# Energy of Big Bird neutrino from IceCube

Big Bird neutrino event has announced two different energies: 2.004 PeV, 2.2 PeV. Both values are scattered over web. It may be that the lesser value is for detected "deposited" energy, while the greater value for guessed original/real neutrino energy. I can not find such distinction though. Does anyone know the real reason for having these two values spread over web?

• It's important to note that your first reference sets that neutrino at $2004^{+236}_{-262}\:\rm TeV$ (event 35 suppl. table 1); this is consistent with the $2.2\:\rm PeV$ value in the press release but that's not how you report things if that's what they've done. Have you got a better source for the second figure? Otherwise, I'd go with the data in the PRL. – Emilio Pisanty Aug 19 '16 at 15:03
• @emilio-pisanty The first place where I saw 2.2 PeV is at a talk, slide 54. – N.K. Aug 19 '16 at 16:16

The calibration of large-scale detectors is an on-going process, so reported values can change as improved calibrations become available.

This is especially true for values—like the extreme energy considered here—that lie outside the usual range of usual events.

It is more than likely that after they collected enough of these very high energy events the Monte Carlo was re-tuned followed by a re-tuning of the energy estimator. That would result in a new best fit value for the energy, possibly with tighter error-bars (though sometimes the additional work reveals that the earlier estimate was optimistic and the error bars grow).

If this is the case you can expect it to be reported in one of the follow-up papers.

The best practice is to use the latest available reported values that includes all the data you are interested in.

I was on the calibration team for KamLAND for a bit over four years and we re-jiggered our understanding of the energy scale in that time.

• I understand that calibrations are getting adjusted over time, and I'm happy that it can lead to more precise values. The arxiv paper (with 2.004 PeV) and the talk (with 2.2 PeV, see a comment below the question) are both from the first half of 2014, thus guessing that they had the same calibrations. And since IceCube has to deal with severe distinctions on deposited vs. original energies (see e.g. the 2.6 PeV event), I wonder whether this 2.2 vs. 2.004 PeV is such a distinction, or if it is just older vs. newer values. – N.K. Aug 19 '16 at 23:56