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Re: 2011 Events Discussion

Posted: Thu Apr 21, 2011 12:24 pm
by PhilG
I was hoping for 500/ub/s easily with 480. Intensity could be higher. Perhaps the next fill will be better.

Going up in 144 bunch steps is good.

Re: 2011 Events Discussion

Posted: Thu Apr 21, 2011 12:38 pm
by DCWhitworth
Kasuha wrote:Isn't LHC breaking its own records for a while already? I believe we'll see a few more of them till it reaches design parameters, but I don't think every step is a big deal anymore...
My personal opinion is that putting over 1000 bunches in the ring during the scrubbing period was much better achievement.
I'd agree with your statement about 1000 bunches being a great achievement but I disagree that each step is no longer a big deal.

My interest in the LHC is as much centred around the technical achievement of running such a vast and complex machine as it is around the physics itself. I'm keen to track every step of the way to full power.

Re: 2011 Events Discussion

Posted: Thu Apr 21, 2011 7:23 pm
by Bornerdogge
PhilG wrote:I was hoping for 500/ub/s easily with 480. Intensity could be higher. Perhaps the next fill will be better.

Going up in 144 bunch steps is good.
Yes it is a bit disappointing indeed. Perhaps because of the slightly lower bunch intensities (1.1e11 in state of ~1.25e11 for the first runs with 336b)...

EDIT: just noticed the 2m squeezing....

I also don't really understand the filling scheme: they arrange for 422 collisions per turn in CMS and ATLAS and 468 in LHCb, though LHCb always has lower luminosity because of the higher beta* (and some other reasons I don't get). Why don't they try to get more collisions in IP1 and 5 with the same number of bunches and reduce in IP8?

Re: 2011 Events Discussion

Posted: Thu Apr 21, 2011 8:20 pm
by zaim
What do you mean about 2m squeeze? I am pretty sure I saw 1.5m at CMS and ALTAS in the 480 fill.

LHCb and ALICE does not have problems with the luminosity directly, but with the number of collisions per bunch crossing. When two high intensity bunches which is squeezed tightly collides, there may be as many as 13 (largest number I have seen) proton-proton collisions per bunch crossing, and it takes a very sophisticated detectors to unravel the data and find the 13 individual events. LHCb and Alice does not cover the full area around the collision point, which makes it difficult for them to handle multiple collisions per crossing.
So LHCb likes many bunches but have difficulties with high intensity and tight squeeze.

Cheers Zaim

Re: 2011 Events Discussion

Posted: Thu Apr 21, 2011 9:18 pm
by Bornerdogge
DCWhitworth wrote:Thought they'd make it easily but they only squeezed to 2m not 1.5m
That's why I said that; I didn't check during the fill...

Thanks for your explanation!

They're filling again and the intensities seem slightly higher...

Re: 2011 Events Discussion

Posted: Thu Apr 21, 2011 9:37 pm
by DCWhitworth
Bornerdogge wrote:
DCWhitworth wrote:Thought they'd make it easily but they only squeezed to 2m not 1.5m
That's why I said that; I didn't check during the fill...
I picked that up from the LHC Announcer which showed them going to 2m but not 1.5m. However I've noticed that over the break this has been changed to only report whole metre changes whereas before it was half metre I think. So it's possible it wouldn't have reported a squeeze to 1.5m

This time I'll check the LHC configuration screen !

Re: 2011 Events Discussion

Posted: Thu Apr 21, 2011 9:55 pm
by DCWhitworth
More than 480 ub/s-1 in ATLAS, another world record smashed ! Nice work guys.

:dance:

Re: 2011 Events Discussion

Posted: Thu Apr 21, 2011 10:07 pm
by Bornerdogge
Great! :clap: They doubled luminosity in a single week!!

Do you happen to know why the lumi in CMS is always ~10% lower than in ATLAS, though the squeeze is tighter and the number of colliding bunches is the same?

Re: 2011 Events Discussion

Posted: Fri Apr 22, 2011 12:09 am
by CharmQuark
Well done guys :thumbup: :clap:

Re: 2011 Events Discussion

Posted: Fri Apr 22, 2011 2:02 pm
by PhilG
Looks like they got the 72 bunch injection right this time. They will probably want to try it at 480 bunches before going up to 624 (?) bunches.

Report on the success of the scrubbing runs and subsequent records at http://cdsweb.cern.ch/record/1345739

Re: 2011 Events Discussion

Posted: Fri Apr 22, 2011 5:41 pm
by photino
4-sigma signs of a nonstandard 115 GeV Higgs... in a leaked memo from ATLAS?
http://resonaances.blogspot.com/2011/04 ... maybe.html

Re: 2011 Events Discussion

Posted: Sun Apr 24, 2011 11:40 am
by tswsl1989
photino wrote:4-sigma signs of a nonstandard 115 GeV Higgs... in a leaked memo from ATLAS?
http://resonaances.blogspot.com/2011/04 ... maybe.html
Internal, unapproved, unreleased document - according to someone within the collaboration the analysis is "woefully incomplete"

I'll wait until something gets published, or at least makes it as far as Arxiv

Re: 2011 Events Discussion

Posted: Sun Apr 24, 2011 5:12 pm
by photino
Internal, unapproved, unreleased document - according to someone within the collaboration the analysis is "woefully incomplete". I'll wait until something gets published, or at least makes it as far as Arxiv
Oh, absolutely. It's really unlikely to hold up. But these rumours are fun ;)

Then again it's a good question whether these leaks-via-blog-comment are a positive development.

Re: 2011 Events Discussion

Posted: Tue Apr 26, 2011 9:40 am
by Bornerdogge
The planning says they're going for stable beams with 640 bunches this afternoon...

This would yield between 650 and 750 (┬Áb)-1, depending on the filling scheme.

Good luck guys!

Re: 2011 Events Discussion

Posted: Tue Apr 26, 2011 5:48 pm
by DCWhitworth
photino wrote:
Internal, unapproved, unreleased document - according to someone within the collaboration the analysis is "woefully incomplete". I'll wait until something gets published, or at least makes it as far as Arxiv
Oh, absolutely. It's really unlikely to hold up. But these rumours are fun ;)

Then again it's a good question whether these leaks-via-blog-comment are a positive development.
I guess it wouldn't have garnered much attention if they hadn't chosen to use the magic H-word. But it's interesting to see some of the internal workings of scientific collaborations revealed.

I'm not sure whether such leaks as positive, but in the 21st century they're inevitable. The Pandora's box of instant communication is open and people want information now not after careful scientific analysis and meticulous publications and refereeing.