Particle and nuclear physics intersect in Florida

27 September 2012

Reporting on a range of topics from CIPANP 2012.


The Conferences on the Intersections of Particle and Nuclear Physics (CIPANP) form a triennial series that focuses on topics of interest to particle physicists, nuclear physicists, astrophysicists, cosmologists and accelerator physicists. Since the first conference took place in Steamboat Springs, Colorado, in 1984, the overlap in the interests of these areas has increased markedly. For example, the LHC is exploring both elementary-particle physics and heavy-ion physics, with the ALICE detector designed in particular for studies of lead-ion collisions. Explorations of the neutrino sector have attracted traditional nuclear physicists as well as particle physicists to measurements of solar neutrinos, reactor neutrinos, cosmic neutrinos, long-baseline neutrinos and neutrinoless double-beta decay. Facilities with rare-isotope beams have opened possibilities for innovative studies of questions in fundamental physics. The searches for physics beyond the Standard Model cover the whole range, from table-top experiments to those at the large collider facilities.

CIPANP 2012, the 11th conference in the series, took place at the Renaissance Vinoy Resort and Golf Club in St Petersburg, Florida, on 28 May – 3 June, the venue and dates being chosen according to well established CIPANP criteria. Plenary and parallel sessions were organized following the 14 topics selected for the conference: the high-energy frontier; the low-energy precision frontier; neutrino masses and neutrino mixing; electroweak tests of the Standard Model; the cosmic frontier; dark matter and dark energy; particle and nuclear astrophysics; heavy flavour and the CKM matrix; QCD, hadron spectroscopy and exotics; hadron physics and spin; nucleon structure; nuclear structure; quark matter and high-energy heavy-ion collisions; new facilities and their instrumentation. Each parallel session was organized with on average five two-hour sessions under two convenors. There were 29 invited plenary talks and a concluding “vision statement”. This report covers some of the highlights from the many excellent presentations at the meeting.

The ATLAS and CMS collaborations reported on results of the first two years of operation of the LHC, giving tantalizing hints at 2.5 σ and 2.8 σ, respectively, at a mass of about 125 GeV for the much searched-for Higgs boson. Within the Standard Model, the Higgs-boson searches plus electroweak precision data give the combined hints for the Higgs from the LHC and the Tevatron a 3.4 σ significance. (These results have been superseded by those reported at CERN on 4 July. The CDF collaboration presented a more precise value for the mass of the W boson with an uncertainty of ± 19 MeV, giving the world average an error of ± 16 MeV.

Elsewhere, the Alpha Magnetic Spectrometer experiment mounted on board the International Space Station may yield information on ultrarelativistic cosmic particles and their interactions. The MuLan and MuCap collaborations at PSI reported their final determinations of the Fermi constant and the nucleon’s weak induced pseudoscalar coupling-constant, respectively. Current and future heavy-flavour experiments will search for evidence of physics beyond the Standard Model and, if found, characterize its make-up. Understanding hadron properties from lattice QCD calculations is making considerable progress.

Sessions on neutrino physics at CIPANP 2012 addressed a variety of questions. What is the hierarchy of the neutrino masses? Are the neutrinos their own antiparticles? What is their mass scale? Are there more than three neutrino species? The talks also covered CP violation in the neutrino sector related to the preponderance of matter over antimatter and the limits on neutrinoless double-beta decay. The highlight in this area was the electron-antineutrino oscillation results from the Daya Bay, RENO and Chooz experiments, with Daya Bay measuring sin2(2θ13) = 0.092 ± 0.016, significantly different from zero.

In the sessions on electroweak tests, emphasis was placed on the two-boson corrections in parity-violating electron scattering, which are important for the Qweak experiment at Jefferson Laboratory and the Olympus experiment at DESY. Consensus is slowly emerging on the corrections that need to be applied in the determination of the Weinberg angle by the NuTeV experiment at Fermilab. The size of the proton is a question that remains, with newer electron-scattering experiments in agreement with the earlier ones. However, the discrepant atomic-spectroscopy result from PSI still stands.

