Influence of resonances on Bose-Einstein correlations of identical pions

The influence of resonances on narrow pair correlations of identical pions is considered in detail. It is shown that kinematic or dynamic restrictions on resonance momenta lead to a substantial anisotropy of the correlation function; variables allowing one to reveal this anisotropy are proposed. An upper estimate of 0.23 for the fraction of directly produced pions is obtained based on experimental data on the resonance yields in high-energy hadron interactions. It is shown that experimental data on like-pion correlations agree with a dominant contribution of the pions from the decays of light resonances. In particular, the observed value of the parameter characterizing the suppression of the interference effect, the decrease of the slope of the correlation function with increase in the relative momentumQ of the like pions in their c.m.s. and the dependence of the time parameter on the pion velocity are explained. It is shown that the slope of the correlation function for the like-pion pairs containing the decay pions atQ>0.1 GeV/c is mainly determined by the size of the resonance production region, which allows one to determine the size of the production region of direct particles (pions and resonances) despite the very low fraction of the pairs of directly produced pions. The fraction of directly produced pions, 0.17±0.09 (stat.)±0.08 (syst.), and the radius of the direct production region, 0.55±0.08 (stat.)±0.10 (syst.) fm, have been determined based on the analysis of the most accurate correlation function measured inpp- and -interaction on ISR at 63 GeV.     

HBT correlations and charge ratios in multiple production of pions

The influence of the HTB effect on the multiplicity distribution and charge ratios of independently produced pions is studied. It is shown that, for a wide class of models, there is a critical point, where the average number of pions becomes very large and the multiplicity distribution becomes very broad. In this regime unusual charge ratios (“centauros”, “anticentauros”) are strongly enhanced. The prospects for reaching this regime are discussed. Received: 25 March 1998 / Published online: 21 August 1998     

Multiparticle azimuthal correlations of negative pions in nucleus-nucleus collisions

Multiparticle azimuthal correlations of ?? ^? mesons have been studied in dC, HeC, CC, CNe, MgMg, (d, He)Ta, CCu, CTa, and OPb collisions at momentum of 4.2, 4.5 GeV/c per nucleon within the standard transverse momentum analysis method of P. Danielewicz and G. Odyniec. The data were obtained by SKM-200-GIBS and Propane Bubble Chamber Collaborations of JINR. The axis has been selected in the phase space and with respect to this axis ?? ^? meson correlations were observed. The values of the coefficient of the correlations linearly depend on the mass numbers of projectile (A _P ) and target (A _T ) nuclei. The Quark-Gluon String Model satisfactorily describes the experimental results.     

Bose-einstein correlations of soft pions in ultrarelativistic nucleus-nucleus collisions

A detailed analysis of pair correlations of positive pions in the target fragmentation region is presented. Data on nuclear collisions at 200 GeV per nucleon were measured with the Plastic Ball in the WA80 experiment at the CERN SPS. The correlation functions are compared with analytical functions and with simulations incorporating Bose-Einstein symmetrization, final-state interactions and detector resolution. Source radii are shown to increase with increasing target size and with centrality. For central collisions the radii are larger than the geometrical sizes of the involved nuclei.     

Inclusive production of soft pions

Amplitudes for inclusive production of pions at zero four-momentum ine ⁺?e ^?, hadron-hadron, and lepton-hadron collisions are computed using traditional soft pion techniques. However, the extrapolation to physical momenta appears to be problematical. Tests involving difference cross sections at relatively low energies are suggested.     

Interference correlations of pions and elementary cell of phase space

The amplitude-symmetrization procedure employed in studying interference correlations of identical pions is shown to be always valid only within one elementary cell 2π? of phase space—that is, within one period of the interference cosine. However, this limitation does not lead to far-reaching consequences in using the interference method to determine the spacetime dimensions of the pion generation volume.     

First evidence for upsilon production by pions

We have measured the production of massive muon pairs in hadronic collisions at the CERN Super Proton Synchrotron (SPS). A clear signal of production of the ? resonance by π⁺ of 200 GeV/c and π^? of 200 and 280 GeV/c on a platinum target is observed.     

γ production and multiplicity correlations between neutral and charged pions in pp interactions at 69 GeV/c

From 3500 γ's observed in the 4.7 m HBC MIRABELLE at Sepukhov, we obtain the dependence on n_? of the average number of produced π^0,s, 〈n₀〉, and the π⁰π⁰ correlation parameter, $\text{?}{}_2{}^{00}$. We present also the $\text{?}{}_2{}^{\mathrm{??}}$ and $\text{?}{}_2{}^{\mathrm{+0}}$ parameters and information concerning KNO scaling. Various momentum distributions are given. The invariant γ cross sections distributions are compared with corresponding data at other energies.     

On the measurement of correlations of neutral pions in a high multiplicity environment

The role of the combinatorial background of photon pairs in the analysis of correlations of neutral pions is investigated. The influence of four-particle effects in the Bose-Einstein enhancement is studied within a simulation. The HBT effect can be observed even in a high multiplicity environment, if the source size is not too large. A new method for neutral pion interferometry is introduced, which would allow also the measurement of large sources in high statistics experiments.     

