First Beam for Large Hadron Collider

Washington, D.C. – An international collaboration of scientists today sent the first beam of protons zooming at nearly the speed of light around the world’s most powerful particle accelerator-the Large Hadron Collider (LHC) located at the CERN laboratory near Geneva, Switzerland. The U.S. Department of Energy (DOE) and the National Science Foundation (NSF) invested a total $531 million in the construction of the accelerator and its detectors, which scientists believe could help unlock extraordinary discoveries about the nature of the physical universe.

Celebrations across the U.S. and around the world mark the LHC’s first circulating beam, an occasion more than 15 years in the making. An estimated 10,000 people from 60 countries have helped design and build the accelerator and its massive particle detectors, including more than 1,700 scientists, engineers, students and technicians from 94 U.S. universities and laboratories supported by DOE’s Office of Science and NSF.

“As the largest and most powerful particle accelerator on Earth, the LHC represents a monumental technical achievement,” said U.S. Department of Energy Undersecretary for Science Raymond L. Orbach. “I congratulate the world’s scientists and engineers who have made contributions to the construction of the accelerator for reaching this milestone. We now eagerly await the results that will emerge from operation of this extraordinary machine.”

The first circulating beam is a major accomplishment on the way to the ultimate goal: high-energy beams colliding in the centers of the LHC’s particle detectors. Beyond revealing a new world of unknown particles, the LHC experiments could explain why those particles exist and behave as they do. They could reveal the origins of mass, shed light on dark matter, uncover hidden symmetries of the universe and possibly find extra dimensions of space.

NSF has focused its support on funding university scientists who have contributed to the design and construction of the two largest detectors, CMS and ATLAS, and promoted the development of advanced computing innovations, essential to address the challenges posed by the enormity and richness of data to be accumulated. Continued support will enable scientists to optimize detector performance, successful data accumulation and sophisticated analysis, necessary for discovery.

“This national and international collaboration of unprecedented scope, and our investment in basic science, fundamental to the NSF mission, provide an exciting opportunity to solve some of the core mysteries of the universe,” said Arden L. Bement, Jr., director of the NSF. “With the operation of the LHC, anticipation of transformative scientific discoveries soars to new heights.”

DOE provided support for the design and construction of the ATLAS and CMS detectors through two DOE national laboratories-Brookhaven National Laboratory in New York and Fermi National Accelerator Laboratory (Fermilab) in Illinois. While the construction was managed through Fermilab and Brookhaven, scientists and engineers at universities and other DOE national laboratories-Argonne National Laboratory in Illinois and Lawrence Berkeley National Laboratory (Berkeley Lab) in California-played key roles in the design and construction and are finalizing preparations to collect and analyze the data at the energy frontier. In addition, DOE supported about 150 scientists, engineers and technicians from three DOE national laboratories-Brookhaven, Fermilab and Berkeley Lab-that built critical components for the LHC accelerator. They are joined by colleagues from DOE’s Stanford Linear Accelerator Center and Texas A&M University in ongoing accelerator R&D.

“The LHC is a discovery machine,” said CERN Director General Robert Aymar, “its research programme has the potential to change our view of the Universe profoundly, continuing a tradition of human curiosity that’s as old as mankind itself.”

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Notes for editors:

Photos and videos from the LHC First Beam day at CERN are available at: http://www.cern.ch/lhc-first-beam

Information about the US participation in the LHC is available at http://www.uslhc.us.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California. Visit our website at www.lbl.gov.

Brookhaven National Laboratory is operated and managed for DOE’s Office of Science by Brookhaven Science Associates. Visit Brookhaven Lab’s electronic newsroom for links, news archives, graphics, and more: http://www.bnl.gov/newsroom.

Fermilab is a U.S. Department of Energy Office of Science national laboratory, operated under contract by the Fermi Research Alliance, LLC. The U.S. Department of Energy Office of Science is the nation’s single-largest supporter of basic research in the physical sciences.

