The structure of t-channel exchanges in KN scattering

Recent phase-shift solutions are used to evaluate KN FESR integrals in order to examine zeros and phases of the t-channel exchange amplitudes in the most model-independent way. The results suggest that the line reversal breaking in KN CEX observed for pL ? 5.5 GeV/c is due to a large EXD breaking component in the A₂ exchange flip amplitude. The ? exchange flip amplitude is well described by a Regge pole amplitude with NWSZ at ?t ≈ 0.5 (GeV/c)². The imaginary parts of ? and ω exchange non-flip amplitudes are both peripheral.     

Tensor exchange in meson-baryon scattering

Amplitudes for A₂ quantum number exchange in K^±N scattering are determined at p_L = 3, 4 and 6 GeV using new K^±N CEX differential cross-section data supplemented by sum rule estimates of polarizations. Amplitudes for ? quantum number exchange are calculated from πN scattering by SU(3) octet symmetry. This is justified by K^±N FESR, which furthermore are used to resolve ambiguities in the analysis. Comparison with other reactions involving charge and hyperchange exchange shows reasonable overall consistency between data, SU(3), and the tensor amplitudes. The phase of the A₂s-channel helicity flip amplitude is well described by a Regge pole term with trajectory displaced downwards relative to that appropriate for the ? flip amplitude. This is shown to be the main mechanism contributing to the difference between differential cross sections for the K^±N CEX processes, connected by line reversal. It is suggested that this mechanism may persist at higher energies. The A₂ non-flip amplitude does not have the standard peripheral form.     

A measurement of the KL0p → KS0p reaction between 4 and 14 GeV/c in the range 0.1 ⩽|t|⩽ 2 GeV2

We present experimental data on the K_L⁰p → K_S⁰p reaction between 4 and 14 GeV/c in the range 0.1 ? |t| ? 2 GeV². This experiment has been performed at the CERN PS, using spark chambers and a large aperture magnet. The results show a break of slope at t = ?0.3 GeV². The ω trajectory deduced from the data has an intercept α(0) = 0.5 and a slope α′ = 0.88. A comparison with various models shows that the non-flip amplitude is dominant.     

SU3 comparison of line reversed charge exchange and hyperchange exchange reactions

The recent data at 10.1 GeV/c on the hypercharge reactions π⁺p → K⁺Σ⁺ (1385) and the line reversed processes are compared with the SU₃ related charge exchange processes K⁺n → K^op and K⁺p →K^oΔ⁺⁺ and their line reversed partners in order to study the systematics of line reversal breaking. Allowing for a t- independent SU₃ breaking between charge and hypercharge exchange the data follow the SU₃ relations. We conclude that the line reversal breaking in the hypercharge exchange reactions is in agreement with the breaking in exchange degeneracy (in both flip and non-flip amplitudes) which is observed for the charge exchange processes.     

Amplitude analysis of Kaon-nucleon scattering data

The KN scattering amplitudes have been extracted from experimental data in the energy range 3 ? k ? 14 GeV/c and for transfer values between ?0.05 and ?0.6 GeV².The ω and P+f helicity-flip amplitudes and the A₂ helicity non-flip amplitude have been neglected; it is shown, that these simplifications are compatible with the data and have no significant influence on our results. One needs to assume the approximate validity of SU(3) symmetry for the ? and A₂ couplings. A very important constraint for this analysis comes from recent experimental data for the reaction K_L⁰p → K_S⁰p. The results for A₂ and ω exchanges are analysed as functions of momentum transfer and energy and we test several current theoretical ideas. Information about f-exchange is also obtained when some further assumptions are made concerning SU(3) symmetry and duality at t = 0. Extrapolating the amplitudes to t = 0 a comparison is made with dispersion relation calculations; at other t-values we compare with results obtained from finite energy sum rules and other analyses based on fixed f analyticity. The predictions for KN data which have not been considered in this analysis are shown to be in good agreement. One of our results is that the ?-ω universality rule is approximately satisfied; we also find a strong indication for a peripheral behaviour of the imaginary part of the non-flip f-exchange amplitude.     

Amplitude analysis and geometrical picture for Δ production processes

In this paper, a complete amplitude analysis is performed to obtain the double flip ? and A₂ contributions. As suggested by the geometrical picture the non-flip and the flip amplitudes are assumed to be identical to the ones already determined from πN and KN reactions up to t-independent real constants. Evidence for the validity of this assumption is given; SU(3) prediction works quite well with the experimental data on KN→KΔ processes.     

Structure in the reaction π+p → Δ++ϱo AT 5 GeV/c

In a high statistics experiment a large dσ/dt′ slope of (23.7 ± 3.2) GeV^?2 is obtained in the forward direction. The natural parity exchange cross-section shows a dip at t′ ≈ 0.2 GeV² and peak at ≈ 0.6 GeV². The ?^o is separated from the S-wave background and we obtain ?₀₀^F ≈ 0.94, at t′ = 0.     

