Coherent photoproduction processes in hadronic heavy-ion collisions

Figure  1.  Raw OS dimuon $ {p}_{T} $ distribution for invariant mass range 2.8 GeV/$ {c}^{2} $ < $ {m}_{{\mu }^{+}{\mu }^{-}} $ < 3.4 GeV/$ {c}^{2} $ in 70%–90% Pb + Pb collisions at $\sqrt{{s}_\rm{NN}}$ = 2.76 TeV. Vertical error bars denote statistical uncertainties. Figure taken from Ref. [12].

Figure  2.  J/ψ ${R}_{{\rm AA}}$ as a function of ${N}_{{\rm part}}$ for three $ {p}_{T} $ intervals in Pb + Pb collisions at $\sqrt{{s}_{{\rm NN}}}$= 2.76 TeV. Figure taken from Ref. [12].

Figure  3.  J/ψ inclusive nuclear modification factor as a function of the number of participants ${N}_{\rm{part}}$ for $ {p}_{T} $ < 0.3 GeV/c in 2.76 TeV Pb + Pb collisions at forward rapidity 2.5 < y < 4. Figure taken from Ref. [23].

Figure  4.  J/ψ inclusive nuclear modification factor as a function of the number of participants ${N}_{\rm{part}}$ in 0.3 < $ {p}_{T} $ < 1 and 1 < $ {p}_{T} $ < 8 GeV/c in forward rapidity 2.5 < y < 4 at LHC 2.76 TeV Pb + Pb collisions. Figure taken from Ref. [23].

Figure  5.  J/ψ invariant yields for Au + Au collisions at $\displaystyle\sqrt{{s}_{\rm NN}}$ = 200 GeV and U + U collisions at $\sqrt{{s}_{{\rm NN}}}$ = 193 GeV as a function of $ {p}_{T} $ for different centralities. The error bars depict the statistical errors and the boxes denote the systematic uncertainties. Figure taken from Ref. [13].

Figure  6.  J/ψ ${R}_{{\rm AA}}$ as a function $ {p}_{T} $ in Au + Au collisions at $\sqrt{{s}_{{\rm NN}}}$ = 200 GeV and U + U collisions at $\sqrt{{s}_{{\rm NN}}}$ = 193 GeV. Figure taken from Ref. [13].

Figure  7.  The $ {p}_{T} $-integrated J/ψ yields ($ {p}_{T} $ < 0.1 GeV/c) with expected hadronic contribution subtracted as a function of ${N}_{\rm{part}}$ for 30%–80% Au + Au collisions and 40%–80% U + U collisions. Lines denote the model calculations for coherent photoproduction in four coupling scenarios. Figure taken from Ref. [13].

Figure  8.  Coherent J/ψ production yields as a function of ${N}_{\rm{part}}$ at $\sqrt{{s}_{{\rm NN}}}$ = 200 GeV in Au + Au, Ru + Ru, and Zr + Zr collisions. Figure taken from Ref. [30].

Figure  9.  Amplitude and momentum distribution patterns of coherent J/ψ photoproduction in different scenarios for b = 10 fm in Au + Au collisions at $\sqrt{{s}_{{\rm NN}}}$ = 200 GeV at midrapidity (y = 0). Figure taken from Ref. [36].

Figure  10.  Amplitude and momentum distribution patterns of coherent J/ψ photoproduction at midrapidity (y = 0) in Au + Au collisions at $\sqrt{{s}_{{\rm NN}}}$ = 200 GeV with a disruptive effect from the overlap region for different impact parameters. Figure taken from Ref. [36].

Figure  11.  Schematic diagram for different charmonium production mechanisms at different transverse momentum regions in semi-central nucleus–nucleus collisions in the presence of both QGP and strong transverse electromagnetic fields. Photoproduction, regeneration, and initial production dominate the J/ψ final yields in extremely low $ {p}_{T} $, low and middle $ {p}_{T} $, and high $ {p}_{T} $ regions, respectively. Figure taken from Ref. [23].

Figure  12.  Charmonium hadroproduction and photoproduction as a function of the number of participants ${N}_{\rm{part}}$ at forward rapidity 2.5 < y < 4 in $\sqrt{{s}_\rm{NN}}$ = 2.76 TeV Pb + Pb collisions in the extremely low transverse momentum region $ {p}_{T} $ < 0.3 GeV/c. $ {B}_{{e}^{+}{e}^{-}} $ is the branch ratio of J/ψ$ \to {e}^{+}{e}^{-} $. Figure taken from Ref. [23].

