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Start Your Monte Carlo Engines! April 6, 2008

Posted by gordonwatts in LHC, physics.

There is a joke going around ATLAS right now. There are various people who are obsessed by their physics studies. Each time something new about the detector is found they want to re-run their analysis. Nothing wrong with that – except that if it requires re-simulating the Monte Carlo that can take real resources (minutes per event just to reconstruct the event – we need millions of events in order to do one out of 1000’s of analyses).

Well, a big one was dropped the other day. Actually, we’ve all heard rumors this was coming, but now it is official, so I can joke about it. This is a big one because it changes everything – the production cross sections, average energy will find in our calorimeter, and other things. So, if you want to know how you are going to discover the Higgs at 10 TeV – well, better restart your simulation.

Of course what really matters is how long the accelerator remains at that energy. I don’t know details (perhaps I’ll learn them at ATLAS week next week) but the release claims that the magnets just need some re-training. If that is the case, that is no big deal and we will be at 10 TeV for less time that it will take the detectors to get themselves in shape to take physics-quality data.

At any rate. I’m sure, in some private cluster, somewhere, some 10 TeV data is being simulated as I type this!



1. Kevin - April 7, 2008

yes – sort of annoying. My personal guess is that if we only run for 2 -3 months at 10 TeV the detectors won’t be calibrated, aligned, and understood enough to do anything with So its probably a small perturbation to the actual activities that will go on with this data. None the less – in principle one could discover something like a Z’ that is just out of reach at the Tevatron with this data (you could probably discover this even if your resolutions are several times worse than expected and your efficiencies are significantly lower …


2. gordonwatts - April 7, 2008

Kevin – I totally understand. But are the differences between 14 TeV and 10 TeV so great that we need to run out now? Why not wait for a year — until data is about to arrive. Then we can all spend time con commissioning and getting the infrastructure ready. By the time the machine starts to turn on we’ll know much better if the 10 TeV is going to stay for 2 months or for 10 – and we’ll be able to make an informed decsion.

Of course, ATLAS is so big we can probably afford to do both…

3. Not Even Wrong » Blog Archive » LHC Startup at 10 TeV - April 7, 2008

[…] Update: I’d been wondering how much extra work this change in energy would cause for the experimentalists, just saw a posting about this by Gordon Watts, entitled Start Your Monte-Carlo Engines! […]

4. The Real Monte Carlo Story « Life as a Physicist - April 14, 2008

[…] Real Monte Carlo Story April 14, 2008 Posted by gordonwatts in ATLAS, physics. trackback A few posts ago I poked fun at the idea that we’d be running 10 TeV Monte Carlo in ATLAS. Not Even Wrong linked to it. […]

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