Production of He-4 and (4) in Pb-Pb collisions at root(NN)-N-S=2.76 TeV at the LHC

Results on the production of He-4 and (4) nuclei in Pb-Pb collisions at root(NN)-N-S = 2.76 TeV in the rapidity range vertical bar y vertical bar <1, using the ALICE detector, are presented in this paper. The rapidity densities corresponding to 0-10% central events are found to be dN/dy4(He) = (0.8 +/- 0.4 (stat) +/- 0.3 (syst)) x 10(-6) and dN/dy4 = (1.1 +/- 0.4 (stat) +/- 0.2 (syst)) x 10(-6), respectively. This is in agreement with the statistical thermal model expectation assuming the same chemical freeze-out temperature (T-chem = 156 MeV) as for light hadrons. The measured ratio of (4)/He-4 is 1.4 +/- 0.8 (stat) +/- 0.5 (syst). (C) 2018 Published by Elsevier B.V.Peer reviewe

K - Pp bound system at J-PARC

The K̄NN bound system, symbolically denoted as "K-pp", is the simplest K̄-nuclear bound system which has been widely discussed as a consequence of the strongly attractive K̄N interaction in I = 0 channels. Many theoretical works have pointed out the existence of the "K-pp" bound system, but the calculated properties such as the binding energy and the width spread out due to the uncertainty of the K̄N interaction below the K̄+N mass threshold. Experimentally, there are several reports on observation of a "K-pp" candidate with the binding energy of around 100 MeV, however, no definitive evidence was available so far. At J-PARC, we conducted a experimental search for the "K-pp" bound system using K- + 3He reaction at 1.0 GeV/c where the "K-pp" is expected to be directly produced via the (K-, n) reaction. We finally observed a bound state below the K- +p+p mass threshold in the Λpn final state, which can be interpreted as the "K- pp" bound state. The possible existence of the "K- pp" state is discussed from both aspects of production and decay. © 2020 Author(s)

Towards the first measurement of matter-antimatter gravitational interaction

The AEgIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) is a CERN based experiment with the central aim to measure directly the gravitational acceleration of antihydrogen. Antihydrogen atoms will be produced via charge exchange reactions which will consist of Rydberg-excited positronium atoms sent to cooled antiprotons within an electromagnetic trap. The resulting Rydberg antihydrogen atoms will then be horizontally accelerated by an electric field gradient (Stark effect), they will then pass through a moiré deflectometer. The vertical deflection caused by the Earth's gravitational field will test for the first time the Weak Equivalence Principle for antimatter. Detection will be undertaken via a position sensitive detector. Around 103 antihydrogen atoms are needed for the gravitational measurement to be completed. The present status, current achievements and results will be presented, with special attention toward the laser excitation of positronium (Ps) to the n=3 state and the production of Ps atoms in the transmission geometry

Towards the first measurement of matter-antimatter gravitational interaction

The AEgIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) is a CERN based experiment with the central aim to measure directly the gravitational acceleration of antihydrogen. Antihydrogen atoms will be produced via charge exchange reactions which will consist of Rydberg-excited positronium atoms sent to cooled antiprotons within an electromagnetic trap. The resulting Rydberg antihydrogen atoms will then be horizontally accelerated by an electric field gradient (Stark effect), they will then pass through a moiré deflectometer. The vertical deflection caused by the Earth's gravitational field will test for the first time the Weak Equivalence Principle for antimatter. Detection will be undertaken via a position sensitive detector. Around 103 antihydrogen atoms are needed for the gravitational measurement to be completed. The present status, current achievements and results will be presented, with special attention toward the laser excitation of positronium (Ps) to the n=3 state and the production of Ps atoms in the transmission geometry

