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Pietro Falgari

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Papers by Pietro Falgari

Higher-order soft and Coulomb corrections to squark and gluino production at the LHC

arXiv (Cornell University), Dec 3, 2013

We present predictions for the total cross sections for pair production of squarks and gluinos at... more We present predictions for the total cross sections for pair production of squarks and gluinos at the LHC including a combined NNLL resummation of soft and Coulomb gluon effects. The NNLL corrections can be up to 25% relative to previous NLL results and reduce the theoretical uncertainties to the 10% level.

Four-fermion production near the W-pair production threshold

W-pair production near threshold in unstable particle effective theory

In this thesis we present a dedicated study of the four-fermion production process e -e + → µ -νµ... more In this thesis we present a dedicated study of the four-fermion production process e -e + → µ -νµ u d X near the W -pair production threshold, in view of its importance for a precise determination of the W -boson mass at the ILC. The calculation is performed in the framework of unstable-particle effective theory, which allows for a gauge-invariant inclusion of instability effects, and for a systematic approximation of the full cross section with an expansion in the coupling constants, the ratio Γ W /M W , and the non-relativistic velocity v of the W boson. The effective-theory result, computed to next-to-leading order in the expansion parameters Γ W /M W ∼ α ew ∼ v 2 , is compared to the full numerical next-toleading order calculation of the four-fermion production cross section, and agreement to better than 0.5 % is found in the region of validity of the effective theory. Furthermore, we estimate the contributions of missing higher-order corrections to the four-fermion process, and how they translate into an error on the W -boson mass determination. We find that the dominant theoretical uncertainty on M W is currently due to an incomplete treatment of initial-state radiation, while the remaining combined uncertainty of the two NLO calculations translates into δM W ≈ 5 MeV. The latter error is removed by an explicit computation of the dominant missing terms, which originate from the expansion in v of next-to-next-to-leading order Standard Model diagrams. The effect of resummation of logarithmically-enhanced terms is also investigated, but found to be negligible.

The top-pair total cross section at NNLL order

Inclusive top-pair production phenomenology

We discuss various aspects of inclusive top-quark pair production based on Topixs, a new, flexibl... more We discuss various aspects of inclusive top-quark pair production based on Topixs, a new, flexible program that computes the production cross section at the Teva- tron and LHC at next-to-next-to-leading logarithmic accuracy in soft and Coulomb re- summation, including bound-state effects and the complete next-to-next-to-leading order result in the q¯ q channel, which has recently become available. We present the calculation of the top-pair cross section in pp collisions at 8TeV centre-of-mass energy, as well as the cross sections for hypothetical heavy quarks in extensions of the standard model. The de- pendence on the parton distribution input is studied. Further we investigate the impact of LHC top cross section measurements at p s = 7TeV on global fits of the gluon distribution

The total top-pair production cross section at NNLL

Nuclear physics, 2013

We present results for the total top-pair production cross section at the Tevatron and the LHC. O... more We present results for the total top-pair production cross section at the Tevatron and the LHC. Our predictions supplement fixed-order results with resummation of soft logarithms and Coulomb singularities to next-to-next-to-leading (NNLL) logarithmic accuracy and include top-antitop bound-state effects. The effects of resummation, the dependence on the PDF set used, the residual sources of theoretical uncertainty and their implication for measurements of the top-quark mass are discussed.

SM single-top production at hadron colliders

Journal of physics, Jul 30, 2013

We give an overview of the status of theoretical predictions for single-top production in the Sta... more We give an overview of the status of theoretical predictions for single-top production in the Standard Model. We focus in particular on recent developments, including calculations of off-shell effects at next-to-leading order beyond the narrow-width approximation, all-order resummation of soft corrections and matching of next-to-leading order parton-level results to Monte Carlo parton showers. Preprint numbers: ITP-UU-13/01, SPIN-13/01. 1 The relative size of the three channels changes slightly depending on the theoretical prediction used.

The top-quark pair production cross section at next-to-next-to-leading logarithmic order

arXiv (Cornell University), Dec 20, 2011

Threshold expansion of massive coloured particle cross sections

Nuclear physics, Aug 1, 2010

Pair production of massive coloured particles in hadron collisions is accompanied by potentially ... more Pair production of massive coloured particles in hadron collisions is accompanied by potentially large radiative corrections related to the suppression of soft gluon emission and enhanced Coulomb exchange near the production threshold. We recently developed a framework to sum both series of corrections for the partonic cross section using soft-collinear and non-relativistic effective theory. If it can be argued that the resummed cross section approximates the complete result over a significant kinematic range, an improvement of the hadronic cross section results, even when the production is not kinematically constrained to the threshold. This is discussed here for the case of top quark production.

NNLL threshold resummation for the total top-pair production cross section

arXiv (Cornell University), May 4, 2012

We present predictions for the total top-quark pair production cross section at the Tevatron and ... more We present predictions for the total top-quark pair production cross section at the Tevatron and the LHC with 7, 8 and 14 TeV centre-of-mass energy, including the resummation of threshold logarithms and Coulomb corrections through next-to-next-to-leading logarithmic order, and t t bound-state contributions. The remaining theoretical and PDF uncertainties and prospects for the measurement of the top mass from the total cross section are discussed.

