Register Now to Watch the Start-Up of the Large Hadron Collider Live at Fermilab!

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.

Craig Hogan to lead particle astrophysics effort

Craig Hogan

Craig Hogan, a member of one of the scientific teams that co-discovered dark energy, will soon assume dual roles as Director of the Center for Particle Astrophysics at the Department of Energy’s Fermi National Accelerator Laboratory and as a Professor of Astronomy & Astrophysics at the University of Chicago.

Hogan is a Professor of Astronomy and Physics at the University of Washington and a member of the international High-z Supernova Search Team that in 1998 co-discovered dark energy, the mysterious force that works against gravity to accelerate the expansion of the universe. Hogan’s hiring is the first joint appointment since the University took a major role in managing Fermi National Accelerator Laboratory for the U.S. Department of Energy in 2007.

“Craig Hogan is an outstanding and respected leader in the field of particle astrophysics,” said Fermilab Director Pier Oddone. “I am delighted that he will bring his energy and vision to Fermilab’s Center for Particle Astrophysics, a vital part of Fermilab’s scientific program.”

Chicago scientists founded the field of particle astrophysics at Fermilab during the 1980s, said Edward “Rocky” Kolb, Professor and Chairman of the Department of Astronomy & Astrophysics at the University of Chicago. In this field, scientists study the connections between forces and objects at the largest and smallest scales of the universe.

“Craig is a high-profile scientist, and he sees a great future in the Fermilab-Chicago connection in particle astrophysics,” Kolb said.

Said Hogan: “The cosmology and particle astrophysics community at Fermilab and the University of Chicago continues to lead the world in exploration of the inner space/outer space frontier. It’s a place of great talent, diversity, creativity and intellectual excitement.”

The cosmological frontier is as much about experiments and data as it is about crazy and cool ideas, he said. “The scientists and engineers at Fermilab build incredible machines-devices of unprecedented precision, sensitivity, sophistication and complexity.

“The physicists recognize that in addition to smashing particles in a lab, they can attack deep mysteries of the nature of time, space, matter and energy by using their powerful tools to study the cosmos. This is pushing technology, literally, to the limits-the smallest and biggest things, the farthest and earliest events, the densest and emptiest places, the bits and pieces of space and time themselves.”

Hogan’s University appointment includes affiliations with the Kavli Institute for Cosmological Physics and the Enrico Fermi Institute, where he began his research career in 1980. He will spend 75 percent of his time at Fermilab and 25 percent at the University. Nevertheless, the University will provide 50 percent of his salary as part of its commitment to operating Fermilab through the Fermi Research Alliance.

He is currently a member of two international scientific collaborations: the Large Synoptic Survey Telescope (LSST), and the Laser Interferometer Space Antenna (LISA). The LSST is a proposed 8.4-meter telescope that will image faint astronomical objects thousands of times across the entire sky, including exploding stars and potentially hazardous near-Earth asteroids.

Expected to launch in the next decade, the satellite-based LISA mission will explore and measure the early universe using gravitational waves. These waves, never directly detected, are predicted in Einstein’s theory of general relativity. Hogan also is pursuing theoretical studies of techniques for probing the quantum nature of space time directly in the laboratory.

Hogan earned his bachelor’s degree in astronomy, with highest honors, from Harvard University in 1976, and his Ph.D. in astronomy from King’s College at the University of Cambridge, England, in 1980. He was an Enrico Fermi Fellow at the University of Chicago in 1980-81, a National Science Foundation Postdoctoral Fellow at Cambridge in 1981-82, and a Bantrell Prize Fellow in Theoretical Astrophysics at the California Institute of Technology from 1982-85.

Hogan joined the University of Arizona faculty in 1985, followed by the University of Washington in 1993. At Washington, he served as chair of the Astronomy Department for six years, as Divisional Dean of Natural Sciences for one year and as Vice Provost for Research for more than three-and-a-half years.

His honors include an Alexander von Humboldt Research Award and an Alfred P. Sloan Foundation Fellowship. He also is the author of The Little Book of the Big Bang. Published in 1998 by Springer-Verlag, the book has been translated into six languages.

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

U.S. experiment retakes the lead in competitive race

Batavia, Ill.—Scientists of the Cryogenic Dark Matter Search experiment today announced that they have regained the lead in the worldwide race to find the particles that make up dark matter. The CDMS experiment, conducted a half-mile underground in a mine in Soudan, Minn., again sets the world’s best constraints on the properties of dark matter candidates.

