Phys. Rev. D Phys. Rev. D Hyperon polarization in $\nu_{\mu}$ charged current interaction at the NOMAD energies Liang Z Liu C 2002 66 We show that, in $\nu_\mu N\to \mu^-\Lambda X$ at the NOMAD energies, it is impossible to separate the products of the fragmentation of the struck quark from those of the nucleon remnant. The latter has a large contribution even in the current fragmentation region and has to be taken into account in calculating $\Lambda$ polarization using different pictures. Based on this, we make a rough estimation for the longitudinal $\Lambda$ polarization in $\nu_{\mu} N \to \mu^- \Lambda X$ at the NOMAD energies. A comparison with the data is given and predictions for $\nu_\mu N\to\mu^-\Sigma^+X$ are presented. research-article

Phys. Rev. D Phys. Rev. D Hyperon polarization in e^-p --> e^-HK with polarized electron beams Liang Z Xu Q 2002 65 We apply the picture proposed in a recent Letter for transverse hyperon polarization in unpolarized hadron-hadron collisions to the exclusive process e^-p --> e^-HK such as e^-p-->e^-\Lambda K^+, e^-p --> e^-\Sigma^+ K^0, or e^-p--> e^-\Sigma^0 K^+, or the similar process e^-p\to e^-n\pi^+ with longitudinally polarized electron beams. We present the predictions for the longitudinal polarizations of the hyperons or neutron in these reactions, which can be used as further tests of the picture. research-article

Nucl. Phys. A Nucl. Phys. A Measurement of the $\Lambda$ hyperon polarization in $\nu_{\mu}$ charged current interactions in the NOMAD experiment Popov B A CERN 2001 692 73 80 The Lambda hyperon polarization in nu /sub 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 the event reconstruction is comparable. We observe a negative polarization along the W-boson direction which is enhanced in the target fragmentation region: P/sub x/(x/sub F/<0) =-0.21+or-0.04(stat)+or-0.02(sys). In the current fragmentation region we find P/sub x/(x/sub F/>0)=-0.09+or-0.06(stat)+or-0.03(sys). These results provide a test of different models describing the nucleon spin composition and the spin transfer mechanisms. We also observe a significant transverse polarization (in the direction orthogonal to the Lambda production plane) for the first time in a neutrino experiment: P/sub y/=-0.22+or-0.03(stat)+or-0.01(sys). The dependence of the absolute value of P/sub y/ on the Lambda transverse momentum with respect to the hadronic jet direction is in qualitative agreement with the results from unpolarized hadron-hadron experiments. The dependence of the Lambda polarization on the type of target nucleon in nu /sub mu / scattering has been also studied. (11 refs). research-article

High Energy Phys. Nucl. Phys. (Beijing) High Energy Phys. Nucl. Phys. (Beijing) 0254-3052 Spin transfer in high-energy hadronization processes and polarization of hyperon in the lepton-induced reactions 2001 25 476 86 We show that measuring the polarization of the hyperon in the lepton induced reactions is an ideal way to study the spin transfer in high- energy hadronization processes. After a brief summary of the polarization of the initial quark or antiquark in these reactions, we give the calculation method of the polarization of the hyperon. As an example, we calculate polarizations of different hyperons in e/sup + /e/sup -/ annihilation at LEP energies and compare these results with the available data. The results show that measurements of such polarizations should provide important information about the question of which picture of spin structure of baryon is more suitable in describing the spin effects in the high-energy fragmentation processes. (17 refs). research-article

Phys. Rev. D Phys. Rev. D Hyperon polarization in semi-inclusive deeply inelastic lepton-nucleon scattering at high energy Liu C Xu Q Liang Z 2001 64 We calculate the polarizations for different octet hyperons produced in the current fragmentation regions of the deeply inelastic lepton-nucleon scatterings $\mu^-N \to \mu^- HX$ and $\nu_{\mu} N \to \mu^- HX$ at high energy using different models for spin transfer in fragmentation processes. The results show that measurements of those hyperon polarizations should provide useful information to distinguish between different models in particular the SU(6) and the DIS pictures used frequently in the literature. We found, in particular, that measuring the polarization of $\Sigma^+$ produced in these processes can give a better test to the validity of the different spin transfer models. research-article

