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1. Radiative corrections to proton-proton fusion in pionless effective field theory

   https://doi.org/10.1103/PhysRevC.110.L041001  

   Combes, Evan; Mereghetti, Emanuele; Platter, Lucas (October 2024, Physical Review C)

   We study the leading radiative correction to proton-proton fusion using the pionless effective field theory framework at leading order. We derive the relevant matrix elements and evaluate them using the method of regions. We benchmark the accuracy of our approximations by carrying out numerical computations of the full expressions. We show that the first order radiative corrections due to the exchange of a Coulomb photon between positron and proton-proton systems map onto the Sirlin function and the O(α) contribution from the Fermi function. We furthermore find that the nuclear structure dependent radiative correction omitted in the previous analysis by Kurylov et al gives an up to 0.2 % correction to the pp fusion S-factor with its size ultimately depending on a two-nucleon counterterm L1A that renormalizes the axial two-body current.Not Available 

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2. Measurement and QCD analysis of double-differential inclusive jet cross sections in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV

   https://doi.org/10.1007/JHEP02(2022)142  

   Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Bergauer, T.; Chatterjee, S.; Damanakis, K.; Dragicevic, M.; Escalante Del Valle, A.; Frühwirth, R.; Jeitler, M.; et al (February 2022, Journal of High Energy Physics)

   A bstract A measurement of the inclusive jet production in proton-proton collisions at the LHC at $$ \sqrt{s} $$ s = 13 TeV is presented. The double-differential cross sections are measured as a function of the jet transverse momentum p T and the absolute jet rapidity |y| . The anti- k T clustering algorithm is used with distance parameter of 0.4 (0.7) in a phase space region with jet p T from 97 GeV up to 3.1 TeV and |y| < 2 . 0. Data collected with the CMS detector are used, corresponding to an integrated luminosity of 36.3 fb − 1 (33.5 fb − 1 ). The measurement is used in a comprehensive QCD analysis at next-to-next-to-leading order, which results in significant improvement in the accuracy of the parton distributions in the proton. Simultaneously, the value of the strong coupling constant at the Z boson mass is extracted as α S ( m Z ) = 0 . 1170 ± 0 . 0019. For the first time, these data are used in a standard model effective field theory analysis at next-to-leading order, where parton distributions and the QCD parameters are extracted simultaneously with imposed constraints on the Wilson coefficient c 1 of 4-quark contact interactions. 

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3. Measurement of the axial vector form factor from antineutrino–proton scattering

   https://doi.org/10.1038/s41586-022-05478-3  

   Cai, T.; Moore, M. L.; Olivier, A.; Akhter, S.; Dar, Z. Ahmad; Ansari, V.; Ascencio, M. V.; Bashyal, A.; Bercellie, A.; Betancourt, M.; et al (February 2023, Nature)

   Abstract Scattering of high energy particles from nucleons probes their structure, as was done in the experiments that established the non-zero size of the proton using electron beams 1 . The use of charged leptons as scattering probes enables measuring the distribution of electric charges, which is encoded in the vector form factors of the nucleon 2 . Scattering weakly interacting neutrinos gives the opportunity to measure both vector and axial vector form factors of the nucleon, providing an additional, complementary probe of their structure. The nucleon transition axial form factor, F A , can be measured from neutrino scattering from free nucleons, ν μ n  →  μ − p and $${\bar{\nu }}_{\mu }p\to {\mu }^{+}n$$ ν ¯ μ p → μ + n , as a function of the negative four-momentum transfer squared ( Q 2 ). Up to now, F A ( Q 2 ) has been extracted from the bound nucleons in neutrino–deuterium scattering 3–9 , which requires uncertain nuclear corrections 10 . Here we report the first high-statistics measurement, to our knowledge, of the $${\bar{\nu }}_{\mu }\,p\to {\mu }^{+}n$$ ν ¯ μ p → μ + n cross-section from the hydrogen atom, using the plastic scintillator target of the MINERvA 11 experiment, extracting F A from free proton targets and measuring the nucleon axial charge radius, r A , to be 0.73 ± 0.17 fm. The antineutrino–hydrogen scattering presented here can access the axial form factor without the need for nuclear theory corrections, and enables direct comparisons with the increasingly precise lattice quantum chromodynamics computations 12–15 . Finally, the tools developed for this analysis and the result presented are substantial advancements in our capabilities to understand the nucleon structure in the weak sector, and also help the current and future neutrino oscillation experiments 16–20 to better constrain neutrino interaction models. 

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4. Measurement of the generalized spin polarizabilities of the neutron in the low-Q2 region

   https://doi.org/10.1038/s41567-021-01245-9  

   Sulkosky, Vincent; Peng, Chao; Chen, Jian-ping; Deur, Alexandre; Abrahamyan, Sergey; Aniol, Konrad A.; Armstrong, David S.; Averett, Todd; Bailey, Stephen J.; Beck, Arie; et al (May 2021, Nature Physics)

   null (Ed.)

   Understanding the nucleon spin structure in the regime where the strong interaction becomes truly strong poses a challenge to both experiment and theory. At energy scales below the nucleon mass of about 1 GeV, the intense interaction among the quarks and gluons inside the nucleon makes them highly correlated. Their coherent behaviour causes the emergence of effective degrees of freedom, requiring the application of non-perturbative techniques such as chiral effective field theory. Here we present measurements of the neutron’s generalized spin polarizabilities that quantify the neutron’s spin precession under electromagnetic fields at very low energy-momentum transfer squared down to 0.035 GeV2. In this regime, chiral effective field theory calculations are expected to be applicable. Our data, however, show a strong discrepancy with these predictions, presenting a challenge to the current description of the neutron’s spin properties. 

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5. Coulomb-free 1S0 p − p scattering length from the quasi-free p + d → p + p + n reaction and its relation to universality

   https://doi.org/10.1038/s42005-023-01221-0  

   Tumino, Aurora; Rapisarda, Giuseppe G.; La Cognata, Marco; Oliva, Alessandro; Kievsky, Alejandro; Bertulani, Carlos A.; D’Agata, Giuseppe; Gattobigio, Mario; Guardo, Giovanni L.; Lamia, Livio; et al (December 2023, Communications Physics)

   Abstract The Coulomb-free 1 S 0 proton-proton ( p - p ) scattering length relies heavily on numerous and distinct theoretical techniques to remove the Coulomb contribution. Here, it has been determined from the half-off-the-energy-shell p - p scattering cross section measured at center-of-mass energies below 1 MeV using the quasi-free p  +  d  →  p  +  p  +  n reaction. A Bayesian data-fitting approach using the expression of the s-wave nucleon-nucleon scattering cross section returned a p - p scattering length $${a}_{pp}=-18.1{7}_{-0.58}^{+0.52}{| }_{stat}\pm 0.0{1}_{syst}$$ a p p = − 18.1 7 − 0.58 + 0.52 ∣ s t a t ± 0.0 1 s y s t fm and effective range r 0  = 2.80 ± 0.05 s t a t  ± 0.001 s y s t fm. A model based on universality concepts has been developed to interpret this result. It accounts for the short-range interaction as a whole, nuclear and residual electromagnetic, according to what the s-wave phase-shift δ does in the description of low-energy nucleon-nucleon scattering data. We conclude that our parameters are representative of the short-range physics and propose to assess the charge symmetry breaking of the short-range interaction instead of just the nuclear interaction. This is consistent with the current understanding that the charge dependence of nuclear forces is due to different masses of up-down quarks and their electromagnetic interactions. This achievement suggests that these properties have a lesser than expected impact in the context of the charge symmetry breaking. 

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