arXiv subjects

P. Schweitzer

Publications and source records attributed to P. Schweitzer.

At least 19 recordsLinked to original sources

arXiv2025

The SRG/eROSITA All-Sky Survey $J$-Band Follow-Up Observations for Selected High-Redshift Galaxy Cluster Candidates

We select galaxy cluster candidates from the high-redshift (BEST_Z > 0.9) end of the first SRG/eROSITA All-Sky Survey (eRASS1) galaxy cluster catalogue, for which we obtain moderately deep J-band imaging data with the OMEGA2000 camera at the 3.5m telescope of the Calar Alto Observatory. We include J-band data of four additional targets obtained with the three-channel camera at the 2m Fraunhofer telescope at the Wendelstein Observatory. We complement the new J-band photometric catalogue with forced photometry in the i- and z-bands of the tenth data release of the Legacy Survey (LSDR10) to derive the radial colour distribution around the eRASS1 clusters. Without assuming a priori to find a cluster red sequence at a specific colour, we try to find a radially weighted colour over-density to confirm the presence of high-redshift optical counterparts for the X-ray emission. We compare our confirmation with optical properties derived in earlier works based on LSDR10 data to refine the existing high-redshift cluster confirmation of eROSITA-selected clusters. We attempt to calibrate the colour-redshift-relation including the new J-band data by comparing our obtained photometric redshift estimate with the spectroscopic redshift of a confirmed, optically selected, high-redshift galaxy cluster. We confirm 9 out of 18 of the selected galaxy cluster candidates with a radial over-density of similar coloured galaxies for which we provide a photometric redshift estimate. We can report an increase in the relative colour measurement precision from 8% to 4% when including J-band data. In conclusion, our findings indicate a not insignificant spurious contaminant fraction at the high-redshift end (BEST_Z > 0.9) of the eROSITA/eRASS1 galaxy cluster catalogue, as well as it underlines the necessity for wide and deep near infrared imaging data for confirmation and characterisation of high-$z$ galaxy clusters.

astro-ph.CO↗

arXiv2025

Parton Distribution Functions and their Generalizations

This article is an introduction to parton distribution functions and their generalizations which describe the quark and gluon structure of hadrons, and can be measured in various high-energy scattering processes. We provide the theoretical background, highlight both historical and recent developments, explain the connections between the different functions, and expose in which processes these functions can be accessed and what we can learn from them about hadron structure.

hep-ph↗

arXiv2024

Colloquium: Gravitational Form Factors of the Proton

The physics of the gravitational form factors of the proton, and their understanding within quantum chromodynamics, has advanced significantly in the past two decades through both theory and experiment. This Colloquium provides an overview of this progress, highlights the physical insights unveiled by studies of gravitational form factors, and reviews their interpretation in terms of the mechanical properties of the proton.

hep-ph↗

arXiv2022

Snowmass 2021 White Paper: Electron Ion Collider for High Energy Physics

Electron Ion Collider (EIC) is a particle accelerator facility planned for construction at Brookhaven National Laboratory on Long Island, New York by the United States Department of Energy. EIC will provide capabilities of colliding beams of polarized electrons with polarized beams of proton and light ions. EIC will be one of the largest and most sophisticated new accelerator facilities worldwide, and the only new large-scale accelerator facility planned for construction in the United States in the next few decades. The versatility, resolving power and intensity of EIC will present many new opportunities to address some of the crucial and fundamental open scientific questions in particle physics. This document provides an overview of the science case of EIC from the perspective of the high energy physics community.

hep-ph↗

arXiv2022

Quark-model relations among TMDs in the parton model

The covariant parton model (CPM) is a consequent application of the parton model concept to the nucleon structure. In this model, there is a choice to put quarks either in a pure-spin state or in a mixed-spin state. We show that the mixed-spin version of the CPM does not support the quark-model relations among transverse momentum dependent parton distributions (TMDs) which were shown to hold in a large class of quark models. One can enforce the quark-model relations to be valid in the CPM by imposing a condition which is equivalent to putting the quarks in a pure-spin state. This gives a complementary perspective on the connection of the pure- and mixed-spin state CPM versions, and provides a fresh view on the question whether the quark-model relations could be realized in QCD as "approximate relations" with some useful numerical accuracy.

hep-ph↗

arXiv2022

CORE -- a COmpact detectoR for the EIC

The COmpact detectoR for the Eic (CORE) Proposal was submitted to the EIC "Call for Collaboration Proposals for Detectors". CORE comprehensively covers the physics scope of the EIC Community White Paper and the National Academies of Science 2018 report. The design exploits advances in detector precision and granularity to minimize size. The central detector includes a 3Tesla, 2.5m solenoid. Tracking is primarily silicon. Electromagnetic calorimetry is based on the high performance crystals. Ring-imaging Cherenkov detectors provide hadronic particle identification.

