Pions In Final State Research Articles

First combined tuning on transverse kinematic imbalance data with and without pion production constraints

We present the first combined tuning, using , of four transverse kinematic imbalance measurements of neutrino-hydrocarbon scattering, both with and without pion final states, from the T2K and MINERvA experiments. As a proof of concept, we have simultaneously tuned the initial state and final-state interaction models (SF-CFG and hA, respectively), producing a new effective model that more accurately describes the data. Published by the American Physical Society 2024

Applying deep learning technique to chiral magnetic wave search* *Supported by the Natural Science Foundation of Shanghai (23JC1400200), the National Natural Science Foundation of China (12225502, 12075061, 12147101) and the National Key Research and Development Program of China (2022YFA1604900)

The chiral magnetic wave (CMW) is a collective mode in quark-gluon plasma originated from the chiral magnetic effect (CME) and chiral separation effect. Its detection in heavy-ion collisions is challenging owing to significant background contamination. In [Y. S. Zhao et al., Phys. Rev. C 106, L051901 (2022)], we constructed a neural network that accurately identifies the CME-related signal from the final-state pion spectra. In this study, we have generalized this neural network to the case of CMW search. We show that, after an updated training, the neural network effectively recognizes the CMW-related signal. Additionally, we have assessed the performance of the neural network in comparison with other known methods for CMW search.

Detecting the chiral magnetic effect via deep learning

The search of chiral magnetic effect (CME) in heavy-ion collisions has attracted long-term attentions. Multiple observables have been proposed but all suffer from obstacles due to large background contaminations. In this Letter, we construct an observable-independent CME-meter based on a deep convolutional neural network. After trained over data set generated by a multiphase transport model, the CME-meter shows high accuracy in recognizing the CME-featured charge separation from the final-state pion spectra. It also exhibits remarkable robustness to diverse conditions including different collision energies, centralities, and elliptic flow backgrounds. In a transfer learning manner, the CME-meter is validated in isobaric collision systems, showing good transferability among different colliding systems. Based on variational approaches, we utilize the DeepDream method to derive the most responsive CME-spectra that demonstrates the physical contents the machine learns.

Differential cross section measurement of charged current νe interactions without final-state pions in MicroBooNE

In this paper we present the first measurements of an exclusive electron neutrino cross section with the MicroBooNE experiment using data from the Booster neutrino beamline at Fermilab. These measurements are made for a selection of charged-current electron neutrinos without final-state pions. Differential cross sections are extracted in energy and angle with respect to the beam for the electron and the leading proton. The differential cross section as a function of proton energy is measured using events with protons both above and below the visibility threshold. This is done by including a separate selection of electron neutrino events without reconstructed proton candidates in addition to those with proton candidates. Results are compared to the predictions from several modern generators, and we find the data agrees well with these models. The data shows best agreement, as quantified by the p-value, with the generators that predict a lower overall cross section, such as GENIE v3 and NuWro.Received 5 August 2022Accepted 29 August 2022DOI:https://doi.org/10.1103/PhysRevD.106.L051102Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Physical SystemsNeutrinosParticles & Fields

QCD analysis of pion fragmentation functions in the xFitter framework

We present the first open-source analysis of fragmentation functions (FFs) of charged pions (entitled IPM-xFitter) computed at next-to-leading order (NLO) and next-to-next-to-leading order (NNLO) accuracy in perturbative QCD using the xFitter framework. This study incorporates a comprehensive and up-to-date set of pion production data from single-inclusive annihilation (SIA) processes, as well as the most recent measurements of inclusive cross-sections of single pion by the BELLE collaboration. The determination of pion FFs along with their theoretical uncertainties is performed in the Zero-Mass Variable-Flavor Number Scheme (ZM-VFNS). We also present comparisons of our FFs set with recent fits from the literature. The resulting NLO and NNLO pion FFs provide valuable insights for applications in present and future high-energy analysis of pion final state processes.

