Hadron therapy trainees come together at CERN-hosted workshop

March 12, 2010 | 4:08 am

Using accelerator technology to treat cancer is one of the most compelling examples of how particle physics can have an impact on the lives of people all over the world. A growing subset of this field is hadron therapy, which uses protons and light ions to treat cancer. From February 21-26 at CERN, the PARTNER network (Particle Training Network for European Radiotherapy) held a workshop entitled, “Hadron therapy: past, present and future,” to provide young researchers with a glimpse of both what the field has done and what they may someday do.

A growing body of research has confirmed that the use of protons or light ions can be a more effective approach than conventional radiotherapy for certain cancer patients. Using beams of hadrons, oncologists can target deep-seated tumors with greater precision. This means that tumors located in sensitive areas could be treated with less damage to surrounding tissue. Hadron therapy has also been successfully applied to radioresistant tumors; meaning that it is a viable alternative for patients who cannot be treated through conventional radiotherapy for cancer.

In the nearly seventy years since the idea of treating cancer with hadrons was proposed, great strides have been made in its research and application. The PARTNER network, coordinated at CERN, is fueling this research for the next generation. Designed as a training program for young researchers, PARTNER brings together students from ten European institutes.

“Look around you,” observed Joanna Gora, a student with MedAustron in Vienna. She gestured across the coffee space, crowded with students and lecturers. “You see people from all over the world. Everyone is doing something similar so it’s an opportunity to share experiences and learn from each other.”

The workshop discussed past and future accelerator development, and topics included cancer management, radiobiology, medical ethics, and the use of grid computing.

Workshop speakers included the co-founders of the Particle Therapy Cancer Research Institute of Oxford, Bleddyn Jones and Ken Peach. Peach, who serves as director of the John Adams Institute for Accelerator Science of Oxford and Royal Holloway University of London, discussed current and potential accelerator applications used in a medical context, including cyclotrons, synchrotrons, compact linear accelerator, and laser-plasma ion accelerators.

“Accelerator physicists use a different language than radiobiologists,” Peach observed during his talk, alluding to the importance of bridging the at times daunting gap between physics and biology.

This idea is crucial to the field of hadron therapy and core to PARTNER’s interdisciplinary approach. The lectures reflected this and were geared to inform students of various scientific backgrounds. The workshop’s success in this regard was reflected in the participants’ enthusiasm about the intersection of different fields.

“This is very useful because we can be updated on what is happening beyond our field of study—in my case, this means with the accelerators and technological modifications,” explained Ahmad Esmaili Torshabi, a researcher working with the hadron therapy facility at the Fondazione CNAO in Pavia, Italy.

The workshop, therefore, became a crossing ground for scientific fields and ideas, as well as people. Ideally, this cross-fostering can be continued throughout the careers of the trainees. The benefit of such a dialogue was clear when students were asked to comment on how this kind of international and interdisciplinary dialogue could affect the future of the field:

“I think we will see these technologies spread out,” said Giovanna Martino, studying at GSI Darmstadt in Germany. “Across European countries, and around the world.”

You can learn more about the PARTNER program by visiting their website.

Daisy Yuhas

Symmetry Intern

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Foiling an attack on general relativity

March 11, 2010 | 6:00 pm

A collection of galaxies from the Sloan Digital Sky Survey (missing slices are obscured by the Milky Way). Red galaxies composed of older stars are more luminous; a sample of 70,000 red luminous galaxies were used to compare galaxy clustering, weak gravitational lensing, and redshift to test various theories of gravity. (Image by Michael Blanton for SDSS.)

Einstein’s General Theory of Relativity explains gravity in terms of the curvature of space by mass. Dating from the second decade of the 20th century, after more than 90 years it is still the basis of our understanding of how gravity works to shape the cosmos.

But as evidence for a universe filled with dark matter and dark energy has mounted, General Relativity’s ability to explain the structure and expansion of the universe has faced new challenges.

Some theorists deny that dark matter or dark energy exist, suggesting that there’s a problem with General Relativity’s handling of gravity. They hope to explain away the apparent gravitational effects of dark matter, and the apparent accelerating expansion of the universe caused by dark energy, with appeals to modified gravitational theories.

