Narrow Results

We examine the possibility of using single-Higgs production at an $e^{+}{e}^{-}$ collider with polarized beams to measure, or constrain, indirectly a possible anomalous triple-Higgs coupling, which can contribute to the process via one-loop diagrams. In the dominant process $e^{+}{e}^{-}\to ZH$, longitudinally polarized beams can lead to an improvement in the cross-section by 50% for $e^{-}$ and $e^{+}$ polarizations of $-0.8$ and $+0.3$, respectively. This corresponds to an improvement in the sensitivity to the triple-Higgs coupling of about 18% for a center-of-mass energy of 250 GeV and an integrated luminosity of 2 ab${}^{-1}$, making a strong case of beam polarization. This also implies that with polarized beams, the luminosity needed to get a particular sensitivity is less by about 33% as compared to that needed with unpolarized beams. Even when only the $e^{-}$ beam is polarized $-0.8$, the improvement in the sensitivity is about 8%. We also study the effect of longitudinal beam polarization on the sensitivity to the triple-Higgs coupling of Higgs production through the subdominant process $e^{+}{e}^{-}\to H\nu \bar{\nu }$ occurring through $WW$ fusion.

The helicity-dependent coherent π⁰-photoproduction in the reaction γd → π⁰d near the η-threshold is investigated. The calculations are performed within an approach which includes the reaction amplitudes of the impulse approximation (IA), two-step process with intermediate πN- and ηN-rescattering, and the higher order terms in the multiple scattering series for the intermediate ηNN interaction. The contribution of γd → π⁰d to the deuteron spin asymmetry is calculated and its contribution to the Gerasimov–Drell–Hearn (GDH) integral is explicitly evaluated by integration up to a photon energy of 900 MeV. In addition, the helicity E-asymmetry is calculated. The results revealed that the doubly polarized differential cross-sections and the helicity E-asymmetry are sensitive to the interference of rescattering effects, specially at photon energies 600–800 MeV and extreme backward pion angles. The sensitivity of the obtained results for the GDH integral to the choice of NN potential model governing the deuteron wave function is discussed. We find that the deviation among results obtained for the deuteron GDH integral using different deuteron wave functions is quite large.

Incoherent ${\pi }^{+}$-photoproduction on the deuteron is investigated for photon energies near threshold with particular focus on beam-target double spin asymmetries. The analysis is based on a $\gamma d\to {\pi }^{+}nn$ reaction model in which realistic elementary amplitudes for $\gamma N\to \pi N$, $NN\to NN$ and $\pi N\to \pi N$ are incorporated. Numerical results on all possible beam-target double spin asymmetries of the differential and total cross-sections in the photon energy region near threshold are presented. Effects of $NN$ and $\pi N$ final-state interactions are investigated and their roles are found to be important.

I review some accelerator physics topics for circular as well as linear colliders, considering both lepton and hadron beams.

We address the commissioning of the experimental equipment and the machine studies required for the first spin-filtering experiment with protons at the COSY ring in Jülich (Germany) at a beam kinetic energy of 49.3 MeV. The implementation of a low-beta insertion made it possible to achieve beam lifetimes of 8000 s in the presence of a dense polarized hydrogen storage cell target. The developed techniques can be directly applied to antiproton machines and allow for the determination of the spin-dependent pbar-p cross sections via spin-filtering.

In the main frame of the PAX (Polarized Antiproton eXperiments) collaboration, which engaged the challenging purpose of polarizing antiproton beams, the possibility to have H or D polarized targets requires a daily switchable source and its diagnostics: mainly change is a dual cavity tunable for H and D. The commissioning of PAX has been fullfilled, for the transverse case, on the COSY (COoler SYnchrotron) proton ring, achieving milestones on spin–dependent cross–section measurements. Now the longitudinal case could provide sensitive polarization results. An H or D source allows the exploration of the spin–filtering process with a deuterium polarized target, and opens new chances for testing Time Reversal Invariance at COSY (TRIC).

The polarized beam for RHIC is produced in the optically-pumped polarized H^- ion source and then accelerated in LINAC to 200 MeV for strip-injection to booster and further accelerated 24.3 GeV in AGS for injection in RHIC. In 2009 run polarized protons was successfully accelerated to 250 GeV beam energy. The beam polarization of about 60 % at 100 GeV beam energy and 36-42 % at 250 GeV energy was measured with the H-jet and p-carbon CNI polarimeters. The gluon contribution to the proton spin was studied in collisions of longitudinally polarized proton beams at 100×100 GeV. At 250×250 GeV an intermediate boson W production with the longitudinally polarized beams was studied for the first time.

We suggest starting an accelerator physics project called the Mainz Energy-recovering Superconducting Accelerator (MESA) as an extension to the experimental facilities at the institute for nuclear physics. MESA may allow us to introduce an innovative internal target regime based on the ERL principle. A second mode of operation will be to use an external polarized electron beam for parity violating experiments. Furthermore, MESA could also allow us to establish a CW source of polarized positrons.

We discuss polarizing a proton beam in a storage ring, either by selective removal or by spin-flip of the stored ions. Prompted by recent, conflicting calculations, we have carried out a measurement of the spin-flip cross section in low-energy electron-proton scattering. The experiment uses the cooling electron beam at COSY as an electron target. A re-analysis of the data leeds to reduced statistical errors, resulting in reduction by a factor of four of the upper limit for the spin-flip cross section. The measured cross sections are too small for making spin-flip a viable tool in polarizing a stored beam.

Based on the technique of fragmentation-induced spin polarization combined with the β-NMR method, we have conducted a series of ground-state nuclear-moment measurements in a region of light neutron-rich nuclei at RIKEN. The research has recently been extended also at GANIL. The ground-state studies will be further enhanced by the upgrade of RIPS proposed in the RIBF Phase-II program. Also, utilizing the technique of fragmentation-induced spin-orientation, nuclear-moment measurements of isomeric state were conducted. Remarkably, we have recently developed a method to produce highly spin-aligned RI beams in a new promising scheme. The method was first examined using BigRIPS, where a highly spin-aligned isomeric ^32mAl beam was successfully produced through the two-step projectile fragmentation reaction.

Quantum or torsion gravity models predict unusual properties of space-time at very short distances. In particular, near the Planck length, around 10⁻³⁵m, empty space may behave as a crystal, singly or doubly refractive. However, this hypothesis remains uncheckable for any direct measurement since the smallest distance accessible in experiment is about 10⁻¹⁹m at the LHC. Here I propose a laboratory test to measure the space refractivity and birefringence induced by gravity. A sensitivity from 10⁻³¹m down to the Planck length could be reached at existent GeV and future TeV energy lepton accelerators using laser Compton scattering. There are already experimental hints for gravity signature at distances approaching the Planck length by 5–7 orders of magnitude, derived from SLC and HERA data.

I review some accelerator physics topics for circular as well as linear colliders, considering both lepton and hadron beams.