Nucl. Phys. A Nucl. Phys. A Spin observables in hyperon production Maggiora M Balestra F Bedfer Y Bertini R Bland L C Brochard F Bussa M P Chalyshev V Choi S Debowski M Dzemidzic M Faivre Jean-Claude Falomkin I V Fava L Ferrero L Foryciarz J Frolov V Fröhlich I Garfagnini R Gill D Grasso A Heinz S Ivanov V V Jacobs W W Kühn W Maggiora A Manara A Panzieri D Pfaff H W Piragino G Pontecorvo G B Popov A Ritman J Salabura P Tosello F Vigdor S E Zosi G 2000 663-664 477c 480c The first exclusive measurements of the spin transfer parameter D sub N sub N in the reaction p-vectorp->pK sup +LAMBDA-vector has been performed at Saturne with the polarized beam and with the DISTO spectrometer. The results suggest an OBE mechanism dominated by kaon exchange. research-article

Longitudinal spin transfer to the Lambda hyperon in leptoproduction Belostotskii S L 2001 PREPRINT

Lambda hyperon production mechanisms and longitudinal spin transfer at HERMES 2003 PREPRINT

Phys. Lett. B Phys. Lett. B A lattice study of the spin structure of the Lambda hyperon Göckeler M Horsley R Pleiter D Rakow P E L Schäfer S Schäfer A Schierholz G 2002 545 112 118 The internal spin structure of the Lambda is of special importance for the understanding of the spin structure of hadrons in general. The comparison between the nucleon and Lambda allows for a test of the relevant flavour-symmetry breaking effects. Using nonperturbatively O(a) improved Wilson fermions in the quenched approximation we have calculated the first moments of the unpolarised, longitudinally polarised and transversity quark distribution functions in the Lambda. The results indicate that flavour symmetry breaking has little effect on the internal spin structure, in accordance with model based expectations. research-article

Nucl. Phys. B, Proc. Suppl. Nucl. Phys. B, Proc. Suppl. The spin structure of the Lambda hyperon in quenched lattice QCD Göckeler M Horsley R Pleiter D Rakow P E L Schäfer S Schäfer A Schierholz G 2002 106 305 307 It has been suggested to use the production of Lambda hyperons for investigating the nucleon spin structure. The viability of this idea depends crucially on the spin structure of the Lambda. Using nonperturbatively O(a) improved Wilson fermions in the quenched approximation we have studied matrix elements of two-quark operators in the Lambda. We present results for the axial vector current, which give us the contributions of the u, d, and s quarks to the Lambda spin. research-article

Lambda polarization measured at HERMES and Lambda spin structure Belostotskii S L Grebenyuk O 1999 PREPRINT

Phys. Lett. B Phys. Lett. B Up and Down Quark Contributions to Spin Content of Lambda from Fragmentation 2001 512 57 64 We check the $u$ and $d$ quark contributions to the spin content of the $\Lambda$ by means of the $q\to\Lambda$ fragmentation and find that the $u$ and $d$ quarks of the $\Lambda$ are likely positively polarized. The parton distributions in the $\Lambda$ are given by a successful statistical model which can reproduce and correlate a vast body of polarized and unpolarized structure function and parton distribution data of the nucleon. With the Gribov-Lipatov relation between the quark distributions and fragmentation functions, the longitudinal spin transfer for the $\Lambda$ production in the polarized charged lepton deep inelastic scattering (DIS) process and the $\Lambda$-polarization in the neutrino (antineutrino) DIS process are predicted. The available experimental data suggests that the $u$ and $d$ quark contributions to the spin of the $\Lambda$ are positive. In addition, our results provide a collateral evidence for the SU(3) symmetry breaking in hyperon semileptonic decays of the octet baryons, which is very important for a deeper understanding of the proton 'spin crisis'. research-article

