U.S. scientists count down to LHC startup

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.”

Notes for editors:

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.

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.

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, 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

 

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

Physicists revive bubble chamber technology to search for WIMPs

Scientists working on the COUPP experiment at the Department of Energy’s Fermi National Accelerator Laboratory today (February 14) announced a new development in the quest to observe dark matter. The Chicagoland Observatory for Underground Particle Physics experiment tightened constraints on the “spin-dependent” properties of WIMPS, weakly interacting massive particles that are candidates for dark matter. Their results, combined with the findings of other dark matter searches, contradict the claims for the observation of such particles by the Dark Matter experiment (DAMA) in Italy and further restrict the hunting ground for physicists to track their dark matter quarry.

The COUPP experiment also proved that dusting off an old technology of particle physics, the bubble chamber, offers extraordinary potential as a tool in the search for dark matter.

“Our first results are extremely encouraging, and bubble-chamber technology is eminently scale-able,” said Juan Collar, a University of Chicago professor and spokesman of the COUPP collaboration, which includes 16 scientists and students from the University of Chicago; Indiana University South Bend; and DOE’s Fermilab. “We expect that COUPP will soon have a sweeping sensitivity to dark matter particles, simultaneously exploring both spin-dependent and spin-independent mechanisms for dark matter interaction. This is just one of the aspects that set our experiment apart from the competition.”

Physicists theorize that dark matter particles interact with ordinary matter via different mechanisms that are either dependent or independent of the nuclear spin of the atoms in the detector material.

Previous experiments had severely constrained the possibility that the DAMA observations result from dark matter spin-independent interactions. COUPP has now ruled out the last region of parameter space that allowed for a spin-dependent explanation. Several experiments worldwide, including DAMA itself, had been racing to prove or disprove DAMA’s initial claim to observe WIMPs. If the DAMA result had been due to spin-dependent WIMPs, then COUPP researchers should have found hundreds of WIMPs. They found none above background.

The COUPP collaboration details the results in a paper, “Improved Spin-Dependent WIMP Limits from a Bubble Chamber,” appearing in the February 15 issue of the journal Science.

WIMPs, if they exist, rarely interact with ordinary matter. COUPP uses a glass jar filled with about a liter of iodotrifluoromethane, a fire-extinguishing liquid known as CF₃I, to detect a particle as it hits a nucleus, triggering evaporation of a small amount of CF₃I. The resulting bubble initially is too small to see but it grows. Using digital cameras, COUPP scientists study the pictures of bubbles once they reach a millimeter in size. They look for statistical variations between photographs that signal whether bubbles were caused by background radiation or by dark matter.

“Eighty-five percent of the total matter of the universe still eludes direct detection,” said Dennis Kovar, acting associate director for high energy physics in the DOE Office of Science. “To discover the nature of dark matter will require both catching dark matter particles with innovative detectors like COUPP’s and making and studying dark matter at particle accelerators.”

The COUPP experiment is located 350 feet underground in a tunnel on the Fermilab site.

“To search for WIMPs, COUPP revived one of the oldest tools in particle physics: the bubble chamber. As other detector technology surpassed the bubble chamber in the past two decades, it became nearly extinct in high-energy physics laboratories,” said James Whitmore, NSF program manager. “Now it is making a comeback in one of the most exciting areas of particle physics, the search for dark matter.”

Other experiments, such as the Cryogenic Dark Matter Search at Fermilab, look for dark matter underground using a different technology.

“COUPP’s use of a bubble chamber is an intriguing technology. It has been improving its reach for spin-dependent research,” said Blas Cabrera, Stanford University professor and CDMS spokesman. “It is a valuable tool in the range of technology in the search for dark matter. It is important to have confirmation from radically different technologies.”

“COUPP is a new player in an extremely competitive arena, and it has already demonstrated it can contribute to the search for dark matter,” said Hugh Montgomery, Fermilab associate director for research. “Now they need to show whether or not they can take it to the next level.”

