Search

We perform a renormalization group (RG) analysis of collinear hadron production in deep inelastic scattering on nuclei. We consider the limit where the parent parton energy E is large, while the medium opacity L/λg remains small. We identify the fixed order and leading ln⁡(E/ξ2L) enhanced medium contributions to the semi-inclusive cross sections and derive RG equations that resum multiple emissions near the endpoints of the splitting functions at first order in opacity. These evolution equations treat the same type of radiation enhancement in matter as the modified Dokshitzer-Gribov-Lipatov-Altarelli-Parisi approach, but differ in the way one regulates the collinear divergences. They provide a unique analytic insight into the problem of resummation and a faster and more efficient path to phenomenology. The new RG evolution framework is applied to study fragmentation in eA reactions.

Local gauge invariance of the baryon wave function leads to the emergence of a baryon junction, where three (or N, in SU(N) gauge theory) string operators merge. The existence of baryon junction dramatically affects the dynamics of baryon stopping at high energies, and the corresponding predictions are supported by the recent data from STAR Collaboration at the Relativistic Heavy Ion Collider. Here we outline the ways in which the baryon junctions can be tested in semi-inclusive deep inelasttic scattering at Jefferson Laboratory and the future Electron Ion Collider.

We describe nuclear effects in structure functions of nuclei in DIS by means of a multiplicative factor β A (x) which differentiates the structure function of the bound nucleons from that of the free nucleons. Our analysis determines that β A (x) establishes a relation between the quark-gluon dynamics expressed by the bound nucleon structure functions and the nuclear dynamics as described by the well-known semi-empirical Bethe-Weizsäcker mass formula. This relation corroborates a connection between the underlying quark-gluon dynamics and the phenomenological nuclear dynamics. [ABSTRACT FROM AUTHOR]

We report a new result for the NfCF3 contribution to the four-loop anomalous dimensions of non-singlet, twist-two operators in Quantum Chromodynamics. This result is obtained through computations of off-shell operator matrix elements. Employing integration-by-parts reductions and differential equations with respect to a tracing parameter allowed us to derive analytic results valid for arbitrary Mellin moment n.

Using the analytical expression for transverse momentum dependent (TMD) gluon density in a proton, a self-consistent simultaneous description of low Q2 data on proton structure function F2(x,Q2), reduced cross section for the electron-proton deep inelastic scattering at HERA and soft hadron production in pp collisions at the LHC is achieved in the framework of color dipole approach and modified quark-gluon string model.

Abstract: Using Soft-Collinear Effective Theory, we develop the transverse-momentum-dependent factorization formalism for heavy flavor dijet production in polarized-proton-electron collisions. We consider heavy flavor mass corrections in the collinear-soft and jet functions, as well as the associated evolution equations. Using this formalism, we generate a prediction for the gluon Sivers asymmetry for charm and bottom dijet production at the future Electron-Ion Collider. Furthermore, we compare theoretical predictions with and without the inclusion of finite quark masses. We find that the heavy flavor mass effects can give sizable corrections to the predicted asymmetry.

Parton distribution functions (PDFs) inscribe details about the hadronic substructure in terms of partons, quarks and gluons collectively, which are the fundamental degrees of freedom of Quantum Chromodynamics (QCD), the theory of strong interactions. Study of PDFs has led to a better comprehension of the partonic structure of hadrons and the proton structure function in deep inelastic scattering. Understanding parton densities within the hadrons is vital to estimate the hard-scattering process results. Owing to theoretical and experimental limitations, PDFs cannot be computed from the first principles. The global analysis of parton distribution functions, therefore, requires an unrelenting endeavour. The aim of the present work is to have a comparative study of the PDFs from the plots obtained using APFEL, which is a PDFs evolution library. We discuss the graphical analyses as well as comparisons of the three global PDFs sets, viz. CT10, MSTW2008 and NNPDF30, in a wide range of momentum fraction x and energy scale Q. A comparative analysis of gluons extracted from these global fits has also been done. [ABSTRACT FROM AUTHOR]

We introduce a physics-informed Bayesian neural network with flow-approximated posteriors using multiplicative normalizing flows for detailed uncertainty quantification (UQ) at the physics event-level. Our method is capable of identifying both heteroskedastic aleatoric and epistemic uncertainties, providing granular physical insights. Applied to deep inelastic scattering (DIS) events, our model effectively extracts the kinematic variables x , Q ^2 , and y , matching the performance of recent deep learning regression techniques but with the critical enhancement of event-level UQ. This detailed description of the underlying uncertainty proves invaluable for decision-making, especially in tasks like event filtering. It also allows for the reduction of true inaccuracies without directly accessing the ground truth. A thorough DIS simulation using the H1 detector at HERA indicates possible applications for the future electron–ion collider. Additionally, this paves the way for related tasks such as data quality monitoring and anomaly detection. Remarkably, our approach effectively processes large samples at high rates.