CERN, the European Organization for Nuclear Research, is the world’s leading laboratory for particle physics. It has its headquarters in Geneva. At present, its Member States are Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Italy, Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom. India, Israel, Japan, the Russian Federation, the United States of America, Turkey, the European Commission and UNESCO have Observer status.

Photos and videos from the LHC First Beam day at CERN are available at: http://www.cern.ch/lhc-first-beam

Information about the US participation in the LHC is available at http://www.uslhc.us.

Batavia, Ill. – Physicists of the DZero experiment at the U.S. Department of Energy’s Fermi National Accelerator Laboratory have discovered a new particle made of three quarks, the Omega-sub-b (Ω_b). The particle contains two strange quarks and a bottom quark (s-s-b). It is an exotic relative of the much more common proton and weighs about six times the proton mass.

The discovery of the doubly strange particle brings scientists a step closer to understanding exactly how quarks form matter and to completing the “periodic table of baryons.” Baryons (derived from the Greek word “barys,” meaning “heavy”) are particles that contain three quarks, the basic building blocks of matter. The proton comprises two up quarks and a down quark (u-u-d).

Combing through almost 100 trillion collision events produced by the Tevatron particle collider at Fermilab, the DZero collaboration found 18 incidents in which the particles emerging from a proton-antiproton collision revealed the distinctive signature of the Omega-sub-b. Once produced, the Omega-sub-b travels about a millimeter before it disintegrates into lighter particles. Its decay, mediated by the weak force, occurs in about a trillionth of a second.

Theorists predicted the mass of the Omega-sub-b baryon to be in the range of 5.9 to 6.1 GeV/c². The DZero collaboration measured its mass to be 6.165 ± 0.016 GeV/c². The particle has the same electric charge as an electron and has spin J=1/2.

The Omega-sub-b is the latest and most exotic discovery of a new type of baryon containing a bottom quark at the Tevatron particle collider at Fermilab. Its discovery follows the observation of the Cascade-b-minus baryon (Ξ_b-), first observed by the DZero experiment in 2007, and two types of Sigma-sub-b baryons (Σ_b), discovered by the CDF experiment at Fermilab in 2006.

“The observation of the doubly strange b baryon is yet another triumph of the quark model,” said DZero cospokesperson Dmitri Denisov, of Fermilab. “Our measurement of its mass, production and decay properties will help to better understand the strong force that binds quarks together.”

According to the quark model, invented in 1961 by theorists Murray Gell-Mann and Yuval Ne’eman as well as George Zweig, the four quarks up, down, strange and bottom can be arranged to form 20 different spin-1/2 baryons. Scientists now have observed 13 of these combinations.

“The measurement of the mass of the Omega-sub-b provides a great test of computer calculations using lattice quantum chromodynamics,” said Fermilab theorist Andreas Kronfeld. “The discovery of this particle is an example of all the wonderful results pouring out of accelerator laboratories over the past few years.”

The Omega-sub-b is a relative of the famous and “even stranger” Omega-minus, which is made of three strange quarks (s-s-s).

“After the discovery of the Omega-minus, people started to accept that quarks really exist,” said DZero co-spokesperson Darien Wood, of Northeastern University. “Its discovery, made with a bubble chamber at Brookhaven National Laboratory in 1964, is the textbook example of the predictive power of the quark model.”

The DZero collaboration submitted a paper that summarizes the details of its discovery to the journal Physical Review Letters. It is available online at: http://www-d0.fnal.gov/Run2Physics/WWW/results/final/B/B08G/

DZero is an international experiment of about 600 physicists from 90 institutions in 18 countries. It is supported by the U.S. Department of Energy, the National Science Foundation and a number of international funding agencies. Fermilab is a national laboratory funded by the Office of Science of the U.S. Department of Energy, operated under contract by Fermi Research Alliance, LLC.

: Six quarks–up, down, strange, charm, bottom and top–are the building blocks of matter. Protons and neutrons are made of up and down quarks, held together by the strong nuclear force. The DZero experiment has discovered the Omega-sub-b particle, which contains two strange quarks (s) and one bottom quark (b).

