The interplay between quark and hadronic degrees of freedom and the structure of the proton (original) (raw)
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Nature, 2015
Quantum Chromodynamics (QCD) provides a fundamental description of the physics binding quarks into protons, neutrons, and other hadrons. QCD is well understood at short distances where perturbative calculations are feasible. Establishing an explicit relation between this regime and the large-distance physics of quark confinement has been a long-sought goal. A major challenge is to relate the parameter Λs, which controls the predictions of perturbative QCD (pQCD) at short distances, to the masses of hadrons. Here we show how new theoretical insights into QCD's behavior at large and small distances lead to an analytical relation between hadronic masses and Λs. The resulting prediction, Λs = 0.341 ± 0.024 GeV agrees well with the experimental value 0.339 ± 0.016 GeV. Conversely, the experimental value of Λs can be used to predict the masses of hadrons, a task which had so far only been accomplished through intensive numerical lattice calculations, requiring several phenomenological...
Low-energy weak interactions of quarks
Physics Reports, 1986
Introduction 321 6.1. Data and kinematics 2. General background of the standard model 322 6.2. Theoretical procedures 2.1. Conventions 322 6.3. Baryonic I1S~= 1 decays 2.2. Electroweak (SU(2)L x 1.1(1)) interactions 322 6.4. Kaon decays 2.3. Strong (SU(3)~) interactions 324 7. Other decay modes 3. A users guide to the quark model 327 8, Physics of the K°K°system 3.1. Spin-color wavefunctions 327 8.1. Overview 3.2. Spatial wavefunctions 330 8.2. Short distance physics 3.3. Connection with plane wave states 335 8.3. The B parameter 3.4. How to calculate matrix elements 336 8.4. Long distance physics 3.5. Limitations to the quark model approach 338 8.5. The KL-KS mass difference 4. Nuclear beta decay 339 8.6. CP-violation 4.1. Tests of CVC 342 9. Nuclear parity violation 4.2. Second class currents 344 10. Weak decays of hypernuclei 4.3. Tests of PCAC 345 11. Recent developments 5. Semileptonic weak decays 348 11.1. Nonleptonic interactions and lattice gauge theory 5.1. Hyperon beta decay 348 11.2. Nonleptonic interactions of chiral solitons 5.2. ii-and K decay 355 12. Conclusions 6.~= 1 hadronic decays 356 References
Heavy quarks and strong binding: A field theory of hadron structure
Physical review, 1975
We investigate in canonical field theory the possibility that quarks may exist in isolation as very heavy particles, M quark >> 1 GeV, yet form strongly bound hadronic states, Mhadron N 1 GeV. In a model with spin5 quarks coupled to scalar gluons we find that a mechanism exists for the formation of bound states which are much lighter than the free constituents. Following Nambu, a color interaction mediated by gauge ,vector mesons is introduced to guarantee that all states with non-vanishing triality have masses much larger than 1 GeV. The possibility of such a solution to a strongly coupled fie'ld theory is exhibited by a calculation employing the variational princi@e in tree approximation. This procedure reduces the field theoretical problem to a set of couljled differential .-equations for classical fields which are just the free parameters of the variational state. A striking property of the solution is that the quark wave function is confined to a thin shell at the surface of the hadronic bound state. Though the quantum corrections to this procedure remain to be investigated systematically, we explore some of the phenomenological im@ications of the trial wave functions so obtained. In particular, we exhibit the low-lying meson and baryon multi@lets of SU(6); their magnetic moments, charge radii, and radiative decays; and the axial charge of the baryons. States of non-vanishing momenta are constructed and the softness of the hadron shell to deformations in scattering processes is discussed qualitatively along with the implications for deep inelastic electron scattering and dual resonance models.
