Dihadron production in DIS at small x at next-to-leading order: Transverse photons
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
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Lattice QCD Determination of the Bjorken- x Dependence of Parton Distribution Functions at Next-to-Next-to-Leading Order
Not Available
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Large-momentum effective theory
Since the parton model was introduced by Feynman more than 50 years ago, much has been learned about the partonic structure of the proton through a large body of high-energy experimental data and dedicated global fits. However, limited progress has been made in calculating partonic observables such as the parton distribution function (PDFs) from the fundamental theory of strong interactions, quantum chromodynamics (QCD). Recently some advocated for a formalism, large-momentum effective theory (LaMET), through which one can extract parton physics from the properties of the proton traveling at a moderate boost factor such as γ ~ 2 – 5 . The key observation behind this approach is that Lorentz symmetry allows the standard formalism of partons in terms of light-front operators to be replaced by an equivalent one with large-momentum states and time-independent operators of a universality class. With LaMET, the PDFs, generalized PDFs or generalized parton distributions, transverse-momentum-dependent PDFs, and light-front wave functions can all be extracted in principle from lattice simulations of QCD (or other nonperturbative methods) through standard effective field theory matching and running. Future lattice QCD calculations with exascale computational facilities could help one to understand the experimental data related to the hadronic structure, including those from the upcoming electron-ion colliders dedicated to exploring the partonic landscape of the proton. In this work, the progress made in the past few years in the development of the LaMET formalism and its applications is reviewed, with an emphasis on a demonstration of its effectiveness from initial lattice QCD simulations.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Reevaluation of the cosmic antideuteron flux from cosmic-ray interactions and from exotic sources
Cosmic-ray antideuterons could be a key for the discovery of exotic phenomena in our Galaxy, such as dark-matter annihilations or primordial black hole evaporation. Unfortunately the theoretical predictions of the antideuteron flux at Earth are plagued with uncertainties from the mechanism of antideuteron production and propagation in the Galaxy. We present the most up-to-date calculation of the antideuteron fluxes from cosmic-ray collisions with the interstellar medium and from exotic processes. We include for the first time the antideuteron inelastic interaction cross section recently measured by the ALICE collaboration to account for the loss of antideuterons during propagation. In order to bracket the uncertainty in the expected fluxes, we consider several state-of-the-art models of antideuteron production and of cosmic-ray propagation.
79 ASTRONOMY AND ASTROPHYSICS↗
Phonon-informed Neural Thermal Scattering (NeTS) Optimization for Crystalline Graphite and Beryllium Metal
Fast neutrons born from fission lose energy through scattering interactions in the process of slowing-down. As neutrons thermalize to the order of $k$ $b$ $T$ (where $k$ $b$ is the Boltzmann constant, and $T$ is the temperature of the medium), their de Broglie wavelength and energy approaches the order of inter-atomic spacing and quantized lattice vibrations, i.e., phonons. At thermal energies, the thermal scattering law (TSL), i.e., $S$($α, β$), captures crystal binding contributions to the total reaction rate, or cross section. This dimensionless material property describes the energy ($β$) and momentum ($α$) exchanges available in a medium. Currently, $S$($α, β$) is evaluated in the Full Law Analysis Scattering System Hub (FLASSH) code for discrete inputs and stored as ENDF/B File 7 for 0-phonon elastic (MT 2) and n-phonon inelastic (MT 4) processes. Further processing recasts $S$($α, β$) into cumulative distribution functions for sampling post-collision scattering kinematics. In practice, interpolation schemes are employed to access data between tabulated values. An improvement to this juncture of the nuclear data pipeline is supplying cross sections on-the-fly (OTF), as has been developed for the un-resolved resonance region to minimize non-physical interpolation errors. This capability may improve simulation accuracy for accident and transient analyses, where rapidly varying changes in temperature and pressure are difficult to predict beforehand. To do so, deep artificial neural networks (ANNs) can be employed which collapse non-linear, complex data into a lightweight dictionary of neural weights and biases. This has been successfully demonstrated for the hydrogen in light water $S$($α, β$) dataset in the form of a Neural Thermal Scattering (NeTS) module. In this work, the NeTS framework is extended to consider the impact of material-dependent dynamical features on optimal neural pre-processing and architecture design decisions, such as number of neurons per hidden layer, residual skip connections and neural depth. New NeTS modules for crystalline graphite and beryllium metal illuminate a novel correlation between dynamical nonlinearity and optimal neural parametrization when deploying $S$($α, β$) on-the-fly.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Collins function for pion-in-jet production in polarized pp collisions: a test of universality and factorization
We present an updated study of the Collins azimuthal asymmetries for pion-in-jet production in polarized pp collisions. To this aim, we employ a recent extraction of the transversity and Collins fragmentation functions from semi-inclusive deep inelastic scattering and e + e - annihilation into hadron pairs processes, obtained within a simplified transverse momentum dependent (TMD) approach at leading order in the strong coupling constant α s . In the present case we adopt a collinear configuration for the initial state, keeping transverse momentum effects only in the fragmentation mechanism. Our theoretical estimates, when compared against 200 GeV and 510 GeV data from the STAR Collaboration, show a generally good agreement for the distributions in the transverse momentum of the jet, the pion longitudinal momentum fraction and its transverse momentum with respect to the jet direction. While not being a proof, due the assumptions and limitations behind the entire approach, these findings corroborate the hypothesis of TMD factorization for such processes as well as of the universality of the Collins function and, once again, of a reduced impact of the proper TMD evolution on azimuthal asymmetries. We will also present predictions based on an extraction of the Collins and transversity distributions where information from data on single spin asymmetry for inclusive pion production in p ↑ p collisions is included through a Bayesian reweighting procedure.
