700 research outputs found
Veröffentlichungen von Prof. Dr. Ulrich Hamm und Mitarbeitern/-innen
No full textVeröffentlichungen von:
U. Hamm
L. Besschaposchnikowa
A. Dahlke
F. Gronefeld
D. Halpin
K. Kohlhoff
J. Michelsen
M. Müller
J. Niessen
A. Radlinsky
T. Richter
M. Rippin
J. Sanders
M. Schermer
O. Schmi
Veröffentlichungen von Prof. Dr. Ulrich Hamm und Mitarbeitern/-innen [Publications of Prof. Dr. Ulrich Hamm and staff]
No full textVeröffentlichungen von:
U. Hamm
L. Besschaposchnikowa
A. Dahlke
F. Gronefeld
D. Halpin
K. Kohlhoff
J. Michelsen
M. Müller
J. Niessen
A. Radlinsky
T. Richter
M. Rippin
J. Sanders
M. Schermer
O. Schmi
Veröffentlichungen von Prof. Dr. Ulrich Hamm und Mitarbeitern/-innen [Publications of Prof. Dr. Ulrich Hamm and staff]
No full textVeröffentlichungen von:
U. Hamm
S. Wild
L. Besschaposchnikowa
A. Dahlke
F. Gronefeld
D. Halpin
K. Kohlhoff
J. Michelsen
M. Müller
J. Niessen
A. Radlinsky
T. Richter
M. Rippin
J. Sanders
M. Schermer
O. Schmi
First measurement of the vertical bar t vertical bar-dependence of coherent J/psi photonuclear production
No full textThe first measurement of the cross section for coherent J/Psi photoproduction as a function of vertical bar t vertical bar, the square of the momentum transferred between the incoming and outgoing target nucleus, is presented. The data were measured with the ALICE detector in ultra-peripheral Pb-Pbcollisions at a centre-of-mass energy per nucleon pair root s(NN) = 5.02 TeV with the J/Psi produced in the central rapidity region vertical bar y vertical bar < 0.8, which corresponds to the small Bjorken-xrange (0.3 - 1.4) x 10(-3). The measured vertical bar t vertical bar-dependence is not described by computations based only on the Pb nuclear form factor, while the photonuclear cross section is better reproduced by models including shadowing according to the leading-twist approximation, or gluon-saturation effects from the impact-parameter dependent Balitsky-Kovchegov equation. These new results are therefore a valid tool to constrain the relevant model parameters and to investigate the transverse gluonic structure at very low Bjorken- x. (C) 2021 The Author(s). Published by Elsevier B.V
J/psi Elliptic Flow in Pb-Pb Collisions at root s(NN)=5.02 TeV
No full textWe report a precise measurement of the J/ψ elliptic flow in Pb-Pb collisions at √sNN=5.02 TeV with the ALICE detector at the LHC. The
J/ψ mesons are reconstructed at midrapidity (|y|<0.9) in the dielectron decay channel and at forward rapidity (2.5<y<4.0) in the dimuon channel, both down to zero transverse momentum. At forward rapidity, the elliptic flow v2 of the J/ψ is studied as a function of the transverse momentum and centrality. A positive v2 is observed in the transverse momentum range 2<pT<8 GeV/c in the three centrality classes studied and confirms with higher statistics our earlier results at √sNN=2.76 TeV in semicentral collisions. At midrapidity, the J/ψ v2 is investigated as a function of the transverse momentum in semicentral collisions and found to be in agreement with the measurements at forward rapidity. These results are compared to transport model calculations. The comparison supports the idea that at low pT the elliptic flow of the J/ψ originates from the thermalization of charm quarks in the deconfined medium but suggests that additional mechanisms might be missing in the models
Study of J/ψ azimuthal anisotropy at forward rapidity in Pb-Pb collisions at √sNN=5.02 TeV
