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Matter-antimatter asymmetry is a research topic of fundamental interest, as it is the basis for the existence of the matter world, which survived annihilation with antimatter in the early Universe. High energy nuclear collisions create conditions similar to the Universe microseconds after the Big Bang, with comparable amounts of matter and antimatter. Much of the antimatter created escapes the rapidly expanding fireball without annihilation, making such collisions an effective experimental tool to create heavy antimatter nuclear objects and study their properties. In this paper, we report the first observation of the antimatter hypernucleus 4Λ¯H¯¯¯¯, composed of an Λ¯, an antiproton and two antineutrons. The discovery was made through its two-body decay after production in ultrarelativistic heavy ion collisions by the STAR experiment at the Relativistic Heavy Ion Collider. In total, 15.6 candidate 4Λ¯H¯¯¯¯ antimatter hypernuclei are obtained with an estimated background count of 6.4. Lifetimes of the antihypernuclei 3Λ¯H¯¯¯¯ and 4Λ¯H¯¯¯¯ are measured and compared with lifetimes of their corresponding hypernuclei, testing the symmetry between matter and antimatter. Various production yield ratios among (anti)hypernuclei and (anti)nuclei are also measured and compared with theoretical model predictions, shedding light on their production mechanism.
The differential cross section for Z0 production, measured as a function of the boson's transverse momentum (pT), provides important constraints on the evolution of the transverse momentum dependent parton distribution functions (TMDs). The transverse single spin asymmetry (TSSA) of the Z0 is sensitive to one of the polarized TMDs, the Sivers function, which is predicted to have the opposite sign in p+p →W/Z+X from that which enters in semi-inclusive deep inelastic scattering. In this Letter, the STAR Collaboration reports the first measurement of the Z0/γ∗ differential cross section as a function of its pT in p+p collisions at a center-of-mass energy of 510 GeV, together with the Z0/γ∗ total cross section. We also report the measurement of Z0/γ∗ TSSA in transversely polarized p+p collisions at 510 GeV.
We report a new measurement of transverse single-spin asymmetries for dijet production in collisions of polarized protons at s√ = 200 GeV. Correlations between the proton spin and the transverse momenta of its partons, each perpendicular to the proton momentum direction, are probed at high Q2 ≈160 GeV2. The associated Sivers observable ⟨kT⟩, the average parton transverse momentum, is extracted using simple kinematics. Nonzero Sivers effects are observed for the first time in dijets from proton-proton collisions, but only when the jets are sorted by their net charge, which enhances the u- or d-quark contributions to separate data samples. This also enables a simple kinematic approach for determination of the individual partonic contributions to the observed asymmetries.
We report a new measurement of transverse single-spin asymmetries for dijet production in collisions of polarized protons at s√ = 200 GeV. Possible correlations between the proton spin and the transverse momenta of its partons, mutually orthogonal, with each perpendicular to the proton momentum direction, are probed at high Q2 ≈160 GeV2. The associated Sivers observable ⟨kT⟩, the average parton transverse momentum, is extracted using simple kinematics. Nonzero Sivers effects are observed for the first time in proton-proton collisions, but only when the jets are sorted by their net charge, which enhances the u- or d-quark contributions to separate data samples. This also enables a determination of the individual partonic contributions to the observed asymmetries.
We report the first measurements of cumulants, up to 4th order, of deuteron number distributions and proton-deuteron correlations in Au+Au collisions recorded by the STAR experiment in phase-I of Beam Energy Scan (BES-I) program at the Relativistic Heavy Ion Collider (RHIC). Deuteron cumulants, their ratios, and proton-deuteron mixed cumulants are presented for different collision centralities covering a range of center of mass energy per nucleon pair sNN−−−√ = 7.7 to 200 GeV. It is found that the cumulant ratios at lower collision energies favor a canonical ensemble over a grand canonical ensemble in thermal models. An anti-correlation between proton and deuteron multiplicity is observed across all collision energies and centralities, consistent with the expectation from global baryon number conservation. The UrQMD model coupled with a phase-space coalescence mechanism qualitatively reproduces the collision-energy dependence of cumulant ratios and proton-deuteron correlations.
The STAR experiment at RHIC reports new measurements of jet quenching based on the semi-inclusive distribution of charged-particle jets recoiling from direct photon (γdir) and neutral pion (π0) triggers in p+p and central Au+Au collisions at √sNN=200 GeV, for triggers in the range 9<EtrigT<20 GeV. The datasets have integrated luminosities of 3.9 nb−1 for Au+Au and 23 pb−1 for p+p collisions. Jets are reconstructed using the anti-kT algorithm with resolution parameters R=0.2 and 0.5. The large uncorrelated jet background in central Au+Au collisions is corrected using a mixed-event approach, which enables precise charged-particle jet measurements at low transverse momentum pchT,jet and large R. Recoil-jet distributions are reported in the range pchT,jet<25 GeV. Comparison of the distributions measured in p+p and Au+Au collisions reveals strong medium-induced jet yield suppression for R=0.2, with markedly less suppression for R=0.5. These data provide new insight into the mechanisms underlying jet quenching, and the angular dependence of medium-induced jet-energy transport.