Inclusive production of neutral pions in hadronic Z decays

A measurement of the inclusive production of π⁰ mesons in hadronic Z decays is presented and compared to Monte Carlo model predictions. The analysis is based on approximately 2 million hadronic events recorded with the ALEPH detector at LEP at a centre-of-mass energy of ?s = 91.2 GeV. Neutral pions are reconstructed using photons measured in the electromagnetic calorimeter and photons from conversion pairs. The inclusive π⁰ momentum spectrum is measured in the range 0.025 < x _p = p/p _beam < 1. In this range the number of π⁰ per hadronic Z is found to be 4.80 ± 0.07(stat) ± 0.31(sys). The differential inclusive π⁰ cross section is also measured as a function of transverse momentum with respect to the event plane (p _T ⁱⁿ and p _T ^out ).     

Final-state interactions in radiative production of pions in colliding-beam experiments

The contribution of final state interactions of the pions in the process e⁺e^?→ππγ are calculated. It is noted that this may be used A) to obtain the zero isospin ππ s-wave in the ?-region, or B) if knowledge of this wave is assumed, to obtain a good estimate of the background for e⁺e^? → ππ     

Correlations between neutral and charged pions in multiparticle production

We make a theoretical and phenomenological study of correlations between neutral and charged pions in multiparticle production in the framework of the so-called σ, π, ? and ?-? models. Following the method of Drijard and Pokorski, we express the predictions of various models in terms of the negative multiplicity distribution, which is known experimentally. In particular we compute the average number of $\text{π}{}^0\text{,}\text{n}{}_0\text{(n\_)}$, and the integral of π⁰?π⁰ correlations, f₀²(n_), as a function of the number of negative pions; we study also the total multiplicity distribution P(N) and its first two moments $\text{N}\text{and}\text{D}{}_{\mathrm{<mtext>tot</mtext>}}{}^2$. We show that with the present experimental accuracy neither $\text{n}{}_0\text{(n\_)}$ allow us to discriminate between the different models.     

Bose-Einstein correlations of three charged pions in hadronic Z^{\bf 0} decays

Bose-Einstein Correlations (BEC) of three identical charged pions were studied in hadronic decays recorded with the OPAL detector at LEP. The genuine three-pion correlations, corrected for the Coulomb effect, were separated from the known two-pion correlations by a new subtraction procedure. A significant genuine three-pion BEC enhancement near threshold was observed having an emitter source radius of and a strength of . The Coulomb correction was found to increase the value by 9% and to reduce by 6%. The measured corresponds to a value of when one takes into account the three-pion sample purity. A relation between the two-pion and the three-pion source parameters is discussed. Received: 7 May 1998 / Published online: 12 August 1998     

Forward-backward multiplicity correlations of pions and protons for different temperature events in heavy-ion interactions

A comparison of transverse momentum (P _T) distribution of the alpha particles emitted as projectile fragments from¹²C-emulsion interaction at 4.5 A GeV/c with double Maxwell-Boltzmann distribution yields two temperatures in the projectile fragmentation region, i.e., 10 MeV and 40 MeV with different reaction mechanisms, thereby giving rise to two classes of events. This work presents a detailed study of the multiplicity characteristics for pions and protons emitted in both forward and backward hemispheres in these two classes of events. The results show some interesting features in these two classes.     

一维谐振子势阱中二全同粒子的空间关联

针对一维谐振子势阱中由两个全同粒子组成的体系,假设其空间波函数分别具有以下3种交换对称性:1)没有交换对称性,2)对于交换是反对称情况,3)对于交换是对称情况,讨论了二粒子空间相对位置的分布概率.并由此将量子力学教材中自由粒子情况下的结论推广至一维谐振子束缚态情形,即两个全同粒子无论是处于自由态还是束缚态,在空间波函数交换对称的情况下,两个粒子靠拢的概率最大,而交换反对称情况下,两个粒子靠近(r→0)的概率趋于零.论文结论有助于加深对量子力学中全同粒子交换对称性及其物理效应的理解.     

Pomeron universality from identical pion correlations at the LHC

Bose-Einstein correlations of identical pions produced in high-energy pp collisions at the LHC allow a probe of the Pomeron exchange mechanism. The size of the domain which emits the pions depends on the multiplicity of events, but not on the collider energy. This confirms the universal structure of Pomeron exchange. The data at relatively low multiplicities indicate that the size of the source created by one-Pomeron exchange is much less than the size of the proton.     

Note on Bose-Einstein correlations of three pions in symmetric heavy-ion interactions at 650 a MeV

In a recent article published in this journal it is stated that a specific three-pion effect is found in an experiment studying Au+Au collisions. The aim of this note is to show that these new data are compatible with two-pion effects leaving no room for a specific three-pion effect. This is in accordance with three-pion interferometry results from pp and e⁺ e^? collisions at a high energy.     

Near threshold production of neutral pions by complex particles

Cross sections for the inclusive neutral pion production cross section have been measured for near threshold energy ³He particles on complex nuclei. The results of these measurements are of order 10^?36 cm²/sr · MeV. The neutral pion cross section for 710 MeV ⁴He on ¹²C has been found to be comparable to the production cross section for nucleons, 10^?30 cm²/sr · MeV. Comparisons are made with a naive model relating complex particle production to nucleon production of pions.     

Scattering of pions on pions in threshold region

It is shown that the integral equations for isoscalar-scattering, obtained from the Mandelstam representation by the method of so-called differential approximation, admit the threshold behaviour of partial amplitudes which is in agreement with the quantum theory of scattering and, moreover, they also admit solutions with other possible threshold behaviours. This result does not depend on whether the conformal mapping technique is used or not.