Structural and magnetic properties of Mn1−tTitAs

The pseudo-binary TiAsMnAs system has been investigated by X-ray and neutron diffraction as well as magnetic measurements (including high fields and applied pressures). The phase diagram is dominated by the NiAs type structure, which prevails up to a miscibility gap at t ≈ 0 95, in a ferro- or in a paramagnetic state Two separate domains of the MnP type structure, a paramagnetic state above T_c and a metastable helimagnetic state at low temperature, are observed for a small amount of T₁ The relation to other Mn_1?tT_tAs (T = V, Cr, Fe and Co) phases reveals that T₁ substituted MnAs behaves as a ‘negative’ pressure system The first-order ferro- to paramagnetic transition in Mn_1?tTi_tAs becomes continuous at t≈ 0 10, and T_c falls to zero at t ≈ 0 65 The T_cvs tdependence is discussed in terms of a magnetostrictive model where the dilution imposed by the non-magnetic T_i atoms plays a major role The dilution suppresses the range of the first-order transition The significance of the anisotropy of the elastic properties and the exchange interactions is examined.     

Amplitude analysis of πN charge exchange at large momentum transfer

We have found evidence for the right-signature zero at t ≈ ?1.5 (GeV/c)² and the second wrong-signature zero at t ≈ ?2.5 (GeV/c)² in the helicity flip ?-Regge-pole exchange from an amplitude analysis of πN charge exchange extended to large momentum transfer. Reconstruction of the imaginary part of the nonflip amplitude suggests a remarkable degree of Regge behaviour out to large ?t. Confirmation of such behaviour would undermine the basic features of absorptive cut models.     

Computable upper bounds for the adiabatic approximation errors

For a given Hermitian Hamiltonian H(s)(s∈[0,1])with eigenvalues Ek(s)and the corresponding eigenstates|Ek(s)(1 k N),adiabatic evolution described by the dilated Hamiltonian HT(t):=H(t/T)(t∈[0,T])starting from any fixed eigenstate|En(0)is discussed in this paper.Under the gap-condition that|Ek(s)-En(s)|λ0 for all s∈[0,1]and all k n,computable upper bounds for the adiabatic approximation errors between the exact solution|ψT(t)and the adiabatic approximation solution|ψadi T(t)to the Schr¨odinger equation i|˙ψT(t)=HT(t)|ψT(t)with the initial condition|ψT(0)=|En(0)are given in terms of fidelity and distance,respectively.As an application,it is proved that when the total evolving time T goes to infinity,|ψT(t)-|ψadi T(t)converges uniformly to zero,which implies that|ψT(t)≈|ψadi T(t)for all t∈[0,T]provided that T is large enough.     

Thermodynamic critical amplitudes in the dipolar critical region of a uniaxial ferromagnet

In zero magnetic field susceptibility, magnetization and specific heat of GdCl₃ follow below t = |T/T_c - 1| ≈0.015 mean field laws with logarithmic corrections. Their amplitudes characterizing the strengths of the singularities are related by an equation predicted by the theory of Larkin and Khmel'nitzkii.     

Measurement of the polarization parameter in pp elastic scattering at 150 GeV/c

The polarization parameter in pp elastic scattering at 150 GeV/c, and in the momentum transfer interval 0.4 ? ?t ? 3.0 GeV², has been measured in an MWPC and scintillation counter experiment at the CERN SPS using a polarized proton target. The polarization is decreasing steadily from zero to ≈ ? 10% in the range 0.4 < ?t < 1.3 GeV²; for higher |t| the data suggests a change of sign. Results are also given for the differential cross section, which exhibits a small dip at ?t = (1.46 ± 0.01) GeV.     

Rho production by virtual photons

The reaction γ_Vp → pπ⁺π^? was studied in the W, Q² region 1.3–2.8 GeV, 0.3–1.4 GeV² using the streamer chamber at DESY. A detailed analysis of rho production viaγ_Vp→?⁰p is presented. Near threshold rho production has peripheral and non-peripheral contributions of comparable magnitude. At higher energies (W > 2 GeV) the peripheral component is dominant. The Q² dependence of σ(γ_Vp→?⁰p) follows that of the rho propagator as predicted by VDM. The slope of dσ/dt at 〈Q²〉 = 0.4 and 0.8 GeV² is within errors equal to its value at Q² = 0. The overall shape of the ?⁰ is t dependent as in photoproduction, but is independent of Q². The decay angular distribution shows that longitudinal rhos dominate in the threshold region. At higher energies transverse rhos are dominant. Rho production by transverse photons proceeds almost exclusively by natural parity exchange, σ_T^N ? (0.83 ± 0.06) σ_T for 2.2 < W < 2.8 GeV. The s-channel helicity-flip amplitudes are small compared to non-flip amplitudes. The ratio R = σ_L/σ_T was determined assuming s-channel helicity conservation. We find R = ξ²Q²/M_?² with ξ² ≈ 0.4 for 〈W〉 = 2.45 GeV. Interference between rho production amplitudes from longitudinal and transverse photons is observed. With increasing energy the phase between the two amplitudes decreases. The observed features of rho electroproduction are consistent with a dominantly diffractive production mechanism for W > 2 GeV.     

