Showing papers on "Proton spin crisis published in 2008"
TL;DR: The consequences of the Myhrer-Thomas explanation of the proton spin problem for the distribution of orbital angular momentum on the valence and sea quarks are derived.
Abstract: We derive the consequences of the Myhrer-Thomas explanation of the proton spin problem for the distribution of orbital angular momentum on the valence and sea quarks. After QCD evolution, these results are found to be in very good agreement with both recent lattice QCD calculations and the experimental constraints from Hermes and JLab.
102 citations
TL;DR: A number of lines of investigation into the structure of the nucleon have converged to the point where one has a consistent explanation of the well known proton spin crisis as mentioned in this paper.
64 citations
TL;DR: In this paper, the consequences of the Myhrer-Thomas explanation of the proton spin problem for the distribution of orbital angular momentum on the valence and sea quarks after QCD evolution were derived.
Abstract: We derive the consequences of the Myhrer-Thomas explanation of the proton spin problem for the distribution of orbital angular momentum on the valence and sea quarks After QCD evolution, these results are found to be in very good agreement with both recent lattice QCD calculations and the experimental constraints from Hermes and JLab
56 citations
TL;DR: In this article, it was shown that the origin of the discrepancy between the original data and the naive expectation of the fraction of spin carried by the quarks and anti-quarks in the proton lies in the nonperturabtive structure of the Proton.
37 citations
TL;DR: The role of the U(1)A anomaly in QCD phenomenology is reviewed in this article, focusing on the relation between quark dynamics and gluon topology, and the first moment sum rule for g 1 р (the ‘proton spin’ problem) is confronted with new data from COMPASS and HERMES on the deuteron structure function and shown to be quantitatively explained in terms of topological charge screening.
Abstract: The role of the U(1)A anomaly in QCD phenomenology is reviewed, focusing on the relation between quark dynamics and gluon topology. Topics covered include a generalisation of the Witten–Veneziano formula for the mass of the η′, the determination of pseudoscalar meson decay constants, radiative pseudoscalar decays and the U(1)A Goldberger–Treiman relation. Sum rules are derived for the proton and photon structure functions g 1 р and g 1 γ measured in polarised deep inelastic scattering (DIS). The first moment sum rule for g1 р (the ‘proton spin’ problem) is confronted with new data from COMPASS and HERMES on the deuteron structure function and shown to be quantitatively explained in terms of topological charge screening. Proposals for experiments on semi-inclusive DIS and polarised two-photon physics at future eр and high-luminosity e+ e- colliders are discussed.
36 citations
TL;DR: The resulting model equation was fitted to observed spin diffusion versus MAS rate data obtained at 298 K on an high-density polyethylene sample, revealing a reduction in the effective spin diffusivity when increasing the MAS rate from 2 to 12 kHz.
Abstract: Starting from the phenomenological Bloembergen-Purcell-Pound equation a relation between magic-angle spinning (MAS) rate and spin diffusion is derived. The resulting model equation was fitted to observed spin diffusion versus MAS rate data obtained at 298 K on an high-density polyethylene sample, revealing a reduction in the effective spin diffusivity by (65 + 5)% when increasing the MAS rate from 2 to 12 kHz. The same model equation enabled the rigid-lattice diffusivity to be estimated and was found to be only slightly higher, by approximately 10%, compared to the spin diffusivity observed at the lowest MAS rate applied (2 kHz). Moreover, the model equation predicts a reduction in the effective spin diffusivity by more than 90% when increasing the MAS rate to more than 30 kHz.
22 citations
TL;DR: Several spin and flavor dependent parameters characterizing the strangeness content of the nucleon have been calculated in the chiral constituent quark model with configuration mixing (chiCQM{sub config}) which is known to provide a satisfactory explanation of the "proton spin crisis" and related issues as discussed by the authors.
