Italy approves SuperB particle collider

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Jan 6, 2011

The Italian government has given final approval for building a new €500m collider that will investigate the small but significant differences between matter and antimatter. The SuperB facility will smash electrons and positrons together to produce particle/antiparticle pairs of B-mesons, D-mesons and tau-leptons. Measuring the subtle differences in how these particles and their antiparticles decay could help shed light on the mystery of why there is so much more matter than antimatter in the universe.

The SuperB facility will be built by Italy's national institute for nuclear and particle-physics research (INFN). It will consist of a 2 km circumference ring with two accelerators – one for electrons and the other for positrons. Collisions will occur within a large detector that will track the decay products and measure their energy.

The facility is expected to produce B-mesons at a rate 50–100 times greater than existing and previous "B factories" such as BaBar in the US and Belle in Japan. Marcello Giorgi from the INFN's lab in Pisa, who is director of the SuperB project board, says that the experiment could begin taking data by 2016.

SuperB will also produce synchrotron radiation, which will be used in a wide range of experiments in condensed-matter physics, chemistry, biology and materials science. The synchrotron facility will have six beamlines – three extracting light from the electron beam and three from the positron beam. Although this is a small number of beamlines compared with other synchrotron facilities, Giorgi told physicsworld.com that "the brilliance of the light will be greater than any existing synchrotron".

The SuperB synchrotron, plans for which were finalized in February 2010, will be run by the Italian Institute of Technology (ITT). Once particle-physics experiments are finished at SuperB, the facility will eventually be devoted solely to synchrotron-radiation research. However, Giorgi, stresses that particle physics is the priority and he does not expect the matter/antimatter studies to be adversely affected by the synchrotron research.

Although the funding announcement has been delayed by a year – due in part to the global financial crisis – Giorgi expects work to begin on the facility later this year. Commissioning of the accelerator is scheduled for late 2015 and the first data should emerge in 2016. Physicists should be able to keep to this tight schedule because many of the accelerator components will be reused from the defunct PEP-II electron–positron collider at SLAC National Accelerator Laboratory in the US, which hosted the BaBar experiment until 2008.

Despite this tight schedule, the INFN has still not decided where to build the facility. The leading candidate is INFN's Frascati lab just outside Rome. Frascati is already home to the DAFNE electron–positron collider, which is used to study CP violation in K-mesons. Although the INFN site is not large enough to hold the entire ring, it could be shared with the adjoining Frascati campus of Italy's national energy research lab ENEA. According to Giorgi, the INFN is in the final stages of negotiating this plan, which includes building tunnels under a main road.

If the Frascati plan falls through, the alternative site is Rome's University of Tor Vergata, which is about 2.4 km from the Frascati lab. According to Giorgi, a site will be chosen by the end of January.

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New particle links dark matter with missing antimatter

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Nov 29, 2010

Physicists in the US and Canada have proposed a new particle that could solve two important mysteries of modern physics: what is dark matter and why is there much more matter than antimatter in the universe?

The yet-to-be-discovered "X" particle is expected to decay mostly to normal matter, whereas its antiparticle is expected decay mostly to "hidden" antimatter. The team claims that its existence in the early universe could explain why there is more matter than antimatter in the universe – and that dark matter is in fact hidden antimatter.

Dark matter is a mysterious substance that appears to make up about 80% of the material universe. Although its existence can be inferred from its gravitational pull on normal matter, physicists have yet to detect it directly and therefore don't know what it is made of. Antimatter, on the other hand, is easy to create and study in the lab. However, the Standard Model of particle physics cannot explain why antimatter is so rare in a universe that is dominated by matter – a mystery called baryon asymmetry.

Now, Hooman Davoudiasl of Brookhaven National Laboratory and colleagues at TRIUMF and the University of British Columbia have proposed a new particle dubbed X that could solve both of these mysteries. X has a mass of about 1000 GeV – making it about a thousand times heavier than a proton. This particle can decay to a neutron or to two hypothetical hidden particles called Y and F. Both hidden particles would have masses of about 2–3 GeV. Its antiparticle, anti-X, decays to an antineutron or to the pair anti-Y and anti-F.

Physicists have tried to try to explain the baryon asymmetry by invoking a violation of the charge–parity (CP) symmetry – the result being that decaying particles are more likely to generate matter than antimatter. CP violation has been observed in laboratories, but the preference for matter is far too small to account for the proportion of matter in the universe.

X also commits CP violation in a way that author Kris Sigurdson of the University of British Columbia calls a "yin yang" decay pattern. While X decays to neutrons more often than anti-X decays to antineutrons, it is balanced by anti-X, which decays to anti-Y and anti-F more often than Y and F. When almost all particles with an available antiparticle annihilated one another in the early universe, these discrepancies left a chunk of visible matter and a heavier chunk of dark antimatter to form the cosmos.

The team has also thought of how the anti-Y and anti-F particles could be detected. Unlike weakly interacting massive particles (WIMPs) – which dominate many theories of dark matter – anti-Y and anti-F do not annihilate each other. However, the antiparticles would cause protons to decay, which is forbidden by the Standard Model. If an anti-Y particle collides with a proton, for instance, a virtual interaction with particle X can break the proton apart, transforming it into a positively charged kaon, and turning the anti-Y particle into a F particle.

A detector looking for proton decays, such as SuperKamiokande in Japan's Kamioka mine, could catch the kaon. Kaons produced this way would have much higher energies than those generated by proton decays allowed by other theories that go beyond the Standard Model. Although protons are expected to be fairly resilient to this decay process, Sigurdson says, "This scenario could be on the boundary of detectability."

"It looks like a very interesting model," says Dan Hooper of Fermilab. Although at least three more models linking the production of dark matter to the baryon asymmetry are in development, he says that the proton-decay signature sets this scenario apart.

Matthew Buckley of Fermilab says that there is a sudden interest in linking dark matter with the baryon asymmetry because of recent experiments that have tried (unsuccessfully) to detect dark matter. Although WIMP models prefer dark-matter particles with masses around 100 GeV, the experiments suggest that dark-matter particles have masses nearer 7 or 8 GeV.

Having such a large mass "definitely isn't what a WIMP is 'supposed to look like'," says Buckley. However, dark matter that also explains the baryon asymmetry seems to be more in line with recent experimental results – which is why Buckley believes it deserves further exploration.

The work is reported in Phys. Rev. Lett. 105 211304.

Kate McAlpine is a science communicator based in the US

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8th Conference on Nuclear and Particle Physics

Conference on Nuclear and Particle Physics (NUPPAC)is the traditional Egyptian conference on nuclear and particle physics organized biennially on a regular basis since 1997. Nuclear and particle scientists meet in friendly atmosphere to present their achievements and discuss future plans.

View the original article here

8th Conference on Nuclear and Particle Physics

Conference on Nuclear and Particle Physics (NUPPAC)is the traditional Egyptian conference on nuclear and particle physics organized biennially on a regular basis since 1997. Nuclear and particle scientists meet in friendly atmosphere to present their achievements and discuss future plans.

View the original article here