“One of the first proper theories of modified gravity is called the tensor-vector-scalar theory, or TeVeS,” says Uros Seljak, a member of Berkeley Lab’s Physics Division, who is also a professor of physics and astronomy at UC Berkeley and a professor of physics at the University of Zurich. “By a ‘proper’ theory, I mean one that makes definite predictions about what we should be able to observe if it is true.”

Testing predictions about the shape and growth of the cosmos requires measurements on the scale of the cosmos itself. Only in recent years have surveys like the Sloan Digital Sky Survey (SDSS), which has collected spectra of well over a million distant stars, quasars, and galaxies since it began operation in 1998, made such universe-spanning measurements possible.

Now Seljak and a group of colleagues including some of his current and former students, as well as James E. Gunn, founder of SDSS, have analyzed some 70,000 red luminous galaxies from SDSS’s collection to test the TeVeS theory of modified gravity, and with it another modified theory of gravity called f(R), which seeks to explain the accelerating universe without recourse to dark energy.

“Our measurement combines gravitational lensing, galaxy clustering, and the growth rate of the large-scale structure of the universe,” Seljak explains. “No one of these by itself could test modified gravity theories because of large uncertainties in the observations at cosmological distances.”

The collaborators report their findings in the March 11, 2010 issue of Nature. First authors of the paper are Princeton University graduate student Reinabelle Reyes and recent Princeton Ph.D. Rachel Mandelbaum. With Seljak and Gunn, the other authors are Tobias Baldauf, Lucas Lombriser, and Robert E. Smith of the University of Zurich.

Combining measurements to reduce uncertainty

An important source of uncertainty in cosmological measurements is so-called “galaxy bias,” which can be observed as the change in the way galaxies cluster according to what type of galaxies they are, for example blue galaxies or more luminous red ones. One explanation is that galaxy bias is due to the difference between the distribution of galaxies and the distribution of the invisible dark matter that underlies them — but this doesn’t help when testing a theory that says there’s no such thing as dark matter.

“Galaxy bias is one of those ‘nuisance parameters’ that tells us nothing by itself,” says Seljak. “Because it tells us nothing on its own about dark matter or dark energy or other cosmological ideas, we’d like to get it out of the way.”

Galaxy bias can essentially be bypassed by combining measures of gravitational lensing – the way intervening mass bends the light from more distant luminous objects, making them appear distorted – with galaxy clustering and the growth of structure. The three together yield a quantity called E_G, originally proposed by Pengjie Zhang of Shanghai Observatory and his collaborators as a way to test cosmological models.

Modified gravitational theories don’t predict the same value of E_G as General Relativity (with dark matter thrown in) when it comes to comparing the mass density of the universe to the growth of its structure. In general, modified theories predict faster growth of structure, making E_G smaller.

Growth rate can be calculated from redshift surveys, which measure velocities of galaxies. Galaxy clustering and weak gravitational lensing – which must be used at cosmological distances, where the distorted shapes of background galaxies can’t be measured directly but have to be derived statistically – can be used to estimate mass density.

The value of E_G that Seljak’s colleagues obtained from their deeper-than-ever probe of cosmological growth still has a large uncertainty, some 16 percent. Even with wide error bars, however, the value is enough to exclude the predictions of the TeVeS “no dark matter” theory.

The best fit of the value of E_G from this survey assumes that dark matter exists and General Relativity is correct. The uncertainty is still too great to rule out f(R) theories that modify gravity so as to exclude dark energy, however.

“To test theories that do away with dark energy, we’ll need much larger data sets for better control of systematic errors,” says Seljak. “Fortunately, SDSS-III is now underway, with most of its telescope time devoted to BOSS.”

BOSS, the Baryon Oscillation Spectroscopic Survey led by David Schlegel of Berkeley Lab’s Physics Division, will collect data from over a million and a half luminous red galaxies and quasars. Though BOSS’s main purpose is to provide an independent measure of dark energy through the technique called baryon acoustic oscillation, the data from BOSS will be some of the best ever obtained on the large-scale structure of the universe and can be used to narrow the uncertainty of measuring E_G.

