Acta Phys. Pol. B Acta Phys. Pol. B Spin content of the $\Lambda$ hyperon Kim H C Praszalowicz M Göke K 2000 31 Using the known experimental data for the hyperon semileptonic decayconstants, we calculate integrated quark densities $\Delta q_\Lambda$ and $\Delta \Sigma_\Lambda$ for the hyperon $\Lambda$ with flavor SU(3) symmetrybreaking taken into account. Symmetry breaking is implemented with the help ofthe chiral quark-soliton model in an approach, in which the dynamicalparameters are fixed by the experimental data for six hyperon semileptonicdecay constants. This parametrization allows us to reproduce the first momentof the $g_1^{{\rm p}}(x)$ of the proton. For the $\Lambda$ we obtain: $\Deltau_{\Lambda}=\Delta d_{\Lambda} \approx 0$ and $\Delta s_{\Lambda}$ of the orderof 1. Unfortunately large experimental errors of $\Xi^-$ decays propagate inour analysis especially in the case of $\Delta\Sigma_{\Lambda}$ and $\Deltas_{\Lambda}$. Only if the errors for these decays are reduced, the accuratetheoretical predictions for $\Delta\Sigma_{\Lambda}$ and $\Delta s_{\Lambda}$will be possible. research-article

AIP Conf. Proc. AIP Conf. Proc. $\Lambda$ and $\overline{\Lambda}$ polarization as a measurement of distribution and fragmentation functions Anselmino M Boglione M Murgia F 2001 588 255 259 A combined analysis of the polarization vector of the Lambda baryons produced in DIS processes may give a relevant insight of the hadronization process which governs the transition from partons to physical hadrons and precise indications on the mechanisms of $spin$ transfer from partons to hadrons. We give here a short review of some interesting results. research-article

Nucl. Phys. B Nucl. Phys. B Measurement of the $\Lambda$ polarization in $\nu_\mu$ charged current interactions in the NOMAD experiment Astier Pierre Autiero D Baldisseri Alberto Baldo-Ceolin Massimilla Banner M Bassompierre Gabriel Benslama K Besson N Bird I Blumenfeld B Bobisut F Bouchez J Boyd S Bueno A G Bunyatov S A Camilleri L L Cardini A Cattaneo Paolo Walter Cavasinni V Cervera-Villanueva A Chukanov A Collazuol G Conforto G Conta C Contalbrigo M Cousins R D Daniels D C Degaudenzi H M Del Prete T De Santo A Dignan T Di Lella L do Couto e Silva E Dumarchez J Ellis M Fazio T Feldman G J Ferrari R Ferrère D Flaminio Vincenzo Fraternali M Gaillard Jean-Marc Gangler E Geiser A Geppert D Gibin D Gninenko S N Godley A Gómez-Cadenas J J Gosset J Gössling C Gouanère M Grant A Graziani G Guglielmi A M Hagner C Hernando J Hubbard D B Hurst P Hyett N Iacopini E Joseph C L Juget F R Kirsanov M M Klimov O L Kokkonen J Kovzelev A Krasnoperov A V Kustov D V Kuznetsov V Lacaprara S Lachaud C Lakic B Lanza A La Rotonda L Laveder M Letessier-Selvon A A Lévy J M Linssen Lucie Ljubicic A Long J Lupi A Marchionni A Martelli F Méchain X Mendiburu J P Meyer J P Mezzetto Mauro Mishra S R Moorhead G F Naumov D V Nédélec P Nefedov Yu A Nguyen-Mau C Orestano D Pastore F Peak L S Pennacchio E Pessard H Petti R Placci Alfredo Polesello G Pollmann D Polyarush A Yu Popov B Poulsen C Rathouit P Rico J Riemann P Roda C Rubbia André Salvatore F Schahmaneche K Schmidt B Schmidt T Sevior M E Sillou D Soler F J P Sozzi G Steele D Stiegler U Stipcevic M Stolarczyk T Tareb-Reyes M Taylor G N Tereshchenko S Toropin A N Touchard A M Tovey Stuart N Tran M T Tsesmelis E Ulrichs J Vacavant L Valdata-Nappi M Valuev V Yu Vannucci François CERN Varvell K E Veltri M Vercesi V Vieira J M Vinogradova T G Weber F Weisse T Wilson F F Winton L J Yabsley B D Zaccone Henri Zuber K Zuccon P 2000 588 3 36 The $\Lambda$ polarization in $\nu_\mu$ charged current interactions has been measured in the NOMAD experiment. The event sample (8087 reconstructed $\Lambda$'s) is more than an order of magnitude larger than that of previous bubble chamber experiments, while the quality of event reconstruction is comparable. We observe negative polarization along the $W$-boson direction which is enhanced in the target fragmentation region: $P_x (x_F < 0) = -0.21 \pm 0.04 \mbox{(stat)} \pm 0.02 \mbox{(sys)}$. In the current fragmentation region we find $P_x (x_F > 0) = -0.09 \pm 0.06 \mbox{(stat)} \pm 0.03 \mbox{(sys)}$. These results provide a test of different models describing the nucleon spin composition and the spin transfer mechanisms. A significant transverse polarization (in the direction orthogonal to the $\Lambda$ production plane) has been observed for the first time in a neutrino experiment: $P_y = -0.22 \pm 0.03 \mbox{(stat)} \pm 0.01 \mbox{(sys)}$. The dependence of the absolute value of $P_y$ on the $\Lambda$ transverse momentum with respect to the hadronic jet direction is in qualitative agreement with the results from unpolarized research-article

