Proton Strangeness Research Articles

Unraveling proton strangeness: Determination of the strangeness sigma term with statistical significance

This study delves into the contribution of the strange quark within the proton, which influences several fundamental proton properties. By establishing a robust relationship between the proton’s quantum anomalous energy and the sigma term, we successfully extract the contribution of the strangeness sigma term in the proton, obtaining it from parametrized fits of the differential cross section using exponential and dipole forms. The extracted sigma term values are estimated to be 455.62±64.60 MeV (exponential fit) and 337.74±106.79 MeV (dipole fit). Additionally, we present novel results for the proton trace anomalous energy, observing values of 0.13±0.02 (exponential fit) and 0.15±0.03 (dipole fit). Our analysis integrates the novel data from the J/ψ−007 and GlueX Collaborations, to some extent providing an experimental phenomenological window into the nonzero strange quark content inside proton, with the statistical significances 7.1σ (exponential fit) and 3.2σ (dipole fit), respectively. Furthermore, we discuss the possibility of scheme independence in the extraction results and examine the uniformity of sigma terms obtained from the datasets provided by the two collaborations. Our analysis may reveals compatibility between the extracted results of the respective experiments. Published by the American Physical Society 2024

Reinterpretation of proton strangeness between ATLAS and CMS measurements

We reexamine the shapes of the strange quark parton distribution functions (PDFs) of the proton by means of quantum chromodynamics (QCD) analysis of {\hera} deep inelastic scattering cross section measurement at DESY, and inclusive gauge boson production and $W$ boson production associated with a charm quark from LHC at CERN. We find that there is an overall agreement on the strange quark distributions obtained from CMS $W$ + charm and ATLAS $W/Z$ data at the parton momentum fraction range $x \lesssim 10^{-2}$. Meanwhile, there is also a strong tension between these data towards large $x$. We find that this tension fades away if the ATLAS measurement of $W/Z$ production is analyzed together with the ATLAS $W$ + charm data. The $W/Z$ and $W$ + charm data both from ATLAS and CMS experiments agree that the proton strangeness is enhanced towards small momentum fraction $x$ and is smoothly suppressed at large $x$. Furthermore, a strong $x$ dependence of the strange-to-non-strange parton ratio $R_s(x,Q^2)$ is observed.

Charge symmetry violation in the electromagnetic form factors of the nucleon

Experimental tests of QCD through its predictions for the strange-quark content of the proton have been drastically restricted by our lack of knowledge of the violation of charge symmetry (CSV). We find unexpectedly tiny CSV in the proton's electromagnetic form factors by performing the first extraction of these quantities based on an analysis of lattice QCD data. The resulting values are an order of magnitude smaller than current bounds on proton strangeness from parity-violating electron-proton scattering experiments. This result paves the way for a new generation of experimental measurements of the proton's strange form factors to challenge the predictions of QCD.

Charge symmetry breaking and parity violating electron-proton scattering

Charge symmetry breaking contributions to the proton's neutral weak form factors must be understood in order for future measurements of parity violating electron-proton scattering to be definitively interpreted as evidence of proton strangeness. We calculate these charge symmetry breaking form factor contributions using chiral perturbation theory with resonance saturation estimates for unknown low-energy constants. The uncertainty of the leading-order resonance prediction is reduced by incorporating nuclear physics constraints. Higher-order contributions are investigated through phenomenological vertex form factors. We predict that charge symmetry breaking form factor contributions are an order of magnitude larger than expected from na\"{\i}ve dimensional analysis but are still an order of magnitude smaller than current experimental bounds on proton strangeness. This is consistent with previous calculations using chiral perturbation theory with resonance saturation.

Using Low-Energy Neutrinos from Pion Decay at Rest to Probe the Proton Strangeness

The study of the neutral current elastic scattering of neutrinos on protons at lower energies can be used as a compelling probe to improve our knowledge of the strangeness of the proton. We consider a neutrino beam generated from pion decay at rest, as provided by a cyclotron or a spallation neutron source and a 1 kton scintillating detector with a potential similar to the Borexino detector. Despite several backgrounds from solar and radioactive sources, it is possible to estimate two optimal energy windows for the analysis, one between 0.65 and 1.1 MeV and another between 1.73 and 2.2 MeV. The expected number of neutral current events in these two regions, for an exposure of 1 yr, is enough to obtain an error on the strange axial charge 10 times smaller than available at present.

Quark model analysis of strangeness form factors of the proton

The present empirical information on the proton strangeness form factors suggests that the uuds subsystem of the uuds \( \bar s \) configuration has the flavor spin symmetry [4] FS [22] F [22] S , mixed orbital symmetry [31] X and that the \( \bar s \) is in the ground state. This uuds \( \bar s \) configuration yields the empirical signs for both the form factors G E s and G M s . Transition matrix elements between the uud and uuds \( \bar s \) components are significant.

Nuclear three-body force effect on a kaon condensate in neutron star matter

We explore the effects of a microscopic nuclear three-body force on the threshold baryon density for kaon condensation in chemical equilibrium neutron star matter and on the composition of the kaon condensed phase in the framework of the Brueckner-Hartree-Fock approach. Our results show that the nuclear three-body force affects strongly the high-density behavior of nuclear symmetry energy and consequently reduces considerably the critical density for kaon condensation provided that the proton strangeness content is not very large. The dependence of the threshold density on the symmetry energy becomes weaker as the proton strangeness content increases. The kaon condensed phase of neutron star matter turns out to be proton rich instead of neutron rich. The three-body force has an important influence on the composition of the kaon condensed phase. Inclusion of the three-body force contribution in the nuclear symmetry energy results in a significant reduction of the proton and kaon fractions in the kaon condensed phase which is more proton-rich in the case of no three-body force. Our results are compared to other theoretical predictions by adopting different models for the nuclear symmetry energy. The possible implications of our results for the neutron star structure are also briefly discussed.

Probing proton strangeness with time-like virtual Compton scattering

We document that p(γ,e+e−)p measurements will yield new, important information about the off-shell time-like nucleon form factors, especially in the φ meson region (q2=M2φ) governing the φN couplings gV,TφNN. Calculations for p(γ,e+e−)p, utilizing vector meson dominance, predict measurable φ enhancements at high |t| compared to the expected φ background production from π, η and Pomeron exchange. The φ form factor contribution generates a novel experimental signature for OZI violation and the proton strangeness content. The φN couplings are determined independently from a combined analysis of the neutron electric form factor and recent high |t| φ photoproduction. The π, η and Pomeron transition form factors are also predicted and the observed π and η transition moments are reproduced.

Proton strangeness induced by instantons

We report on a calculation of the dilute instanton liquid contribution to the strangeness in the proton. Specifically, we express the proton matrix elements of strange-quark operators in terms of a model valence nucleon state and the strangeness producing interactions. This enables us to evaluate the strangeness in different Lorentz channels in the same way. We find that in the context of the MIT bag model only the scalar strangeness is induced by the random instanton liquid. We discuss these results in the light of the recent experiments.

On the instanton-induced portion of the nucleon strangeness

We calculate the instanton contribution to the proton strangeness in the MIT bag enriched by the presence of a dilute instanton liquid. The evaluation is based on expressing the nucleon matrix elements of bilinear strange quark operators in terms of a model valence nucleon state and interactions producing quark-antiquark fluctuations on top of that valence state. Our method combines the usage of the evolution operator containing a strangeness source, and the Feynman-Hellmann theorem. It enables one to evaluate the strangeness in different Lorentz channels in, essentially, the same way. Only the scalar channel is found to be affected by the interaction induced by the random instanton liquid.