G. Chachamis - Hamburg U

G. Chachamis
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Name
G. Chachamis
Affiliation
Hamburg U
City
Hamburg
Country
Germany

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High Energy Physics - Phenomenology (48)
 
High Energy Physics - Theory (9)
 
High Energy Physics - Experiment (4)

Publications Authored By G. Chachamis

Recently, a new family of observables consisting of azimuthal-angle generalised ratios was proposed in a kinematical setup that resembles the usual Mueller-Navelet jets but with an additional tagged jet in the central region of rapidity. Non-tagged minijet activity between the three jets can affect significantly the azimuthal angle orientation of the jets and is accounted for by the introduction of two BFKL gluon Green functions. Here, we calculate the, presumably, most relevant higher order corrections to the observables by now convoluting the three leading-order jet vertices with two gluon Green functions at next-to-leading logarithmic approximation. Read More

We propose the study of new observables in LHC inclusive events with three tagged jets, one in the forward direction, one in the backward direction and both well-separated in rapidity from the each other (Mueller-Navelet jets), together with a third jet tagged in central regions of rapidity. Since non-tagged associated mini-jet multiplicity is allowed, we argue that projecting the cross sections on azimuthal-angle components can provide several distinct tests of the BFKL dynamics. Realistic LHC kinematical cuts are introduced. Read More

A study of differential cross sections for the production of three and four jets in multi-Regge kinematics is presented. The main focus lies on the azimuthal angle dependences in events with two forward/backward jets are tagged in the final state. Furthermore, the tagging of one or two extra jets in more central regions of the detector with a relative separation in rapidity from each other is requested. Read More

