Starting from a factorization theorem in Soft-Collinear Effective Theory, the thrust distribution in e+e- collisions is calculated including resummation of the next-to-next-to-next-to leading logarithms. This is a significant improvement over previous calculations which were only valid to next-to-leading logarithmic order. The fixed-order expansion of the resummed result approaches the exact fixed-order distribution towards the kinematic endpoint. This close agreement provides a verification of both the effective field theory expression and recently completed next-to-next-to-leading fixed order event shapes. The resummed distribution is then matched to fixed order, resulting in a distribution valid over a large range of thrust. A fit to ALEPH and OPAL data from LEP 1 and LEP 2 produces alpha_s(m_Z)= 0.1172 +/- 0.0010 +/- 0.0008 +/-0.0012 +/- 0.0012, where the uncertainties are respectively statistical, systematic, hadronic, and perturbative. This is one of the world's most precise extractions of alpha_s to date.
From soft-collinear effective theory one can derive a factorization formula for the e+e- thrust distribution dsigma/dtau with tau = 1-T that is applicable for all tau. The formula accommodates available O(alpha_s^3) fixed-order QCD results, resummation of logarithms at NNNLL order, a universal nonperturbative soft function for hadronization effects, factorization of nonperturbative effects in subleading power contributions, bottom mass effects and QED corrections. We emphasize that the use of Monte Carlos to estimate hadronization effects is not compatible with high-precision, high-order analy…
We present preliminary results on the resummation of leading and next-to-leading logarithms for the thrust distribution in deep inelastic scattering. Our predictions, expanded to O(alpha_s^2), are compared to corresponding results from the Monte Carlo programs DISASTER++ and DISENT.
We calculate the average multiplicity of jets in e+e- annihilation as a function of both the jet resolution parameter, y_cut, and the thrust T. Our result resums to all orders the leading and next-to-leading logarithms in y_cut and 1-T, and is exact up to second order in alpha_s. This allows a comparison between the number of jets found using jet algorithms and the ability to distinguish different jet topologies via thrust.
The heavy jet mass distribution in e+e- collisions is computed to next-to-next-to-next-to leading logarithmic (NNNLL) and next-to-next-to leading fixed order accuracy (NNLO). The singular terms predicted from the resummed distribution are confirmed by the fixed order distributions allowing a precise extraction of the unknown soft function coefficients. A number of quantitative and qualitative comparisons of heavy jet mass and the related thrust distribution are made. From fitting to ALEPH data, a value of alpha_s is extracted, alpha_s(m_Z)=0.1220 +/- 0.0031, which is larger than, but not in co…
Dressed Gluon Exponentiation (DGE) is used to calculate the thrust and the heavy-jet mass distributions in e+e- annihilation in the two-jet region. We perform a detailed analysis of power corrections, taking care of the effect of hadron masses on the measured observables. In DGE the Sudakov exponent is calculated in a renormalization-scale invariant way using renormalon resummation. Neglecting the correlation between the hemispheres in the two-jet region, we express the thrust and the heavy-jet mass distributions in terms of the single-jet mass distribution. This leads to a simple description …
We directly fit the experimentally measured energy dependence of the average value of 1-Thrust, <1-T>, over the e^+e^- centre-of-mass energy range Q=14 - 172 GeV to the QCD expectation obtained by integrating up the evolution equation for d<1-T>/dlog Q in terms of <1-T>. We fit for Lambda_QCD, uncalculated O(alpha_S^3) and higher perturbative corrections parameterized by the scheme invariant rho_2, and the parameter lambda which characterizes the magnitude of the leading 1/Q power corrections anticipated for <1-T>. A 3-parameter fit yields Lambda_QCD=245^{+20}_{-17} MeV, rho_2=-16\pm 11 and la…
We have calculated the leading and next-to-leading logarithm coefficients of $O(α_s^2)$ $e^+e^-$ annihilation jet cross sections, thrust distribution and energy-energy correlation in the two-jet limit when the jet resolution and the event shape variables vanish. We have compared our results with expectations based on leading logarithm approximations used to resum the pertubative cross sections where this is possible. There is good agreement for the leading and next-to-leading coefficients of jet cross sections in the Durham scheme. Also for the thrust distribution and energy-energy correlation…
We give a factorization formula for the e+e- thrust distribution dsigma/dtau with tau=1-T based on soft-collinear effective theory. The result is applicable for all tau, i.e. in the peak, tail, and far-tail regions. The formula includes O(alphas^3) fixed-order QCD results, resummation of singular partonic alphas^j ln^k(tau)/tau terms with N^3LL accuracy, hadronization effects from fitting a universal nonperturbative soft function defined in field theory, bottom quark mass effects, QED corrections, and the dominant top mass dependent terms from the axial anomaly. We do not rely on Monte Carlo g…
