Longitudinal Asymmetry Research Articles

Measurement of Longitudinal Spin Asymmetries From W → e Boson Decay in Polarized pp Collisions at √s = 500 GeV at RHIC-PHENIX

We report the measurement of the parity violating single spin asymmetries for inclusive high transverse momentum electrons and positrons in polarized p + p collisions at a center of mass energy of √s = 500 GeV with the PHENIX detector at RHIC. These electrons are attributed to the decay of W± and Z0 bosons, and measured production cross section is consistent with the expectations. The W production is confirmed for the first time in p + p collisions. Its spin asymmetry in the polarized p + p collisions is a important probe for the quark flavor decomposition of the proton spin.

Gluon polarization and jet production at STAR

At RHIC kinematics, polarized jet hadroproduction is dominated by gg and qg scattering, making the jet longitudinal double spin asymmetry, ALL, sensitive to gluon polarization in the nucleon. I will present STAR results of ALL from inclusive jet measurements for the RHIC 2005 and 2006 runs totalling 2 pb−1 of integrated luminosity with 50% average beam polarization and 5.4 pb−1 of integrated luminosity with 60% average beam polarization, respectively, at center-of-mass energy 200 GeV. I will also discuss the current status of the analysis of data from the 2009 run, which collected a much larger sample (25 pb−1 with 56% polarization) at 200 GeV. The results are compared with theoretical calculations of ALL based on various models of the polarized gluon distribution function in the nucleon. The STAR data place significant constraints on allowed theoretical models.

Dijet Cross Section and Longitudinal Double Spin Asymmetry Measurements in Polarized Proton-proton Collisions at √s = 200 GeV at STAR

These proceedings show the preliminary results of the dijet cross sections and the dijet longitudinal double spin asymmetries \U0001d49cLL in polarized proton-proton collisions at √s = 200 GeV at the mid-rapidity |η) ≤ 0.8. The integrated luminosity of 5.39 pb−1 collected during RHIC Run-6 was used in the measurements. The preliminary results are presented as functions of the dijet invariant mass Mjj. The dijet cross sections are in agreement with next-to-leading-order pQCD predictions. The \U0001d49cLL is compared with theoretical predictions based on various parameterizations of polarized parton distributions of the proton. Projected precision of data analyzed to date from Run-9 are shown.

π0 Double Longitudinal Helicity Asymmetry Measurements at PHENIX

Measurement of the gluon's contribution to the proton spin, ΔG, is an important component of the RHIC spin program. One particular avenue for constraining ΔG is through the π0 double longitudinal helicity asymmetry, ALL. The large p + p → π0 cross section coupled with the high resolution of the PHENIX EM-Calorimeter make this an attractive measurement. After some discussion of the measurement, existing PHENIX π0 ALL results at center of mass energies √s = 62.4 and 200 GeV are presented, including new 200 GeV results from the RHIC run ending in 2009. Projections for future 500 GeV results are also shown.

ΔG and ALL measurement in π± production at RHIC p-p collider

The measurement of double longitudinal asymmetry in inclusive hadron production in polarized proton-proton collisions, ALL, provides insight into the gluon spin contribution to the total proton spin . One particularly interesting channel is through charged pions as it gives sensitivity to the sign of ΔG. A brief overview on what can be learned from this measurement and analysis methods will be provided. Recent preliminary results from RHIC in p+p collisions at √s = 200 GeV are shown and discussed.

Accessing Gluon Polarization in the Proton with Direct Photons at PHENIX

Direct photon production in polarized pp collisions serves as an excellent probe of the spin structure of the proton. Gluon-quark scattering, g + q → γ + q, dominates direct photon production for p + p collisions. This channel is theoretically clean as it requires no fragmentation function for the photon. In addition, the double longitudinal asymmetry ALLis directly proportional to the quark and gluon polarizations, giving access to both the magnitude and sign of the polarized gluon distribution since the polarized quark distributions are known from polarized DIS. The status of the direct photon cross section measurement and ALLfor center of mass energies 200 and 500 GeV at midrapidity (|η| < 0.35) will be presented.

