We perform a study on the struck quark to the $Λ$-hyperon fragmentation processes by taking into account the anti-quark fragmentations and intermediate decays from other hyperons. We concentrate on how the longitudinally polarized quark fragments to the longitudinally polarized $Λ$, how unpolarized quark and anti-quark fragment to the unpolarized $Λ$, and how quark and anti-quark fragment to the $Λ$ through the intermediate decay processes. We calculate the effective fragmentation functions in the light-cone SU(6) quark-spectator-diquark model via the Gribov-Lipatov relation, with the Melosh-Wigner rotation effect also included. The calculated results are in reasonable agreement with the HERMES semi-inclusive $ep$ experimental data and the OPAL and ALEPH $e^{+}e^{-}$ annihilation experimental data.
The possibility is examined for the inclusive $Λ$ in unpolarized electron-positron annihilation to be transversely polarized. Due to final-state interactions, there exists a novel structure function $\hat F(z,Q^2)$ for the inclusive $Λ$ hyperon (or any other baryons) production from the unpolarized time-like photon fragmentation, which makes contribution to the transverse $Λ$ polarization in the unpolarized electron-positron annihilation.
It has been known for a long time that hyperons produced in hadronic collisions are polarized perpendicular to the production plane of the reaction. This effect cannot be described by using twist-2 collinear parton correlators only. Here we compute the contribution of twist-3 fragmentation functions to the production of transversely polarized hyperons in unpolarized proton-proton collisions in the framework of collinear factorization. By taking into account the relations among the relevant twist-3 fragmentation functions which follow from the QCD equation of motion and the Lorentz invariance p…
We derive the twist-3 gluon fragmentation function (FF) contribution to the transversely polarized hyperon production in semi-inclusive deep inelastic scattering, $ep\to eΛ^\uparrow X$, in the leading order (LO) with respect to the QCD coupling in the framework of the collinear twist-3 factorization. Together with the known result for the contribution from the twist-3 distribution in the proton and the twist-3 quark FFs for the hyperon, this completes the LO cross section for this process. The constraint relations among the twist-3 FFs are taken into account. The formula is relevant to large-$…
A novel method of formulating the twist-3 gluon fragmentation function contribution to hyperon polarization in the proton-proton collision is presented. The method employs a covariant gauge and takes full advantage of the Ward-Takahashi identities before performing the collinear expansion. It provides a robust way of constructing the general cross section formula, and also a clear understanding for the absence of the ghost-like terms in the twist-3 cross section in the leading order with respect to the QCD coupling constant.
We discuss the polarised fragmentation functions of quarks and gluons in Perturbative Quantum Chromodynamics. The Altarelli-Parisi evolution equations governing these fragmentation functions are presented. We find that the first moment of the polarised gluon fragmentation function to order $α_s$ is as important as that of the quark and anti-quark fragmentation functions. The $Λ$ production in polarised $e^+ e^-$ annihilation where this can be realised is discussed. We propose the factorisation method to compute the gluonic contribution to $Λ$ production to order $α_s$. With appropriate operato…
Spin dependent fragmentation functions for heavy flavor quarks to fragment into heavy baryons are calculated in a quark-diquark model. The production of intermediate spin 1/2 and 3/2 excited states is explicity included. $Λ_b$ , $Λ_c$ and $Ξ_c$ production rate and polarization at LEP energies are calculated and, where possible, compared with experiment. A different approach, also relying on a heavy quark-diquark model, is proposed for the small momentum transfer inclusive production of polarized heavy flavor hyperons. The predicted $Λ_c$ polarization is roughly in agreement with experiment.