Infrared power corrections for the average thrust < T > in e+e- annihilation are analyzed in the framework of renormalon resummation, motivated by analogy with the skeleton expansion in QED and the BLM approach. Performing the ``massive gluon'' renormalon integral a renormalization scheme invariant result is obtained. We find that a major part of the discrepancy between the known next-to-leading order (NLO) calculation and experiment can be explained by resummation of higher order perturbative terms. This fact does not preclude the infrared finite coupling interpretation with a substantial 1/Q…
Resummation and power-corrections play a crucial role in the phenomenology of event-shape variables like the thrust T. Previous investigations showed that the perturbative contribution to the average thrust is dominated by gluons of small invariant mass, of the order of 10% of Q, where Q is the center-of-mass energy. The effect of soft gluons is also important, leading to a non-perturbative 1/Q correction. These conclusions are based on renormalon analysis in the single dressed gluon (SDG) approximation. Here we analyze higher moments of the thrust distribution using a similar technique. We fi…
We describe in detail the method we have used to determine the CKM angles gamma, alpha and beta using flavour symmetries between non-leptonic B decays. This method is valid in the context of the SM but also in presence of New Physics not affecting the amplitudes.
We present the exact O(alpha) correction to the process e+ e- -> e+ e- + gamma in the low angle luminosity regime at SLC/LEP energies. We give explicit formulas for the completely differential cross section. As an important application, we illustrate the size of the respective corrections of O(alpha^2) to the SLC/LEP luminosity cross section. We show explicitly that our results have the correct infrared limit, as a cross-check. Some comments are made about the implementation of our results in the framework of a Monte Carlo event generator. This latter implementation will appear elsewhere.
In this paper we extend the calculation of the QED corrections to deep inelastic lepton-proton scattering with a tagged photon, taking into account the full corrections on the lepton side. Comparing to previous results that were obtained by considering only large logarithmic terms at leading and next-to-leading accuray, we find that the difference is in general quite small, however, it may be significant in the region of large $y$ and small $x$.
The strong coupling alpha_s is a fundamental parameter of the Standard Model. In comparison to parameters like alpha_em and M_Z it is relatively poorly known. However the precision of alpha_s measurements has improved dramatically in recent years. More than twenty different types of process, from lattice QCD studies to the highest energy colliders, can be used to measure alpha_s accurately. The most precise determinations now quote uncertainties in alpha_s(M_Z) of less than 5%. There is also a remarkable consistency between the various measurements. The present review provides an update on alp…
To measure the strong coupling alpha_s from event shape observables two ingredients are necessary. A perturbative prediction containing the dependence of observables on alpha_s and a description of the hadronisation process to match the perturbative prediction with the hadronic data. As perturbative prediction O(alpha_s^2), NLLA and combined calculations are available. Beside the well known Monte-Carlo based models also analytical predictions, so called power corrections, exist to describe the hadronisation. Advantages and disadvantages of the different resulting methods for determining the st…
The highest exclusive jet multiplicity studied at LEP experiments is five. In this paper we compute the next-to-leading order QCD corrections to e+e- annihilation to five jets, essentially closing the (pure) perturbative QCD studies of exclusive jetty final states at LEP. We compare fixed-order perturbative results with ALEPH data. We estimate hadronization corrections to five-jet observables using the event generator SHERPA, which employs the CKKW procedure to combine a reliable perturbative treatment of high-multiplicity jet final states with parton showers. We show that a competitive value …
We compute the α_s^2β_0 part of the two-loop QCD corrections to the charged lepton spectrum in b \to c \ell \barν_\ell decays and find them to be about 50\% of the first order corrections at all lepton energies, except those close to the end point. Including these corrections we extract the central values \barΛ=0.33 GeV and λ_1=-0.17 GeV^2 for the HQET matrix elements and use them to determine the $\overline{\rm MS}$ b and c quark masses, and |V_{cb}|.
