Search

A study of the production of prompt J/ψ mesons contained in jets in proton-proton collisions at s=8TeV is presented. The analysis is based on data corresponding to an integrated luminosity of 19.1 fb−1 collected with the CMS detector at the LHC. For events with at least one observed jet, the angular separation between the J/ψ meson and the jet is used to test whether the J/ψ meson is part of the jet. The analysis shows that most prompt J/ψ mesons having energy above 15 GeV and rapidity |y

A measurement is presented of differential cross sections for t-channel single top quark and antiquark production in proton-proton collisions at a centre-of-mass energy of 13 mml:mspace> by the CMS experiment at the LHC. From a data set corresponding to an integrated luminosity of 35.9 mml:mspacefb-1, events containing one muon or electron and two or three jets are analysed. The cross section is measured as a function of the top quark transverse momentum (pT), rapidity, and polarisation angle, the charged lepton pT and rapidity, and the pT of the W boson from the top quark decay. In addition, the charge ratio is measured differentially as a function of the top quark, charged lepton, and W boson kinematic observables. The results are found to be in agreement with standard model predictions using various next-to-leading-order event generators and sets of parton distribution functions. Additionally, the spin asymmetry, sensitive to the top quark polarisation, is determined from the differential distribution of the polarisation angle at parton level to be 0.440 +/- 0.070, in agreement with the standard model prediction.

This paper reports on a search for an extended scalar sector of the standard model, where a new CP-even (odd) boson decays to a Z boson and a lighter CP-odd (even) boson, and the latter further decays to a b quark pair. The Z boson is reconstructed via its decays to electron or muon pairs. The analysed data were recorded in proton- proton collisions at a center-of-mass energy √s = 13 TeV, collected by the CMS experiment at the LHC during 2016, corresponding to an integrated luminosity of 35.9 fb−1. Data and predictions from the standard model are in agreement within the uncertainties. Upper limits at 95% confidence level are set on the production cross section times branching fraction, with masses of the new bosons up to 1000 GeV. The results are interpreted in the context of the two-Higgs- doublet model.

Anisotropies in the initial energy density distribution of the quark-gluon plasma created in high energy heavy ion collisions lead to anisotropies in the azimuthal distributions of the final-state particles known as collective anisotropic flow. Fourier harmonic decomposition is used to quantify these anisotropies. The higher-order harmonics can be induced by the same order anisotropies (linear response) or by the combined influence of several lower order anisotropies (nonlinear response) in the initial state. The mixed highe-rorder anisotropic flow and nonlinear response coefficients of charged particles are measured as functions of transverse momentum and centrality in PbPb collisions at nucleon-nucleon center-of-mass energies root s(NN) = 2.76 and 5.02 TeV with the CMS detector. The results are compared with viscous hydrodynamic calculations using several different initial conditions, aswell asmicroscopic transport model calculations. None of the models provides a simultaneous description of the mixed higher-order flow harmonics and nonlinear response coefficients.

A measurement of the production cross section of top quark pairs in association with two b jets (tt¯bb¯) is presented using data collected in proton-proton collisions at s√= 13 TeV by the CMS detector at the LHC corresponding to an integrated luminosity of 35.9 fb−1. The cross section is measured in the all-jet decay channel of the top quark pair by selecting events containing at least eight jets, of which at least two are identified as originating from the hadronization of b quarks. A combination of multivariate analysis techniques is used to reduce the large background from multijet events not containing a top quark pair, and to help discriminate between jets originating from top quark decays and other additional jets. The cross section is determined for the total phase space to be 5.5 ± 0.3 (stat) +1.6−1.3 (syst) pb and also measured for two fiducial tt¯bb¯ definitions. The measured cross sections are found to be larger than theoretical predictions by a factor of 1.5-2.4, corresponding to 1-2 standard deviations.

