Eta Meson Production Research Articles

Charged current neutrino and antineutrino induced eta production off the nucleon

The charged current (anti)neutrino induced eta production from the nucleons is studied in a model based on the effective Lagrangians to evaluate the contribution from the nonresonant and resonant diagrams. The contribution from the nonresonant background terms has been obtained using a microscopic model based on the SU(3) chiral Lagrangians. The contribution from the resonant diagrams due to the low lying ${S}_{11}(1535)$, ${S}_{11}(1650)$, and ${P}_{11}(1710)$ resonances has been evaluated using an effective phenomenological Lagrangian with its parameters determined from the experimental values of their branching ratios and decay widths to the $N\ensuremath{\eta}$ channel. The model is first used to reproduce satisfactorily the experimental data from the MAINZ and JLab on the total cross sections for the photo- and electro- production of $\ensuremath{\eta}$ mesons, which fixes the model parameters in the vector current interaction. The partially conserved axial vector current (PCAC) hypothesis and generalized Goldberger-Treiman relation are used to fix the parameters of the axial vector current interaction. The model is then applied to study the weak production of eta mesons induced by the neutrinos and antineutrinos, and predicts the numerical values for the ${Q}^{2}$-distribution, $\ensuremath{\eta}$-momentum distribution, and the total cross section for the reactions ${\ensuremath{\nu}}_{\ensuremath{\mu}}+n\ensuremath{\rightarrow}{\ensuremath{\mu}}^{\ensuremath{-}}+p+\ensuremath{\eta}$ and ${\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}+p\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}+n+\ensuremath{\eta}$ in the energy region up to 2 GeV. It is found that the photo, electro, and (anti)neutrino induced production of eta mesons is dominated by the contribution from the ${S}_{11}(1535)$ resonance. The results discussed in this work are relevant for the present and future accelerator experiments like MicroBooNE, T2K, NOvA, MINERvA, T2-HyperK, and DUNE as well as for the atmospheric neutrino experiments.

Experimental Study of the Production of Eta Mesons and Kaons in Cu + Au Interactions at 200 GeV

The first traces of the formation of strongly interacting quark–gluon plasma (sQGP) were found in central collisions of heavy nuclei (A + A) in experiments on the RHIC collider. The quenching of hadron jets, which is seen as a reduction in the yield of particles in A + A collisions relative to their yield in proton–proton collisions, is one observable sign of sQGP formation. Asymmetrical Cu + Au collisions at 200 GeV, which are characterized by a distinct geometry of nucleus overlap that differs from the geometry in symmetrical collision systems (Au + Au or Cu + Cu), are of special interest in systematic studies of the quenching of hadron jets. The results are presented from measuring invariant transverse-momentum spectra and nuclear modification factors of mesons containing strange quarks in Cu + Au collisions at 200 GeV.

Neutral pion and eta meson production in p\u2013Pb collisions at sqrt{s_{mathrm{NN}}} \xa0=\xa05.02\xa0TeV

Neutral pion and eta meson invariant differential yields were measured in non-single diffractive p–Pb collisions at sqrt{s_{mathrm{NN}}} = 5.02 TeV with the ALICE experiment at the CERN LHC. The analysis combines results from three complementary photon measurements, utilizing the PHOS and EMCal calorimeters and the Photon Conversion Method. The invariant differential yields of pi ^{0} and eta meson inclusive production are measured near mid-rapidity in a broad transverse momentum range of 0.3< p_{mathrm{T}} < 20 hbox { GeV}/c and 0.7< p_{mathrm{T}} < 20hbox { GeV}/c, respectively. The measured eta /pi ^{0} ratio increases with p_{mathrm{T}} and saturates for p_{mathrm{T}} > 4 hbox {GeV}/c at 0.483 pm 0.015_{mathrm{stat}} pm 0.015_{mathrm{sys}}. A deviation from m_{mathrm{T}} scaling is observed for p_{mathrm{T}}< 2 hbox {GeV}/c. The measured eta /pi ^{0} ratio is consistent with previous measurements from proton-nucleus and pp collisions over the full p_{mathrm{T}} range. The measured eta /pi ^{0} ratio at high p_{mathrm{T}} also agrees within uncertainties with measurements from nucleus–nucleus collisions. The pi ^{0} and eta yields in p–Pb relative to the scaled pp interpolated reference, R_{{mathrm{pPb}}}, are presented for 0.3 < p_{mathrm{T}}< 20 hbox {GeV}/c and 0.7 < p_{mathrm{T}}< 20 hbox {GeV}/c, respectively. The results are compared with theoretical model calculations. The values of R_{{mathrm{pPb}}} are consistent with unity for transverse momenta above 2 hbox {GeV}/c. These results support the interpretation that the suppressed yield of neutral mesons measured in Pb–Pb collisions at LHC energies is due to parton energy loss in the hot QCD medium.