This paper reports the tenth-order QED contribution to the lepton g-2 from the gauge-invariant set, called Set III(c), which consists of 390 Feynman vertex diagrams containing an internal fourth-order light-by-light-scattering subdiagram. The mass-independent contribution of Set III(c) to the electron g-2 (a_e) is 4.9210(103) in units of (alpha/pi)^5. The mass-dependent contributions to a_e from diagrams containing a muon loop is 0.00370(37) (alpha/pi)^5. The tau-lepton loop contribution is negligible at present. Altogether the contribution of Set III(c) to a_e is 4.9247 (104) (alpha/pi)^5. We…
Order-alpha_s QCD corrections in the soft-gluon approximation to angular distributions of decay charged leptons in the process e+e- -> t tbar, followed by semileptonic decay of t or tbar, are obtained in the e+e- centre-of-mass frame. As compared to distributions in the top rest frame, these have the advantage that they would allow direct comparison with experiment without the need to reconstruct the top rest frame or a spin quantization axis. Analytic expressions for the distribution in the charged-lepton polar angle and triple distribution in the polar angle of t and polar and azimuthal angl…
This paper reports the Feynman-parametric representation of the vacuum-polarization function consisting of 105 Feynman diagrams of the eighth order, and its contribution to the gauge-invariant set called Set I(i) of the tenth-order lepton anomalous magnetic moment. Numerical evaluation of this set is carried out using FORTRAN codes generated by an automatic code generation system gencodevpN developed specifically for this purpose. The contribution of diagrams containing electron loop to the electron g-2 is 0.017 47 (11) (alpha/pi)^5. The contribution of diagrams containing muon loop is 0.000 0…
This paper reports the tenth-order contributions to the g-2 of the electron a_e and those of the muon a_mu from the gauge-invariant Set II(c), which consists of 36 Feynman diagrams, and Set II(d), which consists of 180 Feynman diagrams. Both sets are obtained by insertion of sixth-order vacuum-polarization diagrams in the fourth-order anomalous magnetic moment. The mass-independent contributions from Set II(c) and Set II(d) are -0.116 489 (32)(alpha/pi)^5 and -0.243 00 (29)(alpha/pi)^5, respectively. The leading contributions to a_mu, which involve electron loops only, are -3.888 27 (90)(alpha…
This paper reports the tenth-order QED contribution to lepton g-2 from diagrams of three gauge-invariant sets VI(d), VI(g), and VI(h), which are obtained by including various fourth-order radiative corrections to the sixth-order g-2 containing light-by-light-scattering subdiagrams. In the case of electron g-2, they consist of 492, 480, and 630 vertex Feynman diagrams, respectively. The results of numerical integration, including mass-dependent terms containing muon loops, are 1.8418(95) (alpha/pi)^5 for the Set VI(d), -1.5918(65) (alpha/pi)^5 for the Set VI(g), and 0.1797(40) (alpha/pi)^5 for …
This article reports an automated approach to the evaluation of higher-order terms of QED perturbation to anomalous magnetic moments of charged leptons by numerical means. We apply this approach to tenth-order correction due to a particular subcollection of Feynman diagrams, which have no virtual lepton loops. This set of diagrams is distinctive in that it grows factorially in number as the order increases, and also each of the diagrams holds quite a large number of subtraction terms to be treated along renormalization procedure. Thus some automated scheme has long been required to evaluate co…
The analysis of event shape variables enable studies of QCD and determinations of alpha-s, but require predictions to next-to-leading order. The predictions of two next-to-leading order programs are compared for current jet thrust, current jet-broadening, C parameter and jet-mass in deep inelastic scattering.
