Hadronic Cross Sections Research Articles

Novel cross section ratios as possible signals of saturation in ultraperipheral collisions

We propose new cross section ratios in ultraperipheral A+A and p+A collisions (UPCs) as a potential experimental signal of saturation physics. We consider the ratio R1 of elastic vector meson photoproduction cross section to the inclusive hadron or jet photoproduction cross section. The ratio can be measured in the γ+A and γ+p collisions taking place in the UPCs. We label the ratios R1(A) and R1(p), respectively. Constructing the double ratio RUPC(A)=R1(A)/R1(p), and performing a small-x calculation both in the quasiclassical approximation and by including small-x evolution, we observe that RUPC(A) exhibits a markedly different dependence on the nuclear atomic number inside and outside the saturation region. This result indicates that RUPC(A) and R1(A) measurements in UPCs may help in the experimental searches for the evidence of saturation physics. Published by the American Physical Society 2024

Resolving the muon g − 2 tension through Z′-induced modifications to σhad

The QED hadronic vacuum polarization function plays an important role in the determination of precision electroweak observables and of the anomalous magnetic moment of the muon. These contributions have been computed from data, by means of dispersion relations affecting the electron positron hadronic cross sections, or by first principle lattice-QCD computations in the Standard Model. Today there is a discrepancy between the two approaches for determining these contributions, which affects the comparison of the measurement of the anomalous magnetic moment of the muon with the theoretical predictions. In this article, we revisit the idea that this discrepancy may be explained by the presence of a new light gauge boson that couples to the first generation quark and leptons and has a mass below the GeV scale. We discuss the requirements for its consistency with observations and the phenomenological implications of such a gauge extension.

Centrality-dependent modification of hadron and jet production in electron-nucleus collisions

Centrality-dependent measurements of hadron and jet cross section attenuation in deep inelastic scattering on nuclei can shed new light on the physics of final-state interactions in nuclear matter, including the path-length dependence of the in-medium parton shower formation and evolution. Recent simulation studies have demonstrated the feasibility of experimental centrality determination in eA reactions at the electron-ion collider via neutron detection in the zero-degree calorimeter. Motivated by these results, we present the first theoretical calculation of the production rate modification for hadrons and jets in central and peripheral ePb collisions. We find that the variation in the suppression of inclusive jet cross section as a function of centrality is less than a factor of two. In more differential measurements, such as the distribution of hadrons versus the hadronization fraction zh, the difference can be enhanced up to an order of magnitude.

Electromagnetic calorimeter time measurement applications in the SND physics analysis

The SND is a non-magnetic detector at the VEPP-2000 e+e− collider (BINP, Novosibirsk) designed for hadronic cross-section measurements in the center-of-mass energy range up to 2 GeV. The important part of the detector is a segmented electromagnetic calorimeter (EMC) with three layers of NaI(Tl) counters. The EMC signal shaping and digitizing electronics based on FADC allow one to obtain both the signal amplitude and the arrival time. We describe the EMC signal processing and how the EMC measured time is applied in event reconstruction and physics analysis.

The STRONG2020 and Radio MonteCarLow activities

For over 15 years, the “Radiative Corrections and Monte Carlo Generators for Low Energies” Working Group (Radio MonteCarLow WG) has been providing valuable support to the development of radiative corrections and Monte Carlo generators for low energy positron-electron data and tau-lepton decays. The Radio MonteCarLow WG held 20 meetings in which theorists and experimentalists, experts working in the field of positron-electron physics and partly also from the tau community, produced the higlhy-cited report “Quest for precision in hadronic cross sections at low energy: Monte Carlo tools vs. experimental data”. Recently, parts of the program have been included as a Joint Research Initiative in the group application of the European hadron physics community, STRONG2020, to the European Union. A specific goal of the working group is to create the annotated “PrecisionSM database” for low-energy hadronic cross sections in positron-electron collisions. The database will contain information about the reliability of the data sets, their systematic errors, and the treatment of Radiative Corrections. This proceeding reviews the results published by the Radio MonteCarLow WG and describes the status of the PrecisionSM database.

