Les Houches

People: Kostas Theofilatos, … (add your name if you are interested)

This is a followup to the Higgs+jets comparisons that occurred in Les Houches 2015. The inclusive jet cross section has the widest dynamic range of any process at the LHC, and has served as one of the key benchmark cross sections in global PDF fits. Til now, jet production has been included at NLO, even in NNLO fits due to its importance. Now, for the first time, the fits can be performed with NNLO jets. The Tevatron jet data all had a jet radius of 0.7. At the LHC, data with jet radii of 0.4, 0.5, 0.6 and 0.7 are available. ​The perturbative jet cross sections are corrected for effects from the underlying event and fragmentation. These corrections are determined by Monte Carlo parton shower programs and the assumption made is that corrections determined from parton showers apply equally well to fixed order, i.e. the jet shapes for the two are similar enough for this connection to be valid.

This study will test:

(1) if there are significant resummation (parton shower) effects on top of the fixed order core prediction (2) if the NLO results are incorrect because of the inability of the NLO matrix elements to correctly describe the jet shape; this will be more serious for the smaller jet sizes than the larger ones (3) if the impact from either of the above effects is reduced at NNLO, and if residual corrections are needed in global PDF fits to account for these effects

The study will be undertaken with both fixed order (NLO and NNLO) and ME+PS programs. Results will be quoted both at the parton (parton shower) level and at the hadron level (for ME+PS). The same PDF will be used, and the same core scale (as much as possible) will also be used. A Rivet routine will be provided based on CMS measurements at 13 TeV for R=0.4 and 0.7. It will be supplemented with jet sizes of 0.3, 0.6, and 1.0.

Addendum:

Following the quark/gluon meeting on Saturday morning, we would like to add to the Rivet routine variables measuring the jet mass, the jet width and the Les Houches angularity for each kinematic bin and each R value. Jesse will provide the exact code. These variables, of course, are not measured by CMS, but such a comprehensive study should prove useful for multiple reasons.