We report on the nuclear dependence of transverse single-spin asymmetries (TSSAs) in the production of positively charged hadrons in polarized p↑+p, p↑+Al, and p↑+Au collisions at sNN=200 GeV. The ...measurements have been performed at forward rapidity (1.4<η<2.4) over the range of transverse momentum (1.8<pT<7.0 GeV/c) and Feynman x (0.1<xF<0.2). We observed positive asymmetries for positively charged hadrons in p↑+p collisions, and significantly reduced asymmetries in p↑+A collisions. These results reveal a nuclear dependence of TSSAs for charged-hadron production in a regime where perturbative techniques are applicable. These results provide new opportunities to use p↑+A collisions as a tool to investigate the rich phenomena behind TSSAs in hadronic collisions and to use TSSAs as a new handle in studying small-system collisions.
A detailed study of hadronic interactions is presented using data recorded with the highly granular CALICE silicon–tungsten electromagnetic calorimeter. Approximately 350,000 selected π− events at ...energies between 2 and 10GeV have been studied. The predictions of several physics models available within the GEANT4 simulation tool kit are compared to this data. A reasonable overall description of the data is observed; the Monte Carlo predictions are within 20% of the data, and for many observables much closer. The largest quantitative discrepancies are found in the longitudinal and transverse distributions of reconstructed energy.
During 2015, the Relativistic Heavy Ion Collider (RHIC) provided collisions of transversely polarized protons with Au and Al nuclei for the first time, enabling the exploration of ...transverse-single-spin asymmetries with heavy nuclei. Large single-spin asymmetries in very forward neutron production have been previously observed in transversely polarized p+p collisions at RHIC, and the existing theoretical framework that was successful in describing the single-spin asymmetry in p+p collisions predicts only a moderate atomic-mass-number (A) dependence. In contrast, the asymmetries observed at RHIC in p+A collisions showed a surprisingly strong A dependence in inclusive forward neutron production. The observed asymmetry in p+Al collisions is much smaller, while the asymmetry in p+Au collisions is a factor of 3 larger in absolute value and of opposite sign. The interplay of different neutron production mechanisms is discussed as a possible explanation of the observed A dependence.
A prototype silicon–tungsten electromagnetic calorimeter (ECAL) for an international linear collider (ILC) detector was installed and tested during summer and autumn 2006 at CERN. The detector had ...6480 silicon pads of dimension
1
×
1
cm
2
. Data were collected with electron beams in the energy range 6–45
GeV. The analysis described in this paper focuses on electromagnetic shower reconstruction and characterises the ECAL response to electrons in terms of energy resolution and linearity. The detector is linear to within approximately the 1% level and has a relative energy resolution of
(
16.53
±
0.14
(
stat
)
±
0.4
(
syst
)
)
/
E
(
GeV
)
⊕
(
1.07
±
0.07
(
stat
)
±
0.1
(
syst
)
)
(
%
)
. The spatial uniformity and the time stability of the ECAL are also addressed.
Experimental studies of the collisions of heavy nuclei at relativistic energies have established the properties of the quark–gluon plasma (QGP), a state of hot, dense nuclear matter in which quarks ...and gluons are not bound into hadrons1–4. In this state, matter behaves as a nearly inviscid fluid5 that efficiently translates initial spatial anisotropies into correlated momentum anisotropies among the particles produced, creating a common velocity field pattern known as collective flow. In recent years, comparable momentum anisotropies have been measured in small-system proton–proton (p+p) and proton–nucleus (p+A) collisions, despite expectations that the volume and lifetime of the medium produced would be too small to form a QGP. Here we report on the observation of elliptic and triangular flow patterns of charged particles produced in proton–gold (p+Au), deuteron–gold (d+Au) and helium–gold (3He+Au) collisions at a nucleon–nucleon centre-of-mass energy \\sqrt {s_{{\mathrm{NN}}}\ = 200 GeV. The unique combination of three distinct initial geometries and two flow patterns provides unprecedented model discrimination. Hydrodynamical models, which include the formation of a short-lived QGP droplet, provide the best simultaneous description of these measurements.
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