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Transverse polarization of Lambda hyperons produced inclusively in e N scattering at HERMES Belostotskii S L Grebenyuk O 2001 PREPRINT

Longitudinal polarization of the Lambda in deep inelastic scattering of polarized positrons from nucleons Schnell G 1999 PREPRINT

Ratio of $\sigma_L / \sigma_T$ for $p(e,e'K^+)\Lambda$ Extracted from Polarization Transfer Raue Brian A Ohio U. Florida International U. 2005 The ratio of longitudinal to transverse structure functions, $\sigma_L/\sigma_T$, has been extracted from recent beam-recoil transferred polarization data for the $p(\vec e,e'K^+)\vec\Lambda$ reaction. Results have been obtained for $W$=1.69, 1.84, and 2.03 GeV at an average $Q^2$ of 0.69 GeV$^2$. Our results indicate a ratio approaching zero. This is in contradiction to previously published results using a Rosenbluth separation. A similar difference between Rosenbluth and recoil polarization results has been observed in the measurement of the ratio of electric to magnetic form factors of the proton, $\mu_pG_E/G_M$. PREPRINT

Transverse polarization of Lambda and Antilambda hyperons in quasi-real photon nucleon scattering Brüll A 2002 PREPRINT

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Transversity and Lambda polarization Anselmino M 2004 Two related issues are discussed, which might be easily explored by present and future COMPASS experiments. The first one deals with the new world of transversity, the fundamental polarized parton distribution so far totally unknown. The second issue concerns Lambda production in polarized semi-inclusive processes, with a measurement of the Lambda polarization, which might give novel information on distribution and fragmentation properties of polarized partons. In case of transverse polarization the detection of Lambda's gives access to a new way of measuring transversities. Also the interesting case of Lambda polarization in unpolarized processes is discussed. research-article

Phys. Rev. Lett. Phys. Rev. Lett. 0031-9007 First Measurement of Transferred Polarization in the Exclusive e p --> e' K+ Lambda Reaction Carman D S 2003 90 The first measurements of the transferred polarization for the exclusive ep --> e'K+ Lambda reaction have been performed in Hall B at the Thomas Jefferson National Accelerator Facility using the CLAS spectrometer. A 2.567 GeV electron beam was used to measure the hyperon polarization over a range of Q2 from 0.3 to 1.5 (GeV/c)2, W from 1.6 to 2.15 GeV, and over the full center-of-mass angular range of the K+ meson. Comparison with predictions of hadrodynamic models indicates strong sensitivity to the underlying resonance contributions. A non-relativistic quark model interpretation of our data suggests that the s-sbar quark pair is produced with spins predominantly anti-aligned. Implications for the validity of the widely used 3P0 quark-pair creation operator are discussed. research-article

AIP Conf. Proc. AIP Conf. Proc. $\Lambda$ polarization in the target fragmentation region of SIDIS Kotzinian A M CERN 2001 588 272 276 research-article

Acta Phys. Pol. B Acta Phys. Pol. B Measurement of Lambda and Lambda-bar polarization in muon neutrino charged current interactions in NOMAD Naumov Dmitry V. 2002 33 3791 3796 The Lambda and Lambda-bar polarizations in muon neutrino charged current interactions have been measured in the NOMAD experiment. The event sample (8087 reconstructed Lambda's and 649 Lambda-bar's) is more than an order of magnitude larger than that of previous bubble chamber experiments, while the quality of event reconstruction is comparable. For the Lambda hyperons we observe negative polarization along the W-boson direction which is enhanced in the target fragmentation region: Px(xF < 0) = -0.21 +- 0.04 (stat) +- 0.02 (sys). In the current fragmentation region we find Px(xF > 0) = -0.09 +- 0.06 (stat) +- 0.03(sys). A significant transverse polarization (in the direction orthogonal to the Lambda production plane) has been observed for the first time in a neutrino experiment: Py = -0.22 +- 0.03 (stat) +- 0.01 (sys). The dependence of the absolute value of Py on the Lambda transverse momentum with respect to the hadronic jet direction is in qualitative agreement with the results from unpolarized hadron-hadron experiments. The polarization vector of Lambda-bar hyperons measured for the first time in neutrino interactions is found to be consistent with zero. research-article