Measuring the gravitational free-fall of antihydrogen

Antihydrogen holds the promise to test, for the first time, the universality of free-fall with a system composed entirely of antiparticles. The AEgIS experiment at CERN’s antiproton decelerator aims to measure the gravitational interaction between matter and antimatter by measuring the deflection of a beam of antihydrogen in the Earths gravitational field (g¯¯¯). The principle of the experiment is as follows: cold antihydrogen atoms are synthesized in a Penning-Malberg trap and are Stark accelerated towards a moiré deflectometer, the classical counterpart of an atom interferometer, and annihilate on a position sensitive detector. Crucial to the success of the experiment is the spatial precision of the position sensitive detector. We propose a novel free-fall detector based on a hybrid of two technologies: emulsion detectors, which have an intrinsic spatial resolution of 50 nm but no temporal information, and a silicon strip / scintillating fiber tracker to provide timing and positional information. In 2012 we tested emulsion films in vacuum with antiprotons from CERN’s antiproton decelerator. The annihilation vertices could be observed directly on the emulsion surface using the microscope facility available at the University of Bern. The annihilation vertices were successfully reconstructed with a resolution of 1–2 μmon the impact parameter. If such a precision can be realized in the final detector, Monte Carlo simulations suggest of order 500 antihydrogen annihilations will be sufficient to determine g¯¯¯with a 1 % accuracy. This paper presents current research towards the development of this technology for use in the AEgIS apparatus and prospects for the realization of the final detector.ISSN:0304-3843ISSN:0304-3834ISSN:1572-954

The AEgIS Experiment

The AEgIS experiment aims at performing the first test of the Weak Equivalence Principle of General Relativity in the antimatter sector by measuring the gravitational acceleration acting on a beam of cold antihydrogen to a precision of 1%. The installation of the apparatus is making good progress and large parts were taken into operation. Parasitic detector tests during the beamtime in December 2012 gave essential input for an optimal moiré deflectometer and the detector layout necessary to perform the gravity measurement.ISSN:0304-3843ISSN:0304-3834ISSN:1572-954

Measurement of KN scattering below the KN mass threshold

Abstract. We measured πE invariant mass spectra below and above the K¯N mass threshold in the K−d → NπE reaction in order to study the K¯N interaction and the Λ(1405) resonance. This reaction can be described by the two-step process: (i) K¯N1 → K¯N followed by (ii) K¯N2 → πΣ, where N1 and N2 are nucleons bound in the deuteron. We deduced the S -wave scattering amplitude of K¯N →K¯N in the framework of the K¯N πΣ coupled channel so as to reproduce the observed πΣ spectra in the I = 0 channel. We found a resonance pole at 1417.7-7.4+6.0 (fitting error)-1.0+1.1 (systematic error) - i[26.9-7.9+6.0 (fitting error)-2.0+1.7 (systematic error)]MeV/c2

Measurement of electrons from beauty-hadron decays in p-Pb collisions at sNN=5.02 \sqrt{s_{\mathrm{NN}}}=5.02 TeV and Pb-Pb collisions at sNN=2.76 \sqrt{s_{\mathrm{NN}}}=2.76 TeV

The production of beauty hadrons was measured via semi-leptonic decays at mid-rapidity with the ALICE detector at the LHC in the transverse momentum interval 1<p$_{T}$ < 8 GeV/c in minimum-bias p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV and in 1.3 < p$_{T}$ < 8 GeV/c in the 20% most central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV. The pp reference spectra at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV and $\sqrt{s}=2.76$ TeV, needed for the calculation of the nuclear modification factors R$_{pPb}$ and R$_{PbPb}$, were obtained by a pQCD-driven scaling of the cross section of electrons from beauty-hadron decays measured at $\sqrt{s}=7$ TeV. In the p$_{T}$ interval 3 < p$_{T}$ < 8 GeV/c, a suppression of the yield of electrons from beauty-hadron decays is observed in Pb-Pb compared to pp collisions. Towards lower p$_{T}$, the R$_{PbPb}$ values increase with large systematic uncertainties. The R$_{pPb}$ is consistent with unity within systematic uncertainties and is well described by theoretical calculations that include cold nuclear matter effects in p-Pb collisions. The measured R$_{pPb}$ and these calculations indicate that cold nuclear matter effects are small at high transverse momentum also in Pb-Pb collisions. Therefore, the observed reduction of R$_{PbPb}$ below unity at high p$_{T}$ may be ascribed to an effect of the hot and dense medium formed in Pb-Pb collisions