The international research team that found neutrinos traveling faster than light has done it again.
It conducted another set of experiments and again found neutrinos that exceeded the speed of light.
As in the first experiment, the researchers fired high-intensity, high-energy beams of muon neutrinos from the CERN SPS accelerator in Geneva toward the LNGS underground laboratory in Gran Sasso, Italy, 454 miles (730 km) away. They then measured the speed at which the neutrinos traveled.
This time, however, they used very short beam pulses rather than long beam pulses.
While the latest experiment appears to confirm the accuracy of the timing measurement, more scrutiny and independent measurement are needed before a definitive conclusion can be reached.
Gran Sasso Redux
The experiments are being conducted by the Opera Collaboration. This time, the scientists fired off pulses 3 nanoseconds long, separated by intervals of up to 524 nanoseconds.
This let them more precisely measure the extraction times of the protons that ultimately lead to the neutrino beam.
The 524-nanosecond interval is much longer than the uncertainty in the arrival time, physicist Ethan Siegel wrote. This let observers know definitively which pulse of protons neutrinos spotted in the detector came from.
A neutrino is an electrically neutral elementary subatomic particle with a small mass that usually travels at speeds close to that of light.
About 20 clean neutrino events were measured at the Gran Sasso lab this time around, and they were precisely associated with the pulses leaving CERN. This confirms that Opera’s timing measurements were accurate the first time around, the researchers stated.
CERN is the European Organization for Nuclear Research.
What the Experiment Indicates
The latest batch of experiments resolves two questions Siegel had previously raised: whether the results of the first batch could be a statistical fluke, and whether the neutrinos detected were biased in some way.
The new results narrow the possibilities down to two, Siegel told TechNewsWorld.
These are that either “neutrinos can indeed travel faster than light,” or there’s a “systematic bias” in the way the Opera researchers are measuring the transit time for the neutrinos, Siegel said.
However, this Gran Sasso experiment may have run its course, contended Michael Witherell, vice chancellor of research at the University of California, Santa Barbara’s physics department.
“I think the Opera team did remove some of the concerns about the time structure of the neutrino beam that concerned scientists studying the earlier paper,” Witherell told TechNewsWorld.
“I am not sure what more they can do using this experiment,” Witherell added. “At this point, the only thing that will really change our understanding is to have one or more experiments agree or disagree with Opera’s measurement.”
Checking the Results Again
Teams working on two other experiments at Gran Sasso — Borexino and Icarus — will next year begin cross-checking Opera’s results independently.
Borexino is an experiment focusing around solar neutrino physics being conducted by an international team of researchers. Icarus looks at the usage of liquid argon detectors to study neutrinos.
“It will be very difficult for Borexino and Icarus to conduct these tests directly” because their equipment doesn’t let them conduct timing measurements accurately enough, Siegel said.
The Cold Eyes of Outsiders
Two other groups of researchers will seek to duplicate the Gran Sasso results.
They are Japan’s T2K experiment and the United States’ Minos experiment.
Minos “is the best candidate for this going forward” because it’s claiming its measurements will be “a factor of five or so” better than what Opera’s doing now, Siegel remarked.
Minos and T2K may be able to eliminate some biases that might exist in the Gran Sasso experiment.
“If there is a problem in, for example, determining the distance or time delay from CERN to the Gran Sasso Laboratory, these experiments [at Minos and T2K] should not have the same problem,” UC Santa Barbara’s Witherell pointed out.