2016Nov
Authors: K. Akiba1, M. Akbiyik2, M. Albrow3, M. Arneodo4, V. Avati5, J. Baechler6, O. Villalobos Baillie7, P. Bartalini8, J. Bartels9, S. Baur10, C. Baus11, W. Beaumont12, U. Behrens13, D. Berge14, M. Berretti15, E. Bossini16, R. Boussarie17, S. Brodsky18, M. Broz19, M. Bruschi20, P. Bussey21, W. Byczynski22, J. C. Cabanillas Noris23, E. Calvo Villar24, A. Campbell25, F. Caporale26, W. Carvalho27, G. Chachamis28, E. Chapon29, C. Cheshkov30, J. Chwastowski31, R. Ciesielski32, D. Chinellato33, A. Cisek34, V. Coco35, P. Collins36, J. G. Contreras37, B. Cox38, D. de Jesus Damiao39, P. Davis40, M. Deile41, D. D'Enterria42, D. Druzhkin43, B. Ducloué44, R. Dumps45, R. Dzhelyadin46, P. Dziurdzia47, M. Eliachevitch48, P. Fassnacht49, F. Ferro50, S. Fichet51, D. Figueiredo52, B. Field53, D. Finogeev54, R. Fiore55, J. Forshaw56, A. Gago Medina57, M. Gallinaro58, A. Granik59, G. von Gersdorff60, S. Giani61, K. Golec-Biernat62, V. P. Goncalves63, P. Göttlicher64, K. Goulianos65, J. -Y. Grosslord66, L. A. Harland-Lang67, H. Van Haevermaet68, M. Hentschinski69, R. Engel70, G. Herrera Corral71, J. Hollar72, L. Huertas73, D. Johnson74, I. Katkov75, O. Kepka76, M. Khakzad77, L. Kheyn78, V. Khachatryan79, V. A. Khoze80, S. Klein81, M. van Klundert82, F. Krauss83, A. Kurepin84, N. Kurepin85, K. Kutak86, E. Kuznetsova87, G. Latino88, P. Lebiedowicz89, B. Lenzi90, E. Lewandowska91, S. Liu92, A. Luszczak93, M. Luszczak94, J. D. Madrigal95, M. Mangano96, Z. Marcone97, C. Marquet98, A. D. Martin99, T. Martin100, M. I. Martinez Hernandez101, C. Martins102, C. Mayer103, R. Mc Nulty104, P. Van Mechelen105, R. Macula106, E. Melo da Costa107, T. Mertzimekis108, C. Mesropian109, M. Mieskolainen110, N. Minafra111, I. L. Monzon112, L. Mundim113, B. Murdaca114, M. Murray115, H. Niewiadowski116, J. Nystrand117, E. G. de Oliveira118, R. Orava119, S. Ostapchenko120, K. Osterberg121, A. Panagiotou122, A. Papa123, R. Pasechnik124, T. Peitzmann125, L. A. Perez Moreno126, T. Pierog127, J. Pinfold128, M. Poghosyan129, M. E. Pol130, W. Prado131, V. Popov132, M. Rangel133, A. Reshetin134, J. -P. Revol135, M. Rijssenbeek136, M. Rodriguez137, B. Roland138, C. Royon139, M. Ruspa140, M. Ryskin141, A. Sabio Vera142, G. Safronov143, T. Sako144, H. Schindler145, D. Salek146, K. Safarik147, M. Saimpert148, A. Santoro149, R. Schicker150, J. Seger151, S. Sen152, A. Shabanov153, W. Schafer154, G. Gil Da Silveira155, P. Skands156, R. Soluk157, A. van Spilbeeck158, R. Staszewski159, S. Stevenson160, W. J. Stirling161, M. Strikman162, A. Szczurek163, L. Szymanowski164, J. D. Tapia Takaki165, M. Tasevsky166, K. Taesoo167, C. Thomas168, S. R. Torres169, A. Tricomi170, M. Trzebinski171, D. Tsybychev172, N. Turini173, R. Ulrich174, E. Usenko175, J. Varela176, M. Lo Vetere177, A. Villatoro Tello178, A. Vilela Pereira179, D. Volyanskyy180, S. Wallon181, G. Wilkinson182, H. Wöhrmann183, K. C. Zapp184, Y. Zoccarato185
Affiliations: 1LHC Forward Physics Working Group, 2LHC Forward Physics Working Group, 3LHC Forward Physics Working Group, 4LHC Forward Physics Working Group, 5LHC Forward Physics Working Group, 6LHC Forward Physics Working Group, 7LHC Forward Physics Working Group, 8LHC Forward Physics Working Group, 9LHC Forward Physics Working Group, 10LHC Forward Physics Working Group, 11LHC Forward Physics Working Group, 12LHC Forward Physics Working Group, 13LHC Forward Physics Working Group, 14LHC Forward Physics Working Group, 15LHC Forward Physics Working Group, 16LHC Forward Physics Working Group, 17LHC Forward Physics Working Group, 18LHC Forward Physics Working Group, 19LHC Forward Physics Working Group, 20LHC Forward Physics Working Group, 21LHC Forward Physics Working Group, 22LHC Forward Physics Working Group, 23LHC Forward Physics Working Group, 24LHC Forward Physics Working Group, 25LHC Forward Physics Working Group, 26LHC Forward Physics Working Group, 27LHC Forward Physics Working 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The goal of this report is to give a comprehensive overview of the rich field of forward physics, with a special attention to the topics that can be studied at the LHC. The report starts presenting a selection of the Monte Carlo simulation tools currently available, chapter 2, then enters the rich phenomenology of QCD at low, chapter 3, and high, chapter 4, momentum transfer, while the unique scattering conditions of central exclusive production are analyzed in chapter 5. The last two experimental topics, Cosmic Ray and Heavy Ion physics are presented in the chapter 6 and 7 respectively. Read More

We study differential cross sections for the production of three and four jets in multi-Regge kinematics, the main interest lying on azimuthal angle dependences. The theoretical setup is the jet production from a single BFKL ladder with a convolution of two/three BFKL Green functions, where two forward/backward jets are always tagged in the final state. Furthermore, we require the tagging of one/two further jets in more central regions of the detectors with a relative separation in rapidity. Read More

We discuss a recent study on high-energy jet production in the multi-Regge limit done with the use of the Monte Carlo event generator BFKLex which includes collinear improvements in the form of double-log contributions. We will show results for the average transverse momentum and azimuthal angle of the final state jets when at least one of them is very forward in rapidity and another one is very backward. We also discuss the introduction of a new observable which accounts for the average rapidity ratio among subsequent emissions. Read More

