Nuclear Theory·nucl-th

Thursday·May 10, 2018

8 papers—5 primary·3 cross-listed

06
Kinetic freeze-out properties from transverse momentum spectra of pions in high energy proton-proton collisions
Li-Li Li🇨🇳 · Fu-Hu Liu🇨🇳
Transverse momentum spectra of negative and positive pions produced at mid-(pseudo)rapidity in inelastic or non-single-diffractive proton-proton collisions over a center-of-mass energy, $s$ , range from a few GeV to above 10 TeV are analyzed by the blast-wave fit with Boltzmann (Tsallis) distribution. The blast-wave fit results are well fitting to the experimental data measured by several collaborations. In a particular superposition with Hagedorn function, both the excitation functions of kinetic freeze-out temperature ( $T_{0}$ ) of emission source and transverse flow velocity ( $β_{T}$ ) of produced particles obtained from a given selection in the blast-wave fit with Boltzmann distribution have a hill at $s \approx 10$ GeV, a drop at dozens of GeV, and then an increase from dozens of GeV to above 10 TeV. However, both the excitation functions of $T_{0}$ and $β_{T}$ obtained in the blast-wave fit with Tsallis distribution do not show such a complex structure, but a very low hill. In another selection for the parameters or in the superposition with the usual step function, $T_{0}$ and $β_{T}$ increase generally quickly from a few GeV to about 10 GeV and then slightly at above 10 GeV, there is no such the complex structure, when also studying nucleus-nucleus collisions.
↳ hep-phhep-exnucl-exnucl-thMDPI Physics(2020)·17 citations
07
Electromagnetic couplings of radially excited light vector mesons from QCD sum rules
S. S. Afonin🇷🇺 · T. D. Solomko🇷🇺
The couplings of unflavored vector mesons to the $e^{+} e^{-}$ annihilation are an important source of information on the nature and structure of these resonances which play a prominent role in the hadron phenomenology. The couplings of many radially excited heavy vector mesons are measured, while the corresponding couplings for light vector mesons are not known. We propose a phenomenological method allowing to estimate these unknown couplings. The method is suggested by our observation that the electromagnetic coupling of the $n$ -th radial excitation of $S$ -wave heavy vector meson decouples from the $e^{+} e^{-}$ annihilation with nearly exponential rate with $n$ . It becomes natural to assume that the same effect takes place in the light vector mesons and this would allow to estimate the unknown couplings. We tested this assumption with the help of a generalized version of borelized QCD spectral sum rules saturated by a linear radial trajectory of meson states taken from the phenomenology. This leads to a consistent setup which is able to predict the decoupling rate. The calculated rate turned out to be almost the same as in the heavy vector mesons. Our result may be interpreted as an effective account for non-trivial electromagnetic formfactor in meson decays to $e^{+} e^{-}$ , thus looking beyond the large- $N_{c}$ limit. On the one hand, we argue that the given decoupling does not necessary contradict to the previous large- $N_{c}$ results for the Regge like meson spectra.
↳ hep-phnucl-thEur.Phys.J.Plus(2019)·4 citations
08
Vacuum stabilized by anomalous magnetic moment
Stefan Evans🇺🇸 · Johann Rafelski (Arizona)🇺🇸
An analytical result for Euler-Heisenberg effective action, valid for electron spin $g -$ factor $∣ g ∣ < 2$ , was extended to the domain $∣ g ∣ > 2$ via discovered periodicity of the effective action. This allows for a simplified computation of vacuum instability modified by the electrons measured $g = 2.002319$ . We find a strong suppression of vacuum decay into electron positron pairs when magnetic fields are dominant. The result is reminiscent of mass catalysis by magnetic fields.
↳ hep-phnucl-thPRD(2018)·9 citations

Affiliations

first authorsco-authorsvia INSPIRE

Kinetic freeze-out properties from transverse momentum spectra of pions in high energy proton-proton collisions

Electromagnetic couplings of radially excited light vector mesons from QCD sum rules

Vacuum stabilized by anomalous magnetic moment

Affiliations