Identifying the nature of the QCD transition in heavy-ion collisions with deep learning

In this proceeding, we review our recent work using deep convolutional neural network (CNN) to identify the nature of the QCD transition in a hybrid modeling of heavy-ion collisions. Within this hybrid model, a viscous hydrodynamic model is coupled with a hadronic cascade “after-burner”. As a binary classification setup, we employ two different types of equations of state (EoS) of the hot medium in the hydrodynamic evolution. The resulting final-state pion spectra in the transverse momentum and azimuthal angle plane are fed to the neural network as the input data in order to distinguish different EoS. To probe the effects of the fluctuations in the event-by-event spectra, we explore different scenarios for the input data and make a comparison in a systematic way. We observe a clear hierarchy in the predictive power when the network is fed with the event-by-event, cascade-coarse-grained and event-fine-averaged spectra. The carefully-trained neural network can extract high-level features from pion spectra to identify the nature of the QCD transition in a realistic simulation scenario.

Identifying the nature of the QCD transition in relativistic collision of heavy nuclei with deep learning

Using deep convolutional neural network (CNN), the nature of the QCD transition can be identified from the final-state pion spectra from hybrid model simulations of heavy-ion collisions that combines a viscous hydrodynamic model with a hadronic cascade “after-burner”. Two different types of equations of state (EoS) of the medium are used in the hydrodynamic evolution. The resulting spectra in transverse momentum and azimuthal angle are used as the input data to train the neural network to distinguish different EoS. Different scenarios for the input data are studied and compared in a systematic way. A clear hierarchy is observed in the prediction accuracy when using the event-by-event, cascade-coarse-grained and event-fine-averaged spectra as input for the network, which are about 80%, 90% and 99%, respectively. A comparison with the prediction performance by deep neural network (DNN) with only the normalized pion transverse momentum spectra is also made. High-level features of pion spectra captured by a carefully-trained neural network were found to be able to distinguish the nature of the QCD transition even in a simulation scenario which is close to the experiments.

Heavy quark mass effects in parton-to-kaon hadronization probabilities

We examine the relevance of the heavy quarks masses in the perturbative QCD description of hard interactions where charged kaons are produced in the final state. We extract a set of parton-to-kaon hadronization probabilities from a next to leading order QCD global analysis where a general mass variable flavor number scheme accounting for mass effects is implemented. We compare the results with those obtained in the massless approximation and also with those found in the case of final state pions. At variance with the very significant improvement found for the much more precise pion fragmentation phenomenology, the heavy quark mass dependent scheme improves mildly the overall description of current kaon production data. Nevertheless, we find a noticeable reduction in the charm-to-kaon hadronization probability.

Measurement of total and differential cross sections of neutrino and antineutrino coherent π± production on carbon

Neutrino induced coherent charged pion production on nuclei, $\overline{\nu}_\mu A\to\mu^\pm\pi^\mp A$, is a rare inelastic interaction in which the four-momentum squared transfered to the nucleus is nearly zero, leaving it intact. We identify such events in the scintillator of MINERvA by reconstructing |t| from the final state pion and muon momenta and by removing events with evidence of energetic nuclear recoil or production of other final state particles. We measure the total neutrino and antineutrino cross sections as a function of neutrino energy between 2 and 20 GeV and measure flux integrated differential cross sections as a function of $Q^2$, $E_\pi$ and $\theta_\pi$. The $Q^2$ dependence and equality of the neutrino and anti-neutrino cross-sections at finite $Q^2$ provide a confirmation of Adler's PCAC hypothesis.

Study on space-time structure of Higgs jet with the HBT correlation method in e+e- collision at $ \sqrt{{s}}$ s = 250 GeV

The space-time structure of the Higgs boson decay are carefully studied with the HBT correlation method using e$^+$e$^-$ collision events produced through Monte Carlo generator PYTHIA 8.2 at $\sqrt{s}$=250GeV. The Higgs boson jets (Higgs-jets) are identified by H-tag tracing. The measurement of the Higgs boson radius and decay lifetime are derived from HBT correlation of its decay final state pions inside Higgs-jets in the e$^+$e$^-$ collisions events with an upper bound of $R_H \le 1.03\pm 0.05$ fm and $\tau_H \le (1.29\pm0.15)\times 10^{-7}$ fs. This result is consistent with CMS data.

First measurement of the polarization observable E in the [formula omitted] reaction up to 2.25 GeV

First results from the longitudinally polarized frozen-spin target (FROST) program are reported. The double-polarization observable E, for the reaction γ→p→→π+n, has been measured using a circularly polarized tagged-photon beam, with energies from 0.35 to 2.37 GeV. The final-state pions were detected with the CEBAF Large Acceptance Spectrometer in Hall B at the Thomas Jefferson National Accelerator Facility. These polarization data agree fairly well with previous partial-wave analyses at low photon energies. Over much of the covered energy range, however, significant deviations are observed, particularly in the high-energy region where high-L multipoles contribute. The data have been included in new multipole analyses resulting in updated nucleon resonance parameters. We report updated fits from the Bonn–Gatchina, Jülich–Bonn, and SAID groups.