A study of differential cross sections for the production of four jets in multi-Regge kinematics is presented, the main focus lying on azimuthal angle dependences. The theoretical setup consists in the jet production from a single BFKL ladder with a convolution of three BFKL Green functions, where two forward/backward jets are always tagged in the final state. Furthermore, the tagging of two further jets in more central regions of the detectors with a relative separation in rapidity from each other is requested. Read More

We discuss briefly a recent study of new observables in LHC inclusive events with three tagged jets. One jet is in the forward direction, the second is in the backward direction and well-separated in rapidity from the first, whereas, the third tagged jet is to be found in more central regions of the detector. Taking into consideration that non-tagged mini-jet emissions are allowed and that they may be accounted for by the BFKL gluon Green function, we project the cross sections on azimuthal-angle components and define suitable ratios based on these projections which can provide several distinct tests of the BFKL dynamics. Read More

We discuss briefly the first numerical implementation of the Loop-Tree Duality (LTD) method. We apply the LTD method in order to calculate ultraviolet and infrared finite multi-leg one-loop Feynman integrals. We attack scalar and tensor integrals with up to six legs (hexagons). Read More

We present a method of solution of the Bartels-Kwiecinski-Praszalowicz (BKP) equation based on the numerical integration of iterated integrals in transverse momentum and rapidity space. As an application, our procedure, which makes use of Monte Carlo integration techniques, is applied to obtain the gluon Green function in the odderon case at leading order. The same approach can be used for more complicated scenarios. Read More

In a recent work [1,2], the study of new observables in LHC inclusive events with three tagged jets was proposed. Here, we extend the proposal to events with four-tagged jets following the lines of a previous paper [3]. The events are characterised by one jet in the forward direction, one in the backward direction with a large rapidity distance, Y, from the first and two more jets tagged in more central regions of the detector such that the relative rapidity separation between any two neighbouring jets is actually Y/3 in order to be in accordance with the multi-Regge kinematics ordering. Read More

We discuss recently proposed observables, sensitive to BFKL dynamics, in the context of multijet production at the large hadron collider (LHC). In particular, we consider ratios of azimuthal angle differences in final states with three jets, well separated in rapidity from each other, with two of them being very forward/backward and the third one in the central region. Read More

We propose the study of new observables in LHC inclusive events with three tagged jets, one in the forward direction, one in the backward direction and both well-separated in rapidity from the each other (Mueller-Navelet jets), together with a third jet tagged in central regions of rapidity. Since non-tagged associated mini-jet multiplicity is allowed, we argue that projecting the cross sections on azimuthal-angle components can provide several distinct tests of the BFKL dynamics. Realistic LHC kinematical cuts are introduced. Read More

We present some of the topics covered in a series of lectures under the same title that was given at the "Summer School on High Energy Physics at the LHC: New trends in HEP" in Natal, Brazil. In particular, after some general thoughts on phenomenology we give a pedagogical introduction to the BFKL formalism and we discuss recent BFKL phenomenological studies for LHC observables. Read More

We study high-energy jet production in the multi-Regge limit making use of the Monte Carlo event generator BFKLex which includes collinear improvements in the form of double-log contributions as presented in [1]. Making use of the anti-kt jet algorithm in the FastJet implementation, we present results for the average transverse momentum and azimuthal angle of the produced jets when two tagged forward/backward jets are present in the final state. We also introduce a new observable which accounts for the average rapidity separation among subsequent emissions. Read More

We evaluate differential cross sections for production of four jets in multi-Regge kinematics at a hadron collider. The main focus lies on azimuthal angle dependences. As in previous studies, the ratios of correlation functions of products of cosines of azimuthal angle differences among the tagged jets offer us the cleanest quantities to compare with experimental data. Read More

We investigate the effect of the resummation of collinear double logarithms in the BFKL gluon Green function using the Monte Carlo event generator BFKLex. The resummed collinear terms in transverse momentum space were calculated in Ref. [1] and correspond to the addition to the NLO BFKL kernel of a Bessel function of the first kind whose argument contains the strong coupling and a double logarithm of the ratio of the squared transverse momenta of the reggeized gluons. Read More