Sigma (1385)^{pm } resonance production in Pb–Pb collisions at sqrt{s_{textrm{NN}}}~=~5.02 TeV

Hadronic resonances are used to probe the hadron gas produced in the late stage of heavy-ion collisions since they decay on the same timescale, of the order of 1–10 fm/c, as the decoupling time of the system. In the hadron gas, (pseudo)elastic scatterings among the products of resonances that decayed before the kinetic freeze-out and regeneration processes counteract each other, the net effect depending on the resonance lifetime, the duration of the hadronic phase, and the hadronic cross sections at play. In this context, the Sigma (1385)^{pm } particle is of particular interest as models predict that regeneration dominates over rescattering despite its relatively short lifetime of about 5.5 fm/c. The first measurement of the Sigma (1385)^{pm } resonance production at midrapidity in Pb–Pb collisions at sqrt{s_{textrm{NN}}}= 5.02 TeV with the ALICE detector is presented in this Letter. The resonances are reconstructed via their hadronic decay channel, Lambda pi , as a function of the transverse momentum (p_textrm{T}) and the collision centrality. The results are discussed in comparison with the measured yield of pions and with expectations from the statistical hadronization model as well as commonly employed event generators, including PYTHIA8/Angantyr and EPOS3 coupled to the UrQMD hadronic cascade afterburner. None of the models can describe the data. For Sigma (1385)^{pm }, a similar behaviour as textrm{K}^{*} (892)^{0} is observed in data unlike the predictions of EPOS3 with afterburner.

Renormalization of twist-two operators in covariant gauge to three loops in QCD

The leading short-distance contributions to hadronic hard-scattering cross sections in the operator product expansion are described by twist-two quark and gluon operators. The anomalous dimensions of these operators determine the splitting functions that govern the scale evolution of parton distribution functions. In massless QCD, these anomalous dimensions can be determined through the calculation of off-shell operator matrix elements, typically performed in a covariant gauge, where the physical operators mix with gauge-variant operators of the same quantum numbers. We derive a new method to systematically extract the counterterm Feynman rules resulting from these gauge-variant operators. As a first application of the new method, we rederive the unpolarized three-loop singlet anomalous dimensions, independently confirming previous results obtained with other methods. Employing a general covariant gauge, we observe the explicit cancellation of the gauge parameter dependence in these results.

Analysis of the CMD-3 detector data: selection of low-energy electron-positron annihilation into KKππ0

We explore the process e+e− → KSK+-π−+π0 with the CMD-3 detector at the electron-positron collider VEPP-2000. Here, we present a selection algorithm. The data amassed by the CMD-3 detector in the energy range of 1.2–2 GeV during 2011, 2012, 2017, 2019 runs, with a total luminosity integral of ∼120pb−1 backs the analysis. Two reasons stand behind the study. First, a recent report of anomalous magnetic moment discrepancy broadening to 4.2σ, see Fermilab article [1]. Searching for New Physics demand sharper Hadronic Vacuum Polarization (HVP) estimate. In its turn, HVP computation relies heavily on hadronic cross-sections measurement. Second, an intermediate vector resonance near 2 GeV (ϕ’’) is still a mystery. It might be a state, or a hybrid , or ΛΛ− state. Untangling partial decay widths, measuring isospin 1 and 0 cross-sections for e+e− → KSK+-π−+π0, might discern between different ϕ’’ models.

Dispersive determination of the HVP contribution to the muon g − 2

The determination of hadronic vacuum polarization (HVP) from e+e− → hadrons cross-section data, in the energy region relevant for the anomalous magnetic moment of the muon, has recently been challenged by lattice-QCD calculations, especially for the intermediate window in Euclidean time. In these proceedings we review some frequently-asked questions on the comparison between data-driven and lattice-QCD evaluations of the HVP contribution.

Hadronic Nucleus-Nucleus Cross Section and the Nucleon Size.

Even though the total hadronic nucleus-nucleus cross section is among the most fundamental observables, it has only recently been measured precisely for lead-lead collisions at the LHC. This measurement implies the nucleon width should be below 0.7fm, which is in contradiction with all known state-of-the-art Bayesian estimates. We study the implications of the smaller nucleon width on quark-gluon plasma properties such as the bulk viscosity. The smaller nucleon width dramatically improves the description of several triple-differential observables.

Background suppression with SND electromagnetic calorimeter time channel

The SND is a non-magnetic detector deployed at the VEPP-2000 e + e − collider (BINP, Novosibirsk) for hadronic cross-section measurements in the center of mass energy range below 2 GeV. The important part of the detector is a hodoscopic electromagnetic calorimeter (EMC) with three layers of NaI(Tl) counters. EMC signal shaping and digitizing electronics based on FADC allow us to obtain both the energy deposition and the signal arrival time. We demonstrate how EMC time is applied to detect background pileup and cosmic events.