Acta Phys. Pol. B Acta Phys. Pol. B Lambda Polarization in Deep-Inelastic Production Naumov D V 2002 33 3803 3808 We propose a model for the longitudinal polarization of Lambda baryons produced in deep-inelastic lepton scattering at any xF, based on static SU(6) quark-diquark wave functions and polarized intrinsic strangeness in the nucleon associated with individual valence quarks. Free parameters of the model are fixed by fitting the NOMAD data on the longitudinal polarization of Lambda hyperons in neutrino interactions. Our model correctly reproduces the observed dependences of Lambda polarization on the kinematic variables. Within the context of our model, the NOMAD data imply that the intrinsic strangeness associated with a valence quark has anticorrelated polarization. We also compare our model predictions with results from the HERMES and E665 experiments using charged leptons. Predictions of our model for the COMPASS experiment are also presented. research-article

Eur. Phys. J. C Eur. Phys. J. C Intrinsic Polarized Strangeness and Lambda Polarization in Deep-Inelastic Production Ellis John R. CERN Kotzinian Aram Yerevan Phys. Inst. Dubna, JINR Naumov Dmitry V. Dubna, JINR 2002 25 603 613 We propose a model for the longitudinal polarization of Lambda baryons produced in deep-inelastic lepton scattering at any xF, based on static SU(6) quark-diquark wave functions and polarized intrinsic strangeness in the nucleon associated with individual valence quarks. Free parameters of the model are fixed by fitting NOMAD data on the longitudinal polarization of Lambda hyperons in neutrino collisions. Our model correctly reproduces the observed dependences of Lambda polarization on the kinematic variables. Within the context of our model, the NOMAD data imply that the intrinsic strangeness associated with a valence quark has anticorrelated polarization. We also compare our model predictions with results from the HERMES and E665 experiments using charged leptons. Predictions of our model for the COMPASS experiment are also presented. research-article

Int. J. Mod. Phys. A Int. J. Mod. Phys. A Transverse Lambda polarization in inclusive processes Anselmino M Boer D D'Alesio U Murgia F 2003 18 1237 1246 A formalism proposed to study transverse Lambda polarization in unpolarized hadronic processes, based on a generalized pQCD factorization theorem, is extended to semi-inclusive DIS. Analytical expressions and examples of numerical estimates are given. research-article

Polarization transfer in SIDIS for Lambda production Arestov Y 2001 Polarization transfer from the longitudinally polarized positron to the final-state quark is considered for the underlying QCD subprocesses giving rise to the reaction e+(pol) + p --> e+ + Lambda(pol) + X at the HERMES energy. PREPRINT

Phys. Rev. D Phys. Rev. D Transverse Lambda polarization in semi-inclusive DIS Anselmino M Boer D D'Alesio U Murgia F 2002 65 Extending a previous description of Lambda and Lambda-bar polarization in unpolarized p-p interactions, within a pQCD factorization scheme with new polarizing fragmentation functions, we give predictions for the transverse polarization of Lambda's and Lambda-bar's in semi-inclusive DIS, both with neutral and charged currents. Comparison with existing data is not yet significant, but more experimental results are expected in the near future. research-article