: Once produced, the decay of the Omega-sub-b (Ωb) proceeds like fireworks. The particle travels about a millimeter before it disintegrates into two intermediate particles called J/Psi (J/ψ) and Omega-minus (Ω-). The J/Psi then promptly decays into a pair of muons. The Omega-minus baryon, on the other hand, can travel several centimeters before decaying into yet another unstable particle called a Lambda (Λ) baryon along with a long-lived particle called kaon (K). The Lambda baryon, which has no electric charge, also can travel several centimeters prior to decaying into a proton (p) and a pion (π). (Credit: DZero collaboration)

: Baryons are particles made of three quarks. The quark model predicts the combinations that exist with either spin J=1/2 (this graphic) or spin J=3/2. The graphic shows the various three-quark combinations with J=1/2 that are possible using the three lightest quarks–up, down and strange–and the bottom quark. The DZero collaboration discovered the Omega-sub-b, highlighted in the graphic. There exist additional baryons involving the charm quark, which are not shown. The top quark, discovered at Fermilab in 1995, is too short-lived to become part of a baryon. (Credit: DZero collaboration)

: The DZero collaboration identified 18 events that have the distinctive signature of the expected decay products of the Omega-sub-b. The mass of the particle is 6.165 ± 0.016 GeV/c2. (Credit: DZero collaboration)

: The Fermilab accelerator complex accelerates protons and antiprotons close to the speed of light. Converting energy into mass, the Tevatron collider can produce particles that are heavier than the protons and antiprotons that are colliding. The Tevatron produces millions of proton-antiproton collisions per second, maximizing the chance for discovery. Two experiments, CDF and DZero, search for new types of particles emerging from the collisions.

: The DZero detector is about the size of a 3-story house. The detector surrounds the collision point and records the path, energy and charge of short-lived particles emerging from the collisions. Its subsystems record the “debris” emerging from high-energy proton-antiproton collisions, unveiling the forces governing the subatomic world. Tracing the particle tracks back to the center of the collision, scientists discover what processes take place at the core of proton-antiproton collisions.

: Some of the 600 scientists of the DZero collaboration in front of the DZero detector shortly before it began taking data in 2001.

Photos and graphics of the Large Hadron Collider are available at:
http://multimedia-gallery.web.cern.ch/multimedia-gallery/PhotoGallery_Main.aspx and http://www.uslhc.us/Images.

Fermilab plans September 10 “Pajama Party” to witness first beam at LHC

Batavia, Ill. — Journalists and guests are invited to witness the start-up of the Large Hadron Collider live and in real time at the LHC Remote Operations Center at the Department of Energy’s Fermilab, in Batavia, Illinois in the early morning hours at 1:30 a.m. CDT on Wednesday, September 10. A celebration breakfast will be served following the LHC start-up.

Journalists planning to attend the First-Beam Pajama Party at Fermilab are asked to call the Fermilab Office of Communication at 630-840-2326 or e-mail lizzie@fnal.gov

On September 10, scientists at the Large Hadron Collider in Geneva, Switzerland will attempt for the first time to send a proton beam around the 27-kilometer-long tunnel of the world’s most powerful particle accelerator. Live connections between CERN and Fermilab’s LHC Remote Operations Center will follow the action in Switzerland as it happens.

Beam will begin circulating at about 9 a.m. local time in Switzerland. Due to the time difference between Geneva and Chicago, first beam will occur at about 2 a.m. Chicago time. To allow journalists and guests to watch LHC first-beam operations as they happen, Fermilab will host a “pajama party” at the laboratory, beginning at 1:30 a.m. on Wednesday, September 10.

Fermilab will broadcast a live satellite feed from CERN. Computers in the Remote Operations Center at Fermilab will monitor operations. Scientists from the LHC experiments, CMS and ATLAS, along with accelerator experts, will be on hand to explain first-beam events.