physics.ins-det↗

arXiv2021

The Drell-Yan process with pions and polarized nucleons

The Drell-Yan process provides important information on the internal structure of hadrons including transverse momentum dependent parton distribution functions (TMDs). In this work we present calculations for all leading twist structure functions describing the pion induced Drell-Yan process. The non-perturbative input for the TMDs is taken from the light-front constituent quark model, the spectator model, and available parametrizations of TMDs extracted from the experimental data. TMD evolution is implemented at Next-to-Leading Logarithmic precision for the first time for all asymmetries. Our results are compatible with the first experimental information, help to interpret the data from ongoing experiments, and will allow one to quantitatively assess the models in future when more precise data will become available.

hep-ph↗

arXiv2020

Structure of the nucleon at leading and subleading twist in the covariant parton model

The covariant parton model is generalized to describe quark correlators in a systematic way. Previous results are reproduced for the T-even leading-twist transverse momentum dependent parton distribution functions (TMDs), and for the first time all T-even twist-3 TMDs are evaluated in this model. We apply the approach to evaluate the fully unintegrated quark correlator which allows us to understand the model-specific relations between different TMDs. We verify the consistency of the approach, present numerical results and compare to available TMD parametrizations.

hep-ph↗

arXiv2019

Applications of the WW-type approximation to SIDIS

We explore the complete cross-section for the production of unpolarized hadrons in semi-inclusive deep-inelastic scattering up to power-suppressed $\mathcal{O}(1/Q^2)$ terms in the Wandzura-Wilczek-type (WW-type) approximation, which consists in systematically assuming that $\bar{q}gq$-correlators are much smaller than $\bar{q}q$-correlators. Under the applicability of WW-type approximations, certain relations among transverse momentum dependent parton distribution functions (TMDs) and fragmentation functions (FFs) occur which are used to approximate SIDIS cross-section in terms of a smaller subset of TMDs and FFs. We discuss the applicability of the WW-type approximations on the basis of available data.

hep-ph↗

arXiv2019

Energy-momentum tensor densities in the bag model

The form factors of the energy-momentum tensor can be accessed via studies of generalized parton distributions in hard exclusive reactions. In this talk we present recent results on the energy-momentum tensor form factors and densities in the bag model formulated in the large-$N_c$ limit. The simplicity and lucidity of this quark model allow us to investigate many general concepts which have recently attracted interest, including pressure, shear forces and angular momentum density inside the nucleon. The results from the bag model are theoretically consistent, and comply with all general requirements.

hep-ph↗

arXiv2019

Semi-Inclusive Deep Inelastic Scattering in Wandzura-Wilczek-type approximation

We present the complete cross-section for the production of unpolarized hadrons in semi-inclusive deep-inelastic scattering up to power-suppressed ${\cal O}(1/Q^2)$ terms in the Wandzura--Wilczek-type approximation which consists in systematically assuming that $\bar{q}gq$--terms are much smaller than $\bar{q}q$--correlators. We compute all twist-2 and twist-3 structure functions and the corresponding asymmetries, and discuss the applicability of the Wandzura--Wilczek-type approximations on the basis of available data. We make predictions that can be tested by data from Jefferson Lab, COMPASS, HERMES, and the future Electron-Ion Collider. The results of this paper can be readily used for phenomenology and for event generators, and will help to improve our understanding of the TMD theory beyond leading twist.

hep-ph↗

arXiv2016

On LHCb pentaquarks as a baryon-psi(2S) bound state -- prediction of isospin 3/2 pentaquarks with hidden charm

The pentaquark $P_c^+(4450)$ recently discovered by LHCb has been interpreted as a bound state of $Ψ(2S)$ and nucleon. The charmonium-nucleon interaction which provides the binding mechanism is given, in the heavy quark limit, in terms of charmonium chromoelectric polarizabilities and densities of the nucleon energy-momentum tensor (EMT). In this work we show in model-independent way, by exploring general properties of the effective interaction, that $Ψ(2S)$ can form bound states with nucleon and $Δ$. Using the Skyrme model to evaluate the effective interaction in the large-$N_c$ limit and estimate $1/N_c$ corrections, we confirm the results from prior work which were based on a different effective model (chiral quark soliton model). This shows that the interpretation of $P_c^+(4450)$ is remarkably robust and weakly dependent on the details of the effective theories for the nucleon EMT. We explore the formalism further and present robust predictions of isospin $\frac32$ bound states of $Ψ(2S)$ and $Δ$ with masses around $4.5\,{\rm GeV}$ and widths around $70\,{\rm MeV}$. The approach also predicts broader resonances in the $Ψ(2S)$-$Δ$ channel at $4.9\,{\rm GeV}$ with widths of the order of $150\,{\rm MeV}$. We discuss in which reactions these new isospin $\frac 32$ pentaquarks with hidden charm can be observed.

hep-ph↗

arXiv2016

Transverse pion structure beyond leading twist in constituent models

The understanding of the pion structure as described in terms of transverse-momentum dependent parton distribution functions (TMDs) is of importance for the interpretation of currently ongoing Drell-Yan experiments with pion beams. In this work we discuss the description of pion TMDs beyond leading twist in a pion model formulated in the light-front constituent framework. For comparison, we also review and derive new results for pion TMDs in the bag and spectator models.

