The ϕ meson production in small collision systems observed by PHENIX

The measurements of light hadron production in small collision systems (such as p+Al, p+Au, d+Au, 3He+Au) may allow to explore the quarkgluon plasma formation and to determine the main hadronization mechanism in the considered collisions. Such research has become particularly crucial with the observation of the light hadrons collective behavior in p/d/3He+Au collisions at √SNN = 200 GeV and in p+Al collisions at the same energy at forward and backward rapidities. Among the large variety of light hadrons, ϕ meson is of particular interest since its production is sensitive to the presence of the quark-gluon plasma. The paper presents the comparison of the obtained experimental results on ϕ meson production to different light hadron production in p+Al and 3He+Au at √SNN = 200 GeV at midrapidity. The comparisons of ϕ meson production in p+Al, p+Au, d+Au, and 3He+Au collisions at √SNN = 200 GeV at midrapidity to theoretical models predictions (PYTHIA model and default and string melting versions of the AMPT model) are also provided. The results suggest that the QGP can be formed in p/d/3He+Au collisions, but the volume and lifetime of the produced medium might be insufficient for observation of strangeness enhancement effect. Conceivably, the main hadronization mechanism of ϕ meson production in p+Al collisions is fragmentation, while in p/d/3He+Au collisions this process occurs via coalescence.

Concept of circular-linear energy recovery accelerator to probe the energy frontier

Energy-frontier accelerators provide powerful tools performing high precision measurements confirming the fundamentals of the physics and broadening new research horizons. Such machines are either driven by circular or linear accelerators. The circular machines, having the centre-of-mass (CM) energy values reaching 200 GeV (for leptons) and above, experience beam energy loss and quality dilution, for example, due to synchrotron radiation, limiting the overall CM energy achievable and requiring a constant energy top-up to compensate the loss and the beam quality dilution. Linear colliders overcome these limitations, while the finite capabilities of generating high average current beams limits the luminosity. This is partially compensated by the quality of the colliding beams. In this work, we suggest a novel design of circular-linear accelerator based on the merging of the “non-emitting”, low-energy storage rings and energy recovery linear accelerators. We suggest using the recently considered dual-axis asymmetric cavities to enable the operation of such a system, and in particular the energy recovery from spent, high-intensity beams. The machine considered, under the scope of the SNOWMASS-2021 initiative, can be potentially used to reach ultimate energy frontiers in high-energy physics as well as to drive next generation light sources. The merging of circular and linear systems, and applications of dual axes cavities, should allow the maintaining of high beam quality, high luminosity, and high energy efficiency, while offering a flexible energy management and opening clear opportunity for reducing the running cost. We note that the numbers shown in the paper are for illustration purpose and can be improved further.

Plasma wakefield acceleration beyond the dephasing limit with 400 GeV proton driver

A new regime of proton-driven plasma wakefield acceleration is discovered, in which the plasma nonlinearity increases the phase velocity of the excited wave compared to that of the protons. If the beam charge is much larger than minimally necessary to excite a nonlinear wave, there is sufficient freedom in choosing the longitudinal plasma density profile to make the wave speed close to the speed of light. This allows electrons or positrons to be accelerated to about 200 GeV with a 400 GeV proton driver.