Reaction Pi Research Articles

Pi ^-prightarrow eta ^{(prime )}, pi ^- p in the double-Regge region

The production of eta ^{(prime )}pi pairs constitutes one of the golden channels to search for hybrid exotics, with explicit gluonic degrees of freedom. Understanding the dynamics and backgrounds associated to eta ^{(prime )}pi production above the resonance region is required to impose additional constraints to the resonance extraction. We consider the reaction pi ^-prightarrow eta ^{(prime )} pi ^- ,p measured by COMPASS. We show that the data in 2.4< m_{eta ^{(prime )}pi } < 3.0{mathrm {,GeV}} can be described by amplitudes based on double-Regge exchanges. The angular distribution of the meson pairs, in particular in the eta ' pi channel, can be attributed to flavor singlet exchanges, suggesting the presence of a large gluon content that couples strongly to the produced mesons.

A Perturbative QCD Approach to varvec{pi ^{-}~p rightarrow D^{-}~{varLambda }_{c}^{+}}

We employ the generalized parton picture to analyze the reaction pi ^{-}~p rightarrow D^{-}~{varLambda }_{c}^{+}. Thereby it is assumed that the process amplitude factorizes into one for the perturbatively calculable subprocess bar{u} urightarrow bar{c} c and hadronic matrix elements that can be parameterized in terms of generalized parton distributions for the pi ^-rightarrow D^- and prightarrow {varLambda }_c^+ transitions, respectively. Representing these parton distributions in terms of valence-quark light-cone wave functions for pi , D, p and {varLambda }_c allows us to make numerical predictions for unpolarized differential and integrated cross sections as well as spin observables. In the kinematical region where this approach is supposed to work, i.e. sgtrsim 20 GeV^2 and in the forward hemisphere, the resulting cross sections are of the order of nb. This is a finding that could be of interest in view of plans to measure pi ^{-}~p rightarrow D^{-}~{varLambda }_{c}^{+}, e.g., at J-PARC or COMPASS.

Surface functionality and electrochemical investigations of a graphitic electrode as a candidate for alkaline energy conversion and storage devices.

Graphite is a typical electrocatalyst support in alkaline energy conversion and storage devices such as fuel cells, supercapacitores and lithium ion batteries. The electrochemical behaviour of a graphite electrode in 0.5 M NaOH was studied to elucidate its surface structure/electrochemical activity relationship. Graphite voltammograms are characterized by an anodic shoulder AI and a cathodic peak CI in addition to the oxygen reduction reaction plateaus, PI and PII. AI and CI were attributed to oxidation and reduction of some graphite surface function groups, respectively. Rotating ring disk electrode (RRDE) study revealed two different oxygen types assigned as inner and outer oxygen. The inner oxygen was reduced via the more efficient 4-electron pathway. The outer oxygen reduction proceeded with a lower efficient 2-electron pathway. The calculated percentages of the 4-electron pathway were ranged from 70% to 90%. A full mechanism for the graphite surface function groups changes over the studied potential window was suggested through the combination between the voltammetric, FT-IR and Raman results.

(31)P-MRS of healthy human brain: ATP synthesis, metabolite concentrations, pH, and T1 relaxation times.