The fundamental theory of the strong interaction-quantum chromodynamics (QCD) - provides the foundational framework with which to describe and understand the key properties of atomic nuclei. A deep understanding of the explicit role of quarks and gluons in nuclei remains elusive however, as these effects have thus far been well-disguised by confinement effects in QCD which are encapsulated by a successful description in terms of effective hadronic degrees of freedom. The observation of the EMC effect has provided an enduring indication for explicit QCD effects in nuclei, and points to the medium modification of the bound protons and neutrons in the nuclear medium. Understanding the EMC effect is a major challenge for modern nuclear physics, and several key questions remain, such as understanding its flavor, spin, and momentum dependence. This manuscript provides a contemporary snapshot of our understanding of the role of QCD in nuclei and outlines possible pathways in experiment and theory that will help deepen our understanding of nuclei in the context of QCD.

We investigate the dependence of the deep inelastic proton structure function FL(x,Q2) on different forms of the transverse momentum dependent (TMD, or unintegrated) gluon distribution. We present a comparison of theoretical results with the latest experimental data taken by the H1 and ZEUS Collaborations at HERA. We demonstrate that these data, despite of having quite large uncertainties, can test different kinds of the gluon TMD in a proton. Moreover, different phenomenological models at low x could be tested by future experiments on deep inelastic scattering.

In this paper, a next-to-next-to-leading order (NNLO) quantum chromodynamics (QCD) calculation of gluon distribution function at small- x is presented. The gluon distribution function is explored analytically in the Dokshitzer–Gribov–Lipatov–Altarelli–Parisi approach by a Taylor expansion at small- x as two first-order partial differential equations in two variables: Bjorken x and t (t = ln ( Q 2 Λ 2 )). We have solved the system of equations at LO, NLO and NNLO, respectively, by Lagrange's method. The resulting analytical expressions are compared with the available global parton distribution function fits as well as with the results of the Block–Durand–McKay model. We have further performed an χ 2 test to check the compatibility of our predictions and observed that our results can be consistently described in the context of perturbative QCD. A comparative analysis of the obtained results at LO, NLO and NNLO reveals that the NNLO approximation has a significant contribution to the gluon distribution function particularly in the small- x region. [ABSTRACT FROM AUTHOR]

The behavior of the gluon density in nuclei is investigated in the framework of the rescaling model. [ABSTRACT FROM AUTHOR]

Examining the evolution of the maximum of valence quark distribution, qV, weighted by Bjorken x, h(x,t)≡xqV(x,t), it is observed that h(x,t) at the peak becomes a one-parameter function; h(xp,t)=Φ(xp(t)), where xp is the position of the peak, t=logQ2, and Q2 is the resolution scale. This observation is used to derive a new model-independent relation which connects the partial derivative of the valence parton distribution functions (PDFs) in xp to the quantum chromodynamics (QCD) evolution equation through the xp derivative of the logarithm of the function Φ(xp(t)). A numerical analysis of this relation using empirical PDFs results in an observation of the exponential form of the Φ(xp(t))=h(xp,t)=CeDxp(t) for leading to next-to-next leading order approximations of PDFs for the range of Q2, covering four orders in magnitude. The exponent, D, of the observed “height-position” correlation function converges with the increase in the order of approximation. This result holds for all the PDF sets considered. A similar relation is observed also for the pion valence quark distribution, indicating that the obtained relation may be universal for any non-singlet partonic distribution. The observed “height-position” correlation is used also to indicate that no finite number of exchanges can describe the analytic behavior of the valence quark distribution at the position of the peak at fixed Q2.

We perform a renormalization group (RG) analysis of collinear hadron production in deep inelastic scattering on nuclei. We consider the limit where the parent parton energy E is large, while the medium opacity L / λ g remains small. We identify the fixed order and leading ln ⁡ (E / ξ 2 L) enhanced medium contributions to the semi-inclusive cross sections and derive RG equations that resum multiple emissions near the endpoints of the splitting functions at first order in opacity. These evolution equations treat the same type of radiation enhancement in matter as the modified Dokshitzer-Gribov-Lipatov-Altarelli-Parisi approach, but differ in the way one regulates the collinear divergences. They provide a unique analytic insight into the problem of resummation and a faster and more efficient path to phenomenology. The new RG evolution framework is applied to study fragmentation in e A reactions. [ABSTRACT FROM AUTHOR]

Local gauge invariance of the baryon wave function leads to the emergence of a baryon junction, where three (or N , in S U (N) gauge theory) string operators merge. The existence of baryon junction dramatically affects the dynamics of baryon stopping at high energies, and the corresponding predictions are supported by the recent data from STAR Collaboration at the Relativistic Heavy Ion Collider. Here we outline the ways in which the baryon junctions can be tested in semi-inclusive deep inelasttic scattering at Jefferson Laboratory and the future Electron Ion Collider. [ABSTRACT FROM AUTHOR]

