Weekend of 12-3-09 collision events !

The place to discuss the LHC. Commissioning, operation, issues, events ....
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Texanguy
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Re: *** COLLISION ALERT ***

Post by Texanguy » Sat Dec 05, 2009 7:20 pm

yeah.. coffee break :} heh..

gluon
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Re: *** COLLISION ALERT ***

Post by gluon » Sat Dec 05, 2009 7:38 pm

So, were there any collisions?

It seems only the CMS page reports collisions, I've been following the LHC1 page the whole day without even noticing stable beams.

After the circuits tripping in S12 they are now forecasting the next beams not before 22:30.

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DCWhitworth
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Re: *** COLLISION ALERT ***

Post by DCWhitworth » Sat Dec 05, 2009 7:41 pm

Now posted - no beam before 2230
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Xymox
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Re: *** COLLISION ALERT ***

Post by Xymox » Sat Dec 05, 2009 8:07 pm

We dont know...

You gotta love mystery....

What I am waiting for are 2 bunch or 4 bunch collisions,,, or,,,, collisions at higher energies.


BTW,,, maybe im late to the party on this one,,, but what does "Energy" on this chart mean ? http://op-webtools.web.cern.ch/op-webto ... p?usr=LHC3

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Re: *** COLLISION ALERT ***

Post by daavery » Sat Dec 05, 2009 8:19 pm

It looks like they are plotting the "programmed beam energy" which is displayed at the top center of the page. that way the plot shows both beam intensities and programmed energy.

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Xymox
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Re: *** COLLISION ALERT ***

Post by Xymox » Sat Dec 05, 2009 8:21 pm

I was watching that bounce all around last night... I don't think it matched the programed level... BUT I could be mistaken... Indeed I could...

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Re: *** COLLISION ALERT ***

Post by Xymox » Sat Dec 05, 2009 8:32 pm

I asked some basic questions of Paul Collier who is the leader of the Beams Department at CERN. The answers were interesting for those who do not know.

"How long does a collision last ? How long before the beam is depleted ? Its obviously more then one single bang. Its more like 2 water hoses pointed at each other and the water colliding until you run out of water. The question is how long does the water last ?

What is the collision rate. How many collisions per second ?"
The protons are collected into bunches which travel around the machine together. They go around 11.245 times a second. If there is 1 bunch in each beam they would cross each other at 2 locations in the machine. If there are 4 in each beam the number of crossing points is 8. We arrange it so that 4 of these crossing points occur in the experiments. The other 4 occur in areas where the 2 beams are kept apart.

Each time the two bunches meet there is a chance that some protons from one beam will come close enough to protons from the other beam to collide and interact. The rate at which such collisions occurs is therefore dependent on the number of protons in each beam and the physical dimensions of the beam where they meet. Most times a given proton will not meet another in the opposite direction and will just carry on circulating.

At the state we are at the moment with very low intensities, few bunches and relatively large beam sizes at the crossing points the chances are pretty low. The rate of interactions will probably be less than one per second of which a small fraction will be useful ‘events’ (most are just close encounters). When we approach nominal performance the rate will go up from a Hz to over 500MHz.

The beams can keep circulating while producing collisions for several hours. Slowly protons are lost from the beam and the rate of interactions will fall. Eventually it is not worth keeping the beams any more and we will dump and refill. For these initial physics runs at 450GeV I would expect runs of around 4 hours (depending on the beam lifetime).
I will work this into the info pages someplace..

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Texanguy
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Re: *** COLLISION ALERT ***

Post by Texanguy » Sat Dec 05, 2009 8:38 pm

hmmm... interesting indeed :}

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Re: *** COLLISION ALERT ***

Post by Xymox » Sat Dec 05, 2009 8:44 pm

That is quite something when you consider there will be thousands of bunches eventually..

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Texanguy
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Re: *** COLLISION ALERT ***

Post by Texanguy » Sat Dec 05, 2009 8:48 pm

yep.. makes you wonder what else they'll find out (aside from the possible discovery of the Higgs) :}

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Re: *** COLLISION ALERT ***

Post by Xymox » Sat Dec 05, 2009 8:53 pm

Some exciting moments at the LHCb.. Everything is fine now, but I would guess this was exciting for a moment

"LHCCOM PVSS project died spontaneously"
"communication with LHC and clock status for TFC lost momentanously."

Looks like a memory leak to me

"Machine ran out of memory and stop the data manager."

Looks like it was running for a really long time.. So its a very slow leak..

Of course a minor issue and only needed to be restarted to fix it... Still just for moment I bet it was exciting...

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Re: *** COLLISION ALERT ***

Post by Xymox » Sat Dec 05, 2009 9:02 pm

I will create a thread for this...

Big news...

http://news.nationalgeographic.com/news ... ision.html

Thread on it
viewtopic.php?f=3&t=137&start=0

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Re: *** COLLISION ALERT ***

Post by Harbles » Sat Dec 05, 2009 9:46 pm

The collisions they hope to see in a few hours are to help calibrate the detectors. They will be seeing events that have been studied for over 50 years now in machines like the PS & SPS, Tevatron etc. So by observing relatively few, relatively low energy events they will be able to confirm that the detectors are working properly, or tweak them till they do.
It is still exciting and historic but they are extremely unlikely to view any exotic events for a while yet.

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Re: *** COLLISION ALERT ***

Post by DCWhitworth » Sat Dec 05, 2009 10:30 pm

We have beams again.
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Re: *** COLLISION ALERT ***

Post by Xymox » Sat Dec 05, 2009 10:42 pm

And away we go again...

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