We study the inclusive production of $Λ$ ($\bar Λ$) in several high energy collision processes ($e^+e^-, e^{\pm}p, ν(\bar ν)p, pp$), in view of an accurate determination of the unpolarized and polarized fragmentation functions of a quark into a $Λ$ ($\bar Λ$). For polarized fragmentation functions the inaccuracy and the scarcity of present data do not allow to distinguish between various theoretical models. We will indicate how future measurements will provide ways to discriminate between them and also how to achieve a necessary quark flavor separation. A possible extension to the production o…
We consider Lambda-hyperon production in the target-fragmentation region of semi-inclusive deep-inelastic scattering within the framework of fracture functions. We present a first attempt to determine the flavour and energy dependences of these non-perturbative distributions through a simultaneous QCD-based fit to available neutral- and charged-current semi-inclusive-DIS cross sections. Predictions based on the resulting nucleon-to-Lambda fracture functions are in good agreement with data and observables not included in the regression. The successful prediction of the $Q^2$ dependence of the L…
A simple quark-diquark model for nucleon and $Λ$ structure is used to calculate leading twist light-cone fragmentation functions for a quark to inclusively decay into P or $Λ$. The parameters of the model are determined by fitting to the known deep-inelastic structure functions of the nucleon. When evolved from the initial to the final $Q^2$ scale, the calculated fragmentation functions are in remarkable agreement (for $z>0.4 $) with those extracted from partially inclusive $ep$ and $e^+ e^-$ experiments at high energies. Predictions are made, using no additional parameters, for longitudinally…
Understanding the origin and mechanism of the transverse polarization of hyperons produced in unpolarized proton-proton collision, $pp\to Λ^\uparrow X$, has been one of the long-standing issues in high-energy spin physics. In the framework of the collinear factorization applicable to large-$p_T$ hadron productions, this phenomenon is a twist-3 observable which is caused by multi-parton correlations either in the initial protons or in the process of fragmentation into the hyperon. We derive the twist-3 gluon fragmentation function (FF) contribution to this process in the leading order (LO) with…
We study the longitudinal polarization of hyperons and anti-hyperons at forward pseudorapidity, $2.5<η<4$, in singly polarized $pp$ collisions at RHIC energies by using different parameterizations of the polarized parton densities and different models for the polarized fragmentation functions. The results show that the $Σ^+$ polarization is able to distinguish different pictures on spin transfer in high energy fragmentation processes; and the polarization of $Λ$ and $\barΛ$ hyperons can provide sensitivity to the helicity distribution of strange sea quarks. The influence from beam remnant to h…
We investigate the spin-dependent (naive) T-odd fragmentation function $D^\perp_{1T}$, which can provide an explanation on the transverse polarization of the $Λ^0$ hyperon produced in an unpolarized process. We calculate $D^\perp_{1T}$ for light flavors in the spectator diquark model, with a Gaussian form factor at the hyperon-quark-diquark vertex. We include in the calculation both the scalar diquark and axial-vector diquark spectators. We determine the values of the model parameters by fitting the unpolarized fragmentation function $D^Λ_1$ to the DSV parametrization for $D^Λ_1$. In addition,…
We point out that measuring longitudinal polarizations of different hyperons produced in lepton induced reactions are ideal to study the spin transfer of the fragtmenting quark to produced hadron in high energy hadronization processes. We briefly summarize the method used in calculating the hyperon polarizations in these processes, then present some of the results for e+e- and e-p or νp reactions obtained using two different pictures for the spin structure of hyperon: that drawn from polarized deep inelastic lepton-nucleon scattering data or that using SU(6) symmetric wave functions. The resul…
We calculate the polarizations for different octet hyperons produced in the current fragmentation regions of the deeply inelastic lepton-nucleon scatterings $μ^-N \to μ^- HX$ and $ν_μ N \to μ^- HX$ 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 $Σ^+$ produced in these processes can …
We investigate the transverse polarization of the $Λ$ hyperon in the processes $e^+e^-\toΛ^\uparrow π^\pm X$ and $e^+e^-\toΛ^\uparrow K^\pm X$ within the framework of the transverse momentum dependent~(TMD) factorization. The transverse polarization is contributed by the convolution of the transversely polarizing fragmentation function~(PFF) $D_{1T}^\perp$ of the lambda hyperon and the unpolarized fragmentation function $D_1$ of pion/kaon. We adopt the spectator diquark model result for $D_{1T}^{\perp}$ to numerically estimate the transverse polarization in $e^+e^-\toΛ^\uparrow h X$ process at…
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 fin…
We calculate the longitudinal polarizations of hyperons in high $p_\perp$ jets in $pp$ collisions in which one of the protons is longitudinally polarized at RHIC energies using different models for the spin transfer in fragmentation process. The results show that the measurements of these polarizations can be used to study the spin transfer in high energy fragmentation processes in general and to test the different models in particular. Our results show especially that the magnitude of the polarization of $Λ$ is rather small whereas that of $Σ^+$ is considerably larger in the large rapidity re…
Data for magnetic moments and semileptonic decays show disagreements between experimental values and theoretical predictions not easily explained by simple models for $Λ$ and $Σ$ hyperons.
