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First, congratulations to the guys at Cern for getting the LHC to 1380 bunches, 0.6 beta, 1.3x10^11 protons/bunch

Yesterday they did some vdm scans which I would have thought should have calibrated the luminosities to around the same value as last year whereas on the dashboard, Atlas is at 4.3/nb/s, Cms 5.5nb/s. Anyone know why the difference?

It could simply be that they have not finished analysing the scans yet

PhilG wrote:It could simply be that they have finished analysing the scans yet

Cms with its current max of 5.5/nb/s is closest to the right value?
Atlas with its current max of 4.5/nb/s is closest to the right value?

So where are you placing your bets, guys?

I'm going with Cms

Last year they reached 3.5/nb/s with beta* = 1.0 so with beta* = 0.6 they should expect 3.5/0.6 = 5.8/nb/s assuming intensity and emittance are the same. So the CMS figure looks better.

Analysing the van der Meer scans is not straightforwards and it will take some time before the results are known, and the calibration is applied to the luminosity monitors. Even then, ATLAS and CMS may not agree on the calibration.
Already last year there was considerable disagreement on the integrated luminosity. There was a luminosity workshop in February, you can find all the details in the presentations there:
http://indico.cern.ch/conferenceOtherVi ... fId=162948

Last year they reached 3.5/nb/s with beta* = 1.0 so with beta* = 0.6 they should expect 3.5/0.6 = 5.8/nb/s assuming intensity and emittance are the same. So the CMS figure looks better.

the VdM scans still need analysis before feeding back new calibrations. The "correct" value will lie somewhere between the present values of CMS and ATLAS.

The present luminosity is pretty good - since the intensity per bunch is still quite a bit lower than the peak values from last year. Presently running at 1.3x10+11. Last year the peak was close to 1.5x10+11. Increasing to 1.5x10+11 will give 33% more luminosity than at present! Don't expect this overnight though!

pcatom wrote:The present luminosity is pretty good - since the intensity per bunch is still quite a bit lower than the peak values from last year. Presently running at 1.3x10+11. Last year the peak was close to 1.5x10+11. Increasing to 1.5x10+11 will give 33% more luminosity than at present! Don't expect this overnight though!

It's amusing to see 2010's total integrated luminosity routinely captured in 2.5 hours of running today. 1fb/week will soon be upon us in the coming months.

Not overnight but maybe over a couple of nights. They are aiming for 1.45 E11 now!

PhilG wrote:Not overnight but maybe over a couple of nights. They are aiming for 1.45 E11 now!

They didn't get it to work but nice try.

Looks like the Cms was out of calibration because the recorded instantaneous luminosity has been reduced from 6 to 5.6/nb/s which now matches Atlas.