The transverse momentum (P-T) spectra of inclusively produced A c P baryons are measured via the exclusive decay channel Lambda(+)(c) -> pK(-)pi(+) using the CMS detector at the LHC. Spectra are measured as a function of transverse momentum in proton-proton (pp) and lead-lead (PbPb) collisions at a nucleonnucleon center-of-mass energy of 5.02TeV. The measurement is performed within the Lambda(+)(c) rapidity interval vertical bar Y vertical bar < 1 in the p(T) range of 5-20GeV/c in pp and 10-20GeV/c in PbPb collisions. The observed yields of Lambda(+)(c) for p(T) of 10-20 GeV/c suggest a suppression in central PbPb collisions compared to pp collisions scaled by the number of nucleon-nucleon (NN) interactions. The Lambda(+)(c)/D-0 production ratio in pp collisions is compared to theoretical models. In PbPb collisions, this ratio is consistent with the result from pp collisions in their common p-r range.

A search in an all-jet final state for new massive resonances decaying to WW, WZ, or ZZ boson pairs using a novel analysis method is presented. The analysis is performed on data corresponding to an integrated luminosity of 77.3 fb$^{; ; ; -1}; ; ; $ recorded with the CMS experiment at the LHC at a centre-of-mass energy of 13 TeV. The search is focussed on potential resonances with masses above 1.2 TeV, where the decay products of each W or Z boson are expected to be collimated into a single, large-radius jet. The signal is extracted using a three-dimensional maximum likelihood fit of the two jet masses and the dijet invariant mass, yielding an improvement in sensitivity of up to 30% relative to previous search methods. No excess is observed above the estimated standard model background. In a heavy vector triplet model, spin-1 Z' and W' resonances with masses below 3.5 and 3.8 TeV, respectively, are excluded at 95% confidence level. In a narrow-width bulk graviton model, upper limits on cross sections are set between 27 and 0.2 fb for resonance masses between 1.2 and 5.2 TeV, respectively. The limits presented in this paper are the best to date in the dijet final state.

A search forWWproduction from double-parton scattering processes using same-charge electron-muon and dimuon events is reported, based on proton-proton collision data collected at a center-of-mass energy of 13 TeV. The analyzed data set corresponds to an integrated luminosity of 77.4 fb-1, collected using the CMS detector at the LHC in 2016 and 2017. Multivariate classifiers are used to discriminate between the signal and the dominant background processes. A maximum likelihood fit is performed to extract the signal cross section. This leads to the first evidence for WW production via double-parton scattering, with a significance of 3.9 standard deviations. The measured inclusive cross section is 1.41 +/- 0.28 (stat) +/- 0.28 (syst) pb.

A measurement is presented of differential cross sections for t-channel single top quark and antiquark production in proton-proton collisions at a centre-of-mass energy of 13 mml:mspace> by the CMS experiment at the LHC. From a data set corresponding to an integrated luminosity of 35.9 mml:mspacefb-1, events containing one muon or electron and two or three jets are analysed. The cross section is measured as a function of the top quark transverse momentum (pT), rapidity, and polarisation angle, the charged lepton pT and rapidity, and the pT of the W boson from the top quark decay. In addition, the charge ratio is measured differentially as a function of the top quark, charged lepton, and W boson kinematic observables. The results are found to be in agreement with standard model predictions using various next-to-leading- order event generators and sets of parton distribution functions. Additionally, the spin asymmetry, sensitive to the top quark polarisation, is determined from the differential distribution of the polarisation angle at parton level to be 0.440 +/- 0.070, in agreement with the standard model prediction.

Central exclusive and semiexclusive production of pi(+)pi(-) pairs is measured with the CMS detector in proton-proton collisions at the LHC at center-of-mass energies of 5.02 and 13 TeV. The theoretical description of these non-perturbative processes, which have not yet been measured in detail at the LHC, poses a significant challenge to models. The two pions are measured and identified in the CMS silicon tracker based on specific energy loss, whereas the absence of other particles is ensured by calorimeter information. The total and differential cross sections of exclusive and semiexclusive central pi(+)pi(-) production are measured as functions of invariant mass, transverse momentum, and rapidity of the pi(+)pi(-) system in the fiducial region defined as transverse momentum p(T)(p) > 0.2GeV and pseudorapidity vertical bar eta(p)vertical bar < 2.4. The production cross sections for the four resonant channels f(0)(500), rho(0) (770), f(0)(980), and f(2)(1270) are extracted using a simple model. These results represent the first measurement of this process at the LHC collision energies of 5.02 and 13 TeV.

