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1.
We show that knowledge of the valence quark distribution of a proton at one value of q2, enables one to calculate a contribution to the difference between the distribution of anti-up quarks (up) and anti-down quarks (dp) in the sea of the proton at higher values of q2. This difference can be expressed as a linear combination of the structure functions F1, for νp → νX and e?p → e?p (for which one knows the q2 behaviour of the moments) and for νp → μ?Xandνp → μ+X (for which one knows the q2 behaviour of the odd moments). The calculable contribution involves a non-trivial continuation of the even (odd) moments of the neutral (charged) current structure functions to odd (even) moments. We calculate this contribution and although we find that its sign is negative we point out that this cannot be interpreted as a consequences of the Pauli exclusion principle. We discuss the constraints our results impose on antiquark distributions.  相似文献   

2.
Quark masses     
In quark gluon theory with very small bare masses, -ψMψ, spontaneous breakdown of chiral symmetry generates sizable masses Mu, Md, Ms, … We find (Mu + Md) /2 ≈ mp/ √6 ≈ 312 MeV, and Ms ≈ 432 MeV. Scalar densities have well determined non-zero vaccum expectations 〈0|ua|0〉 ≡ 〈0|ψ(x) (λa/2)ψ(x)/0〉 ≈ ?π2Ma, i.e〈0? uo/vb0〉 ≈ 8 × 10?3 (GeV)3 at an SU(3) breaking of the vacuum c′ ≡ 〈0|u8|〉/〈0|uo|0〉 ≈ ? 16%  相似文献   

3.
The small ω′ behaviour of F2en/F2ep and the apparent difference in the q2 dependences of the magnetic form factor of the proton and of the transition to Δ+(1236) are quantitatively correlated in a model where nucleon consistes of a quarks and a scalar or vector core. The proton and Δ transition form factors suggest that only the scalar core contributes at large q2 and small ω′. As a result the ω′ dependence of F2enF2ep is obtained for ω′ < 3 and predictions for the weak structure functions and polarisation asymmetries at smallω′ are presented. We predict FνpFνnω′→10 asymmetries ω′→11 and also expect that GmnGmp?12 as q2→∞.  相似文献   

4.
By also taking into account off-diagonal contributions to the virtual forward Compton amplitude, scaling in ep scattering is obtained from scaling of the total cross section for e+e? annihilation into hadrons. The parameter which sets the scale for the q2 dependence in ep scattering is calculated to be m2 ? 0.61 m?2 ? 0.36 GeV2.  相似文献   

5.
We investigate transition strengths of right-handed weak charged currents in deep inelastic neutrino scattering, exploiting the dominance of p, n valence quarks in the nucleon. The energy dependence of σt and the average quantities 〈y〉 and 〈Q2〉 are shown to provide sensitive measures of new quark production thresholds and right-handed currents in νN scattering. With our analysis, the present data give an upper bound on the right to left hand structure function ratio of FRνNFLνN12, above a threshold of W≈7.5 GeV.  相似文献   

6.
John Lekner 《Physica A》1982,112(3):544-556
We derive comparison identities for waves satisfying the equation d2Ψ/dz2+q2(z)Ψ=0. One of these identities is used to show that to second order in the product (wavenumber component normal to interface) × (interface thickness), the reflection amplitude is given by r=(1?2q1q2l2)(q1?q2)(q1+q2), where l is a legnth determined by the deviation of the interface profile from a step, and q1, q2 are the normal components of the wave numbers in media 1 and 2 on either side of the interface. For the continuous interfaces discussed, l is about two-fifths of the 10–90 interface thickness. The corresponding formula for the transmission amplitude is t=(1+12(q1?q2)2l2)2q1(q1+q2).  相似文献   

7.
We have searched for the supersymmetric partner of the photon, the photino, by investigating two-photon and single photon final states in e+e? collisions. No significant signals were observed, which excludes the existence of the photino in the mass range 0.08–18 GeV/c2 at the 95% confidence level, subject to the assumptions d=(100 GeV)2 and me?=40 GeV/c2, where d is the supersymmetry breaking scale parameter and me? is the scalar electron mass.  相似文献   

8.
A recently proposed model for dynamical breaking of chiral symmetry in QCD is extended and developed for the calculation of pion and chiral symmetry breaking parameters. The pion is explicitly realized as a massless Goldstone boson and as a bound state of the constituent quarks. We compute, in the limit of exact chiral symmetry, MQ, the constituent quark mass ?π the pion decay coupling, uu〉, the constituent quark loop density, μπ2/mq, the ratio of the Goldstone boson mass squared to the bare quark mass, and 〈r2π, the pion electromagnetic charge radius squared.  相似文献   

9.
Calculations of the proton and neutron charge form factors GEp,n(q2) are presented, based on chiral bag as well as confining Dirac potential models with chiral pion-quark coupling. Special emphasis is placed on a detailed treatment of the charged pion cloud contribution to the nucleon current. The role of a finite extension of the pion-quark vertex in truncating the summation over intermediate quark bag states is studied. Quark core radii (including recoil corrections) are constrained by a simultaneous calculation of the nucleon axial form factor. The proton charge form factor is well reproduced for |q2|12 ? 0.7 GeV with quark core rms radii between 0.5–0.6 fm. About 13 of the proton charge is carried by the pion cloud in this model. The neutron charge form factor is obtained with the correct sign and overall q2 dependence but needs further refinements, probably at the level of the isoscalar form factor.  相似文献   

