Longitudinal Asymmetry Research Articles

Longitudinal double-spin asymmetry and cross section for inclusive neutral pion production at midrapidity in polarized proton collisions ats=200 GeV

We report a measurement of the longitudinal double-spin asymmetry A_LL and the differential cross section for inclusive Pi0 production at midrapidity in polarized proton collisions at sqrt(s) = 200 GeV. The cross section was measured over a transverse momentum range of 1 < p_T < 17 GeV/c and found to be in good agreement with a next-to-leading order perturbative QCD calculation. The longitudinal double-spin asymmetry was measured in the range of 3.7 < p_T < 11 GeV/c and excludes a maximal positive gluon polarization in the proton. The mean transverse momentum fraction of Pi0's in their parent jets was found to be around 0.7 for electromagnetically triggered events.

Monte Carlo simulation of THz radiation detection in GaAs n+ nn+ diodes with inhomogeneously doped n-region

A proper profile of nonuniform doping of GaAs n+ nn+ structure to reach the maximum detection sensitivity is proposed. It is shown that the main role in formation of longitudinal transport asymmetry and THz radiation detection is played by optical phonon emission process. It is found that the detection current independs of frequency in spectral range 0.02–1 THz, reaches maximum near 2.2 THz (10 and 80 K) or 3 THz (300 K) and then becomes to decrease due to the inertia of optical phonon emission process.

Asymmetrical flow effect applied to pumping performance of simple duct channel

In this study, a simple pumping system, composed of a piezoelectric buzzer imbedded in a duct channel, was used to study the effect of longitudinal flow asymmetry on pumping performance in view of its importance in the design of valveless pumping systems, in spite of the fact that this has rarely been addressed before. The physical features of flow asymmetry caused by the Liebau effect, during the asymmetrical or asynchronous vibration of a buzzer in the course of space and time, can generate net mass flow and result in a pumping performance that has been confirmed experimentally. The degree of transversal asymmetry of a buzzer in space and time positively correlates with longitudinal asymmetry for pumping performance. This principle should be useful when designing valveless pumping systems, especially for applications for fields like bio-medicine, bio-chemistry, and environmental testing. Since this pumping system uses simple components, no moving valve structure will not damage any biological particles in a transmission process.

O(α s ) corrections to the polar angle dependence of the longitudinal spin–spin correlation asymmetry in $e^{+}e^{-}\to q\bar{q}$

We provide analytical results for the $O(\alpha_s)$ corrections to the polar angle dependence of the longitudinal spin-spin correlation asymmetry in $e^+e^-\to q\bar q$. For top quark pair production the $O(\alpha_s)$ corrections to the longitudinal spin-spin asymmetry are strongly polar angle dependent and can amount up to $4\%$ in the $q^2$-range from above $t\bar t$ threshold up to $\sqrt{q^2}=1000$ GeV. The $O(\alpha_s)$ radiative corrections to the correlation asymmetry are below $1\%$ in the forward direction where the cross section is largest. In the $e^+e^-\to b\bar b$ case the $O(\alpha_s)$ corrections reduce the asymmetry value from its $m_b=0$ value of $-100\%$ to approximately $-96\%$ for $q^2$-values around the $Z$ peak and are practically independent of the value of the polar angle theta. This reduction can be traced to finite anomalous contributions from residual mass effects which survive the $m_b\to 0$ limit. We discuss the role of the anomalous contributions and the pattern of how they contribute to spin-flip and non-flip terms.

Modelling the Longitudinal Asymmetry in Sunspot Emergence: The Role of the Wilson Depression

The distributions of sunspot longitude at first appearance and at disappearance display an east-west asymmetry that results from a reduction in visibility as one moves from disk centre to the limb. To first order, this is explicable in terms of simple geometrical foreshortening. However, the centre-to-limb visibility variation is much larger than that predicted by foreshortening. Sunspot visibility is also known to be affected by the Wilson effect: the apparent dish shape of the sunspot photosphere caused by the temperature-dependent variation of the geometrical position of the tau=1 layer. In this article we investigate the role of the Wilson effect on the sunspot appearance distributions, deducing a mean depth for the umbral tau=1 layer of 500 to 1500 km. This is based on the comparison of observations of sunspot longitude distribution and Monte Carlo simulations of sunspot appearance using different models for spot growth rate, growth time and depth of Wilson depression.

