Valence and sea contributions to the nucleon spin

The first moments of the polarized valence parton distribution functions (PDFs) truncated to the wide Bjorken $x$ region $0.004<x<0.7$ are directly (without any fitting procedure) extracted in the next to leading order (NLO) QCD from both COMPASS and HERMES data on pion production in polarized semi-inclusive DIS (SIDIS) experiments. The COMPASS and HERMES data are combined in two ways and two scenarios for the fragmentation functions (FFs) are considered. Two procedures are proposed for an estimation of light sea quark contributions to the proton spin. Both of them lead to the conclusion that these contributions are compatible with zero within the errors.Comment: 14 pages; added reference

In-vitro antitumor activity of new quaternary phosphonium salts, derivatives of 3-hydroxypyridine

© 2018 Wolters Kluwer Health, Inc. All rights reserved. This work presents the results of in-vitro biological activity studies of three novel anticancer agents, phosphonium salts based on the 3-hydroxypyridine scaffold, including one derivative of 4-deoxypyridoxine. Proliferation and viability of cells treated with these compounds was assessed by the colony formation and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays. Effects of the compounds on apoptosis and cell cycle were studied by flow cytometry using annexin V-FITC/propidium iodide and propidium iodide staining, respectively. The influence of the compounds on mitochondrial membrane potential and intracellular reactive oxygen species was evaluated using tetramethyl rhodamine ethyl and DCFHA staining. Western blot analysis was used to study the changes in the expression of Bcl-xL, Bax, and caspase-3 apoptotic proteins. The treatment of ovarian adenocarcinoma cells OVCAR-4 with the tested compounds inhibited the growth and induced cell cycle arrest in the G1 phase. 3-Hydroxypyridine derivatives induced apoptosis by hyperexpression of Bax and caspase-3, whereas 4-deoxypyridoxine derivative induced cell death partly by reactive oxygen species generation and caspase-3 hyperexpression. These results indicate that the quaternary phosphonium salts studied represent potential therapeutic agents for the treatment of ovarian cancer

Search for muoproduction of X(3872) at COMPASS and indication of a new state X˜(3872)

We have searched for exclusive production of exotic charmonia in the reaction μ+N→μ+(J/ψπ+π−)π±N′ using COMPASS data collected with incoming muons of 160 GeV/c and 200 GeV/c momentum. In the J/ψπ+π− mass distribution we observe a signal with a statistical significance of 4.1 σ. Its mass and width are consistent with those of the X(3872). The shape of the π+π− mass distribution from the observed decay into J/ψπ+π− shows disagreement with previous observations for X(3872). The observed signal may be interpreted as a possible evidence of a new charmonium state. It could be associated with a neutral partner of X(3872) with C=−1 predicted by a tetraquark model. The product of cross section and branching fraction of the decay of the observed state into J/ψπ+π− is determined to be 71±28(stat)±39(syst) pb

Search for exclusive photoproduction of Zc±_c^{\pm}(3900) at COMPASS

A search for the exclusive production of the $Z_c^{\pm}(3900)$ hadron by virtual photons has been performed in the channel $Z_c^{\pm}(3900)\rightarrow J/\psi \pi^{\pm}$. The data cover the range from 7 GeV to 19 GeV in the centre-of-mass energy of the photon-nucleon system. The full set of the COMPASS data set collected with a muon beam between 2002 and 2011 has been used. An upper limit for the ratio $BR(Z_c^{\pm}(3900)\rightarrow J/\psi \pi^{\pm} )\times \sigma_{ \gamma~N \rightarrow Z_c^{\pm}(3900)~ N} /\sigma_{\gamma~N \rightarrow J/\psi~ N}$ of $3.7\times10^{-3}$ has been established at the confidence level of 90%.Comment: 8 pages, 3 figures, 1 tabl

Collins and Sivers asymmetries in muonproduction of pions and kaons off transversely polarised proton

Measurements of the Collins and Sivers asymmetries for charged pions and charged and neutral kaons produced in semi-inclusive deep-inelastic scattering of high energy muons off transversely polarised protons are presented. The results were obtained using all the available COMPASS proton data, which were taken in the years 2007 and 2010. The Collins asymmetries exhibit in the valence region a non-zero signal for pions and there are hints of non-zero signal also for kaons. The Sivers asymmetries are found to be positive for positive pions and kaons and compatible with zero otherwise.Comment: 15 pages, 13 figures and 1 tabl

Longitudinal double spin asymmetries in single hadron quasi-real photoproduction at high pTp_T