The light speed versus the observer: the Kennedy\u2013Thorndike test from GRAAL-ESRF

High precision tests of the light speed constancy for all observers as a empirical basis of Special Relativity have continuously been among the goals of advanced experimental studies. Based on the Compton edge method proposed by us (Gurzadyan and Margarian in Phys Scr 53:513, 1996), a constraint on the one-way light speed isotropy and Lorentz invariance violation has been obtained at the dedicated GRAAL experiment at European Synchrotron Radiation Facility (ESRF, Grenoble) (Gurzadyan et al. in Mod Phys Lett A 20:1, 2005, Nuovo Cimento 122:515, 2007, Proceedings of the XII M. Grossmann meeting on general relativity, vol B. World Scientific, p 1495. arXiv:1004.2867, 2012; Bocquet et al. in Phys Rev Lett 104:241601, 2010). Using the GRAAL data we now get a new constraint on one of the key tests of Special Relativity—the Kennedy–Thorndike experiment (Kennedy and Thorndike in Phys Rev 42:400, 1932) in probing light speed invariance with respect to the velocity of the observer (apparatus). Our analysis takes advantage of GRAAL’s setup where two separate energy scales are involved: first, via the position of the Compton edge determining the light speed in the reference frame of incident 6 GeV electrons within the tagging system, second, in the calorimeter via the 1.27 MeV photons of the ^{22}Na source. The two energy scales are engaged to each other through production of eta mesons by tagged laser Compton backscattered gamma -rays. The accuracy of the calibration and stability of energies reached in each section enable us to obtain the limit of 7 times 10^{-12} for the Kennedy–Thorndike test, which improves the currently existing limits by three orders of magnitude.

Pi ^{0} and eta meson production in proton-proton collisions at sqrt{s}=8 TeV

An invariant differential cross section measurement of inclusive pi ^{0} and eta meson production at mid-rapidity in pp collisions at sqrt{s}=8 TeV was carried out by the ALICE experiment at the LHC. The spectra of pi ^{0} and eta mesons were measured in transverse momentum ranges of 0.3<p_{ text{ T }} <35 text{ GeV/c } and 0.5<p_{ text{ T }} <35 text{ GeV/c }, respectively. Next-to-leading order perturbative QCD calculations using fragmentation functions DSS14 for the pi ^{0} and AESSS for the eta overestimate the cross sections of both neutral mesons, although such calculations agree with the measured eta /pi ^0 ratio within uncertainties. The results were also compared with PYTHIA 8.2 predictions for which the Monash 2013 tune yields the best agreement with the measured neutral meson spectra. The measurements confirm a universal behavior of the eta /pi ^0 ratio seen for NA27, PHENIX and ALICE data for pp collisions from sqrt{s}=27.5 GeV to sqrt{s}=8 TeV within experimental uncertainties. A relation between the pi ^{0} and eta production cross sections for pp collisions at sqrt{s}=8 TeV is given by m_{ text{ T }} scaling for p_{ text{ T }} >3.5 text{ GeV/c }. However, a deviation from this empirical scaling rule is observed for transverse momenta below p_{ text{ T }} <3.5 text{ GeV/c } in the eta /pi ^0 ratio with a significance of 6.2sigma .

