CERN provided an update regarding the muon-neutrino time of flight measurement performed by the OPERA Collaboration this morning, which I shall now quote:
“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 ArXiv preprint server.” [1]
Comparison with the Original OPERA Measurement
If you’ll recall, the original OPERA experiment measured the time of flight, or how long it takes to go from point A to B, for a muon-neutrino beam traveling from CERN to Gran Sasso (this distance is ~730km). The muon-neutrino beam under study was created using a proton beam taken from CERN’s Super Proton Synchrotron (SPS). In this original measurement, the proton beam taken from the SPS was 10.5 microseconds long in time. The OPERA Collaboration originally reported that the muon-neutrinos traveled 60.7 ± 10.1 nanoseconds faster than the speed of light (FTL)!
But one obvious criticism of the original OPERA Measurement was that they were unable to determine exactly which proton gave rise to a muon-neutrino that struck the OPERA detector. This is a problem since the proton beam time was several orders of magnitude larger than the originally quoted FTL observation. e.g. If a muon neutrino strikes the OPERA Detector and was thought to come from the start of the proton beam, but actually came from the end of the proton beam there would be no observed FTL behavior.
Now in the OPERA Collaboration’s newest measurement, they are still unable to determine which proton created a muon-neutrino that struck the OPERA detector. However, the quote above shows that the OPERA Collaboration repeated their measurement using a proton beam that is only three nanoseconds long and this change in proton beam length has not affected their results! So the fact that you don’t know which proton creates the muon neutrino that strikes the your detector no longer matters! This is because the reported excess in the time of flight of the neutrinos is twenty times the proton beam’s time in this new measurement; as opposed to being three orders of magnitude smaller in the original measurement.
The Future
Whether or not the OPERA publication will be accepted by JHEP, a peer-review journal, remains to be seen. The OPERA measurement also needs to be confirmed by another experiment, to ensure the phenomenon is actually real. But, rumor has it that the MINOS and T2K Experiments are gearing up to repeat the OPERA Measurement. So stay tuned on this rapidly developing phenomenon!
For those of you interested the updated OPERA manuscript can be found on arXiv.org.
Until Next Time,
-Brian
References
[1] CERN, “OPERA experiment reports anomaly in flight time of neutrinos from CERN to Gran Sasso,” http://press.web.cern.ch/press/pressreleases/releases2011/pr19.11e.html, November 18th, 2011.