Information about the event is available at http://www.fnal.gov/pajamaparty/. More information about U.S. participation in the LHC and its experiments is available at http://www.uslhc.us.

Fermilab scientists to explain what will happen on September 10

Batavia, Ill. – To answer reporters’ questions about the upcoming startup of the Large Hadron Collider and what it means for research at the Tevatron collider, the Department of Energy’s Fermilab offers a 2-hour Q&A session with Fermilab scientists on Thursday, Sept. 4, from 10:00 a.m. to noon in Wilson Hall. Reporters also will obtain a tour of the LHC Remote Operations Center at Fermilab.

A few days later, on Sept. 10, Fermilab will host a “First-beam Pajama Party” for scientists, guests and media representatives to celebrate the startup of the LHC in real time, at 1:30 a.m. CDT.

At the Q&A session on Sept. 4, four scientists will be on hand to answer in laymen’s terms such questions as “What does the startup mean for the future of Fermilab?”, “How does the LHC startup compare to the Tevatron startup in 1983?” and “Why do scientists build larger and larger accelerators?” The scientists are Peter Limon, who was instrumental in initiating U.S. participation in the LHC construction and who spent 22 months at CERN helping with its installation and commissioning; Dan Green, who’s led the U.S. participation in the construction of the CMS experiment at the LHC; Roger Dixon, who worked on the construction of the Fermilab Tevatron as a staff member and today is the head of the Fermilab Accelerator Division; and Joe Lykken, who has published scientific papers on extra dimensions and other phenomena that the LHC could discover.

The Large Hadron Collider, about 17 miles in circumference, is the largest scientific instrument ever constructed. On Sept. 10, scientists in Geneva, Switzerland, will attempt for the first time to send a proton beam around the ring. More than 1,700 scientists in the United States participate in one of the LHC experiments. The Department of Energy and the National Science

Foundation have contributed a total of $531 million to the construction of the CMS and ATLAS detectors and the LHC machine over twelve years.

Reporters planning to attend the Q&A session on Sept. 4 should send an email to Kurt Riesselmann, kurtr@fnal.gov, or call 630-840-5681.

Reporters planning to attend the First-Beam Pajama Party at Fermilab should call the Fermilab Office of Communication at 630-840-2326 or e-mail Elizabeth Clements at lizzie@fnal.gov.

The Fermi Research Alliance LLC operates Fermilab under a contract with the U.S. Department of Energy.

Photos and graphics of the Large Hadron Collider are available at:
http://multimedia-gallery.web.cern.ch/multimedia-gallery/PhotoGallery_Main.aspx and http://www.uslhc.us/Images.

Fermilab plans September 10 “Pajama Party” to witness first beam at LHC

On that date, scientists at the Large Hadron Collider in Geneva, Switzerland will attempt for the first time to send a proton beam around the 27-kilometer-long tunnel of the world’s most powerful particle accelerator. Live connections between CERN and Fermilab’s LHC Remote Operations Center will follow the action in Switzerland as it happens.

Journalists planning to attend the First-Beam Pajama Party at Fermilab are asked to call the Fermilab Office of Communication at 630-840-3351 or e-mail jjackson@fnal.gov.

A list of LHC startup events in the U.S. and contact information for each is available at http://www.uslhc.us/first_beam. More information about U.S. participation in the LHC and its experiments is available at http://www.uslhc.us.

Batavia, IL, Berkeley, CA and Upton, NY — On September 10, scientists at the Large Hadron Collider will attempt for the first time to send a proton beam zooming around the 27-kilometer-long accelerator. The LHC, the world’s most powerful particle accelerator, is located at CERN in Geneva, Switzerland. Journalists are invited to attend LHC first beam events at CERN and several locations within the United States. Information about the CERN event and accreditation procedures is available at . A list of LHC startup events in the U.S. and contact information for each is available at http://www.uslhc.us/first_beam.

