[aspagnito (OP)]

Rumor has it that the San Grasso experiment (the idea being that a certain type of neutrino was suspected to be faster than the speed of light) did not come out of nowhere. Apparently, we observed a certain supernova and this kind of neutrinos came to Earth from that supernova earlier than photons. That's where the San Grasso experiment came from.
So an experiment was conducted in San Grasso to confirm this particular observation.
The experiment initially allegedly confirmed these observations and sparked waves of debate in the scientific community - it was even suspected that physics textbooks would have to be "rewritten. " Shortly thereafter the OPERA collaboration announced that it had conducted the experiment with two technical problems and the results were invalid.

The first candidates for neutrino oscillation to tau neutrinos were announced in May 2010 by the OPERA experiment. In total five tau neutrinos were observed, consistent with the expectations from the theory of neutrino oscillation.

On 22 September 2011, the OPERA collaboration garnered international attention when they released a preprint reporting the Faster-than-light neutrino anomaly, wherein neutrinos were measured to be travelling, on average, at faster-than-light speed. On 24 February 2012, the team said they had discovered two problems with their previous test, muddying the validity of the previous result. The preprint has been modified to account for these facts, and indeed the measurement of the neutrino speed, there reported, agrees with the velocity of the light.

https://en.wikipedia.org/wiki/CERN_Neutrinos_to_Gran_Sasso [nofollow]

My question is. . . Why such important and even shocking research results that have moved the entire world of physics have never been confirmed by many other scientific entities (due to discrepancies in results). Isn't that a common practice in science?

[Kryptid]

Probably because of this:

Shortly thereafter the OPERA collaboration announced that it had conducted the experiment with two technical problems and the results were invalid.

So the evidence for faster-than-light neutrinos was considered invalid. That's significantly more probable than actual faster-than-light motion. Science experiments like this are expensive, so if there isn't any good evidence to investigate something, it's not likely to be done.

[Bored chemist]

"Why have the results of the San Grasso experiment were never confirmed?"
Because they were a mistake.
Someone checked and they realised that the measurements were simply wrong.
Nothing had gone faster than light.

https://en.wikipedia.org/wiki/Faster-than-light_neutrino_anomaly#Measurement_errors

[evan_au]

It is a common experience in science that your experiment doesn't work the first time (or the first 10 times!).
- That's why scientists do a lot of calibration tests and cross-checks to ensure the results look sensible.

The apparent "faster than light" neutrinos were such a surprise that the experimenters at Gan Sasso actually published the results with a subtext of "so what did we do wrong?".
- And a couple of faults were found in their timing chain that linked the clock at the LHC to the clock deep inside the Gran Sasso mountain. In particular, a loose connector was delaying the timing pulses.
- Some changes to the experimental method were applied to give a more accurately timed burst of neutrinos from the LHC
- And the apparent faster-than light result disappeared

The consensus today is that neutrinos travel just a tiny bit slower than light - the difference is so small that we can't measure it with current techniques.
- If we knew the rest mass of the 3 neutrino types, we would be able to calculate the velocity from the known energy spectrum of neutrinos from nuclear reactors. But the neutrino mass is known only very roughly.
(Oops! overlap with Bored Chemist)

this kind of neutrinos came to Earth from that supernova earlier than photons

You are talking about SN1987A - the only supernova to date where we have linked a neutrino burst to visible observations.
- The neutrinos were detected over a 13 second period - they basically travel close to c once they are formed in the collapsing core of the star
- However, the intense burst of energy has to propagate to the surface of the star at a much slower rate, dominated by the speed of sound in a dense plasma. It can take hours or days for this energy to reach the surface of the star to produce a visible flash.
- So in practice, astronomers subscribe to alerts from SNEWS (indicating that there has been a burst of neutrinos from a certain direction) and LIGO (indicating that there has been a burst of gravitational waves from a certain direction).
- As soon as an alert occurs, they drop whatever they were doing, and look in the specified direction to see if they can see anything unusual.
- It might take several hours for the astronomers to find something - like waiting for the Sun to set at the location of their telescope (if they find anything at all - mostly they don't)
- LIGO has created many alerts.
- So far, SNEWs has not produced any alerts (the SuperNova Early Warning System was put together after SN1987A). But astronomers think that we are overdue for a supernova within our galaxy, and that should be easily detected by neutrinos.

https://en.wikipedia.org/wiki/Supernova_neutrinos#Detection_Significance

[Zer0]

F.Y.I.

Science Text books are Never Ever opposed to being Rewritten.
(They are modified as and when the need arises)

Ps - There ain't no Kingpins or Popes in Science.
✌️