Dimesoatom breakup in the Coulomb field Afanasyev, L. G.; Gevorkyan, S. R.; Voskresenskaya, O. O.
The European physical journal. A, Hadrons and nuclei,
2020/1, Letnik:
56, Številka:
1
Journal Article
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Odprti dostop
Momentum and angular distributions of charged meson pairs
h
+
h
-
(
h
=
π
,
K
) from elementary atom (EA) breakup (ionization) in the Coulomb field of a target atom are considered in the Born and ...Glauber approximations. Exploiting the fact that the atomic screening of the target Coulomb potential is important at small transfer momenta, while multi-photon exchanges are essential at large transfer momenta, we express the cross sections of EA breakup as a sum of two terms. In the region of modest transfer momenta the cross section is determined by the single-photon exchange (first Born approximation) accounting for the target atoms screening, whereas at large transfer momenta using the unscreened potential allows one to take into account all multi-photon exchanges and obtain the cross section of EA breakup in closed analytical form.
.
The production of two-meson electromagnetic bound states and free meson pairs
π
+
π
-
,
K
+
K
-
,
π
+
K
∓
in relativistic collisions has been considered. It is shown that using of exact Coulomb ...wave functions for dimeson atom (DMA) allows one to calculate the yield of discrete states with the desired accuracy. The relative probabilities of production of DMA and meson pairs in the free state are estimated. The amplitude of DMA transition from 1
S
to 2
P
state, which is essential for the pionium Lamb shift measurements, has been obtained.
After having announced the statistically significant observation (5.6σ) of the new exotic πK atom, the DIRAC experiment at the CERN proton synchrotron presents the measurement of the corresponding ...atom lifetime, based on the full πK data sample: τ=(5.5−2.8+5.0)×10−15 s. By means of a precise relation (≈1%) between atom lifetime and scattering length, the following value for the S-wave isospin-odd πK scattering length a0−=13(a1/2−a3/2) has been derived: |a0−|=(0.072−0.020+0.031)Mπ−1.
The observation of hydrogenlike πK atoms, consisting of π^{-}K^{+} or π^{+}K^{-} mesons, is presented. The atoms are produced by 24 GeV/c protons from the CERN PS accelerator, interacting with ...platinum or nickel foil targets. The breakup (ionization) of πK atoms in the same targets yields characteristic πK pairs, called "atomic pairs," with small relative momenta Q in the pair center-of-mass system. The upgraded DIRAC experiment observed 349±62 such atomic πK pairs, corresponding to a signal of 5.6 standard deviations. This is the first statistically significant observation of the strange dimesonic πK atom.
The adapted DIRAC experiment at the CERN PS accelerator observed for the first time long-lived hydrogenlike π^{+}π^{-} atoms, produced by protons hitting a beryllium target. A part of these atoms ...crossed the gap of 96 mm between the target and a 2.1 μm thick platinum foil, in which most of them dissociated. Analyzing the observed number of atomic pairs, n_{A}^{L}=436_{-61}^{+157}|_{tot}, the lifetime of the 2p state is found to be τ_{2p}=(0.45_{-0.30}^{+1.08}|_{tot})×10^{-11} s, not contradicting the corresponding QED 2p state lifetime τ_{2p}^{QED}=1.17×10^{-11} s. This lifetime value is three orders of magnitude larger than our previously measured value of the π^{+}π^{-} atom ground state lifetime τ=(3.15_{-0.26}^{+0.28}|_{tot})×10^{-15} s. Further studies of long-lived π^{+}π^{-} atoms will allow us to measure energy differences between p and s atomic states and so to discriminate between the isoscalar and isotensor ππ scattering lengths with the aim to check QCD predictions.
The results of a search for hydrogen-like atoms consisting of π∓K± mesons are presented. Evidence for πK atom production by 24 GeV/c protons from CERN PS interacting with a nickel target has been ...seen in terms of characteristic πK pairs from their breakup in the same target (178±49) as well as in terms of produced πK atoms (653±42). Using these results, the analysis yields a first value for the πK atom lifetime of τ=(2.5−1.8+3.0) fs and a first measurement of the S-wave isospin-odd πK scattering length |a0−|=13|a1/2−a3/2|=(0.11−0.04+0.09)Mπ−1 (aI for isospin I).
After observing and investigating the double-exotic (a double-exotic atom is a bound system, in which both oppositely charged components are unstable particles like μ,π,K,…) π+π− atom with the ground ...state lifetime τ of about 3×10−15 s, the upgraded DIRAC experiment at the CERN PS accelerator observes for the first time long-lived states of the same atom with lifetimes of about 10−11 s and more. The number of characteristic pion pairs resulting from the breakup (ionisation) of long-lived π+π− atoms amounts to 436±61, corresponding to a signal-to-error ratio of better than 7 standard deviations. This observation opens a new possibility to measure energy differences between p and s atomic states and so to determine ππ scattering lengths.
Abstract
Problems of optimization of special electrical and electromechanical systems in modeling, creation and design are solved mainly by methods of mathematical programming. The task of ...mathematical programming is to find extremes of the function of many variables in the presence of restrictions on variables, which creates fundamental difficulties. To solve such problems, the number of methods for solving the general problem of mathematical programming is currently expanding significantly. In this regard, the trend in the development of mathematical programming is following the path of highlighting and studying various subclasses of problems. The use of certain specific features of the tasks of the selected subclass creates opportunities for their more effective investigation and solution. Examples of such subclasses give convex, quadratic, linear programming problems, transport-type problems, and others. Geometric programming is also a section of mathematical programming that research a certain class of optimization problems. However, when using geometric programming, you have to apply linear, nonlinear programming, the concept of convex programming. Using optimization methods will allow you to correctly investigate, design and create special electric drives.
The goal of the DIRAC experiment at CERN (PS212) is to measure the π+π− atom lifetime with 10% precision. Such a measurement would yield a precision of 5% on the value of the S-wave ππ scattering ...lengths combination |a0−a2|. Based on part of the collected data we present a first result on the lifetime, τ=2.91−0.62+0.49×10−15 s, and discuss the major systematic errors. This lifetime corresponds to |a0−a2|=0.264−0.020+0.033mπ−1.
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