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Search Results: 1 - 10 of 204475 matches for " Miguel G. Echevarria "
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Factorization Theorem For Drell-Yan At Low q_T And Transverse-Momentum Distributions On-The-Light-Cone
Miguel G. Echevarria,Ahmad Idilbi,Ignazio Scimemi
Physics , 2011, DOI: 10.1007/JHEP07(2012)002
Abstract: We derive a factorization theorem for Drell-Yan process at low q_T using effective field theory methods. In this theorem all the obtained quantities are gauge invariant and the special role of the soft function--and its subtraction thereof--is emphasized. We define transverse-momentum dependent parton distribution functions (TMDPDFs) which are free from light-cone singularities while all the Wilson lines are defined on-the-light-cone. We show explicitly to first order in \alpha_s that the partonic Feynman PDF can be obtained from the newly defined partonic TMDPDF by integrating over the transverse momentum of the parton inside the hadron. We obtain a resummed expression for the TMDPDF, and hence for the cross section, in impact parameter space. The universality of the newly defined matrix elements is established perturbatively to first order in \alpha_s. The factorization theorem is validated to first order in \alpha_s and also the gauge invariance between Feynman and light-cone gauges.
Polarization effects in double open-charm production at LHCb
Miguel G. Echevarria,Tomas Kasemets,Piet J. Mulders,Cristian Pisano
Physics , 2015, DOI: 10.1007/JHEP04(2015)034
Abstract: Double open-charm production is one of the most promising channels to disentangle single from double parton scattering (DPS) and study different properties of DPS. Several studies of the DPS contributions have been made. A missing ingredient so far has been the study of polarization effects, arising from spin correlations between the two partons inside an unpolarized proton. We investigate the impact polarization has on the double open-charm cross section. We show that the longitudinally polarized gluons can give significant contributions to the cross section, but for most of the considered kinematic region only have a moderate effect on the shape. We compare our findings to the LHCb data in the D0D0 final state, identify observables where polarization does have an impact on the distribution of the final state particles, and suggest measurements which could lead to first experimental indications of, or limits on, polarization in DPS.
QCD evolution of (un)polarized gluon TMDPDFs and the Higgs $q_T$-distribution
Miguel G. Echevarria,Tomas Kasemets,Piet J. Mulders,Cristian Pisano
Physics , 2015, DOI: 10.1007/JHEP07(2015)158
Abstract: We provide the proper definition of all the leading-twist (un)polarized gluon transverse momentum dependent parton distribution functions (TMDPDFs), by considering the Higgs boson transverse momentum distribution in hadron-hadron collisions and deriving the factorization theorem in terms of them. We show that the evolution of all the (un)polarized gluon TMDPDFs is driven by a universal evolution kernel, which can be resummed up to next-to-next-to-leading-logarithmic accuracy. Considering the proper definition of gluon TMDPDFs, we perform an explicit next-to-leading-order calculation of the unpolarized ($f_1^g$), linearly polarized ($h_1^{\perp g}$) and helicity ($g_{1L}^g$) gluon TMDPDFs, and show that, as expected, they are free from rapidity divergences. As a byproduct, we obtain the Wilson coefficients of the refactorization of these TMDPDFs at large transverse momentum. In particular, the coefficient of $g_{1L}^g$, which has never been calculated before, constitutes a new and necessary ingredient for a reliable phenomenological extraction of this quantity, for instance at RHIC or the future AFTER@LHC or Electron-Ion Collider. The coefficients of $f_1^g$ and $h_1^{\perp g}$ have never been calculated in the present formalism, although they could be obtained by carefully collecting and recasting previous results in the new TMD formalism. We apply these results to analyze the contribution of linearly polarized gluons at different scales, relevant, for instance, for the inclusive production of the Higgs boson and the $C$-even pseudoscalar bottomonium state $\eta_{b}$. Applying our resummation scheme we finally provide predictions for the Higgs boson $q_T$-distribution at the LHC.