Soft interactions in jet quenching

We study the collisional aspects of jet quenching in a high-energy nuclear collision, especially in the final state pion gas. The jet has a large energy, and acquires momentum transverse to its axis more effectively by multiple soft collisions than by few hard scatterings (as known from analogous systems such as J/ψ production at Hera). Such regime of large E and small momentum transfer corresponds to Regge kinematics and is characteristically dominated by the pomeron. From this insight we estimate the jet quenching parameter in the hadron medium (largely a pion gas) at the end of the collision, which is naturally small and increases with temperature in line with the gas density and compare it to the jet quenching parameter obtained within the quark–gluon plasma (QGP) phase in widely known perturbative approximations. The physics in the quark–gluon plasma/liquid phase is less obvious, and here we revisit a couple of simple estimates that suggest indeed that the pomeron-mediated interactions are very relevant and should be included in analysis of the jet quenching parameter. Finally, since the occasional hard collisions produce features characteristic of a Lèvy flight in the [Formula: see text] plane perpendicular to the jet axis, we suggest one- and two-particle q⊥correlations as interesting experimental probes sensitive to the nature (softness versus hardness) of the interactions of a jet inside the QGP.

Measurement of Coherent Production ofπ±in Neutrino and Antineutrino Beams on Carbon fromEνof 1.5 to 20 GeV

Neutrino-induced coherent charged pion production on nuclei νμA→μ(±)π(∓)A is a rare, inelastic interaction in which a small squared four-momentum |t| is transferred to the recoil nucleus, leaving it intact in the reaction. In the scintillator tracker of MINERvA, we remove events with evidence of particles from nuclear breakup and reconstruct |t| from the final-state pion and muon. We select low |t| events to isolate a sample rich in coherent candidates. By selecting low |t| events, we produce a model-independent measurement of the differential cross section for coherent scattering of neutrinos and antineutrinos on carbon. We find poor agreement with the predicted kinematics in neutrino generators used by current oscillation experiments.

Study on the Energy Dependence of the Source Size of Jets by the HBT Correlation Method in $e^+e^-$ Collisions

The energy dependence of the radii size of jets are studied in detail by the HBT correlation method using Monte Carlo Simulation generator Jetset7.4 to produce 40,000,000 events of e$^+$e$^-$ collisions at $\sqrt s =30$, 50, 70, 91.2, 110, 130, 150 and 170 GeV. The radii of jets are measured using the HBT correlation method with the indistinguishability of identical final state pions. It is found that the average radii of quark-jets and gluon-jets are independent of the c.m. energy of e$^+$e$^-$ collisions. The average radius of quark-jets are obviously larger than that of gluon-jets. The invariable average radii of quark-jets and gluon-jets in e$^+$e$^-$ collisions are obtained at the end of parton evolvement.

Singleπproduction in neutrino-nucleus scattering

We study one pion production in both charged and neutral current neutrino nucleus scattering for neutrino energies below 2 GeV. We use a theoretical model for one pion production at the nucleon level that we correct for medium effects. The results are incorporated into a cascade program that apart from production also includes the pion final state interaction inside the nucleus. Besides, in some specific channels coherent pion production is also possible and we evaluate its contribution as well. Our results for total and differential cross sections are compared with recent data from the MiniBooNE Collaboration. The model provides an overall acceptable description of data, better for NC than for CC channels, although theory is systematically below data. Differential cross sections, folded with the full neutrino flux, show that most of the missing pions lie on the forward direction and at high energies.