Doubly charged Higgs boson production at hadron colliders II: a Zee-Babu case study

Motivated by searches for so-called leptonic scalars at the LHC and the recent measurement of the W boson’s mass at the Tevatron, we revisit the phenomenology of the Zee-Babu model for neutrino masses and the ability to differentiate it from the Type II Seesaw model at the LHC. We conclude that this task is much more difficult than previously believed. All inputs equal in the two scenarios, we find that total and differential rates for producing pairs of doubly and singly charged scalars are identical in shape and only differ in normalization. The normalization is given by the ratio of hadronic cross sections and can be unity. Differences in cross sections are small and can be hidden by unknown branching rates. This holds for Drell-Yan, γγ fusion, and gg fusion, as well as observables at LO and NLO in QCD. This likeness allows us to reinterpret Run II limits on the Type II Seesaw and estimate projections for the HL-LHC. Using updated neutrino oscillation data, we also find that some collider observables, e.g., lepton flavor-violating branching ratios, are now sufficiently precise to provide a path forward. Other means of discrimination are also discussed. As a byproduct of this work, we report the availability of new Universal FeynRules Object libraries, the SM_ZeeBabu UFO, that enable fully differential simulations up to NLO+LL(PS) with tool chains employing MadGraph5_aMC@NLO.

The Central Tracker of the CMD3 detector

The CMD-3 experiment has been operating at the VEPP-2000 electron–positron collider, at the Budker Institute of Nuclear Physics, since December 2010. Its main goal is to measure the hadronic cross sections necessary to evaluate the anomalous magnetic moment of the muon. The discrepancy between the theoretical calculations and the experimental results obtained at the Brookhaven experiments is approximately 3.7 σ. The comparison between the results of the new “g-2” experiment at Fermilab and the theoretical calculation thanks to the new experimental contributions from CMD3 would provide important contributions to this measurement, which could prove the existence of New Physics. A key element for the success the CMD3 experiment is the tracking detector, which is a drift chamber built in the year 2009 at INFN of Lecce. Because of aging effects, its replacement is necessary. This paper presents the innovative design for the new ultralight CMD3 drift chamber.

Doubly-polarized WZ hadronic cross sections at NLO QCD + EW accuracy

We present new results for next-to-leading order (NLO) electroweak (EW) corrections to double polarization signals in the WZ production channel at the LHC using the e^+nu _e mu ^+ mu ^- final state. It is found that the EW corrections are most sizable in the transverse momentum distributions of the doubly longitudinal polarization, being around -,10% compared to the NLO QCD prediction at p_{T,e}approx 200 GeV, which is in the accessible energy range of the current LHC data.

Measurement of the π− -Ar total hadronic cross section at the LArIAT experiment

We present the first measurement of the negative pion total hadronic cross section on argon, which we performed at the Liquid Argon In A Testbeam (LArIAT) experiment. All hadronic reaction channels, as well as hadronic elastic interactions with scattering angle greater than 5~degrees are included. The pions have a kinetic energies in the range 100-700~MeV and are produced by a beam of charged particles impinging on a solid target at the Fermilab Test Beam Facility. LArIAT employs a 0.24~ton active mass Liquid Argon Time Projection Chamber (LArTPC) to measure the pion hadronic interactions. For this measurement, LArIAT has developed the ``thin slice method", a new technique to measure cross sections with LArTPCs. While generally higher than the prediction, our measurement of the ($\pi^-$,Ar) total hadronic cross section is in agreement with the prediction of the Geant4 model when considering a model uncertainty of $\sim$5.1\%.

Development of the micro-RWELL discs for the CMD-3 detector

The CMD-3 is general purpose detector at the VEPP-2000 electron–positron collider at Budker Institute of Nuclear Physics. CMD-3 is intended to measure parameters of light vector mesons and main hadronic cross sections with accuracy better than 1% and study dynamics of multihadron production. In order to increase geometrical acceptance for charged particles and to improve precision of track polar angle measurements the end-cap discs based on micro-resistive-WELL (μ-RWELL) structures are proposed for the upgrade of the CMD-3 tracking system. Two μ-RWELL discs 50 cm in diameter were assembled and tested. The discs have two-layer readout structure with the top layer of quarter-rings with 2 mm pitch in radius and the bottom layer of sectors with average angular pitch of about 0.3 degrees. The quarter-rings occupy only 50% of the disc surface due to gaps between them, thus, allowing the signal to be induced on the bottom layer. The kapton foil with copper layer on top and high-resistivity DLC layer at the bottom, pierced with 80 micron diameter holes located at 140 micron from each other, is glued on top of the readout structure. With the first disc the manufacturer (CERN advanced PCB Workshop) could not reach proper insulation between the copper layer and the DLC and the copper was etched out leaving the disc with thin Ni–Cr adhesion layer on top. The second disc has copper layer on top of the μ-RWELL structure. The readout structure of the discs is connected to front-end electronics based on VMM3a ASICS. The results of study of the main parameters of the detectors with front-end electronics are reported in the paper.

