Most of the methods used in Jet version 4_0 are the same used in the earlier version 3.4. Therefore, one should see the explanation of Jet version 3.4.

The major difference is that jet4_0 makes a three dimensional table for the triply differential jet cross section. The entries in this table are the K factor minus 1, where the K factor is the ratio of the NLO cross section to the LO cross section. Then readjet4_0 can read this table and produce cross sections by interpolation in the table, multiplying the K factor by the LO cross section (which is easy to calculate).

The entries in the table at each point in a lattice of jet variables (xA, xB, y*) are calculated as integrals of (K - 1) over a region near to the lattice point, using a gaussian weight.

For each point (xA, xB, y*) reported, readjet4_0 also gives the values of (ET, y1, y2) for an ideal two jet system with these values of (xA, xB, y*). This transformation is based on 2 parton --> 2 parton kinematics. Thus this is a ``Born level'' relation. This information is intended to convey an idea of what values of jet transverse energies and rapidities are explored by the cross section at this (xA, xB, y*) value.

`
Give X grid: Xmin, Xmax, Number of points
`

One could choose, for example,

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0.01,0.8,11
`

To fix the lattice in y*, the program asks

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Give YSTAR grid: YSTARMAX, Number of points
`

One could choose, for example,

`
2,7
`

To fix smearing distances in log(xA/(1-xA)), log(xB/(1-xB)), and y*, the program asks

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Give smearing distances in ln(x/(1-x)) and ystar
`

One could choose, for example,

`
1,1
`

For each lattice point, the program will calculate an integral of K - 1 times a gaussian weight factor that effectively limits the integral to a region near to the lattice point. Big smearing distances make the region bigger and hence improve the statistical error. However, if the distanes get too big, so that K - 1 varies substantially over one smearing length, then the smearing error (reported by readjet) will go up.

To fix the renormalization and factorization scales, the program asks

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Give scale choices: A_uv, A_co
`

One could choose, for example,

`
1,1
`

(Please see our published paper for the meaning of these parameters.) The program asks how many thousands of Monte Carlo points (or rather ``Reno'' points) you want. The more the better if you want small statistical errors. But of course, ``more'' takes longer. Probably about 1000 thousand is enough.

Davison E. Soper, Institute of Theoretical Science, University of Oregon, Eugene OR 97403 USA soper@bovine.uoregon.edu