Figure  13.  Charmonium prompt nuclear modification factor as a function of transverse momentum for impact parameter b = 10.2 fm in the forward rapidity 2.5 < y < 4 in LHC 2.76 TeV Pb + Pb collisions. Figure taken from Ref. [23].

Figure  14.  (a) Centrality dependence of $ {e}^{+}{e}^{-} $ invariant mass spectra within the STAR acceptance from Au +Au and U + U collisions for pair $ {p}_{T} $ < 0.15 GeV/c. (b) Corresponding ratios of data over cocktail. Figure taken from Ref. [14].

Figure  15.  $ {e}^{+}{e}^{-} $ pair $ {p}_{T} $ distributions within the STAR acceptance for different mass regions in 60%–80% Au + Au and U + U collisions with respect to the cocktail. Figure taken from Ref. [14].

Figure  16.  Centrality dependence of integrated excess yields in the mass regions 0.4–0.76，0.76–1.2，1.2–2.6 GeV/$ {c}^{2} $ in Au + Au and U + U collisions. The centrality dependence of the hadronic cocktail yields in the mass region 0.76–1.2 GeV/$ {c}^{2} $ is also shown for comparison. Figure taken from Ref. [14].

Figure  17.  (a)–(c) Distributions of excess yields within the STAR acceptance for the different mass regions in 60%–80% Au + Au and U + U collisions. (d) Corresponding $ \sqrt{ < {p}_{T}^{2} > } $ of excess yields. Figure taken from Ref. [14].

Figure  18.  Background-subtracted distributions for α (upper row) and A (lower row) in Pb + Pb collisions at $\sqrt{{s}_{{\rm NN}}}$ = 5.02 TeV for different centrality classes. Each distribution is normalized to unity over its measured range. Figure taken from Ref. [15].

Figure  19.  Results of fits to the muon pair α distributions using the sum of Gaussian and background functions. A standard Gaussian function is shown as a solid curve whilst the dotted curve shows a Gaussian function in α convolved with the measured ${p}_{T{\rm avg}}$ distribution. Figure taken from Ref. [15].

Figure  20.  ${k}_{T}^\rm{rms}$ values obtained from the fits shown in Fig. 19, expressed as a function of <${N}_{\rm{part}}$>. Figure taken from Ref. [15].

Figure  21.  Differential pair mass spectrum ${\rm {d}}^{2}N/\left({\rm d}M{\rm d}y\right)$ for (a) electron and (b) muon pairs with gold beams at RHIC and for (c) electron and (d) muon pairs with lead beams at LHC. The different curves in the figure indicate the results for different centrality classes. Figure taken from Ref. [40].

Figure  22.  Mass spectrum of electron pairs for different centrality classes. The mass distributions are compared to hadronic cocktail simulations without the ρ contribution in-medium ρ mass spectrum and QGP thermal radiation. Figure taken from Ref. [40].

Figure  23.  Invariant mass spectrum of $ {e}^{+}{e}^{-} $ pair from coherent photon–photon interaction and decay of coherently produced J/ψ in Au + Au collisions for 60%–80% centrality class as well as Ru + Ru and Zr + Zr collisions for 47%–75% centrality class. Figure taken from Ref. [30].

Figure  24.  $ {p}_{T}^{2} $ distributions of electron–positron pair production within the STAR acceptance for three different mass regions in 60%–80% Au + Au collisions at $\sqrt{{s}_\rm{NN}}$ = 200 GeV. Figure taken from Ref. [47].

Figure  25.  $ \sqrt{ < {p}_{T}^{2} > } $ of electron–positron pairs within the STAR acceptance as a function of the impact parameter b for different mass regions in Au + Au collisions at $\sqrt{{s}_{{\rm NN}}}$ = 200 GeV. Figure taken from Ref. [47].

Figure  26.  Distributions of the broadening variable α obtained from the gEPA1, gEPA2, and QED approaches for muon pairs in Pb + Pb collisions at $\sqrt{{s}_{{\rm NN}}}$ = 5.02 TeV in different centrality classes. Figure taken from Ref. [47].