Production of {pi ^0} and eta mesons up to high transverse momentum in pp collisions at 2.76 TeV

The invariant differential cross sections for inclusive pi ^{0} and eta mesons at midrapidity were measured in pp collisions at sqrt{s}=2.76 TeV for transverse momenta 0.4<p_{mathrm {T}}<40 GeV/c and 0.6<p_{mathrm {T}}<20 GeV/c, respectively, using the ALICE detector. This large range in p_{mathrm {T}} was achieved by combining various analysis techniques and different triggers involving the electromagnetic calorimeter (EMCal). In particular, a new single-cluster, shower-shape based method was developed for the identification of high-p_{mathrm {T}} neutral pions, which exploits that the showers originating from their decay photons overlap in the EMCal. Above 4 GeV/c, the measured cross sections are found to exhibit a similar power-law behavior with an exponent of about 6.3. Next-to-leading-order perturbative QCD calculations differ from the measured cross sections by about 30% for the pi ^{0}, and between 30–50% for the eta meson, while generator-level simulations with PYTHIA 8.2 describe the data to better than 10–30%, except at p_{mathrm {T}}<1 GeV/c. The new data can therefore be used to further improve the theoretical description of pi ^{0} and eta meson production.

Coupled channels approach to photo-meson production on the nucleon

The coupled channels Lagrangian approach of the Giessen model (GiM) for meson production on the nucleon is discussed and applied to a selected set of meson production channels on the nucleon, ranging from πN → πN and γ N → π N , eta-production and associated strangeness production to 2π N channels in the resonance energy region. We present an updated coupled-channel analysis of eta-meson production including all recent photoproduction data on the proton. The dip structure observed in the differential cross sections at c.m. energies W=1.68 GeV is explained by destructive interference between the S 11 (1535) and S 11 (1560) states, not confirming the postulated sharp state. Kaon production on the nucleon is investigated in K Λ and K Σ exit channels. The approach to 2π N production has been significantly improved by using the isobar approximation with σN and π Δ1232 intermediate states. Three-body unitarity is maintained up to interference between the isobar subchannels. We obtain R σ N (1440)=27+4 -9 % and R π Δ (1440)=12+5 -3 % for the for the σ N and π Δ1232 decay branching ratios of N *(1440) respectively. The extracted π N inelasticities and reaction amplitudes are consistent with the results of other groups.

Momentum distribution of N* in nuclei

Due to its dominance in the low energy eta-nucleon interaction, the S11 N$^*$(1535) resonance enters as an important ingredient in the analyses of experiments aimed at finding evidence for the existence of eta-mesic nuclei. The static properties of the resonance get modified inside the nucleus and its momentum distribution is used in deciding these properties as well as the kinematics in the analyses. Here we show that given the possibility for the existence of an N$^*$-$^3$He quasibound state, the relative momentum distribution of an N$^*$ and $^3$He inside such a $^4$He is narrower than that of neutron-$^3$He in $^4$He. Results for the N$^*$-$^{24}$Mg system are also presented. The present exploratory work could be useful in motivating searches of exotic N$^*$-nucleus quasibound states as well as in performing analyses of eta meson production data.

Search forη-mesic4He with the WASA-at-COSY detector

An exclusive measurement of the excitation function for the dd->3Heppi- reaction was performed at the Cooler Synchrotron COSY-Juelich with the WASA-at-COSY detection system. The data were taken during a slow acceleration of the beam from 2.185 GeV/c to 2.400 GeV/c crossing the kinematic threshold for the eta meson production in the dd->4He-eta reaction at 2.336 GeV/c. The corresponding excess energy with respect to the 4He-eta system varied from -51.4MeV to 22MeV. The integrated luminosity in the experiment was determined using the dd->3Hen reaction. The shape of the excitation function for the dd->3Heppi- was examined. No signal of the 4He-eta bound state was observed. An upper limit for the cross-section for the bound state formation and decay in the process dd->(4He-eta)bound->3Heppi- was determined on the 90% confidence level and it varies from 20nb to 27nb for the bound state width ranging from 5MeV to 35MeV, respectively.