10.
11.
We have evaluated the parity-violation contribution in atoms in the framework of SO(3) gauge theory. Various hadronic models have been used: first, for simplicity, the unrealistic five-quark one, next, others involving three ordinary SU(3) triplets for which all unwanted strangeness-changing processes are suppressed, up to order orGαΔM2MW2. In the free quark approximation, we obtain quite similar parity-violation effects which are proportional to GαΔM2MW2 (ΔM2 is the difference of squared masses of leptons (MX02 ? Mν2 = MX02), or of quarks (ΔMq2)). Namely, in large atoms (Z ? 1) the electronic contribution which is proportional to
MX02MW2Zσ?·p?m?
gives the largest effect (σ?, p?and m?are the spin, momentum operators and mass of the lepton). Parity-violating effects in SO(3) gauge models are ?10?4 smaller than those evaluated in the Weinberg theory with a neutral parity-violating current and will remain undetectable in the near future.  相似文献   

12.
Predissociations in the y1Πg and x1Σg? Rydberg states of N2 (configurations u?14pσ and u?13pπ, respectively) and their likely causes, are discussed. Peaking of rotational intensity at unusually low J values, without sharp breaking off, is interpreted as due to case c? or case ci predissociation. Λ doubling in the y state, attributed to interactions with the x1Σg? state and with another, 1Σ+, state of the same electron configuration as x, is analyzed. From this analysis the location of the (unobserved) 1Σg+ state, here labeled x′, is obtained. It is concluded that the predissociation in the Π+ levels of the y state is an indirect one mediated by the interaction with x′ coupled with predissociation of x′ by a 3Σg? state dissociating to 4S + 2P atoms: combined, however, with perturbation of the y state by the k1Πg Rydberg state (configuration g?14dπ), whose Π+ levels are completely predissociated.  相似文献   

13.
Results are presented of a 12 event/μb bubble-chamber experiment; the reactions discussed in detail are K?pK1 (890)?p, K1 (1420)?p and K1 (890)?Δ+.The K1 (890)?p channel is dominated by the forward peak. The suggestion of flattering at cos θ = 1 is more pronounced in (?11 + ?1?1) dσdt; which is mainly natural-parity exchange. Pseudoscalar exchange contributes to ?00Jdσdt; this is more sharply peaked in t. The value of (?11 ? ?1?1) dσdt is somewhat larger than the upper limit from the dominant natural-parity exchange. There is significant structure in ?00Hdσdtat t ≈ ?0.6 (GeV/c)2.The K1 (1420)?p channel is much more pronounced at 3.3 GeV/c than at 3.13 GeV/c, but is not markedly peripheral. The width of the K1 (1420) in the 3.3 GeV/c data is 42 ± 12 MeV/c2.The cross section for K1? Δ+ agrees with that expected from K+pK1Δ, assuming a single t-channel exchange. Our measured density matrix elements are consistent with a strong pseudoscalar exchange.  相似文献   

14.
We report the evidence for a narrow charged peak (5.5 s.d.), which we suggest calling the I, in the 6-prong-V0 topology of pp interactions at 12 GeV/c. The mass, widht and the product of cross section σI times the branching ratio BR into the final state (Ksoτ±τ+τ? are found to be: MI=2.60 ± 0.01 GeV/c2, ΓI?0.018 GeV/c2, σI·BR≈20 μbarn  相似文献   

15.
It is assumed that nucleon consists of three quarks with no admixture of gluons or strange quarks. Gluons as are seen in deep inelastic scattering, appear only as a result of bremsstrahlung by valence quarks. The model gives unique predictions for observable quantaties and imitates the scaling behavior at Q2 ? 2 GeV2 provided the coupling constant of strong interactions is relatively small at such values of Q2 (g2(2 GeV2)4π ≈ 14). The predictions of the model agree with the data within (10 – 20) % accuracy and links consideration of deep inelastic scattering with the most naive quark model. The effect of charmed particles production is estimated within the model developed. It is shown that the standard four-quark model of weak interactions is inconsistent with observed anomalies in ν, ν-interactions.  相似文献   

16.
Using 20.5 GeV electrons on protons, we measured inclusive π0's (of transverse momentum, pT, from 0 to 1.4 GeV/c) produced by virtual photons of energy, ν, from 4 to 16.5 GeV and four-momentum squared, q2, from ?1.8 to ?8.5 (GeV/c)2. Comparing with charged pion data, we find σπ0 = 12π++ σπ?), supporting the quark model. Photon knockout of a quark is favored as the interpretation of these data because of scaling in z = Eπ/ν and similarity in z-dependence of other pion production data. Consistent with this interpretation are the dependence of 〈pT〉 on q2, the azimuthal dependence, and fits to the constituent interchange model. We also observe a possible pT?4 dependence at large |q2| over a limited pT range.  相似文献   

17.
18.
The q2 variation of the factor ?+(q2) in the decay K+π0e+ν has been studied using a sample of even detected in the CERN 1.1 m3 heavy-liquid bubble chamber. The data are consistent with a linear development ?+(q2)=?+(0) (1+λ+q/m2π) with λ+=0.027±0.008.  相似文献   

19.
The order α(Q2) correction to the particle multiplicity ratio in gluon and quark jets is calculated in QCD. We find
r=941?αCA13+N?3CA?2N?CF3C2A
with r=〈ngluon jet/〈nquark jet. The method used is systematic and could be used for an order α(Q2) calculation.  相似文献   

20.
The elastic cross section for proton proton scattering at 6 GeVc was measured using a 70% polarized beam and a 75% polarized target at the Argonne ZGS. In the range P2 = 0.5 → 2.0(GeVc)2 we obtained small error measurements for the ↑↑, ↓↓ and ↑↓ initial spin states perpendicular to the scattering plane. At P2 = 0.5 we also measured the recoil spin and found that the 5 different cross sections were very unequal.  相似文献   

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