hep-ph↗

arXiv2016

Spin-flavor structure of chiral-odd GPDs in the large-N_c limit

We study the spin-flavor structure of the nucleon's chiral-odd generalized parton distributions (transversity GPDs) in the large-N_c limit of QCD. In contrast to the chiral-even case, only three combinations of the four chiral-odd GPDs are non-zero in the leading order of the 1/N_c expansion: E_T-bar = E_T + 2 H_T-tilde, H_T and E_T-tilde. The degeneracy is explained by the absence of spin-orbit interactions correlating the transverse momentum transfer with the transverse quark spin. It can also be deduced from the natural N_c-scaling of the quark-nucleon helicity amplitudes associated with the GPDs. In the GPD E_T-bar the flavor-singlet component u + d is leading in the 1/N_c expansion, while in H_T and E_T-tilde it is the flavor-nonsinglet components u - d. The large-N_c relations are consistent with the spin-flavor structure extracted from hard exclusive pi0 and eta electroproduction data, if it is assumed that the processes are mediated by twist-3 amplitudes involving the chiral-odd GPDs and the chiral-odd pseudoscalar meson distribution amplitudes.

hep-ph↗

arXiv2016

Chiral-odd GPDs in large-N_c QCD

We study the flavor structure of the nucleon's chiral-odd generalized parton distributions (transversity GPDs) in the large-N_c limit of QCD. It is found that in the distributions H_T and E_T-tilde the flavor-nonsinglet component u - d is leading in the 1/N_c expansion, while in E_T and H_T-tilde it is the flavor-singlet component u + d. This pattern is consistent with the flavor structure extracted from hard exclusive pi^0 and eta electroproduction data, assuming that the processes are dominated by the twist-3 mechanism involving the chiral-odd pseudoscalar meson distribution amplitudes.

hep-ph↗

arXiv2015

Transverse-momentum dependent parton distribution functions beyond leading twist in quark models

Higher-twist transverse momentum dependent parton distribution functions (TMDs) are a valuable probe of the quark-gluon dynamics in the nucleon, and play a vital role for the explanation of sizable azimuthal asymmetries in hadron production from unpolarized and polarized deep-inelastic lepton-nucleon scattering observed in experiments at CERN, DESY and Jefferson Lab. The associated observables are challenging to interpret, and still await a complete theoretical explanation, which makes guidance from models valuable. In this work we establish the formalism to describe unpolarized higher-twist TMDs in the light-front framework based on a Fock-space expansion of the nucleon state in terms of free on-shell parton states. We derive general expressions and present numerical results in a practical realization of this picture provided by the light-front constituent quark model. We review several other popular quark model approaches including free quark ensemble, bag, spectator and chiral quark-soliton model. We discuss how higher-twist TMDs are described in these models, and obtain results for several TMDs not discussed previously in literature. This study contributes to the understanding of non-perturbative properties of subleading twist TMDs. The results from the light-front constituent quark model are also compared to available phenomenological information, showing a satisfactory agreement.

hep-ph↗

arXiv2014

Electron Ion Collider: The Next QCD Frontier - Understanding the glue that binds us all

This White Paper presents the science case of an Electron-Ion Collider (EIC), focused on the structure and interactions of gluon-dominated matter, with the intent to articulate it to the broader nuclear science community. It was commissioned by the managements of Brookhaven National Laboratory (BNL) and Thomas Jefferson National Accelerator Facility (JLab) with the objective of presenting a summary of scientific opportunities and goals of the EIC as a follow-up to the 2007 NSAC Long Range plan. This document is a culmination of a community-wide effort in nuclear science following a series of workshops on EIC physics and, in particular, the focused ten-week program on "Gluons and quark sea at high energies" at the Institute for Nuclear Theory in Fall 2010. It contains a brief description of a few golden physics measurements along with accelerator and detector concepts required to achieve them, and it benefited from inputs from the users' communities of BNL and JLab. This White Paper offers the promise to propel the QCD science program in the U.S., established with the CEBAF accelerator at JLab and the RHIC collider at BNL, to the next QCD frontier.

nucl-ex↗

arXiv2014

Pion TMDs in light-front constituent approach, and Boer-Mulders effect in the pion-induced Drell-Yan process

At leading twist the transverse-momentum dependent parton distributions of the pion consist of two functions, the unpolarized $f_{1,π}(x,\boldsymbol k^{\, 2}_\perp)$ and the Boer-Mulders function $h_{1,π}^{\perp}(x,\boldsymbol k^{\, 2}_\perp)$. We study both functions within a light-front constituent model of the pion, comparing the results with different pion models and the corresponding nucleon distributions from a light-front constituent model. After evolution from the model scale to the relevant experimental scales, the results for the collinear pion valence parton distribution function $f_{1,π}(x)$ are in very good agreement with available parameterizations. Using the light-front constituent model results for the Boer-Mulders functions of the pion and nucleon, we calculate the coefficient $ν$ in the angular distribution of Drell-Yan dileptons produced in pion-nucleus scattering, which is responsible for the violation of the Lam-Tung relation. We find a good agreement with data, and carefully discuss the range of applicability of our approach.

hep-ph↗