As to whether or not Einstein needs to be updated, the final answer may have to await BigBOSS, the joint Berkeley Lab/National Science Foundation proposal to survey some 50 million galaxies in both the northern and southern hemispheres over a 10-year period. BigBOSS would produce an astonishingly wide and deep survey of the sky, enough to tighten the error bars around the best gravitational theory of all.

Will it be General Relativity after all? Stay tuned.

Additional information

“Confirmation of general relativity on large scales from weak lensing and galaxy velocities,” by Reinabelle Reyes, Rachel Mandelbaum, Uros Seljak, Tobias Baldauf, James E. Gunn, Lucas Lombriser, and Robert E. Smith, appears in the 11 March 2010 issue of Nature and is available online to subscribers.

In the same issue of Nature, J. Anthony Tyson’s “Cosmology: Gravity tested on cosmic scales,” is a less technical commentary on the General Relativity test.

Read the UC Berkeley press release on the General Relativity test.

More about BOSS

More about BigBOSS

by Paul Preuss, originally published at Berkeley Lab’s Web site.

Guest author

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Earth’s interior heating mechanisms revealed through neutrinos

March 11, 2010 | 11:31 am

The Borexino Collaboration announced the observation of geo-neutrinos at the underground Gran Sasso National Laboratory of Italian Institute for Nuclear Physics (INFN), Italy. The data reveal, for the first time, a definite anti-neutrino signal with the expected energy spectrum due to radioactive decays of uranium and thorium in the Earth well above background.

The International Borexino Collaboration, with institutions from Italy, United States, Germany, Russia, Poland, and France, operates a 300-ton liquid-scintillator detector designed to observe and study low-energy solar neutrinos. The low background of the Borexino detector has been key to the detection of geo-neutrinos. Technologies developed by Borexino Collaborators have achieved very low background levels. The central core of the Borexino scintillator is now the lowest background detector available for these observations. The ultra-low background of Borexino was developed to make the first measurements of solar neutrinos below 1 MeV and has now produced this first, firm observation of geo-neutrinos.

Geo-neutrinos are anti-neutrinos produced in radioactive decays of naturally occurring uranium, thorium, potassium, and rubidium. Decays from these radioactive elements are believed to contribute a significant but unknown fraction of the heat generated inside our planet. The heat generates convective movements in the Earth’s mantle that influence volcanic activity and tectonic plate movements inducing seismic activity, and the geo-dynamo that creates the Earth’s magnetic field.

The importance of geo-neutrinos was pointed out by Eder and Marx in the 1960s, and a seminal study by Krauss, Glashow, and Schramm in 1994 laid the foundation for the field. In 2005 an excess of low-energy antineutrinos above background was reported by KamLAND, a Japan-US collaboration operating a similar detector in the Kamioka mine in Japan.

Owing to a high background from internal radioactivity and antineutrinos emitted from nearby nuclear power plants, the KamLAND collaboration reported that the excess events were an “indication” of geo-neutrinos.

With 100 times lower background than KamLAND, the Borexino data reveal a clear low-background signal for anti-neutrinos that match the energy spectrum of uranium and thorium geo-neutrinos. The lower background is due to scintillator purification and radio-purity aware construction methods developed by the Borexino Collaboration, and to the absence of any nearby nuclear reactor plants.

The origin of the known 40 terawatts of power produced within the earth is one of the fundamental questions of geology. The definite detection of geo-neutrinos by Borexino confirms that radioactivity contributes a significant fraction, possibly most, of the power. Other sources of power are possible, the main one being cooling from the hot primordial condensation of the earth. A powerful natural geo-nuclear reactor at the center of the earth has been suggested, but is ruled out as a significant energy source by the absence of the high rate of geo-reactor anti-neutrinos that should have been observed in the Borexino data.

Although radioactivity can account for a significant part of the earth’s internal heat, measurements with a global array of geo-neutrino detectors above continental and oceanic crust are needed for a detailed understanding. By exploiting the unique features of the geo-neutrino probe, future data from Borexino, KamLAND, and the upcoming SNO+ detector in Canada, will provide a more complete understanding the earth’s interior and the source of its internal heat.

The Borexino Collaboration has submitted a report on this finding to the online pre-print server arXiv.org.