COUPP aims to increase sensitivity by increasing the amount of liquid from one liter to 30 liters in the bubble chamber. Physicists expect soon to start testing the larger chamber at Fermilab. If the larger chamber meets expectations, the experiment could move to a deeper tunnel to reduce the background from cosmic radiation even further.

“No one knows for sure if dark matter is made of WIMPs,” said Andrew Sonnenschein, COUPP collaborator. “If it is, we’ll have a chance with the new chamber to find it. That’s all we can ask for.”

The COUPP collaboration is funded by the National Science Foundation and the U.S. Department of Energy.

Fermilab is a Department of Energy 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.

The National Science Foundation 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.

Batavia, Ill. – Early yesterday morning (Jan. 22), scientists of the U.S. CMS collaboration joined colleagues around the world to celebrate the lowering of the final piece of the Compact Muon Solenoid detector into the underground collision hall at CERN in Geneva, Switzerland. The near completion of the CMS detector marks a pivotal moment for the international experiment, in preparation for the start-up of the Large Hadron Collider this summer.

CMS has approximately 2,300 international collaborators. Supported by the Department of Energy and the National Science Foundation, the U.S. CMS collaboration consists of roughly 500 physicists from 48 U.S. universities and Fermilab. The U.S. is the largest single national group in the experiment, and DOE’s Fermilab is the host laboratory for the U.S. CMS collaboration.

CMS is the first experiment of its kind to be constructed above ground and then lowered, piece by piece, into a cavern 300 feet below. This final piece is a large disk, nearly 45 feet in diameter, with an asymmetrical cap on one face that fits into the central barrel of the experiment. The whole assembly weighs approximately 1,430 tons. It includes fragile detectors that will help identify and measure the energy of particles created in LHC collisions. After eight years of work in the surface hall, the lowering of this final piece moves CMS into its final commissioning stage.

“We have been building the CMS detector for nearly a decade, and now we’re 99.8 percent done,” said Fermilab physicist Dan Green, construction project manager for US CMS and CMS collaboration board chair-elect. “The first collisions are just around the corner.”

For this last large piece, scientists at the University of Wisconsin-Madison designed the large iron disks that help guide the magnetic field created by the detector’s powerful solenoid magnet. “From the design to the construction, we were involved all the way,” said physicist Dick Loveless from the University of Wisconsin-Madison, who watched as the huge gantry crane lowered the disk. “It was phenomenal to see this last piece go down. Everything went down without excitement, which is exactly what we want.” Fermilab and U.S. universities designed and built the cathode strip chambers that are bolted onto the disks. These chambers accurately track muons, the heavier versions of electrons that indicate interesting collisions. U.S. funding also contributed to the plastic scintillating layers and all the electronics in the hadron calorimeter, part of which is the “nose” of the disk that absorbs and measures energies of all particles flying through the detector.

From shedding light on dark matter to searching for extra dimensions of space, experiments at the LHC promise to unlock some of the deepest mysteries of the universe. “This is a very exciting time for physics,” said CMS spokesman Tejinder Virdee. “The LHC is poised to take us to a new level of understanding of our universe.”

Data taking will begin for the CMS experiment in the summer of 2008.

Notes for editors:

Video is available at:
http://cmsinfo.cern.ch/outreach/cmseye/yemin1_lowering.htm

The United States contributions to the CMS experiment and the Large Hadron Collider are funded by the Department of Energy’s Office of Science and the National Science Foundation.

CERN is the European Organization for Nuclear Research, with headquarters in Geneva, Switzerland. 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.

Fermi National Accelerator Laboratory is the host laboratory for the US CMS Collaboration. Fermilab is a Department of Energy National Laboratory operated under a contract with DOE by the Fermi Research Alliance.