Longitudinal Lambda polarization in polarized semi-inclusive DIS Anselmino M Boglione M D'Alesio U Murgia F 2001 We calculate, within pQCD parton model at leading orders, the expression of the longitudinal polarization of Lambda baryons produced in polarized semi-inclusive DIS, including weak interaction effects. We present some numerical estimates in few cases for which data are or will soon be available and discuss how to gather new information on polarized fragmentation functions. PREPRINT

Transverse Lambda polarization in unpolarized semi-inclusive DIS Anselmino M Boer D D'Alesio U Murgia F 2001 The long-standing problem of transverse Lambda polarization in high-energy collisions of unpolarized hadrons can be tackled by considering new, spin and k_T-dependent quark fragmentation functions for an unpolarized quark into a polarized, spin-1/2 hadron. Simple phenomenological parameterizations of these new "polarizing fragmentation functions", which describe quite well the experimental data on Lambda and Lambda-bar hyperons produced in p-A processes, are utilized and extended here to give predictions for transverse Lambda polarization in semi-inclusive DIS PREPRINT

CERN Geneva Lambda-lambda bar polarization correlations Sofer A CERN 1993 technical-report

Nucl. Phys. B Nucl. Phys. B Measurement of the $\overline{\Lambda}$ polarization in $\nu_\mu$ charged current interactions in the NOMAD experiment Astier P. Paris U., VI-VII Autiero D. CERN Baldisseri A. DAPNIA, Saclay Baldo-Ceolin M. INFN, Padua Padua U. Banner M. Paris U., VI-VII Bassompierre G. Annecy, LAPP Besson N. DAPNIA, Saclay Bird I. CERN Lausanne U. Blumenfeld B. Johns Hopkins U. Bobisut F. INFN, Padua Padua U. Bouchez J. DAPNIA, Saclay Boyd S. Sydney U. Bueno A. Harvard U. ETH, Zurich (main) Bunyatov S. Dubna, JINR Camilleri L. CERN Cardini A. UCLA Cattaneo P.W. INFN, Pavia Pavia U. Cavasinni V. INFN, Pisa Pisa U. Cervera-Villanueva A. CERN Valencia U., IFIC Chukanov A. Dubna, JINR Collazuol G. INFN, Padua Padua U. Conforto G. CERN INFN, Florence Urbino U. Conta C. INFN, Pavia Pavia U. Contalbrigo M. INFN, Padua Padua U. Cousins R. UCLA Daniels D. Harvard U. Degaudenzi H. Lausanne U. Del Prete T. INFN, Pisa Pisa U. De Santo A. CERN Dignan T. Harvard U. Di Lella L. CERN do Couto e Silva E. CERN Dumarchez J. Paris U., VI-VII Ellis M. Sydney U. Fazio T. Annecy, LAPP Feldman G.J. Harvard U. Ferrari R. INFN, Pavia Pavia U. Ferrère D. CERN Flaminio V. INFN, Pisa Pisa U. Fraternali M. INFN, Pavia Pavia U. Gaillard J.-M. Annecy, LAPP Gangler E. CERN Paris U., VI-VII Geiser A. Dortmund U. CERN Geppert D. Dortmund U. Gibin D. INFN, Padua Padua U. Gninenko S. CERN Moscow, INR Godley A. Sydney U. Gomez-Cadenas J.