Cross Section and Parity-Violating Spin Asymmetries ofW±Boson Production in Polarizedp+pCollisions ats=500 GeV

Large parity-violating longitudinal single-spin asymmetries A(L)(e+) = -0.86(-0.14) (+0.30) and A(L)(e-) = 0.88(-0.71) (+0.12) are observed for inclusive high transverse momentum electrons and positrons in polarized p+p collisions at a center-of-mass energy of sqrt[s] = 500 GeV with the PHENIX detector at RHIC. These e± come mainly from the decay of W± and Z0 bosons, and their asymmetries directly demonstrate parity violation in the couplings of the W± to the light quarks. The observed electron and positron yields were used to estimate W± boson production cross sections for the e± channels of σ(pp → W+ X) × BR(W+ → e+ ν(e)) = 144.1 ± 21.2(stat)(-10.3) (+3.4) (syst) ± 21.6(norm) pb, and σ(pp → W- X) × BR(W- → e- ν[over ¯](e)) = 31.7 ± 12.1(stat)(-8.2) (+10.1) (syst) ± 4.8(norm) pb.

Rare semileptonicBsdecays toηandη′mesons in QCD

We analyze the rare semileptonic $B_s \to (\eta, \eta') l^+ l^-$, $(l=e, \mu, \tau)$ and $B_s \to (\eta, \eta') \nu \bar{\nu}$ transitions probing the $\bar s s$ content of the $\eta$ and $\eta'$ mesons via three--point QCD sum rules. We calculate responsible form factors for these transitions in full theory. Using the obtained form factors, we also estimate the related branching fractions and longitudinal lepton polarization asymmetries. Our results are in a good consistency with the predictions of the other existing nonperturbative approaches.

Conoscopic evidence of the UV light-induced flexoelectric effect in homeotropic layers of nematic liquid crystal doped with azobenzene derivatives

A digitalized version of the standard method of conoscopy was employed to register the bend deformation of molecular orientation in homeotropic nematic layers caused by an in-plane applied DC electric field, and influenced by UV light illumination. Two guest-host systems prepared by mixing of a nematic liquid crystal and an azobenzene-containing photochromic liquid crystalline material featuring a longitudinal molecular asymmetry, were studied. Upon continuous UV irradiation, a photo-isomerization of the photochromic molecules occurs resulting in an enhanced flexoelectric response of the guest-host mixtures. The dependence of the photoflexoeffect on the field strength and UV light intensity was also examined.

Parity-violating asymmetry in theHe3(n⃗,p)H3reaction

The longitudinal asymmetry induced by parity-violating (PV) components in the nucleon-nucleon potential is studied in the charge-exchange reaction $^{3}\mathrm{He}$($\mathrm{nP\vec},p$)$^{3}\mathrm{H}$ at vanishing incident neutron energies. An expression for the PV observable is derived in terms of $T$-matrix elements for transitions from the ${}^{2S+1}{L}_{J}={}^{1}{S}_{0}$ and ${}^{3}{S}_{1}$ states in the incoming $n$-$^{3}\mathrm{He}$ channel to states with $J=0$ and 1 in the outgoing $p$-$^{3}\mathrm{H}$ channel. The $T$-matrix elements involving PV transitions are obtained in first-order perturbation theory in the hadronic weak-interaction potential, while those connecting states of the same parity are derived from solutions of the strong-interaction Hamiltonian with the hyperspherical-harmonics method. The coupled-channel nature of the scattering problem is fully accounted for. Results are obtained corresponding to realistic or chiral two- and three-nucleon strong-interaction potentials in combination with either the DDH or pionless EFT model for the weak-interaction potential. The asymmetries, predicted with PV pion and vector-meson coupling constants corresponding (essentially) to the DDH ``best values'' set, range from --9.44 to --2.48 in units of ${10}^{\ensuremath{-}8}$, depending on the input strong-interaction Hamiltonian. This large model dependence is a consequence of cancellations between long-range (pion) and short-range (vector-meson) contributions and is of course sensitive to the assumed values for the PV coupling constants.