INFN-Sezione di Catania（意大利国家核物理研究所卡塔尼亚分部）；University of Catania（卡塔尼亚大学）；University of Science and Technology of China（中国科学技术大学）；Anhui University of Science and Technology（安徽理工大学）；Central China Normal University（华中师范大学）；Johann Wolfgang Goethe Universitaet（约翰·沃尔夫冈·歌德法兰克福大学）
We consider mechanism for hyperon polarization in inclusive production. The main role belongs to the orbital angular momentum and polarization of the strange quark-antiquark pairs in the internal structure of the constituent quarks. We consider a nucleon as a core consisting of the constituent quarks embedded into quark condensate. The nonperturbative hadron structure is based on the results of chiral quark models.
We show that, in $ν_μN\to μ^-ΛX$ 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 $Λ$ polarization using different pictures. Based on this, we make a rough estimation for the longitudinal $Λ$ polarization in $ν_μ N \to μ^- ΛX$ at the NOMAD energies. A comparison with the data is given and predictions for $ν_μN\toμ^-Σ^+X$ are presented.
We analyze single-spin asymmetries (SSAs) in the leptoproduction of transversely polarized $Λ$ hyperons within the collinear twist-3 formalism. We calculate both the distribution and fragmentation terms in two different gauges (lightcone and Feynman) and show that the results are identical. This is the first time that the fragmentation piece has been analyzed for transversely polarized hadron production within the collinear twist-3 framework. In lightcone gauge we use the same techniques that were employed in computing the analogous piece in $p^\uparrow p\to π\,X$, which has become an importan…
We consider polarized Lambda hyperon production in proton-proton scattering, p p -> (Λ^\uparrow jet) jet X, in the kinematical region of the LHC experiments, in particular the ALICE experiment. We present a new Lambda polarization observable that arises from the Sivers effect in the fragmentation process. It can be large even at midrapidity and therefore, is of interest for high energy hadron collider experiments. Apart from its potential to shed light on the mechanisms behind the phenomenon of Lambda polarization arising in unpolarized hadronic collisions, the new observable in principle also…
Weak radiative hyperon decays are considered in the framework of a quark model. The phenomenological model includes 1-quark transitions with the effective $sdγ$-vertex and 2-quark ones with the W-exchange $s+u\to u+d+γ$ and turns out to describe well the data and gives predictions for asymmetry of the decays $Λ\to n+γ$ and $Ξ^-\to Σ^- +γ$.
Making use of the collinear expansion technique developed by Ellis, Furmanski and Petrozio, and the special propagator concept invented by Qiu, we present a factorization approach to the photon fragmentation tensor for the inclusive Lambda hyperon production. As a result, the structure function $\tilde F$, which is related to the transverse polarization of the inclusive Lambda hyperon in unpolarized electron-positron annihilation, is expressed as a combination of four parton fragmentation matrix elements. Since the inclusive $Λ$ production we considered is theoretically the simplest, our study…
The model combined with unitarity and impact parameter picture provide a rather simple mechanism of hyperon polarization generation in collision of unpolarized hadrons. We concentrate on a particular problem of $Λ$-hyperon polarization and derive its linear $x_F$-dependence as well as its energy and transverse momentum independence at large $p_\perp$. Mechanism responsible for the single--spin asymmetries in pion production is also discussed.