Press Release

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Demystifying the LHC shutdown

March 11, 2010 | 11:11 am

Yesterday the science news media and twitterverse were abuzz following a BBC News article announcing “LHC to shut down for a year to address design faults.” Readers – and the news outlets that frantically re-reported the BBC article – assumed that CERN had found a new problem with the LHC and announced an imminent shutdown. Neither is the case. Here, we join our fellow science writers and bloggers in setting the record straight about the LHC’s next long shutdown.

The LHC will shut down for about one year – but not until late 2011

What the BBC reported yesterday is true, but is not exactly news. A revised schedule for the LHC’s next few years was announced in early February by CERN. According to the revised schedule, the LHC will run at a maximum energy of 3.5 TeV per beam for a period of about 18 months, starting with the first collisions at 3.5 TeV per beam expected to take place at the end of this month. The long run will end in late 2011 or when the LHC experiments have collected a certain quantity of data (one inverse femtobarn in particle-physics parlance), whichever comes first. At the conclusion of this long run, the LHC will shut down for about one year.

The shutdown will be used to fix problems with the LHC and carry out routine maintenance

The long length of the next major LHC shutdown is due to two main factors: the time necessary to fix problems with magnet connections that currently prevent the LHC from running at its full energy; and the time needed to prepare the LHC for routine maintenance and repair work and then restore the LHC to operational status.

Particle accelerators are incredibly complex machines, and, like any complex machine, require regular maintenance to keep their parts running smoothly, repairs when parts wear out or break down, and occasional upgrades to increase the machine’s performance. Maintenance, repairs and upgrades to the LHC cannot take place while the machine is running, for two reasons. One, the radiation generated in the immediate vicinity of the LHC while it is operating means that technicians cannot enter the LHC tunnel while the machine is running. Two, the LHC’s magnets must be cooled to almost absolute zero to bend high-energy beams of particles, and it takes about one month to warm the accelerator up to room temperature before technicians can access the magnets’ innards.

In the past, CERN – like Fermilab near Chicago, which also operates a supercooled particle collider – ran its accelerators on a one-year schedule. The accelerator ran continuously for eight or nine months, followed by a four or five-month shutdown for maintenance, repairs, and upgrades. But the LHC is unique in that it contains 27 kilometers’ worth of supercooled machinery. (CERN’s previous 27-kilometer-long accelerator wasn’t supercooled, and Fermilab’s is less than 7 kilometers around.) As the LHC takes at least one month to warm up, and another month to cool down, CERN has decided to move to longer running times followed by longer shutdowns.

But the warm-up and cool-down times aren’t the only reason that the LHC’s next shutdown will be lengthy. The 2011-2012 shutdown will also be used to fix problems with the connections between superconducting magnets that prevent the LHC from running at the energies it was designed for. On September 19, 2008, a superconducting connection between two LHC magnets melted, resulting in a chain reaction that damaged more than 50 magnets. The damage took more than one year to fix, and spurred a critical review of the LHC’s design. The result was the decision to run the LHC at half design energy – 3.5 TeV per beam – long enough to give the LHC experiments enough data to remain competitive with Fermilab’s Tevatron experiments in the hunt for the big physics discoveries. And then take all the time necessary to fix the LHC so that it can finally ramp up to its full energy of 7 TeV per beam in 2013.

Katie Yurkewicz

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2009 TopCites: 50 most-cited articles in high-energy physics

March 8, 2010 | 5:02 am

Each year the SPIRES database team compiles a list of the most-cited research articles in high-energy physics. Here we present the most recent addition to this collection.  As usual, the Particle Data Group’s “Review of Particle Physics” tops the 2009 list of the most-cited papers.  The rest of the Top Ten is composed of papers in observational astrophysics/cosmology as well as now-classic string theory papers.

The astrophysics/cosmology contingent, bolstered by SPIRES’  inclusion a few years ago of more astrophysics literature, includes three by WMAP [2,4,10] and one each by the Supernova Cosmology Project [6] and Supernova Search Team [7], as well as the Schlegel-Finkbeiner-Davis paper [5] on maps of dust (a more detailed discussion of many of these papers can be found in Scott Dodelson’s special 2003 astro-ph topcite review).   The string theory classics are the papers of Maldacena [3], Witten [8] and Gubser-Klebanov-Polyakov [9] (more information on these can be found in the 1998 topcites review by Michael Peskin).