Non-perturbative QCD effects in $q_T$ spectra of Drell-Yan and $Z$-boson production
Umberto D'Alesio,Miguel G. Echevarria,Stefano Melis,Ignazio Scimemi
Physics , 2014, DOI: 10.1007/JHEP11(2014)098
Abstract: The factorization theorems for transverse momentum distributions of dilepton/boson production, recently formulated by Collins and Echevarria-Idilbi-Scimemi in terms of well-defined transverse momentum dependent distributions (TMDs), allows for a systematic and quantitative analysis of non-perturbative QCD effects of the cross sections involving these quantities. In this paper we perform a global fit using all current available data for Drell-Yan and $Z$-boson production at hadron colliders within this framework. The perturbative calculable pieces of our estimates are included using a complete resummation at next-to-next-to-leading-logarithmic accuracy. Performing the matching of transverse momentum distributions onto the standard collinear parton distribution functions and recalling that the corresponding matching coefficient can be partially exponentiated, we find that this exponentiated part is spin-independent and resummable. We argue that the inclusion of higher order perturbative pieces is necessary when data from lower energy scales are analyzed. We consider non-perturbative corrections both to the intrinsic nucleon structure and to the evolution kernel and find that the non-perturbative part of the TMDs could be parametrized in terms of a minimal set of parameters (namely 2-3). When all corrections are included the global fit so performed gives a $\chi^2/{\rm d.o.f.} \lesssim 1$ and a very precise prediction for vector boson production at the Large Hadron Collider (LHC).
Effects of TMD evolution and partonic flavor on $e^+e^-$ annihilation into hadrons
Alessandro Bacchetta,Miguel G. Echevarria,Piet J. G. Mulders,Marco Radici,Andrea Signori
Physics , 2015,
Abstract: We calculate the transverse momentum dependence in the production of two back-to-back hadrons in electron-positron annihilations at the medium/large energy scales of BES-III and BELLE experiments. We use the parameters of the transverse-momentum-dependent (TMD) fragmentation functions that were recently extracted from the semi-inclusive deep-inelastic-scattering multiplicities at low energy from HERMES. TMD evolution is applied according to different approaches and using different parameters for the nonperturbative part of the evolution kernel, thus exploring the sensitivity of our results to these different choices and to the flavor dependence of parton fragmentation functions. We discuss how experimental measurements could discriminate among the various scenarios.
QCD Evolution of the Sivers Asymmetry
Miguel G. Echevarria,Ahmad Idilbi,Zhong-Bo Kang,Ivan Vitev
Physics , 2014, DOI: 10.1103/PhysRevD.89.074013
Abstract: We study the QCD evolution of the Sivers effect in both semi-inclusive deep inelastic scattering (SIDIS) and Drell-Yan production (DY). We pay close attention to the non-perturbative spin-independent Sudakov factor in the evolution formalism and find a universal form which can describe reasonably well the experimental data on the transverse momentum distributions in SIDIS, DY lepton pair and $W/Z$ production. With this Sudakov factor at hand, we perform a global fitting of all the experimental data on the Sivers asymmetry in SIDIS from HERMES, COMPASS and Jefferson Lab. We then make predictions for the Sivers asymmetry in DY lepton pair and $W$ production that can be compared to the future experimental measurements to test the sign change of the Sivers functions between SIDIS and DY processes and constrain the sea quark Sivers functions.
Deficiencias en la entrevista médica realizada por alumnos de Medicina Interna bajo observación directa y registro de audio
Canelles Pupo,Marino G.; Moreno Rodríguez,Miguel ángel; Echevarria Parlay,Juan Carlos; Bestard Pavón,Luis Alberto;
Revista Cubana de Medicina Militar , 2003,
Abstract: the medical interview is the most powerful diagnostic tool for physicians, since it is the most important source for obtaining primary data. the aim of this paper was to determine the most frequent deficiencies found in the medical interview made by students from the second semester of the 3rd year of the medical career. a descriptive study was conducted during the academic courses 1999-2000 and 2000-2001. of a total of 99 students, the medical interview was recorded to 50 of them. the collected data were compared with what was witten in the history of the present disease they were evaluated by a survey that classified the imperfections as regards the history of the present disease, types of questions and general aspects. 383 difficulties were found (17.0 % of a possible total of 2 250). 168 (43,8 %) were connected with the history of the present disease, 153 (40.0 %) with the general aspects of the development of the interview and there were 62 mistakes (16.2 %) in relation to the type of question. many deficiencies were observed in the medical interview made by students not only concerning the domain of semiological abilities but also in the interpersonal communication.