The conventional method for measuring brain ATP synthesis is (31)P saturation transfer (ST), a technique typically dependent on prolonged pre-saturation with γ-ATP. In this study, ATP synthesis rate in resting human brain is evaluated using EBIT (exchange kinetics by band inversion transfer), a technique based on slow recovery of γ-ATP magnetization in the absence of B1 field following co-inversion of PCr and ATP resonances with a short adiabatic pulse. The unidirectional rate constant for the Pi → γ-ATP reaction is 0.21 ± 0.04 s(-1) and the ATP synthesis rate is 9.9 ± 2.1 mmol min(-1) kg(-1) in human brain (n = 12 subjects), consistent with the results by ST. Therefore, EBIT could be a useful alternative to ST in studying brain energy metabolism in normal physiology and under pathological conditions. In addition to ATP synthesis, all detectable (31)P signals are analyzed to determine the brain concentration of phosphorus metabolites, including UDPG at around 10 ppm, a previously reported resonance in liver tissues and now confirmed in human brain. Inversion recovery measurements indicate that UDPG, like its diphosphate analogue NAD, has apparent T1 shorter than that of monophosphates (Pi, PMEs, and PDEs) but longer than that of triphosphate ATP, highlighting the significance of the (31)P-(31)P dipolar mechanism in T1 relaxation of polyphosphates. Another interesting finding is the observation of approximately 40% shorter T1 for intracellular Pi relative to extracellular Pi, attributed to the modulation by the intracellular phosphoryl exchange reaction Pi ↔ γ-ATP. The sufficiently separated intra- and extracellular Pi signals also permit the distinction of pH between intra- and extracellular environments (pH 7.0 versus pH 7.4). In summary, quantitative (31)P MRS in combination with ATP synthesis, pH, and T1 relaxation measurements may offer a promising tool to detect biochemical alterations at early stages of brain dysfunctions and diseases.

Phosphate ion targeted colorimetric and fluorescent probe and its use to monitor endogeneous phosphate ion in a hemichannel-closed cell.

Fluorescent probe 1, the first inorganic phosphate (Pi) targeted colorimetric and fluorescent probe to detect endogenous Pi in hemichannel-closed cells, has been developed. Probe 1 undergoes a unique Pi induced hydrolytic reaction in DMSO-HEPES (V/V = 9:1) buffered (0.02 M, pH 7.4) solutions that produces a colorimetric change associated with a 62 nm red-shift in the UV-vis absorption maximum and up to a 780-fold enhancement in the fluorescence intensity. The mechanistic proposal that these spectroscopic changes are associated with reaction Pi with 1 to form coumarin gains support from the results of theoretical calculations and mass spectrometry studies. Observations made in fluorescence imaging studies with HeLa cells and C. elegans show that 1 can be employed to monitor Pi production in vivo caused by apyrase-catalyzed ATP hydrolysis. Moreover, probe 1 was utilized to show that apoptosis of hemichannel-closed Sf9 cells is caused by Inx3 promoted dephosphorylation of Akt (RAC serine/threonine-protein kinase), leading to an elevation of the concentration of Pi. Overall, the study has produced the first fluorescent sensor 1 for endogenous inorganic phosphate. Moreover, the utility of 1 for measuring Pi release in vitro has been demonstrated and utilized to elucidate the mechanism of Inx3 action in hemichannel-closed Sf9 cells.

Pion photoproduction off the proton in a gauge-invariant chiral unitary framework

We investigate pion photoproduction off the proton in a manifestly gauge-invariant chiral unitary extension of chiral perturbation theory. In a first step, we consider meson-baryon scattering taking into account all next-to-leading order contact interactions. The resulting low-energy constants are determined by a fit to s-wave pion-nucleon scattering and the low-energy data for the reaction pi- p --> eta n. To assess the theoretical uncertainty, we perform two different fit strategies. Having determined the low-energy constants, we then analyse the data on the s-wave multipole amplitudes E0+ of pion and eta photoproduction. These are parameter-free predictions, as the two new low-energy constants are determined by the neutron and proton magnetic moments.

Partial wave analysis of theπ−π−π+andπ−π0π0systems and the search for aJPC=1−+meson

A partial wave analysis (PWA) of the pi-pi-pi+ and pi-pi0pi0 systems produced in the reaction pi- p -> (3pi)-p at 18 GeV/c was carried out using an isobar model assumption. This analysis is based on 3.0M pi-pi0pi0 events and 2.6M pi-pi-pi+ events and shows production of the a2(1320), pi2(1670) and \pi(1800) mesons. An earlier analysis of 250K pi-pi-pi+ events from the same experiment showed possible evidence for a J^{PC}=1^{-+}$ exotic meson with a mass of 1.6 GeV/c^2 decaying into rho pi. In this analysis of a higher statistics sample of the (3pi)- system in two charged modes we find no evidence of an exotic meson.

Proposed search for a(0)(0)(980)-f(0)(980) mixing in polarization phenomena.

