Browsing by Author "Stolarski, M"
Now showing 1 - 7 of 7
Results Per Page
Sort Options
- Azimuthal asymmetries of charged hadrons produced in high-energy muon scattering off longitudinally polarised deuteronsPublication . COMPASS collaboration (225 authors); Bordalo, P; Franco, C; Nunes, A S; Quaresma, M; Quintans, C; Ramos, S; Silva, L; Stolarski, MSingle hadron azimuthal asymmetries in the cross sections of positive and negative hadron production in muon semi-inclusive deep inelastic scattering off longitudinally polarised deuterons are determined using the 2006 COMPASS data and also all deuteron COMPASS data. For each hadron charge, the dependence of the azimuthal asymmetry on the hadron azimuthal angle $\phi$ is obtained by means of a five-parameter fitting function that besides a $\phi$-independent term includes four modulations predicted by theory: $\sin\phi$, $\sin 2 \phi$, $\sin 3\phi$ and $\cos\phi$. The amplitudes of the five terms have been first extracted for the data integrated over all kinematic variables. In further fits, the $\phi$-dependence is determined as a function of one of three kinematic variables (Bjorken-$x$, fractional energy of virtual photon taken by the outgoing hadron and hadron transverse momentum), while disregarding the other two. Except the $\phi$-independent term, all the modulation amplitudes are very small, and no clear kinematic dependence could be observed within experimental uncertainties.
- Collins and Sivers asymmetries in muonproduction of pions and kaons off transversely polarised protonsPublication . COMPASS collaboration (209 authors); Bordalo, P; Franco, C; Nunes, A S; Quaresma, M; Quintans, C; Ramos, S; Silva, L; Stolarski, MMeasurements 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.
- Longitudinal double spin asymmetries in single hadron quasi-real photoproduction at high $p_T$Publication . COMPASS collaboration (210 authors); Bordalo, P; Franco, C; Nunes, A S; Quaresma, M; Quintans, C; Ramos, S; Silva, L; Stolarski, MWe 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 $0.05 < x_g < 0.2$.
- Resonance Production and $\pi\pi$ S-wave in $\pi^- + p \rightarrow \pi^- \pi^- \pi^+ + p_{recoil}$ at 190 GeV$/c$Publication . COMPASS collaboration (210 authors); Bordalo, P; Franco, C; Nunes, A S; Quaresma, M; Quintans, C; Ramos, S; Silva, L; Stolarski, MThe COMPASS collaboration has collected the currently largest data set on diffractively produced π-π-π+ final states using a negative pion beam of 190 GeV/c momentum impinging on a stationary proton target. This data set allows for a systematic partial-wave analysis in 100 bins of three-pion mass, 0.5
- Search for exclusive photoproduction of Z$_c^{\pm}$(3900) at COMPASSPublication . COMPASS collaboration (209 authors); Bordalo, P; Franco, C; Nunes, Ana Sofia; Quaresma, M; Quintans, C; Ramos, S; Silva, L; Stolarski, MA search for the exclusive production of the Zc±(3900) hadron by virtual photons has been performed in the channel Zc±(3900)→J/ψπ± . 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(Zc±(3900)→J/ψπ±)×σγN→Zc±(3900)N/σγN→J/ψN of 3.7×10−3 has been established at the confidence level of 90%.
- Sivers asymmetry extracted in SIDIS at the hard scales of the Drell–Yan process at COMPASSPublication . COMPASS collaboration (225 authors); Bordalo, P; Franco, C; Nunes, A S; Quaresma, M; Quintans, C; Ramos, S; Silva, L; Stolarski, MEight proton transverse-spin-dependent azimuthal asymmetries are extracted in four regions of the photon virtuality Q2 from the COMPASS 2010 semi-inclusive hadron measurements in deep inelastic muon–nucleon scattering. These Q2 regions correspond to the four regions of the di-muon mass Q2 used in the ongoing analyses of the COMPASS Drell–Yan measurements, which allows for a future direct comparison of the nucleon transverse-momentum-dependent parton distribution functions extracted from these two alternative measurements. In addition, for the azimuthal asymmetries induced by the Sivers transverse-momentum-dependent parton distribution function various two-dimensional kinematic dependences are presented. The integrated Sivers asymmetries are found to be positive with an accuracy that appears to be sufficient to test the sign change of the Sivers function predicted by Quantum Chromodynamics.
- Transverse target spin asymmetries in exclusive $\rho^0$ muoproductionPublication . COMPASS collaboration (213 authors); Bordalo, P; Franco, C; Nunes, A.S; Quaresma, M; Quintans, C; Ramos, S; Silva, L; Stolarski, MExclusive production of $\rho^0$ mesons was studied at the COMPASS experiment by scattering 160 GeV/$c$ muons off transversely polarised protons. Five single-spin and three double-spin azimuthal asymmetries were measured as a function of $Q^2$, $x_{Bj}$, or $p_{T}^{2}$. The $\sin \phi_S$ asymmetry is found to be $-0.019 \pm 0.008(stat.) \pm 0.003(syst.)$. All other asymmetries are also found to be of small magnitude and consistent with zero within experimental uncertainties. Very recent calculations using a GPD-based model agree well with the present results. The data is interpreted as evidence for the existence of chiral-odd, transverse generalized parton distributions.