“With our new result we are leapfrogging the competition,” said Blas Cabrera of Stanford University, co-spokesperson of the CDMS experiment, for which the Department of Energy’s Fermi National Accelerator Laboratory hosts the project management. “We have achieved the world’s most stringent limits on how often dark matter particles interact with ordinary matter and how heavy they are, in particular in the theoretically favored mass range of more than 40 times the proton mass. Our experiment is now sensitive enough to hear WIMPs even if they ring the ‘bells’ of our crystal germanium detector only twice a year. So far, we have heard nothing.”

WIMPs, or weakly interacting massive particles, are leading candidates for the building blocks of dark matter, which accounts for 85 percent of the entire mass of the universe. Hundreds of billions of WIMPs may have passed through your body as you read these sentences.

“We were disappointed about not seeing WIMPs this time. But the absence of background in our sample shows the power of our detectors as we enter into very interesting territory,” said CDMS co-spokesperson Bernard Sadoulet, of the University of California, Berkeley.

If they exist, WIMPs might interact with ordinary matter at rates similar to those of low-energy neutrinos, elusive subatomic particles discovered in 1956. But to account for all the dark matter in the universe and the gravitational pull it produces, WIMPs must have masses about a billion times larger than those of neutrinos. The CDMS collaboration found that if WIMPs have 100 times the mass of protons (about 100 GeV/c²) they collide with one kilogram of germanium less than a few times per year; otherwise, the CDMS experiment would have detected them.

“The nature of dark matter is one of the mysteries in particle physics and cosmology,” said Dr. Dennis Kovar, Acting Associate Director for High Energy Physics in the U.S. Department of Energy’s Office of Science. “Congratulations to the CDMS collaboration for improved sensitivity and a new limit in the search for dark matter.”

The CDMS experiment is located in the Soudan Underground Laboratory, shielded from cosmic rays and other particles that could mimic the signals expected from dark matter particles. Scientists operate the ultrasensitive CDMS detectors under clean-room conditions at a temperature of about 40 millikelvin, close to absolute zero. Physicists expect that WIMPs, if they exist, travel right through ordinary matter, rarely leaving a trace. If WIMPs crossed the CDMS detector, occasionally one of the WIMPs would hit a germanium nucleus. Like a hammer hitting a bell, the collision would create vibrations of the detector’s crystal grid, which scientists could detect. Not having observed such signals, the CDMS experiment set limits on the properties of WIMPs.

“Observations made with telescopes have repeatedly shown that dark matter exists. It is the stuff that holds together all cosmic structures, including our own Milky Way. The observation of WIMPs would finally reveal the underlying nature of this dark matter, which plays such a crucial role in the formation of galaxies and the evolution of our universe,” said Joseph Dehmer, director of the Division of Physics for the National Science Foundation.

The discovery of WIMPs would require extensions to the theoretical framework known as the Standard Model of particles and their forces. On Feb. 22, the CDMS collaboration presented its result to the scientific community at the Eighth UCLA Dark Matter and Dark Energy symposium.

“This is a fantastic result,” said UCLA professor David Cline, organizer of the conference.

The CDMS result tests the viability of new theoretical concepts that have been proposed.

“Our results constrain theoretical models such as supersymmetry and models based on extra dimensions of space-time, which predict the existence of WIMPs,” said CDMS project manager Dan Bauer, of DOE’s Fermilab. “For WIMP masses expected from these theories, we are again the most sensitive in the world, retaking the lead from the Xenon 10 experiment at the Italian Gran Sasso laboratory. We will gain another factor of three in sensitivity by continuing to take more data with our detector in the Soudan laboratory until the end of 2008.”

A new phase of the CDMS experiment with 25 kilograms of germanium is planned for the SNOLAB facility in Canada.

“The 25-kilogram experiment has clear discovery potential,” said Fermilab Director Pier Oddone. “It covers a lot of the territory predicted by supersymmetric theories.”

The CDMS collaboration includes more than 50 scientists from 16 institutions and receives funding from the U.S. Department of Energy, the National Science Foundation, foreign funding agencies in Canada and Switzerland, and from member institutions.

Fermilab is a DOE Office of Science national laboratory operated under contract by the Fermi Research Alliance, LLC. The DOE Office of Science is the single largest supporter of basic research in the physical sciences in the nation.

NSF is an independent federal agency that supports fundamental research and education across all fields of science and engineering. NSF funds reach all 50 states through grants to more than 1,700 universities and institutions.

