Message-ID: <Pine.NEB.4.63.0505121613000.22333@panix3.panix.com>
From: Alan Sondheim <sondheim@panix.com>
To: Cyb <cybermind@listserv.aol.com>,
"WRYTING-L : Writing and Theory across Disciplines" <WRYTING-L@LISTSERV.UTORONTO.CA>
Subject: Physics News Update 731 (fwd)
Date: Thu, 12 May 2005 16:13:05 -0400 (EDT)
---------- Forwarded message ---------- Date: Thu, 12 May 2005 15:07:26 -0400 From: physnews@aip.org To: sondheim@PANIX.COM Subject: Physics News Update 731 PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 731 May 12, 2005 by Phillip F. Schewe, Ben Stein MOST PRECISE MASS CALCULATION FOR LATTICE QCD. A team of theoretical physicists have produced the best prediction of a particle's mass. And within days of their paper being submitted to Physical Review Letters, that very particle's mass was accurately measured at Fermilab, providing striking confirmation of the predicted value. How do the known particles acquire the mass they have? The answer might come from lattice QCD, the name for a computational approach to understanding how quarks interact. Imagine quarks placed at the interstices of a crystal-like structure. Then let the quarks interact with each other via the exchange of gluons along the links between the quarks. The gluons are the designated carriers of the strong nuclear force under the general auspices of the theory called quantum chromodynamics (QCD). >From this sort of framework the mass of the known hadrons (quark-containing composite particles such as mesons and baryons) can be calculated. Until recently, however, the calculations were marred by a crude approximation. A big improvement came only in 2003, when uncertainties in mass predictions went from the 10% level to the 2% level (see Davies et al., Physical Review Letters, 16 January 2004). The mass of the proton, for example, could be calculated within a few percent of the actual value. Progress has come from a better treatment of the light quarks and from greater computer power. Together the improvements provide the researchers with a realistic treatment of the "sea quarks," the virtual quarks whose ephemeral presence has a noticeable influence over the "valence" quarks that are considered the nominal constituents of a hadron. A proton, for example, is said to consist of three valence quarks---two up quarks and one down quark---plus a myriad of sea quarks that momentarily pop into existence in pairs. Now, for the first time, the mass of a hadron has been predicted with lattice QCD. Andreas Kronfeld (ask@fnal.gov, 630-840-3753) and his colleagues at Fermilab, Glasgow University, and Ohio State report a mass calculation for the charmed B meson (Bc, for short, consisting of an anti-bottom quark and a charmed quark). The value they predict is 6304 +/- 20 MeV---the remarkable precision stems not only from the improvements discussed above, but also from the researchers' methods for treating heavy quarks. A few days after they submitted their Letter for publication, the first good experimental measurement of the same particle was announced 6287 +/- 5 MeV. This successful confirmation is exciting, because it bolsters confidence that lattice QCD can be used to calculate many other properties of hadrons. (Allison et al., Physical Review Letters,6 May 2005, Lattice QCD website at http://lqcd.fnal.gov/ ) NEUTRINO PULSAR. A new hypothesis suggests that we should be able to see beams of TeV (trillion electron volt) neutrinos coming from certain pulsars in the sky. A pulsar is a rotating neutron star possessing high magnetic fields and spewing energy in a searchlight pattern, usually observed at radio wavelengths. According to Bennett Link of Montana State University, the potent nature of a young, rapidly spinning neutron star---emitting the energy of our sun but from a surface 5 billion times smaller, and in the form of x rays---creates electric fields of fantastic strength, some 10^15 volts. These fields will whip protons in the vicinity up to PeV (10^15 eV) energies. When such protons collide with the x rays emanating from the star, delta particles (essentially heavy protons) can be created. When these subsequently decay energetic neutrinos are formed. This whole production mechanism---proton acceleration, delta creation, daughter neutrino cascades---sweeps around like the radio waves normally seen from a pulsar. With the right detector, the pulsar would reveal itself through neutrinos. If such a neutron star were as far away as our sun, the Earth would receive about a million 50-TeV neutrinos per square cm per second. Actual pulsars are, of course, much further away from us. Nevertheless, Link (link@physics.montana.edu) estimates that there are about 10 neutrino pulsars within a distance of 15,000 light years from Earth. He believes that these energetic sources might result in about 10 neutrino detections per year in a square-kilometer detector, which is about the effective size of the so-called IceCube facility being built now. Neutrino pulsars could be the brightest continuous high-energy neutrino sources in the universe and their detection would help to bolster the idea of neutrino astronomy. (Link and Burgio, Physical Review Letters, 13 May 2005) *********** PHYSICS NEWS UPDATE is a digest of physics news items arising from physics meetings, physics journals, newspapers and magazines, and other news sources. It is provided free of charge as a way of broadly disseminating information about physics and physicists. For that reason, you are free to post it, if you like, where others can read it, providing only that you credit AIP. Physics News Update appears approximately once a week. AUTO-SUBSCRIPTION OR DELETION: By using the expression "subscribe physnews" in your e-mail message, you will have automatically added the address from which your message was sent to the distribution list for Physics News Update. If you use the "signoff physnews" expression in your e-mail message, the address in your message header will be deleted from the distribution list. Please send your message to: listserv@listserv.aip.org (Leave the "Subject:" line blank.)