, as well as a possible slow μ⁻ production. All of these unique muon beams will be developed for the next generation of μSR experiments. With the development of the keV μ⁺ source particularly in mind, a pilot station is now under construction at UT-MSL/KEK. Possible new μSR experiments are also reviewed.     

Study of the charge-exchange reactions\pi ^ - p \to (\pi ^0 ,\eta ,\eta \prime )n at 63 GeV

Muon electron pairs were detected in an Al multiplate spark chamber, exposed to a neutrino beam from the CERN PS. The leptons were not accompanied by other particles, except occasionally by protons. The background came mainly from muon associated π⁰ production, with one decay gamma lost. It was determined empirically, together with the small contribution from υ _e reactions. For electron energies above 2 GeV the background is 5.7±1.5 events, whereas 18 (μe)-candidates have been observed. Hence the effect is established, with a rate of about 10^?4 as compared to the muonic reactions above 3 GeV. Charm creation as the origin of this (μe)-production process is excluded; heavy neutral lepton production does not fit the kinematics observed. Instead the events are compatible with the two-body decay of an object with variable invariant mass of order 1 GeV, possibly resulting from axion interactions.     

Spin physics with COMPASS

COMPASS is a fixed target experiment at CERN studying nucleon spin structure in polarised deep inelastic muon nucleon scattering and hadron spectroscopy using hadron beams. The main goal of the COMPASS spin physics program is the measurement of the helicity contribution of the gluons to the nucleon spin, ΔG. This quantity is accessible via the photon-gluon-fusion process which can be selected by open charm production or production of hadron pairs with large transverse momenta. The spin physics program of COMPASS includes also measurements with a transversely polarised target. These allow to measure the transverse structure function.COMPASS has up to now successfully finished three runs with a muon beam of 160 GeV and a longitudinally polarized⁶LiD target in the years 2002, 2003 and 2004. An overview of the physics addressed by the muon program, with an emphasis on the ΔG/G measurement will be presented. The status of the analysis of the highpt hadron pairs, open charm, longitudinal and transverse asymmetries will be reviewed.     

Muon Motion Induced by a Superintense Laser in Muon‐Catalyzed Fusion

Considering the mixture after muon‐catalyzed fusion (μ CF) reaction as overdense plasma, we study muon motion in the plasma produced by a superintense linearly polarized femtosecond laser pulse. Muon drift along the propagation of laser radiation remains after the end of the laser pulse. At the peak laser intensity of 10²¹W/cm², muon goes from the skin layer into field‐free matter at short time which is much less than the pulse duration, before the laser pulse reaches its maximum. Besides, the influence of the laser on other particles in the plasma is less. Hence, this work can avoid muon sticking to alpha (α) effectively and reduce muon‐loss probability in μ CF. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Surface muon production in medium energy heavy ion reaction at RIKEN

A new type of beam transport system for secondary light charged particles (“Large Ω” Beam Course) has been constructed and used to transport surface muons from the decay of pions produced in heavy-ion reactions at RIKEN Ring Cyclotron (RRC). In an experiment carried out using a¹⁴N beam of 135 MeV/u and a carbon target of 0.9 g/cm² thickness, the surface muon intensity obtained in 5×5 cm² sample was around 100 1/s for 500 nA of the primary beam. This number may be increased by two orders if the energy were doubled.     

Beam chopper development at LAMPF

In order to reduce pileup limitations on μSR data rates, a fast chopper for surface muon beams was built and tested at LAMPF. The system allowed one muon at a time to be stopped in a μSR sample in the following way: A surface beam from the LAMPF Stopped Muon Channel was focused through a crossed-field beam separator and onto a chopper slit. With the separator E and B fields adjusted properly, the beam could pass through the slit. The beam to the μSR sample was turned on or off (chopped) rapidly by switching the high voltage applied to the separator plates on or off within approximately 500 ns; with the E field off, the B field deflected the beam, dumping it near the slit. We demonstrated that, with improved electronics, we will be able to stop a single muon in a μSR sample as frequently as once every 20 μs and that data rates for the system can be a factor of five higher than is attainable with unchopped beams. The observed positron contamination of the beam was less than five percent, and the ratio of the muon rate with beam on to the rate with beam off was 1540.     

A search for free quarks in deep inelastic muon scattering

A search was made at the CERN SPS for long-lived fractionally charged particles produced in deep inelastic muon interactions on a Be target using the existing muon beam line as a spectrometer. No such particles were found, leading to upper limits for the production cross section of the order of 10^?36 cm² for 200 GeV incident muon momentum and quark masses below 9 GeV for the $\text{2}\text{3}$ charge and 15 GeV for $\text{1}\text{3}$ charge.     

Second-order corrections to correlations in muon capture

Muon capture by a nucleus with an arbitrary spin is considered. Second-order terms in 1/M in the effective weak-interaction Hamiltonian are taken into account. New terms in the Hamiltonian associated with the nucleon-nucleus potential are found. A general expression for the angular distribution of neutrinos (recoil nuclei) is derived for polarized muons and oriented target nuclei. Second-order contributions to the amplitudes M _u (k) are obtained. This allows one to calculate second-order corrections to any integral and correlation characteristics in muon capture that are expressed in terms of M _u (k).