Other lists, including those from past years, can be interesting to look at.  Pay special attention to the lists broken down by eprint archives, which identify papers of interest both from and within the various subfields of high-energy physics.

Keep in mind that citation counts can never be exact; there is something like a 5 percent error in most of these numbers. Please do not fret about number 32 versus 33, as this is often not a statistically significant difference. Remember the detailed warning about the accuracy of these counts.

Also note that the counts shown and used in the rankings are the counts as of Thursday March 4th 2010. Further, the counts shown by the ranking are only the cites satisfying the criteria for that list. Actual citation numbers in the database may change as corrections are made and papers are added; the links will take you to the updated numbers. The lists, however, will not update.

The first number for each entry is the number of papers in SPIRES that cited this paper in 2009.  The second number, “total citations in SPIRES,”  is the total number of papers in SPIRES that have cited this paper in all years.

1. 2202 “Review of Particle Physics” by the Particle Data Group. This review is published every other year.  The most recent version is published in Phys.Lett.B667:1,2008.  [2374 total citations for the most recent version, and a total of 36,001 citations in SPIRES for all the versions over the years.]

2. 1058 “Five-year Wilkinson Microwave Anisotropy Probe (WMAP) observations: cosmological interpretation” by the WMAP Collaboration. Published in Astrophys.J.Suppl.180:330-376,2009(arXiv:0803.0547) [1953 total citations in SPIRES]

3. 706“The Large N limit of superconformal field theories and supergravity” by Juan Martin Maldacena (Harvard University.) Published in Adv.Theor.Math.Phys.2:231-252,1998, Int.J.Theor.Phys.38:1113-1133,1999(arXiv:hep-th/9711200) [6662 total citations in SPIRES]

4. 595 “Wilkinson Microwave Anisotropy Probe (WMAP) three-year results: implications for cosmology,” by the WMAP Collaboration.  Published in Astrophys.J.Suppl.170:377,2007(arXiv:astro-ph/0603449) [3993 total citations in SPIRES]

5. 578“Maps of dust IR emission for use in estimation of reddening and CMBR foregrounds” by David J. Schlegel (Durham University) and Douglas P. Finkbeiner and Marc Davis (UC Berkeley). Published in Astrophys.J.500:525,1998(arXiv:astro-ph/9710327) [4604 total citations in SPIRES]

6. 540 “Measurements of Omega and Lambda from 42 high-redshift supernovae” by the Supernova Cosmology Project.  Published in Astrophys.J.517:565-586,1999(arXiv:astro-ph/9812133) [4816 total citations in SPIRES]

7. 509 “Observational evidence from supernovae for an accelerating universe and a cosmological constant” by the Supernova Search Team. Published in Astron.J.116:1009-1038,1998(arXiv:astro-ph/9805201) [4678 total citations in SPIRES]

8. 466“Anti-de Sitter space and holography” by Edward Witten (Princeton University, Institute for Advanced Study). Published in Adv.Theor.Math.Phys.2:253-291,1998(arXiv:hep-th/9802150) [4437 total citations in SPIRES]

9. 421“Gauge theory correlators from noncritical string theory” by S.S. Gubser, Igor R. Klebanov, and Alexander M. Polyakov (Princeton University). Published in Phys.Lett.B428:105-114,1998(arXiv:hep-th/9802109) [3919 total citations in SPIRES]

10. 416 “First year Wilkinson Microwave Anisotropy Probe (WMAP) observations: Determination of cosmological parameters”  by the WMAP Collaboration. Published in Astrophys.J.Suppl.148:175-194,2003(arXiv:astro-ph/0302209) [5652 total citations in SPIRES]

Read the rest of this entry »

Travis Brooks

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Honoring women in particle physics

March 8, 2010 | 4:56 am

CERN and Fermilab are celebrating International Women’s Day today, March 8, to honor the past and current contributions of women at the two laboratories. CERN has encouraged its staff and users to enable as many women as possible to be on shift in the LHC experiment control rooms and the CERN Control Centre. Poster exhibitions will also highlight the presence of women scientists in the laboratory. At Fermilab, women will take the lead in select control rooms and lead special guided tours focusing on how women have contributed to the experimental facilities at the Intensity Frontier.