Azimuthal asymmetries of charged hadrons produced by high-energy muons scattered off longitudinally polarised deuterons

Azimuthal asymmetries in semi-inclusive production of positive (h^+) and negative hadrons (h^-) have been measured by scattering 160 GeV muons off longitudinally polarised deuterons at CERN. The asymmetries were decomposed in several terms according to their expected modulation in the azimuthal angle phi of the outgoing hadron. Each term receives contributions from one or several spin and transverse-momentum-dependent parton distribution and fragmentation functions. The amplitudes of all phi-modulation terms of the hadron asymmetries integrated over the kinematic variables are found to be consistent with zero within statistical errors, while the constant terms are nonzero and equal for h^+ and h^- within the statistical errors. The dependencies of the phi-modulated terms versus the Bjorken momentum fraction x, the hadron fractional momentum z, and the hadron transverse momentum p_h^T were studied. The x dependence of the constant terms for both positive and negative hadrons is in agreement with the longitudinal double-spin hadron asymmetries, measured in semi-inclusive deep-inelastic scattering. The x dependence of the sin phi-modulation term is less pronounced than that in the corresponding HERMES data. All other dependencies of the phi-modulation amplitudes are consistent with zero within the statistical errors.

Effect of scanner in asymmetry studies using diffusion tensor imaging

The purpose of this study was to evaluate the effects of longitudinal drift in scanner hardware, inter-scanner variability (bias) and scanner upgrade on asymmetries of diffusion properties using longitudinal data obtained on two scanners of the exact same model at one institution. A total of 224 normal subjects (63 females and 161 males) were included in this study. Each subject was scanned twice, at an interval of about 1year (mean interval=1.0±0.11years, range=0.6–1.3years), using two 3.0-T scanners of the exact same model. Both scanners were simultaneously upgraded during the study period (159 subjects underwent a follow-up scan before upgrade, and the remaining 65 subjects underwent a follow-up scan after upgrade). The subjects were divided into 4 groups according to the combination of scanners used. With the use of tract-based spatial statistics (TBSS), we investigated the effects of scanner drift and inter-scanner variability (bias) on asymmetries of fractional anisotropy (FA) and mean diffusivity (MD). We also investigated the effect of scanner upgrade on FA and MD asymmetries. The voxel-wise analyses revealed a number of regions with significant longitudinal changes in FA and MD asymmetries in the groups where baseline and follow-up images were obtained on different scanners. Even with scanners of the exact same model, inter-scanner variability (bias) significantly affected FA and MD asymmetries, which were relatively stable within the same scanner. Scanner upgrade had a small effect on FA and MD asymmetries. The results indicate that the use of multiple scanners increases variability of DTI asymmetry measurements, and can affect the results of cross-sectional and especially longitudinal DTI asymmetry studies.

Single production of sleptons with polarized tops at the large hadron collider

We study the production of a single charged slepton in association with a top quark in a R-parity violating supersymmetric model with lepton number violating interactions at the Large Hadron Collider. We find that the longitudinal polarization asymmetry of the top quark in such a production mode is significantly different from that in the production of a single top or a top pair in the Standard Model for a wide range of slepton masses. Our signal analysis shows that the top-slepton associate production leads to final states with distinct kinematic signatures, which differ from the Standard Model background.