η-meson production in the resonance-energy region

We perform an updated coupled-channel analysis of eta-meson production including all recent photoproduction data on the proton. The dip observed in the differential cross sections at c.m. energies W=1.68 GeV is explained by destructive interference between the $S_{11}(1535)$ and $S_{11}(1560)$ states. The effect from $P_{11}(1710)$ is found to be small but still important to reproduce the correct shape of the differential cross section. For the $\pi^- N \to \eta N$ scattering we suggest a reaction mechanism in terms of the $S_{11}(1535)$, $S_{11}(1560)$, and $P_{11}(1710)$ states. Our conclusion on the importance of the $S_{11}(1535)$, $S_{11}(1560)$, and $P_{11}(1710)$ resonances in the eta-production reactions is in line with our previous results. No strong indication for a narrow state with a width of 15 MeV and the mass of 1680 MeV is found in the analysis. $\eta N$ scattering length is extracted and discussed.

Accessing baryon to meson transition distribution amplitudes in meson production in association with a high invariant mass lepton pair at GSI-FAIR withP¯ANDA

Nucleon antinucleon annihilation into a near backward (or forward) produced meson and a high invariant mass lepton pair admits a factorized description in terms of antinucleon (or nucleon) distribution amplitudes and nucleon to meson (or antinucleon to meson) transition distribution amplitudes. We estimate the cross section of backward (and forward) pion and eta meson production in association with a high invariant mass lepton pair for the kinematical conditions of GSI-FAIR. The cross sections are found to be large enough to be measured with the PANDA detector. Interesting phenomenological applications of the approach are thus expected.

Investigation of near-threshold eta-meson production in the reaction π − p→ ηn

Differential and total cross sections for eta-meson production in the reaction π−p → ηn were measured within the experimental program eta-meson physics implemented in the pion channel of the synchrocyclotron of the Petersburg Nuclear Physics Institute (PNPI, Gatchina). These measurements were performed at incident-pion momenta (700, 710, 720, and 730 MeV/c) in the vicinity of the threshold for the process under study by using the neutral-meson spectrometer designed and created at the Meson Physics Laboratory of PNPI. It is shown that, in the immediate vicinity of the threshold (685 MeV/c), the process of eta-meson production proceeds predominantly via S11(1535)-resonance formation followed by the decay S11(1535) → ηn (the respective branching fraction is Br ≈ 60%), but that, as the momentum of incident pions increases, the role of the D wave becomes ever more important. A detailed analysis of this effect indicates that it is due to the increasing contribution of the D13(1520) resonance. Although the branching fraction of the decay of this resonance through the ηn channel is assumed to be very small (BR ≈ 0.24%), the effect is enhanced owing to the interference between the D wave and the dominant resonance S11(1535).

Production of neutral pions and eta-mesons in pp collisions measured with ALICE

Invariant cross sections for neutral pions and η mesons in pp collisions at , 2.76 and 7 TeV were measured by the ALICE detector at the LHC. Next-to-leading order perturbative QCD calculations describe the π0 and η spectra at 0.9 TeV, but overestimate the measured cross sections at 2.76 and 7 TeV. The measured η/π0 ratio is consistent with mT scaling at 2.76 TeV. At 7 TeV, indications for a violation of mT scaling were found.

η-meson production in proton-proton collisions at excess energies of40and72MeV

The production of eta mesons in proton-proton collisions has been studied using the WASA detector at the CELSIUS storage ring at excess energies of Q = 40 MeV and Q = 72 MeV. The eta was detected t ...

