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Multidimensional partial wave analysis of SIDIS dihadron beam spin asymmetries at CLAS12

C. Dilks

SciPost Phys. Proc. 8, 152 (2022) · published 14 July 2022 | · pdf

Dihadron beam spin asymmetries provide a wide range of insights into nucleon structure and hadronization. Recent measurements at CLAS12 provide the first empirical evidence of nonzero $G_1^\perp$, the parton helicity-dependent dihadron fragmentation function (DiFF) encoding spin-momentum correlations in hadronization. These measurements also allow for a point-by-point extraction of the subleading-twist PDF $e(x)$ in a collinear framework. We observe different behavior of the asymmetries in different invariant mass regions, motivating a fully multidimensional study. The DiFFs also expand in terms of partial waves, each corresponding to the interference of dihadrons of particular polarizations. Altogether a fully multidimensional partial wave analysis is needed, and this presentation will summarize the efforts and results obtained thus far.

1 citation
Drell-Yan transverse spectra at the LHC: a comparison of parton branching and analytical resummation approaches

Aron Mees van Kampen

SciPost Phys. Proc. 8, 151 (2022) · published 14 July 2022 | · pdf

I report on precision comparisons of theoretical predictions for Drell-Yan (DY) transverse momentum spectra from two approaches: the analytical resummation approach based on Collins-Soper-Sterman (CSS) formalism and the parton branching (PB) approach to the evolution of transverse momentum dependent (TMD) parton distributions.

1 citation
Exclusive electro-weak production of a charmed meson at high energy

B. Pire, L. Szymanowski, J. Wagner

SciPost Phys. Proc. 8, 150 (2022) · published 14 July 2022 | · pdf

Exclusive electro-weak processes have peculiar features which make them complementary to usually discussed deeply virtual electroproduction processes such as deep virtual Compton scattering or meson production (and the corresponding crossed reactions). They allow in particular single charmed meson production, which we study in two different contexts : electroproduction at an electron ion collider and neutrino-production at a medium energy neutrino facility. We rely on the QCD collinear factorization framework where generalized parton distributions allow physicists to perform a nucleon tomography.
Multidimensional, high precision beam spin asymmetry measurements of semi-inclusive pion production off the proton with CLAS12

S. Diehl

SciPost Phys. Proc. 8, 149 (2022) · published 14 July 2022 | · pdf

High precision measurements of the polarized electron beam-spin asymmetry in SIDIS from the proton have been performed using a 10.6 GeV incident electron beam and the CLAS12 spectrometer at Jefferson Lab. The proceeding reports a multidimensional study of the structure function ratio $F^{sin\phi}_{LU}/F_{UU}$ extracted from single pion ($\pi^{+}$, $\pi^{-}$, $\pi^{0}$) SIDIS data over a large kinematic range in $z$, $x_{B}$, $P_{T}$ and virtualities $Q^{2}$ ranging from 1~GeV$^2$ up to 7~GeV$^2$. $F^{sin\phi}_{LU}$ is a twist-3 quantity that can reveal novel properties of quark-gluon correlations within the nucleon.

1 citation
Subnucleon fluctuations in coherent and incoherent ultra-peripheral AA collisions at LHC and RHIC with the Sartre event generator

Tobias Toll

SciPost Phys. Proc. 8, 148 (2022) · published 14 July 2022 | · pdf

Sartre has been extensively used for describing photon-nuclei processes at the electron-ion collider (EIC) as well as ultra-peripheral collisions (UPC) at LHC and RHIC. Sartre is an event generator which implements the dipole model for DIS, and models the transverse geometry of the target nucleus or proton in coordinate space. It uses the Good-Walker mechanism for simulating fluctuations which contribute to the incoherent cross section for which the target breaks up after the interaction. With improved precision of UPC measurements in the last years, a detailed test of the dipole model has become possible, and Sartre's model was found lacking. In these proceedings we add subnucleon fluctuations to the nucleus and show that this is sufficient for describing the vast majority of the present measurements. We also find that for larger momentum transfers in the nucleus, which probes gluon fluctuations at higher resolution, the current complexity of the model may not suffice. Future measurements at the LHC, RHIC and especially the EIC has the potential to reveal these gluon vacuum fluctuations and glean novel insights into the self-interacting quantum field of QCD.