A combination of four searches for new physics involving signatures with at least one photon and large missing transverse momentum, motivated by generalized models of gauge-mediated supersymmetry (SUSY) breaking, is presented. All searches make use of proton-proton collision data at t root s = 13 TeV, which were recorded with the CMS detector at the LHC in 2016, and correspond to an integrated luminosity of 35.9 fb(-1. Signatures with at least one photon and large missing transverse momentum are categorized into events with two isolated photons, events with a lepton and a photon, events with additional jets, and events with at least one high-energy photon. No excess of events is observed beyond expectations from standard model processes, and limits are set in the context of gauge-mediated SUSY. Compared to the individual searches, the combination extends the sensitivity to gauge-mediated SUSY in both electroweak and strong production scenarios by up to 100 GeV in neutralino and chargino masses, and yields the first CMS result combining various SUSY searches in events with photons root s = 13 TeV.

A search is presented for τ slepton pairs produced in proton-proton collisions at a center-of-mass energy of 13 TeV. The search is carried out in events containing two τ leptons in the final state, on the assumption that each τ slepton decays primarily to a τ lepton and a neutralino. Events are considered in which each τ lepton decays to one or more hadrons and a neutrino, or in which one of the τ leptons decays instead to an electron or a muon and two neutrinos. The data, collected with the CMS detector in 2016 and 2017, correspond to an integrated luminosity of 77.2 fb−1. The observed data are consistent with the standard model background expectation. The results are used to set 95% confidence level upper limits on the cross section for τ slepton pair production in various models for τ slepton masses between 90 and 200 GeV and neutralino masses of 1, 10, and 20 GeV. In the case of purely left-handed τ slepton production and decay to a τ lepton and a neutralino with a mass of 1 GeV, the strongest limit is obtained for a τ slepton mass of 125 GeV at a factor of 1.14 larger than the theoretical cross section.

A study of the B+→J/ψΛ¯¯¯¯p decay using proton-proton collision data collected at s√ = 8 TeV by the CMS experiment at the LHC, corresponding to an integrated luminosity of 19.6 fb−1, is presented. The ratio of branching fractions B(B+→J/ψΛ¯¯¯¯p)/B(B+→J/ψK∗(892)+) is measured to be (1.054 ± 0.057(stat) ± 0.035(syst) ± 0.011(B))%, where the last uncertainty reflects the uncertainties in the world-average branching fractions of Λ¯¯¯¯ and K*(892) + decays to reconstructed final states. The invariant mass distributions of the J/ψΛ¯¯¯¯, J/ψp, and Λ¯¯¯¯p systems produced in the B+→J/ψΛ¯¯¯¯p decay are investigated and found to be inconsistent with the pure phase space hypothesis. The analysis is extended by using a model-independent angular amplitude analysis, which shows that the observed invariant mass distributions are consistent with the contributions from excited kaons decaying to the Λ¯¯¯¯p system.

A search for a light charged Higgs boson (H+) decaying to a W boson and a CP-odd Higgs boson (A) in final states with eμμ or μμμ is performed using data from pp collisions at √s=13 TeV, recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of 35.9 fb−1. In this search, it is assumed that the H+ boson is produced in decays of top quarks, and the A boson decays to two oppositely charged muons. The presence of signals for H+ boson masses between 100 and 160 GeV and A boson masses between 15 and 75 GeV is investigated. No evidence for the production of the H+ boson is found. Upper limits at 95% confidence level are obtained on the combined branching fraction for the decay chain, t→bH+→bW+A→bW+μ+μ−, of 1.9×10−6 to 8.6×10−6, depending on the masses of the H+ and A bosons. These are the first limits for these decay modes of the H+ and A bosons.

