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Blogging ICHEP 2010

A collective forum about the 35th edition of
the International Conference on High Energy Physics (Paris, July 2010)

Wednesday, May 26, 2010

What should we expect from LHC?

June is coming, summer conferences are approaching, LHC physicists are feverishly working to produce results to show.

In the next few months there will be three main conferences where physics results from the LHC experiments will be presented: the nearest one is Physics At LHC, that will take place at Desy in Germany the second week of June; the second one is, erm... you know... ICHEP; the third one is the Hadron Collider Physics Symposium in Toronto, at the end of August. The kind of results one might expect to be presented at each of these conferences is rather different. The LHC is in fact steadily delivering proton-proton collisions at 7 TeV: the farther in time the conference, the more integrated luminosity the experiments will be able to use for their analyzes.

Could we try to guess what is likely to be shown at ICHEP by ATLAS and CMS? Well, it's definitively not an easy prediction: even assuming a perfect efficiency of the two experiments in collecting the data and analyzing it, the LHC beam conditions are improving every day, and the exploitable integrated luminosity at - let's say - mid July can largely vary.

Let's then try first a different exercise: which results are more likely to be seen at a conference as a function of the integrated luminosity collected at 7 TeV, from the small amount we already know as been secured by the experiments to the 1 fb-1 promised by the machine for the end of the 2010-2011 running? Warning: what follows is a very approximate list, I might have missed important signals here and there, and my judgment is certainly biased by my ATLAS experience. Here's what we'll get (or what we already got):
1. 10-100 μb-1: millions of charged pions to happily redo the charged multiplicity analysis published with the 900 GeV data collected in 2009; a few tens of $J/\psi \to \mu \mu$, a few jets here and there. Any resonance that can be spot using the tracker system (like K's and $\Lambda$'s) has been been seen at this point; signal from $\pi^0$ and $\eta$ decaying in photons pairs is found and well isolated.
2. 100-1000 μb-1: any hint of a $J/\psi \to \mu \mu$ peak should now be clearly visible;
3. 1-10 nb-1: more jets. And of course more jets-related measurements.
4. 10-100 nb-1: a few tens of W begins to appears in the data. The lucky ones might have seen a few Z bosons. A first observation of prompt inclusive electrons should be at reach at this point.
5. 100-1000 nb-1: more and more jets. The first inclusive muon measurements should be feasible. Signal from prompt photons should have been isolated.
6. 1-10 pb-1: at this point ATLAS and CMS should have secured enough W and Z to dare to attempt a first cross-section measurement. They might be able to pretend to have seen the top quark.
7. 10-100 pb-1: first B-physics related measurements. Something could already be said about some exotic scenarios, and some SUSY points.
8. 100-1000 pb-1: at this point, one could even optimistically hope in some timid news about the Higgs boson (exclusion), at least where the sensitivity is higher.
Where do we stand today? ATLAS and CMS are today around point 4. (more around the 10 nb-1 lower end, anyway), and that kind of results will most likely be shown at Physics At LHC together with a lot of performance studies. The question is then: how much more luminosity will the machine be able to deliver before ICHEP? Since this post is already long enough, I will postpone my educated guesses to the next ones. Stay tuned.