We present a first numerical implementation of the Loop-Tree Duality (LTD) method for the direct numerical computation of multi-leg one-loop Feynman integrals. We discuss in detail the singular structure of the dual integrands and define a suitable contour deformation in the loop three-momentum space to carry out the numerical integration. Then, we apply the LTD method to the computation of ultraviolet and infrared finite integrals, and present explicit results for scalar integrals with up to five external legs (pentagons) and tensor integrals with up to six legs (hexagons). Read More

We review the recent progress on the numerical implementation of the Loop-Tree Duality Method (LTDM) for the calculation of scattering amplitudes. A central point is the analysis of the singularities of the integrand. In the framework of the LTDM some of these singularities cancel out. Read More

We define new observables sensitive to BFKL dynamics in the context of multijet production at the large hadron collider (LHC). We propose the study of the inclusive production of three jets well separated in rapidity from each other, with two of them being very forward. We show that the tagging of a third jet in the central region of rapidity allows for a very strong test of the BFKL formalism. Read More

We present a study within the kT-factorisation scheme on single bottom quark production at the LHC. In particular, we calculate the rapidity and transverse momentum differential distributions for single bottom quark/anti-quark production. In our setup, the unintegrated gluon density is obtained from the NLx BFKL Green function whereas we included mass effects to the Lx heavy quark jet vertex. Read More

We review the recent developments of the loop-tree duality method, focussing our discussion on analysing the singular behaviour of the loop integrand of the dual representation of one-loop integrals and scattering amplitudes. We show that within the loop-tree duality method there is a partial cancellation of singularities at the integrand level among the different components of the corresponding dual representation. The remaining threshold and infrared singularities are restricted to a finite region of the loop momentum space, which is of the size of the external momenta and can be mapped to the phase-space of real corrections to cancel the soft and collinear divergences. Read More

We analyse the singular behaviour of one-loop integrals and scattering amplitudes in the framework of the loop--tree duality approach. We show that there is a partial cancellation of singularities at the loop integrand level among the different components of the corresponding dual representation that can be interpreted in terms of causality. The remaining threshold and infrared singularities are restricted to a finite region of the loop momentum space, which is of the size of the external momenta and can be mapped to the phase-space of real corrections to cancel the soft and collinear divergences. Read More

We discuss the result with full mass dependence for the virtual NNLO QCD corrections to the W boson pair production in the quark-anti-quark annihilation channel. We also report on our progress regarding the treatment of the double-real radiative corrections which, along with the virtual-real corrections, are the other two necessary ingredients for a theoretical prediction of the total cross section for W+ W- production to NNLO accuracy. Read More

We comment on the calculation of the finite part of the heavy quark impact factor at next-to-leading logarithmic (NLx) accuracy. The result is presented in a form suitable for phenomenological studies such as the calculation of the cross-section for single heavy quark production at the LHC within the kT-factorization scheme. Read More

We present the calculation of the finite part of the heavy quark impact factor at next-to-leading logarithmic accuracy in a form suitable for phenomenological studies such as the calculation of the cross-section for single bottom quark production at the LHC within the kT-factorization scheme. Read More

We discuss aspects of our recent derivation of the gluon Regge trajectory at two loop from Lipatov's high energy effective action. We show how the gluon Regge trajectory can be rigorously defined through renormalization of the high energy divergence of the reggeized gluon propagator. We furthermore provide some details on the determination of the two-loop reggeized gluon self-energy. Read More

We discuss computational details of our recent result, namely, the first derivation of the two-loop gluon Regge trajectory within the framework of Lipatov's high energy effective action. In particular, we elaborate on the direct evaluation of Feynman two-loop diagrams by using the Mellin-Barnes representations technique. Our result is in precise agreement with previous computations in the literature, providing this way a highly non-trivial test of the effective action and the proposed subtraction and renormalization scheme combined with our approach for the treatment of the loop diagrams. Read More

