0000000000279373
AUTHOR
T. Sefzick
An Isotensor Dibaryon in the $pp \to pp\pi^+\pi^-$ Reaction?
Exclusive measurements of the quasi-free $pp \to pp\pi^+\pi^-$ reaction have been carried out at WASA@COSY by means of $pd$ collisions at $T_p$ = 1.2 GeV. Total and differential cross sections have been extracted covering the energy region $T_p = 1.08 - 1.36$ GeV, which is the region of $N^*(1440)$ and $\Delta(1232)\Delta(1232)$ resonance excitations. Calculations describing these excitations by $t$-channel meson exchange are at variance with the measured differential cross sections and underpredict substantially the experimental total cross section. An isotensor $\Delta N$ dibaryon resonance with $I(J^P) = 2(1^+)$ produced associatedly with a pion is able to overcome these deficiencies.
ATRAP antihydrogen experiments
Antihydrogen (Hbar) was first produced at CERN in 1996. Over the past decade our ATRAP collaboration has made massive progress toward our goal of producing large numbers of cold Hbar atoms that will be captured in a magnetic gradient trap for precise comparison between the atomic spectra of matter and antimatter. The AD at CERN provides bunches of 3 × 107 low energy Pbars every 100 seconds. We capture and cool to 4 K, 0.1% of these in a cryogenic Penning trap. By stacking many bunches we are able to do experiments with 3 × 105 Pbars. ∼100 e+/sec from a 22Na radioactive source are captured and cooled in the trap, with 5 × 106 available experiments.We have developed 2 ways to make Hbar from t…
Drift chamber calibration and particle identification in the P-349 experiment
The goal of the P-349 experiment is to test whether 3.5 GeV/c antiprotons produced in high-energy proton-proton collisions are polarized in view of the preparation of a polarized antiproton beam. In this article, we present the details of the ongoing analysis focused on the drift chambers calibration and particle identification with DIRC.
Pumped helium system for cooling positron and electron traps to 1.2 K
Abstract Extremely precise tests of fundamental particle symmetries should be possible via laser spectroscopy of trapped antihydrogen ( H ¯ ) atoms. H ¯ atoms that can be trapped must have an energy in temperature units that is below 0.5 K—the energy depth of the deepest magnetic traps that can currently be constructed with high currents and superconducting technology. The number of atoms in a Boltzmann distribution with energies lower than this trap depth depends sharply upon the temperature of the thermal distribution. For example, ten times more atoms with energies low enough to be trapped are in a thermal distribution at a temperature of 1.2 K than for a temperature of 4.2 K. To date, H…
Feasibility study for the measurement of πN transition distribution amplitudes at P¯ANDA in p¯p→J/ψπ0
The exclusive charmonium production process in (P) over barp annihilation with an associated pi 0 meson (p) over barp -> J/psi pi(0) is studied in the framework of QCD collinear factorization. The feasibility of measuring this reaction through the J/psi -> e(+) e(-) decay channel with the AntiProton ANnihilation at DArmstadt ((P) over bar ANDA) experiment is investigated. Simulations on signal reconstruction efficiency as well as the background rejection from various sources including the (P) over barp -> pi(+)pi(-)pi(0) and (p) over barp -> J/psi pi(0)pi(0) reactions are performed with PANDAROOT, the simulation and analysis software framework of the (P) over bar ANDA experiment. It is show…
Adiabatic Cooling of Antiprotons
Adiabatic cooling is shown to be a simple and effective method to cool many charged particles in a trap to very low temperatures. Up to 3 x 10(6) (p) over bar are cooled to 3.5 K-10(3) times more cold (p) over bar and a 3 times lower (p) over bar temperature than previously reported. A second cooling method cools (p) over bar plasmas via the synchrotron radiation of embedded (p) over bar (with many fewer (p) over bar than (p) over bar) in preparation for adiabatic cooling. No (p) over bar are lost during either process-a significant advantage for rare particles.
Polarization analysis of $\bar{p}$ produced in pA collisions
A quite simple procedure for the generation of a polarized antiproton beam could be worked out if antiprotons are produced with some polarization. In order to investigate this possibility measurements of the polarization of produced antiprotons have been started at a CERN/PS test beam. The polarization will be determined from the asymmetry of the elastic antiproton scattering at a liquid hydrogen target in the CNI region for which the analyzing power is well known. The data are under analysis and an additional measurement is done in 2018. Details on the experiment and the ongoing data analysis will be given.
