Razvoj sustava silicijskih detektora za opažanje protona i mjerenje trostrukih koincidencija u elektronskim raspršenjima na jezgrama 12C

A silicon detector system has been developed for proton detection in electron scattering reactions at MAMI. The use of digital algorithms for detector signal processing enabled maintaining the acceptable energy resolution at high counting rates. Triple-coincidence reactions 12C(e, e´pπ-)11C and 12C(e, e´pp)10Be were studied, where in the latter, the differential cross section for the transition to berilium ground-state has been extracted. By comparison with theoretical models, this result could contribute to understanding of nucleon-nucleon correlations and thus the properties of atomic nuclei.Razvijen je sustav silicijskih detektora za opažanje protona u reakcijama elektronskog raspršenja na ubrzivaču MAMI. Za obradu detektorskih signala upotrijebljeni su digitalni algoritmi, čime je omogućeno zadržavanje prihvatljive energijske razlučivosti uz visoki tok čestica kroz detektorski sustav. Proučavane su trostruko-koincidentne reakcije 12C(e, e´ pπ-)11C, te 12C(e, e´ pp)10Be u kojoj je određen diferencijalni udarni presjek za prijelaz u osnovno stanje berilija. Taj bi rezultat, usporedbom s teorijskim modelima, mogao doprinjeti razumijevanju nukleon-nukleon korelacija, a time i svojstava atomske jezgre

Low-mass vector-meson production at forward rapidity in p + p collisions at √s = 200 GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured low-mass vector-meson, ω, ρ, and ϕ, production through the dimuon decay channel at forward rapidity (1.2<|y|<2.2) in p+p collisions at √s=200  GeV. The differential cross sections for these mesons are measured as a function of both pT and rapidity. We also report the integrated differential cross sections over 1<pT<7  GeV/c and 1.2<|y|<2.2: dσ/dy(ω+ρ→μμ)=80±6(stat)±12(syst)  nb and dσ/dy(ϕ→μμ)=27±3(stat)±4(syst)  nb. These results are compared with midrapidity measurements and calculations

Cross section and transverse single-spin asymmetry of η mesons in p↑+p collisions at s√=200 GeV at forward rapidity

We present a measurement of the cross section and transverse single-spin asymmetry (AN) for η mesons at large pseudorapidity from √s=200  GeV p↑+p collisions. The measured cross section for 0.5<pT<5.0  GeV/c and 3.0<|η|<3.8 is well described by a next-to-leading-order perturbative-quantum-chromodynamics calculation. The asymmetries AN have been measured as a function of Feynman-x (xF) from 0.2<|xF|<0.7, as well as transverse momentum (pT) from 1.0<pT<4.5  GeV/c. The asymmetry averaged over positive xF is ⟨AN⟩=0.061±0.014. The results are consistent with prior transverse single-spin measurements of forward η and π0 mesons at various energies in overlapping xF ranges. Comparison of different particle species can help to determine the origin of the large observed asymmetries in p↑+p collisions

Medium Modification of Jet Fragmentation in Au + Au Collisions at √sNN=200 GeV Measured in Direct Photon-Hadron Correlations

The jet fragmentation function is measured with direct photon-hadron correlations in p+p and Au+Au collisions at √sNN=200  GeV. The pT of the photon is an excellent approximation to the initial pT of the jet and the ratio zT=phT/pγT is used as a proxy for the jet fragmentation function. A statistical subtraction is used to extract the direct photon-hadron yields in Au+Au collisions while a photon isolation cut is applied in p+p. IAA, the ratio of hadron yield opposite the photon in Au+Au to that in p+p, indicates modification of the jet fragmentation function. Suppression, most likely due to energy loss in the medium, is seen at high zT. The associated hadron yield at low zT is enhanced at large angles. Such a trend is expected from redistribution of the lost energy into increased production of low-momentum particles

Nuclear matter effects on J/ψ production in asymmetric Cu + Au collisions at √sNN=200 GeV

We report on J/ψ production from asymmetric Cu + Au heavy-ion collisions at √sNN=200 GeV at the Relativistic Heavy Ion Collider at both forward (Cu-going direction) and backward (Au-going direction) rapidities. The nuclear modification of J/ψ yields in Cu + Au collisions in the Au-going direction is found to be comparable to that in Au + Au collisions when plotted as a function of the number of participating nucleons. In the Cu-going direction, J/ψ production shows a stronger suppression. This difference is comparable in magnitude and has the same sign as the difference expected from shadowing effects due to stronger low-x gluon suppression in the larger Au nucleus

Measurements of directed, elliptic, and triangular flow in Cu + Au collisions at √sNN=200 GeV

Measurements of anisotropic flow Fourier coefficients (vn) for inclusive charged particles and identified hadrons π±, K±, p, and p¯ produced at midrapidity in Cu + Au collisions at √sNN = 200 GeV are presented. The data were collected in 2012 by the PHENIX experiment at the Relativistic Heavy-Ion Collider (RHIC). The particle azimuthal distributions with respect to different-order symmetry planes n, for Ψn = 1, 2, and 3 are studied as a function of transverse momentum pT over a broad range of collision centralities. Mass ordering, as expected from hydrodynamic flow, is observed for all three harmonics. The charged-particle results are compared with hydrodynamical and transport model calculations. We also compare these Cu + Au results with those in Cu + Cu and Au + Au collisions at the same √sNN and find that the v2 and v3, as a function of transverse momentum, follow a common scaling with 1/(εnN1/3 part)

Promjene svojstava Delta u nuklearnoj sredini

In the experiments at the Mainz Microtron, MAMI, ∆0 particles in the electron scattering reactions 12C (e, e ′∆0 ) 11C have been produced in nuclear medium. The three high-resolution magnetic spectrometers of the A1 collaboration have been used in triple coincidence measurements 12C (e, e ′p π −) 11C. Indications for substantial changes of delta properties in the nuclear medium have been obtained. Because of low statistics, these results cannot yet be taken as conclusive. A new setup for measurements at MAMI with silicon detectors for proton detection, which subtend larger solid angle, is described.U eksperimentima s mikrotronom u Mainzu, MAMI, proizvodili smo u nuklearnoj sredini čestice ∆0 reakcijom 12C (e, e ′∆0 ) 11C. U okviru suradnje A1, rabili smo tri magnetska spektrometra visokog razlučivanja za trosudesna mjerenja 12C (e, e ′p π −) 11C. Podaci ukazuju na promjene svojstava delta čestica u nuklearnoj sredini. Zbog slabe statistike, ti se ishodi još ne mogu smatrati konačnima. Opisuje se i nov mjerni sustav za detekciju protona sastavljen od silicijskih detektora koji zahvaća veći prostorni kut

Measurements of the γ∗p→Δ reaction at low Q2: Probing the mesonic contribution

The determination of nonspherical angular momentum amplitudes in nucleons at long ranges (low Q2) was accomplished through the p(, e'p)0 reaction in the region at Q2=0.060, 0.127, and 0.200 (GeV/c)2 at the Mainz Microtron with an accuracy for the cross sections of 4%. The results for the dominant transition magnetic dipole amplitude and the quadrupole to dipole ratios have been obtained with an estimated model uncertainty that is approximately the same as the experimental uncertainty. Lattice and effective field theory predictions agree with our data within the relatively large estimated theoretical uncertainties. Phenomenological models are in good agreement with experiment when the resonant amplitudes are adjusted to the data. To check reaction model calculations additional data were taken for center-of-mass energies below resonance and for the LT' structure function. These results confirm the dominance, and general Q2 variation, of the pionic contribution at large distances