Saturday, September 26, 2015

LHC13: the first inverse femtobarn collected

In the Wall Street Journal on Thursday, David Gross and Ed Witten promoted Nima's Chinese \(100\TeV\) collider. But let's back to the LHC.

In 2012, at the \(8\TeV\) center-of-mass energy, the Large Hadron Collider has collected something like 27 inverse femtobarns of data per detector out of which about 20 inverse femtobarns is being analyzed by the papers.

The 2015 collisions at \(13\TeV\) were rather slow but if you look at the LHC luminosity chart of the LHC control panel, you may see that the LHC tends to nicely collect about 0.1/fb i.e. 100/pb at a time – in a fill that lasts 11 hours or so. The data is currently being collected at the rate about 100/fb/year i.e. 3000/μb/sec.

The right sidebar of this blog, Atlas.CH, or a statistics page at CERN is currently telling us that in 2015, each major detector has already collected more than 1/fb of the data. Congratulations.

This is still 20-30 times less (Lumo English) than in 2012. But because the higher-energy collisions are much more sensitive to hypothetical particles at higher masses, there exist possible phenomena in new physics for which the 2015 run has already been more sensitive than the 2012 run, e.g. the new gauge bosons at masses such as \(5\TeV\) we became excited by a month or two ago.

Because some of those \(2,3,5\TeV\) gauge bosons were already seen in 70/pb i.e. 0.07/fb of data and the 2015 run has already collected 15 times more collisions than that, it is rather likely that if those new heavy particles are real, the LHC should have seen several if not many other individuals from those new particle species.

For those very heavy particles, the LHC has basically done its job and the LHC physicists and their followers must simply open the box and see the results. My point is that even though 1/fb is a small fraction of what the LHC will collect at this energy – or at \(14\TeV\) where the LHC may be switched soon – it is already "equivalent" to the high integrated luminosities, at least when it comes to some spectacular, strongly enough interacting, but high-mass new particles.

Meanwhile, much lighter particles – such as the superpartners around or beneath \(1\TeV\) – need a lot of luminosity to be produced. So what the LHC will do in coming months and later will be very important for the fate of those theories.

At any rate, I am sure that just like your humble correspondent, many of you are greatly curious about the question whether the LHC has seen something interesting in the first new inverse femtobarn of the proton-proton collisions. Let us stay tuned.

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