# BrickCompare

## Comparison of radiative energy loss curves from the brick problem

Below is a figure comparing the ASW/BDMPS curves and the radiative component of WHDG/GLV for the brick with L=2 fm and deltaE/E = 0.2.

The main curves are the red and black which are from the ASW and WHDG as posted on this Wiki. The thin lines are a from the publicly available quenching weights routines. The ASW calculation is identical to the quenching weights (the small visible difference is due to different values of alpha_s).

The 'QS-SH N=1' curve uses the single-hard approximation as described in the ASW paper. One of the differences between this curve and the WHDG curve is the treatment of the limit where deltaE approaches E; the WHDG calculations use a (1-x) factor to cut of emissions with deltaE > E.

## Systematic comparison of energy loss curves and fragmentation functions

(update 1-Dec-2008, Marco van Leeuwen)

Below are two figures for the brick problem. Still using L=2 fm and E=10 GeV, the left panel shows a comparison of the energy loss curve for ASW (DE/E=0.1) to a set of values for WHDG. The middle curve has the same DE/E, the others are variations around it.

The right panel shows the ratio of fragmentation functions (using KKP LO charged pions as input) for AA and pp, using a simple convolution. This should be comparable to Higher Twist and YaJem as well.

My main conclusion is that whatever you do, significant differences are visible in the fragmentation functions for ASW and WHDG, so measuring the fragmentation function (with enough precision...) is going to constrain the models!

## Gluon spectra

[Update 14 May 2009, Marco van Leeuwen]

For a more detailed comparison, here are the gluon spectra for L=2 fm, T=450 MeV and E=100 GeV. The large E was take to reduce the effect of the kinematic limit in WHDG [(1-x) in kmax]

The ASW OE curves are the SW opacity expansion, but with the factor L/lambda calculated for the thermal medium (like in WHDG). So L/lambda != 1.

For lower T=250 MeV, the difference becomes more striking: