25 research outputs found
High Energy Resummation of Jet Observables
In this paper we investigate the extension of high energy resummation at LLx
accuracy to jet observables. In particular, we present the high energy resummed
expression of the transverse momentum distribution of the outgoing parton in
the general partonic process . In order to reach this
result, several new ideas are introduced and exploited. First we prove that LLx
resummation is achieved by dressing with hard radiation an off-shell gluon
initiated LO process even if its on-shell limit is vanishing or trivial. Then
we present a gauge-invariant framework where these calculations can be
performed by using the modern helicity techniques. Finally, we show a possible
way to restore gluon indistinguishability in the final state, which is
otherwise lost in the resummation procedure, at all orders in at
LLx. All partonic channels are then resummed and cross-checked against
fixed-order calculations up to Comment: 31 pages, 6 figure
High energy resummation of transverse momentum distributions:Higgs in gluon fusion
We derive a general resummation formula for transverse-momentum distributions
of hard processes at the leading logarithmic level in the high-energy limit, to
all orders in the strong coupling. Our result is based on a suitable
generalization of high-energy factorization theorems, whereby all-order
resummation is reduced to the determination of the Born-level process but with
incoming off-shell gluons. We validate our formula by applying it to Higgs
production in gluon fusion in the infinite top mass limit. We check our result
up to next-to-leading order by comparison to the high energy limit of the exact
expression and to next-to-next-to leading by comparison to NNLL order trasverse
momentum (Sudakov) resummation, and we predict the high-energy behaviour at
next-to-leading order. We also show that the structure of the result in the
small transverse momentum limit agrees to all orders with general constraints
from Sudakov resummation.Comment: 28 pages, 6 figures, Final version published in JHEP: several typos
corrected (including in equations
On the Higgs cross section at NLO+NLL and its uncertainty
We consider the inclusive production of a Higgs boson in gluon-fusion and we
study the impact of threshold resummation at next-to-next-to-next-to-leading
logarithmic accuracy (NLL) on the recently computed fixed-order prediction
at next-to-next-to-next-to-leading order (NLO). We propose a conservative,
yet robust way of estimating the perturbative uncertainty from missing higher
(fixed- or logarithmic-) orders. We compare our results with two other
different methods of estimating the uncertainty from missing higher orders: the
Cacciari-Houdeau Bayesian approach to theory errors, and the use of algorithms
to accelerate the convergence of the perturbative series. We confirm that the
best convergence happens at , and we conclude that a
reliable estimate of the uncertainty from missing higher orders on the Higgs
cross section at 13 TeV is approximately %.Comment: 27 pages, 6 figures. Version to be published in JHE
Top Quark Pair Production beyond NNLO
We construct an approximate expression for the total cross section for the
production of a heavy quark-antiquark pair in hadronic collisions at
next-to-next-to-next-to-leading order (NLO) in . We use a
technique which exploits the analyticity of the Mellin space cross section, and
the information on its singularity structure coming from large N (soft gluon,
Sudakov) and small N (high energy, BFKL) all order resummations, previously
introduced and used in the case of Higgs production. We validate our method by
comparing to available exact results up to NNLO. We find that NLO
corrections increase the predicted top pair cross section at the LHC by about
4% over the NNLO.Comment: 34 pages, 9 figures; final version, to be published in JHEP;
reference added, minor improvement
Combined threshold and transverse momentum resummation for inclusive observables
We present a combined resummation for the transverse momentum distribution of a colorless final state in perturbative QCD, expressed as a function of transverse momentum pT and the scaling variable x. Its expression satisfies three requirements: it reduces to standard transverse momentum resummation to any desired logarithmic order in the limit pT \ue2\u86\u92 0 for fixed x, up to power suppressed corrections in pT; it reduces to threshold resummation to any desired logarithmic order in the limit x \ue2\u86\u92 1 for fixed pT, up to power suppressed correction in 1 \ue2\u88\u92 x; upon integration over transverse momentum it reproduces the resummation of the total cross cross at any given logarithmic order in the threshold x \ue2\u86\u92 1 limit, up to power suppressed correction in 1 \ue2\u88\u92 x. Its main ingredient, and our main new result, is a modified form of transverse momentum resummation, which leads to threshold resummation upon integration over pT, and for which we provide a simple closed-form analytic expression in Fourier-Mellin (b, N) space. We give explicit coefficients up to NNLL order for the specific case of Higgs production in gluon fusion in the effective field theory limit. Our result allows for a systematic improvement of the transverse momentum distribution through threshold resummation which holds for all pT, and elucidates the relation between transverse momentum resummation and threshold resummation at the inclusive level, specifically by providing within perturbative QCD a simple derivation of the main consequence of the so-called collinear anomaly of SCET