Abstract: Several spin and flavor dependent parameters characterizing the strangeness content of the nucleon have been calculated in the chiral constituent quark model with configuration mixing ({chi}CQM{sub config}) which is known to provide a satisfactory explanation of the ''proton spin crisis'' and related issues. In particular, we have calculated the strange spin polarization {delta}s, the strangeness contribution to the weak axial vector couplings {delta}{sub 8} etc., strangeness contribution to the magnetic moments {mu}(p){sup s} etc., the strange quark flavor fraction f{sub s}, the strangeness dependent quark flavor ratios (2s/u+d) and (2s/u+d) etc. Our results are consistent with the recent experimental observations.
21 citations
TL;DR: In this article, it was shown that the origin of the discrepancy between experiment and the naive expectation of the fraction of spin carried by the quarks and anti-quarks in the proton lies in the nonperturabtive structure of the Proton.
Abstract: The twenty years since the announcement of the proton spin crisis by the European Muon Collaboration has seen tremendous progress in our knowledge of the distribution of spin within the proton. The problem is reviewed, beginning with the original data and the suggestion that polarized gluons may play a crucial role in resolving the problem through the U(1) axial anomaly. The discussion continues to the present day where not only have strong limits have been placed on the amount of polarized glue in the proton but the experimental determination of the spin content has become much more precise. It is now clear that the origin of the discrepancy between experiment and the naive expectation of the fraction of spin carried by the quarks and anti-quarks in the proton lies in the non-perturabtive structure of the proton. We explain how the features expected in a modern, relativistic and chirally symmetric description of nucleon structure naturally explain the current data.
20 citations
TL;DR: It is observed that in the absence of microwave irradiation and radical a transient negative polarization is observed for the methyl signals of acetone and DMSO, and it is suggested that this polarization arises from rotational tunneling levels in this system.
Abstract: Dynamic nuclear polarization (DNP) is often carried out at low temperatures to utilize the high spin polarization of the radical electrons at these temperatures. We have observed that in the absence of microwave irradiation and radical a transient negative polarization is observed for the methyl signals of acetone and DMSO. We suggest that this polarization arises from rotational tunneling levels in this system. For samples dissolved in these solvents, we see a diminished polarization with a microwave frequency of ωe − ωN compared to ωe + ωN, and we relate the two effects due to constructive/destructive interference with proton spin diffusion and spin symmetry diffusion mediating the intermolecular transfer of polarization. Perdeuteration of the solvents acts to nullify this effect. Awareness of this additional factor in the temperature jump DNP experiment allows improved experiment design and polarization of samples which have otherwise proven virtually impossible.
17 citations
01 Jan 2008
TL;DR: A review of the present understanding of the QCD spin structure of the proton can be found in this paper, where the present and next generation of experiments being undertaken to resolve the Proton's spin-flavor structure are discussed.
Abstract: This article reviews the present understanding of the QCD spin structure of the proton. The author first outlines the proton spin puzzle and its possible resolution in QCD. Then the review explores the present and next generation of experiments being undertaken to resolve the proton's spin-flavor structure, explaining the theoretical issues involved, the present status of experimental investigation, and the open questions and challenges for future investigation.
14 citations
TL;DR: In this article, a large amount of analysis done in conjunction with the polarized proton program at RHIC is described, including elastic scattering data of protons on protons in colliding beam or fixed target mode and proton beams on carbon targets.
Abstract: This paper serves as a report on the large amount of analysis done in conjunction with the polarized proton program at RHIC. This comprises elastic scattering data of protons on protons in colliding beam or fixed target mode and proton beams on carbon targets. In addition to providing a model for the energy dependence of the analyzing power of elastic scattering needed for proton polarimetry, it also provides some significant information about the spin dependence of dominant Regge poles. Most notably, the data indicates that the Pomeron has a significant spin-flip coupling. This allows the exploration of the double spin flip asymmetry ANN for which some data over a wide energy range is now available, along with a concrete realization of a proposed Odderon search.
06 Feb 2008
TL;DR: A 50-year overview of the development of the tools of proton spin physics is presented in this paper, including nuclear scattering, ion sources for polarized protons and deuterons based on atomic beam and optical pumping methods, and polarized gas targets.