We use the meson cloud model and the Sullivan mechanism to estimate the sea flavor asymmetry in the Σ^+ baryon and calculate the distribution functions of both sea and valence quarks. We find large deviations from SU(3).
We calculate magnetic moments of nucleons and hyperons and N -> Delta + gamma transition characteristics using a manifestly Lorentz covariant chiral quark approach for the study of baryons as bound states of constituent quarks dressed by a cloud of pseudoscalar mesons.
We explore how well one can probe the s quark chirality of the fundamental weak interaction of nonleptonic B decay using the spin-analyzing property of the Lambda hyperon. We present the prediction of the Standard Model as quantitatively as possible in a perturbative QCD picture avoiding detailed form-factor calculation involving quark mass corrections. A clean test of chirality will be possible with the decay B-bar to Lambda X.
For the omega-hyperon passing through matter the phenomena of spin rotation and oscillation has investigated quantitatively. Connection of these phenomena with constituent quark rescattering has been determined. It allows one to investigate quark rescattering directly without background of a single scattering.
We investigate the transverse polarization of hyperons produced by the photon induced reactions using the quark recombination model. This model reproduces polarizations of hadrons produced by the hadron-hadron collisions and accounts for the origin of the empirical rule by DeGrand and Miettinen. We find significant polarizations in the hyperon photoproduction by applying this model to the $γN \ra \Lam $ $(Σ^{0}) + X$ reaction.
A relativistic constituent quark model is used to calculate the semileptonic beta decay of nucleons and hyperons. The parameters of the model, namely, the constituent quark mass and the confinement scale, are fixed by a previous calculation of the magnetic moments of the baryon octet within the same model. We discuss the momentum dependence of the form factors, possible configuration mixing and SU(3) symmetry breaking. We conclude that the relativistic constituent quark model is a good framework to analyze electroweak properties of the baryons.
A continuing mystery in particle physics is the large polarization observed in inclusive hyperon production in high energy p-p collisions. In this paper the authors advance the concept that the polarization effects can be accounted for in a simple model based on quarks becoming polarized in the direct q-q scattering process and where, at a fundamental level, the s quark is treated no differently than the u and d, except that it is required to have been created as part of a s-sbar pair prior to the collision. The q-q polarization parameters are extracted from p-p elastic scattering using a prev…
It is argued that the results of recent precision measurements by LHCb of the lifetimes of charmed and bottom hyperons are very well consistent with the description within heavy quark expansion and allow to accurately determine matrix elements of light-flavor nonsinglet four-quark operators over the hyperons and to accurately reproduce the difference of lifemes of $Λ_b$ and $Ξ_b^-$. When combined with the recent LHCb results on the decay $Ξ_b^- \to Λ_b π^-$ this leads to prediction of a lower bound on the rate of the decays $Ξ_c \to Λ_c π$.
The paper describes the quantization of the SU(3) smibosonized Nambu-Jona-Lasinio model and results for mass splittings, including isospin splittings, and axial couplings. The agreement with the data is surprisingly good.
We investigate the semileptonic hyperon decays within the framework of the self-consistent SU(3) chiral quark-soliton model ($χ$QSM). We take linear $1/N_c$ rotational as well as linear $m_s$ corrections into account and apply the symmetry conserving quantization. We present the results for the form factors $f_1(Q^2)$, $f_2(Q^2)$ and $g_1(Q^2)$ in addition to the semileptonic decay constants of hyperons. We also have calculated the radii and dipole masses of these form factors for all relevant strangeness-conserving and strangeness-changing transitions.