Recent Longitudinal Spin Asymmetry Measurements for Inclusive Jet Production at STAR

We present measurements of the longitudinal spin asymmetry, A LL , for the inclusive jet signal at STAR. The data presented here are mid-rapidity jets in the transverse momentum range of 5 < p T < 35 GeV/c and come from polarized proton-proton collisions at center of mass energies of s = 200 GeV . We compare our measured A LL values to predictions derived from various parameterizations of the polarized gluon distribution function. The results are shown to provide significant constraints for allowable gluon parameterizations within the measurement's kinematic Bjorken-x range of 0.03 < x < 0.3.

Analysis of the rare semileptonic decays ofBstof0(980)andK0*(1430)scalar mesons in QCD sum rules

We investigate the rare semileptonic decays ${B}_{s}\ensuremath{\rightarrow}[{f}_{0}(980),{K}_{0}^{*}(1430)]{l}^{+}{l}^{\ensuremath{-}}$, ($l=e$, $\ensuremath{\mu}$, $\ensuremath{\tau}$), and ${B}_{s}\ensuremath{\rightarrow}[{f}_{0}(980),{K}_{0}^{*}(1430)]\ensuremath{\nu}\overline{\ensuremath{\nu}}$ in the framework of the three-point QCD sum rules. These decays are important to study because the ${f}_{0}(980)$ and ${K}_{0}^{*}(1430)$ are the scalar mesons with total spin 0 and even parity and the quark content of them are still controversial in high energy physics. These rare decays occur at loop level by electroweak penguin and weak box diagrams in the standard model via the flavor changing neutral current transitions of $b\ensuremath{\rightarrow}d$, $s$, and not allowed by tree level. Considering the effective contributions of the nonperturbative parts of the correlation function, we calculate the relevant form factors of these transitions. The branching fractions and longitudinal lepton polarization asymmetry are also investigated.

The 27-Day and 22-Year Cycles in Solar and Geomagnetic Activity

We study the evolution of the longitudinal asymmetry in solar activity through the wave packet technique applied to the period domain of 25 – 31 days (centered at the 27-day solar rotation period) for the sunspot number and geomagnetic aa index. We observe the occurrence of alternating smaller and larger amplitudes of the 11-year cycle, resulting in a 22-year periodicity in the 27-day signal. The evolution of the 22-year cycle shows a change of regime around the year 1912 when the 22-year period disappears from the sunspot number series and appears in the aa index. Other changes, such as a change in the correlation between solar and geomagnetic activity, took place at the same time. Splitting the 27-day frequency domain of aa index shows an 11-year cycle for higher frequencies and a pure22-year cycle for lower frequencies, which we attribute to higher latitude coronal holes. This evidence is particularly clear after 1940, which is another benchmark in the evolution of the aa index. We discuss briefly the mechanisms that could account for the observed features of the 22-year cycle evolution.

Bs→K(*)−K(*)+,K(*)−π+,K(*)−ρ+decays in R-parity violating supersymmetry

With the first measurements of the branching ratios and the direct CP asymmetries of B{sub s}{yields}K{sup -}K{sup +}, K{sup -}{pi}{sup +} decays by the CDF collaboration, we constrain the relevant parameter space of the minimal supersymmetric standard model with R-parity violation. Using the constrained R-parity violating couplings, we further examine their possible effects in B{sub s}{yields}K{sup -}*{pi}{sup +}, K{sup (*)-}{rho}{sup +} and K{sup (*){+-}}K{sup (*){+-}} decays. We find that some branching ratios and CP asymmetries are very sensitive to the R-parity violating couplings. The direct longitudinal CP asymmetries of tree-dominated process B{sub s}{yields}K*{sup -}{rho}{sup +} could be enlarged to {approx}70% and the longitudinal polarizations of B{sub s}{yields}K*{sup -}K*{sup +}, K*{sup -}{rho}{sup +} decays could be suppressed very much by the squark exchange couplings. Near future experiments at CERN LHC can test these predictions and shrink/reveal the parameter spaces of RPV SUSY.

Probing the spin structure of the proton via heavy flavor and hyperon measurements at PHENIX

We describe the latest PHENIX results on double longitudinal spin asymmetry (ALL) and single transverse spin asymmetry (AN) of open charm production, as well as the results of spin transfer to hyperons. With transversely and longitudinally polarized proton beams at the RHIC, we can measure both ALL and AN. The PHENIX experiment collected 10 pb−1 (beam polarization ∼60%) and 0.35 pb−1 (beam polarization ∼35%) data from year 2006 and 2003 runs, respectively. In this paper, the preliminary results of ALL and AN in open charm production at forward rapidities from year 2006 runs are shown. In addition, the method to extract the spin transfer to from PHENIX data, and the distribution of spin transfer with pT from 2003 run data is also presented in this paper.