Abstract: This paper was part of the general‐interest session on lecture day, and is thus addressed to a general audience. A 50‐year historic overview of the development of the tools of proton spin physics is presented: nuclear scattering, ion sources for polarized protons and deuterons based on atomic beam and optical pumping methods, and polarized gas targets.
TL;DR: In this article, it was shown that the ratio of the squares of the electric and magnetic proton form factors is proportional to the proportion of the cross sections for the elastic scattering of an unpolarized electron on a partially polarized proton with and without proton spin flip.
Abstract: The ratio of the squares of the electric and magnetic proton form factors is shown to be proportional to the ratio of the cross sections for the elastic scattering of an unpolarized electron on a partially polarized proton with and without proton spin flip. The initial proton at rest should be polarized along the direction of the motion of the final proton. Similar results are valid for both radiative ep scattering and the photoproduction of pairs on a proton in the Bethe-Heitler kinematics. When the initial proton is fully polarized in the direction of the motion of the final proton, the cross section for the ep → ep process, as well as for the ep → epγ and γp → \( e\bar ep \) processes, without (with) proton spin flip is expressed only in terms of the square of the electric (magnetic) proton form factor. Such an experiment on the measurement of the cross sections without and with proton spin flip would make it possible to acquire new independent data on the behavior of GE2(Q2) and GM2(Q2), which are necessary for resolving the contradictions appearing after the experiment of the JLab collaboration on the measurement of the proton form factors with the method of polarization transfer from the initial electron to the final proton.
Journal Article•
TL;DR: In this article, it was shown that the proton spin puzzle and the origin of quark mass are natural consequences of the compositeness of quarks which also generates a continuous symmetry breaking.
Abstract: This work shows that the proton spin puzzle and the origin of quark mass are natural consequences of the compositeness of quarks which also generates a continuous symmetry breaking. And is also quark compositeness what is behind the Kobaiashi-Maskawa matrix. Moreover, the paper shows that prequarks (primons) have already been found by the first EMC experiment in the 1980s.
TL;DR: In this article, it was shown that the ratio of the squares of the electric and magnetic proton form factors is proportional to the proportion of the cross sections for the elastic scattering of an unpolarized electron on a partially polarized proton with and without proton spin flip.
Abstract: The ratio of the squares of the electric and magnetic proton form factors is shown to be proportional to the ratio of the cross sections for the elastic scattering of an unpolarized electron on a partially polarized proton with and without proton spin flip. The initial proton at rest should be polarized along the direction of the motion of the final proton. Similar results are valid for both radiative $ep$ scattering and the photoproduction of pairs on a proton in the Bethe--Heitler kinematics. When the initial proton is fully polarized in the direction of the motion of the final proton, the cross section for the $ep \to ep$ process, as well as for the $ep \to ep \gamma$ and $\gamma p \to e \bar e p$ processes, without (with) proton spin flip is expressed only in terms of the square of the electric (magnetic) proton form factor. Such an experiment on the measurement of the cross sections without and with proton spin flip would make it possible to acquire new independent data on the behavior of $G_E^2(Q^2)$ and $G_M^2(Q^2)$, which are necessary for resolving the contradictions appearing after the experiment of the JLab collaboration on the measurement of the proton form factors with the method of polarization transfer from the initial electron to the final proton.
TL;DR: In this paper, the PHENIX experiment collected 3.5 pb -1 (beam polarization ∼50%) and 10 pb − 1 (beam polarized ∼60%) data from year 2005 and 2006 runs, respectively.