The central tracker of SCTF and CMD3 detectors

The CMD3 experiment has been operating at the VEPP-2000 electron-positron collider, at the Budker Institute of Nuclear Physics, since December 2010. Its main goal is to measure the hadronic cross sections necessary to evaluate the anomalous magnetic moment of the muon. The discrepancy between the theoretical calculations and the experimental results obtained at the Brookhaven experiments is approximately 3.7 σ.The comparison between the results of the new “g-2” experiment at Fermilab and the theoretical calculation with the new experimental contributions from CMD3 could confirm the discrepancy, which is a new important hint of New Physics.A key element for the success the CMD3 experiment is the tracking detector, which is a drift chamber built in the year 2009 at INFN of Lecce. Due to aging effects, its replacement is necessary, so that an innovative tracking detector, named TraPId (Tracking and Particle Identification), has been designed: an ultra-light drift chamber equipped with cluster counting/timing readout techniques, which exploits the expertise gained with the successful construction of the MEG II drift chamber. The drift chamber proposed for CMD3 will be also the prototype for the tracking system of the future Super Charm-Tau Factory detector (SCTF).In this paper, the new design of TraPId is described, with a focus on the mechanical design of the end plates, their novel tension recovery scheme and the expected performances.

Data-driven evaluations of Euclidean windows to scrutinize hadronic vacuum polarization

In this paper, we discuss how windows in Euclidean time can be used to isolate the origin of potential conflicts between evaluations of the hadronic-vacuum-polarization (HVP) contribution to the anomalous magnetic moment of the muon in lattice QCD and from e+e−→hadrons cross-section data. We provide phenomenological comparison numbers evaluated from e+e−→hadrons data for the window quantities most commonly studied in lattice QCD, complete with the correlations among them. We discuss and evaluate modifications of window parameters that could be useful in dissecting the energy dependence of tensions in the HVP integral and emphasize that further optimizations require a precise knowledge of the full covariance matrix in lattice-QCD calculations as well.

Nuclear matter effects on jet production at electron-ion colliders

In these proceedings we report recent progress on understanding hadron and jet production in electron-nucleus collisions at the future Electron-Ion Collider [1,2]. These processes will play an essential role in the exploration of the partonic structure of nuclei and the study of parton shower evolution in strongly-interacting matter. We employ the framework of soft-collinear effective theory, generalized to include in-medium interactions, to present the first theoretical results for inclusive hadron and jet cross sections, as well as the jet charge modification in deep inelastic scattering on nuclei. We further demonstrate how to separate initial-state and final-state effects.

Onset of Color Transparency in Holographic Light-Front QCD

The color transparency (CT) of a hadron, propagating with reduced absorption in a nucleus, is a fundamental property of QCD (quantum chromodynamics) reflecting its internal structure and effective size when it is produced at high transverse momentum, Q. CT has been confirmed in many experiments, such as semi-exclusive hard electroproduction, eA→e′πX, for mesons produced at Q2>3GeV2. However, a recent JLab (Jefferson Laboratory) measurement for a proton electroproduced in carbon eC→e′pX, where X stands for the inclusive sum of all produced final states, fails to observe CT at Q2 up to 14.2 GeV2. In this paper, the onset of CT is determined by comparing the Q2-dependence of the hadronic cross sections for the initial formation of a small color-singlet configuration using the generalized parton distributions from holographic light-front QCD. A critical dependence on the hadron’s twist, τ, the number of hadron constituents, is found for the onset of CT, with no significant effects from the nuclear medium. This effect can explain the absence of proton CT in the present kinematic range of the JLab experiment. The proton is predicted to have a “two-stage” color transparency with the onset of CT differing for the spin-conserving (twist-3, τ=3) Dirac form factor with a higher onset in Q2 for the spin-flip Pauli (twist-4) form factor. In contrast, the neutron is predicted to have a “one-stage” color transparency with the onset at higher Q2 because of the dominance of its Pauli form factor. The model also predicts a strong dependence at low energies on the flavor of the quark current coupling to the hadron.