APS News

Five Takes on the Future of Particle Physics

By Pamela Zerbinos

For the first time, this year the annual meeting of the APS Division of Particles and Fields (DPF) was held in conjunction with the APS April meeting. To mark the occasion a special session on "The Future of Particle Physics" took place in the auditorium of the University of Pennsylvania's Museum of Archaeology and Anthropology. The five speakers gave differing but complementary views of what lies ahead in particle physics.

One of the talks at the session was the Primakoff Lecture, named in memory of Henry Primakoff, who coincidentally spent many years at the University of Pennsylvania. The Primakoff Lecture is an annual feature at the April meeting, and this year it was given by Michael Turner of the University of Chicago and Fermilab, on "Connecting Quarks to the Cosmos." Turner focused on the connections between particle physics and cosmology that promise to deepen in the coming years. Particulate dark matter, which constitutes one-third of the universe, is of concern to scientists of both disciplines, and tests will need to be performed in both terrestrial and heavenly laboratories.

Other opportunities for the fields to collaborate include the study of strong field gravity, ultra-high- energy cosmic rays, baryogenesis, and "extreme physics," which includes the study of black holes, plasmas and neutron stars.

The University of Michigan's Homer Neal discussed the Large Hadron Collider currently under construction at CERN. Over 3,500 physicists worldwide are involved in the LHC project, which is scheduled for completion in 2007.

Neal described the two big detectors, ATLAS and CMS, and highlighted the work of U.S. institutions in the project; currently the US has the highest percentage of contributing scientists and institutions. They are helping with everything from building machine components to acting as computing centers in the data grid that will do the processing of the petabytes of data expected to be produced once the LHC is up and running.

He also discussed some of the physics expected to come out of the LHC, including the search for the Higgs boson and for supersymmetric particles. Neal also touched on his own work in elastic scattering at high energies, which he hopes will be illuminated by the LHC, expected to reach a center of mass energy of 14 TeV.

Princeton's Peter Meyers spoke about the future of neutrino oscillation physics. The hottest experiment right now is MiniBooNE at Fermilab, set to confirm or refute the controversial results of the LSND collaboration at Los Alamos. A confirmation of the results could mean there is a fourth, sterile neutrino, whose existence would definitely require more than Standard Model physics. As results from the current round of neutrino experiments start to come in, a clear and consistent picture should start to emerge and point the way to the next generation of experiments. Meyers said he expects this will require larger, more capable detectors and more intense beams (His rallying cry of, "Bigger! Slower! More expensive!" drew laughs from the audience).

Natalie Roe, from the Lawrence Berkeley National Laboratory, focused her talk on CP violation. Although the latest results from the B physics experiments at SLAC and at KEK in Japan have found CP violation at the expected levels, thereby confirming the Standard Model one more time, increasingly precise measurements will be available soon. She stressed that the baryon asymmetry of the universe remains a mystery that is not explained in the context of CP violation in the Standard Model, and speculated that further precision measurements of CP violation might shed light on this question. In addition, she said it might be possible to observe CP violation in neutrinos, which could also help explain the baryon asymmetry of the universe.

Edward Witten, from the Institute for Advanced Study, spoke about the pros and cons of supersymmetry, and although he said he gets out of bed most mornings believing in the SUSY model, he focused primarily on the cons during his talk.

The biggest problem with the SUSY model is that supersymmetric particles haven't been found yet, although he said that wasn't surprising. But SUSY favors a light Higgs and as the bounds on the Higgs mass are pushed up it begins to get uncomfortable. In addition, the supersymmetric extension of the Standard Model reopens some problems that the ordinary Standard Model had solved nicely, such as the natural conservation of baryon and lepton numbers.

Witten remarked, "To me, the central drawback of Super- symmetry is that we don't have a convincing workable picture of what the TeV superworld would really look like," and said that if nature really were supersymmet-ric it would be quite dramatic to see how all these problems managed to get solved.

After the session, attendees were treated to refreshments while they socialized and gazed at the antiquities comprising the museum's internationally renowned collections.


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