Zbirka eseja kroz koje autor popularizira znanost, s naglaskom na fiziku, te kritičko mišljenje. Kroz primjere iz osobnog života i reminiscencije na djetinjstvo kontekstualiziraju se najrazličitiji fizikalni koncepti, od termodinamike i dinamike fluida, do opće i specijalne teorije relativnosti. Priče su osobne i pomalo duhovite, a čak i ona najteža fizika objašnjena je na pitak i zabavan, ali i iznad svega točnan i znanstveno precizan način.

A search for decays of the Higgs and Z boson to pairs of J/psi or Y(nS)(n = 1, 2, 3) mesons, with their subsequent decay to mu(+)mu(-) pairs, is presented. The analysis uses data from proton-proton collisions at root s = 13 TeV, collected with the CMS detector at the LHC in 2017 and corresponding to an integrated luminosity of 37.5 fb(-1). While an observation of such a decay with this sample would indicate the presence of physics beyond the standard model, no significant excess is observed. Upper limits at 95% confidence level are placed on the branching fractions of these decays. In the J/psi pair channel, the limits are 1.8 x 10(-3) and 2.2 x 10(-6) for the Higgs and Z boson, respectively, while in the combined Y(nS) pair channel, the limits are 1.4 x 10(-3) and 1.5 x 10(-6), respectively, when the mesons from the Higgs and Z boson decay are assumed to be unpolarized. When fully longitudinal and transverse polarizations are considered the limits reduce by about 22-29% and increase by about 10-13%, respectively.

A search for narrow low-mass resonances decaying to quark-antiquark pairs is presented. The search is based on proton-proton collision events collected at 13 TeV by the CMS detector at the CERN LHC. The data sample corresponds to an integrated luminosity of 35.9 fb−1, recorded in 2016. The search considers the case where the resonance has high transverse momentum due to initial-state radiation of a hard photon. To study this process, the decay products of the resonance are reconstructed as a single large-radius jet with two-pronged substructure. The signal would be identified as a localized excess in the jet invariant mass spectrum. No evidence for such a resonance is observed in the mass range 10 to 125 GeV. Upper limits at the 95% confidence level are set on the coupling strength of resonances decaying to quark pairs. The results obtained with this photon trigger strategy provide the first direct constraints on quark-antiquark resonance masses below 50 GeV obtained at a hadron collider.

A search for new massive particles decaying into a pair of Higgs bosons in proton-proton collisions at a center-of-mass energy of 13 TeV is presented. Data were collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb−1. The search is performed for resonances with a mass between 0.8 and 3.5 TeV using events in which one Higgs boson decays into a bottom quark pair and the other decays into two W bosons that subsequently decay into a lepton, a neutrino, and a quark pair. The Higgs boson decays are reconstructed with techniques that identify final state quarks as substructure within boosted jets. The data are consistent with standard model expectations. Exclusion limits are placed on the product of the cross section and branching fraction for generic spin- 0 and spin-2 massive resonances. The results are interpreted in the context of radion and bulk graviton production in models with a warped extra spatial dimension. These are the best results to date from searches for an HH resonance decaying to this final state, and they are comparable to the results from searches in other channels for resonances with masses below 1.5 TeV.

A search for the production of events containing three W bosons predicted by the standard model is reported. The search is based on a data sample of proton-proton collisions at a center-of-mass energy of 13 TeV recorded by the CMS experiment at the CERN LHC and corresponding to a total integrated luminosity of 35.9 fb−1. The search is performed in final states with three leptons (electrons or muons), or with two same-charge leptons plus two jets. The observed (expected) significance of the signal for W±W±W∓ production is 0.60 (1.78) standard deviations, and the ratio of the measured signal yield to that expected from the standard model is 0.34 +0.62/−0.34. Limits are placed on three anomalous quartic gauge couplings and on the production of massive axionlike particles.

A search for the production of events containing three W bosons predicted by the standard model is reported. The search is based on a data sample of proton-proton collisions at a center-of-mass energy of 13 TeV recorded by the CMS experiment at the CERN LHC and corresponding to a total integrated luminosity of 35.9 fb−1. The search is performed in final states with three leptons (electrons or muons), or with two same-charge leptons plus two jets. The observed (expected) significance of the signal for W±W±W∓ production is 0.60 (1.78) standard deviations, and the ratio of the measured signal yield to that expected from the standard model is 0.34+0.62−0.34. Limits are placed on three anomalous quartic gauge couplings and on the production of massive axionlike particles.