Phys. Rev. D Phys. Rev. D Lambda polarization from unpolarized quark fragmentation Anselmino M Boer D D'Alesio U Murgia F 2001 63 The longstanding problem of explaining the observed polarization of Lambda hyperons inclusively produced in the high energy collisions of unpolarized hadrons is tackled by considering spin and k_T dependent quark fragmentation functions. The data on Lambda's and Lambda-bar's produced in p-N processes are used to determine simple phenomenological expressions for these new "polarizing fragmentation functions", which describe the experiments remarkably well. research-article

The contribution of $\Sigma^* \to \Lambda\pi$ to measured $\Lambda$ polarization Ashery D Lipkin Harry Jeannot 2000 Calculations of the polarization of $\Lambda$ and $\bar{\Lambda}$ particlesafter fragmentation of a polarized quark produced in processes like $Z$-decayand deep inelastic polarized lepton scattering must include $\Lambda$ and$\bar{\Lambda}$ produced as decay products of $\Sigma^0$ and $\Sigma^*$ as wellas those produced directly. These decay contributions are significant and notfeasibly included in theoretical calculations based on QCD without additionalinput from other experimental data. Furthermore these contributions depend onthe spin structure of the $\Sigma^0$ or $\Sigma^*$ and are not directly relatedto the structure function of the $\Lambda$ PREPRINT

Phys. Lett. B Phys. Lett. B $\Lambda$ and $\overline{\Lambda}$ polarization in polarized DIS Anselmino M Boglione M Murgia F 2000 481 253 262 We consider the polarization of Lambda + Lambda-bar baryons produced in polarized Deep Inelastic Scattering at leading order, with various spin configurations: longitudinally polarized leptons and unpolarized nucleon; unpolarized leptons and longitudinally or transversely polarized nucleons; longitudinally polarized leptons and nucleons. We show how the different results in the different cases are related to different aspects of the elementary dynamics and to the spin properties of the distribution and fragmentation functions and show how a combined analysis might give useful information. We give numerical results according to several sets of polarized fragmentation functions recently proposed. research-article

Eur. Phys. J. C Eur. Phys. J. C $\Lambda$, $\overline{\Lambda}$ polarization and spin transfer in lepton deep-inelastic scattering Ma B Q Schmidt I Soffer J 2000 16 657 664 The flavor and helicity distributions of the $\Lambda$ and $\bar{\Lambda}$ hyperons for both valence and sea quarks are calculated in a perturbative QCD (pQCD) based model. We relate these quark distributions to the fragmentation functions of the $\Lambda$ and $\bar{\Lambda}$, and calculate the $z$- and $p_T$-dependence of the longitudinal spin transfer to the $\Lambda$ and spin transfer to the $\Lambda$ is compatible with the first HERMES results at DESY and further tests are suggested. We also make predictions for the $z$- and $p_T$-dependence of the $\Lambda$ and $\bar{\Lambda}$ longitudinal polarizations in neutrino (antineutrino) DIS processes. We investigate the sea contribution to the fragmentation functions, and we test a possible scenario where sea quarks in $\Lambda$ (or sea antiquarks in $\bar{\Lambda}$) are negatively polarized, whereas sea antiquarks in the $\Lambda$ (or sea quarks in fragmentation functions of sea quarks and antiquarks to $\Lambda$ and experiment at FNAL. research-article

