KEK Proton Synchrotron Research Articles

EXTRACTION OF ΛΛ SCATTERING LENGTH

We determine ΛΛ scattering parameters from a ΛΛ invariant mass spectrum that was obtained by 12 C (K-, K+ΛΛ) reaction at the KEK Proton Synchrotron. In the framework of Watson's procedure, the obtained scattering length [Formula: see text] and effective range [Formula: see text] are most consistent with the values predicted by using the Nijmegen soft core models (NSC97's). However, the predicted values by using the Nijmegen hard-core ND ( G -matrix) and the extended soft-core (ESC00) models are out of two standard deviations from the determined scattering parameters.

Strangeness Nuclear Physics at J-PARC

The old KEK proton synchrotron, which was shut down in 2005, had played an important role for the development of strangeness nuclear physics together with the BNL AGS since 1990s. Here, I would like to pick up several important achievements.

PRODUCTION OF DOUBLE STRANGENESS HYPERNUCLEI IN 12C(K-,K+) REACTION AT 1.67 GeV/c

We have measured (K-,K+) reaction at 1.67 GeV/cK- at the KEK proton synchrotron. A scintillating fiber active target was employed to view both secondary interactions and decays of particles produced in the (K-,K+) reaction. This tracking capability for the vertex region provides us for studying the fate of Ξ- hypernuclei, which is advantageous over the previous two experiments. We present a preliminary result on the production cross sections for [Formula: see text], and also on the branching fractions into the decay modes with charged particles and/or Λ hyperon(s).

Adiabatic damping of the bunch length in the induction synchrotron

We observed that the bunch length decreases with acceleration in an induction synchrotron (IS) experiment, where a single proton bunch injected from a 500 MeV booster ring was accelerated to 6 GeV in the KEK proton synchrotron (KEK-PS). A novel technique that can be used to quantitatively predict the adiabatic phenomenon in barrier–bucket acceleration has been newly developed on the basis of a hypothesis that the particle oscillation amplitude varies inversely proportional to the square root of its oscillation frequency. This approach was verified by comparing the analytic prediction with experimental results which indicates that the bunch length in barrier–bucket acceleration does not continue to shrink, but reaches a constant value depending on the time duration between barrier voltages. It turns out that the experimental result and analytical prediction are in good agreement.

Medium modification of vector mesons observed in 12 GeV p+A reactions

The invariant mass spectra of e+e− pairs produced in 12 GeV p+A reactions are measured at the KEK Proton Synchrotron. We observed a significant enhancement over the known hadronic sources on the low-mass side of the ω meson peak for C and Cu data. The 95% CL allowed parameter regions for ρ/ω ratio are obtained as ρ/ω< 0.15 and ρ/ω< 0.31 for C and Cu targets, respectively. As for the ϕ meson, the data obtained with a Cu target revealed a significant excess on the low-mass side of the ϕ meson peak mainly in the βγϕ < 1.25 region.

Steering Beam of Charged Particles using Silicon Crystals

Two experiments on the deflection of electron and proton beams using silicon crystals were performed to study the channeling effect. An experiment on deflection of a 150-MeV electron beam by a crystal with the thickness of 16 µm was conducted at the REFER ring (Relativistic Electron Facility for Education and Research, Hiroshima University). The maximum deflection angle of 0.2 mrad was achieved. A 12-GeV proton beam was deflected by an 1-cm long crystal, which was bent at an angle of 32.6 mrad, at the KEK Proton Synchrotron. Results of these experiments are presented in this article. As for application, a possibility to create a deflection system for the J-PARC (Japan Proton Accelerator Complex) and a collimator for the ILC (International Linear Collider) are discussed as well.