Abstract: The measurement of spin asymmetries in polarized p+p collisions provides an opportunity to probe the spin structure of nucleons. With transversely and longitudinally polarized proton beams at RHIC, we can measure both double longitudinal spin asymmetry ALL and single transverse spin asymmetry A N . At the RHIC energy, heavy quark (charm and beauty) production is dominated by gluon-gluon interactions, so measurements of ALL and AN will allow us to directly probe the polarized gluon distribution and gluon's Sivers functions, respectively. PHENIX experiment collected 3.5 pb -1 (beam polarization ∼50%) and 10 pb -1 (beam polarization ∼60%) data from year 2005 and 2006 runs, respectively. In this analysis, the J/ Ψ have been measured through the J/Ψ→ μ + μ - channel at forward rapidities, and about 30000 J/ψ candidates are reconstructed from Lv12 triggered data production. We present the latest results of J/ψA LL and AN measurements at forward rapidities from the PHENIX experiment.
TL;DR: In this paper, the effects of quark-antiquark pairs (u anti-u, d anti-d and s anti-s) are taken into account in an explicit form via a microscopic, QCD-inspired, quark antiquark creation mechaniscm.
Abstract: We present the formalism for a new generation of unquenched quark models for baryons in which the effects of quark-antiquark pairs (u anti-u, d anti-d and s anti-s) are taken into account in an explicit form via a microscopic, QCD-inspired, quark-antiquark creation mechaniscm. The present approach is an extension of the flux-tube breaking model of Geiger and Isgur in which now the contributions of quark-antiquark pairs an be studied for any initial baryon and for any flavor of the q anti-q pair. It is shown that the inclusion of q anti-q paris leads to a large contribution of orbital angular momentum to the proton spin.
TL;DR: By measuring the lifetime of the negative muon in pure protium (1H), the MuCap experiment determines the rate of muon capture on the proton, from which the pseudoscalar coupling g ≥ p may be inferred as mentioned in this paper.
Abstract: By measuring the lifetime of the negative muon in pure protium (1H), the MuCap experiment determines the rate of muon capture on the proton, from which the proton’s pseudoscalar coupling g
p
may be inferred. A precision of 15% for g
p
has been published; this is a step along the way to a goal of 7%. This coupling can be calculated precisely from heavy baryon chiral perturbation theory and therefore permits a test of QCD’s chiral symmetry. Meanwhile, the MuSun experiment is in its final design stage; it will measure the rate of muon capture on the deuteron using a similar technique. This process can be related through pionless effective field theory and chiral perturbation theory to other two-nucleon reactions of astrophysical interest, including proton-proton fusion and deuteron breakup.
Posted Content•
02 May 2008
TL;DR: In this paper, it was shown that the ratio of the squares of the electric and magnetic proton form factors is proportional to the proportion of the cross sections for the elastic scattering of an unpolarized electron on a partially polarized proton with and without proton spin flip.
Abstract: The ratio of the squares of the electric and magnetic proton form factors is shown to be proportional to the ratio of the cross sections for the elastic scattering of an unpolarized electron on a partially polarized proton with and without proton spin flip. The initial proton at rest should be polarized along the direction of the motion of the final proton. Similar results are valid for both radiative $ep$ scattering and the photoproduction of pairs on a proton in the Bethe--Heitler kinematics. When the initial proton is fully polarized in the direction of the motion of the final proton, the cross section for the $ep \to ep$ process, as well as for the $ep \to ep \gamma$ and $\gamma p \to e \bar e p$ processes, without (with) proton spin flip is expressed only in terms of the square of the electric (magnetic) proton form factor. Such an experiment on the measurement of the cross sections without and with proton spin flip would make it possible to acquire new independent data on the behavior of $G_E^2(Q^2)$ and $G_M^2(Q^2)$, which are necessary for resolving the contradictions appearing after the experiment of the JLab collaboration on the measurement of the proton form factors with the method of polarization transfer from the initial electron to the final proton.
01 Jan 2008
TL;DR: In this paper, the effects of quark-antiquark pairs (u, d, and s) are taken into account in an explicit form, and it is shown that the inclusion of the quark and antique pairs leads to an excess of \( \bar d \) over ǫ quarks in the proton as well as a relatively large contribution of orbital angular momentum to theproton spin.