Leading-order determination of the gluon polarization from high-p T hadron electroproduction

Longitudinal double-spin asymmetries of charged hadrons with high transverse momentum $p_T$ have been measured in electroproduction using the \hermes\ detector at \hera. Processes involving gluons in the nucleon have been enhanced relative to others by selecting hadrons with $p_T$ typically above 1 GeV. In this kinematic domain the gluon polarization has been extracted in leading order making use of the model embedded in the Monte Carlo Generator \Pythia\ 6.2. The gluon polarization obtained from single inclusive hadrons in the $p_T$ range 1 GeV $< p_T <$ 2.5 GeV using a deuterium target is $\frac{\Delta g}{g}(\langle x\rangle, \langle \mu^2\rangle)=0.049\pm 0.034 (stat)\pm 0.010 (sys\textrm{-}exp)^{+0.126}_{-0.099}(sys\textrm{-}models)$ at a scale $\la\mu^2\ra=1.35~{\rm GeV}^2$ and $\langle x\rangle = 0.22$. For different final states and kinematic domains, consistent values of \DGG\ have been found within statistical uncertainties using hydrogen and deuterium targets.

Exclusive rare Bs → (K, η, η′)ℓ+ℓ− decays in the light-front quark model

Using the light-front quark model, we calculate the transition form factors, decay rates and longitudinal lepton polarization asymmetries for the exclusive rare ) (ℓ = e, μ, τ) decays within the standard model, taking into account the η − η′ mixing angle. For the mixing angle θ = −20° (−10°) in the octet-singlet basis, we obtain , BR(Bs → ημ+μ−) = 1.5(2.4) × 10−7, BR(Bs → ητ+τ−) = 3.8(5.8) × 10−8, , BR(Bs → η′μ+μ−) = 2.4(1.8) × 10−7 and BR(Bs → η′τ+τ−) = 3.4(2.6) × 10−8, respectively. The branching ratios for the decays are at least an order of magnitude smaller than those for the decays. The averaged values of the lepton polarization asymmetries for Bs → (K, η(′))ℓ+ℓ− are obtained as , ⟨PKL⟩τ = −0.24, ⟨PηL⟩τ = −0.20 and , respectively.

Helicity parton distributions from spin asymmetries inW-boson production at RHIC

We present a next-to-leading order QCD calculation of the cross section and longitudinal spin asymmetry in single-inclusive charged-lepton production, pp -> l X, at RHIC, where the lepton is produced in the decay of an electroweak gauge boson. Our calculation is presented in terms of a multi-purpose Monte-Carlo integration program that may be readily used to include experimental spin asymmetry data in a global analysis of helicity parton densities. We perform a toy global analysis, studying the impact of anticipated RHIC data on our knowledge about the polarized anti-quark distributions.

Uneven weighting of stations in the Dst index

We note in this paper that the average disturbances of the four Dst stations are systematically different and, therefore, the stations contribute to the Dst index by unequal weights. This is an important problem, e.g., for the estimated longitudinal asymmetries of the ring current and the long-term averages of the Dst index where the contribution of the most dominant station (HON) is twice as large as the weakest station (KAK). We use an extended network of stations to demonstrate that the averaged local Dst indices are ordered according to the station's geographic longitude, with westernmost stations depicting the largest disturbances and contributions to the Dst index and easternmost the smallest. We show that the problem is related to the way that the quiet days are treated in the Dst recipe. We modify the recipe so that UT-fixed quiet days are used in all stations, whence the corrected local Dcx indices have equal weights at all stations. This gives strong support for using the corrected Dcx index instead of the Dst index.

Phrenic nerve morphometry in male and female spontaneously hypertensive rats

Histological examination of the diaphragm showed gender differences in fiber composition but gender differences on phrenic nerve morphometry were not thoroughly addressed. Ventilatory differences were described between male and female rats, as well as among different rat strains. However, the morphology of the phrenic nerve was not investigated in spontaneously hypertensive (SHR) and normotensive Wistar‐Kyoto (WKY) rats. After arterial pressure and heart rate recordings, phrenic nerves of 20 week‐old male and female SHR and WKY were prepared for epoxy resin embedding and light microscopy. Morphometry was performed with the aid of computer software. Our results showed for male and female SHR remarkable longitudinal asymmetry on both sides and an asymmetry between sides on distal segments, which were not present on WKY nerves. Phrenic nerves were generally larger in males compared to females on both strains but larger on WKY compared to SHR for both genders. Myelinated fiber number and density were significantly larger on females of both groups and remarkably larger on WKY compared to SHR in both genders. Strain and gender differences on phrenic nerve myelinated fiber number is described for the first time in this experimental model of hypertension, pointing to the need for thorough functional studies of this nerve on male and female SHR.Grant Funding Source: FAPESP

