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The heavy expansion in B decays

Description: We examine the 1/mc and 1/mb expansions in B^(*)->D^(*) processes, and point out that there are relationships among the form factors that do not receive corrections in any order of 1/mc.A different set of relationships are unchanged by (1/mc)^n corrections, while the (1/mc)^n preserved relationships are also unaffected by terms proportional to powers of Alphas(mc).All relationships are modified when terms of the form 1/(mbmc) or radiative corrections proportional to powers of Alphas(mb) are included.
Date: August 1, 1993
Creator: Roberts, Winston & Roberts, Winston
Partner: UNT Libraries Government Documents Department

Radiative effects in the processes of exclusive photon electroproduction from polarized protons

Description: Radiative effects in the electroproduction of photons in polarized ep-scattering are calculated in the leading log approximation and analyzed numerically for kinematical conditions of current measurement at Jefferson Lab. Radiative corrections to the cross sections, their azimuthal distributions and Fourier coefficients are in particular focus. Kinematical regions where the radiative corrections are considerable are identified.
Date: March 1, 2012
Creator: Igor Akushevich, Alexander Ilyichev
Partner: UNT Libraries Government Documents Department

Quadratic electroweak corrections for polarized Moller scattering

Description: The paper discusses the two-loop (NNLO) electroweak radiative corrections to the parity violating electron-electron scattering asymmetry induced by squaring one-loop diagrams. The calculations are relevant for the ultra-precise 11 GeV MOLLER experiment planned at Jefferson Laboratory and experiments at high-energy future electron colliders. The imaginary parts of the amplitudes are taken into consideration consistently in both the infrared-finite and divergent terms. The size of the obtained partial correction is significant, which indicates a need for a complete study of the two-loop electroweak radiative corrections in order to meet the precision goals of future experiments.
Date: January 1, 2012
Creator: A. Aleksejevs, S. Barkanova, Y. Kolomensky, E. Kuraev, V. Zykunov
Partner: UNT Libraries Government Documents Department

Contributions From yZ Box Diagrams to Parity Violating Elastic e-p Scattering

Description: Parity-violating (PV) elastic electron-proton scattering measures Q-weak for the proton, Q{sub W}{sup p}. To extract Q{sub W}{sup p} from data, all radiative corrections must be well-known. Recently, disagreement on the {gamma}Z box contribution to Q{sub W}{sup p} has prompted the need for further analysis of this term. Here, we support one choice of a debated factor, go beyond the previously assumed equality of electromagnetic and {gamma}Z structure functions, and find an analytic result for one of the {gamma}Z box integrals. Our numerical evaluation of the {gamma}Z box is in agreement within errors with previous reports, albeit somewhat larger in central value, and is within the uncertainty requirements of current experiments.
Date: June 1, 2011
Creator: Benjamin Rislow, Carl Carlson
Partner: UNT Libraries Government Documents Department

Natural Little Hierarchy from Partially Goldstone Twin Higgs

Description: We construct a simple theory in which the fine-tuning of the standard model is significantly reduced. Radiative corrections to the quadratic part of the scalar potential are constrained to be symmetric under a global U(4) x U(4){prime} symmetry due to a discrete Z{sub 2} 'twin' parity, while the quartic part does not possess this symmetry. As a consequence, when the global symmetry is broken the Higgs fields emerge as light pseudo-Goldstone bosons, but with sizable quartic self-interactions. This structure allows the cutoff scale, {Lambda}, to be raised to the multi-TeV region without significant fine-tuning. In the minimal version of the theory, the amount of fine-tuning is about 15% for {Lambda} = 5 TeV, while it is about 30% in an extended model. This provides a solution to the little hierarchy problem. In the minimal model, the 'visible' particle content is exactly that of the two Higgs doublet standard model, while the extended model also contains extra vector-like fermions with masses {approx} (1 {approx} 2) TeV. At the LHC, our minimal model may appear exactly as the two Higgs doublet standard model, and new physics responsible for cutting off the divergences of the Higgs mass-squared parameter may not be discovered. Several possible processes that may be used to discriminate our model from the simple two Higgs doublet model are discussed for the LHC and for a linear collider.
Date: October 20, 2005
Creator: Chacko, Z.; Nomura, Yasunori; Papucci, Michele & Perez, Gilad
Partner: UNT Libraries Government Documents Department

