Since 2010, STAR Collaboration has been investigating the QCD phase structure, especially the search for QCD critical point, with the Beam Energy Scan (BES) program at the Relativistic Heavy Ion Collider (RHIC) in Brookhaven National Laboratory. Over a wide energy range from 3 GeV to 200 GeV Au+Au collisions, the RHIC BES program has recorded the world's most precise data. In this talk, I will present selected results from the first phase of the Beam Energy Scan with focus on collective dynamics and fluctuations in high-energy nuclear collisions. Physics implications of these results and future prospects, especially the QCD phase structure at the high baryon density region, will be discussed.
The high-energy physics (HEP) research in the post-LHC era relies on a next circular collider. The energy of a circular collider is limited by the strength of the bending dipoles, and its luminosity by the strength of the final focus quadrupoles. These considerations explain the continuous interest of the HEP and accelerator communities to stronger superconducting (SC) accelerator magnets. The ultimate field of SC magnets at given operation temperature is limited by the upper critical field Bc2 and critical current density Jc of the superconductor. The maximum field of the Nb-Ti magnets used in present high-energy machines, including the LHC, is limited by 10 T at 1.9 K. The fields above 10 T are now possible thanks to the recent progress with the Nb3Sn composite wires and the associated magnet technologies. It was shown that Nb3Sn magnets can operate at fields up to 15 T. To move beyond 15 T requires high-field high-temperature superconductors (HTS), such as BSCCO and REBCO. Operation above 15 T also put additional requirements to magnet designs, technologies and performance. Due to the substantially higher HTS cost and lower Jc at low magnetic fields, a hybrid approach is a cost-effective option for the high-field magnets. This presentation describes the status and main results of the practical superconductors and high-field accelerator magnets, and discusses the design, technology, and performance issues beyond 15 T.
Nearly two decades ago, the Brookhaven muon g-2 experiment measured the muon magnetic anomaly to a precision of 540 ppb. The central value of the anomaly is more than three standard deviations away from the Standard Model prediction. Is it a sign of new physics or a fluctuation? To answer this, a new experiment has been developed at Fermilab which uses the Brookhaven storage ring with new muon beam and detectors. I will describe the experiment, data analysis emphasizing systematic accuracy, and present the first result which has precision slightly better than the Brookhaven measurement.
The most popular directions of model building beyond the Standard Model focus on new phenomena at the high-energy scales of the early Universe. As an alternative direction, we have developed late-Universe solutions to the neutrino mass and strong CP problems at a new low-energy gravitational scale, which is numerically coincident with the scale of dark energy. In my talk, I will focus on the neutrino mass model and discuss some of its phenomenological implications, in particular the weakening of the cosmological neutrino mass bounds and the distinction between Majorana and Dirac neutrinos through astrophysical neutrino decays. This talk is based on 1602.03191, 1608.08969, 1811.01991, 1905.01264, and 2102.13618.
After decades of both theoretical and experimental efforts, the Standard Model of Particle Physics is complete. While this represents an incredible achievement, we also know this is not the full story. The gaps in our understanding include the nature of dark matter and neutrino masses, as well as potential flavour anomalies and the lack of constraints for non-perturbative observables. One of the tools that physicists use to fill in some of these gaps is Lattice Field Theory. By discretising spacetime, not only is the UV behaviour of the theory rendered finite, but it also becomes well suited to numerical methods. For example, lattice methods are what allows physicists to carry out first principle explorations of the low energy spectrum of QCD. However, working at finite lattice spacing and in finite volumes carries a cost - things that we take for granted in the continuum may no longer hold. In some cases, the result is a theoretical issue, where we are simply not sure how to write down the desired theory on a discretised spacetime. Other times, what results are numerical limitations, where finite resources require the development of clever algorithms and new methodologies. In this talk, I will focus on two questions - how to implement chiral gauge theories on the lattice and how to extract scattering information from finite volume measurements - in order to demonstrate that while life on the lattice is not always simple, the payoff is very much worth it.
Hard probes such as heavy flavor quarks, jets, and virtual and real photons convey valuable information from the heart of high energy nuclear collisions, opening a window into the microscopic nature of QCD matter. These probes have been used to study both hadronic states and also nuclear matter under extreme conditions. In addition, the spin degree of freedom of the colliding proton provides a fresh perspective on the quantum nature of nuclear matter, enabled by the unique capabilities of RHIC. The rareness of hard probes demands detectors capable of high precision and high rate, which in turn drives the design and the innovation of the next generation of nuclear physics collider experiments, such as sPHENIX and future EIC detectors. I will recount a story told by hard probes of nuclear collisions through selected results from PHENIX, the plans for sPHENIX, and the possibilities at the EIC.
Lattice gauge theory is a numerical approach to the Feynman path integral, and is the only systematically improvable approach to make theoretical predictions of hadronic properties from the underlying theory of quarks and gluons. I will present theoretical numerical calculations of hadronic properties that represent theoretical input to flavour physics, quark flavour mixing, and standard model CP violation in the Kaon, D and B mesons. These lead to constraints on CKM flavour mixing constants of the standard model, and searches for new physics.
The overwhelming observational evidence for the existence of dark matter is only matched by the awkward scarcity of information about what it might actually be. Laboratory searches for dark matter now appear to exclude many of the "weakly interacting massive particle" models that were favored by particle physicists for decades. Where does that leave the hunt for dark matter? If we've left the WIMP behind, what are we looking for? We give a brief, biased, and largely fictional history of the WIMP in order to establish what has and has not been excluded, and why it matters. This general-interest presentation grew out of discussions with astronomers who wanted to understand why some of their particle physics colleagues are "searching for WIMPs" while the others have decided to live in a "post-WIMP world".
URL of online video: https://bluejeans.com/s/DOxtW/
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