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OPERA
experiment reports anomaly in flight
time of neutrinos from CERN to Gran
Sasso
23.09.2011
UPDATE 18
November 2011
Following the OPERA
collaboration's presentation at CERN
on 23 September, inviting scrutiny
of their neutrino time-of-flight
measurement from the broader
particle physics community, the
collaboration has rechecked many
aspects of its analysis and taken
into account valuable suggestions
from a wide range of sources. One
key test was to repeat the
measurement with very short beam
pulses from CERN. This allowed the
extraction time of the protons, that
ultimately lead to the neutrino
beam, to be measured more precisely.
The beam sent from
CERN consisted of pulses three
nanoseconds long separated by up to
524 nanoseconds. Some 20 clean
neutrino events were measured at the
Gran Sasso Laboratory, and precisely
associated with the pulse leaving
CERN. This test confirms the
accuracy of OPERA's timing
measurement, ruling out one
potential source of systematic
error. The new measurements do not
change the initial conclusion.
Nevertheless, the observed anomaly
in the neutrinos' time of flight
from CERN to Gran Sasso still needs
further scrutiny and independent
measurement before it can be refuted
or confirmed.
On 17 November, the collaboration
submitted a paper on this
measurement to the peer reviewed
Journal of High Energy Physics
(JHEP). This paper is also available
on the Inspire
website.
Geneva,
23 September 2011. The OPERA1 experiment,
which observes a neutrino beam from CERN2 730
km away at Italy’s INFN Gran Sasso
Laboratory, will present new results in
a seminar at CERN this afternoon at
16:00 CEST. The seminar will be webcast
at http://webcast.cern.ch.
Journalists wishing to ask questions may
do so via twitter using the hash tag
#nuquestions, or via the usual CERN
press office channels.
The OPERA
result is based on the observation of
over 15000 neutrino events measured at
Gran Sasso, and appears to indicate that
the neutrinos travel at a velocity 20
parts per million above the speed of
light, nature’s cosmic speed limit.
Given the potential far-reaching
consequences of such a result,
independent measurements are needed
before the effect can either be refuted
or firmly established. This is why the
OPERA collaboration has decided to open
the result to broader scrutiny. The
collaboration’s result is available on
the preprint server arxiv.org: http://arxiv.org/abs/1109.4897.
The OPERA
measurement is at odds with
well-established laws of nature, though
science frequently progresses by
overthrowing the established paradigms.
For this reason, many searches have been
made for deviations from Einstein’s
theory of relativity, so far not finding
any such evidence. The strong
constraints arising from these
observations makes an interpretation of
the OPERA measurement in terms of
modification of Einstein’s theory
unlikely, and give further strong reason
to seek new independent measurements.
" This
result comes as a complete surprise,” said
OPERA spokesperson, Antonio Ereditato of
the University of Bern. “After
many months of studies and cross checks
we have not found any instrumental
effect that could explain the result of
the measurement. While
OPERA researchers will continue their
studies, we are also looking forward to
independent measurements to fully assess
the nature of this observation.”
"When
an experiment finds an apparently
unbelievable result and can find no
artefact of the measurement to account
for it, it’s normal procedure to invite
broader scrutiny, and this is exactly
what the OPERA collaboration is doing,
it’s good scientific practice,” said
CERN Research Director Sergio
Bertolucci. “If
this measurement is confirmed, it might
change our view of physics, but we need
to be sure that there are no other, more
mundane, explanations. That will require
independent measurements.”
In order
to perform this study, the OPERA
Collaboration teamed up with experts in
metrology from CERN and other
institutions to perform a series of high
precision measurements of the distance
between the source and the detector, and
of the neutrinos’ time of flight. The
distance between the origin of the
neutrino beam and OPERA was measured
with an uncertainty of 20 cm over the
730 km travel path. The neutrinos’ time
of flight was determined with an
accuracy of less than 10 nanoseconds by
using sophisticated instruments
including advanced GPS systems and
atomic clocks. The time response of all
elements of the CNGS beam line and of
the OPERA detector has also been
measured with great precision.
"We
have established synchronization between
CERN and Gran Sasso that gives us
nanosecond accuracy, and we’ve measured
the distance between the two sites to 20
centimetres,” said
Dario Autiero, the CNRS researcher who
will give this afternoon’s seminar. “Although
our measurements have low systematic
uncertainty and high statistical
accuracy, and we place great confidence
in our results, we’re looking forward to
comparing them with those from other
experiments."
" The
potential impact on science is too large
to draw immediate conclusions or attempt
physics interpretations. My
first reaction is that the neutrino is
still surprising us with its mysteries.” said
Ereditato. “Today’s seminar is
intended to invite scrutiny from the
broader particle physics community.”
The OPERA
experiment was inaugurated in 2006, with
the main goal of studying the rare
transformation (oscillation) of muon
neutrinos into tau neutrinos. One first
such event was observed in 2010, proving
the unique ability of the experiment in
the detection of the elusive signal of
tau neutrinos.
Further information:
OPERA website
Quantum diaries blog post: Elementary,
my dear neutrino...
Photos from the OPERA collaboration:
http://www.infn.it/comunicazione/scambio/
CNRS
Photos of the
seminar on OPERA Results
Contact:
CERN Press Office, press.office@cern.ch
+41 22 767 34 32
+41 22 767 21 41
Follow CERN at:
www.cern.ch
http://twitter.com/cern/
http://www.youtube.com/user/CERNTV
http://www.quantumdiaries.org/
1. OPERA has been designed and is being
conducted by a team of researchers from
Belgium, Croatia, France, Germany,
Israel, Italy, Japan, Korea, Russia,
Switzerland and Turkey. The experiment
constitutes a complex scientific
enterprise that has been realised thanks
to the skill of a large number of
scientists, engineers, technicians and
students, and with the strong commitment
of the various actors of the project. In
particular we mention the LNGS/INFN and
CERN laboratories, and the major
financial support of Italy and Japan
with substantial contributions from
Belgium, France, Germany and
Switzerland. The OPERA Collaboration
presently includes about 160 researchers
from 30 institutions and 11 countries:
IIHE-ULB Brussels, Belgium; IRB Zagreb,
Croatia; LAPP Annecy, France; IPNL Lyon,
France; IPHC Strasbourg, France;
Hamburg, Germany; Technion Haifa,
Israel; Bari, Italy; Bologna, Italy;
LNF, Italy, L’Aquila, Italy; LNGS,
Italy; Naples, Italy; Padova, Italy;
Rome, Italy; Salerno, Italy; Aichi,
Japan; Toho, Japan; Kobe, Japan; Nagoya,
Japan; Utsunomiya, Japan; GNU Jinju,
Korea; INR RAS Moscow, Russia; LPI RAS
Moscow, Russia; ITEP Moscow, Russia;
SINP MSU Moscow, Russia; JINR Dubna,
Russia; Bern, Switzerland; ETH Zurich,
Switzerland; METU Ankara, Turkey.
2. CERN, the European Organization for
Nuclear Research, is the world's leading
laboratory for particle physics. It has
its headquarters in Geneva. At present,
its Member States are Austria, Belgium,
Bulgaria, the Czech Republic, Denmark,
Finland, France, Germany, Greece,
Hungary, Italy, the Netherlands, Norway,
Poland, Portugal, Slovakia, Spain,
Sweden, Switzerland and the United
Kingdom. Romania is a candidate for
accession. India, Israel, Japan, the
Russian Federation, the United States of
America, Turkey, the European Commission
and UNESCO have Observer status.
Source: Public
Cern Web |