The K+ and K0 meson mass difference induces the mixing of the a(0)(0)(980) and f(0)(980) resonances, the amplitude of which, between the K+K- and K0(-)K(0) thresholds, is large in magnitude, of the order of m(K)m(2)(K0)sqrt[-m(2)(K+)] approximately sqrt[alpha] m(2)(K), and possesses the phase sharply varying by about 90 degrees. We suggest performing the polarized target experiments on the reaction pi(-)p-->etapi(0)n at high energy in which the fact of the existence of a(0)(0)(980)-f(0)(980) mixing can be unambiguously and very easily established through the presence of a strong jump in the azimuthal asymmetry of the etapi(0) S wave production cross section near the K(-)K thresholds. The presented estimates of the polarization effect to be expected in experiment are to a great extent model independent.

Dynamics of the pi(-)p-->pi(0)pi(0)n reaction for p(pi(-))

Data are presented for the reaction pi(-)p-->pi(0)pi(0)n in the range from threshold to p(pi(-))=750 MeV/c. The systematics of the data and multipole analyses are examined for sensitivity to a f(0)(600) ("sigma") meson. A one-pion-exchange mechanism is found to be very weak, or absent. The reaction appears to become dominated by sequential pi(0) decays through the Delta(1232) resonance as the beam momentum increases, along with substantial interference effects from several competing mechanisms.

Determination of the quadratic slope parameter in eta-->3pi(0) decay.

We have determined the quadratic slope parameter alpha for eta-->3pi(0) to be alpha = -0.031(4) from a 99% pure sample of 10(6)eta-->3pi(0) decays produced in the reaction pi(-)p-->n(eta) close to the eta threshold using the Crystal Ball detector at the AGS. The result is four times more precise than the present world data and disagrees with current chiral perturbation theory calculations by about four standard deviations.

Observation of exotic meson production in the reaction pi- p --> eta'pi- p at 18 GeV/c.

An amplitude analysis of an exclusive sample of 5765 events from the reaction pi- p-->eta'pi- p at 18 GeV/c is described. The eta'pi- production is dominated by natural parity exchange and by three partial waves: those with J(PC) = 1(-+), 2(++), and 4(++). A mass-dependent analysis of the partial-wave amplitudes indicates the production of the a2(1320) meson as well as the a4(2040) meson, observed for the first time decaying to eta'pi-. The dominant, exotic (non- qq) 1(-+) partial wave is shown to be resonant with a mass of 1.597+/-0.010(+0.045)(-0.010) GeV/c2 and a width of 0.340+/-0.040+/-0.050 GeV/c2. This exotic state, the pi1(1600), is produced with a t dependence which is different from that of the a2(1320) meson, indicating differences between the production mechanisms for the two states.

Reaction pi +p--> pi + pi 0p near threshold and chiral symmetry breaking.

We have measured total cross sections for the reaction [pi][sup +][ital p][r arrow][pi][sup +][pi][sup [minus]][ital p] at incident pion kinetic energies of 190, 200, 220, 240, and 260 MeV. We use this result to deduce a new value of the chiral symmetry breaking parameter, [xi]=[minus]0.25[plus minus]0.10, in a global constrained fit of the five [pi][pi][ital N] near-threshold amplitudes. Consequently, we report new soft pion model values for the [ital s]-wave [pi][pi] scattering lengths.

Analysis of the reaction pi +d-->pp to 500 MeV.

An energy-dependent and set of single-energy partial-wave analyse have been completed for the reaction ${\mathrm{\ensuremath{\pi}}}^{+}$d\ensuremath{\rightarrow}pp. Amplitudes are presented for pion laboratory kinetic energies from threshold to 500 MeV. These results are compared with those found in other recent analyses. We comment on the present database and make suggestions for future experiments.

Relations between unnatural exchange amplitudes in the reaction pi N--> pi + pi -N with transversely polarized target.