US CMS member institutions
(48 institutions, from 22 states and Puerto Rico)

California
California Institute of Technology, Pasadena
Lawrence Livermore National Laboratory, Livermore
University of California, Davis
University of California, Los Angeles
University of California, Riverside
University of California, San Diego
University of California, Santa Barbara

Colorado
University of Colorado, Boulder

Connecticut
Fairfield University, Fairfield

Florida
Florida Institute of Technology, Melbourne
Florida International University, Miami
Florida State University, Tallahassee
University of Florida, Gainesville

Illinois
Fermi National Accelerator Laboratory, Batavia
Northwestern University, Evanston
University of Illinois at Chicago

Indiana
Purdue University, West Lafayette
Purdue University Calumet, Hammond
University of Notre Dame, Notre Dame

Iowa
University of Iowa, Iowa City

Kansas
Kansas State University, Manhattan
University of Kansas, Lawrence

Maryland
Johns Hopkins University, Baltimore
University of Maryland, College Park

Massachusetts
Boston University, Boston
Massachusetts Institute of Technology, Cambridge
Northeastern University, Boston

Minnesota
University of Minnesota, Minneapolis

Mississippi
University of Mississippi, Oxford

Nebraska
University of Nebraska, Lincoln

New Jersey
Princeton University, Princeton
Rutgers, The State University of New Jersey, Piscataway

New York
Cornell University, Ithaca
Rockefeller University, New York
State University of New York at Buffalo
University of Rochester, Rochester

Ohio
Ohio State University, Columbus

Pennsylvania
Carnegie Mellon University, Pittsburgh

Puerto Rico
University of Puerto Rico, Mayaguez

Rhode Island
Brown University, Providence

Tennessee
University of Tennessee, Knoxville
Vanderbilt University, Nashville

Texas
Rice University, Houston
Texas A&M University, College Station
Texas Tech University, Lubbock

Virginia
University of Virginia, Charlottesville Virginia Polytechnic Institute and State University, Blacksburg

Wisconsin
University of Wisconsin, Madison

Batavia, Ill. — Scientists of the U.S. CMS collaboration today (Dec. 20) joined colleagues around the world in announcing the successful installation of the world’s largest silicon tracking detector at CERN in Geneva, Switzerland. Just before midnight on Wednesday, Dec. 12, the six-ton CMS Silicon Strip Tracking Detector began a ten-mile, three-hour journey from the main CERN site to the CMS experimental facility. Later that day, workers carefully lowered it 90 meters into the underground collision hall for the CMS experiment at the Large Hadron Collider particle accelerator. Installation began on Saturday, Dec. 15, and concluded early Sunday morning.

Of the CMS collaboration’s approximately 2,300 physicists, about 500 are U.S. scientists, from more than 45 U.S. universities and Fermilab, supported by the Department of Energy and the National Science Foundation. The U.S. is the largest single national group in the experiment, and U.S. scientists have built and delivered several key elements of the CMS detector to CERN.

Physicist Dennis Kovar, acting associate director for High Energy Physics at DOE’s Office of Science was on the scene in Geneva as the tracker descended into place. “It was remarkable to watch the team of scientists as the CMS detector comes to completion,” Kovar said. “The tracker represents an extraordinary technological feat. I congratulate the CMS collaboration on their achievement and look forward to celebrating their next milestone.”

The DOE’s Fermi National Accelerator Laboratory near Chicago is the host laboratory for U.S. CMS. Fermilab participated in the construction along with Brown University, University of California Riverside, University of California at Santa Barbara, University of Illinois at Chicago, University of Kansas, Massachusetts Institute of Technology, and University of Rochester.

“This is a major milestone,” said Joseph Incandela of the University of California at Santa Barbara, U.S. tracker project leader. “All of the myriad components from universities and laboratories around the world are now assembled in one place. The detector is finally taking shape in its home. For some of us, this road started ten years ago, and the final destination is very satisfying.”

Physicists from the U.S. built and tested 135 of the 205 square meters of the Silicon Strip Tracking Detector. With an area about the size of a singles tennis court, it is by far the largest semiconductor silicon detector ever constructed. Its sensors are patterned to provide a total of 10 million individual sensing strips, each read out by one of 80,000 custom-designed microelectronics chips. Forty thousand optical fibers then transport data into the CMS data acquisition system.