Abstract: We present two applications of an unquenched quark model for baryons in which the effects of quark-antiquark pairs (uū, d \( \bar d \) and s \( \bar s \)) are taken into account in an explicit form. It is shown that the inclusion of the quark-antiquark pairs leads to an excess of \( \bar d \) over ū quarks in the proton as well as to a relatively large contribution of orbital angular momentum to the proton spin.
TL;DR: In this article, a theoretical consideration is given to three types of prohibition of transitions between the rotational states of spin isomers of an H216O molecule, which are based on the molecular symmetry.
Abstract: A theoretical consideration is given to three types of prohibition of transitions between the rotational states of spin isomers of an H216O molecule, which are based on the molecular symmetry. This is the symmetry of the electron shell of the molecule, of the proton spin functions, of the spatial position of molecular nuclei, and of the rotational Hamiltonian. The prohibition of dipole transitions between isomers and the prohibition of transitions on the basis of the Pauli principle were known earlier. Another prohibition exists which is a consequence of the symmetric position of protons relative to the oxygen nucleus. Conditions are indicated under which the prohibition of ortho-para transitions in a water molecule disappear. In the general form these conditions are realized when the molecule loses the above-listed symmetries. Transitions are allowed in the dipole approximation if the proton spin moments are free and do not form superposition states and the O-H bond lengths are different because of nonlinearity of the molecular vibrations. The transitions are induced by the dipole-moment component due to the deformation of the electron shell of the molecule.
01 Jan 2008
TL;DR: In this paper, the color boundary term is exploited to obtain the missing piece in the axial charge associated with the gluon Casimir energies, and the result is that the flavor singlet axial current is small independent of the confinement (bag) size.
Abstract: The flavor singlet axial charge has been a source of study in the last years due to its relation to the so called Proton Spin Problem. The relevant flavor singlet axial current is anomalous, i.e., its divergence contains a piece which is the celebrated UA(1) anomaly. This anomaly is intimately associated with the η ' meson, which gets its mass from it. When the gauge degrees of freedom of QCD are confined within a volume as is presently understood, the UA(1) anomaly is known to induce color anomaly leading to "leakage" of the color out of the confined volume (or bag). For consistency of the theory, this anomaly should be canceled by a boundary term. This "color boundary term" inherits part or most of the dynamics of the volume (i.e., QCD). In this paper, we exploit this mapping of the volume to the surafce via the color boundary condition to perform a complete analysis of the flavor singlet axial charge in the chiral bag model using the Cheshire Cat Principle. This enables us to obtain the hitherto missing piece in the axial charge associated with the gluon Casimir energies. The result is that the flavor singlet axial charge is small independent of the confinement (bag) size ranging from the skyrmion picture to the MIT bag picture, thereby confirming the (albeit approximate) Cheshire Cat phenomenon. .
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TL;DR: In this article, the authors examined the single-spin asymmetry caused by the quark component of the proton for semi-inclusive electroproduction of charged pions in deepinelastic scattering on a transversely polarized hydrogen target.
Abstract: We examine the single-spin asymmetry (SSA) caused by the five-quark componentsof the proton for semi-inclusive electroproduction of charged pions in deep-inelastic scat-tering on a transversely polarized hydrogen target. The large SSA is considered to haveclose relation with quark orbital motion in the proton and suggests that the quark orbitalangular momentum is nonzero. For the five-quark qqqqq¯ components of the proton, thelowest configurations with qqqq system orbitally excited and the ¯q in the ground statewould give spin-orbit correlations naturally for the quarks in a polarized proton. Weshow that based on the basic reaction γq → πq ′ , the orbital-spin coupling of the probedquarks in the five-quark configuration leads to the single-spin asymmetry consistent withrecent experiment results. 1 Introduction The spin composition of the proton in terms of its fundamental quark and gluon degrees offreedom is a central focus of proton structure. Whether the quark orbital angular momentumis zero or not is one of the key points to solve this problem. The importance of quark orbitalangular momentum, which one might have taken to vanish in the ground state, has beenevident since the work of Sehgal [1]. The orbital angular momentum structure of the proton is
TL;DR: A variety of measurements performed utilizing transversely polarized proton-proton collisions at the Relativistic Heavy Ion Collider (RHIC) are now avail- able as discussed by the authors.