Azimuthal asymmetries↗
Impact of LHC vector boson production in heavy ion collisions on strange PDFs
Abstract The extraction of the strange quark parton distribution function (PDF) poses a long-standing puzzle. Measurements from neutrino-nucleus deep inelastic scattering (DIS) experiments suggest the strange quark is suppressed compared to the light sea quarks, while recent studies of $$W^\pm /Z$$ W ± / Z boson production at the LHC imply a larger strange component at small x values. As the parton flavor determination in the proton depends on nuclear corrections, e.g. from heavy-target DIS, LHC heavy ion measurements can provide a distinct perspective to help clarify this situation. In this investigation we extend the nCTEQ15 nPDFs to study the impact of the LHC proton-lead $$W^\pm /Z$$ W ± / Z production data on both the flavor differentiation and nuclear corrections. This complementary data set provides new insights on both the LHC $$W^\pm /Z$$ W ± / Z proton analyses and the neutrino-nucleus DIS data. We identify these new nPDFs as nCTEQ15WZ . Our calculations are performed using a new implementation of the nCTEQ code ( nCTEQ++ ) based on C++ which enables us to easily interface to external programs such as HOPPET, APPLgrid and MCFM. Our results indicate that, as suggested by the proton data, the small x nuclear strange sea appears larger than previously expected, even when the normalization of the $$W^{\pm }/Z$$ W ± / Z data is accommodated in the fit. Extending the nCTEQ15 analysis to include LHC $$W^\pm /Z$$ W ± / Z data represents an important step as we advance toward the next generation of nPDFs.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Determination of the strong coupling and its running from measurements of inclusive jet production
The value of the strong coupling α S is determined in a comprehensive analysis at next-to-next-to-leading order accuracy in quantum chromodynamics. The analysis uses double-differential cross section measurements from the CMS Collaboration at the CERN LHC of inclusive jet production in proton-proton collisions at centre-of-mass energies of 2.76, 7, 8, and 13 TeV, combined with inclusive deep-inelastic data from HERA. The value α S (m z ) = 0.1176 $^{+0.0014}_{-0.0016}$ is obtained at the scale of the Z boson mass. By using the measurements in different intervals of jet transverse momentum, the running of α S is probed for energies between 100 and 1600 GeV.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Strangeness in the proton from $W+$ charm production and SIDIS data
We perform a global QCD analysis of unpolarized parton distribution functions (PDFs) in the proton, including new 𝑊+ charm production data from 𝑝𝑝 collisions at the LHC and semi-inclusive pion and kaon production data in lepton-nucleon deep-inelastic scattering, both of which have been suggested for constraining the strange quark PDF. Compared with a baseline global fit that does not include these datasets, the new analysis reduces the uncertainty on the strange quark distribution over the range 0.01 < 𝑥 < 0.3, and provides a consistent description of processes sensitive to strangeness in the proton. Including the new datasets, the ratio of strange to nonstrange sea quark distributions is $R_s = (s + \bar{s})/(\bar{u} +\bar{d})$ $=$ {$0.72^{+0.52}_{−0.34}, 0.46^{+0.30}_{−0.20}, 0.32^{+0.23}_{−0.15}$} for 𝑥 ={$0.01, 0.04, 0.1$} at 𝑄 2 $=$ 4 GeV 2 . The data place more stringent constraints on the strange asymmetry $(s - \bar{s})$, which is found to be consistent with zero in this range.