In-medium ω meson mass and quark condensate in a Nambu–Jona-Lasinio model constrained by recent experimental data

We have determined the relation between the in-medium $\ensuremath{\omega}$ meson mass and quark condensate in the framework of a Nambu\char21{}Jona-Lasinio model constrained by some recent experimental data on the meson properties in nuclei. In addition to the usual four-quark interactions, we have included eight-quark terms in the Lagrangian. The parameters of this model have been determined using the meson properties in the vacuum as well as in the medium. More particularly, we have constrained both the in-medium pion decay constant to the value measured in experiments on deeply bound pionic atoms and the in-medium $\ensuremath{\omega}$ meson mass to the experimental value obtained either by the TAPS collaboration or by the E325 experiment at KEK Proton Synchrotron. Our results are compared to several scaling laws and in particular to that of G. E. Brown and M. Rho [(Phys. Rep. 398, 301 (2004)].

Experimental demonstration of the KEK induction synchrotron

Recent progress in the KEK induction synchrotron is presented. In the recent experiment, by using a newly developed induction acceleration system instead of radio-wave acceleration devices, a single proton bunch injected from the 500 MeV Booster ring and captured by the barrier bucket created by the induction step-voltages was accelerated to 6 GeV in the KEK proton synchrotron.

STUDY OF IN-MEDIUM MESON MODIFICATION IN 12 GeV p + A REACTIONS

Invariant mass spectra of low-mass vector mesons in the e+e- channel are measured in 12 GeV p + C and p + Cu reactions [Formula: see text] at the KEK Proton Synchrotron. Significant excess is observed at the low-mass side of ω meson peak over the known hadronic sources both in the C and Cu target data. Also below the ϕ meson peak, an excess is found in the Cu target data for slowly moving mesons whose βγ is less than 1.25. They can be interpreted as signatures of the spectral modification of vector mesons in cold nuclear matter.

Experimental Demonstration of the Induction Synchrotron

We report an experimental demonstration of the induction synchrotron, the concept of which has been proposed as a future accelerator for the second generation of neutrino factory or hadron collider. The induction synchrotron supports a superbunch and a superbunch permits more charge to be accelerated while observing the constraints of the transverse space-charge limit. By using a newly developed induction acceleration system instead of radio-wave acceleration devices, a single proton bunch injected from the 500 MeV booster ring and captured by the barrier bucket created by the induction step voltages was accelerated to 6 GeV in the KEK proton synchrotron.

First observation of ϕ-meson mass modification in nuclear medium

We have measured e + e − invariant mass spectra in 12 GeV p + A interactions at the KEK Proton-Synchrotron. The aim of the experiment is to detect possible in-medium modification of vector mesons at normal nuclear density. We used carbon and copper targets to study the nuclear size dependence of the e + e − invariant mass spectra. A significant enhancement on the low-mass side of the ϕ meson peak was observed in the low βγ region ( β γ ϕ 1.25 ) in the copper data. On the other hand, in the higher βγ region ( β γ ϕ > 1.25 ), both the spectral shapes obtained from carbon and copper targets were consistent with the expected one from the simulation. This observation is consistent with a picture of the ϕ modification in a nucleus, i.e. normal nuclear density, because such an effect should be visible only for slowly moving mesons produced in a larger nucleus.

Experimental Signature of Medium Modifications forρandωMesons in the 12 GeVp+AReactions

The invariant mass spectra of e+e- pairs produced in 12 GeV proton-induced nuclear reactions are measured at the KEK Proton Synchrotron. On the low-mass side of the meson peak, a significant enhancement over the known hadronic sources has been observed. The mass spectra, including the excess, are well reproduced by a model that takes into account the density dependence of the vector meson mass modification, as theoretically predicted.

Observation of the Acceleration of a Single Bunch by Using the Induction Device in the KEK Proton Synchrotron

A single rf bunch in the KEK proton synchrotron was accelerated with an induction acceleration method from the injection energy of 500 MeV to 5 GeV.