Search for Mesic He with the WASA-at-COSY facility in the And Reactions
We report on the experimental search for the bound state of an η meson and He3 nucleus performed using the WASA-at-COSY detector setup. In order to search for the η-mesic nucleus decay, the pd→3He2γ and pd→3He6γ channels have been analysed. These reactions manifest the direct decay of the η meson bound in a He3 nucleus. This non-mesonic decay channel has been considered for the first time. When taking into account only statistical errors, the obtained excitation functions reveal a slight indication for a possible bound state signal corresponding to a $^{3}$He-η nucleus width Γ above 20 MeV and binding energy Bs between 0 and 15 MeV. However, the determined cross sections are consistent with…
Cross section ratio and angular distributions of the reaction p + d -> 3He + eta at 48.8 MeV and 59.8 MeV excess energy
We present new data for angular distributions and on the cross section ratio of the p + d -> 3He + eta reaction at excess energies of Q = 48.8 MeV and Q = 59.8 MeV. The data have been obtained at the WASA-at-COSY experiment (Forschungszentrum J\"ulich) using a proton beam and a deuterium pellet target. While the shape of obtained angular distributions show only a slow variation with the energy, the new results indicate a distinct and unexpected total cross section fluctuation between Q = 20 MeV and Q = 60 MeV, which might indicate the variation of the production mechanism within this energy interval.
Search for polarization effects in the antiproton production process
For the production of a polarized antiproton beam various methods have been suggested including the possibility that antiprotons may be produced polarized which will be checked experimentally. The polarization of antiprotons produced under typical conditions for antiproton beam preparation will be measured at the CERN/PS. If the production process creates some polarization a polarized antiproton beam could be prepared by a rather simple modification of the antiproton beam facility. The detection setup and the expected experimental conditions are described. For the production of a polarized antiproton beam various methods have been suggested including the possibility that antiprotons may be …
Search for the $��$ mesic $^3$He in the $pd\rightarrow d p ��^{0}$ reaction with the WASA-at-COSY facility
The excitation function for the $pd\rightarrow$ $d p ��^{0}$ reaction has been measured by WASA-at-COSY experiment with the aim of searching for $^{3}\hspace{-0.03cm}\mbox{He}$-$��$ mesic nuclei. The measurement in the vicinity of $��$ meson production was performed using a ramped proton beam. The data analysis and interpretation was carried out with the assumption that the $��$-mesic Helium decays via the formation of an intermediate N$^{*}$(1535) resonance. No direct signal of the $��$-mesic nucleus is observed in the excitation function. We determine a new improved upper limit for the total cross section for the bound state production and decay in the $pd\rightarrow$ $(^{3}\hspace{-0.03c…
Spin dependence of {\eta} meson production in proton-proton collisions close to threshold
Taking advantage of the high acceptance and axial symmetry of the WASA-at-COSY detector, and the high degree of the polarized proton beam of COSY, the reaction pp{\to} pp{\eta} has been measured close to threshold to explore the analyzing power Ay. The angular distribution of Ay is determined with the precision improved by more than one order of magnitude with respect to previous results allowing a first accurate comparison with theoretical predictions. The determined analyzing power is consistent with zero for an excess energy of Q = 15 MeV signaling s wave production with no evidence for higher partial waves. At Q = 72 MeV the data reveals strong interference of P s and P p partial waves …
Study of doubly strange systems using stored antiprotons
Bound nuclear systems with two units of strangeness are still poorly known despite their importance for many strong interaction phenomena. Stored antiprotons beams in the GeV range represent an unparalleled factory for various hyperon-antihyperon pairs. Their outstanding large production probability in antiproton collisions will open the floodgates for a series of new studies of systems which contain two or even more units of strangeness at the PANDA experiment at FAIR. For the first time, high resolution gamma-spectroscopy of doubly strange Lambda Lambda-hypernuclei will be performed, thus complementing measurements of ground state decays of Lambda Lambda-hypernuclei at J-PARC or possible …
Single-component plasma of photoelectrons
Abstract Ten-nanosecond pulses of photoelectrons liberated by intense UV laser pulses from a thin gold layer are captured into a single-component plasma that is ideally suited to cool antiprotons ( p ¯ ) for antihydrogen ( H ¯ ) production. Up to a billion electrons are accumulated using a series of laser pulses, more than are needed for efficient p ¯ cooling in the large traps now being used for loading p ¯ for H ¯ production. The method is demonstrated within an enclosed vacuum space that is entirely at 4 K, and is thus compatible with the exceptional cryogenic vacuum that is desirable for the long-term storage of antihydrogen. The pitfalls of other electron accumulation methods are entir…
Antihydrogen production within a Penning-Ioffe trap.