Anderson, Trey [College of William and Mary, Willi↗
Factorized QED and QCD contribution to deeply inelastic scattering
We present the first calculation of next-to-leading order (NLO) factorized QED and QCD contributions to the short-distance hard coefficients of inclusive lepton-hadron deep inelastic scattering (DIS) in a joint QED and QCD factorization approach. Unlike the traditional radiative correction approach to handle the collision-induced QED contributions to DIS, QED radiation from all charged leptons and quarks are treated equally, and their collinear sensitivities are systematically factorized into corresponding universal lepton and parton distribution functions. We demonstrate that the NLO factorized short-distance QED contribution is completely infrared safe and calculable without the need of any parameters other than the standard factorization scale in the same way as the factorized short-distance QCD contribution. We discuss the potential impact of this joint factorization approach on the extraction of partonic information from lepton-hadron DIS.
Deep inelastic scattering↗
Measurements of the $Z$ 0 /$γ$* cross section and transverse single spin asymmetry in 510 GeV $p$ + $p$ collisions
The differential cross section for Z 0 production, measured as a function of the boson’s transverse momentum (p T ), provides important constraints on the evolution of the transverse momentum dependent parton distribution functions (TMDs). The transverse single spin asymmetry (TSSA) of the Z 0 is sensitive to one of the polarized TMDs, the Sivers function, which is predicted to have the opposite sign in p + p → W/Z + X from that which enters in semi-inclusive deep inelastic scattering. In this Letter, the STAR Collaboration reports the first measurement of the Z 0 /γ* differential cross section as a function of its p T in p+p collisions at a center-of-mass energy of 510 GeV, together with the Z 0 /γ* total cross section. We also report the measurement of Z 0 /γ* TSSA in transversely polarized p+p collisions at 510 GeV.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Investigating the role of strangeness in baryon–antibaryon annihilation at the LHC
Annihilation dynamics plays a fundamental role in the baryon–antibaryon interaction ($B–\bar{B}$) at low-energy and its strength and range are crucial in the assessment of possible baryonic bound states. Experimental data on annihilation cross sections are available for the $p–\bar{p}$ system but not in the low relative momentum region. Data regarding the $B–\bar{B}$ interaction with strange degrees of freedom are extremely scarce, hence the modeling of the annihilation contributions is mainly based on nucleon–antinucleon ($N–\bar{N}$) results, when available. In this letter we present a measurement of the $p–\bar{p}$, $p–\bar{Λ}$⊕$p–{Λ}$ and $Λ–\bar{Λ}$ interaction using correlation functions in the relative momentum space in high-multiplicity triggered pp collisions at $\sqrt{s}$=13 TeV recorded by ALICE at the LHC. In the $p–\bar{p}$ system the couplings to the mesonic channels in different partial waves are extracted by adopting a coupled-channel approach with recent χEFT potentials. The inclusion of these inelastic channels provides good agreement with the data, showing a significant presence of the annihilation term down to zero momentum. Predictions obtained using the Lednický–Lyuboshits formula and scattering parameters obtained from heavy-ion collisions, hence mainly sensitive to elastic processes, are compared with the experimental $p–\bar{Λ}$⊕$p–{Λ}$ and $Λ–\bar{Λ}$ correlations. The model describes the $Λ–\bar{Λ}$ data and underestimates the $p–\bar{Λ}$⊕$p–{Λ}$ data in the region of momenta below 200 MeV/c. The observed deviation indicates a different contribution of annihilation channels to the two systems containing strange hadrons.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Quantum vacuum processes in the extremely intense light of relativistic plasma mirror sources
Abstract The advent of petawatt-class laser systems allows generating electromagnetic fields of unprecedented strength in a controlled environment, driving increasingly more efforts to probe yet unobserved processes through their interaction with the quantum vacuum. Still, the lowest intensity scale governing these effects lies orders of magnitude beyond foreseen capabilities, so that such endeavor is expected to remain extremely challenging. In recent years, however, plasma mirrors have emerged as a promising bridge across this gap, by enabling the conversion of intense infrared laser pulses into coherently focused Doppler harmonic beams lying in the X-UV range. In this work, we present predictions on the quantum vacuum signatures produced when such beams are focused to intensities between 10 24 and 10 28 W cm −2 , specifically photon–photon scattering and electron–positron pair creation. These signatures are computed via the stimulated vacuum formalism, combined with a model of perfectly focused beam built from PIC-generated harmonics spectra, and implemented on state-of-the-art massively parallel numerical tools. In view of identifying experimentally favorable configurations, we also consider the coupling of the focused harmonic beam with an auxiliary optical beam, and provide comparison with other established schemes. Our results show that a single coherently focused harmonic beam can produce as much scattered photons as two infrared pulses in head-on collision, and confirm that the coupling of the harmonic beam to an auxiliary beam gives rise to significant levels of inelastic scattering, and hence holds the potential to strongly improve the attainable signal to noise ratios in experiments.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Constraining the Nucleon Size with Relativistic Nuclear Collisions