We discuss the solution to the BFKL equation in the adjoint representation at LO and NLO accuracy for the N = 4 SUSY theory. We use Monte Carlo techniques to study numerically the Gluon Green's function at LO and NLO directly written in the transverse momentum space which allows for the factorization of its infrared divergencies. Finally, we discuss the applicability of our approach to phenomenological searches for the BKP Odderon at the LHC. Read More

We calculate the finite part of the heavy quark impact factor at next-to-leading logarithmic accuracy in a form suitable for phenomenological studies such as the calculation of the cross-section for single bottom quark production at the LHC. Read More

We present the derivation of the two-loop gluon Regge trajectory using Lipatov's high energy effective action and a direct evaluation of Feynman diagrams. Using a gauge invariant regularization of high energy divergences by deforming the light-cone vectors of the effective action, we determine the two-loop self-energy of the reggeized gluon, after computing the master integrals involved using the Mellin-Barnes representations technique. The self-energy is further matched to QCD through a recently proposed subtraction prescription. Read More

In the context of evolution equations and scattering amplitudes in the high energy limit of the N=4 super Yang-Mills theory we investigate in some detail the BFKL gluon Green function at next-to-leading order. In particular, we study its collinear behaviour in terms of an expansion in different angular components. We also perform a Monte Carlo simulation of the different final states contributing to such a Green function and construct the diffusion pattern into infrared and ultraviolet modes and multiplicity distributions, making emphasis in separating the gluon contributions from those of scalars and gluinos. Read More

We determine both real and virtual next-to-leading order corrections to the gluon induced forward jet vertex, from the high energy effective action proposed by Lipatov. For these calculations we employ the same regularization and subtraction formalism developed in our previous work on the quark-initiated vertex. We find agreement with previous results in the literature. Read More

Using Monte Carlo integration techniques, we investigate running coupling effects compatible with the high energy bootstrap condition to all orders in the strong coupling in evolution equations valid at small values of Bjorken x in deep inelastic scattering. A model for the running of the coupling with analytic behavior in the infrared region and compatible with power corrections to jet observables is used. As a difference to the fixed coupling case, where the momentum transfer acts as an effective strong cut-off of the diffusion to infrared scales, in our running coupling study the dependence on the momentum transfer is much milder. Read More

We review Lipatov's high energy effective action and show that it is a useful computational tool to calculate scattering amplitudes in (quasi)-multi-Regge kinematics. We explain in some detail our recent work where a novel regularization and subtraction procedure has been proposed that allows to extend the use of this effective action beyond tree level. Two examples are calculated at next-to-leading order: forward jet vertices and the gluon Regge trajectory. Read More

We investigate dijet production at large rapidity separation in QCD and N = 4 SYM, showing that both theories give similar predictions for observables only sensitive to conformal properties of the scattering such as ratios of azimuthal angle correlations. Renormalization prescriptions are important in this comparison. Read More

Lipatov's high-energy effective action is a useful tool for computations in the Regge limit beyond leading order. Recently, a regularisation/subtraction prescription has been proposed that allows to apply this formalism to calculate next-to-leading order corrections in a consistent way. We illustrate this procedure with the computation of the gluon Regge trajectory at two loops. Read More

We study the solution of the BFKL equation in the adjoint representation for the N=4 SUSY theory at NLO accuracy. Consistency with the large momentum transfer solution obtained by Fadin and Lipatov is found. We investigate, for large and small values of the momentum transfer, the growth with energy of the Green function, its collinear behaviour and the expansion in azimuthal angle Fourier components. Read More

An iterative solution best suited for a Monte Carlo implementation is presented for the non-forward BFKL equation in a generic color representation. We introduce running coupling effects compatible with bootstrap to all orders in perturbation theory. A numerical analysis is given showing a smooth transition from a hard to a soft pomeron when accounting for running effects. Read More

The 2011 Les Houches workshop was the first to confront LHC data. In the two years since the previous workshop there have been significant advances in both soft and hard QCD, particularly in the areas of multi-leg NLO calculations, the inclusion of those NLO calculations into parton shower Monte Carlos, and the tuning of the non-perturbative parameters of those Monte Carlos. These proceedings describe the theoretical advances that have taken place, the impact of the early LHC data, and the areas for future development. Read More