Gluon polarisation in the nucleon and longitudinal double spin asymmetries from open charm muoproduction

The gluon polarisation in the nucleon has been determined by detecting charm production via D0 meson decay to charged K and π in polarised muon scattering off a longitudinally polarised deuteron target. The data were taken by the COMPASS Collaboration at CERN between 2002 and 2006 and correspond to an integrated luminosity of 2.8 fb−1. The dominant underlying process of charm production is the photon–gluon fusion to a cc¯ pair. A leading order QCD approach gives an average gluon polarisation of 〈Δg/g〉x=−0.49±0.27(stat)±0.11(syst) at a scale μ2≈13 (GeV/c)2 and at an average gluon momentum fraction 〈x〉≈0.11. The longitudinal cross-section asymmetry for D0 production is presented in bins of the transverse momentum and the energy of the D0 meson.

B→K0*(1430)l+l−decays in supersymmetric theories

The weak decays of $B \to K^{\ast}_0(1430) l^{+} l^{-}$ ($l=\mu, \tau$) are investigated in Minimal Supersymmetric Standard Model (MSSM) and also in Supersymmetric (SUSY) SO(10) Grand Unified Models. Neutral Higgs bosons are the point of main focus in MSSM because they make quite a large contribution in exclusive $B \to X_{s} l^{+} l^{-}$ decays at large $\tan{\beta}$ regions of parameter space of SUSY models, as part of SUSY contributions is proportional to $\tan^{3}{\beta}$. The analysis of decay rate, forward-backward asymmetries and lepton polarization asymmetries in $B \to K^{\ast}_0(1430) l^{+} l^{-}$ show that the values of these physical observables are greatly modified by the effects of neutral Higgs bosons. In SUSY SO(10) GUT model, the new physics contribution comes from the operators which are induced by the neutral Higgs boson penguins and also from the operators with chirality opposite to that of the corresponding Standard Model (SM) operators. SUSY SO(10) effects show up only in the decay $B \to K^{\ast}_0 \mu^{+} \mu^{-}$ where the transverse lepton polarization asymmetries deviate significantly from the SM value while the effects in the decay rate, forward-backward asymmetries, the longitudinal and normal lepton polarization asymmetries are very mild. The transverse lepton polarization asymmetry is almost zero in SM and in MSSM model, whereas it can reach to -0.3 in SUSY SO(10) GUT model which could be seen at the future colliders; hence this asymmetry observable can be used to discriminate between different SUSY models.

A CATALOG OF X-RAY POINT SOURCES FROM TWO MEGASECONDS OF CHANDRA OBSERVATIONS OF THE GALACTIC CENTER

We present a catalog of 9017 X-ray sources identified in Chandra observations of a 2 by 0.8 degree field around the Galactic center. We increase the number of known X-ray sources in the region by a factor of 2.5. The catalog incorporates all of the ACIS-I observations as of 2007 August, which total 2.25 Msec of exposure. At the distance to the Galactic center (8 kpc), we are sensitive to sources with luminosities >4e32 erg/s (0.5-8.0 keV; 90% confidence) over an area of one square degree, and up to an order of magnitude more sensitive in the deepest exposure (1.0 Msec) around Sgr A*. The positions of 60% of our sources are accurate to <1 (95% confidence), and 20% have positions accurate to <0.5. We search for variable sources, and find that 3% exhibit flux variations within an observation, 10% exhibit variations from observation-to-observation. We also find one source, CXOUGC J174622.7-285218, with a periodic 1745 s signal (1.4% chance probability), which is probably a magnetically-accreting cataclysmic variable. We compare the spatial distribution of X-ray sources to a model for the stellar distribution, and find 2.8 sigma evidence for excesses in the numbers of X-ray sources in the region of recent star formation encompassed by the Arches, Quintuplet, and Galactic center star clusters. These excess sources are also seen in the luminosity distribution of the X-ray sources, which is flatter near the Arches and Quintuplet than elsewhere in the field. These excess point sources, along with a similar longitudinal asymmetry in the distribution of diffuse iron emission that has been reported by other authors, probably have their origin in the young stars that are prominent at l~0.1 degree.