We study pion production $\ensuremath{\pi}N\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}N$ on polarized targets for dipion masses below 1000 MeV where the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ system is produced predominantly with dipion spins $J=0$ ($S$ wave) and $J=1$ ($P$ wave). We find that pion-exchange amplitudes can be expressed in terms of ${A}_{1}$-exchange amplitudes and data on polarized targets. Extrapolations of pion-exchange amplitudes to the unphysical region to obtain $\ensuremath{\pi}\ensuremath{\pi}$ scattering phase shifts thus depend on the model for ${A}_{1}$-exchange amplitudes. The usual assumption that ${A}_{1}$-exchange amplitudes all vanish is ruled out by the data on polarized targets.

Anisotropy function for pion-proton elastic scattering

By using the generalised Chou-Yang model and the experimental data on pi -p elastic scattering at 200 GeV/c, the anisotropic function which reflects the non-isotropic nature of elastic scattering is compared for the reaction pi -p to pi -p.

Enzymic characteristics of ecto-phosphoprotein phosphatase in goat epididymal intact spermatozoa.

Intact washed spermatozoa from goat cauda epididymis possess an ecto-phosphoprotein phosphatase that causes dephosphorylation of phosphoserine and phosphothreonine residues of exogenous 32P-labelled histones. The cell-bound ecto-enzyme has high affinity for proteins (histones, casein, phosvitin, and protamine) rather than phosphate esters, such as p-nitrophenyl phosphate, beta-glycerophosphate, AMP, and ATP. The activity of the enzyme is inhibited by 4 mM Mg2+, Ca2+, Mn2+, or Co2+. Pi (10 mM), NaF (10 mM), and Zn2+ (1 mM) inhibit the enzyme by approximately 50, 35, and 100%, respectively. Polyamines such as spermine and spermidine at 10 mM each caused significant inhibition (60 and 30%, respectively) of the cell-bound phosphoprotein phosphatase activity, whereas cAMP, orthovanadate, and calmodulin (with or without Ca2+) had no appreciable effect. Under the standard assay conditions, spermatozoa remain intact as evidenced by assay of cytosolic enzyme markers. Both the washed and "native" intact spermatozoa showed nearly the same specific activity of the ectoenzyme. The product of the reaction (Pi) was found in the extracellular medium. Sonication doubled the enzymic activity of the intact cells. The specific activity of the enzyme was nearly fourfold higher in the intact forwardly motile cells than the "composite" spermatozoa. These data provide further support for the localization of a phosphoprotein phosphatase on the external surface of spermatozoa and that the ectoenzyme may have a role in the regulation of flagellar motility.

Inclusive ϕ-meson production in π-Be interactions at 85 GeV/c

The inclusive reaction pi -Be to phi +X has been studied for 0<or=xF<or=0.4 and pT2<or=3.0 (GeV/c)2 at 85 GeV/c incident momentum. Differential cross sections d sigma /dxF and d sigma /dpT2 are presented and it is found that the naive parton model as used by Daum et al. (1983) does not give an adequate description of the data. Furthermore, no significant excess of strange particles is found associated with phi production. The inclusive cross section for the reaction is calculated and found to be 1826+or-29 mu b per Be nucleus. Assuming a linear dependence on the atomic mass number, A, this corresponds to a value of 202+or-3 mu b per nucleon for the above process.

Π-p bremsstrahlung at 300 MeV/c

Cross sections are presented for the reaction pi -p to pi -p gamma at square root s=1234 MeV.

Gluon admixtures in the 0-neutral mesons: a survey of the quark-line rule

Gluon admixtures in neutral pseudoscalar mesons are considered to test the quark-line rule for the reactions pi p to eta Delta , eta n, pp to pi pi eta , etc. It is found that the experimental data on these reactions support the possibility of a small gluonium admixture in the eta and eta ' states. The results have also been used to predict some electromagnetic decay rates of the pseudoscalar glueball states l(1440) along with those of eta and eta '.

Pole plus cut model and recent polarisation results for the reaction π-p to π0n

A pole plus cut model has been used to fit simultaneously the data on d sigma /dt, P(t) and Delta sigma for the reaction pi -p to pi 0n at high energies; the most recent measurements of polarisation are included in the fit.