The notion of the "size" of nucleons and their constituents plays a pivotal role in the current paradigm of the formation and the fluctuations of the quark-gluon plasma produced in high-energy nuclear collision experiments. Here, we report on state-of-the-art hydrodynamic results showing that the correlation between anisotropic flow, $v^{2}_{n}$, and the mean transverse momentum of hadrons, [$p_t$], possesses a unique sensitivity to the nucleon size in off-central heavy-ion collisions. We argue that existing experimental measurements of this observable support a picture where the relevant length scale characterizing the colliding nucleons is of order 0.5 fm or smaller, and we discuss the broad implications of this finding for future global Bayesian analyses aimed at extracting initial state and medium properties from nucleus-nucleus collision data, including $v^{2}_{n}$-[$p_t$] correlations. Determinations of the nucleon size in heavy-ion collisions will provide a solid independent constraint on the initial state of small system collisions, and will establish a deep connection between collective flow data in nucleus-nucleus experiments and data on deep inelastic scattering on protons and nuclei.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Observation of microwave shielding of ultracold molecules
Harnessing the potential wide-ranging quantum science applications of molecules will require control of their interactions. Here, we used microwave radiation to directly engineer and tune the interaction potentials between ultracold calcium monofluoride (CaF) molecules. By merging two optical tweezers, each containing a single molecule, we probed collisions in three dimensions. The correct combination of microwave frequency and power created an effective repulsive shield, which suppressed the inelastic loss rate by a factor of six, in agreement with theoretical calculations. The demonstrated microwave shielding shows a general route to the creation of long-lived, dense samples of ultracold polar molecules and evaporative cooling.
Anderegg, Loïc↗
Reweighting the Sivers function with jet data from STAR
The reweighting procedure that using Bayesian statistics incorporates the information contained in a new data set, without the need of re-fitting, is applied to the quark Sivers function extracted from Semi-Inclusive Deep Inelastic Scattering (SIDIS) data. We exploit the recently published single spin asymmetry data for the inclusive jet production in polarized pp collisions from the STAR Collaboration at RHIC, which cover a much wider x region compared to SIDIS measurements. The reweighting method is extended to the case of asymmetric errors and the results show a remarkable improvement of the knowledge of the quark Sivers function.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurements of ${\Xi }{^-}$ and $\overline{\Xi }{^+}$ production in proton–proton interactions at $\sqrt{s_{NN}}$ = 17.3 $\hbox {Ge}\hbox {V}$ in the NA61/SHINE experiment
The production of $\Xi (1321)^{-}$ and $\overline{\Xi }(1321)^{+}$ hyperons in inelastic $p+p$ interactions is studied in a fixed target experiment at a beam momentum of 158 $\hbox {Ge}\hbox {V}\!/\!c$. Double differential distributions in rapidity ${y}$ and transverse momentum $p_{T}$ are obtained from a sample of 33M inelastic events. They allow to extrapolate the spectra to full phase space and to determine the mean multiplicity of both ${\Xi }{^-}$ and $\overline{\Xi }{^+} $. The rapidity and transverse momentum spectra are compared to transport model predictions. The ${\Xi }{^-} $ mean multiplicity in inelastic $p+p$ interactions at 158 $\hbox {Ge}\hbox {V}\!/\!c$ is used to quantify the strangeness enhancement in A+A collisions at the same centre-of-mass energy per nucleon pair.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Multinucleon transfer in 48 Ti + 48 Ti collisions at 11.5 MeV/nucleon
In this work, experimental data of projectile fragment distributions from a preliminary experimental study of the reaction of 11.5 MeV/nucleon 48 Ti on 48 Ti analyzed with the MARS recoil separator at the Cyclotron Institute of Texas A&M University are presented. Production cross sections, momentum distributions and excitation-energy distributions are extracted and compared with calculations with the Deep Inelastic Transfer (DIT) model and the Constrained Molecular Dynamics model (CoMD). Despite the limited extent of the present dataset, an overall agreement of the models with the data is found pointing at the prevailing nucleon-exchange character of the collisions at this energy.
Souliotis, Georgios↗