Relativistic quantum mechanics and the quark-pair creation model

In the context of a ${}^{3}\phantom{\rule{-0.16em}{0ex}}{P}_{0}$ quark-pair creation model for the process $\ensuremath{\rho}\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi}$, a method is developed for taking relativity into account in the calculation of hadron decays. Following a brief review of relativistic quantum mechanics, an expression is derived for the general relation between a momentum-space, two-particle, instant form wave function in an arbitrary frame and the wave function associated with the c.m. frame. This relation is used to develop relativistic wave functions for the $\ensuremath{\pi}$ and $\ensuremath{\rho}$ mesons. Second quantized state vectors for $\ensuremath{\pi}\ensuremath{\pi}$ and $\ensuremath{\rho}$ states are constructed with the help of these relativistic wave functions. The $\ensuremath{\rho}\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi}$ transition amplitude is obtained by using these state vectors to calculate matrix elements of a second quantized ${}^{3}\phantom{\rule{-0.16em}{0ex}}{P}_{0}$ quark-pair creation operator derived from a scalar Lagrangian density. The amplitude differs from the one obtained using nonrelativistic wave functions in the appearance of Wigner rotations. In spite of the complications arising from these rotations the calculation of the relativistic amplitude is reduced to carrying out a two-dimensional integral. The amplitude is of the same form as one derived from an effective $\ensuremath{\rho}\ensuremath{\pi}\ensuremath{\pi}$ Lagrangian except for the presence of a form factor that depends on the magnitude of the three-momentum of a final-state pion. The shape of the form factor is determined by the relativistic $\ensuremath{\pi}$ and $\ensuremath{\rho}$ wave functions. Using the $\ensuremath{\rho}\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi}$ transition amplitude as a vertex interaction in a relativistic model of $\ensuremath{\pi}\ensuremath{\pi}$ scattering, the $p$-wave, $\ensuremath{\pi}\ensuremath{\pi}$ scattering amplitude is calculated and fit to data by adjusting the interaction strength and the $\ensuremath{\rho}$ bare mass. This leads to a mass shift and decay width for the $\ensuremath{\rho}$ meson. Using nonrelativistic wave functions to calculate the form factor leads to a negligible mass shift, whereas using the relativistic wave functions leads to a bare $\ensuremath{\rho}$ mass of 855.7 MeV, corresponding to a physical $\ensuremath{\rho}$ mass of 775.5 MeV. The quark-pair creation operator strength parameter for the relativistic case is roughly a factor of 2 larger than that for the nonrelativistic case.

P.3.b.003 Characterization of [3H]-LY508869 – a novel selective metabotropic glutamate 2 positive allosteric potentiator ligand

First results from the longitudinally polarized frozen-spin target (FROST) program are reported. The double-polarization observable E, for the reaction γ→p→→π+n, has been measured using a circularly polarized tagged-photon beam, with energies from 0.35 to 2.37 GeV. The final-state pions were detected with the CEBAF Large Acceptance Spectrometer in Hall B at the Thomas Jefferson National Accelerator Facility. These polarization data agree fairly well with previous partial-wave analyses at low photon energies. Over much of the covered energy range, however, significant deviations are observed, particularly in the high-energy region where high-L multipoles contribute. The data have been included in new multipole analyses resulting in updated nucleon resonance parameters. We report updated fits from the Bonn–Gatchina, Jülich–Bonn, and SAID groups.

Hadronic decays of theωmeson

The WASA detector at COSY have measured the ω meson in the reaction channel p + d → 3He + ω. With this data we aim to study two hadronic decays of the ω meson, ω → π+ π− π0 and ω → π+ π−. The goal for the π+π−π0 study is to extract a Dalitz plot of the final state pions. An high statistics Dalitz plot would enable tests of theoretical predictions for the decay mechanism. The goal for the π+π− study is to perform an independent verification of the branching ratio.

Λ-HYPERNUCLEAR PRODUCTION IN $(K_{{\rm{stop}}}^-, \pi)$ REACTIONS

In the present contribution, we report on calculation of the Λ-hypernuclear production induced by the stopped kaon K-. We performed the calculation within the framework of the distorted wave impulse approximation and used chirally motivated transition amplitudes for the microscopic description of the elementary kaon-nucleon process. The sensitivity of the model to several effects was tested with a special attention paid to the impact caused by variations of the initial kaon and final state pion wave functions. The calculated production rates are reported for target nuclei from Lithium to Oxygen.

Pion Production Via Resonance Decay in a Non-extensive Quark-Gluon Medium with Non-additive Energy Composition Rule

Resonance production and decay into pion pairs is simulated in a non-extensive quark matter with multi-particle interactions. Final state pion spectra are found to take the form of the Tsallis distribution, in accordance with measurements. It has also been shown that, if a large number of particles with these multi-particle interactions are constrained to a constant energy hyper-surface in phase space, the one-particle distribution is the Tsallis distribution.