A portion of the women on the ATLAS experiment, from the ATLAS International Women's Day poster

The idea for these celebrations began at CERN, with Pauline Gagnon from Indiana University, a scientist on the ATLAS experiment. Gagnon hopes that spotlighting women physicists at CERN will send an encouraging message to young women interested in science.

Webcams, accessible from the CERN Women’s Day website, show scenes from LHC control rooms throughout the day. The website also offers video interviews with women at CERN discussing why celebrating International Women’s Day is important to them. A poster series, also visible on the website, will present women from each of the LHC experiments and side by side photographs documenting the increasing presence of women scientists at CERN over the past several decades.

Paula Collins developed the concept for the LHCb experiment’s poster to focus on the varied roles that women in physics fulfill, whether at home or on the job. Collins believes that seeing women fulfill so many roles successfully is heartening for those considering a career in science, and points to her own sister as a model that has encouraged her. Collins, as both an experimental project leader and busy mother, is well aware of the complex balancing act that many women in the field face.

“When I heard about women’s day, I thought it was very exciting because I think it’s a positive gesture that CERN is able to make,” explains Collins. “I think that CERN can set the example to institutes and schools to show that it is really possible for women to be full partners in science and this is our opportunity to do it.”

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Women of the Intensity Frontier at Fermilab

At Fermilab, Women’s Day is part of a month-long Women’s History Month celebration. A videoconference at 8:30 a.m. Fermilab time, will link the laboratory to CERN for a live discussion on the contributions of women in physics. Speakers will include CERN’s Director-General Rolf Heuer and Coordinator for External Relations Felicitas Pauss; Fermilab’s Director Pier Oddone and Deputy Director Young-kee Kim of Fermilab; and experiment spokespeople Fabiola Gianotti of ATLAS and Guido Tonelli of CMS.

During Women’s History Month at Fermilab, weekly lunchtime discussions will focus on the experiences of women during various decades at the laboratory. Donn Hicks will be speaking about her experiences during the 1980’s. Hicks began working with Fermilab in 1980 with the technical division, where she was the second woman in her group. Her curiosity and enthusiasm for her work have driven her to push through many challenges.

Hicks was encouraged by Fermilab’s Karen Kephart and Dan Bollinger to pursue a degree in physics. In 2000, she completed her degree while working full time at Fermilab and fulfilling her duties as a single mother.

“The important thing is to reach out and learn as much as you can from those around you,” advises Hicks to young women pursuing science.

The task of encouraging young women to pursue an interest in physics has proven difficult in many countries, including the United States. At Fermilab, a lecture on this topic will be led by Professor Sandra Hanson of Catholic University. The lecture “Gender, Race and Science Education,” is free and open to the public and will be held on March 9.

International Women's Day poster from the CMS experiment

Chiara Mariotti, who encouraged Women’s Day participation on the CMS experiment at CERN, can recall how when she first came to CERN twenty years ago, there were far fewer women and their experiences were not easy. The experience of women in physics is changing however, and she hopes that this event will send that message to young women interested in science. She herself credits female role models in science as being formative in her pursuit of physics:

“We can show that it is possible for women to have a career in physics and it is possible to come to CERN. It’s possible to have a life and a job and be successful. I was quite lucky because I came from the Istituto Nazionale di Fisica Nucleare in Torino, an institute which is about 40 percent women. My advisor was a woman, my professors were women. Having a role model, I think, is really important.”

by Daisy Yuhas

Symmetry Intern

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Exotic antimatter detected at RHIC

March 5, 2010 | 2:04 pm

STAR Detector

An international team of scientists studying high-energy collisions of gold ions at the Relativistic Heavy Ion Collider, a 2.4-mile-circumference particle accelerator located at the US Department of Energy’s  Brookhaven National Laboratory, has published evidence of the most massive antinucleus discovered to date. The new antinucleus, discovered at RHIC’s STAR detector, is a negatively charged state of antimatter containing an antiproton, an antineutron, and an anti-Lambda particle. It is also the first antinucleus containing an anti-strange quark. The results were published online yesterday by Science Express.

