Multiplicities of charged pions and unidentified charged hadrons from deep-inelastic scattering of muons off an isoscalar target

Multiplicities of charged pions and unidentified hadrons produced in deep-inelastic scattering were measured in bins of the Bjorken scaling variable $x$, the relative virtual-photon energy $y$ and the relative hadron energy $z$. Data were obtained by the COMPASS Collaboration using a 160 GeV muon beam and an isoscalar target ($^6$LiD). They cover the kinematic domain in the photon virtuality $Q^2$ > 1(GeV/c$)^2$, $0.004 < x < 0.4$, $0.2 < z < 0.85$ and $0.1 < y < 0.7$. In addition, a leading-order pQCD analysis was performed using the pion multiplicity results to extract quark fragmentation functions

Multiplicities of charged kaons from deep-inelastic muon scattering off an isoscalar target

Precise measurements of charged-kaon multiplicities in deep inelastic scattering were performed. The results are presented in three-dimensional bins of the Bjorken scaling variable x, the relative virtual-photon energy y, and the fraction z of the virtual-photon energy carried by the produced hadron. The data were obtained by the COMPASS Collaboration by scattering 160 GeV muons off an isoscalar 6LiD target. They cover the kinematic domain View the MathML source in the photon virtuality, 0.0045 GeV/c2 in the invariant mass of the hadronic system. The results from the sum of the z -integrated K+ and K 12 multiplicities at high x point to a value of the non-strange quark fragmentation function larger than obtained by the earlier DSS fit

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

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. © 2015

The gain in Thick GEM multipliers and its time-evolution

In the context of a project to upgrade the gas photon detectors of COMPASS RICH-1, we have performed an R&D programme aimed to develop photon detectors based on multi-layer arrangements of thick GEM electron multipliers coupled to a CsI photoconverter. For this purpose, thick GEMs have been characterised in detail including the gain performance, its dependance on the geometrical parameters and its time-evolution, a feature exhibited by the gas detectors with open insulator surfaces. The variation due to this evolution drammatically depends on the parameters themselves. In the present article we summarise the outcomes of the studies dedicated to the thick GEM gain and its evolution versus time. We also include a qualitative model which accounts for the peculiar details of the observed thick GEM gain time-evolution

Status of the development of large area photon detectors based on THGEMs and hybrid MPGD architectures for Cherenkov imaging applications

We report about the development status of large area gaseous single photon detectors based on a novel hybrid concept for RICH applications. The hybrid concept combines Thick Gaseous Electron Multipliers (THGEMs) coupled to CsI, working as a photon sensitive pre-amplification stage, and Micromegas, as a multiplication stage. The most recent achievements within the research and development programme consist in the assembly and study of View the MathML source hybrid photon detectors, the optimization of front-end electronics, and engineering towards large area detectors. Hybrid detectors with an active area of View the MathML source have been successfully operated in laboratory conditions and at a CERN PS T10 test beam, achieving effective gains in the order of 105 and good time resolution (View the MathML source); APV25 front-end chips have been coupled to the detector resulting in noise levels lower than 1000 electrons; the production and characterization of View the MathML source THGEMs is ongoing. A set of hybrid detectors with View the MathML source active area is envisaged to upgrade COMPASS RICH-1 at CERN in 2016

Ion back flow reduction in a THGEM based detector2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC)

Cherenkov imaging counters requiring large photosensitive areas, the capability to stand high rates and to operate in magnetic field environments could benefit from the use of micropattern gas detectors based on THick Gaseous Electron Multiplier (THGEM) coupled to a solid state CsI photo-cathode. Nevertheless, the ions produced in the charge multiplication processes, which end up in the CsI photocathode Ion Back Flow (IBF) compromise the detector performance: fast ageing of the CsI photocathode, as well as electron extraction resulting in spurious signals and eventual discharges can occur. To avoid and limit these undesired events, several configurations of THGEM based detectors were considered. Some changing the whole detector geometry by changing the relative position of individual THGEMs to take advantage of the microscopic diffusion properties of electrons and ions. One other configuration changing directly the geometry of the THGEM itself to better create an ion trap, the THCOBRA, is also studied. In this work, experimental and simulation studies of these configurations is performed, particularly concerning IBF and gain. Finite element method calculations and Monte-Carlo simulations are performed for a better understanding of the results

Search for exclusive photoproduction of Z(c)(+/-) (3900) at COMPASS

A search for the exclusive production of the Z(c)(+/-)(3900) hadron by virtual photons has been performed in the channel Z(c)(+/-)(3900). J/Psi pi(+/-). The data cover the range from 7GeV to 19GeV 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)(+/-)(3900)-> J/Psi pi(+/-)) x sigma(gamma N) -> Z(c)(+/-)(3900) N/sigma gamma N -> J/Psi N 3.7 x10(-3) has been established at the confidence level of90%. (C) 2015 The Authors. Published by Elsevier B.V.CERN managemen

Spin alignment and violation of the OZI rule in exclusive omega and 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 xF and on the invariant mass M-pV of the system formed by fast proton p(fast) and vector meson V is discussed in terms of diffractive production of p(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-pV 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-pV resonant region, the OZI rule is found to be violated by a factor of eight, independently of x(F). (C) 2014 CERN for the benefit of the COMPASS Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/).DFG [1102]; ICTP programme for Training and Research in Italian Laboratories (TRIL); German Bundesministerium fur Bildung und Forschung; Czech Republic MEYS Grants [ME492, LA242]; SAIL (CSR), Govt. of India; CERN-RFBR Grants [08-02-91009, 12-02-91500]; Portuguese FCT - Fundacao para a Ciencia e Tecnologia [CERN/FP/109323/2009, CERN/FP/116376/2010, CERN/FP/123600/2011]; MEXT; JSPS [18002006, 20540299, 18540281]; Daiko Foundation; Yamada Foundation; DFG cluster of excellence 'Origin and Structure of the Universe'; EU FP7 (HadronPhysics3) [283286]; Israel Science Foundation; Polish NCN Grant [DEC-2011/01/M/ST2/02350

Domatic Number of a Graph and its Variants (Extended Abstract)

This chapter presents some numerical invariants of graphs that are related to the concept of domination—namely, the domatic number and its variants.. The word domatic was coined from the words dominating and chromatic in the same way as the word smog was composed from the words smoke and fog. This concept is a certain analogy of the chromatic number, but instead of independent sets, dominating sets are used in its definition. A subset D of the vertex set V(G) of an undirected graphs G is called dominating if for each x V(G) − D there exists a vertex yD adjacent to x. A domatic partition of G is a partition of V(G), all of whose classes are dominating sets in G. The maximum number of classes of a domatic partition of G is called the “domatic number” of G and denoted by d(G). R. Laskar and S. T. Hedetniemi have introduced the connected domatic number d, (G) of a graph G. It is the maximum number of classes of a partition of V(G) into dominating sets that induce connected subgraphs of G.DFG [1102]; German Bundesministerium fur Bildung und Forschung; Czech Republic MEYS [ME492, LA242]; SAIL (CSR), Govt. of India; CERN-RFBR [08-02-91009, 12-02-91500]; Portuguese FCT - Fundacao para a Ciencia e Tecnologia [CERN/FP/109323/2009, CERN/FP/116376/2010, CERN/FP/123600/2011]; MEXT; JSPS [18002006, 20540299, 18540281]; Daiko Foundation; Yamada Foundation; DFG; EU [283286]; Israel Science Foundation; Polish NCN [DEC-2011/01/M/ST2/02350