Measurement of the neutrino velocity with the OPERA detector in the CNGS beam

with 7 comments

The OPERA neutrino experiment at the underground Gran Sasso Laboratory has measured the velocity of neutrinos from the CERN CNGS beam over a baseline of about 730 km with much higher accuracy than previous studies conducted with accelerator neutrinos. The measurement is based on high-statistics data taken by OPERA in the years 2009, 2010 and 2011. Dedicated upgrades of the CNGS timing system and of the OPERA detector, as well as a high precision geodesy campaign for the measurement of the neutrino baseline, allowed reaching comparable systematic and statistical accuracies. An early arrival time of CNGS muon neutrinos with respect to the one computed assuming the speed of light in vacuum of (60.7 \pm 6.9 (stat.) \pm 7.4 (sys.)) ns was measured. This anomaly corresponds to a relative difference of the muon neutrino velocity with respect to the speed of light (v-c)/c = (2.48±0.28 (stat.)±0.30 (sys.)) x 10-5……..

…… Conclusions
The OPERA detector at LNGS, designed for the study of neutrino oscillations in appearance mode, has provided a precision measurement of the neutrino velocity over the 730 km baseline of the CNGS neutrino beam sent from CERN to LNGS through the Earth’s crust. A time of flight measurement with small systematic uncertainties was made possible by a series of accurate metrology techniques. The data analysis took also advantage of a large sample of about 16000 neutrino interaction events detected by OPERA.
The analysis of internal neutral current and charged current events, and external νµ CC interactions from the 2009, 2010 and 2011 CNGS data was carried out to measure the neutrino velocity. The sensitivity of the measurement of (v-c)/c is about one order of magnitude better than previous accelerator neutrino experiments.
The results of the study indicate for CNGS muon neutrinos with an average energy of 17 GeV an early neutrino arrival time with respect to the one computed by assuming the speed of light in vacuum:
δt = (60.7 ± 6.9 (stat.) ± 7.4 (sys.)) ns.
The corresponding relative difference of the muon neutrino velocity and the speed of light
(v-c)/c = δt /(TOF’c – δt) = (2.48 ± 0.28 (stat.) ± 0.30 (sys.)) ×10-5.
with an overall significance of 6.0 σ.
The dependence of δt on the neutrino energy was also investigated. For this analysis the
data set was limited to the 5489 νµ CC interactions occurring in the OPERA target. A measurement performed by considering all νµ CC internal events yielded δt = (60.3 ± 13.1 (stat.)± 7.4 (sys.)) ns, for an average neutrino energy of 28.1 GeV. The sample was then split into two bins of nearly equal statistics, taking events of energy higher or lower than 20 GeV. The results for the low- and high-energy samples are, respectively, δt = (53.1 ± 18.8 (stat.).) ± 7.4 (sys.)) ns and (67.1 ± 18.2 (stat.).) ± 7.4 (sys.)) ns. This provides no clues on a possible energy dependence of δt in the domain explored by OPERA within the accuracy of the measurement.
Despite the large significance of the measurement reported here and the stability of the
analysis, the potentially great impact of the result motivates the continuation of our studies in order to investigate possible still unknown systematic effects that could explain the observed anomaly. We deliberately do not attempt any theoretical or phenomenological interpretation of the results.
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Written by physicsgg

September 23, 2011 at 7:39 am

7 Responses

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  1. Two questions:

    How was the length of the baseline established?

    Did the neutrinos follow the baseline?


    September 24, 2011 at 12:35 pm

  2. Did they take into account that both the emitter and receiver are moving – the earth is rotating isn’t it??? I


    October 5, 2011 at 2:42 am

  3. Einstein is either right or wrong…. no grey area here.
    Before we start looking for neutrinos escaping the ‘brane, travelling through the bulk and re-entering the ‘brane
    This is a job for Occam,s Razor.
    If the muon neutrinos are arriving 60ns early then they must have been emitted 60ns early.
    ie:- The neutrinos have a head start. This measurement may even prove to be a constant. The distance of 730 kms is of no significance

    Duncan Pemberton

    October 25, 2011 at 3:14 pm

  4. Are the atomic clocks at Cern and Gran Sasso compensated for possible differences in gravitational potential local to the two laboratories

    John Humphreys

    October 26, 2011 at 2:31 pm

  5. David, they are moving. Was thinking though that they move at different speeds due to differences in latitude – hence different reference frames 🙂

    Paul Davidson

    November 19, 2011 at 11:43 am

    • Paul, Ii I have the math right the approximate 4 degree latitude difference would only amount to an approximate 82km/hr difference in rotational speed – about 22 m/s. In the experiment they did if one consider the target as moving towards the transmitter the required speed would be on the order of 7400 m/s.

      In my original post I was wondering if something transmitted at the speed of light from a moving object towards a receiver on another object going the same speed in the same direction would appear to be going faster than the speed of light if one just measured the time from transmission to reception. Seems to me like to the classic math problem of two trains approaching one another at different speeds.


      November 20, 2011 at 1:15 am

  6. Is there a wave/particle duality issue here? The neutrinos are are apparently arriving 60nS too soon. Assuming the speed of light, this is equivalent to approx. 18 metres too soon. What if this was the wavelength (or factor of) of the neutrinos? If the muon detectors at CERN trigger when the neutrino leaves (tail of the wave) and the OPERA detectors trigger on the leading edge of the wave at arrival, this could create an error. I tried the maths and it appears to work for low energy neutrinos (~10 to the minus 27 eV) and depends on the detector functionality. I can’t make the maths work for the high energy (17GeV) neutrinos fired from CERN though . . . What do you think?

    Chris Tolmie

    November 27, 2011 at 3:53 pm

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