Flying wire beam profile monitors at the KEK PS main ring

Transverse beam profile monitors called “Flying Wires” have been installed and operated at the 12-GeV main ring of the KEK Proton Synchrotron. A carbon wire of 7μm in diameter scans the beam with a maximum speed of 20m/s and produces secondary particles from the beam–wire scattering. The minimum wire material and fast scanning speed have been chosen to achieve the precise profile measurement and minimum beam destruction because the requirements are critical for the lowest kinetic energy of 500MeV. The basic performance has been thoroughly tested. A new stroboscopic procedure has been established to reconstruct beam profiles that rapidly change with a time scale of 1ms or less. The monitors have demonstrated capability of obtaining profitable information for the mechanism of the halo formation and beam loss.

Beam study of irradiated ATLAS-SCT prototypes

Prototypes of ATLAS-SCT modules with ABCD readout chips were tested in a 4 GeV/ c pion beam at KEK's proton synchrotron. Of both SCT module geometries—barrel and forward—three identical modules were placed in the beam. One module of each type had been irradiated to 3×10 14 protons/cm 2 in the CERN PS previous to the beam test. A method has been developed to reconstruct the time-resolved shaper pulse from the binary hit information, allowing a more detailed study of the timing properties of the ABCD. The present results will be compared to a simulation of the charge collection and Front End electronics response.

Longitudinal impedance tuner using new material FINEMET

We designed an impedance tuner consisting of an inductive material, FINEMET, to cancel the space charge impedance in the longitudinal direction. It was installed in the KEK Proton Synchrotron (PS) main ring. We observed the frequency shift of the coherent quadrupole oscillations and inferred the shift of the incoherent synchrotron oscillation. The total reactive impedance can be estimated as the coefficient between the shift and the beam intensity. The measured impedance is reduced from −j2475Ω to −j1182Ω by the impedance tuner which consists of 12 pieces of FINEMET cores. We demonstrated that the space charge impedance is compensated by the impedance tuner. This is the first time for FINEMET to be equipped with an accelerator component. One may think that the characteristics of FINEMET deteriorate under an environment with strong radiation generated by unavoidable beam loss. We have proved that the radiation dose not affect FINEMET even with a total neutron dose of 1.83×1012(n cm−2), which is considered to be the highest dose of the main ring.

High-precision magnetic field mapping with a three-dimensional Hall probe for a T-violation experiment in K μ3 decay

High-precision magnetic-field mapping was performed for an experiment to search for a violation of time-reversal invariance in the K + → π 0 μ + ν μ decay at the KEK proton synchrotron. A commercially available three-dimensional Hall probe was used in conjunction with a specially designed mapping device and a goniometer system. Details concerning the measurement principle, calibration, actual measurements and analysis are described.

Microwave Instability at Transition Crossing: Experiments and a Proton-Klystron Model

Longitudinal bunch shapes in the KEK proton synchrotron were measured by a fast bunch-monitor system, which showed the rapid growth of the instability at the frequency of {approximately}1GHz and significant beam loss just after transition energy. Temporal evolution of the microwave instability is explained for the first time with a proton-klystron model. {copyright} {ital 1997} {ital The American Physical Society}

Space-charge-induced resonances in a synchrotron

We studied the space-charge-induced resonances in a low-energy proton synchrotron. Nonstructure as well as structure resonances are excited by linear and nonlinear space-charge forces. Taking the KEK proton synchrotron (PS) as a test lattice, we looked at the emittance growth as a whole beam due to those resonances by multi-particle tracking. The transverse phase advance was taken as a parameter. We found that both the space-charge-induced nonstructure and structure resonances affect the emittance in a synchrotron.

Performance studies of a lead-scintillation fiber calorimeter prototype for the linear collider detector

We constructed calorimeter modules composed of lead plates and scintillating fibers as an R&D program for the experiment at a future electron-positron linear collider. We tested the performance of the modules using electron and pion beams at the KEK proton synchrotron. The results of the beam tests are presented in this paper.