Angular distribution in neutrino-induced single pion production processes

A partial wave decomposition of \({v \mathord{\left/ {\vphantom {v {\bar v}}} \right. \kern-0em} {\bar v}}\) single pion production is used for studying resonant and nonresonant contributions. The dominant resonance excitation is dynamically described by a semirelativistic quark model. Nonresonant background is considered to arise from Born-terms diminuished by the lowest order partial waves (which are determined by resonances alone.) The method permits evaluation of interferences between resonance and background amplitudes as well as, more importantly, among resonances themselves. Predicted interference patterns are reflected by the pion angular distribution coefficients which compare well with recent data. Results obtained this way are also in agreement with momentum transfer measurements if higher resonance excitation form factors are chosen to resemble those tested in pion photoproduction, rendering simultaneously any nonresonant background small.     

Constraining the low-energy pion electromagnetic form factor with spacelike data

The pionic contribution to the g-2 of the muon involves a certain integral over the modulus squared of F_π(t), the electromagnetic form factor of the pion. We extend techniques that use cut-plane analyticity properties of F_π(t) in order to account for present day estimates of the pionic contribution and experimental information at a finite number of points in the spacelike region. Using data from several experiments over a large kinematic range for |t|, we find bounds on the expansion coefficients of F_π(t), sub-leading to the charge radius. The value of one of these coefficients in chiral perturbation theory respects these bounds. Furthermore, we present a sensitivity analysis to the inputs. A brief comparison with results in the literature that use observables other than the g-2 and timelike data is presented.     

Neutrino-excitation of baryon resonances and single pion production

This is an attempt to describe all existing data on neutrino production of single pions in the resonance region up to W = 2 GeV in terms of the relativistic quark model of Feynman, Kislinger and Ravndal (FKR). We considered single pion production to be mediated by all interfering resonances below 2 GeV. A simple noninterfering, nonresonant background of isospin $\text{1}\text{2}$ was added. It improved agreement with experiment, particularly in the ratio of isospin amplitudes in charged current reactions, at the expense of one additional constant. All total cross sections, cross section ratios and W-distributions are well reproduced at low and high energies, with charged and neutral currents (supposing the Salam-Weinberg theory with sin²$\text{θ}{}_{\mathrm{w}}\text{≈}\text{1}\text{4}$ to be correct), and for neutrinos and antineutrinos, giving predictions where data are lacking. New predictions have been made for complex angular distributions in $\text{N}$π channels exhibiting strong interference between neighbouring resonances. These are sensitive (for 1.1 GeV ? W ? 1.5 GeV) to the sign of the Roper resonance P₁₁(1450) which is controversial in photoproduction experiments.     

On the strength of absorption in single pion production reactions

From data on the reactions π^?p → π^?π⁺n and K⁺n → K⁺π^?p we determine the strength of absorptive corrections to the pion exchange Bornterm as a function of the ππ and Kπ mass and angular momentum.     

A study of single pion production in nucleon-nucleon collisions

A pion exchange model for NN pion production from threshold up to about 6 GeV/c is constructed. In contrast to other models of this type the full information from πN scattering is fed in whereby the πN partial waves on- and off-shell are identified with each other. Detailed comparison with the data for both the channels isospin one and zero, reveals that the shapes of angle and momentum distributions are, in general, well reproduced but the overall magnitude comes out too small for p_L ? 1.5 GeV/c. It is argued that this defect may be due to dibaryon resonances. For reaction cross sections their effects are quantitatively estimated.     

Constraining parameter space of the little Higgs model using data from tera-Z factory and ILC

The Standard Model(SM) prediction on the forward-backward asymmetry for bˉb production(A b FB) is well consistent with the data of LEP at the Z-pole, but deviates from the data at√s =89.55 and 92.95 Ge V which are slightly away from the pole. This deviation implies that there is still room for new physics. We calculate the A b FB at the vicinity of the Z-pole in the little Higgs model as well as other measurable parameters such as R b and R c,by which we may constrain the parameter space of the little Higgs model. This can be further tested in the newly proposed tera-Z factory. With the fitted parameters we further make predictions on A b FB and A t FB for tˉt production at the International Linear Collider(ILC).     

