Precision measurement of W boson mass portends stricter limits for Higgs

Batavia, Ill.--Scientists of the CDF and DZero collaborations at theDepartment of Energy's Fermi National Accelerator Laboratory have observedparticle collisions that produce single top quarks. The discovery of thesingle top confirms important parameters of particle physics, includingthe total number of quarks, and has significance for the ongoing searchfor the Higgs particle at Fermilab's Tevatron, currently the world's mostpowerful operating particle accelerator.Previously, top quarks had only been observed when produced by the strongnuclear force. That interaction leads to the production of pairs of topquarks. The production of single top quarks, which involves the weaknuclear force and is harder to identify experimentally, has now beenobserved, almost 14 years to the day of the top quark discovery in 1995.Searching for single-top production makes finding a needle in a haystacklook easy. Only one in every 20 billion proton-antiproton collisionsproduces a single top quark. Even worse, the signal of these rareoccurrences is easily mimicked by other "background" processes that occurat much higher rates."Observation of the single top quark production is an important milestonefor the Tevatron program," said Dr. Dennis Kovar, Associate Director ofthe Office of Science for High Energy Physics at the U.S. Department ofEnergy. "Furthermore, the highly sensitive and successful analysis is animportant step in the search for the Higgs."Discovering the single top quark production presents challenges similar tothe Higgs boson search in the need to extract an extremely small signalfrom a very large background. Advanced analysis techniques pioneered forthe single top discovery are now in use for the Higgs boson search. Inaddition, the single top and the Higgs signals have backgrounds in common,and the single top is itself a background for the Higgs particle.To make the single-top discovery, physicists of the CDF and DZerocollaborations spent years combing independently through the results ofproton-antiproton collisions recorded by their experiments, respectively.Each team identified several thousand collision events that looked the wayexperimenters expect single top events to appear. Sophisticatedstatistical analysis and detailed background modeling showed that a fewhundred collision events produced the real thing. On March 4, the twoteams submitted their independent results to Physical Review Letters.The two collaborations earlier had reported preliminary results on thesearch for the single top. Since then, experimenters have more thandoubled the amount of data analyzed and sharpened selection and analysistechniques, making the discovery possible. For each experiment, theprobability that background events have faked the signal is now only onein nearly four million, allowing both collaborations to claim a bona fidediscovery that paves the way to more discoveries."I am thrilled that CDF and DZero achieved this goal," said FermilabDirector Pier Oddone. "The two collaborations have been searching for thisrare process for the last fifteen years, starting before the discovery ofthe top quark in 1995. Investigating these subatomic processes in moredetail may open a window onto physics phenomena beyond the StandardModel."Media Contacts:Judy Jackson, Fermilab, +1-630-840-3351, http://tr.mc371.mail.yahoo.com/mc/compose?to=jjackson@fnal.govKurt Riesselmann, Fermilab, +1-630-840-3351, http://tr.mc371.mail.yahoo.com/mc/compose?to=kurtr@fnal.govGraphics and photos are available at:http://www.fnal.gov/pub/presspass/images/Single-Top-Quark-2009.htmlNotes for Editors:Fermilab, the U.S. Department of Energy's Fermi National AcceleratorLaboratory located near Chicago, operates the Tevatron, the world'shighest-energy particle collider. The Fermi Research Alliance LLC operatesFermilab under a contract with DOE.CDF is an international experiment of 635 physicists from 63 institutionsin 15 countries. DZero is an international experiment conducted by 600physicists from 90 institutions in 18 countries. Funding for the CDF andDZero experiments comes from DOE's Office of Science, the National ScienceFoundation, and a number of international funding agencies.CDF collaborating institutions are athttp://www-cdf.fnal.gov/collaboration/index.htmlDZero collaborating institutions are athttp://www-d0.fnal.gov/ib/Institutions.htmlCopies of the two scientific papers submitted to Physical Review Lettersare available at: * http://arxiv.org/PS_cache/arxiv/pdf/0903/0903.0885v1.pdf * http://arxiv.org/PS_cache/arxiv/pdf/0903/0903.0850v1.pdfInterAction Collaboration media contacts:A full list of InterAction media contacts is available at:http://www.interactions.org/presscontacts/.