We report the first measurement of inclusive antiproton production at midrapidity in Au+Au collisions at square root of s(NN) = 130 GeV by the STAR experiment at RHIC. The antiproton transverse mass ...distributions in the measured transverse momentum range of 0.25<p( perpendicular)<0.95 GeV/c are found to fall less steeply for more central collisions. The extrapolated antiproton rapidity density is found to scale approximately with the negative hadron multiplicity density.
We have measured the ratio R=Γ(KL→γγ)/Γ(KL→π0π0π0) using the KLOE detector. From a sample of ∼109φ-mesons produced at DAΦNE, the Frascati φ-factory, we select ∼1.6×108KL-mesons tagged by observing ...KS→π+π− following the reaction e+e−→φ→KLKS. From this sample we select 27,375 KL→γγ events and obtain R=(2.79±0.02stat±0.02syst)×10−3. Using the world average value for BR(KL→π0π0π0), we obtain BR(KL→γγ)=(5.89±0.07±0.08)×10−4 where the second error is due to the uncertainty on the π0π0π0 branching fraction.
The first measurements of light antinucleus production in Au+Au collisions at the Relativistic Heavy-Ion Collider are reported. The observed production rates for d macro and (3)He macro are much ...larger than in lower energy nucleus-nucleus collisions. A coalescence model analysis of the yields indicates that there is little or no increase in the antinucleon freeze-out volume compared to collisions at CERN SPS energy. These analyses also indicate that the (3)He macro freeze-out volume is smaller than the d macro freeze-out volume.
A model for the defect dynamics in YBa sub(2)Cu sub(3)O sub(7- delta ) (YBCO) single crystals elucidating the changes in the transition temperature after neutron irradiation and annealing is ...presented. The influence of neutron irradiation is due to the elastic energy transfer of the incident neutron to the primary recoil atom. Therefore, a full spectrum of defects is obtained, ranging from point defects in all sub-lattices. The data are compared to experimental T sub(c ) values on a single crystal after repeated irradiation and annealing. These changes are found to be closely related to the calculated concentration of vacancies at the Cu-O chain sites.
A model is presented for the defect dynamics in YBa sub 2 Cu sub 3 O sub 7- delta crystals elucidating the changes in the transition temperature after neutron irradiation and subsequent annealing. ...These changes are found to be closely related to the calculated concentration of vacancies at the Cu-O chain sites.
The new spectrometer ANKE has been put into operation at the accelerator COSY of the Forschungszentrum Jülich. An initial scientific goal is to study K
+-production in pA collisions at subthreshold ...energies below the free NN-threshold of
T = 1.58 GeV. First measurements of double differential cross sections in p
12C collisions at emission angles around 0° have been performed at
T = 1.0, 1.2 and 2.0 GeV. The challenge is to identify the kaons in a huge background of pions and protons, since the signal to background ratio decreases to about 10
−6 at
T = 1.0 GeV. For background suppression detectors and a trigger system based on energy-loss and time-of-flight measurements have been developed. In the analysis the decay of kaons (
τ = 12.4 ns) stopped in the detection system into
μ
+ and
π
+ is exploited as well as the track information from the wire chambers.
Phys. Rev. Lett. 122, 082003 (2019) The adapted DIRAC experiment at the CERN PS accelerator observed for the
first time long-lived hydrogen-like $\pi^+\pi^-$ atoms, produced by protons
hitting a ...beryllium target. A part of these atoms crossed the gap of 96~mm and
got broken up in the 2.1~\textmu{}m thick platinum foil. Analysing the observed
number of atomic pairs, $n_A^L= \left.436^{+157}_{-61}\right|_\mathrm{tot}$,
the lifetime of the 2$p$ state is found to be
${\tau_{2p}=(\left.0.45^{+1.08}_{-0.30}\right|_\mathrm{tot}) \cdot10^{-11}}$s,
not contradicting the corresponding QED $2p$ state lifetime
${\tau_{2p}^\mathrm{QED}=1.17 \cdot 10^{-11}}$s. This lifetime value is three
orders of magnitude larger than our previously measured value of the
$\pi^+\pi^-$ atom ground state lifetime
$\tau=(\left.3.15^{+0.28}_{-0.26}\right|_\mathrm{tot})\cdot 10^{-15}$s. Further
studies of long-lived $\pi^+\pi^-$ atoms will allow to measure energy
differences between $p$ and $s$ atomic states and so to determine $\pi\pi$
scattering lengths with the aim to check QCD predictions.
Two-pion correlation functions in Au+Au collisions at square root of s(NN) = 130 GeV have been measured by the STAR (solenoidal tracker at RHIC) detector. The source size extracted by fitting the ...correlations grows with event multiplicity and decreases with transverse momentum. Anomalously large sizes or emission durations, which have been suggested as signals of quark-gluon plasma formation and rehadronization, are not observed. The Hanbury Brown-Twiss parameters display a weak energy dependence over a broad range in square root of s(NN).
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