The silicon sensors are precision mounted onto 15,200 modules. These are in turn mounted onto a very-low-mass carbon fiber structure that maintains the position of the sensors to 100 microns, or less than the diameter of a human hair. “The silicon strip detector operates like a high speed photographic camera, capable of taking 40 million images a second,” said Fermilab physicist Slawek Tkaczyk.

Component fabrication started in clean-room facilities at Fermilab and the University of California at Santa Barbara in 2004. Final assembly of the silicon tracking detector began in December 2006 and reached completion in March 2007. Collaborators then partially commissioned the detector’s systems in a test phase, operating 20 percent of the full detector over several months and recording the tracks from five million cosmic rays. Physicists rapidly analyzed the results from these data, using the experiment’s Grid-based distributed computing system. This partial commissioning demonstrated that the detector fully meets the experiment’s requirements.

“Constructing a scientific instrument of this size and complexity, designed to operate at the LHC without intervention for more than ten years, is a major engineering and scientific achievement,” said CMS spokesman Tejinder Virdee. “More than five hundred scientists and engineers from fifty-one research institutions world-wide have contributed to the success of the project.”

Full commissioning will start soon in the underground collision hall to prepare for data taking in the spring or summer of 2008.

“We are now one major step closer to discovering new physics that promises to change our understanding of the universe,” said Joseph Dehmer, director of the Physics Division at NSF. “We are proud of the U.S. scientists’ significant contribution to this international state-of-the-art detector.”

Institutions involved in the CMS tracker project are located in Austria, Belgium, CERN, Finland, France, Germany, Italy, Switzerland, the United Kingdom and the United States.

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Notes for editors:

The United States contributions to the CMS experiment and the Large Hadron Collider are funded by the Department of Energy’s Office of Science and the National Science Foundation.

CERN is the European Organization for Nuclear Research, with headquarters in Geneva, Switzerland. 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.

Fermi National Accelerator Laboratory is the host laboratory for the US CMS Collaboration. Fermilab is a Department of Energy National Laboratory operated under a contract with DOE by the Fermi Research Alliance.

US CMS member institutions
(47 institutions, from 22 states and Puerto Rico)

California
California Institute of Technology, Pasadena
Lawrence Livermore National Laboratory, Livermore
University of California, Davis
University of California, Los Angeles
University of California, Riverside
University of California, San Diego
University of California, Santa Barbara

Colorado
University of Colorado, Boulder

Connecticut
Fairfield University, Fairfield

Florida
Florida Institute of Technology, Melbourne
Florida International University, Miami
Florida State University, Tallahassee
University of Florida, Gainesville

Illinois
Fermi National Accelerator Laboratory, Batavia
Northwestern University, Evanston
University of Illinois at Chicago

Indiana
Purdue University, West Lafayette
Purdue University Calumet, Hammond
University of Notre Dame, Notre Dame

Iowa
University of Iowa, Iowa City

Kansas
Kansas State University, Manhattan
University of Kansas, Lawrence

Maryland
Johns Hopkins University, Baltimore
University of Maryland, College Park

Massachusetts
Boston University, Boston
Massachusetts Institute of Technology, Cambridge
Northeastern University, Boston

Minnesota
University of Minnesota, Minneapolis

Mississippi
University of Mississippi, Oxford

Nebraska
University of Nebraska, Lincoln

New Jersey
Princeton University, Princeton
Rutgers, The State University of New Jersey, Piscataway

New York
Cornell University, Ithaca
Rockefeller University, New York
State University of New York at Buffalo
University of Rochester, Rochester

Ohio
Ohio State University, Columbus

Pennsylvania
Carnegie Mellon University, Pittsburgh

Puerto Rico
University of Puerto Rico, Mayaguez

Rhode Island
Brown University, Providence

Tennessee
University of Tennessee, Knoxville
Vanderbilt University, Nashville

Texas
Rice University, Houston
Texas A&M University, College Station
Texas Tech University, Lubbock

Virginia
University of Virginia, Charlottesville

Wisconsin
University of Wisconsin, Madison