-J. CERN Valencia U., IFIC Gosset J. DAPNIA, Saclay Gößling C. Dortmund U. Gouanère M. Annecy, LAPP Grant A. CERN Graziani G. Florence U. INFN, Florence Guglielmi A. INFN, Padua Padua U. Hagner C. DAPNIA, Saclay Hernando J. Valencia U., IFIC Hubbard D. Harvard U. Hurst P. Harvard U. Hyett N. Melbourne U. Iacopini E. Florence U. INFN, Florence Joseph C. Lausanne U. Juget F. Lausanne U. Kirsanov M. Moscow, INR Klimov O. Dubna, JINR Kokkonen J. CERN Kovzelev A. Moscow, INR INFN, Pavia Pavia U. Krasnoperov A. Annecy, LAPP Dubna, JINR Kustov D. Dubna, JINR Kuznetsov V. Dubna, JINR CERN Lacaprara S. INFN, Padua Padua U. Lachaud C. Paris U., VI-VII Lakić B. Boskovic Inst., Zagreb Lanza A. INFN, Pavia Pavia U. La Rotonda L. Calabria U. INFN, Cosenza Laveder M. INFN, Padua Padua U. Letessier-Selvon A. Paris U., VI-VII Levy J.-M. Paris U., VI-VII Linssen L. CERN Ljubičić A. Boskovic Inst., Zagreb Long J. Johns Hopkins U. Lupi A. Florence U. INFN, Florence Marchionni A. Florence U. INFN, Florence Martelli F. INFN, Florence Urbino U. Méchain X. DAPNIA, Saclay Mendiburu J.-P. Annecy, LAPP Meyer J.-P. DAPNIA, Saclay Mezzetto M. INFN, Padua Padua U. Mishra S.R. Harvard U. South Carolina U. Moorhead G.F. Melbourne U. Naumov D. Dubna, JINR Nédélec P. Annecy, LAPP Nefedov Yu. Dubna, JINR Nguyen-Mau C. Lausanne U. Orestano D. INFN, Rome3 Rome III U. Pastore F. INFN, Rome3 Rome III U. Peak L.S. Sydney U. Pennacchio E. INFN, Florence Urbino U. Pessard H. Annecy, LAPP Petti R. CERN INFN, Pavia Pavia U. Placci A. CERN Polesello G. INFN, Pavia Pavia U. Pollmann D. Dortmund U. Polyarush A. Moscow, INR Popov B. Dubna, JINR Paris U., VI-VII Poulsen C. Melbourne U. Rico J. ETH, Zurich (main) Riemann P. Dortmund U. Roda C. CERN INFN, Pisa Pisa U. Rubbia A. CERN ETH, Zurich (main) Salvatore F. INFN, Pavia Pavia U. Schahmaneche K. Paris U., VI-VII Schmidt B. Dortmund U. CERN Schmidt T. Dortmund U. Sevior M. Melbourne U. Sillou D. Annecy, LAPP Soler F.J.P. CERN Sydney U. Sozzi G. Lausanne U. Steele D. Johns Hopkins U. Lausanne U. Stiegler U. CERN Stipčević M. Boskovic Inst., Zagreb Stolarczyk Th. DAPNIA, Saclay Tareb-Reyes M. Lausanne U. Taylor G.N. Melbourne U. Tereshchenko V. Dubna, JINR Toropin A. Moscow, INR Touchard A.-M. Paris U., VI-VII Tovey S.N. CERN Melbourne U. Tran M.-T. Lausanne U. Tsesmelis E. CERN Ulrichs J. Sydney U. Vacavant L. Lausanne U. Valdata-Nappi M. Calabria U. INFN, Cosenza Valuev V. Dubna, JINR UCLA Vannucci F. Paris U., VI-VII Varvell K.E. Sydney U. Veltri M. INFN, Florence Urbino U. Vercesi V. INFN, Pavia Pavia U. Vidal-Sitjes G. CERN Vieira J.-M. Lausanne U. Vinogradova T. UCLA Weber F.V. Harvard U. CERN Weisse T. Dortmund U. Wilson F.F. CERN Winton L.J. Melbourne U. Yabsley B.D. Sydney U. Zaccone H. DAPNIA, Saclay Zuber K. Dortmund U. Zuccon P. INFN, Padua Padua U. 2001 605 3 14 We present a measurement of the polarization of $\alam$ hyperons produced in $\nu_\mu$ charged current interactions. The full data sample from the NOMAD experiment has been analyzed using the same $\vo$ identification procedure and analysis method reported in a previous paper~\cite{NOMAD-polar} for the case of $\lam$ hyperons. The $\alam$ polarization has been measured for the first time in a neutrino experiment. The polarization vector is found to be compatible with zero. research-article

