Results 1  10
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39
The BFKL Equation at NexttoLeading Level and Beyond ∗
, 1998
"... On the basis of a renormalization group analysis of the kernel and of the solutions of the BFKL equation with subleading corrections, we propose and calculate a novel expansion of a properly defined effective eigenvalue function. We argue that in this formulation the collinear properties of the kern ..."
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On the basis of a renormalization group analysis of the kernel and of the solutions of the BFKL equation with subleading corrections, we propose and calculate a novel expansion of a properly defined effective eigenvalue function. We argue that in this formulation the collinear properties of the kernel are taken into account to all orders, and that the ensuing nexttoleading truncation provides a much more stable estimate of hard Pomeron and of resummed anomalous dimensions.
Virtual NexttoLeading Corrections to the Lipatov Vertex
"... We compute the virtual nexttoleading corrections to the Lipatov vertex in the helicityamplitude formalism. These agree with previous results by Fadin and collaborators, in the conventional dimensionalregularization scheme. We discuss the choice of reggeization scale in order to minimize its impa ..."
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We compute the virtual nexttoleading corrections to the Lipatov vertex in the helicityamplitude formalism. These agree with previous results by Fadin and collaborators, in the conventional dimensionalregularization scheme. We discuss the choice of reggeization scale in order to minimize its impact on the nexttoleading logarithmic corrections to the BFKL equation. On leave of absence from I.N.F.N., Sezione di Torino, Italy. 1 Introduction Recently, a long awaited calculation of the nexttoleadinglogarithmic (NLL) corrections to the BalitskyFadinKuraevLipatov (BFKL) equation [1][3] has been completed [4]. The BFKL program is designed to resum the large logarithms of type ln(s=j tj) in semihard stronginteraction processes, which are characterized by two large and disparate kinematic scales: s, the squared parton centerofmass energy and j tj, of the order of the squared momentum transfer. At leading logarithmic (LL) accuracy there can be large dependence on the exa...
The C parameter distribution in e + e − annihilation
, 2003
"... Abstract: We study perturbative and non–perturbative aspects of the distribution of the C parameter in e + e − annihilation using renormalon techniques. We perform an exact calculation of the characteristic function, corresponding to the C parameter differential cross section for a single off–shell ..."
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Abstract: We study perturbative and non–perturbative aspects of the distribution of the C parameter in e + e − annihilation using renormalon techniques. We perform an exact calculation of the characteristic function, corresponding to the C parameter differential cross section for a single off–shell gluon. We then concentrate on the two–jet region, derive the Borel representation of the Sudakov exponent in the large–β0 limit and compare the result to that of the thrust T. Analysing the exponent, we distinguish two ingredients: the jet function, depending on Q 2 C, summarizing the effects of collinear radiation, and a function describing soft emission at large angles, with momenta of order QC. The former is the same as for the thrust upon scaling C by 1/6, whereas the latter is different. We verify that the rescaled C distribution coincides with that of 1−T to next–to–leading logarithmic accuracy, as predicted by Catani and Webber, and demonstrate that this relation breaks down beyond this order owing to soft radiation at large angles. The pattern of power corrections is also similar to that of the thrust: corrections appear as odd powers of Λ/(QC). Based on the size of the renormalon ambiguity, however, the shape function is different: subleading power corrections for the C distribution appear to be significantly smaller than those for the thrust.
Azimuthal decorrelations between QCD jets at all orders, Phys
 Lett. B
"... A quantity that promises to reveal important information on perturbative and nonperturbative QCD dynamics is the azimuthal decorrelation between jets in different hard processes. In order to access this information fixedorder NLO predictions need to be supplemented by resummation of logarithmic te ..."
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A quantity that promises to reveal important information on perturbative and nonperturbative QCD dynamics is the azimuthal decorrelation between jets in different hard processes. In order to access this information fixedorder NLO predictions need to be supplemented by resummation of logarithmic terms which are large in the region where the jets are nearly backtoback in azimuth. In the present letter we carry out this resummation to nextto–leading logarithmic accuracy explaining the important role played by the recombination scheme in general resummations for such jet One of the most commonly measured jet observables in experimental QCD studies is the azimuthal decorrelation ∆φ between hard finalstate jets. When compared to theoretical estimates of the same, this quantity is expected to provide valuable information both on QCD parameters (strong coupling, pdfs) as well as dynamics in the near backto–
Lowx QCD studies with forward jets in protonproton collisions at √ s = 14 TeV
, 812
"... Abstract. Forward (di)jet measurements are a useful tool to constrain the Parton Distribution Functions (PDFs) at low values of parton momentum fraction x and to study the possible onset of BFKL or gluon saturation QCD evolutions in the proton. We present studies of jet reconstruction capabilities i ..."
