The Incredible Shrinking Proton

Project Overview

This project used novel means of studying the proton wave function by considering small size configurations in which the proton shrinks to much smaller than its usual size. These fluctuations of the proton wave function involve so-called intrinsic charm states, which include very heavy charm quarks. Although such states were first proposed in 1980, they have not definitively been observed, although evidence for their existence has been presented during the course of this project. These configurations, involving only the three valence quarks that give the proton its identity, along with a charm–anticharm pair, represent the smallest sized protons possible. This project focused on theoretical calculations that provide predictions for the intrinsic charm production, in particular for experiments most likely to lead to its definitive observation. The calculations were two-fold, employing perturbative quantum chromodynamics (QCD) for standard or "extrinsic" charm production and the intrinsic charm contribution. The calculations of the total charm and J/ψ cross sections using perturbative QCD provide an important constraint on the intrinsic charm contribution. We employed the improved color evaporation model to calculate both the production and polarization of J/ψ in the collinear factorization approach. We advanced the capability of the color-evaporation model to incorporate feed-down contribution from excited states of charmonia in hadro-production. We also explored the production mechanism via photo-production in electron-proton collisions to predict intrinsic charm in the next NIF-scale US nuclear physics facility, the Electron Ion Collider (EIC). We showed that the intrinsic charm contribution is especially significant at low center-of-mass energies where the boost due to the center of mass energy is smallest. We also showed that kinematic regions forward of the center of mass and large transverse momentum of the charm hadrons are most favorable for detection. We also showed that, due to the difference in the nuclear dependence of the perturbative and intrinsic charm contributions, there is a limit of the nuclear-suppression factor (RpA) at all energies. Our work has set the stage for potentially going from "evidence for" intrinsic charm to "discovery of" its existence.

Mission Impact

This project supports LLNL's core competency in Nuclear, Chemical and Isotopic Science and Technology by studying proton wave functions advancing our understanding of intrinsic charm states, which include very heavy charm quarks. We will leverage science insights developed in this LDRD to awarded (a leadership role in the DOE Heavy Flavor Theory (HEFTY) for QCD Matter program) and proposed work from the DOE Office of Science Nuclear Physics program, leading to an application for a DOE Office of Science Early Career funding for the Postdoc hired through this project, who is being integrated into LLNL’s nuclear data and nuclear materials detection program. This LDRD also supports LLNL's involvement in the California Electron Ion Collider (EIC), including the submission of a proposal to etablish a new long-term collaborative framework in EIC theory. Finally, ths project has enabled LLNL's participation in the Long-Range Plan (LRP) for Nuclear Science, spearheaded by the Nuclear Science Advisory Committee with cooperation with the DOE Nuclear Physics office and the National Science Foundation. The PI was recently named to the LRP writing committee that will set the priorities for nuclear physics in the next decade.

Publications, Presentations, and Proposals

Vogt, R., 2021. "Limits on Intrinsic Charm Production from the SeaQuest Experiment." Physical Review C 103: 035204. https://doi.org/10.1103/PhysRevC.103.035204. LLNL-JRNL-818026.

Vogt, R. "Constraints on Intrinsic Charm from the SeaQuest Experiment." Conference: 10th International Workshop on CHARM Physics (2021): 054. https://doi.org/10.22323/1.385.0038. 2021. LLNL-CONF-825510.

Cheung, V., and R. Vogt. "Quarkonium Production and Polarization in High-Energy Collisions." Conference: 10th International Workshop on CHARM Physics. 2021. 054. https://doi.org/10.22323/1.385.0054. LLNL-PROC-826319.

Vogt, R., and A. Angerami, 2021c. "Bottom Tetraquark Production at RHIC?" Physical Review D 104 (November): 094025. https://doi.org/10.1103/PhysRevD.104.094025. LLNL-JRNL-826228.

Cheung, V., and R. Vogt, 2021. "Production and Polarization of Direct J/ψ to O(αs3) in the Improved Color Evaporation Model in Collinear Factorization." Physical Review D 104 (2021): 094026. https://doi.org/10.1103/PhysRevD.104.094026. LLNL-JRNL-819612.

Cheung, V., and R. Vogt, 2022. "Quarkonium Polarization in Pb+Pb Collisions in the Improved Color Evaporation Model." Physical Review C 105 (2022): 055202. https://doi.org/10.1103/PhysRevC.105.055202. LLNL-JRNL-832929.

Vogt, R., 2022. "Energy Dependence of Intrinsic Charm Production: Determining the Best Energy for Observation." Physical Review C 106 (2022): 025201. https://doi.org/10.1103/PhysRevC.106.025201. LLNL-JRNL-837220.

Vogt, R., 2022. "Evidence at Last that the Proton has Intrinsic Charm." Nature 608 (2022): 477-479. https://doi.org/10.1038/d41586-022-02186-w. LLNL-JRNL-838589.

Vogt, R. "Cold Nuclear Matter J/ψ Production with SeaQuest." QWG14: 14th International Workshop on Heavy Quarkonium. 2021. LLNL-PRES-820696.

Vogt, R. "Cold Nuclear Matter Effects on J/ψ Production at High Baryon Densities." ECT.* Workshop on Probing High Matter with Rare Probes. 2021. LLNL-PRES-828061.

Cheung, V. "J/ψ Production in the ICEM." California EIC Consortium Workshop. 2022. LLNL-PRES-837659.

Vogt, R., 2022. "LLNL Status and Plans." California EIC Consortium Workshop 2022. LLNL-PRES-837661.

Vogt, R. "Forward Charm Production." California EIC Consortium Workshop 2022. LLNL-PRES-837746.

Cheung, V. "J/ψ Production in Pb+Pb Collisions in the ICEM." QWG 2022, 15th International Workshop on Heavy Quarkonium. 2022. LLNL-PRES-840377.