Particle tracks and the mechanism of decoherence in a model bubble chamber

We put forward a toy model for a “bubble chamber” and study its interaction with an incoming object particle. We discuss the notion of particle “tracks” inside the bubble chamber and analyze the mechanisms that provoke a loss of quantum mechanical coherence (decoherence). The model is solvable and provides interesting insights into some of the most salient features of the interaction between a microscopic particle and a macroscopic device.     

Cross-section measurements of single pion production in charged current neutrino and antineutrino interactions

All six exclusive single pion production processes from neutrino and antineutrino charged current interactions are studied in the energy range between 3 and 30 GeV. Using a quark model for single pion production from Rein and Sehgal we fitted the aximal mass parameter from total cross sections and compare the results with values from other experiments and the world-averages.     

The excluded volume hadron gas model and pion production at the SPS

Experimental data for nucleus-nucleus collisions at the CERN SPS suggest that an ideal hadron gas model is unable to account simultaneously (same baryonic chemical potential and temperature at freeze-out) for the strange anti-baryon to baryon ratios and pion abundances. Using a thermodynamically consistent excluded volume model we examine possibilities to account for the observed excess of pions.     

Coherent single pion production by antineutrino charged current interactions and test of PCAC

The cross section for coherent production of a single π^? meson in charged current antineutrino interactions on neon nuclei has been measured in BEBC to be (175±25) 10^?40 cm²/neon nucleus, averaged over the energy spectrum of the antineutrino wide band beam at the CERN SPS; this corresponds to (0.9±0.1) % of the total charged current \(\bar v_\mu \) cross section. The distributions of kinematical variables are in agreement with theoretical predictions based on the PCAC hypothesis and the meson dominance model; in particular, theQ ² dependence is well described by a propagator containing a massm=(1.35±0.18) GeV. The absolute value of the cross section is also in agreement with the model. This analysis thus provides a test of the PCAC hypothesis in the antineutrino energy range 5–150 GeV.     

An analysis of the gargamelle freon data concerning pion production by the weak neutral current

Semi-inclusive pion production of all three charge states by the weak neutral current has been analysed in the Gargamelle Freon neutrino and antineutrino experiments. Using the complete neutral current sample a κ² fit of the measured charge ratios to the hypothesis of a purely isoscalar current has a confidence level of less than 10^?4. Using a restricted pion sample, corresponding to current fragment pions, a κ² fit of the π⁺/π^- ratios in νv and $\text{ν}$ to the predictions of an isovector current has confidence level 0.017. The sign of the isovector-isoscalar interference term is found to be consistent with that predicted by the Weinberg-Salam model.     

Reformulation of the dual pion model

The dual pion model is reformulated in another Fock space. The basic conjecture about the decoupling of the ground state is proved, and all the on-shell gauge operators are found.     

Single spin asymmetry in inclusive pion production,Collins effect and the string model

We calculated the single spin asymmetry in the inclusive pion production in the fragmentation region of transversely polarized proton-proton collisions. We generated the asymmetry at the level of fragmentation function (Collins effect) by the Lund coloured string mechanism. We compared our results to the presently available experimental data. We obtained a qualitative agreement with the data after assuming that the transverse polarizations of the u and the d quarks in the proton are +1 and ? 1, respectively, at x_B=1.     

