Papers by Philip Ratcliffe
arXiv (Cornell University), 1996
The plenary presentations of the conference are summarised, highlighting some aspects that were o... more The plenary presentations of the conference are summarised, highlighting some aspects that were of particular interest and attempting to link a few of the topics covered. Particular emphasis is placed on the problem of deep-inelastic scattering and questions still to be answered with regard to the distribution functions, strange-quark and gluon contributions, and the possible rôle of orbital angular momentum. Passing reference is also made to some of the parallel session presentations.
Universe
The setting of the renormalization scale (μr) in the perturbative QCD (pQCD) is one of the crucia... more The setting of the renormalization scale (μr) in the perturbative QCD (pQCD) is one of the crucial problems for achieving precise fixed-order pQCD predictions. The conventional prescription is to take its value as the typical momentum transfer Q in a given process, and theoretical uncertainties are then evaluated by varying it over an arbitrary range. The conventional scale-setting procedure introduces arbitrary scheme-and-scale ambiguities in fixed-order pQCD predictions. The principle of maximum conformality (PMC) provides a systematic way to eliminate the renormalization scheme-and-scale ambiguities. The PMC method has rigorous theoretical foundations; it satisfies the renormalization group invariance (RGI) and all of the self-consistency conditions derived from the renormalization group. The PMC has now been successfully applied to many physical processes. In this paper, we summarize recent PMC applications, including event shape observables and heavy quark pair production near ...
The transverse-spin structure of the proton
WORLD SCIENTIFIC eBooks, 2003
European Physical Journal C, 1999
Within the framework of a simple model, we study single-spin asymmetries for pion production in h... more Within the framework of a simple model, we study single-spin asymmetries for pion production in hadron-hadron collisions at highenergies with one hadron polarised. The asymmetries are generated via a mechanism of final (initial) state interactions. For peripheral kinematics, when the pion belongs to the fragmentation region of the polarised proton, we find non-zero asymmetries in the high-energy limit. Numerical results and comparision with existing experimental data are presented. We also discuss the relationship with odderon exchange phenomenology.
arXiv (Cornell University), Jul 8, 2023
A key issue in making precise predictions in QCD is the uncertainty in setting the renormalizatio... more A key issue in making precise predictions in QCD is the uncertainty in setting the renormalization scale µ r and thus determining the correct values of the QCD running coupling α s (µ r) at each order in the perturbative expansion of a QCD observable. It has often been conventional to simply set the renormalization scale to the typical scale of the process Q and vary it in the range µ r ∈ [Q/2, 2Q] in order to estimate the theoretical error. This is the practice of Conventional Scale Setting (CSS). The resulting CSS prediction will however depend on the theorist's choice of renormalization scheme and the resulting pQCD series will diverge factorially. It will also disagree with renormalization scale setting used in QED and electroweak theory thus precluding grand unification. A solution to the renormalization scale-setting problem is offered by the Principle of Maximum Conformality (PMC), which provides a systematic way to eliminate the renormalization scaleand-scheme dependence in perturbative calculations. The PMC method has rigorous theoretical foundations, it satisfies Renormalization Group Invariance (RGI) and preserves all self-consistency conditions derived from the renormalization group. The PMC cancels the renormalon growth, reduces to the Gell-Mann-Low scheme in the N c → 0 Abelian limit and leads to scale-and scheme-invariant results. The PMC has now been successfully applied to many high-energy processes. In this article we summarize recent developments and results in solving the renormalization scale and scheme ambiguities in perturbative QCD. In particular, we present a recently developed method the PMC ∞ and its applications, comparing the results with CSS. The method preserves the property of renormalizable SU(N)/U(1) gauge theories defined as Intrinsic Conformality (iCF). This property underlies the scale invariance of physical observables and leads to a remarkably efficient method to solve the conventional renormalization scale ambiguity at every order in pQCD. This new method reflects the underlying conformal properties displayed by pQCD at NNLO, eliminates the scheme dependence of pQCD predictions and is consistent with the general properties of the PMC. A new method to identify conformal and β-terms, which can be applied either to numerical or to theoretical calculations is also shown. We present results for the thrust and C-parameter distributions in e + e − annihilation showing errors and comparison with the CSS. We also show results for a recent innovative comparison between the CSS and the PMC ∞ applied to the thrust distribution investigating both the QCD conformal window and the QED N c → 0 limit. In order to determine the thrust distribution along the entire renormalization group flow from the highest energies to zero energy, we consider the number of flavors near the upper boundary of the conformal window. In this flavor-number regime the theory develops a perturbative
Orbital angular momentum effects
Nuclear physics, Apr 1, 1999
SU(3) breaking in hyperon semi-leptonic decays is discussed. The SU(3) parameters F and D, releva... more SU(3) breaking in hyperon semi-leptonic decays is discussed. The SU(3) parameters F and D, relevant to the "proton-spin puzzle", are extracted and a prediction is presented for the decay Ξ 0 → Σ + eν, currently under study by the KTeV collaboration. The values found are g1/f1 = 1.16 ± 0.03 ± 0.01 and Γ = (0.80 ± 0.03 ± 0.01) • 10 6 s −1 .