In the large $N_c$ limit, all hyperon decays involving the same quark diagram $Q\to Q'$ are described by a single weak form factor $η_{QQ'}(w)$. No assumption on the mass of $Q$ or $Q'$ is necessary, making our results applicable to both $b\to c$ and $c\to s$ transitions. This same form factor describes both $Λ_Q\toΛ_{Q'}$ and $Σ^{(*)}_Q\toΣ^{(*)}_{Q'}$ transitions. The (non-)commutativity between the heavy quark and the large $N_c$ limits is briefly discussed under the definite example of $Λ_b\toΛ_c$ decay.
First next-to-next-to-leading-order extraction of fragmentation functions for Lambda hyperons
Université Paris-Saclay（巴黎萨克雷大学）；CEA（法国原子能及替代能源委员会）；University of the Basque Country (EHU)（巴斯克大学）；The Higgs Centre for Theoretical Physics, University of Edinburgh（爱丁堡大学希格斯理论物理中心）；IKERBASQUE, Basque Foundation for Science（伊克尔巴斯基克科学基金会）
The model combined with unitarity and impact parameter picture provides simple mechanism for generation of hyperon polarization in collision of unpolarized hadrons. We concentrate on a particular problem of $Λ$-hyperon polarization and derive its linear $x_F$-dependence as well as its energy and transverse momentum independence at large $p_\perp$ values. Mechanism responsible for the single--spin asymmetries in pion production is also discussed.
Baryonic correlation functions are calculated within an effective chiral quark model motivated by the instanton liquid model of QCD. Using a flavour SU(3) symmetry for the local four-quark interaction and taking rotational zero modes for the quantization into account low-energy hadronic observables are in surprising agreement with experimental data. (Talk presented at the Conference on Hypernuclear and Strange Particle Physics (HYP94), Vancouver, B.C., Canada, 4.-8- Juli 1994)
We make a detailed study of the longitudinal polarization of hyperons and anti-hyperons in semi-inclusive deep-inelastic lepton-nucleon scattering. We present the numerical results for spin transfer in quark fragmentation processes, analyze the possible origins for a difference between the polarization for hyperon and that for the corresponding anti-hyperon. We present the results obtained in the case that there is no asymmetry between sea and anti-sea distribution in nucleon as well as those obtained when such an asymmetry is taken into account. We compare the results with the available data …
It is shown that $Λ$-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 $Λ$-hyperon at large $x$. Numerical predictions are given for the spin transfers of the produced $Λ$, when the target nucleon is polarized either longitudinally or transversely, and with the nucleon and $Λ$ 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 predi…
The spectrum of the C=1 hyperons is well described by the constituent quark model, if the fine structure interaction between the light and strange quarks is mediated by the $SU(3)_F$ octet of light pseudoscalar mesons, which are the Goldstone bosons of the hidden approximate chiral symmetry of QCD. With the addition of a phenomenological flavor exchange interaction of the same form between the light and the charm quarks to describe the $Σ_c-Σ_c^*$ and $Ξ_c^s-Ξ_c^*$ splittings, the splittings between the C=1 states fall within 10-30 MeV of the empirical values. Predictions are presented for the…
Hyperon and antihyperon production is investigated using two microscopical models: {\bf (1)} the fast hadronization of quark matter as given by the ALCOR model; {\bf (2)} string formation and fragmentation as in the HIJING/B model. We calculate the particle numbers and momentum distributions for Pb+Pb collisions at CERN SPS energies in order to compare the two models with each other and with the available experimental data. We show that these two theoretical approaches give similar yields for the hyperons, but strongly differ for antihyperons.
The chiral quark model gives a reasonably good description of many low-energy observables by incorporating the effective degrees carried by the constituent quarks and Goldstone bosons. We calculate the decuplet to octet transition magnetic moments and the decay widths of several excited hyperons using this model. The various radiative decay widths from the chiral quark roughly agree with experimental data including the recent JLAB measurement.