Rare decaysBs→l+l−andB→Kl+l−in the topcolor-assisted technicolor model

We examine the rare decays ${B}_{s}\ensuremath{\rightarrow}{l}^{+}{l}^{\ensuremath{-}}$ and $B\ensuremath{\rightarrow}K{l}^{+}{l}^{\ensuremath{-}}$ in the framework of the topcolor-assisted technicolor ($TC2$) model. The contributions of the new particles predicted by this model to these rare decay processes are evaluated. We find that the values of their branching ratios are larger than the standard model predictions by one order of magnitude in wide range of the parameter space. The longitudinal polarization asymmetry of leptons in ${B}_{s}\ensuremath{\rightarrow}{l}^{+}{l}^{\ensuremath{-}}$ can approach $\mathcal{O}({10}^{\ensuremath{-}2})$. The forward-backward asymmetry of leptons in $B\ensuremath{\rightarrow}K{l}^{+}{l}^{\ensuremath{-}}$ is not large enough to be measured in future experiments. We also give some discussions about the branching ratios and the asymmetry observables related to these rare decay processes in the littlest Higgs model with T-parity.

Exclusive semileptonic decays ofΛb→Λl+l−in supersymmetric theories

The weak decays of ${\ensuremath{\Lambda}}_{b}\ensuremath{\rightarrow}\ensuremath{\Lambda}{l}^{+}{l}^{\ensuremath{-}}$ ($l=e$, $\ensuremath{\mu}$) are investigated in the minimal supersymmetric standard model (MSSM) and also in supersymmetric (SUSY) SO(10) grand unified models. In the MSSM special attention is paid to the neutral Higgs bosons (NHBs) as they make quite a large contribution in exclusive $B\ensuremath{\rightarrow}{X}_{s}{l}^{+}{l}^{\ensuremath{-}}$ decays at large $\mathrm{tan}\ensuremath{\beta}$ regions of parameter space of SUSY models, since part of SUSY contributions is proportional to ${tan}^{3}\ensuremath{\beta}$. The analysis of decay rate, forward-backward asymmetries, lepton polarization asymmetries, and the polarization asymmetries of the $\ensuremath{\Lambda}$ baryon in ${\ensuremath{\Lambda}}_{b}\ensuremath{\rightarrow}\ensuremath{\Lambda}{l}^{+}{l}^{\ensuremath{-}}$ show that the values of these physical observables are greatly modified by the effects of NHBs. In the SUSY SO(10) grand unified theory model, the new physics contribution comes from the operators which are induced by the NHBs' penguins and also from the operators having chirality opposite to that of the corresponding standard model (SM) operators. SUSY SO(10) effects show up only in the decay ${\ensuremath{\Lambda}}_{b}\ensuremath{\rightarrow}\ensuremath{\Lambda}+{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ where the longitudinal and transverse lepton polarization asymmetries deviate significantly from the SM value while the effects in the decay rate, forward-backward asymmetries, and polarization asymmetries of final state $\ensuremath{\Lambda}$ baryon are very mild. The transverse lepton polarization asymmetry in ${\ensuremath{\Lambda}}_{b}\ensuremath{\rightarrow}\ensuremath{\Lambda}+{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ is almost zero in the SM and in the MSSM model. However, it can reach to $\ensuremath{-}0.1$ in the SUSY SO(10) grand unified theory model and could be seen at the future colliders; hence this asymmetry observable will provide us useful information to probe new physics and discriminate between different models.

Longitudinal parity-violating asymmetry in hadronic decays of weak bosons in polarized proton collisions

We investigate the possible measurement of parity-violating spin asymmetries in jet pair production in proton-proton collisions at the Brookhaven Relativistic Heavy Ion Collider (RHIC), with the goal to constrain longitudinally polarized quark and antiquark distribution functions. A measurable asymmetry could be observed in the vicinity of the massive weak $W$ boson resonance, where the parity-violating signal appears above the parity-conserving background and is enhanced by interference of the strong and electroweak production amplitudes. We discuss the potential for such measurements, perhaps the first opportunity to measure a parity-violating asymmetry in proton-proton collisions at RHIC. Sensitivity of this measurement to the polarization of down-type antiquarks is demonstrated.

Intrinsic parton motion soft mechanisms and the longitudinal spin asymmetry ALL in high energy pp → πX

The longitudinal double spin asymmetry ALL in the reaction pp → πX has been measured at RHIC with extremely interesting consequences. If the gluon polarization in a proton were as big as needed to resolve the famous ‘spin crisis’ then ALL would be large and positive. Latest RHIC results indicate that ALL is small and disfavour large positive values of the gluon polarization. We examine whether the soft mechanisms (Collins, Sivers, Boer–Mulders), essential for generating transverse single spin asymmetries, have any significant influence on ALL, and whether they could alter the conclusion that the gluon polarization is necessarily small. It turns out that the contribution from these effects is essentially negligible.