Calculation of Radiative Corrections to Hyperfine Splitting in p1/2 States

Description: Techniques to calculate one-loop radiative corrections to hyperfine splitting including binding corrections to all orders have been developed in the last decade for s states of atoms and ions. In this paper these methods are extended to p{sub 1/2} states for three cases. In the first case, the point-Coulomb 2p{sub 1/2} hyperfine splitting is treated for the hydrogen isoelectronic sequence, and the lowest order result, {alpha}/4{pi} E{sub F}, is shown to have large binding corrections at high Z. In the second case, neutral alkalis are considered. In the third case, hyperfine splitting of the 2p{sub 1/2} state of lithium-like bismuth is treated. In the latter two cases, correlation corrections are included and, in addition, the point is stressed that uncertainties associated with nuclear structure, which complicate comparison with experiment for s states, are considerably reduced because of the smaller overlap with the nucleus.
Date: September 20, 2006
Creator: Sapirstein, J & Cheng, K T
Partner: UNT Libraries Government Documents Department

QCD CORRECTIONS TO DILEPTON PRODUCTION NEAR PARTONIC THRESHOLD IN PP SCATTERING.

Description: We present a recent study of the QCD corrections to dilepton production near partonic threshold in transversely polarized {bar p}p scattering, We analyze the role of the higher-order perturbative QCD corrections in terms of the available fixed-order contributions as well as of all-order soft-gluon resummations for the kinematical regime of proposed experiments at GSI-FAIR. We find that perturbative corrections are large for both unpolarized and polarized cross sections, but that the spin asymmetries are stable. The role of the far infrared region of the momentum integral in the resummed exponent and the effect of the NNLL resummation are briefly discussed.
Date: October 2, 2005
Creator: SHIMIZU, H.; STERMAN, G.; VOGELSANG, W. & YOKOYA, H.
Partner: UNT Libraries Government Documents Department

Quark-Hadron Duality and Intrinsic Transverse Momentum

Description: It is demonstrated in several exclusive processes involving the pion that a local quark-hadron duality prescription is equivalent to using an effective (bar)qq (two-body) light-cone wave function Psi (sup) (LD) (x, k (sub)perpendicular) for the pion. This wave function models soft dynamics of all higher (bar)qG...Gq Fock components of the standard light-cone approach. Contributions corresponding to higher Fock components in a hard regime appear in this approach as radiative corrections and are suppressed by powers of alpha(sub)s / Pi.
Date: November 1, 1995
Creator: Radyushkin, Anatoly
Partner: UNT Libraries Government Documents Department

Radiative corrections to the decays K{sub L}{sup 0} {r_arrow} e{sup +}e{sup {minus}} and K{sub L}{sup 0} {r_arrow} {mu}{sup +} {mu}{sup {minus}}

Description: The authors calculate the rates and lepton ({ell}) invariant mass distributions for decays of the form 0{sup {minus}+} {r_arrow} {ell}{sup +}{ell}{sup {minus}}{gamma}, which are important radiative corrections to the purely leptonic decays 0{sup {minus}+} {r_arrow} {ell}{sup +}{ell}{sup {minus}}. The approach uses the loop diagrams which arise by including the two photon intermediate state and they retain the imaginary parts of the loops--a radiative extension of the unitarity bound for the process. These results are compared with those obtained using a model in which the meson couples directly to the leptons.
Date: December 31, 1998
Creator: Dicus, D.A. & Repko, W.W.
Partner: UNT Libraries Government Documents Department

Spin-dependent Drell-Yan and double prompt photon production to NLO QCD

Description: The authors present the complete O({alpha}{sub s}{sup 2}) radiative corrections to the (non singlet) polarized Drell Yan cross section for the production of a lepton pair with a nonzero q{sub T}. The helicity of the incoming states is arbitrary. In the case of double photon, results for the longitudinal asymmetries and on the p{sub T} behavior of the cross section are also given (to O({alpha}{sub em}{sup 2}{alpha}{sub s})) in the central rapidity region of the tagged photon.
Date: July 1, 1997
Creator: Chang, S.; Coriano, C.; Field, R.D. & Gordon, L.E
Partner: UNT Libraries Government Documents Department

