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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 Oscillation Project with Emulsion-tRackingApparatus: instrument built to detect tau neutrinos from muon neutrino oscillations • Collaboration of: • -CERN • -LaboratoriNazionali 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 5. an iron graphite target stops the particles & the neutrinos continue unaffected… Number of muons measured and compared to the number arriving at detector!!
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 Accuracy of BASELINE measurement Accuracy of TIME OF FLIGHT measurement • 2010 geodesy campaign • 730 km travel path, 20 cm uncertainty!!! • including Earth crust movements (continental drift, earthquaqes etc.) • Tidal effects negligible • 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: Degree of superluminosity is independent of the energy
Infinite energy would be required • 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 < 0 energy 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) Possible explanation
Cohen & Glashow (2011) 2. Loss of energy Contradiction • 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 (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, distance traveled by the photons < Sbasel. • Photon reaches detector when: (distance covered by detector and photon equals the original separation) Lorentz contraction
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 Possible explanation Using the baseline instead of the clock ref. frame overestimates time of flight !!
Sahu & Zhang (2011) 4. Pseudoscalar potential • Superluminal propagation possible in a pseudoscalarpotential • φ> 0 • can be energy dependent • constant in space • power law logarithmic • adjusting E0 and C, the OPERA data can be interpreted if where but not the SN 1987A data! Possible explanation
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
Phase velocity > c But group velocity = c • Refraction index of neutrinos in matter < 1 • 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) Possible explanation
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) Possible explanations