CDMS home page
http://cdms.berkeley.edu/index.html

: In these figures, the dotted red line divides events into those determined not to be WIMPs based on the relative timing of the heat to charge signals (left side) and those that could potentially be WIMPs based on that parameter (right side). The solid red box delineates the area of the graph in which WIMPs should occur based on both timing and the heat to charge ratio. Two events in separate detectors demonstrated the characteristics scientists predicted a WIMP would have. Credit: CDMS

: The curves dipping through this figure represent the results of several dark matter search experiments. The vertical scale represents the rate of WIMP scatters with nuclei while the horizontal scale is the mass of the WIMP. The gray line represents the 2008 results from the CDMS experiment. The blue line represents the most recent CDMS results. The solid black line represents the two results combined. The dotted black line represents the curve the combined results would have formed if CDMS had found no candidate events in 2009. The green and gray backgrounds represent areas that two theories of supersymmetry predict would contain dark matter. Credit: CDMS

: Dark matter detectors. The Cryogenic Dark Matter Search experiment uses five towers of six detectors each. Credit: Fermilab

: Dan Bauer, CDMS project manager and Fermilab scientist, removes one tower of detectors used in the Cryogenic Dark Matter Search experiment. Credit: Fermilab

: Closeup of a CDMS detector, made of crystal germanium. Credit: Fermilab

: The CDMS detectors, made of germanium, are located inside an ice box. A fridge provides the coolant to keep the detectors at close to absolute zero. Shielding material around the icebox minimizes the number of cosmic rays and other background particles that hit the detectors. Credit: CDMS collaboration

: The CDMS experiment has achieved the world’s most stringent limits on how often dark particles interact with ordinary matter and how heavy they are, in particular in the theoretically favored mass range of more than 40 times the proton mass (about 40 GeV/c²). The regions excluded are those above the solid lines. The black line is the most stringent limit. The bottom axis indicates the WIMP mass and the left axis refers to the frequency with which WIMPs interact with ordinary matter.

: Closeup of a detector in its mount. A detector of this kind, made of Silicon, was operated in the 1998 run. The photolithographically-fabricated thin film on the surface is the phonon sensor and represents a significant advance over the detectors used in the 1999 run. Silicon and germanium detectors, weighing 100 g and 250 g respectively, are used in CDMS II runs in the Soudan Mine.

: Project manager Dan Bauer from Fermilab holds one tower of detectors as Vuk Mandic, now at the University of Minnesota, examines them. Each tower of detectors contains 1 kilogram of germanium for detecting dark matter and 200 grams of silicon to distinguish WIMPs from neutrons. Thin layers of silicon, aluminum, and tungsten covering the detector surfaces measure both the heat and charge released when a particle interacts inside.

: A view of the inner layers of the cryostat with two towers installed. Detector towers are mounted in the holes covered by hexagonal plates. The coldest part of the cryostat stays at 10 mK (millikelvin, or thousandths of a degree above absolute zero) during operation. The surrounding layers are higher temperature stages of the cryostat. The cryostat is constructed using radiopure copper to provide a low-radioactivity environment for the extremely sensitive CDMS detectors.

: A scientist examines the shielding around the cryostat.

: The first detectors arrive at the Soudan Mine on February 21, 2003.

: A collaboration meeting at Soudan in March, 2003. The 12-institution collaboration includes 45 scientists.

: The Soudan Underground Mine was closed in 1963 and placed on the National Register of Historic Places in 1966. It is operated as a State Park by the Minnesota Department of Natural Resources, with 14 tours a day taking the historic elevator for a fast and clamorous ride nearly a half-mile below the surface. After descending, hard hat-wearing tourists can view old mine caverns with some of the equipment still standing in place. Since May 2002, tourists can also view the cavern housing the CDMS detector.

: Soudan is part of Minnesota’s Iron Range. Rich ore deposits were discovered in the area in 1865. Today, underground mines have largely given way to surface mining. The Soudan Underground Mine has served as a physics laboratory since 1979. The photo shows the view from the top of the tower above the Soudan Mine shaft.

This video (1 min.) shows a time lapse of the construction of the CDMS experiment in 2003-2004. Watch video (QuickTime movie. May not work in all browsers.)

Scientists of the Cryogenic Dark Matter Search experiment are listening for whispers of dark matter. Inspired by his brother Erik’s research, musician Karl Ramberg built a musical model of the CDMS detector, in collaboration with CDMS scientists. Erik Ramberg and Priscilla Cushman translated real CDMS data into a format that accurately converts the energy, location and type of particles striking the CDMS detectors into sound and light. Cushman created this 5-minute video.
Credit: Priscilla Cushman

Background information

What is dark matter?
Judging by the way galaxies rotate, scientists have known for 70 years that the matter we can see does not provide enough gravitational pull to hold the galaxies together. There must exist some form of matter that does not emit or reflect light. Ordinary matter (made of quarks) makes up only 15% of the matter contents in the universe. An unknown form of dark matter makes up 85%. (In terms of the full matter and energy content of the universe, ordinary matter contributes 4%, dark matter makes up 23% and dark energy represents 73%.)