Deficiencias en la entrevista médica realizada por alumnos de Medicina Interna bajo observación directa y registro de audio
Marino G. Canelles Pupo,Miguel ángel Moreno Rodríguez,Juan Carlos Echevarria Parlay,Luis Alberto Bestard Pavón
Revista Cubana de Medicina Militar , 2003,
Abstract: La entrevista médica es la herramienta diagnóstica más poderosa con que cuenta el médico, constituye la fuente más importante de la obtención de datos primarios. El objetivo del trabajo fue determinar las deficiencias más frecuentes encontradas en la entrevista médica por alumnos del segundo semestre de tercer a o de la carrera de medicina. Se realizó un trabajo descriptivo durante los cursos académicos 1999-2000 y 2000-2001, de un total de 99 alumnos se les grabó la entrevista médica a 50. Se compararon los datos recogidos con lo transcripto en la historia de la enfermedad actual, estos fueron evaluados mediante una encuesta que clasificó las imperfecciones con respecto a la historia de la enfermedad actual, tipos de preguntas y aspectos generales. Se encontraron 383 dificultades (17,0 % de un total posible de 2 250); en relación con la historia de la enfermedad actual fueron 168 (43,8 %); en relación con los aspectos generales del desarrollo de la entrevista, 153 (40,0 %) y con el tipo de pregunta, 62 errores (16,2 %). Se presentaron numerosas deficiencias en el interrogatorio médico realizado a pacientes por los alumnos y estas fueron tanto en el dominio de las habilidades semiológicas como en las de comunicación interpersonal. The medical interview is the most powerful diagnostic tool for physicians, since it is the most important source for obtaining primary data. The aim of this paper was to determine the most frequent deficiencies found in the medical interview made by students from the second semester of the 3rd year of the medical career. A descriptive study was conducted during the academic courses 1999-2000 and 2000-2001. Of a total of 99 students, the medical interview was recorded to 50 of them. The collected data were compared with what was witten in the history of the present disease They were evaluated by a survey that classified the imperfections as regards the history of the present disease, types of questions and general aspects. 383 difficulties were found (17.0 % of a possible total of 2 250). 168 (43,8 %) were connected with the history of the present disease, 153 (40.0 %) with the general aspects of the development of the interview and there were 62 mistakes (16.2 %) in relation to the type of question. Many deficiencies were observed in the medical interview made by students not only concerning the domain of semiological abilities but also in the interpersonal communication.
SCET, Light-Cone Gauge and the T-Wilson Lines
Miguel Garcia-Echevarria,Ahmad Idilbi,Ignazio Scimemi
Physics , 2011, DOI: 10.1103/PhysRevD.84.011502
Abstract: Soft-Collinear Effective Theory (SCET) has been formulated since a decade now in covariant gauges. In this work we derive a modified SCET Lagrangian applicable in both classes of gauges: regular and singular ones. This extends the range of applicability of SCET. The new Lagrangian must be used to obtain factorization theorems in cases where the transverse momenta of the particles in the final states are not integrated over, such as semi-inclusive deep inelastic scattering, Drell-Yan and the Higgs production cross-section at low transverse momentum. By doing so all non-perturbative matrix elements appearing in the factorized cross-sections are gauge invariant.
Single center experience in laparoscopic colectomy for cancer
Jacobs M.,Misiakos E.,Pelaez-Echevarria L.,Plasencia G.
Annals of Gastroenterology , 2007,
Abstract: SUMMARY Objective: The application of laparoscopic colectomy for colorectal carcinoma has been disputable regarding its efficacy as an oncological procedure. The aim of this study was to assess the early and long-term results of laparoscopic colectomy for malignant disease. Method: Between 1990 and 1997, 243 patients underwent laparoscopic colectomy for colon carcinoma, in our center. Morbidity and mortality data were analyzed retrospectively along with disease-free and overall patient survival. Results: Laparoscopic colectomy was successfully completed in 216 of 243 patients (89%). A perioperative morbidity rate of 22% and mortality rate of 1.4% were observed. The overall estimated 1, 2, 3, 5, and 7- year survival rates were 92%, 82%, 74%, 65%, and 45%, respectively. Only one case (<0.5%) with a trocar site recurrence was observed in this series. There were no recurrences at the wound extraction site, when the wound was protected. The overall estimated 5- and 7-year disease-free survival rates were 79% and 76%, respectively. Conclusion: Laparoscopic colectomy for cancer can be performed safely and effectively with perioperative morbidity, mortality and survival rates comparable to open colon resection. Key words: Laparoscopic surgery, colectomy, colorectal carcinoma
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