Restricted ECFA

Radiation Beam Experiment

Relativistic Heavy Ion Collider (at Brookhaven)

No "the" before RHIC

Acronym doesn't need spelling out for the CERN Courier

Root mean square (not "r.m.s.")

use hyphen

Radiation Safety Support Officer (HSE unit)

Rheinisch-Westfälische Technische Hochschule Aachen, a research university in Germany

Acronym doesn’t need spelling out for the CERN Courier

Safety Policy Committee

Short-baseline (concerning neutrino experiments)

not "Secretariat", except when referring to a specific secretariat, e.g. the Council Secretariat

use hyphen

Preferable to colloquium in web texts. We're writing in English, not Latin.

Single-Event Upset

no hyphen

In 2013, the Large Hadron Collider (LHC) will start its first long shutdown for maintenance.

Do not confuse the noun with the phrasal verb:

The research project was shut down due to lack of funding.

Number, no hyphen (except as a compound adjective), lower case "s"

Particle physicists describe the certainty of a result on a scale that goes up to 5 sigma. One sigma could be a random statistical fluctuation in the data, 3 sigma counts as evidence, but only a full 5-sigma result is a discovery. By definition, the probability that a 5-sigma result is wrong is less than one in a million.

1 sigma

3 sigma

5 sigma, etc. 

The certainty of the result was given as 3 sigma.