Fri·Feb 26, 2021Friday·February 26, 2021

1. 01*

   Transverse charge density and the radius of the proton

   Alexander V. Gramolin🇺🇸 · Rebecca L. Russell🇺🇸

   A puzzling discrepancy exists between the values of the proton charge radius obtained using different experimental techniques: elastic electron-proton scattering and spectroscopy of electronic and muonic hydrogen. The proton radius is defined through the slope of the electric form factor, $G_E(Q^2)$, at zero four-momentum transfer, which is inaccessible in scattering experiments. We propose a novel method for extracting the proton radius from scattering data over a broad $Q^2$ range rather than attempting to directly determine the slope of $G_E$ at $Q^2=0$. This method relates the radius of the proton to its transverse charge density, which is the two-dimensional Fourier transform of the Dirac form factor, $F_1(Q^2)$. We apply our method to reanalyze the extensive data obtained by the A1 Collaboration [J. C. Bernauer et al., Phys. Rev. Lett. 105, 242001 (2010)] and extract a radius value, $r_E=0.889(5{)}_{\text{stat}}(5{)}_{\text{syst}}(4{)}_{\text{model}}\text{fm}$, that is consistent with the original result. We also provide new parametrizations for the Dirac and Pauli form factors and the transverse charge and magnetization densities of the proton. Our reanalysis shows that the proton radius discrepancy cannot be explained by issues with fitting and extrapolating the A1 data to $Q^2=0$.

   nucl-exhep-exhep-phnucl-thPRD(2022)·18 citations
2. 02*

   Masses of positive- and negative-parity hadron ground-states, including those with heavy quarks

   Pei-Lin Yin🇨🇳 · Zhu-Fang Cui🇨🇳 · Craig D. Roberts🇨🇳 · Jorge Segovia🇪🇸

   A symmetry-preserving treatment of a vector$\times$vector contact interaction is used to compute spectra of ground-state $J^P=0^{\pm },1^{\pm }$ $(f\bar{g})$ mesons, their partner diquark correlations, and $J^P=1/2^{\pm },3/2^{\pm }$ $(fgh)$ baryons, where $f,g,h\in \{u,d,s,c,b\}$. Results for the leptonic decay constants of all mesons are also obtained, including scalar and pseudovector states involving heavy quarks. The spectrum of baryons produced by this chiefly algebraic approach reproduces the 64 masses known empirically or computed using lattice-regularised quantum chromodynamics with an accuracy of 1.4(1.2)%. It also has the richness of states typical of constituent-quark models and predicts many baryon states that have not yet been observed. The study indicates that dynamical, nonpointlike diquark correlations play an important role in all baryons; and, typically, the lightest allowed diquark is the most important component of a baryon's Faddeev amplitude.

   ↳ hep-phhep-exhep-latnucl-ex+1EPJC(2021)·66 citations
3. 03*

   $\varphi$-meson lepto-production near threshold and the strangeness $D$-term

   Yoshitaka Hatta🇺🇸 · Mark Strikman🇺🇸

   We present a model of exclusive $\varphi$-meson lepto-production $ep\to e^{\prime }{p}^{\prime }\varphi$ near threshold which features the strangeness gravitational form factors of the proton. We argue that the shape of the differential cross section $d\sigma /dt$ is a sensitive probe of the strangeness D-term of the proton.

   ↳ hep-phnucl-exPLB(2021)·44 citations
4. 04*

   Factorization and transverse phase-space parton distributions

   Bin Wu🇨🇭

   We first revisit impact-parameter dependent collisions of ultra-relativistic particles in quantum field theory. Two conditions sufficient for defining an impact-parameter dependent cross section are given, which could be violated in proton-proton collisions. By imposing these conditions, a general formula for the impact-parameter dependent cross section is derived. Then, using soft-collinear effective theory, we derive a factorization formula for the impact-parameter dependent cross section for inclusive hard processes with only colorless final-state products in hadron and nuclear collisions. It entails defining thickness beam functions, which are Fourier transforms of transverse phase-space parton distribution functions. By modelling non-perturbative modes in thickness beam functions of large nuclei in heavy-ion collisions, the factorization formula confirms the cross section in the Glauber model for hard processes. Besides, the factorization formula is verified up to one loop in perturbative QCD for the inclusive Drell-Yan process in quark-antiquark collisions at a finite impact parameter.

   ↳ hep-phhep-exnucl-exnucl-thJHEP(2021)·10 citations
5. 05*

   Evidence for X(3872) in PbPb collisions and studies of its prompt production at $\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV

   CMS Collaboration

   The first evidence for X(3872) production in relativistic heavy ion collisions is reported. The X(3872) production is studied in lead-lead (PbPb) collisions at a center-of-mass energy of $\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV per nucleon pair, using the decay chain X(3872) $\to$ J$/\psi {\pi }^{+}{\pi }^{-}\to$ ${\mu }^{+}{\mu }^{-}{\pi }^{+}{\pi }^{-}$. The data were recorded with the CMS detector in 2018 and correspond to an integrated luminosity of 1.7 nb${}^{-1}$. The measurement is performed in the rapidity and transverse momentum ranges $|y|$ $<$ 1.6 and 15 $<$ $p_{\mathrm{T}}$ $<$ 50 GeV$/c$. The significance of the inclusive X(3872) signal is 4.2 standard deviations. The prompt X(3872) to $\psi$(2S) yield ratio is found to be ${\rho }^{\mathrm{PbPb}}=$ 1.08 $\pm$ 0.49 (stat) $\pm$ 0.52 (syst), to be compared with typical values of 0.1 for pp collisions. This result provides a unique experimental input to theoretical models of the X(3872) production mechanism, and of the nature of this exotic state.

   ↳ hep-exnucl-exPRL(2022)·132 citations
6. 06*

   First measurement of large area jet transverse momentum spectra in heavy-ion collisions

   CMS Collaboration

   Jet production in lead-lead (PbPb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV is studied with the CMS detector at the LHC, using PbPb and pp data samples corresponding to integrated luminosities of 404 $\mu$b${}^{-1}$ and 27.4 pb${}^{-1}$, respectively. Jets with different areas are reconstructed using the anti-$k_{\mathrm{T}}$ algorithm by varying the distance parameter $R$. The measurements are performed using jets with transverse momenta ($p_{\mathrm{T}}$) greater than 200 GeV and in a pseudorapidity range of $|\eta |$ $<$ 2. To reveal the medium modification of the jet spectra in PbPb collisions, the properly normalized ratio of spectra from PbPb and pp data is used to extract jet nuclear modification factors as functions of the PbPb collision centrality, $p_{\mathrm{T}}$ and, for the first time, as a function of $R$ up to 1.0. For the most central collisions, a strong suppression is observed for high-$p_{\mathrm{T}}$ jets reconstructed with all distance parameters, implying that a significant amount of jet energy is scattered to large angles. The dependence of jet suppression on $R$ is expected to be sensitive to both the jet energy loss mechanism and the medium response, and so the data are compared to several modern event generators and analytic calculations. The models considered do not fully reproduce the data.

   ↳ hep-exnucl-exJHEP(2021)·136 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.