A search for long-lived particles decaying to displaced, nonprompt jets and missing transverse momentum is presented. The data sample corresponds to an integrated luminosity of 137 fb(-1) of proton-proton collisions at a center-of-mass energy of 13 TeV collected by the CMS experiment at the CERN LHC in 2016-2018. Candidate signal events containing nonprompt jets are identified using the timing capabilities of the CMS electromagnetic calorimeter. The results of the search are consistent with the background prediction and are interpreted using a gauge-mediated supersymmetry breaking reference model with a gluino next-to-lightest supersymmetric particle. In this model, gluino masses up to 2100, 2500, and 1900 GeV are excluded at 95% confidence level for proper decay lengths of 0.3, 1, and 100 m, respectively. These are the best limits to date for such massive gluinos with proper decay lengths greater than similar to 0.5 m.

Results are presented for an extraction of the top quark Yukawa coupling from top quark-antiquark (t¯t) kinematic distributions in the lepton plus jets final state in proton-proton collisions, based on data collected by the CMS experiment at the LHC at √s=13 TeV, corresponding to an integrated luminosity of 35.8 fb−1. Corrections from weak boson exchange, including Higgs bosons, between the top quarks can produce large distortions of differential distributions near the energy threshold of t¯t production. Therefore, precise measurements of these distributions are sensitive to the Yukawa coupling. Top quark events are reconstructed with at least three jets in the final state, and a novel technique is introduced to reconstruct the t¯t system for events with one missing jet. This technique enhances the experimental sensitivity in the low invariant mass region, Mt¯t. The data yields in Mt¯t, the rapidity difference |yt−y¯t|, and the number of reconstructed jets are compared with distributions representing different Yukawa couplings. These comparisons are used to measure the ratio of the top quark Yukawa coupling to its standard model predicted value to be 1.07+0.34−0.43 with an upper limit of 1.67 at the 95% confidence level.

“Blesimetar” je osobni blog jednog fizičara i bundžije (kako autor sam sebe titulira) koji se od 2010. objavljuje na portalu Jutarnjeg lista. U njemu se obrađuju teme koje su pobudile interes široke publike zbog svoje kontroverznosti, kao što su cijepljenje i homeopatija, ali i nekim konstantnim "znanstveno neutemeljenim" pojavama u društvu, kao što je igranje lota. Sve teme bi se moglo svesti na četiri osnovne kategorije: znanost, obrazovanje, skepticizam (kao kritičko mišljenje, ne filozofska grana), te psihologija (točnije, pokušaj razumjevanja zašto su ljudi po prirodi šašavi). Svim temama autor pristupa sa znanstvenog stajališta, temeljito i sa znanstveno provjerljivim argumentima, istovremeno koristeći jezik koji svatko može razumijeti. Ova knjiga sadrži tekstove objavljene u "Blesimetru" od njegovog početka 8. veljače 2010. do prvog (neuspjelog) pokušaja prestanka, 12. lipnja 2012

Within the previously developed Dubna-Mainz-Taipei meson-exchange model, the singularity structure of the ¼N scattering amplitudes has been investigated. For all partial waves up to F waves and c.m. energies up to W ~ 2 GeV, the T-matrix poles have been calculated by three different techniques: analytic continuation into the complex energy plane, speed-plot, and regularization method. For all 4-star resonances except the S11(1535), we find very good agreement between the analytic continuation and the regularization method. We also find resonance poles for resonances that are not so well established, but in these cases the pole positions and residues obtained by analytic continuation can substantially differ from the results predicted by the speed-plot and regularization methods.

Eta meson production in the proton– proton scattering is dominated by the low-mass meson exchange. We present a brief study on how the type of the exchanged mesons within coupled-channel and multi-resonance model influences the scattering observables. We show under which circumstances the eta exchange may explain the shape of the observed cross-sections, and present a few selected results: total cross-section in the full energy range, and the proton– proton energy distribution at 15.5 MeV.

