From the γγ→pp¯ reaction to the production of pp¯ pairs in

Abstract

In this paper we consider the production of proton-antiproton pairs in two-photon interactions in electron-positron and heavy-ion collisions. We try to understand the dependence of the total cross section on the photon-photon c.m. energy as well as corresponding angular distributions measured by the Belle Collaboration for the γγ → pp process. To understand the Belle data we include the proton-exchange, the f 2 (1270) and f 2 (1950) s-channel exchanges, as well as the handbag mechanism. The helicity amplitudes for the γγ → f 2 → pp process are written explicitly based on a Lagrangian approach. The parameters of vertex form factors are adjusted to the Belle data. Having described the angular distributions for the γγ → pp process we present first predictions for the ultraperipheral, ultrarelativistic, heavy-ion reaction 208 Pb 208 Pb → 208 Pb 208 Pb pp. Both, the total cross section and several differential distributions for experimental cuts corresponding to the ALICE, ATLAS, CMS, and LHCb experiments are presented. We find the total cross section 100 µb for the ALICE cuts, 160 µb for the ATLAS cuts, 500 µb for the CMS cuts, and 104 µb taking into account the LHCb cuts. This opens a possibility to study the γγ → pp process at the LHC. 25.75.Dw,13.60.Rj,13.90.+i

Recent Theoretical Results for Electromagnetically-induced Ultraperipheral Reactions of Heavy Ions

“…cess is shown for example in Fig.11. In our studies we included also some resonances [11]. In Fig.12 we show our predictions for M pp and rapidity distributions for P bP b → P bP bpp process at √ s N N = 5.02 TeV.…”

Tensor Pomeron and low- x deep inelastic scattering

“…In our global fit we have as parameters also the pomeron-γ * γ * coupling functionsâ j (Q 2 ) andb j (Q 2 ) (j = 0, 1); see table 1 and (A.18), (A. 19). The latter are parametrised with the help of cubic splines; see appendix C. In figures 12 to 15 we show the fit results for these functions which are discussed further in appendices D and E. Note that above Q 2 = 50 GeV 2 the displayed curves are extrapolations beyond the last spline knot.…”

“…Figure 15: The pomeron-and reggeon-γ * γ * coupling functionsb j (Q 2 ) for j = 0 (hard pomeron), j = 1 (soft pomeron), and j = 2 (reggeon); see (3.9), (3.10), (A. 19), and (A.28). The shaded bands indicate the experimental uncertainties.…”

“…In [11] the tensor pomeron was introduced for soft reactions and many of its properties were derived from comparisons with experiment. Further applications of the tensorpomeron concept were given for photoproduction of pion pairs in [13] and for a number of exclusive central-production reactions in [14,15,16,17,18,19,20]. In [21] the helicity structure of small-|t| proton-proton elastic scattering was calculated in three models for the pomeron: tensor, vector, and scalar.…”

“…The pomeron-γ * γ * coupling functionsâ j (Q 2 ) for j = 0 (hard pomeron) and j = 1 (soft pomeron); see (3.9), (3.10), and (A 19)…”