The thrust distribution in e+e- annihilation is calculated exploiting its exponentiation property in the two-jet region t = 1-T << 1. We present a general method (DGE) to calculate a large class of logarithmically enhanced terms, using the dispersive approach in renormalon calculus. Dressed Gluon Exponentiation is based on the fact that the exponentiation kernel is associated primarily with a single gluon emission, and therefore the exponent is naturally represented as an integral over the running coupling. Fixing the definition of Lambda is enough to guarantee consistency with the exact expon…
We present the first determination of the strong coupling constant from the three-jet rate in e+e- annihilation at LEP, based on a next-to-next-to-leading order (NNLO) perturbative QCD prediction. More precisely, we extract alpha_s by fitting perturbative QCD predictions at O(alpha_s^3) to data from the ALEPH experiment at LEP. Over a large range of the jet-resolution parameter ycut this observable is characterised by small non-perturbative corrections and an excellent stability under renormalisation scale variation. For the three-jet rate at ln(ycut) = -3.9 we find alpha_s(MZ) = 0.1175 +/- 0.…
Improved values for the two- and three-loop mass-dependent QED contributions to the anomalous magnetic moments of the electron, muon, and tau lepton are presented. The Standard Model prediction for the electron (g-2) is compared with its most precise recent measurement, providing a value of the fine-structure constant in agreement with a recently published determination. For the tau lepton, differences with previously published results are found and discussed. An updated value of the fine-structure constant is presented in "Note added after publication."
We present the leading order differential and total rates for J/ψproduction at LEP. By leading order we mean all terms of the form alpha_s[alpha_s log(M_Z^2/M_{psi}^2)]^n and alpha_s^{n+1} log^l(z^2) log^m(M_Z^2/M_{psi}^2), (l+m=2n-1), in the regions z=2E_psi/M_Z ~ O(1) and z << 1, respectively. In the intermediate region we interpolate using the available data. This resummation eliminates the O[alpha_s(M_psi)/alpha_s(M_Z)]~ 2 theoretical uncertainties in previous calculations. The log(z) resummation results in a suppression of the small z region due to coherent gluon emission. Comparing the z…
We complete our study of resummed event-shape distributions in DIS by presenting results for the class of observables that includes the current jet mass, the C-parameter and the thrust with respect to the current-hemisphere thrust axis. We then compare our results to data for all observables for which data exist, fitting for alpha_s and testing the universality of non-perturbative 1/Q effects. A number of technical issues arise, including the extension of the concept of non-globalness to the case of discontinuous globalness; singularities and non-convergence of distributions other than in the …
In this thesis exact results on O(alpha^2) single bremsstrahlung corrections to low angle Bhabha scattering at LEP/SLC energies are given. The calculation represents the last outstanding theoretical second order subleading electroweak contribution for that process, needed to determine the experimental luminosity at second generation LEP detectors below the 0.1% precision threshold. The exact, fully differential result is obtained by employing analytical as well as computer-algebraic methods and includes terms up to O(0.05%) relative to the Born cross section. The initial output of over 20,000 …
If the reported excess (over the standard model prediction) for Z->bb from LEP persists, and is explained by supersymmetric particles in loops, then we show that (1) a superpartner (chargino and/or stop) will be detected at LEP2, and probably at LEP1.5 in 1995, (2) the basic parameter tan(beta) is at its lower perturbative limit, (3) BR(t->t1+chi0) is at or above 0.4, (4) the upper limit on m_h is considerably reduced, and (5) several important consequences arise for the form of a unified supersymmetric theory. Our analysis is done in terms of a general weak scale Lagrangian and does not depen…
A complete parton level analysis of 2l2v2j and 4l2j, l = mu,e production at the LHC is presented, including all processes at order alpha^6, alpha^4*alpha_s^2. The infinite Higgs mass scenario, which is considered as a benchmark for strong scattering theories and is the limiting case for composite Higgs models, and one example of Strongly Interacting Light Higgs models are confronted with the Standard Model light Higgs predictions. This analysis is combined with the results in the lv4j, the ll4j and the 3lv2j channels presented in previous papers, in order to determine whether these alternative…
