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From LaThuile to Venice through the MEG experiment

March 11, 2011

Here I am, back with my second post, hoping Tommaso’s patience not to be running out because of my idleness!

In this amazing starry night at Gran Sasso (sometimes physicists are really hard-living, aren’t they?!), giving a look at the Neutel Program,  I was noticing many links to talks presented at the LaThuile Conference. Actually, the “Rencontres de Physique” covered a much broader physics program with respect to the Venice Conference, spreading from Cosmology to Physics of Hadronic Interactions, from Neutrinos to Flavor Physics, from Rare decays and CP violation to Electrowaek and top physics. But “Neutrino Telescopes”, in addition to a rich and broad neutrino physics program (suggested by its own name), is exploring some interesting items at the boundary of the “traditional” neutrino physics, such as the look for muon decay into an electron and a photon.

Feynmann diagrams of the muon decay into an electron and a photon as prediced by the Standard Mondel (on the left) and SUSY (on the right)

In my opinion it is fascinating how such a simple, elementary process could become a clean probe of new physics: it actually is a lepton flavor violating process, strongly suppressed in Standard Model (with a branching ratio 10E-54 with respect to the decay process into an electron and two neutrinos), but enhanced in SUSY and other new physics theories.

The MEG Collaboration



A nice experiment, actually data taking at the PSI, is MEG (or perhaps I’m just interested in the Collaboration, which seems to be pretty party oriented!). Being a precision experiment, it is really challenging in calibration (in particular concerning liquid Xenon) and in background rejection: resolutions and PDFs are evaluated on data outside the signal region, which is taken closed until analysis is fixed.


Preliminary 2009 results, presented by L. Galli at La Thuile, indicate a sensitivity of 6 x 10E-12 with 0 signal, to be improved in next years run. However new results should be soon available, hopefully presented in Venice by A. Baldini.

(posted by A. Fava)

One Comment leave one →
  1. March 12, 2011 9:55 am

    Hi Angela,

    I hope somebody will install a telescope for those clear nights at the Gran Sasso. When you do, please call me over.

    I’ll admit I did not know that the SM BR for muon into electron photon was so ridiculously tiny. We call “unobservably small” a branching ratio when it is in the 10^-10 range, so 10^-50 (not willing to even consider the second digit as significant!) is astonishing to me. At such rates, one might even imagine that gravitational effect become important. Unfortunately we cannot compute them…


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