$R_{e^ + e^ - } ,\,\Gamma _{had}^{Z^0 } $ AND αs: DO THE EXPERIMENTAL DATA AGREE WITH PERTURBATIVE QCD?
Modern Physics Letters A, Mar 7, 1991
We examine the present experimental determinations of the two related quantities: [Formula: see t... more We examine the present experimental determinations of the two related quantities: [Formula: see text] and [Formula: see text] and compare their values with the predictions of perturbative QCD. Both sets of data consistently lie systematically above the theoretical values. However, they are shown to be mutually consistent with a strong-interaction correction roughly twice the magnitude of that calculated within the framework of perturbative QCD. We conclude that this seems to point to the failure of this approach to correctly account for the non-trivial structure of the QCD vacuum and thus of long-distance effects which may pervade even the high-energy regime.
We perform a NLO numerical study of the double transverse-spin asymmetries in the J/ψ resonance r... more We perform a NLO numerical study of the double transverse-spin asymmetries in the J/ψ resonance region for proton-antiproton collisions. We analyze the large x kinematic region, relevant for the proposed PAX experiment at GSI, and discuss the implication of the results for the extraction of the transversity densities.
Spin asymmetries in single selection production at electron-positron colliders
Perturbing thoughts
Physics World, Jun 1, 1989
Nucleation and Atmospheric Aerosols, 2005
A review is presented of some aspects of semi-inclusive deeply inelastic scattering and transvers... more A review is presented of some aspects of semi-inclusive deeply inelastic scattering and transversity. In particular, the role of k T-dependent and higher-twist (or multi-parton) distributions in generating single-spin asymmetries is discussed.
Comment on “analysis of data on polarized lepton-nucleon scattering”
Physics Letters B, Jul 1, 1995
ABSTRACT
Physics Letters B, Jun 1, 1990
The problem of analysing hyperon semi-leptonic decay data is discussed with particular reference ... more The problem of analysing hyperon semi-leptonic decay data is discussed with particular reference to SU (3) symmetry breaking effects and the resulting predictions for the spin structure of the proton. It turns out that the present decay data can be accommodated exceedingly well by a simple approach treating solely the so-called recoil effect or centre-of-mass correction. The extracted F and D parameters, of particular relevance to present discussions of the structure functions for polarized deep-inelastic scattering, are very stable and strikingly close to the results of earlier analyses. The implication is that the F and D thus extracted may reliably be used in predicting the flavour non-singlet contribution to the proton gl. This last being thus still in marked conflict with the EMC/SLAC results on polarized deep-inelastic scattering.
Transverse spin effects
Presented at, 1992
arXiv (Cornell University), Apr 20, 2006
We perform a NLO numerical study of the double transverse-spin asymmetries in the J/ψ resonance r... more We perform a NLO numerical study of the double transverse-spin asymmetries in the J/ψ resonance region for proton-antiproton collisions. We analyze the large x kinematic region, relevant for the proposed PAX experiment at GSI, and discuss the implication of the results for the extraction of the transversity densities.
Spin in hadronic physics and QCD
Physics Letters B, Feb 1, 1995
In the framework of Anisotropic Chromodynamics, a non-perturbative realization of QCD, we develop... more In the framework of Anisotropic Chromodynamics, a non-perturbative realization of QCD, we develop the Low-Nussinov picture of the Pomeron. In this approach all the usual problems of low p T perturbative calculations (infrared divergence) are naturally absent. Thus, we are able to perform an ab initio calculation of the hadron-hadron total cross section. The result is a cross section of the same magnitude as indicated experimentally and approximately energy-independent (with a log 2 s growth). We further discuss the p T dependence of the hadron-hadron elastic-scattering cross section, which displays all the experimentally observed features.
European Physical Journal C, May 1, 1999
We analyse the twist-three amplitudes that can give rise to single-spin asymmetries in hadron-had... more We analyse the twist-three amplitudes that can give rise to single-spin asymmetries in hadron-hadron scattering; in so doing we bring to light a novel factorisation property. As already known, the requirement of an imaginary part leads to consideration of twist-three contributions that are also related to transverse spin in deep-inelastic scattering. In particular, when an external line becomes soft in contributions arising from three-parton correlators, the imaginary part of an internal propagator may be exposed. As shown here, it is precisely this kinematical configuration that permits the factorisation. An important feature is the resulting simplification: the calculation of tens of Feynman diagrams normally contributing to such processes is reduced to the evaluation of products of the simple factors derived here and known two-body helicity amplitudes. We thus find clarifying relations between the spin-dependent and spin-averaged cross-sections and formulate a series of selection rules. In addition, the kinematical dependence of such asymmetries, is rendered more transparent.
Transversity in inclusive leptoproduction
Transverse Spin Physics, 2003
Uploads
Papers by Philip Ratcliffe