We determine the O(alpha_s^2) corrections to the partonic hemisphere soft function relevant for thrust and jet mass distributions in e+e- annihilation in the dijet limit. In this limit the distributions can be described by a factorization theorem that sums large logarithmic terms and separates perturbative from nonperturbative effects. Using the known O(alpha_s^2) contributions of the jet functions and the hard coefficients in the factorization theorem, constraints from renormalization group evolution and nonabelian exponentiation, and results from numerical integration of O(alpha_s^2) QCD mat…
At the LHC and Tevatron strong initial-state radiation (ISR) plays an important role. It can significantly affect the partonic luminosity available to the hard interaction or contaminate a signal with additional jets and soft radiation. An ideal process to study ISR is isolated Drell-Yan production, pp -> X l+l- without central jets, where the jet veto is provided by the hadronic event shape beam thrust tau_B. Most hadron collider event shapes are designed to study central jets. In contrast, requiring tau_B << 1 provides an inclusive veto of central jets and measures the spectrum of ISR. For t…
Among 12672 Feynman diagrams contributing to the electron anomalous magnetic moment at the tenth order, 6354 are the diagrams having no lepton loops, i.e., those of quenched type. Because the renormalization structure of these diagrams is very complicated, some automation scheme is inevitable to calculate them. We developed an algorithm to write down FORTRAN programs for numerical evaluation of these diagrams, where the necessary counterterms to subtract out ultraviolet subdivergence are generated according to Zimmermann's forest formula. Thus far we have evaluated crudely integrals of 2232 te…
This paper reports the values of contributions to the electron g-2 from 300 Feynman diagrams of the gauge-invariant Set III(a) and 450 Feynman diagrams of the gauge-invariant Set III(b). The evaluation is carried out in two versions. Version A is to start from the sixth-order magnetic anomaly M_6 obtained in the previous work. The mass-independent contributions of Set III(a) and Set III(b) are 2.1275 (2) and 3.3271 (6) in units of (alpha/pi)^5, respectively. Version B is based on the recently-developed automatic code generation scheme. This method yields 2.1271 (3) and 3.3271 (8) in units of (…
We report on some technical aspects of our calculation of alpha_s^4 corrections to R(s) and the semi-leptonic tau decay width [1-3]. We discuss the inner structure of the result as well as the issue of its correctness. We demonstrate recently appeared independent evidence positively testing one of two components of the full result.
Precise measurements of the lepton properties provide stringent tests of the Standard Model structure and accurate determinations of its parameters. We overview the present status of a few selected topics: lepton universality, QCD tests and the determination of alpha_s and m_s from hadronic tau decays, the anomalous lepton magnetic moments and neutrino oscillations.
The Drell-Yan mechanism for the production of lepton pairs is one of the most basic processes for physics studies at hadron colliders. It is therefore important to have accurate theoretical predictions. In this work we compute the two-loop virtual mixed QCD x QED corrections to Drell-Yan production. We evaluate the Feynman diagrams by decomposing the amplitudes into a set of known master integrals and their coefficients, which allows us to derive an analytical result. We also perform a detailed study of the ultraviolet and infrared structure of the two-loop amplitude and the corresponding pole…
The program TOPAZ0 was developed for computing a variety of physical observables which are related to the e+e- annihilation into fermion pairs and to the large angle Bhabha scattering around the Z resonance. Among them, the Z parameters or pseudo-observables, the de-convoluted cross sections and those dressed with QED radiation, and finally the forward-backward asymmetries. The calculations are performed both for a completely inclusive experimental set-up and for a realistic one, i.e. a set-up with cuts on the acollinearity angle, on the energy of the outgoing fermions or on their invariant ma…
We derive the initial condition for the perturbative fragmentation function of a heavy quark through order O(alpha_s^2) in the MS-bar scheme. This initial condition is useful for computing heavy quark (or lepton, in case of QED) energy distributions from calculations with massless partons. In addition, the initial condition at O(alpha_s^2) can be used to resum collinear logarithms ln(Q^2/m^2) in heavy quark energy spectrum with next-to-next-to-leading logarithmic accuracy by solving the DGLAP equation.
