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Register a new userParametrization of the $bar PP$ Elastic Scattering Differential Cross Section Between 2 GeV/c $leq P_{lab}leq$ 16 GeV/c
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A parameterization of the $bar pp$ differential elastic scattering cross section in the beam momentum range from 2 to 16 GeV/c is proposed. The parameterization well describes the existing data including the observed diffraction pattern at four-momentum transfer $|t|$ up to 1.5-2.0 GeV$^2$. It can be used for detailed calculations of the radiation load on the detectors being designed for the PANDA detector at the future FAIR facility in Darmstadt.
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The exclusive production cross sections for $omega$ and $phi$ mesons have been measured in proton-proton reactions at $p_{lab}=3.67$ GeV/c. The observed $phi/omega$ cross section ratio is $(3.8pm0.2^{+1.2}_{-0.9})times 10^{-3}$. After phase space corrections, this ratio is enhanced by about an order of magnitude relative to naive predictions based upon the Okubo-Zweig-Iizuka (OZI) rule, in comparison to an enhancement by a factor $sim 3$ previously observed at higher beam momenta. The modest increase of this enhancement near the production threshold is compared to the much larger increase of the $phi/omega$ ratio observed in specific channels of $bar pp$ annihilation experiments. Furthermore, differential cross section results are also presented which indicate that although the $phi$ meson is predominantly produced from a $^3P_1$ proton-proton entrance channel, other partial waves contribute significantly to the production mechanism at this beam momentum.
The cross section of the $ep to e p gamma$ reaction has been measured at $Q^2 = 0.33$ (GeV/c)$^2$. The experiment was performed using the electron beam of the MAMI accelerator and the standard detector setup of the A1 Collaboration. The cross section is analyzed using the low-energy theorem for virtual Compton scattering, yielding a new determination of the two structure functions $P_LL}-P_{TT}/epsilon$ and $P_{LT}$ which are linear combinations of the generalized polarizabilities of the proton. We find somewhat larger values than in the previous investigation at the same $Q^2$. This difference, however, is purely due to our more refined analysis of the data. The results tend to confirm the non-trivial $Q^2$-evolution of the generalized polarizabilities and call for more measurements in the low-$Q^2$ region ($le$ 1 (GeV/c)$^2$).
Quasielastic $^{12}$C$(e,ep)$ scattering was measured at space-like 4-momentum transfer squared $Q^2$~=~8, 9.4, 11.4, and 14.2 (GeV/c)$^2$, the highest ever achieved to date. Nuclear transparency for this reaction was extracted by comparing the measured yield to that expected from a plane-wave impulse approximation calculation without any final state interactions. The measured transparency was consistent with no $Q^2$ dependence, up to proton momenta of 8.5~GeV/c, ruling out the quantum chromodynamics effect of color transparency at the measured $Q^2$ scales in exclusive $(e,ep)$ reactions. These results impose strict constraints on models of color transparency for protons.
The TOTEM collaboration has measured the elastic proton-proton differential cross section ${rm d}sigma/{rm d}t$ at $sqrt{s}=13$ TeV LHC energy using dedicated $beta^{*}=90$ m beam optics. The Roman Pot detectors were inserted to 10$sigma$ distance from the LHC beam, which allowed the measurement of the range $[0.04$ GeV$^{2}$$; 4 $GeV$^{2}$$]$ in four-momentum transfer squared $|t|$. The efficient data acquisition allowed to collect about 10$^{9}$ elastic events to precisely measure the differential cross-section including the diffractive minimum (dip), the subsequent maximum (bump) and the large-$|t|$ tail. The average nuclear slope has been found to be $B=(20.40 pm 0.002^{rm stat} pm 0.01^{rm syst})~$GeV$^{-2}$ in the $|t|$-range $0.04~$GeV$^{2}$ to $0.2~$GeV$^{2}$. The dip position is $|t_{rm dip}|=(0.47 pm 0.004^{rm stat} pm 0.01^{rm syst})~$GeV$^{2}$. The differential cross section ratio at the bump vs. at the dip $R=1.77pm0.01^{rm stat}$ has been measured with high precision. The series of TOTEM elastic pp measurements show that the dip is a permanent feature of the pp differential cross-section at the TeV scale.
The production of the hidden-charm pentaquarks $P_{c}$ via pion-induced reaction on a proton target is investigated within an effective Lagrangian approach. Three experimentally observed states, $P_c(4312)$, $P_c(4440)$, and $P_c(4457)$, are considered in the calculation, and the Reggeized $t$-channel meson exchange is considered as main background for the reaction $pi ^{-}prightarrow J/psi n$. The numerical results show that the experimental data of the total cross section of the reaction $pi^{-}prightarrow J/psi n$ at $Wsimeq 5$ GeV can be well explained by contribution of the Reggeized $t$ channel with reasonable cutoff. If the branching ratios $Br[P_{c}rightarrow J/psi N]simeq 3%$ and $Br[P_{c}rightarrow pi N]simeq 0.05%$ are taken, the average value of the cross section from the $P_{c}(4312)$ contribution is about 1.2 nb/100 MeV, which is consistent with existing rude data at near-threshold energies. The results indicate that the branching ratios of the $P_{c}$ states to the $J/psi N$ and $pi N$ should be small. The shape of differential cross sections shows that the Reggeized $t$-channel provides a sharp increase at extreme forward angles, while the differential cross sections from the $P_{c}$ states contributions are relatively flat. High-precision experimental measurements on the reaction $pi ^{-}prightarrow J/psi n$ at near-threshold energies are suggested to confirm the LHCb hidden-charm pentaquarks as genuine states, and such experiments are also helpful to understand the origin of these resonance structures.
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