Analysis of pion electroproduction data in terms of a pion distribution function of the proton

Experimental data on the longitudinal π⁺ electroproduction on hydrogen have been analyzed in terms of a pion distribution function of the proton. This interpretation is based on the assumption that the pion can be considered as a parton in the nucleon for low momentum transfer Q². For the kinematical conditions photon mass Q² < 1 GeV² and electron energy loss ν > 2.2 GeV the pion electroproduction in the direction of the virtual photon can be viewed upon as quasielastic eπ⁺ → e′π⁺ scattering. Using the impulse approximation the pion distribution function of the proton can be deduced. According to the distribution function evaluated from pion electroproduction in the infinite momentum frame, the physical proton has a 3% admixture of the nπ⁺ state and the π⁺ in the nπ⁺ state carries 0.6% of the proton momentum.     

An analysis of the new pion form factor data

A form factor F(t) for the pion is constructed which is compatible with analyticity and the data in the space-like and time-like region. For the mean square pion radius 〈r²〉 = (0.46_?0.08^+0.06) fm² is obtained. Typical errors of the extrapolated F(t) are given (e.g. F(t =?8 GeV²/c²) = 0.07_?0.10^+0.04). Assuming F(t) ≈ β/(?t)^α at the end of the space-like data region we obtain β = 0.31, α = 0.81 for t in GeV²/c² together with the error contours of (α, β). No conclusive answer on the existence of zeroes of F(t) can be given.     

The holographic bubble chamber experiment and the determination of the effective charmed quark mass and theK-factor for hadronic charm production

In the first holographic bubble chamber experiment — the HOBC experiment — we have accumulated a total of 40000 holograms with particle interactions. We have determined the total charm pair cross section inpN collisions to be 23.3 _?7.7 ⁺¹⁰ μb and 3.6 _?1.7 ^+2.3 μb for 360 and 200 GeV/c incident protons respectively. We have assumed a linear dependence of the cross section on the atomic number of the target. This experiment has demonstrated the feasibility of holographic recording in small bubble chambers. Assuming that the charm cross section can be described by the standard QCD factorized expression with gluon fusion and quark-antiquark annihilation, we have used our measured charm cross sections with other measurements to determine the effective charmed quark mass to be 1.8 _?0.35 ^+0.25 GeV/c². TheK factor, which describes the importance of the higher order corrections, is calculated to be 9.8 _?6.9 ^+12.5 (See noted added in proof.)     

Investigation of low energy pion-nucleus interaction using electrofission data for heavy nuclei at the pion threshold

A theoretical approach to describe electro- and photofission processes at intermediate energies was worked out. Photopion reabsorption mechanisms by two and three nucleons (2NA and 3NA) were incorporated in the calculations. The comparison with electrofission data for preactinides showed that a substantial 3NA component should be added in the pion absorption to fit the data near photopion threshold, in accordance with a recent theoretical estimate. It was also shown that the shape of the fission response curve is sensitive to detailed aspects of the pion mean free path. Received: 10 March 1998 / Revised version: 12 March 1999     

On the dynamics of moving single bubble sonoluminescence

It is well known that the primary Bjerknes force is the origin of the trapping of sonoluminescing bubble in the sound field in liquid. In the present Letter, the quantitative investigation of the behavior of hydrodynamic force on the moving sonoluminescing (SL) bubble introduces the new role of stabilizing the trajectory motion of the bubble for primary Bjerknes force. Using a complete force balanced radial-translational dynamics, it is analytically discussed that by increasing the bubble distance from the antinode of the sound field the increase of the magnitude of inward Bjerknes force, controls the size of the domain of the bubble trajectory. At this time the wake produced by the rapid variation of the bubble's relative translational velocity to the surrounding liquid, changes the bubble direction of motion through the effect of history force. The required momentum for accelerating the SL bubble around the central antinode is produced by the added mass force at the bubble collapse. It is revealed in a re-examination of the coupled radial-translational dynamics for a trapping bubble that because of the bubble lower translational acceleration caused due to the lower added mass force and the bubble attraction towards the acoustic antinodes in presence of inward Bjerknes force, the small bubble will be trapped at the antinode of the sound field.