Eur. Phys. J. C Eur. Phys. J. C $\Lambda$ and $\overline{\Lambda}$ polarization from deep inelastic muon scattering Adams M R 2000 17 263 267 We report results of the first measurements of Lambda and Antilambda polarization produced in deep inelastic polarized muon scattering on the nucleon. The results are consistent with an expected trend towards positive polarization with increasing x_F. The polarizations of Lambda and Antilambda appear to have opposite signs. A large negative polarization for Lambda at low positive x_F is observed and is not explained by existing models.A possible interpretation is presented. research-article

Phys. Lett. B Phys. Lett. B Expected Polarization of $\Lambda$ particles produced in deep inelastic polarized lepton scattering Ashery D Lipkin Harry Jeannot 1999 469 263 269 We calculate the polarization of Lambda and Anti-Lambda particles produced in deep inelastic polarized lepton scattering. We use two models: the naive quark model and a model in which SU(3)$_F$ symmetry is used to deduce the spin structure of SU(3) octet hyperons from that of the proton. We perform the calculations for \la and \lab produced directly or as decay products of research-article

Lambda polarization in lepton-induced reactions Kotzinian A M Dubna, JINR 1997 Different phenomenological approaches for Lambda and Lambda-bar polarization in polarized semi-inclusive deep inelastic scattering and electron-positron annihilation at Z^0 pole are considered. Current and future experiments will soon provide accurate enough data to study spin phenomena in these reactions and distinguish between various models. PREPRINT

Eur. Phys. J. C Eur. Phys. J. C $\Lambda$ and $\overline\Lambda$ Polarization in Lepton Induced Processes Kotzinian A M Bravar A Von Harrach D 1998 2 329 337 The study of the longitudinal polarization of Lambda and Lambda-bar hyperons produced in polarized deep inelastic scattering, neutrino scattering, and in Z0 decays allows to access the spin dynamics of the quark fragmentation process. Different phenomenological spin transfer mechanisms are considered and predictions for the Lambda and Lambda-bar longitudinal polarization in various processes using unpolarized and polarized targets are made. Current and future semi-inclusive deep inelastic scattering experiments will provide soon accurate enough data to study these phenomena and distinguish between various models for the spin transfer mechanisms. research-article

Measurement of Longitudinal Spin Transfer to $\Lambda$ Hyperons in Deep-Inelastic Lepton Scattering Airapetian A 1999 Spin transfer in deep-inelastic Lambda electroproduction has been studied with the HERMES detector using the 27.5 GeV polarized positron beam in the HERA storage ring. For an average fractional energy transfer z=0.45, the measured longitudinal spin transfer from the virtual photon to the Lambda is 0.11 +/- 0.17 (stat) +/- 0.03 (sys). This quantity is expected to be sensitive to the up quark polarization in the Lambda hyperon and to the assumption of helicity conservation in the fragmentation process. The experimental result is interpreted in relation to various models of the Lambda spin content and found to favor the naive QPM. However, the present statistical precision is not yet sufficient to exclude a significant up quark polarization in the Lambda. PREPRINT

Phys. Lett. B Phys. Lett. B Flavor and Spin Structure of $\Lambda$-Baryon at Large x Ma B Q Schmidt I 2000 477 107 113 It is shown that perturbative QCD (pQCD) and the SU(6) quark-diquark model give significant different predictions concerning the flavor and spin structure for the quark distributions of the $\Lambda$-baryon near $x=1$. Detailed predictions for the ratios $u(x)/s(x)$ of unpolarized quark distributions, up and down quarks of the $\Lambda$ are given from the quark-diquark model and from a pQCD based model. It is found that the up and down quarks are positively polarized at large $x$, even though their net spin contributions to the between different predictions can provide clean tests of pQCD. research-article

The strange quark spin of the proton in semi-inclusive $\Lambda$ leptoproduction Lu W Ma B Q 1995 Considering the possible interpretation of the Ellis-Jaffe sum rule violation that the strange quark in the polarized proton is remarkably polarized in the opposite direction of the proton spin, we investigate its implication in the semi-inclusive \Lambda production in deep inelastic process with the electron beam unpolarized and proton target polarized longitudinally. As a result, we find that the measurement of the \Lambda polarization in the process considered can provide clean information about the strange quark spin distribution in the proton. PREPRINT

Z. Phys. C Z. Phys. C The proton spin puzzle and $\Lambda$ polarization in deep-inelastic scattering Ellis Jonathan Richard CERN Kharzeev Dima E Kotzinian A M 1996 69 467 474 We point out that measurements of longitudinal \Lambda polarization in the target fragmentation region of deep--inelastic \nu \,N and \mu \,N or e \, N scattering may test dynamical mechanisms invoked to explain the proton spin puzzle. A previously-proposed model for polarized \bar s s pairs in the proton wave function reproduces successfully the negative \Lambda polarization found in the WA59 \bar \nu \, N experiment, and makes predictions that could be tested in future \mu \, N and e \, N experiments. research-article