About 150 scientists from three U.S. Department of Energy Office of Science National Laboratories – Brookhaven National Laboratory on Long Island, Fermi National Accelerator Laboratory in Illinois and Lawrence Berkeley National Laboratory in California – have built crucial LHC accelerator components. They are joined by colleagues from the Stanford Linear Accelerator Center and the University of Texas at Austin in commissioning and continuing R&D for the LHC.

United States contributions to the Large Hadron Collider are supported by the U.S. Department of Energy Office of Science and the National Science Foundation.

The LHC will go for a test drive this weekend, when the first particles are injected into a small section of the LHC. The LHC is the final step in a series of accelerators that bring beam particles from a standstill to energies of 7 TeV. In the injection test this weekend, scientists will make the first attempt to send protons into the LHC, steering them around approximately one-eighth of the LHC ring before safely disposing of the low-intensity beam.

Next up is a series of tests to confirm that the entire LHC machine is capable of accelerating beams to an energy of 5 TeV, the target energy for 2008. On September 10, LHC scientists will go full throttle and try for the first circulating beam. First collisions of protons in the center of the LHC experiments are expected four to eight weeks later.

“We’re finishing a marathon with a sprint,” said CERN’s Lyn Evans, the LHC project leader. “It’s been a long haul, and we’re all eager to get the LHC research program underway.”

About 1,600 scientists from 93 U.S. institutions participate in the LHC experiments, which will analyze the LHC’s high-energy collisions in search of extraordinary discoveries about the nature of the physical universe. The LHC experiments could reveal the origins of mass, shed light on dark matter, uncover hidden symmetries of the universe and possibly find extra dimensions of space.

U.S. first beam events will take place at Fermilab near Chicago, Illinois, Brookhaven Lab in Upton, New York, and in the San Francisco Bay area. More information is available at http://www.uslhc.us/first_beam.
Notes for editors:

More information about U.S. participation in the LHC and its experiments is available at http://www.uslhc.us.

A list of the U.S. institutions participating in the LHC and its experiments is available at: http://www.uslhc.us/The_US_and_the_LHC/Collaborating_Institutions

Fermilab, the U.S. Department of Energy’s Fermi National Accelerator Laboratory located near Chicago, operates the Tevatron, the world’s highest-energy particle collider. The Fermi Research Alliance LLC operates Fermilab under a contract with DOE.

Photos and graphics of the Large Hadron Collider are available at:
http://multimedia-gallery.web.cern.ch/multimedia-gallery/PhotoGallery_Main.aspx and http://www.uslhc.us/Images.

Joint CDF, DZero effort lands Fermilab in Higgs territory

Batavia, Ill. — Scientists from the CDF and DZero collaborations at the U.S. Department of Energy’s Fermilab have combined Tevatron data from the two experiments to advance the quest for the long-sought Higgs boson. Their results indicate that Fermilab researchers have for the first time excluded, with 95 percent probability, a mass for the Higgs of 170 GeV. This value lies near the middle of the possible mass range for the particle established by earlier experiments. This result not only restricts the possible masses where the Higgs might lie, but it also demonstrates that the Tevatron experiments are sensitive to potential Higgs signals.

“These results mean that the Tevatron experiments are very much in the game for finding the Higgs,” said Pier Oddone, director of Fermilab.

Combining results from the two collider experiments effectively doubles the data available for analysis by experimenters and allows each experimental group to cross check and confirm the other’s results. In the near future, the Fermilab experimenters expect to test more and more of the available mass range for the Higgs.

The Standard Model of Particles and Forces–the theoretical framework for particle physics–predicts the existence of a particle, the Higgs boson, that interacts with other particles of matter to give them mass. The mechanism by which particles acquire different mass values is unknown, and finding evidence for the existence of the Higgs boson would address this fundamental mystery of nature.

The CDF and DZero experiments each comprise some 600 physicists from universities and laboratories from across the nation and around the world. Currently, Fermilab’s plans call for the Tevatron experiments to continue operating through 2010. In that time, both groups expect to double their analysis data sets, improving their chances to observe the Higgs.