Abstract: A variety of measurements performed utilizing transversely polarized proton- proton collisions at the Relativistic Heavy Ion Collider (RHIC) are now avail- able. Recent results from the PHENIX and BRAHMS experiments are presented and discussed.
TL;DR: In this article, the impact of very precise CLAS and COMPASS g 1/F 1 data on polarized parton densities and higher twist effects is discussed, and it is demonstrated that low Q 2 CLAS data improve essentially our knowledge of higher twist corrections to the spin structure function g 1, while the large Q 2 COMPASS data influence mainly the strange quark and gluon polarizations.
Abstract: The impact of the recent very precise CLAS and COMPASS g 1/F 1 data on polarized parton densities and higher twist effects is discussed. It is demonstrated that the low Q 2 CLAS data improve essentially our knowledge of higher twist corrections to the spin structure function g 1, while the large Q 2 COMPASS data influence mainly the strange quark and gluon polarizations. It is also shown that the uncertainties in the determination of the polarized parton densities are significantly reduced. We find also that the present inclusive DIS data cannot rule out a negative polarized and changing in sign gluon densities. The present status of the proton spin sum rule is discussed.
TL;DR: In this paper, the proton spin budget is discussed and results from both inclusive and semi-inclusive deep inelastic scattering and from deeply virtual Compton scattering are presented for the first time.
Abstract: The proton spin budget is discussed. Results are presented from inclusive and semi-inclusive deep inelastic scattering and from deeply virtual Compton scattering. They permit interpretations towards the determination of various contributions to the proton spin.
15 Oct 2008
TL;DR: In this paper, the distribution of spin and orbital angular momentum in the proton has been studied in the context of QCD evolution and the distinction between "chiral" and "invariant" spin.
Abstract: We discuss recent theoretical progress in understanding the distribution of spin and orbital angular momentum in the proton. Particular attention is devoted to the effect of QCD evolution and to the distinction between “chiral” and “invariant” spin. This is particularly significant with respect to the possible presence of polarized strange quarks.
09 Jul 2008
TL;DR: In this article, the authors described the application of the muon spin rotation (μSR) technique to condensed matter and liquid phase systems, with primary emphasis reflecting their own interests and to some extent those of the μSR collaboration at the Los Alamos Meson Physics Facility (LAMPF).
Abstract: Polarized positive muons decay via weak beta decay into a positron and a pair of neutrinos. Since the muon decay is asymetric with respect to its spin direction, the positron is emitted preferentially in the direction of the muon spin at the time of decay. Detection of the positron provides information on the magnetic interaction of the muon with the environment in which it is implanted. These experimental facts form the basis for the muon spin rotation (μSR) technique which will be described in this paper. Applications of μSR to condensed matter and liquid phase systems will be discussed with primary emphasis reflecting my own interests and, to some extent, those of the μSR collaboration at the Los Alamos Meson Physics Facility (LAMPF).
12 May 2008
TL;DR: The spin muon collaboration (SMC) has studied polarized deep inelastic scattering of muons on protons and deuterons using a high energy muon beam at CERN as mentioned in this paper.
Abstract: The spin muon collaboration (SMC) has studied polarized deep inelastic scattering of muons on protons and deuterons using a high energy muon beam at CERN. We present here a summary of the results obtained from data taken in the last two years.
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TL;DR: In this article, a numerical study of QED radiative corrections for the SMC experiment at SPS is performed, where the semi-analytical program POLRAD is used to get the size of the radiative correction for the proton to obtain the measurements of the spin dependent structure functions.
Abstract: A numerical study of QED radiative corrections for the SMC experiment at SPS is been performed. The semi-analytical program POLRAD is been used to get the size of the radiative corrections for the proton to get the size of the radiative corrections for the measurements of the proton spin dependent structure functions $g_1^p(x)$ and $g_2^p(x)$. A brief description of the program POLRAD is given.