Bulletin of the American Physical Society
2006 APS April Meeting
Saturday–Tuesday, April 22–25, 2006; Dallas, TX
Session P1: DPF and DPB Prize Session |
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Sponsoring Units: DPB DPF Chair: Gerald Dugan, Cornell University Room: Hyatt Regency Dallas Landmark A |
Monday, April 24, 2006 10:45AM - 11:31AM |
P1.00001: Theories beyond the standard model, one year before the LHC Invited Speaker: Next year the Large Hadron Collider at CERN will begin what may well be a new golden era of particle physics. I will discuss three theories that will be tested at the LHC. I will begin with the supersymmetric standard model, proposed with Howard Georgi in 1981. This theory made a precise quantitative prediction, the unification of couplings, that has been experimentally confirmed in 1991 by experiments at CERN and SLAC. This established it as the leading theory for physics beyond the standard model. Its main prediction, the existence of supersymmetric particles, will be tested at the large hadron collider. I will next overview theories with large new dimensions, proposed with Nima Arkani-Hamed and Gia Dvali in 1998. This links the weakness of gravity to the presence of sub-millimeter size dimensions, that are presently searched for in experiments looking for deviations from Newton's law at short distances. In this framework quantum gravity, string theory, and black holes may be experimentally investigated at the large hadron collider. I will end with the recent proposal of split supersymmetry with Nima Arkani-Hamed. This theory is motivated by the possible existence of an enormous number of ground states in the fundamental theory, as suggested by the cosmological constant problem and recent developments in string theory and cosmology. It can be tested at the large hadron collider and, if confirmed, it will lend support to the idea that our universe and its laws are not unique and that there is an enormous variety of universes each with its own distinct physical laws. [Preview Abstract] |
Monday, April 24, 2006 11:31AM - 12:02PM |
P1.00002: Photonic Band Gap accelerator demonstration at Ku-band. Invited Speaker: We report the design, fabrication and high power testing of a high gradient electron accelerator with a photonic band gap (PBG) structure. The photonic band gap structure confines a fundamental TM$_{01}$-like accelerating mode, but does not support higher order modes (HOM). The absence of HOM is a major advantage of the PBG accelerator, since it suppresses dangerous beam instabilities caused by wakefields. The PBG structure was designed as a triangular lattice of metal rods with a missing central rod forming a defect confining the TM$_{01}$-like mode and also allowing the electron beam to propagate along the axis. The design frequency of the six-cell structure was 17.14 GHz, to match an available klystron and linac. The absence of HOM was confirmed in cold test. The PBG structure was excited by 2 MW, 100 ns pulses from the klystron. A 16.5 MeV electron beam was transmitted through the PBG accelerator. The observed electron beam energy gain of 1.4 MeV, measured using a magnetic spectrometer, corresponds to an accelerating gradient of 35 MeV/m, in excellent agreement with theory. PBG accelerators are a promising approach to future high gradient accelerators. [Preview Abstract] |
Monday, April 24, 2006 12:02PM - 12:33PM |
P1.00003: Search for high energy axions with the CAST calorimeter Invited Speaker: The observed $CP$ conservation, in the strong interactions is an unexpected and unresolved feature of the theory of QCD. The introduction of a new $U(1)$ symmetry can resolve this so-called ``strong-$CP$ problem''. This symmetry, however, leads to a new boson, the axion, which is predicted to couple to photons and nucleons and may be produced in the nuclear and plasma processes of stars. The CERN axion solar telescope (CAST) experiment is designed to detect such solar axions by converting them into real photons in a magnetic field. We focus on the CAST $\gamma$-ray calorimeter which extends the sensitivity of the CAST experiment into the MeV region by searching for an excess signal during solar alignment due to high energy axions emitted in nuclear processes in the sun. The large increase in ``axion luminosity'' provided by the sun and the increased axion-to-photon conversion probability in the refurbished LHC magnet make the CAST experiment uniquely sensistive to an axion signal. In the case of zero signal above background, background subtraction from the solar alignment ``tracking'' data allows a direct search for anomalous excess events. Using existing helioseismology limits on the axion flux from the sun, the mass and photon-coupling of an axion or new axion-like boson are constrained using limits on the observed flux of axions in the detector. In this way, limits are obtained without requiring detailed knowledge of nuclear mixing matrices for each production mechanism and the CAST helioscope search can be extended beyond specific nuclear transitions and can consider nuclear axion emission from the sun more generally. For a 5.5 MeV axion-photon conversion spectrum, which is a highly motivated channel, the limit on the axion-to-photon coupling obtained is $g_{a\gamma\gamma}\leq2\times10^{-9}$ GeV$^{-1}$ for $0.1\leq m_a\leq0.9$ eV, which is are slightly more restrictive than both the current experimental limits as well as those from helioseismology. [Preview Abstract] |
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