Most of the ordinary matter is invisible, too. It exists across the universe in form of hydrogen, dust clouds and very dim clumps of matter called massive compact halo objects. These MACHOs include planets and cold dead stars like brown dwarfs and black holes.

Neutrinos, very light particles left over from the big bang in massive quantities, make up a small amount of the dark matter that is not made of quarks. WIMPs, or weakly interactive massive particles, may make up the rest. Neutrinos move at nearly the speed of light. That’s why they are considered “hot dark matter.”

What is a WIMP?
Weakly interactive massive particles may make up most of the dark matter, if they have a mass of 10 to 10,000 times the mass of the proton. They only interact with ordinary matter via gravity and a weak force (not the strong or electromagnetic force), so they only disturb atoms when they collide with a nucleus. Atoms contain mostly empty space, so this rarely happens. As many as 10 trillion WIMPs should pass through one kilogram of the Earth in a second but perhaps as few as one per day will interact.

What is supersymmetry?
The Standard Model describes all of the particles and forces in the universe, but it does not adequately explain the origin of mass. To solve this problem, in 1982 some theorists proposed an extension to the Standard Model where every mass particle (the quark, electron, etc) and every force-carrying particle (the photon, graviton, etc.) has an associated “superpartner” that differs only in its spin and mass. Since we have not yet detected superpartners, they must be much more massive than the particles observed so far.

The lightest neutral supersymmetric particle is the neutralino. With an expected mass of 50-1,000 billion electron volts (GeV) – the mass of a proton is 1 GeV — and weak interaction with everyday matter, the neutralino is a prime candidate for being a WIMP.

If it is a WIMP, it travels through the universe at 1/1000 the speed of light, making it “cold dark matter.” Neutralinos were produced at the beginning of the universe but exist in fewer numbers than the neutrino because their great mass makes them harder to produce, and they annihilate each other. Both types of particles pass through the Earth in large quantities.

How does the CDMS experiment work?
The experimental set-up for the Cryogenic Dark Matter Search contains five towers of detectors. Each tower contains germanium for detecting dark matter and silicon to distinguish WIMPs from neutrons. The CDMS towers have a total of four kilograms of germanium. Supersymmetry models predict that only a few WIMPs per year, one per day at most, will interact with the detectors. The biggest challenge involves sorting them from background interactions due to electrons, neutrons, and gamma rays.

When a WIMP hits a germanium nucleus, the nucleus recoils and vibrates the whole germanium crystal. This warms the thin aluminum and tungsten outer layers, which an electrical circuit measures. Photons and electrons, however, strike the germanium’s electrons. A charge collection plate measures ionization resulting from this type of collision and uses it to separate these interactions from those of WIMPs. The ratio of charge to heat for each event tells whether a particle struck the nucleus, as WIMPs do, or simply rattled the electrons surrounding the nucleus, as most background particles do.

Incoming neutrons also strike the germanium nucleus, so they more closely resemble WIMPs. The germanium detectors sit in a stack with detectors made of silicon. A silicon atom has a smaller nucleus, and so will be hit less frequently by WIMPs. The strong nuclear force does not affect WIMPs, but it does affect neutrons and so neutrons will hit nuclei of different sizes at about the same rate. A higher collision rate in the germanium than the silicon will indicate the interaction of WIMPs.

Why is the CDMS experiment underground?
Cosmic rays hit the surface of the Earth and the reactions produce neutrons. Placing the detectors deep underground shields them from most of the cosmic rays that would produce neutrons.

Why are the CDMS detectors so cold?
A cryostat cools the detectors to 40 millikelvin (thousandths of a degree above absolute zero.) This reduces the background vibrations of the detector’s atoms and makes them more sensitive to individual particle collisions.

Institutions participating in CDMS:

Brown University
California Institute of Technology
Case Western Reserve University
Fermi National Accelerator Laboratory
Lawrence Berkeley National Laboratory
Massachusetts Institute of Technology
Queens University
Santa Clara University
Stanford University
Syracuse University
University of California, Berkeley
University of California, Santa Barbara
University of Colorado Denver
University of Florida
University of Minnesota
University of Zurich