It is argued in [1] that when the strong coupling to the K Lambda channel is considered, Breit-Wigner mass of the lightest orbital excitation of the nucleon N(1535) shifts to a lower value. The new value turned out to be smaller than the mass of the lightest radial excitation N(1440), which effectively solved the long-standing problem of conventional constituent quark models. In this Comment we show that it is not the Breit-Wigner mass of N(1535) that is decreased, but its bare mass. [1] B. C. Liu and B. S. Zou, Phys. Rev. Lett. 96, 042002 (2006).

Partial wave scattering matrix poles, representing a link between experimental data and quark-model resonant states, contain two sources of ambiguities and uncertainties: fundamental (continuum ambiguities) and factual (quality of input data). Furthermore, two types of scattering matrix singularities are identifed when energy dependence of partial wave data is implemented through a coupled-channel model: bare and dressed Green function poles. Both types of uncertainties, for both type of poles, are strongly reduced by extending the data base in the direction of increasing the number of accessible and utilized channels. As we strongly suspect that the quality of data in one channel is of less importance then the overall number of used channels, new measurements in inelastic meson-nucleon sector are recommended, and recognized as a task of prime importance.

Dvije model-neovisne metode razvijene su nametanjem fizikalnih zahtjeva na općeniti oblik matrice raspršenja. Nametanjem unitarnosti razvili smo metodu kojom se mogu dobiti Breit-Wignerovi parametri iz T matrice parametrizirani kao polovi K matrice. Nametanjem analitičnosti razvili smo tzv. regularizacijsku metodu kojom je moguće odrediti polove matrice raspršenja znajući samo njezine vrijednosti na realnoj energijskoj osi. Obje metode ne zahtijevaju dodatno modeliranje pozadine ili drugih doprinosa, dosta su jednostavnije od ostalih modela u literaturi, a regularizacijska metoda je i mnogo preciznija od standardne metode (tzv. speed plot) koja se koristi za istu svrhu

The method of avoiding continuum ambiguities in a pion-nucleon partial wave analysis in the inelastic region by using the coupled channel formalism is discussed. The very number of poles of the analytic partial wave T-matrix, their position in the complex energy plane and their residues depend strongly on the number of channels used for constraining the free parameters of the model. The criteria for determining the minimal number of poles needed to describe the given input are discussed, and the procedure of increasing the number of poles necessary for simultaneously describing additional channels is introduced. The interplay of the pole structure and the number of inelastic channels is demonstrated for the P11 partial wave for the case of inclusion of pi N -> eta N channel into the coupled channel partial wave analysis in addition to the full pi N elastic data base. The N(1710) P11 resonance is a clear example when the continuum ambiguity, present when solely the pi N elastic scattering data are analyzed, is spontaneously eliminated by increasing the number of resonant states when the piN -> eta N channel data are included in the framework of coupled channel partial wave analysis formalism.

The pole structure of the P11 pion-nucleon partial wave is examined with the emphasis on the 1700 MeV energy domain. The mechanism of eliminating continuum ambiguities in pion-nucleon partial wave analyses by using the coupled channel formalism, presented elsewhere for the piN -> etaN channel, is applied for the piN -> K Lambda channel, with the aim to clarify the issue whether physical reality requires none (VPI/GWU), one (KH80, CMB, Kent, Pittsburgh/ANL, Giessen), or possibly two (Zagreb) poles of the partial wave T-matrix in the 1700 MeV range. The role of second inelastic channel for resolving the dilemma is demonstrated. It is pointed out that the experiments for the piN -> K Lambda and piN -> K Sigma channel, extremely important for the 1700 MeV range, are old and inconclusive so an urgent need for remeasuring that channel is stressed., 4 pages, 5 figures; talk held at NSTAR 2005 in Tallahassee, FL

In spite of prolonged polemics, the agreement on the existence of N(1710) P11 resonance has not until now been reached, and the Particle Data Group declares it as a 3-star resonance only. We show that the proper inclusion of inelastic channels in the coupled-channel formalism indisputably demands the existence of N(1710) P11 state, and that it presumably stays "hidden" within the continuum ambiguity of any typical single channel partial wave analyses. Consequently, its Particle Data Group confidence rating should be raised to a 4-star resonance.

given on the link.

