Session H11: Muon Colliders and Nu Beams

Muon Beam Cooling and Muon Collider Prospects

Progress in the theory and simulations of new cooling concepts and techniques has been substantial just in the last five years. New technologies that support high luminosity, high energy colliders have similarly shown great progress, especially in the development of high field magnets and RF cavities that can operate in the conditions of muon cooling channels. While these recent muon cooling developments have greatly improved the prospects for muon colliders, much work remains to achieve a complete design of a machine that could leap-frog the LHC to the next energy frontier. We report the status of muon cooling R{\&}D, including demonstration experiments, and outline the next steps to an energy frontier lepton collider.   

Muon Bunching and Phase-Energy Rotation for a Neutrino Factory and Muon Collider

We have developed scenarios for capture, bunching and phase-energy rotation of muons from a proton source, using high-frequency rf systems. The method captures a maximal number of muons into a string of rf bunches with initial application in the neutrino factory design studies. For a muon collider, these bunches must be recombined for maximal luminosity, and our initial design produced a relatively long bunch train. In this paper we present more compact scenarios that obtain a smaller number of bunches, and, after some optimization, obtain cases that are better for both neutrino-factory and collider scenarios. We also consider further modification by incorporating hydrogen gas-filled rf cavities for bunching and cooling. We describe these examples and consider variations toward an optimal factory + collider scenario.   

Plasma Lens for Muon and Neutrino Beams

The plasma lens is examined as an alternate to focusing horns and solenoids for use in a neutrino or muon beam facility. The plasma lens concept is based on a combined high-current lens/target configuration. The current is fed at electrodes located upstream and downstream from the target where pion capturing is needed. The current flows primarily in the plasma, which has a lower resistivity than the target. A second plasma lens section, with an additional current feed, follows the target to provide shaping of the plasma stability. The geometry of the plasma is shaped to provide optimal pion capture. Simulations of this plasma lens system have shown a 25{\%} higher neutrino production than the horn system. A plasma lens has additional advantage: larger axial current than horns, minimal neutrino contamination during antineutrino running, and negligible pion absorption or scattering. Results from particle simulations using a plasma lens will be presented.   

A New Concept of Liquid Lithium Lens for Muon Cooling

A new concept of liquid lithium lens is presented. The interest in the liquid lithium lens has been its potentially strong focusing for beam cooling, higher repetition rate than a few cycles per second and longer lifetime than solid lithium lens. Prototype liquid lithium lens for the Fermilab antiproton source was built and tested at BINP in Russia by G. Silvestrov and colleagues in the 1990s with some success, which circulated the liquid hot lithium using a liquid-metal pump. We present here a detailed conceptual design of the liquid lithium lens using push-pull action on the liquid lithium for circulation. The design and construction appears to be simple. We discuss the muon beam cooling possibility with this Li lens system.   

MANX, a 6-D Muon Cooling Experiment

The MANX experiment is to prove that effective six-dimensional (6D)~muon beam cooling can be achieved in a Helical Cooling Channel (HCC) using ionization-cooling with helical and solenoidal magnets in a novel configuration. The aim is to demonstrate that 6D muon beam cooling is understood well enough to plan intense neutrino factories and high-luminosity muon colliders. The experiment consists of the HCC magnets that envelop a liquid helium energy absorber, upstream and downstream instrumentation to measure the particle or beam parameters before and after cooling, and emittance matching sections between the detectors and the HCC. Studies are presented of the effects of detector resolution and magnetic field errors on the beam cooling measurements.   

Comparison of 6D Ring Cooler Schemes and Dipole Cooler for $\mu^{+} \mu^{-}$ Collider Development

We discuss the various schemes to use ring coolers for 6D cooling for $\mu ^{+} \quad \mu ^{-}$ colliders. The earliest successful cooler used dipoles and quadrupoles and a high dispersion low beta region. This was also proposed in the form of solenoids. Recently there have been many new ideas. The simplest is to use a simple dipole ring with high-pressure gas absorber or lithium hydride. We show the recent results of simulations and compare with the results for other cooler schemes.   

Muons Produced in a Beam Dump by 8 GeV and 120 GeV Incident Protons

When a high energy proton beam is stopped in a beam dump, muons typically emerge with momenta in the range of hundreds of MeV/c. The production rates, momentum spectra, spatial and angular distributions of muons emerging from various beam dump configurations have been studied using G4Beamline, a Geant4-based simulation program. In addition, calculated rates of surviving pions, protons, and neutrons will be presented. These results are intended to be useful for planning experiments that require a source of low energy muons, such as the MANX muon cooling experiment. The proton energies, 8 GeV and 120 GeV, correspond to those available at the Fermilab Booster and Main Injector, respectively.   

Intense Stopping Muon Beams

The study of rare processes using stopping muon beams provides access to new physics that cannot be addressed at energy frontier machines. The flux of muons into a small stopping target is limited by the kinematics of the production process and by stochastic processes in the material used to slow the particles. Innovative muon beam cooling techniques are being applied to the design of stopping muon beams in order to increase the event rates in such experiments. Such intense stopping beams will also aid the development of applications such as muon spin resonance and muon-catalyzed fusion.   

Colliding neutrino beams

Neutrino oscillation experiments tell us that neutrinos have mass. However, they don't tell us what mechanism is responsible for producing this neutrino mass. Current or planned neutrino experiments utilize neutrino beams and long-baseline detectors to explore flavor mixing but do not address the question of the origin of neutrino mass. In order to answer that question, neutrino interactions at much higher center-of-mass energies are required. I will describe several possibilities for neutrino beams to be used in colliding beam configurations.