We measured the longitudinal double spin asymmetries $A_{LL}$ for single hadron muo-production off protons and deuterons at photon virtuality $Q^2$ < 1(GeV/$\it c$)$^2$ for transverse hadron momenta $p_T$ in the range 0.7 GeV/$\it c$ to 4 GeV/$\it c$ . They were determined using COMPASS data taken with a polarised muon beam of 160 GeV/$\it c$ or 200 GeV/$\it c$ impinging on polarised $\mathrm{{}^6LiD}$ or $\mathrm{NH_3}$ targets. The experimental asymmetries are compared to next-to-leading order pQCD calculations, and are sensitive to the gluon polarisation $\Delta G$ inside the nucleon in the range of the nucleon momentum fraction carried by gluons $0.05 < x_g < 0.2$

Measurement of the charged-pion polarisability

The COMPASS collaboration at CERN has investigated pion Compton scattering, $\pi^-\gamma\rightarrow \pi^-\gamma$, at centre-of-mass energy below 3.5 pion masses. The process is embedded in the reaction $\pi^-\mathrm{Ni}\rightarrow\pi^-\gamma\;\mathrm{Ni}$, which is initiated by 190\,GeV pions impinging on a nickel target. The exchange of quasi-real photons is selected by isolating the sharp Coulomb peak observed at smallest momentum transfers, $Q^2<0.0015$\,(GeV/$c$)$^2$. From a sample of 63\,000 events the pion electric polarisability is determined to be $\alpha_\pi\ =\ (\,2.0\ \pm\ 0.6_{\mbox{\scriptsize stat}}\ \pm\ 0.7_{\mbox{\scriptsize syst}}\,) \times 10^{-4}\,\mbox{fm}^3$under the assumption$\alpha_\pi=-\beta_\pi$, which relates the electric and magnetic dipole polarisabilities. It is the most precise measurement of this fundamental low-energy parameter of strong interaction, that has been addressed since long by various methods with conflicting outcomes. While this result is in tension with previous dedicated measurements, it is found in agreement with the expectation from chiral perturbation theory. An additional measurement replacing pions by muons, for which the cross-section behavior is unambigiously known, was performed for an independent estimate of the systematic uncertainty.Comment: Published version: 9 pages, 3 figures, 1 tabl

Spin alignment and violation of the OZI rule in exclusive ω\omega and ϕ\phi production in pp collisions

Exclusive production of the isoscalar vector mesons $\omega$ and $\phi$ is measured with a 190 GeV$/c$ proton beam impinging on a liquid hydrogen target. Cross section ratios are determined in three intervals of the Feynman variable $x_{F}$ of the fast proton. A significant violation of the OZI rule is found, confirming earlier findings. Its kinematic dependence on $x_{F}$ and on the invariant mass $M_{p\mathrm{V}}$ of the system formed by fast proton $p_\mathrm{fast}$ and vector meson $V$ is discussed in terms of diffractive production of $p_\mathrm{fast}V$ resonances in competition with central production. The measurement of the spin density matrix element $\rho_{00}$ of the vector mesons in different selected reference frames provides another handle to distinguish the contributions of these two major reaction types. Again, dependences of the alignment on $x_{F}$ and on $M_{p\mathrm{V}}$ are found. Most of the observations can be traced back to the existence of several excited baryon states contributing to $\omega$ production which are absent in the case of the $\phi$ meson. Removing the low-mass $M_{p\mathrm{V}}$ resonant region, the OZI rule is found to be violated by a factor of eight, independently of $x_\mathrm{F}$.Comment: 23 pages, 13 figures and 5 table

Leading-order determination of the gluon polarisation from semi-inclusive deep inelastic scattering data

Using a novel analysis technique, the gluon polarisation in the nucleon is re-evaluated using the longitudinal double-spin asymmetry measured in the cross section of semi-inclusive single-hadron muoproduction with photon virtuality $Q^2>1~({\rm GeV}/c)^2$. The data were obtained by the COMPASS experiment at CERN using a 160 GeV/$c$ polarised muon beam impinging on a polarised $^6$LiD target. By analysing the full range in hadron transverse momentum $p_{\rm T}$, the different $p_{\rm T}$-dependences of the underlying processes are separated using a neural-network approach. In the absence of pQCD calculations at next-to-leading order in the selected kinematic domain, the gluon polarisation $\Delta g/g$ is evaluated at leading order in pQCD at a hard scale of $\mu^2= \langle Q^2 \rangle = 3 ({\rm GeV}/c)^2$. It is determined in three intervals of the nucleon momentum fraction carried by gluons, $x_{\rm g}$, covering the range $0.04 \!<\! x_{ \rm g}\! <\! 0.28$~ and does not exhibit a significant dependence on $x_{\rm g}$. The average over the three intervals, $\langle \Delta g/g \rangle = 0.113 \pm 0.038_{\rm (stat.)}\pm 0.036_{\rm (syst.)}$ at $\langle x_{\rm g} \rangle \approx 0.10$, suggests that the gluon polarisation is positive in the measured $x_{\rm g}$ range.Comment: 14 pages, 6 figure