Outline
Natasa: Part I. Opera Experiment – An Introduction
Mar:
Part II. Explanations & Contradictions
John:
Part III. Consequences
Neutrinos…faster than light?
PART I. OPERA EXPERIMENT INTRODUCTION
OPERA experiment
Oscillation Project with Emulsion-tRacking Apparatus: instrument built
to detect tau neutrinos from muon neutrino oscillations
Collaboration of:
-CERN
-Laboratori Nazionali del Gran Sasso (LNGS)
-Project “CERN Neutrinos to Gran Sasso” (directs beam of neutrinos
from CERN to LNGS)
- Super Proton Synchrotron (SPS) accelerator as a source of high-energy
protons.
2010: FIRST tau neutrino event observed with OPERA!!
And in pictures…
LNGS:
-largest underground lab for particle
physics/astrophysics
-1400 m rock coverage!! Meaning
reduction factor 1,000,000 in cosmic
ray influx
60 miles outside Rome, 1 mile
below the surface..
Experiment: general plan and setup
Initial Expectations: estimated trip duration 2.43 milliseconds to complete 730 km
MAIN GOAL: analyse neutrino oscillations  expect that some muon neutrinos
will convert into tau neutrinos during flight
But how is the experiment carried out?
From protons to neutrinos…
1. SPS sends proton beam
2. collision with a graphite
target results in mostly kaon
& pion particles
3. focused by magnetic
lensing and travel for 1 km
down a tunnel in a vacuum
tube
4. decay into muons &
muon neutrinos
Number of muons measured
and compared to the number
arriving at detector!!
5. an iron graphite target
stops the particles & the
neutrinos continue
unaffected…
But...OPERA Neutrino Anomaly
• Neutrinos strike 150,000 “bricks” of
photographic emulsion films interleaved
with lead plates at OPERA detector
•Combining experiment data from 2009,
2010 & 2011
• Timing more than 16,000 neutrinos
Neutrinos’ speed faster than light by a
fraction of 20 parts per million!!!
Speed of light:
299,792,458 m/s
Measured neutrino speed:
299,798,454 m/s
Accuracy claimed by OPERA scientists
1. Accuracy of BASELINE measurement
• 2010 geodesy campaign
• 730 km travel path, 20 cm uncertainty!!!
• including Earth crust movements (continental drift, earthquaqes etc.)
• Tidal effects negligible
1. Accuracy of TIME OF FLIGHT measurement
•
•
•
Using GPS systems & Cs atomic clocks
Uncertainty less than 10 nanoseconds
Arrival 60 nanoseconds earlier than expected
6-sigma detection
(5-sigma required for particle physics
experiments)
What about past Neutrino Speed
Measurements?
Kamiokande II Experiment, Japan
• SN1987A
• 168,000 light years baseline
• neutrinos faster by 1 part in 100,000,000 of light speed
(compared to 2 parts in 100,000 from OPERA)
Kamiokande detector
Fermilab’s MINOS Experiment
• Baseline Chicago to Minnesota
• 2007 results: indication for early arrival of neutrinos
• precision not enough to rule out error (1.8 sigma
detection)
Front face of MINOS far detector
Results
Early arrival time of muon neutrinos with average
energy of 17 GeV by:
60.7 ± 6.9 (stat.)± 7.4 (sys.) ns
Relative difference to the speed of light:
2.48 ± 0.28 (stat.) ± 0.30 (sys.) ns
Result checked for energy dependence (none found within
the domain explored by OPERA)!
See article “Measurement of the neutrino velocity with the OPERA detector in the CNGS beam”,
arXiv:1109.4897v1
Testing the Results
• CERN neutrino speed (re-)calculation using a different technique
- results expected by November 21st
Independent (replica) experiments planned to test the OPERA result:
• T2K experiment using Kamiokande detector (baseline 295 km)
• Fermilab: after upgrade of MINOS detectors (baseline 730 km)
- results expected during 2012
SUPERLUMINAL
NEUTRINOS
Part II. Explanations &
Contradictions
Franklin (2011)
1. Superluminal propagation
in matter
Arrival times found for 2 different neutrino energy ranges:
E1 = 13.9 GeV
E2 = 42.9 GeV
The difference between the light time of flight and the neutrino
time of flight lead to relative neutrino velocities:
D1 = (2.18 ± 0.77 ± 0.30) ´10-5
D 2 = (2.76 ± 0.75 ± 0.30)´10
-5
D º vn m -1
2
Degree of superluminosity is independent of the energy
Superluminal speeds are not forbidden by special relativity, but:
Acceleration of a particle with fixed mass from subluminal to
superluminal speed is forbidden:
E=
mc 2
Infinite energy would be required
1- v 2 / c 2
Particles produced at superluminal speeds are consistent with relativity:
Tachyons
negative mass, m2 < 0
energy dependent superluminal speeds
The ratio of velocities should then be:
But no energy dependence observed!