Examining the evolution of the maximum of valence quark distribution, q V , weighted by Bjorken x, h (x , t) ≡ x q V (x , t) , it is observed that h (x , t) at the peak becomes a one-parameter function; h (x p , t) = Φ (x p (t)) , where x p is the position of the peak, t = log Q 2 , and Q 2 is the resolution scale. This observation is used to derive a new model-independent relation which connects the partial derivative of the valence parton distribution functions (PDFs) in x p to the quantum chromodynamics (QCD) evolution equation through the x p derivative of the logarithm of the function Φ (x p (t)) . A numerical analysis of this relation using empirical PDFs results in an observation of the exponential form of the Φ (x p (t)) = h (x p , t) = C e D x p (t) for leading to next-to-next leading order approximations of PDFs for the range of Q 2 , covering four orders in magnitude. The exponent, D, of the observed "height-position" correlation function converges with the increase in the order of approximation. This result holds for all the PDF sets considered. A similar relation is observed also for the pion valence quark distribution, indicating that the obtained relation may be universal for any non-singlet partonic distribution. The observed "height-position" correlation is used also to indicate that no finite number of exchanges can describe the analytic behavior of the valence quark distribution at the position of the peak at fixed Q 2 . [ABSTRACT FROM AUTHOR]

We address novel features of deep inelastic lepton scattering on nuclei at small Bjorken variable xBj. In this regime the lepton-nuclear cross section involves the interference between the standard lepton-quark scattering amplitude for the deep inelastic scattering (DIS) process on a single nucleon and a two-step process where diffractive scattering on a first nucleon combines with the amplitude for DIS on a second nucleon. The phases associated with the t-channel exchanges to the diffractive amplitude can produce either a destructive or constructive quantum-mechanical interference of the one-step and two-step amplitudes. This provides a mechanism regulating the respective amounts of shadowing suppression and anti-shadowing enhancement at low xBj. Furthermore, the standard leading-twist operator product and handbag diagram analyses of the forward virtual Compton amplitude on the nucleus are inapplicable, barring a conventional probabilistic interpretation. A main observable consequence is the impossibility of extracting momentum and spin sum rules from nuclear structure functions. We present numerical predictions supporting this picture and test them against DIS neutrino-nucleus and charged-lepton-nucleus scattering data.

The cross section for deep inelastic lepton-proton scattering (DIS) ℓp→ℓ′X includes a diffractive deep inelastic (DDIS) contribution ℓp→ℓ′p′X, in which the proton remains intact with a large longitudinal momentum fraction xF greater than 0.9 and small transverse momentum. The DDIS events, which can be identified with Pomeron exchange in the t-channel, account for approximately 10% of all of the DIS events. Thus, when one measures DIS, one automatically includes the leading-twist Bjorken-scaling DDIS events as a contribution to the DIS cross section, whether or not the final-state proton p′ is detected. In such events, the missing momentum fraction xp′∼0.9 carried by the final-state proton p′ in the DDIS events could be misidentified with the light-front momentum fraction carried by sea quarks or gluons in the protons' Fock structure. As we shall show in this article, the underlying QCD Pomeron-exchange amplitude which produces the DDIS events does not obey the operator product expansion nor satisfy momentum sum rules. Thus we conclude that the quark and gluon distributions measured in DIS experiments will be misidentified, unless the measurements explicitly exclude the DDIS events and that a correct determination of the parton distribution functions (PDFs) derived from the DIS data requires the explicit subtraction of the DDIS contribution from the full DIS cross section.

Based on the observation of sizeable target-transverse-spin asymmetries in single-hadron and hadron-pair production in Semi-Inclusive measurements of Deep Inelastic Scattering (SIDIS), the chiral-odd transversity quark distribution functions h1q are nowadays well established. Several possible channels to access these functions were originally proposed. One candidate is the measurement of the polarisation of Λ hyperons produced in SIDIS off transversely polarised nucleons, where the transverse polarisation of the struck quark might be transferred to the final-state hyperon. In this article, we present the COMPASS results on the transversity-induced polarisation of Λ and Λ¯ hyperons produced in SIDIS off transversely polarised protons. Within the experimental uncertainties, no significant deviation from zero was observed. The results are discussed in the context of different models taking into account previous experimental results on h1u and h1d.

We discuss Z-production in deep inelastic scattering e + p → e + Z + X using the parton model, in the context of the Standard Model at leading order. In contrast to the deep inelastic ep-scattering ( e + p → e + X ), where Q ~ 2 , the momentum transfer square, is unambiguous, in the case of boson production it depends upon the mechanism involved, that is, it is related to the electroweak interactions. We present estimates for the total cross-section as a function of s , the energy of the ep system, in the range 300 ≤ s ≤ 1300 GeV, and also for different assignements of Q ~ 2 . [ABSTRACT FROM AUTHOR]