The two loop (NLO) diagrams with quark content contributing to the gluon Regge trajectory are computed within the framework of Lipatov's effective action for QCD, using the regularization procedure for longitudinal divergencies recently proposed by two of us in http://arXiv.org/abs/arXiv:1110.6741. Read More

We factorize the infrared divergences of the non-forward BFKL Green function for a general t-channel projection of the color quantum numbers and study the properties of the infrared finite remainder in the case of color octet exchange. The octet Green function is compared with the singlet case for different values of the momentum transfer. The octet Green function plays an important role in the calculation of the finite remainder of the two-loop six-point MHV planar amplitude in N = 4 SYM as it was demonstrated by Bartels, Lipatov and one of us in http://arXiv. Read More

Ratios of azimuthal angle correlations between two jets produced at large rapidity separation are studied in the N=4 super Yang-Mills theory (MSYM). It is shown that these observables, which directly prove the SL(2,C) symmetry present in gauge theories in the Regge limit, exhibit an excellent perturbative convergence. They are compared to those calculated in QCD for different renormalization schemes concluding that the momentum-substraction (MOM) scheme with the Brodsky-Lepage-Mackenzie (BLM) scale-fixing procedure captures the bulk of the MSYM results. Read More

We analyze neutral Higgs boson decays into squark pairs in the minimal supersymmetric extension of the Standard Model and improve previous analyses. In particular the treatment of potentially large higher-order corrections due to the soft SUSY breaking parameters A_b, the trilinear Higgs coupling to sbottoms, and mu, the Higgsino mass parameter, is investigated. The remaining theoretical uncertainties including the SUSY-QCD corrections are analyzed quantitatively. Read More

We compare two Monte Carlo implementations of resummation schemes for the description of parton evolution at small values of Bjorken x. One of them is based on the Balitsky-Fadin-Kuraev-Lipatov (BFKL) evolution equation and generates fully differential parton distributions in momentum space making use of reggeized gluons. The other one is based on the Catani-Ciafaloni-Fiorani-Marchesini (CCFM) partonic kernel where QCD coherence effects are introduced. Read More

This report summarizes the activities of the SM and NLO Multileg Working Group of the Workshop "Physics at TeV Colliders", Les Houches, France 8-26 June, 2009. Read More

We study the exclusive production of heavy flavors at central rapidities in hadron-hadron collisions within the kT factorisation formalism. Since this involves regions of small Bjorken x in the unintegrated gluon densities, we include the next-to-leading order BFKL contributions working directly in transverse momentum representation. Our results are presented in a form suitable for Monte Carlo implementation. Read More

Discoveries at the LHC will soon set the physics agenda for future colliders. This report of a CERN Theory Institute includes the summaries of Working Groups that reviewed the physics goals and prospects of LHC running with 10 to 300/fb of integrated luminosity, of the proposed sLHC luminosity upgrade, of the ILC, of CLIC, of the LHeC and of a muon collider. The four Working Groups considered possible scenarios for the first 10/fb of data at the LHC in which (i) a state with properties that are compatible with a Higgs boson is discovered, (ii) no such state is discovered either because the Higgs properties are such that it is difficult to detect or because no Higgs boson exists, (iii) a missing-energy signal beyond the Standard Model is discovered as in some supersymmetric models, and (iv) some other exotic signature of new physics is discovered. Read More

We discuss the recent derivation of the one-loop squared virtual QCD corrections to the W boson pair production in the quark-anti-quark-annihilation channel in the limit where all kinematical invariants are large compared to the mass of the W boson. In particular, we elaborate on the combined use of the helicity matrix formalism with the Mellin-Barnes representations technique. Read More

We discuss the recent derivation of the two loop virtual QCD corrections to the W boson pair production in the quark-anti-quark-annihilation channel in the limit where all kinematical invariants are large compared to the mass of the W boson. In particular, we describe the use of the PSLQ algorithm on an example integral. Read More