“This experimental discovery may have unprecedented consequences for our view of the world,” commented theoretical physicist Horst Stoecker, vice president of the Helmholtz Association of German National Laboratories. “This antimatter pushes open the door to new dimensions in the nuclear chart — an idea that just a few years ago would have been viewed as impossible.”

The discovery may help elucidate models of neutron stars and opens up exploration of fundamental asymmetries in the early universe.

New nuclear terrain

All terrestrial nuclei are made of protons and neutrons, which both consist of up and down quarks. The standard Periodic Table of Elements is arranged according to the number of protons, which determine each element’s chemical properties. Physicists use a more complex, three-dimensional chart to convey information on the number of neutrons, which may change in different isotopes of the same element, and a quantum number known as “strangeness,” which depends on the presence of strange quarks (see diagram). Nuclei containing one or more strange quarks are called hypernuclei.

The diagram above is known as the 3-D chart of the nuclides. The familiar Periodic Table arranges the elements according to their atomic number, Z, which determines the chemical properties of each element. Physicists are also concerned with the N axis, which gives the number of neutrons in the nucleus. The third axis represents strangeness, S, which is zero for all naturally occurring matter, but could be non-zero in the core of collapsed stars. Antinuclei lie at negative Z and N in the above chart, and the newly discovered antinucleus (magenta) now extends the 3-D chart into the new region of strange antimatter.

For all ordinary matter, with no strange quarks, the strangeness value is zero and the chart is flat. Hypernuclei appear above the plane of the chart. The new discovery of strange antimatter with an antistrange quark (an antihypernucleus) marks the first entry below the plane.

This study of the new antihypernucleus also yields a valuable sample of normal hypernuclei, and has implications for our understanding of the structure of collapsed stars.

“The strangeness value could be non-zero in the core of collapsed stars,” said Jinhui Chen, one of the lead authors, a postdoctoral researcher at Kent State University and currently a staff scientist at the Shanghai Institute of Applied Physics, “so the present measurements at RHIC will help us distinguish between models that describe these exotic states of matter.”

The findings also pave the way towards exploring violations of fundamental symmetries between matter and antimatter that occurred in the early universe, making possible the very existence of our world.

Collisions at RHIC fleetingly produce conditions that existed a few microseconds after the big bang, which scientists believe gave birth to the universe as we know it some 13.7 billion years ago. In nucleus-nucleus collisions at RHIC as well as in the big bang, quarks and antiquarks emerge with equal abundance. At RHIC, among the collision fragments that survive to the final state, matter and antimatter are still close to equally abundant, even in the case of the relatively complex antinucleus and its normal-matter partner featured in the present study. In contrast, antimatter appears to be largely absent from the present-day universe.

“Understanding precisely how and why there’s a predominance of matter over antimatter remains a major unsolved problem of physics,” said Brookhaven physicist Zhangbu Xu, another one of the lead authors. “A solution will require measurements of subtle deviations from perfect symmetry between matter and antimatter, and there are good prospects for future antimatter measurements at RHIC to address this key issue.”

In a single collision of gold nuclei at RHIC, many hundreds of particles are emitted most created from the quantum vacuum via the conversion of energy into mass in accordance with Einstein's famous equation E = mc². The particles leave telltale tracks in the STAR detector (shown here from the end and side). Scientists analyzed about a hundred million collisions to spot the new antinuclei, identified via their characteristic decay into a light isotope of antihelium and a positive pi-meson. Altogether, 70 examples of the new antinucleus were found.

The STAR team has found that the rate at which their heaviest antinucleus is produced is consistent with expectations based on a statistical collection of antiquarks from the soup of quarks and antiquarks generated in RHIC collisions. Extrapolating from this result, the experimenters believe they should be able to discover even heavier antinuclei in upcoming collider running periods. Theoretical physicist Stoecker and his team have predicted that strange nuclei with roughly double the mass of the newly discovered state should be particularly stable.

RHIC’s STAR collaboration is now poised to resume antimatter studies with greatly enhanced capabilities. The scientists expect to increase their data by about a factor of 10 in the next few years.

The STAR collaboration is composed of 54 institutions from 13 countries. Research at RHIC is funded primarily by the DOE’s Office of Science and by various national and international collaborating institutions. Here’s the full list of RHIC funding agencies.

