Category Archives: Particle Physics

LHC Shut Down By Weasel

It was reported last week that the LHC will be shut down for a few weeks due to a weasel gnawing through a power cable. The weasel, as you might expect, did not survive.

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Edelweiss Releases New WIMP Limits

The Edelweiss experiment has released a new preprint including updated limits in the low mass region from their WIMP dark matter search using germanium bolometers. There are still some stronger limits, but one interesting thing is that this further bolsters the case that the various purported WIMP signals from other experiments are probably not actually dark matter. The results from experiments like CoGeNT, CRESST, and DAMA all lie above the limit shown here.

New Article on Sterile Neutrinos

Symmetry has a fairly new article on sterile neutrinos, explaining some of the basic ideas about what they are and why we’re interested in them. Measurements of the Z peak in e+/e- collisions at LEP showed that there are only 3 neutrinos, but there are some caveats to that. The measurements showing that there are 3 neutrinos really mean that there are 3 neutrinos that (1) have less than half the Z mass (91.2 GeV) and (2) interact with Standard Model particles via the weak force.

If we can instead add some “neutrinos” that don’t interact through the weak force, then there’s room for more neutrinos. One of the main ways people search for them is to find problems with the standard picture of 3-neutrino oscillations. If there are sterile neutrinos that mix with the three usual flavors (electron, muon, and tau), then maybe we can find evidence of neutrinos oscillating into sterile neutrinos. That is, regular neutrinos seemingly disappearing altogether rather than changing from one type to another.

New e+/e- Collider Turns On

SuperKEKB, an upgraded version of the KEK B electron/positron collider at the KEK lab in Tsukuba has started up. There are no collisions yet, but they are starting to run beams around the main ring. The Belle II experiment will use he SuperKEKB facility to study B physics – that is, the physics of B mesons (and other particles involving b quarks). These are particularly interesting because the lifetimes of many of these particles decay weakly with long enough lifetimes to actually measure how far they travelled. B physics allows for high precision tests of various aspects of the Standard Model, including things like CP violation in the quark sector (i.e. matter/antimatter differences), particle spectroscopy (measuring the properties of the various kinds of composite particles), and searches for various kinds of new physics.

Antares Looks for Dark Matter Signals

The ANTARES neutrino telescope has a new result looking for “secluded” dark matter, where dark matter annihilation is mediated through some new mediator that then decays into Standard Model particles. They claim that this can explain the high energy bump in the positron/electron ratio and can also still be a thermal relic from the Big Bang.

They look at several different channels, including one where the mediator actually lives long enough to reach Earth and decay in the atmosphere, and others where neutrinos in the final state are measured.

For this model, the result is actually stronger than direct detection experiments for spin-dependent interactions and is stronger at very high masses in the spin-independent channel. While this result isn’t particularly groundbreaking, the paper mentions that it is the first search of this kind for this type of dark matter, and I think the model, which I hadn’t heard much of previously, sounds quite interesting.

DM-Ice Releases Results

The DM-Ice experiment has released their first results for a search for an annually modulating signal of dark matter. They’re currently about an order of magnitude off from the purported DAMA/LIBRA signal but hopefully will improve significantly in the future.

DM-Ice is a NaI(Tl)-based experiment looking for signals of dark matter in their scintillating crystals. The big purpose of DM-Ice is to test various theories for why the DAMA/LIBRA experiment, a NaI(Tl) experiment at Gran Sasso, has seen an annual modulation in its event rate for many years. Various people have proposed that maybe DAMA/LIBRA is just seeing a seasonal effect. DM-Ice is in Antarctica, so any seasonal effects will be very different. If DM-Ice sees the same modulation as DAMA/LIBRA, then that would rule out many of the proposed explanation, since dark matter will modulate in the same way no matter where the detector is but most other things will be location dependent.