Longitudinal polarizations of different kinds of hyperons produced in e+e- annihilation at LEP I and LEP II energies in different event samples are calculated using two different pictures for the spin structure of hyperon: that drawn from polarized deep inelastic lepton-nucleon scattering data or that using SU(6) symmetric wave functions. The result shows that measurements of such polarizations should provide useful information to the question of which picture is more suitable in describing the spin effects in the fragmentation processes.
Weak radiative hyperon decays present us with a long-standing puzzle, namely the question of validity of a hadron-level theorem proved by Hara. We briefly discuss the conflict between expectations based on Hara's theorem and experiment as well as the way in which the quark model evades the theorem. Violation of Hara's theorem in the quark model is traced back to the issue of hadron compositeness and the nonequivalence of standard ways of imposing gauge-invariance condition at quark and hadron levels. This suggests that our understanding of nonlocal composite nature of hadrons may require some …
We study the polarization of hyperon in different processes in singly polarized $pp$ collisions, in particular its relation to the polarized parton distributions. We show that by measuring hyperon polarization in particularly chosen processes, one can extract useful information on these parton distributions. We show in particular that, by measuring the $Σ^+$ polarization in high $p_T$ direct photon production process, one can extract information on the gluon helicity distribution; and by measuring the transverse polarization of hyeprons with high $p_T$ in singly polarized reactions, one can ob…
We investigate the transverse target spin asymmetry $A^{\sinϕ_{S}}_{UT}$ for the unpolarized $Λ$ production in semi-inclusive deep inelastic scattering with the transverse momentum of the final-state lambda hyperon being integrated out. The asymmetry is contributed by the product of the transversity distribution function $h_1(x)$ of the nucleon and the collinear twist-3 fragmentation function $\tilde{H}(z)$ of the $Λ$ hyperon. The later one originates from the quark-gluon-quark correlation and is a naive time-reversal-odd function. We calculate $\tilde{H}$ of the $Λ$ hyperon by adopt a diquark…
We study the production of transversely polarized Lambda hyperons in high-energy collisions of protons with large nuclei. The large gluon density of the target at saturation provides an intrinsic semi-hard scale which should naturally allow for a weak-coupling QCD description of the process in terms of a convolution of the quark distribution of the proton with the elementary quark-nucleus scattering cross section (resummed to all twists) and a fragmentation function. In this case of transversely polarized Lambda production we employ a so-called polarizing fragmentation function, which is an od…
Longstanding puzzles in spin physics can be confronted at the high energies of the LHC. Will large s-quark and c-quark polarization be observed through heavy hyperon production? Top quarks are expected to have significant polarization - single spin asymmetries. How can such observations sort out possible QCD mechanisms? Leptoproduction provides a means to access those mechanisms. TMDs, GPDs and Fracture Functions all provide different model approaches to the polarization phenomena. Their implications will be described.
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.
We investigate the hyperon semileptonic decays and the quark spin content of the proton $ΔΣ$ taking into account flavor SU(3) symmetry breaking. Symmetry breaking is implemented with the help of the chiral quark-soliton model in an approach, in which the dynamical parameters are fixed by the experimental data for six hyperon semileptonic decay constants. As a result we predict the unmeasured decay constants, particularly for $Ξ^0 \to Σ^+$, which will be soon measured and examine the effect of the SU(3) symmetry breaking on the spin content $ΔΣ$ of the proton. Unfortunately large experimental e…
We investigate the ''spontaneous'' hyperon transverse polarization in $e^+e^-$ annihilation and semi-inclusive deep inelastic scattering processes as a test of the universality of the naive-time-reversal-odd transverse momentum dependent fragmentation functions. We find that universality implies definite sign relations among various observables. This provides a unique opportunity to study initial/final state interaction effects in the fragmentation process and test the associated factorization.