First time of topics such as the cosmic frontier, dark matter and dark energy

This was the first time that CIPANP included prominently such topics as the cosmic frontier and the related fields of dark matter and dark energy. Cosmological observations indicate that only 4.5% of the mass/energy of the universe is baryonic matter, with the remaining 95% still unknown. Of the latter, 22% is dark matter, which interacts via gravity like ordinary matter. The evidence for this physics beyond the Standard Model is entirely based on cosmological observations, since many laboratory experiments undertaken so far have not presented any compelling evidence. Searches for dark matter (as well as neutrinoless double-beta decay) rely on the ultraquiet environment afforded by current and planned deep-underground laboratories with the depth and volume of the detectors being the most important parameters.

The sensitivity of gravitational-wave detectors is steadily improving with the laser interferometer experiments, Advanced LIGO and Advanced VIRGO. It is possible that at the next Intersections Conference the first results from gravitational-wave astronomy may be presented.

With the baryon-to-photon ratio well determined by the Wilkinson Microwave Anisotropy Probe, standard Big Bang nucleosynthesis no longer has any free parameters. The theoretical predictions for the abundances of 2H, 4He and 7Li can be compared with the observed abundances, indicating an over-prediction of 7Li by a factor of four. Rare isotopes with unusual proton-to-neutron ratios are the stepping-stones to nuclear element synthesis and the generation of nuclear energy in stellar explosions. The ultimate configuration in this context is a neutron star wrapped with a layer of rare isotopes. It is the rare-isotope beam facilities that elucidate the intricacies of these processes.

The quest for super-heavy elements continues

The structure of the nucleon is as complex an object as can be imagined. After a fair measure of scrutiny the electric and magnetic form factors are now well established. There is however a plethora of required descriptions of the quark and gluon distributions, especially if the longitudinal and transverse spins of the nucleon are included (Boer-Mulders, Collins, Sivers functions). The overriding question is: where is the spin of the nucleon hidden?

Understanding nuclear structure and nuclear reactions from first principles with input from QCD, and employing Hamiltonians constructed within chiral effective field theory, have come far. The nuclear interaction comprises two-nucleon, three-nucleon, and even four-nucleon components. Questions remain however about incorporating relativistic effects.

The quest for super-heavy elements continues. With the recent acceptance of the evidence for elements with Z = 114 and 116, further investigations are focusing on the elements with Z = 118, 113 and 115. The formation of doubly magic nuclei with neutron number N = 184 and the (possibly) matching proton numbers of Z = 120 or 126 may not be too far off in the future.

The utilization of high-energy heavy-ion collisions has allowed the detailed study of the quark–gluon plasma in the laboratory under conditions like those that existed in the first instances of the universe. The recent studies performed at the LHC with the ALICE detector and at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven have enabled a mapping out of the phase diagram of nuclear matter.

For the future

Upgrades for the LHC and the LHCb experiment at CERN were presented at the conference, as well as for RHIC and the PHENIX experiment, and for the 12 GeV Continuous Electron Beam Accelerator Facility at Jefferson Laboratory. An illuminating talk discussed the science and prospects for an electron–ion collider, with proposals from Brookhaven (e-RHIC) and Jefferson Laboratory (EIC) – soon to be amalgamated to become a priority item as part of the US Nuclear Science Advisory Committee’s Long Range Plan for Nuclear Physics – and from CERN (LHeC). The status of the Facility for Antiproton and Ion Research at GSI with its all-encompassing PANDA detector was another topic presented. Also discussed were the planned Facility for Rare Isotope Beams at Michigan State University and TRIUMF’s rare-isotope beam programme with the Isotope Separator and Accelerator facility and the Advanced Rare Isotope Laboratory, as well as Project-X at Fermilab, which has an important future high-intensity frontier research programme.

Ernest J Moniz, from Massachusetts Institute of Technology (MIT) and its Energy Initiative Institute gave the traditional public lecture, entitled “Energy and the Future (a Worldwide Perspective)”. The banquet speech was an exposé on the life and art of Salvador Dali given by Peter Tush of the Dali Museum in St Petersburg. CIPANP 2012 ended with a vision statement presented by Richard G Milner, director of the Laboratory for Nuclear Science at MIT.

CIPANP 2012 was organized with the help of TRIUMF and Jefferson Laboratory.

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