## Sunday, September 26, 2010

### LHC: ATLAS, CMS surpass 1/femtobarn/year of luminosity

For three weeks or so, daily observers of the LHC performance were irritated because the collider hasn't done much physics. However, everything is working again and October 2010 is hopefully going to be exciting, adding an order of magnitude to the maximum luminosity.

Already now, we have something to celebrate. Recall that a realistic - but not guaranteed - plan of the LHC is to accumulate 1 inverse femtobarn per each detector by the end of 2011. The collider will be stopped once this "dream" will be achieved, or at the end of December 2011, whichever comes first.

What about the current status and achievements that have been done?

According to the latest "published" numbers which are 1-2 days old or so, ATLAS has accumulated 362 billion collisions which translates to 5.07 inverse picobarns. You should obviously assume that the CMS has collected approximately the same amount of data - so the total LHC's "wealth of knowledge" is about two times the ATLAS "wealth".

(LHCb can't extract all the relevant information about new physics from the p-p collisions: it focuses on CP-violation as seen by bottom quarks only; ALICE is mostly waiting for heavy ions and is turned off when the proton beams are one.)

A trivial clarification concerning the cross section of the proton-proton collisions

If you divide 5.07 inverse picobarns i.e. 5.07 x 10^{+36} cm^{-2} by 362 billion collisions, you obtain 1.4 x 10^{+25} cm^{-2} or 14 inverse barns. The inverse of this number is about 0.07 barns or 70 millibarns - an estimate for the cross section of a proton-proton collision at 2x 3.5 TeV. The actual total inelastic cross section is larger, about 120 millibarns, but almost 1/2 of the events are immediately thrown out.

Maximum luminosity in inverse femtobarns per year

Also, atlas.ch shows that the maximum achieved luminosity so far has been 36 x 10^{30}/cm^{2}/s which is 36 inverse microbarns per second. Multiply it by 86,400 and by 365.2422 to get 1.136 inverse femtobarns per year. See also Phil Gibbs' blog that frequently, cleverly, and comprehensibly informs about such news.

This looks like enough to achieve the inverse femtobarn of data in each detector by the end of 2011. However, note that 1.136/fb/year is the maximum achieved luminosity. The LHC won't be running all the time but only 1/3 of the time or so, and during the active periods, the average luminosity is just about 1/2 of the maximum one because it's decreasing after reaching the maximum etc.

So it means that you need to achieve the maximum immediate luminosity of 6/fb/year or so to actually collect 1/fb during one year. But it's likely that they will achieve this threshold during October because they're still going to substantially raise the number of bunches in the beams.

SUSY within two weeks: can't be ruled out

I said that ATLAS has collected 362 billion collisions. Now, about 1 trillion collisions seems enough to see signals of new physics in many relatively realistic and "generic" supersymmetric models. A trillion of collisions should become a reality within a week or two. So there's a nonzero chance that something really new will be seen really soon.

The advocates of the end of physics and various enemies of theoretical physics - Shitorgans, Smoits, Swolins, and many others - are recommended to lose their sleep (starting from today on) and get ready for a possible act of splashing themselves into the lavatory which will be their only reasonable option in the case that the discoveries will actually take place. ;-)

Already now, when it is in the active mode, the LHC is producing a higher number of top quarks, Higgs bosons, and other heavy particles per unit of time than the Tevatron: see Dorigo's blog.

In one month, the leadership will be improved to one order of magnitude. A month after month, the number of people who will be able to see that it doesn't significantly help physics to continue the running of the Tevatron will be increasing.

MinibooNE confirms LSND?

A decade ago, the LSND experiment located in Los Alamos detected some strange signals about neutrino oscillations that indicated either CP-violation or new flavors of the neutrinos besides those in the Standard Model - or something with similar effects.

Remarkably, Mark Trodden claims that the MinibooNE people are currently convinced that their brand new data pretty much confirm the highly controversial and usually dismissed LSND result!

This would be an evidence of a shock or evidence of the MinibooNE people's having taken too much LSD - and recall that LSND has been mocked for being located in Mini-boonlocks, so the fun is in both teams.