Phys. Lett. B Phys. Lett. B The proton spin puzzle and depolarization in $\overline{p}$p --> $\overline{\Lambda}\Lambda$ Alberg M A Ellis Jonathan Richard CERN Kharzeev Dima E 1995 356 113 117 We point out that the measurement of target spin depolarization D_{nn} in the \bar{p}p\to\bar{\Lambda}\Lambda reaction may test dynamical mechanisms invoked to explain the proton spin puzzle revealed by polarized deep--inelastic scattering experiments. In particular, models with {\it negatively} polarized \bar{s}s pairs in the proton wave function predict D_{nn}<0, whereas models with {\it positively} polarized gluons would predict D_{nn}>0. research-article

Academic Press Academic Press Deep Inelastic Scattering of Leptons and Hadrons in the QCD Parton Model and Experimental Tests Bourrely C Soffer J 2002 1565 1581 We present the basic aspects of deep inelastic phenomena in the framework of the QCD parton model. After recalling briefly the standard kinematics, we discuss the physical interpretation of unpolarized and polarized structure functions in terms of parton distributions together with several important sum rules. We also make a rapid survey of the experimental situation together with phenomenological tests, in particular concerning various QCD predictions. In the summary, we try to identify some significant open questions, to clarify where we stand and to see what we expect to learn in the future. research-article

Phys. Rev. D Phys. Rev. D The Flavor and Spin Structure of Hyperons from Quark Fragmentation Ma B Q Schmidt I Soffer J 2000 62 We systematically study the hadron longitudinal polarizations of the octet baryons at large $z$ from quark fragmentations in $e^+e^-$-annihilation, polarized charged lepton deep inelastic scattering (DIS) process, and neutrino (antineutrino) DIS process, based on predictions of quark distributions for the octet baryons in the SU(6) quark-spectator-diquark model and a perturbative QCD based counting rule analysis. We show that the $e^+e^-$-annihilation and polarized charged lepton DIS process are able to distinguish between the two different predictions of the hyperon polarizations. We also find that the neutrino/antineutrino DIS process is ideal in order to study both the valence content of the hyperons and the antiquark to hyperon (quark to anti-hyperon) fragmentations, which might be related to the sea content of hyperons. research-article

Phys. Lett. B Phys. Lett. B The Quark-Antiquark Asymmetry of the Nucleon Sea from $\Lambda$ and $\bar{\Lambda}$ Fragmentation Ma B Q Schmidt I Soffer J 2000 489 293 299 We present a general analysis of the spin transfer for $\Lambda$ and $\bar{\Lambda}$ production in deep-inelastic scattering of polarized charged leptons on the nucleon, and find that the pattern of different behaviors of $\Lambda$ and $\bar{\Lambda}$ production observed by the E665 Collaboration suggests the possibility of quark-antiquark asymmetries either in the quark to $\Lambda$ fragmentation functions and/or in the quark and antiquark distributions of the target proton. We also point out that the strange-antistrange asymmetry of the nucleon sea may produce an observable contribution to the different behaviors of $\Lambda$ and $\bar{\Lambda}$ production. We find that a softer $\bar{s}(x)$ than $s(x)$ as predicted by the light-cone baryon-meson fluctuation model of intrinsic quark-antiquark pairs of the nucleon sea might lead to a reasonable picture. However, the magnitude is still too small to explain the E665 data and the conclusion has also strong model-dependence. This may suggest the importance of quark-antiquark asymmetry in the quark to $\Lambda$ fragmentation functions, provided that the E665 data are confirmed. research-article

Phys. Rev. Lett. Phys. Rev. Lett. 0031-9007 Quark Flavor Separation in $\Lambda$-Baryon Fragmentation Ma B Q Soffer J 1999 82 It is shown that neutrino and antineutrino deep inelastic scattering of unpolarized and polarized $\Lambda$ and $\bar{\Lambda}$ productions, can provide a clean separation of unpolarized and polarized fragmentation functions of a quark into a $\Lambda$, for both light-flavor quarks and antiquarks and also for strange quarks. Combining with $\Lambda$ and $\bar{\Lambda}$ productions, in polarized electron deep inelastic scattering, one can systematically measure or check the various flavor and spin dependent fragmentation functions. Such measurements can provide crucial tests of different predictions concerning the spin structure of hadrons and the quark-antiquark asymmetry of the nucleon sea. research-article