COMPASS Spin Dependent Longitudinal Asymmetries on Deuteron Target

The COMPASS results of double spin longitudinal asymmetries obtained in the inclusive and semi-inclusive inelastic scattering of a polarized 160 GeV/ c muon beam off a polarized deuteron target are presented. The data were collected in the years 2002-2004.

Mesozoic and Cenozoic vertical movements in the Atlas system (Algeria, Morocco, Tunisia): An overview

The E–W trending Atlas System of Maghreb consists of weakly shortened, intra-continental fold belts associated with plateau areas (“Mesetas”), extending between the south-westernmost branch of the Mediterranean Alpine Belt (Rif-Tell) and the Sahara Platform. Although the Atlas system has been erected contemporaneously from Morocco to Algeria and Tunisia during the Middle Eocene to Recent, it displays a conspicuous longitudinal asymmetry, with i) Paleozoic outcrops restricted to its western part; ii) highest elevation occurring in the west, both in the Atlas System and its foreland (Anti-Atlas); iii) low elevation corridors (e.g. Hodna) and depressed foreland (Tunisian Chotts and Sahel area) in the east. We analyse the origin of these striking contrasts in relation with i) the Variscan heritage; ii) crustal vertical movements during the Mesozoic; iii) crustal shortening during the Cenozoic and finally, iv) the occurrence of a Miocene–Quaternary hot mantle anomaly in the west. The Maghreb lithosphere was affected by the Variscan orogeny, and thus thickened only in its western part. During the Late Permian–Triassic, a paleo-high formed in the west between the Central Atlantic and Alpine Tethys rift systems, giving birth to the emergent/poorly subsident West Moroccan Arch. During the late Middle Jurassic–Early Cretaceous, Morocco and western Algeria were dominantly emergent whereas rifting lasted on in eastern Algeria and Tunisia. We ascribe the uplift of the western regions to thermal doming, consistent with the Late Jurassic and Barremian gabbroic magmatism observed there. After the widespread transgression of the high stand Cenomanian–Turonian seas, the inversion of the Atlas System began during the Senonian as a consequence of the Africa–Eurasia convergence. Erosion affected three ENE-trending uplifted areas of NW Africa, which we consider as lithospheric anticlines related to the incipient Africa–Europe convergence. In contrast, in eastern Algeria and Tunisia a NW-trending rift system developed contemporaneously (Sirt rifting), normal to the general trend of the Atlas System. The general inversion and orogenesis of the Atlas System occurred during two distinct episodes, Middle–Late Eocene–Oligocene and Late Miocene–Pliocene, respectively, whereas during the intervening period, the Africa–Europe convergence was mainly accommodated in the Rif-Tell system. Inversion tectonics and crustal thickening may account for the moderate uplift of the eastern Atlas System, not for the high elevation of the western mountain ranges (Middle Atlas, High Atlas, Anti-Atlas). In line with previous authors, we ascribe part of the recent uplift of the latter regions to the occurrence of a NE-trending, high-temperature mantle anomaly, here labelled the Moroccan Hot Line (MHL), which is also marked by a strip of late Miocene–Quaternary alkaline magmatism and significant seismicity.

Gaugino-pair production in polarized and unpolarized hadron collisions

We present an exploratory study of gaugino-pair production in polarized and unpolarized hadron collisions, focusing on the correlation of beam polarization and gaugino/Higgsino mixing in the general minimal supersymmetric standard model. Helicity-dependent cross sections induced by neutral and charged electroweak currents and squark exchanges are computed analytically in terms of generalized charges, defined similarly for chargino-pair, neutralino-chargino associated, and neutralino-pair production. Our results confirm and extend those obtained previously for negligible Yukawa couplings and nonmixing squarks. Assuming that the lightest chargino mass is known, we show numerically that measurements of the longitudinal single-spin asymmetry at the existing polarized $pp$ collider RHIC and at possible polarization upgrades of the Tevatron or the LHC would allow for a determination of the gaugino/Higgsino fractions of charginos and neutralinos. The theoretical uncertainty coming from factorization scale and squark mass variations and the expected experimental error on the lightest chargino mass is generally smaller than the one induced by the polarized parton densities, so that more information on the latter would considerably improve on the analysis.