D1 / D2 = 9
- neutrinos produced with subluminal speed
- propagation through matter produces superluminal
speed via an energy dependent potential
(only for neutrinos with mass < potential causing the superluminosity)
2. Loss of energy
Cohen & Glashow (2011)
Muon neutrinos mean energy = 17. 5 GeV
Exceed speed of light by 7.5 km/s
They should lose energy as they propagate via:
Bremsstrahlung emission of electron-positrons pairs
n m ® n m + e- + e+
(Threshold energy for the OPERA experiment = 140 MeV)
No neutrinos (or very few) with energy > 12.5 GeV should arrive to
Gran Sasso!!
The observation of neutrinos with E > 12.5 GeV cannot be reconciled
with the superluminal neutrino vel. measurement
Van Elburg (2011)
3. Detector observed from satellite
Source-detector distance = Sbasel. (in their baseline ref. frame)
In the satellite ref. frame, there are 2 movements after a photon
is emitted:
1. photon travels towards detector at c
2. detector moves towards photon emission location at velocity v
In the satellite ref. frame,
Lorentz
distance traveled by the photons < Sbasel. contraction
Ssat. =
Sbasel.
g
Photon reaches detector when:
g=
1
1- v 2 / c 2
t sat.original
= Ssat.separation)
(distance covered by detector and photonctequals
the
sat. + v
Time of flight in the satellite ref. frame:
Ssat.
Sbasel.
t sat. =
=
c + v g (c + v)
The OPERA authors project the time provided by the satellite’s
clock back to the baseline and use:
t basel. =
Sbasel.
c
However, they should observe the Lorentz transformationcorrected time of flight as measured in the satellite ref. frame:
Sbasel.
Observed time of flight = t 0 = gt sat. =
c+v
From GPS satellite’s orbit and velocity
e = t basel. - t 0 = 32ns
2e = 64ns
Using the baseline instead of the clock
ref. frame overestimates time of flight !!
4. Pseudoscalar potential
Sahu & Zhang (2011)
Superluminal propagation possible in a pseudoscalar potential
φ> 0
can be energy dependent
constant in space
power law logarithmic
a
æ En ö æ En ö
f (En ) = C ç ÷ ln ç ÷
è E0 ø è E0 ø
adjusting E0 and C, the OPERA data can be interpreted if
df
f
where
f
=
> 2f
dEn
En
but not the SN 1987A data!
5. Coherent interaction in matter
c
n=
v
determines the phase velocity of propagation of
almost massless particles through the medium
Refraction index
If n < 1
phase velocity of particles through medium
can be larger than c
(fully compatible with relativity)
Neutrinos created in a coherent quantum state in CERN
They interact only coherently with matter while they propagate
(coherent enhancement scattering)
OPERA measures the phase velocity of the coherent
neutrino wave, which depends on n
Refraction index of neutrinos in matter < 1
Phase velocity > c
But group velocity = c
Consistent with data from SN 1987A, if there is coherent
neutrino wave interacting with matter
Does not apply to solar neutrinos, since they are not affected by a
coherent enhancement
Brustein & Semikoz (2011)
6. Other possibilities
Superluminal group velocity that arises from constructive and
destructive interference deforming the leading and trailing edges
of the pulse
Mecozzi & Bellini (2011)
Morris (2011)
Neutrinos coupled to a new gauge field sourced by the Earth (e.g.,
similar to the existing electro-magnetic field)
 Local magnetic field modifies local gravitational background
 Neutrino’s velocity becomes larger than c
Oda & Taira (2011)