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Abstract. Forward (di)jet measurements are a useful tool to constrain the Parton Distribution Functions (PDFs) at low values of parton momentum fraction x and to study the possible onset of BFKL or gluon saturation QCD evolutions in the proton. We present studies of jet reconstruction capabilities in the CMS Hadron Forward (HF) calorimeter (3< η  <5). The expected sensitivity of the inclusive forward jet pT spectrum to the proton PDF, as well as the azimuthal decorrelation of MuellerNavelet jets with a large rapidity separation are presented for pp collisions at √ s = 14 TeV.
RapiditySeparation Dependence and the Large NexttoLeading Corrections to the BFKL Equation
, 1999
"... Recent concerns about the very large nexttoleading logarithmic (NLL) corrections to the BFKL equation are addressed by the introduction of a physical rapidityseparation parameter ∆. At the leading logarithm (LL) this parameter enforces the constraint that successive emitted gluons have a minimum ..."
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Recent concerns about the very large nexttoleading logarithmic (NLL) corrections to the BFKL equation are addressed by the introduction of a physical rapidityseparation parameter ∆. At the leading logarithm (LL) this parameter enforces the constraint that successive emitted gluons have a minimum separation in rapidity, yi+1 −yi> ∆. The most significant effect is to reduce the BFKL Pomeron intercept from the standard result as ∆ is increased from 0 (standard BFKL). At NLL this ∆dependence is compensated by a modification of the BFKL kernel, such that the total dependence on ∆ is formally nexttonexttoleading logarithmic. In this formulation, as long as ∆> ∼ 2.2 (for αs = 0.15): (i) the NLL BFKL pomeron intercept is stable with respect to variations of ∆, and (ii) the NLL correction is small compared to the LL result. Implications for the applicability of the BFKL Recently, the longawaited nexttoleadinglogarithmic (NLL) corrections to the Balitsky
Small x Resummation with Quarks: DeepInelastic Scattering CERNPHTH/2008014 Edinburgh 2007/49
, 802
"... We extend our previous results on small x resummation in the pure Yang–Mills theory to full QCD with nf quark flavours, with a resummed twobytwo matrix of resummed quark and gluon splitting functions. We also construct the corresponding deep–inelastic coefficient functions, and show how these can ..."
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We extend our previous results on small x resummation in the pure Yang–Mills theory to full QCD with nf quark flavours, with a resummed twobytwo matrix of resummed quark and gluon splitting functions. We also construct the corresponding deep–inelastic coefficient functions, and show how these can be combined with parton densities to give fully resummed deep–inelastic structure functions F2 and FL at the nexttoleading logarithmic level. We discuss how this resummation can be performed in different factorization schemes, including the commonly used MS scheme. We study the importance of the resummation effects by comparison with fixedorder perturbative results, and we discuss the corresponding renormalization and factorization scale variation uncertainties. We find that for x below 10 −2 the resummation effects are comparable in size to the fixed order NNLO corrections, but differ in shape. We finally discuss the phenomenological impact of the small–x resummation, specifically in the extraction of parton distribution from present day experiments and their extrapolation to the kinematics relevant for future colliders such as the LHC. CERNPHTH/2008014 January
Low x news for Monte Carlo
"... : This talk is a review of news in low x physics which, I think, would be useful for writing Monte Carlo codes. The following topics are discussed here: (i) the nexttoleading order BFKL Pomeron; (ii) two indications for shadowing corrections (SC) in DIS from HERA data; (iii) matching of "soft ..."
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: This talk is a review of news in low x physics which, I think, would be useful for writing Monte Carlo codes. The following topics are discussed here: (i) the nexttoleading order BFKL Pomeron; (ii) two indications for shadowing corrections (SC) in DIS from HERA data; (iii) matching of "soft" and "hard" photon  proton interactions; and (iv) survival probability for large rapidity gap (LRG) processes in hadronhadron scattering and DIS. I hope, that our current understanding of these topics will allow us to narrow the gap between the MC codes and our microscopic theory  QCD. 1 Introduction Goals: The main goal of this talk is to share with you my understanding of the current situation in low x physics looking at this subject from the angle of possible improvement of existing Monte Carlo codes. Everyone knows that the typical MC code for deep inelastic scattering (DIS) contains three parts: the perturbative QCD cascade, the hadronization stage and the matching between "soft" and "h...
Resummed event shapes at hadron colliders ∗
, 2004
"... We present recently defined jetobservables for hadronhadron dijet production, which are designed to reconcile the seemingly conflicting theoretical requirement of globalness, which makes it possible to resum them (automatically) at NLL accuracy and the limited experimental reach of detectors, so t ..."
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We present recently defined jetobservables for hadronhadron dijet production, which are designed to reconcile the seemingly conflicting theoretical requirement of globalness, which makes it possible to resum them (automatically) at NLL accuracy and the limited experimental reach of detectors, so that they are measurable at the Tevatron and at the LHC. PACS numbers: 12.38.Cy 1.