Asymmetry AN Research Articles

Towards Accurate Diagnosis of Skin Lesions Using Feedforward Back Propagation Neural Networks.

In the automatic detection framework, there have been many attempts to develop models for real-time melanoma detection. To effectively discriminate benign and malign skin lesions, this work investigates sixty different architectures of the Feedforward Back Propagation Network (FFBPN), based on shape asymmetry for an optimal structural design that includes both the hidden neuron number and the input data selection. The reason for the choice of shape asymmetry was based on the 5–10% disagreement between dermatologists regarding the efficacy of asymmetry in the diagnosis of malignant melanoma. Asymmetry is quantified based on lesion shape (contour), moment of inertia of the lesion shape and histograms. The FFBPN has a high architecture flexibility, which indicates it as a favorable tool to avoid the over-parameterization of the ANN and, equally, to discard those redundant input datasets that usually result in poor test performance. The FFBPN was tested on four public image datasets containing melanoma, dysplastic nevus and nevus images. Experimental results on multiple benchmark data sets demonstrate that asymmetry A2 is a meaningful feature for skin lesion classification, and FFBPN with 16 neurons in the hidden layer can model the data without compromising prediction accuracy.

Feasibility studies for the measurement of single-spin asymmetry in inclusive K0 s production at pion beam at U-70

In the Spring 2018, the first physics data was accumulated in the new SPASCHARM experiment at U-70 accelerator of IHEP, Protvino. The first stage of SPASCHARM’s physics programs prursues the goal of studying spin effects in the beam fragmentation region at an unpolarized negative 28 GeV beam, interacting with a frozen polarized proton target. In this resport, the feasibility of measuring the single spin asymmetry AN in the reaction: π − + p↑→K 0 S + X is evaluated by Monte-Carlo simulations. We present estimates of the detection efficiency as well as for expected event statistics. It is shown that, in the process of interest above, the attainable statistical errors for AN would be at the scale of a few percents.

On the A-dependence of the neutron single-spin asymmetry in pA-collisions

Preliminary results of the PHENIX experiment on the single-spin asymmetry (AN) for a neutron production in proton-nucleus collisions are discussed. The asymmetry AN changes its sign and increases three-fold as the transition from p + p to p + Au interactions occurs. We call this phenomena “anomalous A-dependence of AN”. This unusual behavior is explained in the framework of the chromomagnetic polarization of quarks (CPQ) model. Dependence of AN on centrality of collisions and the “ridge” effect in heavy ions collisions are discussed.

Study of the sign change of the Sivers function from STAR collaboration W/Z production data

Recent data on the transverse single spin asymmetry AN measured by the STAR Collaboration for p↑p → W±/Z0X reactions at RHIC allow the first investigation of the Sivers function in Drell-Yan processes and of its expected sign change with respect to SIDIS processes. A new extraction of the Sivers functions from the latest SIDIS data is performed and a critical assessment of the significance of the STAR data is attempted.

Polarimetry with inclusive charged pions at U-70 accelerator of IHEP

A feasibility of the proton beam polarimetry based on exploiting the observed large single-spin asymmetry AN in inclusive charged pion production is evaluated for the SPASCHARM experiment at IHEP, Protvino, Russia. It is shown that, for a few hours of beam exposition time, the beam polarization could be measured at the statistical errors of ∼3-5%. The inclusive pion polarimetry at SPASCHARM does not require construction of a special polarimeter. The polarimetry will be carried out entirely by the main SPASCHARM spectrometer simultaneously with physics data taking.

Single-spin asymmetry in pp and pA-collisions

Experimental data on the transverse single-spin asymmetry AN in the collisions of polarized protons with protons and nuclear targets are analyzed. The existing data are compared with predictions from the chromomagnetic polarization of quarks (CPQ) model for the processes of π±, K±, p and antiproton production in the inclusive reactions. The results of An calculations for the above processes are presented in the following kinematic region: 8.77 ≤ √s ≤ 500 GeV, 0 < xF ≤ 0.83, 0 ≤ pT ≤ 9 GeV/c. Predictions of the CPQ model can be used for planning of experiments SPASCHARM(IHEP), SPD(JINR), STAR and PHENIX.

Precision measurements of [formula omitted] in the deep inelastic regime

We have performed precision measurements of the double-spin virtual-photon asymmetry A1 on the neutron in the deep inelastic scattering regime, using an open-geometry, large-acceptance spectrometer and a longitudinally and transversely polarized 3He target. Our data cover a wide kinematic range 0.277≤x≤0.548 at an average Q2 value of 3.078 (GeV/c)2, doubling the available high-precision neutron data in this x range. We have combined our results with world data on proton targets to make a leading-order extraction of the ratio of polarized-to-unpolarized parton distribution functions for up quarks and for down quarks in the same kinematic range. Our data are consistent with a previous observation of an A1n zero crossing near x=0.5. We find no evidence of a transition to a positive slope in (Δd+Δd¯)/(d+d¯) up to x=0.548.