Spectral quark model and low-energy hadron phenomenology
Physical Review D, 2003
We propose a spectral quark model which can be applied to low energy hadronic physics. The approach is based on a generalization of the Lehmann representation of the quark propagator. We work at the one-quark-loop level. Electromagnetic and chiral invariance are ensured with help of the gauge technique which provides particular solutions to the Ward-Takahashi identities. General conditions on the quark spectral function follow from natural physical requirements. In particular, the function is normalized, its all positive moments must vanish, while the physical observables depend on negative moments and the so-called log-moments. As a consequence, the model is made finite, dispersion relations hold, chiral anomalies are preserved, and the twist expansion is free from logarithmic scaling violations, as requested of a low-energy model. We study a variety of processes and show that the framework is very simple and practical. Finally, incorporating the idea of vector-meson dominance, we present an explicit construction of the quark spectral function which satisfies all the requirements. The corresponding momentum representation of the resulting quark propagator exhibits only cuts on the physical axis, with no poles present anywhere in the complex momentum space. The momentum-dependent quark mass compares very well to recent lattice calculations. A large number of predictions and relations, valid at the low-energy scale of the model, can be deduced from our approach for such quantities as the pion light-cone wave function, non-local quark condensate, pion transition form factor, pion valence parton distribution function, etc. These quantities, obtained at a low-energy scale of the model, have correct properties, as requested by symmetries and anomalies. They also have pure twist expansion, free of logarithmic corrections, as requested by the QCD factorization property.
Quark degrees of freedom in hadronic systems
Nuclear Physics A, 2001
The role of models in Quantum Chromodynamics is to produce simple physical pictures that connect the phenomenological regularities with the underlying structure. The static properties of hadrons have provided experimental input to define a variety of very successful Quark Models. We discuss applications of some of the most widely used of these models to the high energy regime, a scenario for which they were not proposed. The initial assumption underlying our presentation will be that gluon and sea bremsstrahlung connect the constituent quark momentum distributions with the partonic structure functions. The results obtained are encouraging but lead to the necessity of more complex structures at the hadronic scale. This initial hypothesis may be relaxed by introducing some non perturbative model for the constituent quarks. Within this scheme we will discuss some relevant problems in nucleon structure as seen in high energy experiments.
Theory Division, CERN, CH-1211 Geneva 23, Switzerland
1998
In a series of four lectures, I present the theory and phenomenology of heavy-quark symmetry, exclusive w eak decays of B mesons, inclusive decay rates and lifetimes o f b hadrons, and CP violation in B-meson decays. 1. HEAVY-QUARK SYMMETRY This lecture gives an introduction to the ideas of heavy-quark symmetry [8]{[13] and the heavy-quark eective theory [14]{[24], which provide the modern theoretical framework for the description of the properties and decays of hadrons containing a heavy quark. For a more detailed description of this subject, I refer to the review articles in Refs. [25]{ [30].
Sub-structures in hadrons and proton structure functions
Nuclear Physics B - Proceedings Supplements, 2001
We calculate the partonic structure of constituent quark in the Next-to-Leading Order. Using a convolution method, Structure function of proton is presented. While the constituent quark structure is generated purely perturbatively and accounts for the most part of the hadronic structure, there is a few percent contributions coming from the nonperturbative sector in the hadronic structure. This contribution plays the key role in explaining the SU(2) symmetry breaking of the nucleon sea and the observed violation of Gottfried sum rule. Excellent agreement with data in a wide range of z = [10e6, l] and @ = [0.5,5000] GeV2 for F2p is reached.
The strangeness form factors of the proton within nonrelativistic constituent quark model revisited
Physics Letters B, 2011
We reexamine, within the nonrelativistic constituent quark model (NRCQM), a recent claim that the current data on the strangeness form factors indicates that the uudss component in the proton is such that the uuds subsystem has the mixed spatial symmetry [31] X and flavor spin symmetry [4] F S [22] F [22] S , withs in S state (configuration I). We find this claim to be invalid if corrected expressions for the contributions of the transition current to G s A and G s E are used. We show that, instead, it is the lowest-lying uudss configuration with uuds subsystem of completely symmetric spatial symmetry [4] X and flavor spin symmetry [4] F S [22] F [22] S , withs in P state (configuration II), which could account for the empirical signs of all form factors G s E , G s M , and G s A. Further, we find that removing the center-of-mass motion of the clusters will considerably enhance the contributions of the transition current. We also demonstrate that it is possible to give a reasonable description of the existing form factors data with a tiny probability P ss = 0.025% for the uudss component. We further see that with a small admixture of configuration I , the agreement of our prediction with the data for G s A at low-q 2 region can be markedly improved. We find that without removing CM motion, P ss would be overestimated by about a factor of four in the case when transition current dominates. We also explore the consequence of a recent estimate reached from analyzing the existing data ond −ū , s +s , andū +d − s −s, that P ss lies between 2.4 − 2.9%. It would lead to a large size for the five-quark system and a small bump in both G s E + ηG s M and G s E in the region of q 2 ≤ 0.1 GeV 2 within the considered model.