Slow antihydrogen (H) is produced within a Penning trap that is located within a quadrupole Ioffe trap, the latter intended to ultimately confine extremely cold, ground-state H[over ] atoms. Observed H[over ] atoms in this configuration resolve a debate about whether positrons and antiprotons can be brought together to form atoms within the divergent magnetic fields of a quadrupole Ioffe trap. The number of detected H atoms actually increases when a 400 mK Ioffe trap is turned on.
Determination of theη′-Proton Scattering Length in Free Space
Taking advantage of both the high mass resolution of the COSY-11 detector and the high energy resolution of the low-emittance proton beam of the cooler synchrotron COSY, we determine the excitation function for the $pp\ensuremath{\rightarrow}pp{\ensuremath{\eta}}^{\ensuremath{'}}$ reaction close to threshold. Combining these data with previous results, we extract the scattering length for the ${\ensuremath{\eta}}^{\ensuremath{'}}$-proton potential in free space to be $\mathrm{Re}({a}_{p{\ensuremath{\eta}}^{\ensuremath{'}}})=0\ifmmode\pm\else\textpm\fi{}0.43\text{ }\text{ }\mathrm{fm}$ and $\mathrm{Im}({a}_{p{\ensuremath{\eta}}^{\ensuremath{'}}})={0.37}_{\ensuremath{-}0.16}^{+0.40}\text{ }\t…
Measurement of the $pn \to pp\pi^0\pi^-$ Reaction in Search for the Recently Observed Resonance Structure in $d\pi^0\pi^0$ and $d\pi^+\pi^-$ systems
Exclusive measurements of the quasi-free $pn \to pp\pi^0\pi^-$ reaction have been performed by means of $pd$ collisions at $T_p$ = 1.2 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region $\sqrt s$ = (2.35 - 2.46) GeV, which includes the region of the ABC effect and its associated resonance structure. No ABC effect, {\it i.e.} low-mass enhancement is found in the $\pi^0\pi^-$-invariant mass spectrum -- in agreement with the constraint from Bose statistics that the isovector pion pair can not be in relative s-wave. At the upper end of the covered energy region $t$-channel processes for Roper, $\Delta(1600)$ and $\Delta…
Status of the analysis for the search of polarization in the antiproton production process
The P-349 experiment aims to test whether for antiprotons the production process itself can be a source of polarization in view of the preparation of a polarized antiproton beam. In this article we present the details of performed measurements and report on the status of the ongoing analysis.
Studies on Antihydrogen Atoms with the ATRAP Experiment at CERN
The CPT theorem predicts the same properties of matter and antimatter, however, in the nearby Universe, we observe a huge imbalance of matter and antimatter. Therefore, it is intriguing to measure the properties of particles and antiparticles in order to contribute to an explanation of this phenomena. In this article, we will describe the experimental efforts of the ATRAP Collaboration in order to test the CPT theorem using antihydrogen atoms.
Search for the $\eta$ mesic $^3$He in the $pd\rightarrow d p \pi^{0}$ reaction with the WASA-at-COSY facility
The excitation function for the $pd\rightarrow$ $d p \pi^{0}$ reaction has been measured by WASA-at-COSY experiment with the aim of searching for $^{3}\hspace{-0.03cm}\mbox{He}$-$\eta$ mesic nuclei. The measurement in the vicinity of $\eta$ meson production was performed using a ramped proton beam. The data analysis and interpretation was carried out with the assumption that the $\eta$-mesic Helium decays via the formation of an intermediate N$^{*}$(1535) resonance. No direct signal of the $\eta$-mesic nucleus is observed in the excitation function. We determine a new improved upper limit for the total cross section for the bound state production and decay in the $pd\rightarrow$ $(^{3}\hspa…
Cryogenic Particle Accumulation In ATRAP And The First Antihydrogen Production Within A Magnetic Gradient Trap For Neutral Antimatter
ATRAP has made many important improvements since CERN's Antiproton Decelerator (AD) was restarted in 2006. These include substantial increases in the number of positrons (e+) and antiprotons (Pbars) used to make antihydrogen (Hbar) atoms, a new technique for loading electrons (e−) that are used to cool Pbars and e+, implementation of a completely new, larger and more robust apparatus in our second experimental zone and the inclusion of a quadrupole Ioffe trap intended to trap the coldest Hbar atoms produced. Using this new apparatus we have produced large numbers of Hbar atoms within a Penning trap that is located within this quadrupole Ioffe trap using a new technique which shows promise f…
Determination of the eta'-proton scattering length in free space
Taking advantage of both the high mass resolution of the COSY-11 detector and the high energy resolution of the low-emittance proton-beam of the Cooler Synchrotron COSY we determine the excitation function for the pp --> pp eta' reaction close-to-threshold. Combining these data with previous results we extract the scattering length for the eta'-proton potential in free space to be Re(a_{p eta'}) = 0+-0.43 fm and Im(a_{p eta'}) = 0.37(+0.40)(-0.16) fm.