Neutral pion cross section and spin asymmetries at intermediate pseudorapidity in polarized proton collisions ats=200 GeV

The differential cross section and spin asymmetries for neutral pions produced within the intermediate pseudorapidity range 0.8<η<2.0 in polarized proton-proton collisions at s=200 GeV are presented. Neutral pions were detected using the end cap electromagnetic calorimeter in the STAR detector at RHIC. The cross section was measured over a transverse momentum range of 5<pT<16 GeV/c and is found to agree with a next-to-leading order perturbative QCD calculation. The longitudinal double-spin asymmetry ALL is measured in the same pseudorapidity range and spans a range of Bjorken-x down to x≈0.01. The measured ALL is consistent with model predictions for varying degrees of gluon polarization. The parity-violating asymmetry AL is also measured and found to be consistent with zero. The transverse single-spin asymmetry AN is measured over a previously unexplored kinematic range in Feynman-x and pT. Such measurements may aid our understanding of the onset and kinematic dependence of the large asymmetries observed at more forward pseudorapidity (η≈3) and their underlying mechanisms. The AN results presented are consistent with a twist-3 model prediction of a small asymmetry over the present kinematic range.2 MoreReceived 6 September 2013DOI:https://doi.org/10.1103/PhysRevD.89.012001© 2014 American Physical Society

Longitudinal spin structure of the nucleon at COMPASS (SPS CERN)

We present new results on longitudinal inclusive double-spin asymmetry A1,p(x) in deep-inelastic muon-proton scattering and proton spin-dependent structure function g1p(x, Q2). New COMPASS data on longitudinal polarised NH3 target were collected during the year 2011 with beam of positive muons with energy E = 200 GeV. Kinematical threshold Q2 ≥ 1 (GeV/c)2 and the fractional energy 0.1 < y < 0.9 allow us to cover low x region down to 0.025.

Measurement of the spin-structure function g 2 and the semi-inclusive double-spin asymmetries at HERMES

A measurement of the virtual-photon asymmetry A2 and of the spin-structure function g2 of the proton are presented for the kinematic range of the HERMES experiment carried out at the HERA electron storage ring at DESY. Semi-inclusive longitudinal double-spin asymmetries provide new insight into the valence quark helicity distributions Δuv and Δdv.

Single spin asymmetry [formula omitted] in polarized proton–proton elastic scattering at [formula omitted

We report a high precision measurement of the transverse single spin asymmetry AN at the center of mass energy s=200 GeV in elastic proton–proton scattering by the STAR experiment at RHIC. The AN was measured in the four-momentum transfer squared t range 0.003⩽|t|⩽0.035 (GeV/c)2, the region of a significant interference between the electromagnetic and hadronic scattering amplitudes. The measured values of AN and its t-dependence are consistent with a vanishing hadronic spin-flip amplitude, thus providing strong constraints on the ratio of the single spin-flip to the non-flip amplitudes. Since the hadronic amplitude is dominated by the Pomeron amplitude at this s, we conclude that this measurement addresses the question about the presence of a hadronic spin flip due to the Pomeron exchange in polarized proton–proton elastic scattering.

Forward Transverse Single Spin Asymmetries at PHENIX

Recent measurements of single transverse spin asymmetries in proton-proton collisions measured by the PHENIX experiment at RHIC are presented. The focus is on the single particle left-right asymmetry AN for π0 at √s = 200 GeV and √s = 62.4 GeV and the measurement of di-hadron correlations at √s = 200 GeV which are produced by the fragmentation of a transversely polarized quark via the Interference Fragmentation Function (IFF) H1< and thus provide a probe for the quark transversity distribution function.

Flavour separation of helicity distributions from deep inelastic muon–deuteron scattering

We present a LO evaluation of helicity densities of valence, Δuv+Δdv, non-strange sea, Δu¯+Δd¯, and strange quarks, Δs (assumed to be equal to Δs¯). They have been obtained from the inclusive asymmetry A1,d and the semi-inclusive asymmetries A1,dπ+, A1,dπ−, A1,dK+, A1,dK− measured in polarised deep inelastic muon–deuteron scattering. The full deuteron statistics of COMPASS (years 2002–2004 and 2006) has been used. The data cover the range Q2>1 (GeV/c)2 and 0.004<x<0.3. Both non-strange densities are found to be in a good agreement with previous measurements. The distribution of Δs(x) is compatible with zero in the whole measured range, in contrast to the shape of the strange quark helicity distribution obtained in most LO and NLO QCD fits. The sensitivity of the values of Δs(x) upon the choice of fragmentation functions used in the derivation is discussed.

