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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. - PowerPoint PPT PresentationTRANSCRIPT
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OutlineNatasa: Part I. Opera Experiment – An IntroductionMar: Part II. Explanations & ContradictionsJohn: Part III. Consequences
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Neutrinos…faster than light?
PART I. OPERA EXPERIMENT INTRODUCTION
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OPERA experimentOscillation Project with Emulsion-tRacking Apparatus: instrument built to detect tau neutrinos from muon neutrino oscillationsCollaboration 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!!
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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..
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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?
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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
5. an iron graphite target stops the particles & the neutrinos continue unaffected…
Number of muons measured and compared to the number arriving at detector!!
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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
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Accuracy claimed by OPERA scientists
1. Accuracy of BASELINE measurement
2. Accuracy of TIME OF FLIGHT measurement
6-sigma detection(5-sigma required for particle
physics experiments)
• Using GPS systems & Cs atomic clocks• Uncertainty less than 10 nanoseconds• Arrival 60 nanoseconds earlier than expected
• 2010 geodesy campaign • 730 km travel path, 20 cm uncertainty!!!• including Earth crust movements (continental drift, earthquaqes etc.)• Tidal effects negligible
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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)
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
Kamiokande detector
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ResultsEarly 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
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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
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SUPERLUMINAL NEUTRINOSPart II. Explanations & Contradictions
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1. Superluminal propagation in matter
Arrival times found for 2 different neutrino energy ranges:E1 = 13.9 GeVE2 = 42.9 GeV
The difference between the light time of flight and the neutrino time of flight lead to relative neutrino velocities:
Degree of superluminosity is independent of the
energy
Franklin (2011)
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Superluminal speeds are not forbidden by special relativity, but: Acceleration of a particle with fixed mass from subluminal to superluminal speed is forbidden:
Particles produced at superluminal speeds are consistent with relativity:
Tachyons negative mass, m2 < 0energy dependent superluminal speeds
The ratio of velocities should then be:But no energy dependence observed!
- 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)
Infinite energy would be required
Possible explanation
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2. Loss of energyMuon neutrinos mean energy = 17. 5 GeVExceed speed of light by 7.5 km/s
They should lose energy as they propagate via: Bremsstrahlung emission of electron-positrons pairs
(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
Cohen & Glashow (2011)
Contradiction
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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, distance traveled by the photons < Sbasel.
Photon reaches detector when: (distance covered by detector and photon equals the original separation)
Van Elburg (2011)
Lorentz contracti
on
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Time of flight in the satellite ref. frame:
The OPERA authors project the time provided by the satellite’s clock back to the baseline and use:
However, they should observe the Lorentz transformation-corrected time of flight as measured in the satellite ref. frame:
Observed time of flight =
From GPS satellite’s orbit and velocity Using the baseline instead of the clock ref. frame overestimates time of flight !!
Possible explanation
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4. Pseudoscalar potential
Superluminal propagation possible in a pseudoscalar potentialφ> 0can be energy dependentconstant in spacepower law logarithmicadjusting E0 and C, the OPERA data can be interpreted if
where
but not the SN 1987A data!
Sahu & Zhang (2011)
Possible explanation
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5. Coherent interaction in matter
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
determines the phase velocity of propagation of almost massless particles through the medium
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Refraction index of neutrinos in matter < 1
Consistent with data from SN 1987A, if there is coherent neutrino wave interacting with matterDoes not apply to solar neutrinos, since they are not affected by a coherent enhancement
Phase velocity > cBut group velocity = c
Brustein & Semikoz (2011)
Possible explanation
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6. Other possibilitiesSuperluminal 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)
Possible explanations