Upper limit of the total cross section for thepn→pnη′reaction

The upper limit of the total cross section for the pn --> pn eta' reaction has been determined near the kinematical threshold in the excess energy range from 0 to 24 MeV. The measurement was performed using the COSY-11 detector setup, a deuteron cluster target, and the proton beam of COSY with a momentum of 3.35 GeV/c. The energy dependence of the upper limit of the cross section was extracted exploiting the Fermi momenta of nucleons inside the deuteron. Comparison of the determined upper limit of the ratio R_eta' = sigma(pn --> pn eta') / sigma(pp --> pp eta') with the corresponding ratio for eta-meson production does not favor the dominance of the N*(1535) resonance in the production process of the eta' meson and suggests nonidentical production mechanisms for eta and eta' mesons.

Level crossing of particle–hole and mesonic modes in eta-mesonic nuclei

We study eta-meson properties in the infinite nuclear matter and in atomic nuclei with an emphasis on effects of the eta coupling to N ∗ ( 1535 ) -nucleon–hole modes. The N ∗ ( 1535 ) resonance, which dominates the low-energy eta-nucleon scattering, can be seen as a chiral partner of the nucleon. The change of the chiral mass gap between the N ∗ and the nucleon in a nuclear medium has an impact on the properties of the eta-nucleus system. If the N ∗ -nucleon mass gap decreases with a density increase (chiral symmetry restoration) the calculations show the existence of the resonance state at the energy about 60 MeV and two bound eta-nucleus states with the binding energies about − 80 MeV . These states can have strong effect on predicted cross sections of the 12C ( γ , p ) 11B reaction with eta-meson production.

η-meson production in nucleon-nucleon collisions within an effective Lagrangian model

We investigate the pp → ppη and pn → pnη reactions within an effective Lagrangian model for laboratory kinetic energies ranging from very close to the eta meson production threshold to about 10 GeV. Production amplitudes include contributions from the mechanism of excitation, propagation and decay of N ∗ (1535), N ∗ (1650), and N ∗ (1710) baryonic resonances. The initial interaction between two incoming nucleons is modeled by the exchange of π, ρ, ω and σ mesons where the vertex parameters are taken to be the same as those used in the previous applications of this model. Parameters of the resonance vertices also have been taken from our earlier studies wherever applicable. Calculations have been done for total as well as differential η production cross sections. To describe the data for energies closer to the production threshold final state interactions among the out-going particles have been included by means of a generalized WatsonMigdal method. Terms corresponding to the excitation of N ∗ (1535) resonance and pion exchange process dominate the cross sections. With a single set of vertex parameters our model is able to describe the available data well on total cross sections for beam energies ranging from close to threshold to upto 10 GeV.

Mechanism of Near-Threshold Production of theηMeson

Measurements of the analyzing power for the pp-->pp eta reaction have been performed at excess energies of Q=10 and 36 MeV. The determined analyzing power is essentially consistent with zero, implying dominance of the s wave at both excess energies. The angular dependence of the analyzing power, combined with the isospin dependence of the total cross section for the eta meson production in nucleon-nucleon collisions, reveal that the excitation of the nucleon to the S11(1535) resonance is predominantly due to the exchange of the pi meson between the colliding nucleons.

CELSIUS PHYSICS: PAST, PRESENT AND FUTURE

The experimental program on meson production in light-ion collisions at the CELSIUS cooler/storage ring of the The Svedberg Laboratory in Uppsala, is reviewed. Production of pions and eta-mesons have been studied in pp and pd collisions using the PROMICE/WASA detector. This program is now continued at CELSIUS with the WASA4π detector together with studies of meson decays.

Production ofπ0and η mesons at large transverse momenta inπ−pandπ−Beinteractions at515GeV/c

We present results on the production of high transverse momentum pizero and eta mesons in pi-p and pi-Be interactions at 515 GeV/c. The data span the kinematic ranges 1 < p_T < 11 GeV/c in transverse momentum and -0.75 < y < 0.75 in rapidity. The inclusive pizero cross sections are compared with next-to-leading order QCD calculations and to expectations based on a phenomenological parton-k_T model.