Soft-fermion-pole contribution to single-spin asymmetry for pion production in pp collisions

We study the single transverse spin asymmetry for the inclusive pion production in the nucleon–nucleon collision, p↑p→πX, based on the twist-3 mechanism in the collinear factorization. We derive the soft-fermion-pole (SFP) contribution to the twist-3 single-spin-dependent cross section associated with the twist-3 quark–gluon correlation functions in the polarized nucleon. We find that the SFP can give rise to a large effect to the asymmetry AN owing to the large partonic hard cross sections with the large color factor, if the SFP function has a similar magnitude as the soft-gluon-pole (SGP) function, in spite of the absence of the “derivative term” for the SFP function unlike for the SGP function.

Quark-Hadron Duality in Neutron (He3) Spin Structure

We present experimental results of the first high-precision test of quark-hadron duality in the spin-structure function g_{1} of the neutron and 3He using a polarized 3He target in the four-momentum-transfer-squared range from 0.7 to 4.0 (GeV/c);{2}. Global duality is observed for the spin-structure function g_{1} down to at least Q;{2}=1.8 (GeV/c);{2} in both targets. We have also formed the photon-nucleon asymmetry A1 in the resonance region for 3He and found no strong Q2 dependence above 2.2 (GeV/c);{2}.

Probing proton spin structure via heavy flavor production in PHENIX

The measurement of spin asymmetries in polarized p+p collisions provides an opportunity to probe the spin structure of nucleons. With transversely and longitudinally polarized proton beams at RHIC, we can measure both double longitudinal spin asymmetry ALL and single transverse spin asymmetry AN. At the RHIC energy, heavy quark (charm and beauty) production is dominated by gluon–gluon interactions, so measurements of ALL and AN will allow us to directly probe the polarized gluon distribution and gluon's Sivers functions, respectively. PHENIX experiment collected 3.5 pb−1 (beam polarization ∼50%) and 10 pb−1 (beam polarization ∼60%) data from year 2005 and 2006 runs, respectively. In this analysis, the J/Ψ have been measured through the J/Ψ → μ+μ− channel at forward rapidities, and about 30 000 J/Ψ candidates are reconstructed from Lvl2 triggered data production. We present the latest results of J/ΨALL and AN measurements at forward rapidities from the PHENIX experiment.

Double spin asymmetry in exclusive ρ0 muoproduction at COMPASS

The longitudinal double spin asymmetry A1 ρ for exclusive leptoproduction of ρ0 mesons, μ+N→μ+N+ρ, is studied using the COMPASS 2002 and 2003 data. The measured reaction is incoherent exclusive ρ0 production on polarised deuterons. The Q2 and x dependence of A1 ρ is presented in a wide kinematical range, 3×10-3<Q2< 7 (GeV/c)2 and 5×10-5<x<0.05. The results presented are the first measurements of A1 ρ at small Q2 (Q2< 0.1 (GeV/c)2) and small x (x<3×10-3). The asymmetry is in general compatible with zero in the whole kinematical range.

Proton Spin Structure in the Resonance Region

We have examined the spin structure of the proton in the region of the nucleon resonances (1.085 GeV<W<1.910 GeV) at an average four momentum transfer of Q2=1.3 GeV2. Using the Jefferson Lab polarized electron beam, a spectrometer, and a polarized solid target, we measured the asymmetries A|| and A(perpendicular) to high precision, and extracted the asymmetries A1 and A2, and the spin structure functions g1 and g2. We found a notably nonzero A(perpendicular), significant contributions from higher-twist effects, and only weak support for polarized quark-hadron duality.

Contents of the supplement F to vol. 56 (2006)

The transverse single-spin asymmetry AN observed in high energy proton-proton collisions pp → πX has been found to increase with the momentum fraction xF of the pion up to the largest measured xF ∼ 0.8, where AN ≃ 40%. We consider the possibility that the asymmetry is due to a non-perturbatively generated spin-flip coupling in soft rescattering on the target proton. We demonstrate using perturbation theory that a non-vanishing asymmetry can be generated through interference between exchanges of even and odd charge conjugation provided both helicity flip and non-flip couplings contribute. Pomeron and odderon exchange can thus explain the energy independence of the asymmetry and predicts that the asymmetry should persist in events with large rapidity gaps.

Operator relations for SU(3) breaking contributions to K and K* distribution amplitudes

We derive constraints on the asymmetry a1 of the momentum fractions carried by quark and antiquark in K and K* mesons in leading twist. These constraints follow from exact operator identities and relate a1 to SU(3) breaking quark-antiquark-gluon matrix elements which we determine from QCD sum rules. Comparing our results to determinations of a1 from QCD sum rules based on correlation functions of quark currents, we find that, for a1^\parallel(K*) the central values agree well and come with moderate errors, whereas for a1(K) and a1^\perp(K*) the results from operator relations are consistent with those from quark current sum rules, but come with larger uncertainties. The consistency of results confirms that the QCD sum rule method is indeed suitable for the calculation of a1. We conclude that the presently most accurate predictions for a1 come from the direct determination from QCD sum rules based on correlation functions of quark currents and are given by: a1(K) = 0.06\pm 0.03, a1^\parallel(K*) = 0.03\pm 0.02, a1^\perp(K*) = 0.04\pm 0.03.