Light-front quark model analysis of the exclusive rareBc→D(s)(ℓ+ℓ−,νℓν¯ℓ)decays

We investigate the exclusive rare ${B}_{c}\ensuremath{\rightarrow}{D}_{(s)}{\ensuremath{\nu}}_{\ensuremath{\ell}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ and $B\ensuremath{\rightarrow}{D}_{(s)}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ ($\ensuremath{\ell}=e$, $\ensuremath{\mu}$, $\ensuremath{\tau}$) decays within the standard model and the light-front quark model constrained by the variational principle for the QCD-motivated effective Hamiltonian. The form factors ${f}_{\ifmmode\pm\else\textpm\fi{}}({q}^{2})$ and ${f}_{T}({q}^{2})$ are obtained from the analytic continuation method in the ${q}^{+}=0$ frame. While the form factors ${f}_{+}({q}^{2})$ and ${f}_{T}({q}^{2})$ are free from the zero mode, the form factor ${f}_{\ensuremath{-}}({q}^{2})$ is not free from the zero mode in the ${q}^{+}=0$ frame. We discuss the covariance (i.e. frame independence) of our model calculation and quantify the zero-mode contributions to ${f}_{\ensuremath{-}}({q}^{2})$ for ${B}_{c}\ensuremath{\rightarrow}{D}_{(s)}$ decays. The branching ratios and the longitudinal lepton polarization asymmetries are calculated with and without the long-distance contributions. Our numerical results for the nonresonant branching ratios for ${B}_{c}\ensuremath{\rightarrow}D({D}_{s})\ensuremath{\sum}_{}^{}{\ensuremath{\nu}}_{\ensuremath{\ell}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ and ${B}_{c}\ensuremath{\rightarrow}D({D}_{s}){\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ are in the order of ${10}^{\ensuremath{-}8}$ (${10}^{\ensuremath{-}7}$) and ${10}^{\ensuremath{-}9}$ (${10}^{\ensuremath{-}8}$), respectively. The averaged values of the lepton polarization asymmetries obtained from the linear (harmonic oscillator) potential parameters are found to be $\ensuremath{-}0.99$ ($\ensuremath{-}0.99$) for ${B}_{c}\ensuremath{\rightarrow}D{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ and $\ensuremath{-}0.16$ ($\ensuremath{-}0.15$) for ${B}_{c}\ensuremath{\rightarrow}D{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$, and $\ensuremath{-}0.98$ ($\ensuremath{-}0.98$) for ${B}_{c}\ensuremath{\rightarrow}{D}_{s}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ and $\ensuremath{-}0.14$ ($\ensuremath{-}0.12$) for ${B}_{c}\ensuremath{\rightarrow}{D}_{s}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$, respectively.

Analysis of rare semileptonicBc→Ds0*(2317)l+l−decays

We analyze the rare semileptonic B{sub c{yields}}D{sub s0}*l{sup +}l{sup -}, (l=e, {mu}, {tau}) and B{sub c{yields}}D{sub s0}*{nu}{nu} decays in the framework of the three-point QCD sum rules. D{sub s0}* is a scalar meson with total spin 0 and even parity. Taking into account the gluon condensate contributions as the important correction of the nonperturbative parts of the correlation function and the large effects of Coulombic corrections, the relevant form factors of these transitions have been calculated. The branching fractions and longitudinal lepton polarization asymmetry are also investigated.