The new and improved treatment of eta meson exchange diagrams turns out to be essential in order to fully describe both total cross-sections and, in particular, the challenging pp invariant mass distributions. Contrary to other approaches, the eta meson contribution in our model is comparable with the leading pi meson exchange term, and using the phenomenological final state interaction we have no need to include other mesons, like rho and omega, in order to obtain good agreement with experiment.

The partial wave T-matrices for the piN, etaN and pi^2N channels have been obtained within the framework of the coupled channel model using the piN elastic and piN - etaN data base as input. It has been shown that for the P11partial wave an equally good representation of the experimental data (namely the T_{; ; ; pi N, pi N}; ; ; and T_{; ; ; pi N, eta N}; ; ; T-matrices) can be obtained using either three, or four poles for the Green function propagator. However, the three Green function pole solution is not acceptable due to the structure of the extracted resonances. The two out of four P11 resonances, those lying in the energy range 1700 MeV < M_R < 1800 MeV, are poorly determined, but they seem to be strongly inelastic. The inclusion of other inelastic channels is needed to determine masses and widths of missing resonances with greater precision.

Dvočestične amplitude raspršenja dobivene unitarnim višerezonantnim modelom s vezanim kanalima primjenjene su u analizi višečestičnih procesa. Najjednostavniji višečestični proces koji se u potpunosti može odrediti (korištenjem) amplituda je pp --> pp eta. Dobar opis eksperimentalnih podataka postignut je korištenjem s-vala i za energije udaljene od praga. Također se pokazuje da vrlo važan doprinos ima međudjelovanje u konačnom stanju (FSI). Za dobar opis eksperimentalnih podataka izbor modela FSI je ključan, posebno u slučaju pp podsistema. Svi dosadašnji teorijski modeli predviđali su dominaciju izmjene rho mezona. Nasuprot tome, destruktivna interferencija prilikom izmjene pi i eta mezona vrlo dobro opisuje totalni udarni presjek.

Vrijednosti parametara nukleonskih rezonancija dobivenih u višekanalnom, višerezonantnom i unitarnom modelu, korištene su za opis inelasticnog raspršenja piona na protonu za kanal KL. Uz pretpostavku da se proces može dobro opisati koristeci koherentni zbroj jedno-rezonantnih dijagrama za S_11, P_11 i P_13 parcijalne valove pokazano je da proracun zasnovan na standardnim parametrima iznesenim u [3] ne daje dobro slaganje posebno s oblikom diferencijalnog udarnog presjeka [4, 5]. Slaganje ukupnog udarnog presjeka s mjerenim vrijednostima je dobro. Korištenje novopredloženih parametara, a i u potpunosti otklanja neslaganje. Potrebno je, stoga, vrijednost standardno prihvacenih parametara S_11, P_11 i P_13 rezonancija uskladiti s novim saznanjima.

Dvočestične amplitude raspršenja dobivene u višekanalnom, višerezonantnom i unitarnom modelu primjenjene su u analizi višečestičnih procesa.

To check the applicability of the Zagreb-UCLA-ANL meson-nucleon T matrices, we have calculated the total cross section for p p --> p p eta process up to 4.5 GeV kinetic energy. Since there is no successful treatment of the initial and the final state interaction, comparing with experimental data posses large uncertainties. Hence, we have aligned our result with published theoretical results of relevant models, calculated in the simplest approximations.

Saznanja o međudjelovanju eta mezona i alfa čestice u procesu eta produkcije u deuteron-deuteron raspršenju u blizini praga reakcije smo primijenili na traženje kuta miješanja pi0 i eta mezona u svrhu određivanja stupnja lomljenja nabojne simetrije. Osnova metode sastoji se u analitičkom produženju amlitude raspršenja eta mezona na energije ispod praga reakcije gdje se nalaze jedini eksperimentalni podaci koji ukazuju na mogućnost postojanja tog efekta.