LHCf Experment

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LHCf Experment

Post by Xymox » Thu Nov 12, 2009 10:16 am

What exactly is the purpose of the LHCf detector ? Im confuzed :(


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Re: LHCf Experment

Post by jepson » Wed Dec 02, 2009 12:05 am

A late, but hopefully helpful, answer: the LHCf provides better data for identifying Extremely High Energy Cosmic Rays (lab equivalent of 10^17 eV and up).

Here's how I've understood it:

* The problem: All we have on EHECRs ATM is theories based on whatever low-energy lab data has been gathered so far, coupled with the few rays we've been able to record.
* EHECRs are incredibly rare, striking the planet a couple of times a decade. Hence the usual approach of capturing empirical data from nature is more or less useless.
* What little empirical data is available points to galactic nuclei as the sources; this means protons are likely the biggest part of the payload (with Fe nuclei mixed in for good measure, but we can ignore that for now).
* The rays strike the planet at a very acute angle, colliding at LHC-style speed. This leads to the detected "air showers".
* From the above (at least if you're a radio astronomer or physicist) it's vital to get the best possible model for detecting EHECRs. This involves finding and measuring the collisions.

The experiment:

* Two things are required for advancing the model: the total inelastic cross section and the energy spectrum of the secondaries from the collisions.
* TOTEM measures everything including bad acronyms^W^W^W^W the cross section better than anything before it.
* LHCf looks at the energy of the secondaries to narrow the detection spectrum.
* Another question this is supposed to answer is whether the GZK cutoff holds. Some data seems to suggest super-GZK events (my personal view is "that's probably a measurement error", but I'd be thrilled to be proven wrong here).


* The "forward" part refers to the collision angle. You can't get more forward than a head-on collision :) The particle physicist lingo for this is "created in the forward cone".
* Nothing the LHCf produces will be immediately useful, but might in the coming few decades lead to better detection, identification and a better understanding of the origin of EHECRs.
* Formally, what the LHCf counts are neutral pions.
* There are a couple of talks and articles out there. This article in the Journal of Instrumentation has a nice overview of the physics.

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