Discussion of sPHENIX note sPH-cQCD-2017-001

[Jamie Nagle <jamie.nagle AT colorado.edu>]

Hello All,

Following on useful discussions with John Lajoie and Christine Aidala, the Colorado group discussed a bit more what the additional Forward Calorimeter could add to the sPHENIX jet program.    Attached are a few slides with calculations from Dennis Perepelitsa at the PYTHIA level.   These just reflect the basic kinematics of p+p @ 200 GeV and the correct number of equivalent N+N collisions sampled in the Au+Au data taking.

We assume that sPHENIX can measure in the barrel trigger photons > 15 GeV and trigger jets > 20 GeV, and then correlated jets at forward down to > 10 GeV.   Note that for correlations, the underlying event background fluctuation contribution is substantially reduced (aka fake jets) and one can subtract remaining pieces statistically.    

If one thought this was worth pursuing, we believe the case focuses on the ability to measure dijets and gamma-jet where one pushes to high x1.   This is interesting in p+Au where it tests thinking like the shrinking proton picture (high x fluctuations of the proton result in a smaller gluon cloud) and also cold nuclear matter energy loss (which is predicted by Ivan Vitev to be a dominant effect at very high x).   In Au+Au, one combines this with jets passing through a different pseudorapidity range and thus a slightly different medium.    One can then check if results across rapidities scale with x (for example as they do in p+Pb for ATLAS) or other kinematics or medium variables.

Aside from these direct measurements, the additional coverage is sure to help with characterizing the underlying event in general for even sPHENIX barrel jet measurements and provides pseudorapidity separated flow characterizations (also useful by itself and for the underlying event).   Lastly, as searches for medium response probe to larger R values (R ~ 1), having an event characterization over a larger pseudorapidity range is helpful.     

The slides are available in the public area here:

https://www.phenix.bnl.gov/WWW/publish/nagle/sPHENIX/nagle_sphenixandforwardjets_05262017.pdf

BTW - these small size limits on the email lists are a pain.   Also, not having an individual sPHENIX web area is a pain.

Sincerely,

Jamie and Dennis

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|| James L. Nagle   
|| Professor of Physics, University of Colorado, Boulder
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