Unpolarized Case Research Articles

Polarized EMC effect in the Thermodynamical Bag Model

We determine the polarized quark distributions and structure functions for nuclear media such as Li7 and Al27 by using a phenomenological model known as Thermodynamical Bag Model. The evaluation of nuclear medium modifications to single nucleon structure function discusses the predictions of the polarized EMC effect. The deviation of polarized EMC from unpolarized case shows quenching of polarized quark distributions and proves the significance of this study as adding the spin observables will explore more about medium modification of nuclear structure and the nature of the strong interaction.

Unitary polarized Fermi gas under adiabatic rotation

We discuss the effect of an adiabatic rotation on the phase separation between the superfluid and normal component of a trapped polarized Fermi gas at unitarity and zero temperature, under the assumption that quantized vortices are not formed. We show that the Chandrasekhar-Clogston limit ${n}_{\ensuremath{\downarrow}}∕{n}_{\ensuremath{\uparrow}}$ characterizing the local polarization in the normal phase at the interface is enhanced by the rotation as a consequence of the centrifugal effect. The density profiles (local and column integral) of the two spin species are calculated as a function of the angular velocity for different values of the polarization. The critical value of the angular velocity at which the superfluid exhibits a spontaneous quadrupole deformation is also calculated for the unpolarized case.

First [formula omitted] heavy flavor contributions to deeply inelastic scattering

In the asymptotic limit Q 2 ≫ m 2 , the heavy flavor Wilson coefficients for deep–inelastic scattering factorize into the massless Wilson coefficients and the universal heavy flavor operator matrix elements resulting from light–cone expansion. In this way, one can calculate all but the power corrections in ( m 2 / Q 2 ) k , k > 0 . The heavy flavor operator matrix elements are known to NLO . We present the last 2–loop result missing in the unpolarized case for the renormalization at 3–loops and first 3–loop results for terms proportional to the color factor T F 2 in Mellin–space. In this calculation, the corresponding parts of the NNLO anomalous dimensions [S.A. Larin, T. van Ritbergen and J.A.M. Vermaseren, Nucl. Phys. B427 (1994) 41; S. Moch, J.A.M. Vermaseren and A. Vogt, Nucl. Phys. B688 (2004) 101; S.A. Larin, P. Nogueira, T. van Ritbergen and J.A.M. Vermaseren, Nucl. Phys. B492 (1997) 338; A. Vogt, S. Moch and J.A.M. Vermaseren, Nucl. Phys. B691 (2004) 129] are obtained as well.

Reduction in the Threshold Voltage of a Polymer Light-Emitting Diode by High Molecular Density on a Photo-Crosslinking Layer

The operation voltage of a polymer light-emitting diode (PLED) is significantly reduced using a photo-crosslinking layer whose thickness is of the order of 10 nm. A thin photo-crosslinking layer of a poly(methyl methacrylate)-based photopolymer, coated on the hole injection electrode (anode), was treated with a linearly polarized ultraviolet (LPUV) light. Compared to the unpolarized UV exposure case, for a poly(2-methoxy,5-(2′-ethyl-hexoxy)-1,4-phenylenevinylene) (MEH-PPV) film spin-coated on the LPUV exposed photo-crosslinking layer, the threshold voltage of the PLED was found to be reduced by about 35% and the current density was greatly enhanced. The underlying physical mechanism comes from the increase of the packing density in addition to a partial order of the MEH-PPV on the photo-crosslinking polymer upon the LPUV exposure.

A first principles study of the optical properties of B xC y single wall nanotubes

The optical properties of small radius (<1 nm) single wall carbon nanotubes (SWCNTs) alloyed with boron were examined using relaxed C–C bond length ab initio calculations in the long wavelength limit. The magnitude of the static dielectric constant essentially depends on the B concentration as well as the direction of polarization. The maximum value of the absorption coefficient is shown to strongly depend on the concentration of B in a non-linear way with a minimum at a critical concentration of 0.40 for both the parallel polarization and the un-polarized cases and of 0.29 for perpendicular polarization of the electromagnetic field. The peak of the loss function in parallel polarization and unpolarized cases shifts to a lower frequency with increasing concentration up to 50% but then shifts to a higher frequency. The non-linear fits to the plasma resonance frequency variation with B concentration indicate the existence of a unique minimum. All these factors may shed light on the nature of collective excitations in B-alloyed SWCNTs.

