Giovedì, 18 Ottobre 2018
ROME

Italians see third 'shape-shifting' neutrino

English
© ANSA

Rome, March 26 - Italian researchers have observed
the third shape-shifting' neutrino ever seen, spreading fresh
light on these enigmatic sub-atomic particles.
The observation, like the previous two, was made in the
Gran Sasso laboratory of Italy's National Nuclear Physics
Institute (INFN), deep under the largest mountain in Italy
outside the Alps, scientists said.
The INFN researchers in the OPERA (Oscillation Project with
Emulsion-tRacking Apparatus) project again saw one type of
neutrino changing into another kind as it zipped in from the
CERN European nuclear research centre in the Alps near Geneva.
This type of spontaneous "flip-flopping" had never been
seen before May 2010 when the Gran Sasso lab announced the first
instance in what was hailed as potentially the most exciting
find in particle physics in decades.
Scientists say further observations of this behaviour may
shed light on how matter came to dominate over antimatter in the
universe, and what happens to missing neutrinos.
For 40 years scientists have been wondering why many fewer
neutrinos arrive from the Sun and other stars than models
predict.
The most likely hypothesis is that they have not in fact
gone astray but have simply changed form.
The OPERA experiment was set up five years ago to verify
the theory.
OPERA International Director Giovanni De Lellis said
finding the third transformed neutrino was "an important
confirmation of the previous two observations.
"This event has characteristics which make it unmistakable
compared to other processes," he stressed.
The so-called 'oscillation' could lead to a radical rethink
in particle physics, he said.
The third transformation of a muon neutrino into a tau
neutrino during the 730km, 2.4 millisecond trip from the CERN
lab, "makes us confident, from a statistical standpoint, that we
will be able to confirm the oscillation," De Lellis said.
OPERA will be on the look-out for more tau neutrinos that
were originally muons for another two years, he said, in a bid
to "definitively prove this very rare phenomenon".
As well as likely accounting for the apparent disappearance
of neutrinos on their trip to Earth, he said, the phenomenon
also contradicts the Standard Model of particle physics which
states that neutrinos do not have a mass.

EXPERIMENT STARTED IN 2006.
The ground-breaking neutrino experiment started on
September 11, 2009, when CERN sent its first burst of
neutrinos down to OPERA.
Since then, billions and billions of the particles have
arrived at the lab.
The CERN Neutrino To Gran Sasso (CNGS) experiment was
expressly set up to establish that neutrinos can change
'flavour' - an hypothesis first raised almost 70 years ago by
famed Italian physicist Guido Pontecorvo.
Neutrinos come in three flavours: electron neutrinos
(associated with the electron), muon neutrinos (the muon is a
bit bigger than the electron) and tau neutrinos (bigger
still).
Previously, US and Japanese experiments had only observed
the disappearance of muon neutrinos.
By contrast, CNGS's neutrino bursts have now shown muon
neutrinos changing into tau neutrinos.
If neutrinos really are oscillating, this could go a
long way to explaining why the mass of the visible universe
only adds up to a fraction of the total mass value derived
from the observed dynamics in galaxies.
Physicists have long been wondering where the majority of
the mass in the universe could be.
If neutrinos oscillate then theory dictates that they
must have mass.
It is probably only a very tiny mass, but there are so
many neutrinos around in the universe - almost a billion
times as many as there are protons - that they could account
for at least as much mass as exists in visible stars.
A breakthrough of similar magnitude happened last year with
the discovery of the Higg's Boson, long theorised as a key
particle in giving the Universe mass.

photo: CERN Neutrino to Gran Sasso project

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