AIP Conf. Proc. AIP Conf. Proc. Measurement of Lambda polarization in muon neutrino charged current interactions in NOMAD Naumov Dmitry V. Dubna, JINR 2000 570 489 493 The Lambda polarization in muon neutrino charged current interactions has been measured in the NOMAD experiment. We observe negative polarization along the W - boson direction which is enhanced in the target fragmentation region: Px (xF < 0) = -0.21 +/- 0.04(stat) +/- 0.02(sys). In the current fragmentation region we find: Px (xF > 0) = -0.09 +/- 0.06(stat) +/- 0.03(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: Py = -0.22 +/- 0.03(stat) +/- 0.01(sys). The dependence of the absolute value of Py on the Lambda transverse momentum with respect to the hadronic jet direction is in qualitative agreement with the results from unpolarized hadron-hadron experiments. 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. Lett. B Phys. Lett. B Ratio of $\bar{\Lambda}/\Lambda$ in Semi-inclusive Electroproduction Schmidt Ivan 2003 574 35 40 It is shown that the $\bar{\Lambda}/\Lambda$ cross section ratio in semi-inclusive electroproduction of $\Lambda$ and $\bar{\Lambda}$ hyperons in deep inelastic scattering of charged lepton on a nucleon target, can provide useful information on the quark to $\Lambda$ fragmentation functions. This ratio is calculated explicitly in a quark-diquark model, a pQCD based analysis, and an SU(3) symmetry model, with three different options for the contribution from the unfavored fragmentation functions. The $x$-dependence of this ratio is sensitive to the ratio of unfavored fragmentation functions over favored fragmentation functions, $D_{\bar{u}}^{\Lambda}(z)/D_{u}^{\Lambda}(z)$, whereas the $z$-dependence is sensitive to the flavor structure of the fragmentation functions, i.e., the ratio $D_u^{\Lambda}(z)/D_s^{\Lambda}(z)$. Future measurements by the HERMES Collaboration at DESY can discriminate between various cases. research-article

Phys. Rev. D Phys. Rev. D Helicity and Transversity Distribution of Nucleon and $\Lambda$-Hyperon from $\Lambda$ Fragmentation Ma B Q Schmidt I Soffer J 2001 64 It is shown that $\Lambda$-hyperon fragmentation in charged lepton deep inelastic scattering (DIS) on a polarized nucleon target can provide sensitive information concerning the quark helicity and transversity distributions for both nucleon and $\Lambda$-hyperon at large $x$. Numerical predictions are given for the spin transfers of the produced $\Lambda$, when the target nucleon is polarized either longitudinally or transversely, and with the nucleon and $\Lambda$ quark distributions evaluated both in an SU(6) quark-spectator-diquark model and in a perturbative QCD (pQCD) based model. It is also shown that the predicted spin transfers have different behaviors for proton and neutron targets, and this can provide sensitive tests of different predictions for the quark helicity and transversity distributions of the $d$ valence quark of the proton at large $x$. research-article

Nucl. Phys. A Nucl. Phys. A $q \to \Lambda$ Fragmentation Function and Nucleon Transversity Distribution in a Diquark Model 2002 699 562 578 Based on a simple quark-diquark model, we propose a set of unpolarized, longitudinally polarized and transversely polarized fragmentation functions for the $\Lambda$ by fitting the unpolarized $\Lambda$ production data in $e^+ e ^- $ annihilation. It is found that the helicity structure of the obtained $\Lambda$ fragmentation functions is supported by the all available experimental data on the longitudinal $\Lambda$ polarization. Within the same framework of the diquark model, the nucleon transversity distributions are presented and consistent descriptions of the available HERMES data on the azimuthal spin asymmetries in pion electroproduction are obtained. Furthermore, the spin transfers to the transversely polarized $\Lambda$ in the charged lepton DIS on a transversely polarized nucleon target are predicted for future experiments. research-article