On exotic hybrid meson production in γ*γ collisions

We present a theoretical study of exotic hybrid meson (JPC=1- +) production in photon-photon collisions where one of the photons is deeply virtual, including twist two and twist three contributions. We calculate the cross section of this process, which turns out to be large enough to imply sizeable counting rates in the present high luminosity electron–positron colliders. We emphasize the importance of the πη decay channel for the detection of the hybrid meson candidate π1(1400) and calculate the cross section and the angular distribution for π η pair production in the unpolarized case. This angular distribution is a useful tool for disentangling the hybrid meson signal from the background. Finally, we calculate the single spin asymmetry associated with one initial longitudinally polarized lepton.

Effect of top quark spin on theWtbcouplings ine+pcollisions

In our previous work [Phys. Rev. D 70, 037503 (2004)] for the ${e}^{+}p\ensuremath{\rightarrow}t\overline{\ensuremath{\nu}}+X$ process, we have shown that the top quark possesses a high degree of spin polarization when its spin decomposition axis is along the incoming lepton beam. In this work, the potential of $ep$ collisions to probe an anomalous $Wtb$ vertex is investigated via the polarized single top quark production process for $\mathrm{TESLA}+\mathrm{HERAp}$ energy. The effects of the top quark polarization to $Wtb$ couplings ${F}_{2L}$ and ${F}_{2R}$ are discussed. It is possible to define a polarization axis for the top quark that is more sensitive to new physics than the unpolarized case.

Performance evaluation of optically preamplified receivers with partially polarised noise and arbitrary optical filtering: a rigorous approach

A new rigorous formulation to evaluate the performance of optical receivers with arbitrary optical filtering and partially polarised noise is proposed. The formulation is based on the calculation of the moment generating function (MGF) of the current at the receiver output and is validated by comparison of the probability density function (PDF) of the current obtained from the MGF with the PDF obtained by Monte Carlo simulation. It is shown that there are always two orthogonal directions over which the noise-polarised component can be projected so that the noise projections are statistically uncorrelated. As a consequence, it is concluded that the MGF of the current depends only on the noise degree of polarisation and on the angle between signal and noise polarisations. An explicit dependence of the mean and variance of the signal-amplified spontaneous emission (ASE) and ASE-ASE beat noises on those two factors is presented. It is shown that, when the noise polarisation is parallel to the signal polarisation, the receiver sensitivity is maintained (in comparison with the unpolarised ASE noise case), even in case of highly polarised noise. If the noise polarisation is orthogonal to the signal polarisation, the sensitivity degrades with the degree of polarisation increase, mainly due to signal power reduction.

Efficient evolution of unpolarized and polarized parton distributions with QCD- Pegasus

The Fortran package QCD- Pegasus is presented. This program provides fast, flexible and accurate solutions of the evolution equations for unpolarized and polarized parton distributions of hadrons in perturbative QCD. The evolution is performed using the symbolic moment-space solutions on a one-fits-all Mellin inversion contour. User options include the order of the evolution including the next-to-next-to-leading order in the unpolarized case, the type of the evolution including an emulation of brute-force solutions, the evolution with a fixed number n f of flavors or in the variable- n f scheme, and the evolution with a renormalization scale unequal to the factorization scale. The initial distributions are needed in a form facilitating the computation of the complex Mellin moments. Program summary Title of program: QCD- Pegasus Version: 1.0 Catalogue identifier: ADVN Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ADVN Program obtainable from: CPC Program Library Queen's University of Belfast, N. Ireland License: GNU Public License Computers: all Operating systems: all Program language: Fortran 77 (using the common compiler extension of procedure names with more than six characters) Memory required to execute: negligible ( < 1 MB ) Other programs called: none External files needed: none Number of lines in distributed program, including test data, etc.: 8157 Number of bytes in distributed program, including test data, etc.: 240 578 Distribution format: tar.gz Nature of the physical problem: Solution of the evolution equations for the unpolarized and polarized parton distributions of hadrons at leading order (LO), next-to-leading order and next-to-next-to-leading order of perturbative QCD. Evolution performed either with a fixed number n f of effectively massless quark flavors or in the variable- n f scheme. The calculation of observables from the parton distributions is not part of the present package. Method of solution: Analytic solution in Mellin space (beyond LO in general by power-expansion around the lowest-order expansion) followed by a fast Mellin inversion to x-space using a fixed one-fits-all contour. Restrictions on complexity of the problem: The initial distributions for the evolution are required in a form facilitating an efficient calculation of their complex Mellin moments. The ratio of the renormalization and factorization scales μ r / μ has to be a fixed number. Typical running time: One to ten seconds, on a PC with a 2.0 GHz Pentium-IV processor, for performing the evolution of 200 initial distributions to 500 ( x , μ ) points each. For more details see Section 6.