2 citations
Probing quantum entanglement and collectivity effects in e+p collisions at HERA H1

Chuan Sun

SciPost Phys. Proc. 8, 147 (2022) · published 14 July 2022 | · pdf

Charged particle multiplicity spectra are measured at HERA H1 in DIS process at 319 GeV. The hadron entropy determined from the multiplicity spectra is compared to the gluon entropy predicted from a quantum-entanglement model. On the other hand, observed collective behaviours in high multiplicity pA, pp and ultra-peripheral PbPb collisions at RHIC and LHC motivate a study in ep collisions. Two- and multi-particle correlations are studied in DIS, as well as photoproduction events with collision energy <Wγp>~270 GeV.
Transverse spin asymmetries for inclusive $\rho^0$ production in SIDIS at COMPASS

A. Kerbizi

SciPost Phys. Proc. 8, 146 (2022) · published 14 July 2022 | · pdf

The production of vector mesons in SIDIS is a particularly interesting channel to study the polarized fragmentation and related phenomena. Preliminary COMPASS results for the first measurement of inclusive $\rho^0$ Collins and Sivers transverse-spin asymmetries are presented here for the first time. The analysis is based on the data-set collected by COMPASS in $2010$ using a $160\, \rm{GeV}/c$ $\mu^+$ beam and a transversely polarized $NH_3$ target. The asymmetries are extracted as function of Bjorken-$x$, of the total transverse momentum of the oppositely charged hadron pair and of the fraction of available energy $z$ carried by the pair. Indications for positive Collins and Sivers asymmetries are obtained as expected from models.
Photoproduction of diffractive dijets in Pythia 8

Ilkka Helenius

SciPost Phys. Proc. 8, 145 (2022) · published 14 July 2022 | · pdf

The new framework for the simulations of hard diffractive events in photoproduction within Pythia 8 is presented. The model, originally introduced for proton-proton collisions, applies the dynamical rapidity gap survival probability based on the multiparton interaction model in Pythia. These additional interactions provide a natural explanation for the observed factorization-breaking effects in hard diffraction by filling up the rapidity gaps used to classify the events of diffractive origin. The generated cross sections are well in line with the existing data from HERA experiments and predictions for the future electron-ion collider are presented. In addition, also predictions for ultra-peripheral collisions at the LHC have been calculated where the factorization-breaking effects are found to be more pronounced.
TMD observables in unpolarised Semi-Inclusive DIS at COMPASS

Andrea Moretti

SciPost Phys. Proc. 8, 144 (2022) · published 14 July 2022 | · pdf

In 2016 and 2017, the COMPASS Collaboration at CERN collected a large sample of DIS events with a longitudinally polarised 160 GeV/$c$ muon beam scattering off a liquid hydrogen target. Part of the collected data has been analysed to extract preliminary results for the amplitudes of the modulations in the azimuthal angle of the charged hadrons and for their transverse-momentum distributions. These observables give relevant information for the study of the transverse momentum and spin structure of the nucleon. Similarly to the results obtained in COMPASS with a deuteron target, the azimuthal asymmetries exhibit interesting kinematic dependences, while the squared-transverse-momentum distributions can be described by two exponentials.
QCD factorization for hadronic quarkonium production at high $p_T$

Kyle Lee, Jian-Wei Qiu, George Sterman, Kazuhiro Watanabe

SciPost Phys. Proc. 8, 143 (2022) · published 14 July 2022 | · pdf

Heavy quarkonium production at high transverse momentum ($p_T$) in hadronic collisions is explored in the QCD factorization approach. We find that the leading power in the $1/p_T$ expansion is responsible for high $p_T$ regime, while the next-to-leading power contribution is necessary for the low $p_T$ region. We present the first numerical analysis of the scale evolution of coupled twist-2 and twist-4 fragmentation functions (FFs) for heavy quarkonium production and demonstrate that the QCD factorization approach is capable of describing the $p_T$ spectrum of hadronic $J/\psi$ production at the LHC.

4 citations

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