Charge Symmetry Breaking in dd->4He{\pi}0 with WASA-at-COSY
Charge symmetry breaking (CSB) observables are a suitable experimental tool to examine effects induced by quark masses on the nuclear level. Previous high precision data from TRIUMF and IUCF are currently used to develop a consistent description of CSB within the framework of chiral perturbation theory. In this work the experimental studies on the reaction dd->4He{\pi}0 have been extended towards higher excess energies in order to provide information on the contribution of p-waves in the final state. For this, an exclusive measurement has been carried out at a beam momentum of p=1.2 GeV/c using the WASA-at-COSY facility. The total cross section amounts to sigma(tot) = (118 +- 18(stat) +- 13…
Antiproton confinement in a Penning-Ioffe trap for antihydrogen.
Antiprotons ((p) over bar) remain confined in a Penning trap, in sufficient numbers to form antihydrogen ((H) over bar) atoms via charge exchange, when the radial field of a quadrupole Ioffe trap is added. This first demonstration with (p) over bar suggests that quadrupole Ioffe traps can be superimposed upon (p) over bar and e(+) traps to attempt the capture of (H) over bar atoms as they form, contrary to conclusions of previous analyses.
Centrifugal Separation of Antiprotons and Electrons
Centrifugal separation of antiprotons and electrons is observed, the first such demonstration with particles that cannot be laser cooled or optically imaged. The spatial separation takes place during the electron cooling of trapped antiprotons, the only method available to produce cryogenic antiprotons for precision tests of fundamental symmetries and for cold antihydrogen studies. The centrifugal separation suggests a new approach for isolating low energy antiprotons and for producing a controlled mixture of antiprotons and electrons.
Density and geometry of single component plasmas
Abstract The density and geometry of p ¯ and e + plasmas in realistic trapping potentials are required to understand and optimize antihydrogen ( H ¯ ) formation. An aperture method and a quadrupole oscillation frequency method for characterizing such plasmas are compared for the first time, using electrons in a cylindrical Penning trap. Both methods are used in a way that makes it unnecessary to assume that the plasmas are spheroidal, and it is shown that they are not. Good agreement between the two methods illustrates the possibility to accurately determine plasma densities and geometries within non-idealized, realistic trapping potentials.
One-Particle Measurement of the Antiproton Magnetic Moment
\DeclareRobustCommand{\pbar}{\HepAntiParticle{p}{}{}\xspace} \DeclareRobustCommand{\p}{\HepParticle{p}{}{}\xspace} \DeclareRobustCommand{\mup}{$\mu_{p}${}{}\xspace} \DeclareRobustCommand{\mupbar}{$\mu_{\pbar}${}{}\xspace} \DeclareRobustCommand{\muN}{$\mu_N${}{}\xspace For the first time a single trapped \pbar is used to measure the \pbar magnetic moment ${\bm\mu}_{\pbar}$. The moment ${\bm\mu}_{\pbar} = \mu_{\pbar} {\bm S}/(\hbar/2)$ is given in terms of its spin ${\bm S}$ and the nuclear magneton (\muN) by $\mu_{\pbar}/\mu_N = -2.792\,845 \pm 0.000\,012$. The 4.4 parts per million (ppm) uncertainty is 680 times smaller than previously realized. Comparing to the proton moment measured using…
On the Production of an Isotensor Dibaryon in the $pp \to pp\pi^+\pi^-$ Reaction
Exclusive measurements of the quasi-free $pp \to pp\pi^+\pi^-$ reaction have been performed by means of $pd$ collisions at $T_p$ = 1.2 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region $T_p = 1.08 - 1.36$ GeV ($\sqrt s$ = 2.35 - 2.46 GeV), which includes the regions of $N^*(1440)$ and $\Delta(1232)\Delta(1232)$ resonance excitations. Calculations describing these excitations by $t$-channel meson exchange are at variance with experimental differential cross sections and underpredict substantially the measured total cross section. An isotensor $\Delta N$ dibaryon resonance with $I(J^P) = 2(1^+)$ produced associatedly…