Prelude to the Higgs: A work for two bosons in the key of Z

Fermilab's DZero experiment observes rare ZZ diboson production

The discovery of ZZ production (red check mark) is an essential prelude to finding or excluding the Higgs boson at the Tevatron particle collider at DOE's Fermilab.

Scientists of the DZero collaboration at the US Department of Energy’s Fermilab have announced the observation of pairs of Z bosons, force-carrying particles produced in proton-antiproton collisions at the Tevatron, the world’s highest-energy particle accelerator. The properties of the ZZ diboson make its discovery an essential prelude to finding or excluding the Higgs boson at the Tevatron.

The observation of the ZZ, announced at a Fermilab seminar on July 25, connects to the search for the Higgs boson in several ways. The process of producing the ZZ is very rare and hence difficult to detect. The rarest diboson processes after ZZ are those involving the Higgs boson, so seeing ZZ is an essential step in demonstrating the ability of the experimenters to see the Higgs. The signature for pairs of Z bosons can also mimic the Higgs signature for large values of the Higgs mass. For lower Higgs masses, the production of a Z boson and a Higgs boson together, a ZH, makes a major contribution to Higgs search sensitivity, and the ZZ shares important characteristics and signatures with ZH.

The ZZ is the latest in a series of observations of pairs of the so-called gauge bosons, or force-carrying particles, by DZero and its sister Tevatron experiment, CDF. The series began with the study of the already rare production of W bosons plus photons; then Z bosons plus photons; then observation of W pairs; then WZ. The ZZ is the most massive combination and has the lowest predicted likelihood of production in the Standard Model. Earlier this year, CDF found evidence for ZZ production; the DZero results presented on Friday for the first time showed sufficient significance, well above five standard deviations, to rank as a discovery of ZZ production.

“Final analysis of the data for this discovery was done by a thoroughly international team of researchers including scientists of American, Belgian, British, Georgian, Italian and Russian nationalities,” said DZero cospokesperson Darien Wood. “They worked closely and productively together to achieve this challenging and exciting experimental result.”

DZero searched for ZZ production in nearly 200 trillion proton-antiproton collisions delivered by the Tevatron. Scientists used two analyses that look for Z decays into different combinations of secondary particles. One analysis looked for one Z decaying into electrons or muons, the other decaying into “invisible” neutrinos. The neutrino signature is challenging experimentally, but worthwhile because it is more plentiful. In the even rarer mode, both Z bosons decay to either electrons or muons. Just three events were observed in this mode, but the signature is remarkably distinctive, with an expected background of only two tenths of one event.

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FY 2009 Appropriations Bills update

From AIP FYI, July 28, 2008

Fiscal Year 2009 begins two months from this Friday. Yet appropriations work on Capitol Hill has become seriously bogged down, and it now appears that it may not be until March 2009 - about six months into the new fiscal year - when the FY 2009 appropriations' cycle will be finished.

No one thought this year's appropriations' cycle would be easy. It is very unusual for all appropriations bills to be passed by the start of a new fiscal year. Congress routinely passes stopgap funding bills (known as continuing resolutions) to maintain funding at the current level until final appropriations legislation is passed. An increasingly common approach in securing passage is to bundle two or more appropriations bills into a larger bill. This was, for instance, done last year when a long-running dispute between President Bush and Congress resulted in the enactment of the phone-book-sized FY 2008 funding bill in the week before Christmas.

The outlook for congressional consideration of the appropriations bills initially seemed somewhat promising. Five weeks ago House Appropriations Committee Chairman David Obey (D-WI) told his colleagues to expect committee meetings on Monday and Friday because of "a very heavy workload in July." Senate Appropriations Committee Chairman Robert Byrd (D-WV) predicted that his committee would complete work on all of the twelve appropriations bills by the end this month.

The House schedule changed during the second week of July when Democratic and Republican appropriators clashed following a Republican effort to allow expanded offshore oil drilling. After Republicans attempted and failed to amend the FY 2009 Interior Bill to permit drilling, a similar attempt was made with a highly unusual amendment during the markup of the Labor, Health and Human Services, Education FY 2009 bill. At that point Chairman Obey announced there would be no more markups. Although five of the twelve appropriations bills had been approved by the full committee by June 25, none were filed. Since that time there have been no further markups.

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