The STAR Collaboration presents measurements of the semi-inclusive distribution of charged-particle jets recoiling from energetic direct-photon γdir and neutral-pion (π0) triggers in p+p and central Au+Au collisions at √sNN=200 GeV over a broad kinematic range, for jet resolution parameters R=0.2 and 0.5. Medium-induced jet yield suppression is observed to be larger for R=0.2 than for 0.5, reflecting the angular range of jet energy redistribution due to quenching. The magnitude of suppression is similar for γdir- and π0-triggered data, which constrains the color-charge and path-length dependence of jet quenching. Theoretical model calculations incorporating jet quenching do not fully describe the measurements.
The longitudinal and transverse spin transfers to Λ (Λ¯¯¯¯) hyperons in polarized proton-proton collisions are expected to be sensitive to the helicity and transversity distributions, respectively, of (anti-)strange quarks in the proton, and to the corresponding polarized fragmentation functions. We report improved measurements of the longitudinal spin transfer coefficient, DLL, and the transverse spin transfer coefficient, DTT, to Λ and Λ¯¯¯¯ in polarized proton-proton collisions at √s = 200 GeV by the STAR experiment at RHIC. The data set includes longitudinally polarized proton-proton collisions with an integrated luminosity of 52 pb−1, and transversely polarized proton-proton collisions with a similar integrated luminosity. Both data sets have about twice the statistics of previous results and cover a kinematic range of |ηΛ(Λ¯¯¯¯)| < 1.2 and transverse momentum pT,Λ(Λ¯¯¯¯) up to 8 GeV/c. We also report the first measurements of the hyperon spin transfer coefficients DLL and DTT as a function of the fractional jet momentum z carried by the hyperon, which can provide more direct constraints on the polarized fragmentation functions.
The STAR Collaboration presents measurements of the semi-inclusive distribution of charged-particle jets recoiling from energetic direct-photon γdir and neutral-pion (π0) triggers in p+p and central Au+Au collisions at sNN−−−√=200 GeV over a broad kinematic range, for jet resolution parameters R=0.2 and 0.5. Medium-induced jet yield suppression is observed to be larger for R=0.2 than for 0.5, reflecting the angular range of jet energy redistribution due to quenching. The magnitude of suppression is similar for γdir- and π0-triggered data, which constrains the color-charge and path-length dependence of jet quenching. Theoretical model calculations incorporating jet quenching do not fully describe the measurements.
Von A bis Å. (Fast) alles über die Frankfurter Skandinavistik. Ausgabe 7 ; Wintersemester 2023/24
(2023)
Von A bis Å. (Fast) alles über die Frankfurter Skandinavistik. Ausgabe 8 ; Sommeremester 2024
(2024)
Weiträumige Kontaktnetzwerke sorgen für Verbreitung und Transfer von Wissen und Gütern sowie von kulturellen Werten. Der Transport von Lasten und Menschen kann als einer der wichtigsten Eckpfeiler solcher Austauschsysteme gesehen werden. Daher dürften die Suche nach Transportmöglichkeiten und die Entwicklung geeigneter Vehikel in der menschlichen Gedankenwelt seit jeher fest verankert sein. Die hier vorliegenden Beiträge basieren auf den Vorträgen der Tagung „Transporte, Transportwege und Transportstrukturen“ der Arbeitsgemeinschaft Bronzezeit und des Sonderforschungsbereiches 1070 RessourcenKulturen. Sie fassen im archäologischen Befund der Bronzezeit vorhandene Evidenzen zu Transportwegen und -fahrzeugen sowie Aussagen zu Infrastruktur nicht nur zusammen, sondern ergänzen diese um zahlreiche wissenswerte Aspekte. Was können diese Befunde über die Transportvehikel und ihre Bedeutung aussagen? Welche Eigenschaften wiesen diese auf? Handelt es sich bei den Fundstücken um abgenutzte oder mutwillig zerstörte Fahrzeuge bzw. Teile von solchen? Welche Implikationen auf technologischer und sozialer Ebene lassen sich mit den Befunden verbinden? Wie muss man sich die bronzezeitliche Infrastruktur in unterschiedlichen Regionen vorstellen? Inwiefern bildeten Verkehrswege und Austausch eine Ressource? Der detaillierten Beantwortung dieser Fragen ist dieser Band gewidmet, woraus eine übergreifende Zusammenschau von Funden, Befunden und Theorien entstanden ist.