All-order colour structure and two-loop anomalous dimension of soft radiation in heavy-particle pair production at the LHC

arXiv (Cornell University), Jan 26, 2010

We consider the factorization and resummation of soft and Coulomb gluons for pair-production proc... more We consider the factorization and resummation of soft and Coulomb gluons for pair-production processes of heavy coloured particles at hadron colliders, and discuss: the construction of a colour basis that diagonalizes the leading soft function to all orders in perturbation theory; the determination of the two-loop soft anomalous dimension needed for NNLL resummations; and a general formula that provides all logarithmically enhanced O(α 2 s ) correction requiring as processindependent input only the one-loop hard matching coefficients.

Finite-width effects in unstable-particle production at hadron colliders

Journal of High Energy Physics, May 1, 2013

A bstract We present a general formalism for the calculation of finite-width contributions to the... more A bstract We present a general formalism for the calculation of finite-width contributions to the differential production cross sections of unstable particles at hadron colliders. In this formalism, which employs an effective-theory description of unstable-particle production and decay, the matrix element computation is organized as a gauge-invariant expansion in powers of Γ X /m X , with Γ X and m X the width and mass of the unstable particle. This framework allows for a systematic inclusion of off-shell and non-factorizable effects whilst at the same time keeping the computational effort minimal compared to a full calculation in the complex-mass scheme. As a proof-of-concept example, we give results for an NLO calculation of top-antitop production in the $ q\overline{q} $ partonic channel. As already found in a similar calculation of single-top production, the finite-width effects are small for the total cross section, as expected from the naïve counting ~ Γ t /m t ~ 1%. However, ...

Off-shell effects for<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>t</mml:mi></mml:math>-channel and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>s</mml:mi></mml:math>-channel single-top production at next-to-leading order in...

Physical review, May 10, 2011

In this work we present a calculation of both t-channel and s-channel singletop production at nex... more In this work we present a calculation of both t-channel and s-channel singletop production at next-to-leading order in QCD for the Tevatron and for the LHC at a centre-of-mass energy of 7 TeV. All the cross sections and kinematical distributions presented include leading non-factorizable corrections arising from interferences of the production and decay subprocesses, extending previous results beyond the narrow-width approximation. The new off-shell effects are found to be generally small, but can be sizeable close to kinematical end-points and for specific distributions.

BFKL next-to-next-to-leading order

Nuclear Physics B, Oct 1, 2007

We determine an approximate expression for the O(α 3 s ) contribution χ 2 to the kernel of the BF... more We determine an approximate expression for the O(α 3 s ) contribution χ 2 to the kernel of the BFKL equation, which includes all collinear and anticollinear singular contributions. This is derived using recent results on the relation between the GLAP and BFKL kernels (including running-coupling effects to all orders) and on small-x factorization schemes. We present the result in various schemes, relevant both for applications to the BFKL equation and to small-x evolution of parton distributions.

PoS(Confinement X)225 The total top-pair production cross section at NNLL

We present results for the total top-pair production cross section at the Tevatron and the LHC. O... more We present results for the total top-pair production cross section at the Tevatron and the LHC. Our predictions supplement fixed-order results with resummation of soft logarithms and Coulomb singularities to next-to-next-to-leading (NNLL) logarithmic accuracy and include top-antitop boundstate effects. The effects of resummation, the dependence on the PDF set used, the residual sources of theoretical uncertainty and their implication for measurements of the top-quark mass are discussed.

Inclusive top-pair production phenomenology

We discuss various aspects of inclusive top-quark pair production based on Topixs, a new, flexibl... more We discuss various aspects of inclusive top-quark pair production based on Topixs, a new, flexible program that computes the production cross section at the Teva- tron and LHC at next-to-next-to-leading logarithmic accuracy in soft and Coulomb re- summation, including bound-state effects and the complete next-to-next-to-leading order result in the q¯ q channel, which has recently become available. We present the calculation of the top-pair cross section in pp collisions at 8TeV centre-of-mass energy, as well as the cross sections for hypothetical heavy quarks in extensions of the standard model. The de- pendence on the parton distribution input is studied. Further we investigate the impact of LHC top cross section measurements at p s = 7TeV on global fits of the gluon distribution

W-pair production near threshold in unstable particle effective theory

In this thesis we present a dedicated study of the four-fermion production process e−e+ → μν̄μud̄... more In this thesis we present a dedicated study of the four-fermion production process e−e+ → μν̄μud̄X near the W -pair production threshold, in view of its importance for a precise determination of the W -boson mass at the ILC. The calculation is performed in the framework of unstable-particle effective theory, which allows for a gauge-invariant inclusion of instability effects, and for a systematic approximation of the full cross section with an expansion in the coupling constants, the ratio ΓW/MW , and the non-relativistic velocity v of the W boson. The effective-theory result, computed to next-to-leading order in the expansion parameters ΓW /MW ∼ αew ∼ v2, is compared to the full numerical next-toleading order calculation of the four-fermion production cross section, and agreement to better than 0.5% is found in the region of validity of the effective theory. Furthermore, we estimate the contributions of missing higher-order corrections to the four-fermion process, and how they tran...