Search

The spontaneous muonium to antimuonium conversion is one of the interesting charged lepton flavor violation processes. It serves as a clear indication of new physics and plays an important role in constraining the parameter space beyond Standard Model. MACE is a proposed experiment to probe such a phenomenon and expected to enhance the sensitivity to the conversion probability by more than two orders of magnitude from the current best upper constraint obtained by the PSI experiment two decades ago. Recent developments in the theoretical and experimental aspects to search for such a rare process are summarized., Comment: 13 pages, 10 figures, 3 tables, contribution to Snowmass 2021

The $\mu$E4-LEM beamline at Paul Scherrer Institute (PSI, Switzerland) is a special muon beamline combining the hyprid type surface muon beamline $\mu$E4 with the low energy muon facility (LEM) and delivers ${\mu}^{+}$ with tunable energy up to 30 keV for low-energy muon spin rotation experiments (LE-$\mu$SR). We investigate a possible upgrade scenario for the surface muon beamline $\mu$E4 by replacing the last set of quadrupole triplet with a special solenoid to obtain 1.4 times original beam intensity on the LEM muon moderator target. In order to avoid the muon beam intensity loss at the LEM spectrometer due to the stray magnetic field of the solenoid, three kinds of solenoid models have been explored and the stray field of the solenoid at the LEM facility is finally reduced to the magnitude of the geomagnetic field. A more radical design, "Super-$\mu$E4", has also been investigated for further increasing the brightness of the low energy muon beam, where we make use of the current $\mu$E4 channel and all sets of quadrupole triplets are replaced by large aperture solenoids. Together with the new slanted muon target E, at least 2.9 times the original muon beam intensity can be expected in the Super-$\mu$E4 beamline. Our work demonstrates the feasibility of upgrading surface muon beamlines by replacing quadrupole magnets with normal-conducting solenoids, resulting in higher muon rates and smaller beam spot sizes., Comment: 27 pages, 25 figures

Back-streaming neutrons from the spallation target of the China Spallation Neutron Source (CSNS) that emit through the incoming proton channel were exploited to build a white neutron beam facility (the so-called Back-n white neutron source), which was completed in March 2018. The Back-n neutron beam is very intense, at approximately 2*10^7 n/cm^2/s at 55 m from the target, and has a nominal proton beam with a power of 100 kW in the CSNS-I phase and a kinetic energy of 1.6 GeV and a thick tungsten target in multiple slices with modest moderation from the cooling water through the slices. In addition, the excellent energy spectrum spanning from 0.5 eV to 200 MeV, and a good time resolution related to the time-of-flight measurements make it a typical white neutron source for nuclear data measurements; its overall performance is among that of the best white neutron sources in the world. Equipped with advanced spectrometers, detectors, and application utilities, the Back-n facility can serve wide applications, with a focus on neutron-induced cross-section measurements. This article presents an overview of the neutron beam characteristics, the experimental setups, and the ongoing applications at Back-n., Comment: 11 pages, 9 figures

The Supper Proton-Proton Collider is a next-generation hadron collider that is now being designed. A baseline design aims for a peak luminosity of about 1*10^35 cm^-2 s^-1. The focus of this article is the effect of beam-beam interactions which are expected to strongly influence stability in the beams. We start with a discussion of a scheme to generate the crossing angles at the interaction points while also correcting the dispersion thus created. The optics constraints on the achievable \b{eta}* were studied. Weak-strong simulations were performed to study single particle dynamics via tune footprints, frequency map analysis and dynamic aperture calculations. The long-range interactions with the smallest separations are shown to determine the dynamic aperture. Empirical scaling laws for the dependence of the dynamic aperture on the transverse separations and on the number of long-range interactions are found. A tune scan shows several alternative working points with slightly better dynamic aperture than the baseline choice. Finally an option to significantly increase the dynamic aperture by increasing the crossing angle for different choices of \b{eta}* was studied., Comment: 21 pages,15 figures

The discovery of the neutrino mixing angle $\theta_{13}$ opens new opportunities for the discovery of the leptonic CP violation for high intensity neutrino beams. MOMENT a future neutrino facility with a high-power proton beam of 15 MW from a continuous-wave linac is focused on that discovery. The high power of the proton beam causes extreme radiation conditions for the facility and especially for the target station where the pion capture system of five superconducting solenoids is located. In this paper initial studies are performed for the effects of the radiation on the solenoid structure and the area surrounding it. A concept cooling system is also proposed., Comment: 7 pages, 24 figures, to be submitted to Chinese Physics C

The ADS accelerator in China is a CW (Continuous-Wave) proton linac with 1.5 GeV in beam energy, 10 mA in beam current, and 15 MW in beam power. To meet the extremely low beam loss rate requirement and high reliability, it is very important to study the beam halo caused by beam mismatch, which is one major source of beam loss. To avoid the envelope instability, the phase advances per period are all smaller than 90 degree in the main linac design. In this paper, the results of the emittance growth and the envelope oscillations caused by mismatch in the main linac section are presented. To meet the emittance growth requirement, the transverse and longitudinal mismatch factors should be smaller than 0.4 and 0.3, respectively., Comment: 6 pages, 9 figures

For the injector Scheme-I test stand of the China-ADS, a beam with the maximum power of 100 kW will be produced and transported to the beam dump. At the beam dump, the beam power will be converted to thermal load and brought away by the cooling water. Two measures are taken to deal with the huge power density at the target. One is to enlarge the contact area between the beam and the target, and this is to be accomplished by expanding the beam profile at the target and using two copper plates each having a 20o inclination angle relative to the beam direction. The other is to produce more homogenous beam profile at the target to minimize the maximum power density. Here the beam dump line is designed to meet the requirement of beam expansion and homogenization, and the step-like field magnets are employed for the beam spot homogenization. The simulations results including space charge effects and errors show that the beam line can meet the requirements very well at the three different energies (3.2 MeV, 5 MeV and 10 MeV). In the meantime, the alternative beam design using standard multipole magnets is also presented., Comment: 5 pages, 6 tables

Neutrino beam with about 300 MeV in energy, high-flux and medium baseline is considered a rational choice for measuring CP violation before the more powerful Neutrino Factory will be built. Following this concept, a unique neutrino beam facility based on muon-decayed neutrinos is proposed. The facility adopts a continuous-wave proton linac of 1.5 GeV and 10 mA as the proton driver, which can deliver an extremely high beam power of 15 MW. Instead of pion-decayed neutrinos, unprecedentedly intense muon-decayed neutrinos are used for better background discrimination. The schematic design for the facility is presented here, including the proton driver, the assembly of a mercury-jet target and capture superconducting solenoids, a pion/muon beam transport line, a long muon decay channel of about 600 m and the detector concept. The physics prospects and the technical challenges are also discussed., Comment: 18 pages, 16 figures, 3 tables

The China ADS (C-ADS) project is proposed to build a 1000 MW Accelerator Driven sub-critical System around 2032. The accelerator will work in CW mode with 10 mA in beam current and 1.5 GeV in final beam energy. The linac is composed of two major sections: the injector section and the main linac section. There are two different schemes for the injector section. The Injector-I scheme is based on a 325-MHz RFQ and superconducting spoke cavities of same RF frequency and the Injector-II scheme is based on a 162.5-MHz RFQ and superconducting HWR cavities of same frequency. The main linac design will be different for different injector choice. The two different designs for the main linac have been studied according to the beam characteristics from the different injector schemes., Comment: 7pages,17 figures, The paper is submitted to "Chinese Physics C"