Standard modelCPviolation in polarizedb→dl+l−

In the standard model, we study CP violating rate asymmetries in the decay $\stackrel{\ensuremath{\rightarrow}}{b}{\mathrm{dl}}^{+}{l}^{\ensuremath{-}}$ when one of the leptons is polarized. We find an asymmetry of (5--15)% in the polarized decay spectrum which is comparable to the known results for the unpolarized case. In the kinematic region separating the $\ensuremath{\rho}\ensuremath{-}\ensuremath{\omega}$ and $c\overline{c}$ resonances, which is also theoretically cleanest, the polarized contribution to the asymmetry is larger than the unpolarized results. In order to observe a $3\ensuremath{\sigma}$ signal for direct CP violation in the polarized spectrum, assuming 100% efficiency, about ${10}^{10}$ $B\overline{B}$ pairs are required at a B factory. Our results indicate an asymmetric contribution from the individual polarization states to the unpolarized CP asymmetry. Taking advantage of this, one can attribute any new physics to be most sensitive to a specific polarization state.

Progress in the calculation of nucleon form factors and parton distribution functions

Even though current lattice calculations are limited to unrealistically large quark masses, it is possible to implement the model independent constraints of chiral symmetry in extrapolations to the physical region. We discuss the role of the Δ-isobar in the extrapolation of the moments of spin dependent parton distribution functions. Unlike the unpolarised case, the Δ plays a crucial role for the isovector spin dependent distributions. We also present initial results for the extrapolation of isovector nucleon form factors, finding reasonably good agreement with experimental data.

Investigation of the Muon Catalyzed Fusion in the Spin Polarized Condition

The cross-sections of the muonic atom interactions in the muon catalyzed fusion (μCF) cycle are spin dependent. In this paper we answer an interesting question about the efficiency of μCF: "Dose the efficiency of μCF increase by spin polarization of the injected beam of muons in the spin polarized D/T mixture?" To answer this question we investigate the spin polarization effects on the kinetics of the μCF cycle by simulating the collisional processes of the μt atoms by the Monte–Carlo method. The themalization and spin-flip rates are determined and used to simulate the kinetics of μCF in the spin polarized condition. Then, the total number of fusions per muon in two cases, spin polarized and unpolarized conditions, are compared. We have shown the spin polarization condition is rapidly converted to the unpolarized case in μCF cycle and its effects can be ignored, especially if the concentration of tritium increases.

SYMMETRY BREAKING IN THE PARTON DISTRIBUTION FUNCTIONS OF THE NUCLEON

We study flavour symmetry breaking in the nucleon's parton distribution functions (PDF) using the meson cloud model and 'Pauli blocking' mechanism. It was found that the 'Pauli blocking' contribution to the integrated polarized asymmetry is much larger than the meson cloud, in contrast to approximate equality in the unpolarized case. We also investigate charge symmetry breaking in the nucleon's PDF using the meson cloud model. Our results are very different from the quark model calculations.

Anomalous dimensions of Wilson operators in N=4 SYM theory

We present the results of two-loop calculations of the anomalous dimension matrix for the Wilson twist-2 operators in the N=4 Supersymmetric Yang–Mills theory for polarized and unpolarized cases. This matrix can be transformed to a triangle form by the same similarity transformation as in the leading order. The eigenvalues of the anomalous dimension matrix are expressed in terms of an universal function with its argument shifted by integer numbers. In the end we discuss relations between the weak and strong coupling regimes in the framework of the AdS/CFT correspondence.

Single-spin asymmetry in pion production in polarized proton–proton collisions and odderon

Single-spin asymmetry appears due to the interference of single and double gluon exchanges between protons. A heavy fermion model is used to describe the jet production in the interaction of the gluon with the proton implying further averaging over its mass. As usual in one-spin correlations, the imaginary part of the double gluon exchange amplitude plays the relevant role. The asymmetry in the inclusive set-up with the pion tagged in the fragmentation region of the polarized proton does not depend on the centre of mass energy in the limits of its large values. The lowest order radiative corrections to the polarized and unpolarized contributions to the differential cross sections are calculated in the leading logarithmic approximation. In general, a coefficient of logarithm of the ratio of cms energy to the pion mass depends on the transversal momentum of the pion. This ratio of the lowest order contribution to the asymmetry may be interpreted as the partial contribution to the odderon intercept. The ratio of the relevant contributions in the unpolarized case can be associated with the partial contribution to the pomeron intercept. The numerical results given for the model describe the jet as heavy fermion decay fragments.