Scientists expect operations to begin at the Large Hadron Collider at CERN, in Europe, sometime later this year. Observation of the Higgs is also a key goal for LHC experiments.

The Tevatron accelerator and the experiments are operating at peak performance. The Tevatron continues to break records for luminosity, the number of high-energy proton-antiproton collisions it produces. The more luminosity the Tevatron delivers, the more chances experimenters have to see the Higgs. Moreover, by continually improving their experimental techniques, the CDF and DZero physicists have been able to boost their sensitivity to the Higgs and other phenomena by more than the margin afforded by the increased data alone.

“The Fermilab collider program is running at full speed,” said Dennis Kovar, associate director of the Office of Science for High Energy Physics at the U.S. Department of Energy. “In the past year alone, the two experiments have produced 77 Ph.D.s and 100 publications that advance the state of our knowledge across the span of particle physics at the energy frontier.”

The new Higgs results are among the approximately 150 results that the two experiments presented at the International Conference on High Energy Physics in Philadelphia held July 29-August 5.

“The discovery of the Higgs boson would answer one of the big questions in physics today,” said Joseph Dehmer, director of the Division of Physics for the National Science Foundation. “We have not heard the last from the Tevatron experiments.”

: According to the Standard Model of particles and forces, the Higgs mechanism gives mass to elementary particles such as electrons and quarks. Its discovery would answer one of the big questions in physics: What is the origin of mass?

: Scientists from the CDF and DZero collaborations at DOE’s Fermilab have combined Tevatron data from their two experiments to increase sensitivity for their search for the Higgs boson. While no Higgs boson has been found yet, the results announced today exclude a mass for the Higgs of 170 GeV/c2 with 95 percent probability (see graphs). This is the first time that the Tevatron experiments directly restrict the Higgs mass. Earlier experiments at the Large Electron-Positron Collider at CERN excluded a Higgs boson with a mass of less than 114 GeV/c2 at 95 percent probability. The results show that CDF and DZero are sensitive to potential Higgs signals. The Fermilab experimenters will test more and more of the available mass range for the Higgs as their experiments record more collision data and as they continue to refine their experimental analyses. The expected exclusion limit (red-dotted line with green and yellow bands in lower graph) will move up as the two collaborations collect and analyze more data.

: Scientists from the CDF and DZero collaborations at DOE’s Fermilab have combined Tevatron data from their two experiments to increase sensitivity for their search for the Higgs boson. While no Higgs boson has been found yet, the results announced today exclude a mass for the Higgs of 170 GeV/c2 with 95 percent probability (see graphs). This is the first time that the Tevatron experiments directly restrict the Higgs mass. Earlier experiments at the Large Electron-Positron Collider at CERN excluded a Higgs boson with a mass of less than 114 GeV/c2 at 95 percent probability. The results show that CDF and DZero are sensitive to potential Higgs signals. The Fermilab experimenters will test more and more of the available mass range for the Higgs as their experiments record more collision data and as they continue to refine their experimental analyses. The expected exclusion limit (red-dotted line with green and yellow bands in lower graph) will move up as the two collaborations collect and analyze more data.

: The Fermilab accelerator complex accelerates protons and antiprotons close to the speed of light. The Tevatron produces millions of proton-antiproton collisions per second, maximizing the chance for discovery. Two experiments, DZero and CDF, search for new types of particles emerging from the collisions.

: The CDF detector, about the size of a 3-story house, weighs about 6,000 tons. Its subsystems record the “debris” emerging from each high-energy proton-antiproton collision produced by the Tevatron. The detector records the path, energy and charge of the particles emerging from the collisions. This information can be used to look for particles emerging from the decay of a short-lived Higgs particle.

: The DZero detector records particles emerging from high-energy proton-antiproton collisions produced by the Tevatron. Tracing the particles back to the center of the collision, scientists understand the subatomic processes that take place at the core of proton-antiproton collisions. Scientists search for the tiny fraction of collisions that might have produced a Higgs boson.