Precise measurements of the tau lepton properties provide stringent tests of the Standard Model structure and accurate determinations of its parameters. We overview the present status of a few selected topics: lepton universality, QCD tests and the determination of alpha_s, m_s and V_us from hadronic tau decays, and lepton flavor violation phenomena.
Using recently developed methods for the evaluation of five-loop amplitudes in perturbative QCD, corrections of order alpha_s^4 for the cross section of electron-positron annihilation into hadrons and for the decay rates of the Z-boson and the tau-lepton into hadrons are evaluated. The new terms lead to a significant stabilization of the perturbative series, to a reduction of the theory uncertainly in the strong coupling constant alpha_s, as extracted from these measurements, and to a small shift of the central value, moving two central values closer together. The agreement between two values …
We present an algorithm for unweighted event generation in the partonic process pp -> WZ (j) with leptonic decays at next-to-leading order in alpha_S. Monte Carlo programs for processes such as this frequently generate events with negative weights in certain regions of phase space. For simulations of experimental data one would like to have unweighted events only. We demonstrate how the phase space from the matrix elements can be combined to achieve unweighted event generation using a second stage Monte Carlo integration over a volume of real emissions (jets). Observable quantities are kept fi…
We analyze the order alpha_s^2 corrections to the single inclusive jet cross section in lepton-nucleon deep inelastic scattering. The full calculation is done analytically, in the small cone approximation, obtaining finite NLO partonic level cross sections for these processes. A detailed study of the different underlying partonic reactions is presented focusing in the size of the corrections they get at NLO accuracy, their relative weight, and the residual scale uncertainty they leave in the full cross section depending on the kinematical region explored. The dominant partonic process in very …
In the framework of the effective field theory (EFT) we discuss the electroweak (EW) corrections at LEP energies. We obtain the effective Lagrangian in the large m_t limit, and reproduce analytically the dominant EW corrections to the LEP2 processes e+ e- --> gamma Z and e+ e- --> Z Z. To include effects of finite top-quark and Higgs masses, we use the effective Lagrangian at tree level and fit LEP1/SLD observables with four arbitrary parameters, plus alpha_s(m_Z). The EFT approach works remarkably well. Using the effective couplings determined from the fit, and tree-level EFT formulae, we pre…
We calculate the radiative corrections of order O(alpha E_e/m_N) as next-to-leading order corrections in the large nucleon mass expansion to Sirlin's radiative corrections of order O(alpha/pi) to the neutron lifetime. The calculation is carried out within a quantum field theoretic model of strong low-energy pion--nucleon interactions described by the linear sigma-model (LsM) with chiral SU(2)xSU(2) symmetry and electroweak hadron-hadron, hadron-lepton and lepton-lepton interactions for the electron-lepton family with SU(2)_L x U(1)_Y symmetry of the Standard Electroweak Model (SEM). Such a qua…
Data recorded by the JADE experiment at the PETRA e^+e^- collider were used to measure the event shape observables thrust, heavy jet mass, wide and total jet broadening and the differential 2-jet rate in the Durham scheme. For the latter three observables, no experimental results have previously been presented at these energies. The distributions were compared with resummed QCD calulations (O(alpha_s^2)+NLLA), and the strong coupling constant alpha_s(Q) was determined at different energy scales Q=sqrt{s}. The results, α_s(22 GeV) = 0.161 ^{+0.016}_{-0.011}, α_s(35 GeV) = 0.143 ^{+0.011}_{-0.00…
We discuss the determination of the CKM angles gamma and alpha using recent data from non-leptonic B decays together with flavour symmetries. Penguin effects are controlled by means of the CP-averaged branching ratio B_d \to π^\pm K^\mp. The information from A_{CP}(B_d \to J/ΨK_S) (two solutions for phi_d), Rb and gamma allow us to determine beta, even in presence of New Physics not affecting Delta B=1 amplitudes. In this context we address the question of to what extent there is still space for New Physics.