E/Bdecomposition of finite pixelized CMB maps

Separation of the E and B components of a microwave background polarization map or a weak lensing map is an essential step in extracting science from it, but when the map covers only part of the sky and/or is pixelized, this decomposition cannot be done perfectly. We present a method for decomposing an arbitrary sky map into a sum of three orthogonal components that we term ``pure E,'' ``pure B,'' and ``ambiguous.'' The fluctuations in the pure E and B maps are due only to the E and B power spectra, respectively, whereas the source of those in the ambiguous map is completely indeterminate. This method is useful both for providing intuition for experimental design and for analyzing data sets in practice. We show how to find orthonormal bases for all three components in terms of bi-Laplacian eigenfunctions, thus providing a type of polarized signal-to-noise eigenmodes that simultaneously separate both angular scale and polarization type. The number of pure and ambiguous modes probing a characteristic angular scale \ensuremath{\theta} scales as the map area over ${\ensuremath{\theta}}^{2}$ and as the map boundary length over \ensuremath{\theta}, respectively. This implies that fairly round maps (with short perimeters for a given area) will yield the most efficient $E/B$ decomposition and also that the fraction of the information lost to ambiguous modes grows towards larger angular scales. For real-world data analysis, we present a simple matrix eigenvalue method for calculating nearly pure E and B modes in pixelized maps. We find that the dominant source of leakage between E and B is aliasing of small-scale power caused by the pixelization, essentially since derivatives are involved. This problem can be eliminated by heavily oversampling the map, but is exacerbated by the fact that the E power spectrum is expected to be much larger than the B power spectrum and by the extremely blue power spectrum that cosmic microwave background polarization is expected to have. We found that a factor of 2 to 3 more pixels are needed in a polarization map to achieve the same level of contamination by aliased power than in a temperature map. Oversampling is therefore much more important for the polarized case than for the unpolarized case, which should be reflected in experimental design.

Structure of radiative interferences andg=2for vector mesons

The result of Burnett and Kroll (BK) states that for radiative decays, the interference of $O({\ensuremath{\omega}}^{\ensuremath{-}1})$ in the photon energy $\ensuremath{\omega}$ vanishes after the sum over polarizations of the involved particles. Using radiative decays of vector mesons, we show that if the vector meson is polarized, the $O({\ensuremath{\omega}}^{\ensuremath{-}1})$ terms are null only for the canonical value of the magnetic dipole moment of the vector meson, namely, $\mathbf{g}=2$ in Bohr magneton units. A subtle cancellation of all $O({\ensuremath{\omega}}^{\ensuremath{-}1})$ terms happens when summing over all polarizations to recover the Burnett-Kroll result. We also show the source of these terms and the corresponding cancellation for the unpolarized case and exhibit a global structure that can make them individually vanish in a particular kinematical region.

Small-xbehavior of the singlet polarized structure functiong2in the double logarithmic approximation

The small-$x$ behavior of the singlet contributions to the polarized structure function ${g}_{2}{(x,Q}^{2})$ is calculated in the double-logarithmic approximation of perturbative QCD. The dominant contribution is due to the gluons which, in contrast with the unpolarized case, mix with the fermions also in the small-$x$ domain. We find a powerlike growth in $1/x$ in the odd-signature parts of the amplitude with the same power as in the singlet function ${g}_{1}{(x,Q}^{2})$ at $x\ensuremath{\ll}1.$

Polarized version of the CCFM equation for gluons

A derivation for a polarized CCFM evolution equation which is suitable to describe the scaling behavior of the the unintegrated polarized gluon density is given. We discuss the properties of this polarized CCFM equation and compare it to the standard CCFM equation in the unpolarized case.

Next-to-leading order QCD analysis of deeply virtual Compton scattering amplitudes

We present a next-to-leading order (NLO) QCD analysis of unpolarized and polarized deeply virtual Compton scattering (DVCS) amplitudes, for two different input scenarios, in the $\bar{MS}$ scheme. We illustrate and discuss the size of the NLO effects and the behavior of the amplitudes in skewedness, $\zeta$, and photon virtuality, $Q^2$. In the unpolarized case, at fixed $Q^2$, we find a remarkable effective power-law behaviour in $\zeta$, akin to Regge factorization, over several orders of magnitude in $\zeta$. We also quantify the ratio of real to imaginary parts of the DVCS amplitudes and their sensitivity to changes of the factorization scale.