Notes for editors:

CDF is an international experiment of 635 physicists from 63 institutions in 15 countries. DZero is an international experiment conducted by 600 physicists from 90 institutions in 18 countries. Funding for the CDF and DZero experiments comes from DOE’s Office of Science, the National Science Foundation, and a number of international funding agencies.

CDF collaborating institutions are at http://www-cdf.fnal.gov/collaboration/index.html

DZero collaborating institutions are at http://www-d0.fnal.gov/ib/Institutions.html

More information is available in the conference paper at
http://www-d0.fnal.gov/Run2Physics/WWW/results/prelim/HIGGS/H64/

Fermilab’s DZero experiment observes rare ZZ diboson production

Batavia, Ill.— 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.

: 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 Fermi National Accelerator Laboratory. The discovery is the latest in a series of observations of so-called gauge bosons, or force-carrying particles, by DZero and its sister Tevatron experiment, CDF. The series began (from left) with the study of collisions that produced a single W or Z boson and the already rare production of a W boson plus photon; then Z boson plus photon. In the last couple of years, Tevatron experiments discovered the even rarer production of W pairs, then WZ. Now, DZero has discovered the ZZ production. The ZZ process is the final step before reaching the even rarer process of a Higgs boson decaying into a pair of W bosons.

: The DZero collaboration searched for signs for ZZ production in nearly 200 trillion proton-antiproton collisions delivered by the Tevatron. In one analysis, scientists looked for Z bosons decaying into pairs of electrons or muons. Just three events were observed in this mode. But the signature is remarkably distinctive: the predicted background is only two tenths of one event (see graph). (Note: Electrons and muons belong to a class of particles known as leptons.)

: One of the three ZZ events recorded by the DZero experiment at Fermilab: Each Z boson decayed into a pair of high-energy muons, yielding four muon tracks in the DZero detector. The green bars indicate the direction associated with each muon.

: The Fermilab accelerator complex accelerates protons and antiprotons close to the speed of light. Converting energy into mass, the Tevatron collider can produce particles that are heavier than the protons and antiprotons that are colliding. The Tevatron produces billions of proton-antiproton collisions per second, maximizing the chance for discovery. Two experiments, CDF and DZero, search for new types of particles emerging from the collisions.

: The DZero detector is about the size of a 3-story house. The detector surrounds the collision point and records the path, energy and charge of short-lived particles emerging from the collisions. Its subsystems record the “debris” emerging from high-energy proton-antiproton collisions, unveiling the forces governing the subatomic world. Tracing the particle tracks back to the center of the collision, scientists discover what processes take place at the core of proton-antiproton collisions.

: Some of the 700 scientists of the DZero collaboration in front of the DZero detector shortly before it began taking data in 2001.

Notes for editors:

Fermilab, the US Department of Energy’s Fermi National Accelerator Laboratory, located near Chicago, operates the Tevatron, the world’s highest-energy particle collider. The Fermi Research Alliance LLC operates Fermilab under a contract with DOE.

DZero is an international experiment conducted by about 600 physicists from 90 institutions in 18 countries. Funding for the DZero experiment comes from the Department of Energy’s Office of Science, the National Science Foundation, and a number of international funding agencies.

DZero collaborating institutions are at http://www-d0.fnal.gov/ib/Institutions.html

Fermilab Director Pier Oddone expects to announce to all employees the official suspension of involuntary layoffs at Fermilab, as a result of increased funding for science provided in the supplemental funding bill signed by the President today. U.S. Senator Richard Durbin, Congresswoman Judy Biggert, Congressman Bill Foster and Acting Deputy Secretary of Energy Jeffrey Kupfer will make remarks. There will be a brief media opportunity immediately following the meeting.

Media representatives wishing to attend should make arrangements as soon as possible. Please contact Kurt Riesselmann at (630) 840-5681 or kurtr@fnal.gov. To allow for a prompt start for the meeting, media are asked to arrive at Wilson Hall no later than 11:15 a.m.