Mössbauer investigation of Mn2Sb doped with Fe and Cr

The alloy systems Mn_2?xFe_xSb and Mn_1.98?xCr_xFe_0.02Sb have been investigated by Mössbauer spectroscopy of ⁵⁷Fe in the region x? 0.2.In Mn_2?xFe_xSb the spinflop transition known to exist in pure Mn₂Sb at T_t = 240 K is observed. At T_t the magnetic hyperfine field H changes from -50 to -80 kOe and the electric quadrupole interaction QS from positive to negative with increasing T. The value of ΔH at T_t can be understood in terms of dipolar contributions to H. Fe is deduced to occupy the Mn_I sites in the lattice.In Mn_1.98?xCr_xFe_0.02Sb the transition from the ferrimagnetic to the antiferromagnetic state is observed. In the antiferromagneti c state we find | H| ≈ 15 kOe.     

A comparison of direct photon, π0 in pp and pp interactions at the CERN ISR

We have measured the production of direct photons, π⁰'s, and η's in p$\text{p}$ and pp collisions at √s=53 GeV in the range 2≈p_T≈6 GeV/c for the central rapidity region |y| 0.4. No statistically significant difference between pp? and pp interactions is observed.     

Forward K1+ (892) production in K+p → π+Ks0p at 12.7 GeV/c

We have measured 618 K⁺p → π⁺K_S⁰p events at 12.7 GeV/c incident lab momentum, mass range 790 ? m_π⁺Ks⁰ ? 990 MeV and t range 0.01 ? ?t ? 0.60 (GeV/c)². The π⁺K_S⁰ mass spectrum is dominated by the K¹⁺ (892) resonance and a Breit-Wigner fit yields a mass m = 893.5 ± 1.1 MeV and a width Γ = 33.2 ± 4.1 MeV which is much narrower than measured hitherto. The t distribution of K¹⁺ (892) events shows a dip in the forward direction and an exponential fall off thereafter, consistent with dominance of helicity flip amplitudes. The spin density matrix is almost saturated by ρ₁₁ and ρ_1?1 which are very close to their maximum allowed value of $\text{1}\text{2}$ throughout the measured t range except in the very forward direction where ρ₀₀ and Re ρ₁₀ deviate from zero. Natural parity exchanges, therefore, dominate with unnatural parity exchanges being restricted to a small region in the forward direction. A Regge pole analysis of the differential cross sections of the present measurement in conjunction with previously measured total cross sections supports the f-coupled-pomeron hypothesis.     

Analysis of the πN invariant amplitudes in terms of algebraic functions and a new determination of the πN low-energy parameters

We have analysed the energy dependence of the πN invariant amplitudes in terms of algebraic functions which automatically fulfill fixed-t dispersion relations. The amplitudes were taken from several phase shift solutions. The analysis was repeated for nine t-values between 0 ? t ? ?0.3 GeV². By evaluating the resulting analytic amplitudes at threshold and at ν = 0 we recalculate the S, P, D scattering lengths and the current algebra σ term. We also discuss the trajectories of the zeros and poles in the complex energy plane.     

Muon charge exchange and muonium spin exchange in gases

The spin dynamics of the positive muon undergoing cyclic charge exchange (μ⁺⇌Mu) while it is slowing down is compared with that in the case of repeated muonium spin exchange after thermalization. The expectation value of the spin polarization at timet aftern spin exchange collisions (att ₁,t ₂, ...,t _n ) are calculated explicitly from time dependent wave functions, and the quantity is averaged over the statistical distribution of the times of collisions and over all possible numbers of collisions betweent=0 and the observation timet. This result is complementary and equivalent to the conventional density matrix formalism, but offers an insight into the roles of spin flip and spin non-flip processes. The neutral fraction during slowing down is also discussed.     

Differential cross sections of elastic pp scattering in the energy range 8–70 GeV

In this paper we present tables of absolute differential cross sections of elastic pp scattering together with the values of the slope parameter B and the real-part parameter α, where $\text{B=}\text{d}\text{d}\text{t}\text{In}\text{dσ}\text{d}\text{t}\text{α=}\text{Re A(0)}\text{Im A(0)}$ and A(0) is the amplitude of elastic pp scattering at t = 0. The cross-section data have been obtained at the Serpukhov accelerator from 8 to 70 GeV in the |t|-range 0.0007 ? 0.12 (GeV/c)².     

Observation of a dip-bump structure in differential cross section for pp → nn in the 700–760 MeV/c momentum range

Based on a sample of about 3500 events, we have measured the total and differential cross sections of $\text{p}\text{p}\text{→}\text{n}\text{n}$ in the 700–760 MeV/c incident momentum region. It is found that σ_CE = 10.7 ± 0.2 mb at the average momentum of 730 MeV/c. The differential angular distribution is characterised by a sharp peak and a dip in the forward direction followed by a secondary maximum. The position of the dip corresponds to |t| ≈ m_π². These results are compared with the predictions of the model of Bryan-Phillips. On the other hand, this dip-bump structure can be well understood on a simple picture involving a π exchange and a constant background (for |t| ? 3 m_π²).