This release was issued on March 4, 2010, by Brookhaven National Laboratory.

Press Release

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Sky-wide neutrino search seeks supernovae in our backyard

March 4, 2010 | 5:02 pm

This composite image shows the effects of a powerful shock wave moving away from supernova 1987A. The outburst was visible to the naked eye, and is the brightest known supernova in almost 400 years. Credit: X-ray: NASA/CXC/PSU/S.Park & D.Burrows.; Optical: NASA/STScI/CfA/P.Challis

Astronomers use telescopes to scan the sky for signs of supernovae, extremely energetic explosions that occur at the end of a star’s life. In order to spot a supernova with a telescope, scientists need to peer in the right direction at the right time. By using machines built for particle physics, however, scientists can scour the entire sky at once.

When supernovae explode, for about 10 seconds they release a burst of neutrinos and antineutrinos that will arrive at Earth several hours before photons, or visible light, from the explosion. Physicists have been using neutrino detectors to search for these bursts for about 20 years.

Neutrinos are among the most abundant particles in the universe, but they interact very rarely with other matter. Though trillions of naturally occurring neutrinos from the sun and other celestial bodies rain down on us each second, they can pass through the entire Earth without bumping into another particle. As we learned at the recent meeting of the Americal Physical Society, only about one in four people will be hit by a neutrino once in a lifetime. (Don’t worry, you won’t feel a thing.)

No matter where a neutrino detector is located on Earth, it has a chance of noticing a burst of neutrinos from elsewhere in the galaxy. Thanks to the carefree manner in which neutrinos can zip through matter, they can pass straight through the Earth and interact with a detector on the opposite side.

For decades, a network of neutrino detectors, including those located at the Gran Sasso Underground Laboratory in Italy and the Super-Kamiokande experiment in Japan, has been searching for signs of supernovae. In 1987, the Kamiokande II experiment in Japan detected a supernova originating in the Large Magellanic Cloud, a neighboring galaxy. The detector recorded signs of 11 neutrinos about three hours before telescopes saw the first visible light emitted by the burst, named Supernova 1987A.

Physicists using neutrino detectors have yet to come across any definitive signs of supernovae in our galaxy. Collaborators from the MiniBooNE neutrino experiment at Fermilab in Illinois recently reported in the journal Physical Review D that during the time period from Dec. 14, 2004, to July 31, 2008, most of the Milky Way seems to have been supernova-free.

This isn’t too surprising, as astronomers predict that in our galaxy, only between one and 12 supernovae occur each century. Astronomer Johannes Kepler observed the Milky Way’s last known supernova in 1604. Scientists still study the remnant of the massive explosion, called Kepler’s star.

If physicists ever do catch a supernova in the act, they plan to send out an alert to observatories across the world. That way they can tell them the coordinates of a spectacular light show on its way.

Kathryn Grim

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Deep underground science: new issue of symmetry out today

March 3, 2010 | 3:20 pm

symmetry magazine special issue: underground science

If you’re a dark matter particle or a neutrino, it’s a constant struggle to make yourself heard. The universe is an exceptionally noisy place, filled with a rain of cosmic-ray particles—mainly high-energy protons. One of the few places to escape the noise is deep underground, where the rock, earth, or water above shields against cosmic rays and allows other particles to tell whatever they are trying to say.

This issue of symmetry explores a range of particle physics and other sciences that can be only be performed deep underground.

Some highlights of the issue: plans for a US deep underground science and engineering laboratory, taking clean equipment to an extreme in the Enriched Xenon Observatory in a salt deposit in New Mexico, the trial faced by the earthquake-stricken Abruzzo region and the Gran Sasso laboratory in Italy, the search for “dark life“, and a day in the life of the Soudan underground lab in Minnesota.

David Harris

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Top quark turns 15 today

March 2, 2010 | 11:38 am

Former Fermilab Director John Peoples talks to the press on March 2, 1995, the day that the laboratory announced the discovery of the top quark by CDF and DZero experiments. Today marks the 15 year anniversary of that discovery.

Fermilab scientist Alvin Tollestrup dons a top hat in honor of the top quark discovery in a photo from 1995.

Guest author

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