LHC portal

Looks like they are starting the 10 bunch run. If I understand correctly the big deal of beam intensity is that the particles that they hope to see are exceedingly rare and mixed in with an overwhelming number of more mundane interactions so the higher the collision rate the more likely that particles of interest (such as the Higgs) will be detected. Is that correct?

@Hokie_Engineer, you are right. Intensity is the number of particles in the beam. Increasing intensity leads to higher luminosity which means more collisions and you need a lot of those to see new physics.

There are other ways to increase luminosity, such as squeezing the bunches down to make a narrower beam at the interaction points, but increasing intensity is the biggest part of it, and that is what they are now working on.

Whoa! 9e11 and ramping!

Keep it coming!

@jmayes: the scale containing the 9e11 is not for the ramping, the scale for the ramp is the one at the left side going up to 3.5TeV. The intensity which the left scale with the 9e11 is referring to is only changed in steps, so called bunches so the intensity graph looks like steps of a stairs during injection.
Or did you only mean they alredy injected a intensity of 9e11 and start to ramp now?

chriwi wrote:@jmayes: Or did you only mean they alredy injected a intensity of 9e11 and start to ramp now?

Yes, Exactly

Ohhh! An 1e12+ beam test!!! Looks like 12 bunches too!

Did not last long but still a milestone! (ok, kilostone)

woohoo

A new 9 bunch filling scheme with 6 collsions per turn next for physics

How many collisions are they aiming for to have enough to do their science? Have they got a target number? I can't find on any of the sites how many collisions they think will be enough. ATLAS is up to nearly 4 billion collisions - but how much does this mean against their target number? Maybe they have not even scratched the surface yet...maybe they are nearly there and will be able to stop soon? Have they got an estimated number of collisions in mind to be able to find new science? Hope someone can offer a guide

First of all they have only begone to scratch the surface. They need about 10,000 times more data than they have now, to be able to say anything certain about e.g. the Higgs mechanism.
When this is said they where able to publish the first physics results already months ago, with only very little data.

The number of collisions are not a very good measure of how much data they have, and how much physics they can do with it. A better measure is the integrated luminisity. You can find a discussion about luminosity in the science forum. But in short; if a process e.g. production of W-bosons, have a cross section S, and your machine have produced the integrated luminosity L, then you have produced L*S W-bosons. The cross section i.e. a measure of how often a process occur, and can for most processes be calculated from fundemental physical theories.

Now the integrated luminosity so far is 0.1 pb^-1, and the aim for 2010 is ~100 pb^-1 and for 2011 before the long shot down in 2012 the goal is 1000 pb^-1, at which point they will be able to talk about new physics.

Cheers Anders

Thanks zaim, that's a great explanation and certainly helps to put the current position into in overall perspective. There's a long way to go then.

zaim wrote:The number of collisions are not a very good measure of how much data they have, and how much physics they can do with it. A better measure is the integrated luminisity.

Integrated luminosity is just number of collisions multiplied by certain coefficient and written in different units. This coefficient may differ for different accelerators but in case of LHC they are apparently using the same coefficient corresponding to design beam parameters since the beginning even though they didn't reach design beam parameters yet.

They are planning to attempt multibunch injections for the first time. That means sending more than one bunch from the SPS into the LHC in one go. it will be interesting to see what that looks like on the vistas.

That was an excellent run this morning with 9 bunches and good luminosity around 0.8 . Probably added about 25 to 30 inverse nanobarns in one run. Next they are stepping up to 12 bunches.

Whooo, 12 bunch run, looks like a new luminosity record, about 1.5 x 10e30 in CMS (albeit briefly)