No full textThe second (v2) and third (v3) flow harmonic coefficients of J/ψ mesons are measured at forward rapidity (2.5 < y < 4.0) in Pb-Pb collisions at √sNN = 5.02 TeV with the ALICE detector at the LHC. Results are obtained with the scalar product method and reported as a function of transverse momentum, pT, for various collision centralities. A positive value of J/ψ v3 is observed with 3.7σ significance. The measurements, compared to those of prompt D0 mesons and charged particles at mid-rapidity, indicate an ordering with vn(J/ψ) < vn(D0) < vn(h±) (n = 2, 3) at low and intermediate pT up to 6GeV/c and a convergence with v2(J/ψ) ≈ v2(D0) ≈ v2(h±) at high pT above 6–8 GeV/c. In semi- central collisions (5–40% and 10–50% centrality intervals) at intermediate pT between 2 and 6 GeV/c, the ratio v3/v2 of J/ψ mesons is found to be significantly lower (4.6σ) with respect to that of charged particles. In addition, the comparison to the prompt D0-meson ratio in the same pT interval suggests an ordering similar to that of the v2 and v3 coefficients. The J/ψ v2 coefficient is further studied using the Event Shape Engineering technique. The obtained results are found to be compatible with the expected variations of the eccentricity of the initial-state geometry
Energy dependence of forward-rapidity J / ψ and ψ ( 2 S ) production in pp collisions at the LHC
No full textWe present results on transverse momentum (pT) and rapidity (y) differential production cross sections, mean transverse momentum and mean transverse momentum square of inclusive J / ψ and ψ(2 S) at forward rapidity (2.5 15 GeV/c the non-prompt contribution reaches up to 50% of the total charmonium yield
Inclusive J/ψ production at mid-rapidity in pp collisions at √s = 5.02 TeV
No full textInclusive J/ψ production is studied in minimum-bias proton-proton collisions at a centre-of-mass energy of s = 5.02 TeV by ALICE at the CERN LHC. The measurement is performed at mid-rapidity (|y| T, using a data sample corresponding to an integrated luminosity of Lint = 19.4 ± 0.4 nb−1. The measured pT-integrated inclusive J/ψ production cross sec- tion is dσ/dy = 5.64 ± 0.22(stat.) ± 0.33(syst.) ± 0.12(lumi.) μb. The pT-differential cross section d2σ/dpTdy is measured in the pT range 0–10 GeV/c and compared with state-of- the-art QCD calculations. The J/ψ 〈pT〉 and 〈pT2〉 are extracted and compared with results obtained at other collision energies. [Figure not available: see fulltext.]
Measurement of the inclusive J/psi polarization at forward rapidity in pp collisions at root s=8 TeV
No full textWe report on the measurement of the inclusive J/ψ polarization parameters in pp collisions at a center of mass energy s=8 TeV with the ALICE detector at the LHC. The analysis is based on a data sample corresponding to an integrated luminosity of 1.23 pb- 1. J/ψ resonances are reconstructed in their di-muon decay channel in the rapidity interval 2.5 < y< 4.0 and over the transverse-momentum interval 2 < pT< 15 GeV / c. The three polarization parameters (λθ, λφ, λθ φ) are measured as a function of pT both in the helicity and Collins-Soper reference frames. The measured J/ψ polarization parameters are found to be compatible with zero within uncertainties, contrary to expectations from all available predictions. The results are compared with the measurement in pp collisions at s=7 TeV
Energy dependence of exclusive J/ photoproduction off protons in ultra-peripheral p-Pb collisions at NN=5.02 TeV
No full textThe ALICE Collaboration has measured the energy dependence of exclusive photoproduction of J/ψ vec- tor mesons off proton targets in ultra–peripheral p–Pb colli- sions at a centre-of-mass energy per nucleon pair √sNN = 5.02 TeV. The e+ e− and μ+ μ− decay channels are used to measure the cross section as a function of the rapidity of the J/ψ in the range −2.5 < y < 2.7, correspond- ing to an energy in the γp centre-of-mass in the interval 40 < Wγ p < 550 GeV. The measurements, which are consis- tent with a power law dependence of the exclusive J/ψ pho- toproduction cross section, are compared to previous results from HERA and the LHC and to several theoretical models. They are found to be compatible with previous measure- ments
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