Spin-dependent Drell-Yan and double prompt photon production to NLO QCD

Description: We present the complete O({alpha}{sub s}{sup 2}) radiative corrections to the (non singlet) polarized Drell Yan cross section for the production of a lepton pair with a nonzero qT. The helicity of the incoming states is arbitrary. In the case of double photon, results for the longitudinal asymmetries and on the pT behavior of the cross section are also given (to O({alpha}{sub em}{sup 2}{alpha}{sub s})) in the central rapidity region of the tagged photon.
Date: September 1, 1997
Creator: Chang, Sanghyeon; Coriano, C.; Field, R.D. & Gordon, L.E.
Partner: UNT Libraries Government Documents Department

Radiative corrections for (e,e{prime}p) reactions at GeV energies

Description: A general framework for applying radiative corrections to (e,e{prime}p) coincidence reactions at GeV energies is presented, with special emphasis to higher-order Bremsstrahlung effects, radiation from the scattered hadron, and the validity of peaking approximations. The sensitivity to the assumptions made in practically applying radiative corrections to (e,e{prime}p) data is extensively discussed. The general framework is tested against experimental data of the {sup 1}H(e,e{prime}p) reaction at momentum transfer values larger than 1.0 (GeV/c){sup 2}, where radiative processes become a dominant source of uncertainty. The formulas presented here can easily be modified for any other electron-induced coincidence reaction.
Date: May 1, 2000
Creator: Ent, R.; Filippone, B. W.; Makins, N. C. R.; Milner, R. G.; O'Neill, T. G. & Wasson, D. A.
Partner: UNT Libraries Government Documents Department

Supersymmetric radiative corrections at large tan {beta}

Description: In the minimal supersymmetric extension of the Standard Model (MSSM), fermion masses and Yukawa couplings receive radiative corrections at one loop from diagrams involving the supersymmetric particles. The corrections to the relation between down-type fermion masses and Yukawa couplings are enhanced by tan {beta}, which makes them potentially very significant at large tan {beta}. These corrections affect a wide range of processes in the MSSM, including neutral and charged Higgs phenomenology, rare B meson decays, and renormalization of the CKM matrix. We give a pedagogical review of the sources and phenomenological effects of these corrections.
Date: February 20, 2001
Creator: Logan, H.E.
Partner: UNT Libraries Government Documents Department

Calculation of the QED correction to the recoil proton polarization by the electron structure function method

Description: Model independent radiative correction to the recoil proton polarization for the elastic electron-proton scattering is calculated within method of electron structure functions. The explicit expressions for the recoil proton polarization are represented as a contraction of the electron structure and the hard part of the polarization dependent contribution into cross-section. The calculation of the hard part with first order radiative correction is performed. The obtained representation includes the leading radiative corrections in all orders of perturbation theory and the main part of the second order next-to-leading ones. Numerical calculations illustrate our analytical results.
Date: December 1, 2000
Creator: Afanasev, A.V.; Akushevich, I. & Merenkov, N.P.
Partner: UNT Libraries Government Documents Department

Can we distinguish an MSSM higgs from a SM higgs at a linear collider?

Description: The authors study the prospects for distinguishing the CP-even Higgs boson of the minimal supersymmetric extension of the Standard Model (MSSM) from the Standard Model (SM) Higgs boson by measuring its branching ratios at an e{sup +}e{sup {minus}} linear collider. The regions of the M{sub A} - tan {beta} plane in which an MSSM Higgs boson can be distinguished from the SM Higgs boson depend strongly upon the supersymmetric parameters that enter the radiative corrections to the Higgs mass matrix and the Higgs couplings to fermions. In some regions of parameter space it is possible to extract the supersymmetric correction to the relation between the b quark mass and its Yukawa coupling from Higgs branching ratio measurements.
Date: January 4, 2001
Creator: Logan, H.E.
Partner: UNT Libraries Government Documents Department

QED Radiative Corrections in Processes of Exclusive Pion Electroproduction

Description: Formalism for radiative correction (RC) calculation in exclusive pion electroproduction on the proton is presented. A FORTRAN code EXCLURAD is developed for the RC procedure. The numerical analysis is done in the kinematics of current Jefferson Lab experiments.
Date: March 1, 2002
Creator: Afanasev, Andrei; Akushevich, I.; Burkert, Volker & Joo, K.
Partner: UNT Libraries Government Documents Department