A precise empirical relation between the electromagnetic coupling alpha(m_Z) and sin^2(theta^ell_{eff}) --where theta^ell_{eff} is the effective electroweak mixing angle extracted from Z leptonic decays-- is made manifest: alpha(m_Z) = sin^3(theta^ell_{eff})*cos(theta^\ell_{eff}}/(4π}.
We compute the short distance coefficients for the NRQCD factorization formulas of the meson-to-vacuum matrix elements for the axial vector and vector parts of the charged weak current in the $S$-wave spin-singlet and -triplet bar{b}c mesons, respectively. The computation is carried out to order alpha_s including relativistic corrections of all orders in vec{q}^{2n}, where vec{q} is the relative momentum of the bar{b} and c in the meson rest frame. The relativistic corrections at order alpha_s are new. The results reveal that the relativistic corrections to the leptonic decay rate of the B_c m…
We compute the O(alpha_s^2) QCD corrections to the fully differential cross-section pp \to W X \to l νX, retaining all effects from spin correlations. The knowledge of these corrections makes it possible to calculate with high precision the W boson production rate and acceptance at the LHC, subject to realistic cuts on the lepton and missing energy distributions. For certain choices of cuts we find large corrections when going from next-to-leading order (NLO) to next-to-next-to-leading order (NNLO) in perturbation theory. These corrections are significantly larger than those obtained by parton…
Agentic AI -- Physicist Collaboration in Experimental Particle Physics: A Proof-of-Concept Measurement with LEP Open Data
University of Chicago, Enrico Fermi Institute（芝加哥大学恩里科·费米研究所）；Vanderbilt University（范德堡大学）；Laboratory for Nuclear Science, Massachusetts Institute of Technology（麻省理工学院核科学实验室）
We extract the value of the strong coupling constant alpha_s from a single-parameter pointlike fit to the photon structure function F_2^gamma at large x and Q^2 and from a first five-parameter full (pointlike and hadronic) fit to the complete F_2^gamma data set taken at PETRA, TRISTAN, and LEP. In next-to-leading order and the MSbar renormalization and factorization schemes, we obtain alpha_s(m_Z)=0.1183 +/- 0.0050(exp.)^+0.0029_-0.0028(theor.) [pointlike] and alpha_s(m_Z)=0.1198 +/- 0.0028(exp.)^+0.0034_-0.0046(theor.) [pointlike and hadronic]. We demonstrate that the data taken at LEP have r…
We present a general procedure for incorporating higher-order information into the scale-setting prescription of Brodsky, Lepage and Mackenzie. In particular, we show how to apply this prescription when the leading coefficient or coefficients in a series in the strong coupling alpha_s are anomalously small and the original prescription can give an unphysical scale. We give a general method for computing an optimum scale numerically, within dimensional regularization, and in cases when the coefficients of a series are known. We apply it to the heavy quark mass and energy renormalization in latt…
We apply a previously developed scheme to consistently include the twist-3 distribution amplitudes for transversely polarized rho meson in order to evaluate, in the framework of kT factorization, the helicity amplitudes for exclusive leptoproduction of a light vector meson, at leading order in alphaS. We compare our results with high energy experimental data for the ratios of helicity amplitudes T11/T00 and T01/T00 and get a good description of the data.
We study the hydrogen and muonic hydrogen within an effective field theory framework. We perform the matching between heavy baryon effective theory coupled to photons and leptons and the relevant effective field theory at atomic scales. This matching can be performed in a perturbative expansion in alpha, 1/m_p and the chiral counting. We then compute the O(m_{l_i}^3 alpha^5/m_p^2 x logarithms) contribution (including the leading chiral logarithms) to the Hyperfine splitting and compare with experiment. They can explain about 2/3 of the difference between experiment and the pure QED prediction …