Sfermion precision measurements at a linear collider

Description: At future e{sup +}e{sup -} linear colliders, the event rates and clean signals of scalar fermion production--in particular for the scalar leptons--allow very precise measurements of their masses and couplings and the determination of their quantum numbers. Various methods are proposed for extracting these parameters from the data at the sfermion thresholds and in the continuum. At the same time, NLO radiative corrections and non-zero width effects have been calculated in order to match the experimental accuracy. The substantial mixing expected for the third generation sfermions opens up additional opportunities. Techniques are presented for determining potential CP-violating phases and for extracting tan {beta} from the stau sector, in particular at high values. The consequences of possible large mass differences in the stop and sbottom system are explored in dedicated analyses.
Date: September 25, 2003
Creator: al., A. Freitas et
Partner: UNT Libraries Government Documents Department

Recent progress in one-loop multi-parton calculations

Description: The authors describe techniques that simplify the calculation of one-loop QCD amplitudes with many external legs, which are needed for next-to-leading-order (NLO) corrections to multi-jet processes. The constraints imposed by perturbative unitarity, collinear singularities and a supersymmetry-inspired organization of helicity amplitudes are particularly useful. Certain sequences of one-loop helicity amplitudes may be obtained for an arbitrary number of external gluons using these techniques. They also report on progress in completing the set of one-loop helicity amplitudes required for NLO three-jet production at hadron colliders, namely the amplitudes with two external quarks and three gluons.
Date: September 1, 1994
Creator: Bern, Z.; Dixon, L.; Dunbar, D. C. & Kosower, D. A.
Partner: UNT Libraries Government Documents Department

Introduction to Electroweak Symmetry Breaking

Description: The Standard Model (SM) is the backbone of elementary particle physics-not only does it provide a consistent framework for studying the interactions of quark and leptons, but it also gives predictions which have been extensively tested experimentally. In these notes, I review the electroweak sector of the Standard Model, discuss the calculation of electroweak radiative corrections to observables, and summarize the status of SM Higgs boson searches. Despite the impressive experimental successes, however, the electroweak theory is not completely satisfactory and the mechanism of electroweak symmetry breaking is untested. I will discuss the logic behind the oft-repeated statement: 'There must be new physics at the TeV scale'. These lectures reflect my strongly held belief that upcoming results from the LHC will fundamentally change our understanding of electroweak symmetry breaking. In these lectures, I review the status of the electroweak sector of the Standard Model, with an emphasis on the importance of radiative corrections and searches for the Standard Model Higgs boson. A discussion of the special role of the TeV energy scale in electroweak physics is included.
Date: October 2, 2008
Creator: Dawson,S.
Partner: UNT Libraries Government Documents Department

Soft-X-ray spectra of highly charged Os, Bi, Th, and U ions in an electron beam ion trap

Description: Systematic variation of the electron-beam energy in an electron-beam ion trap has been employed to produce soft-X-ray spectra of Os, Bi, Th, and U with highest charge states ranging up to Ni-like ions. Guided by relativistic atomic structure calculations, the strongest lines have been identified with {Delta}n = 0 (n = 4 to n' = 4) transitions in Rb- to Cu-like ions. The rather weak 4p-4d transitions are much less affected by QED contributions than the dominant 4s-4p transitions. Our wavelength measurements consequently provide benchmarks with and (almost) without QED. Because the radiative corrections are not very sensitive to the number of electrons in the valence shell, our data, moreover, provide benchmarks for the evaluation of electron-electron interactions.
Date: December 3, 2004
Creator: Trabert, E.; Beiersdorfer, P.; Fournier, K. B. & Chen, M. H.
Partner: UNT Libraries Government Documents Department

Optimal use of information for measuring M(t) in lepton + jets t anti-t events

Description: The observation of the top (t) quark served as one of the major confirmations of the validity of the standard model (SM) of particle interactions. Through radiative corrections of the SM, the mass of the top quark, along with that of the W boson, provide the best indication for the value of the mass of the hypothesized Higgs boson. The mass of the W is known to a precision of < 0.1%, while the uncertainty on the mass of the top quark is at the 4% level. Improvements in both measurements are required to limit the range of mass that the Higgs boson can assume in the SM, and, of course, to check whether that agrees with expectation. It is therefore important to develop techniques for extracting the mass of the top quark that can provide the sharpest values possible.
Date: October 14, 2003
Creator: Estrada, Juan
Partner: UNT Libraries Government Documents Department