Double-spin asymmetries for production of charged pions and kaons in semi-inclusive deep-inelastic muon scattering have been measured by the COMPASS experiment at CERN. The data, obtained by ...scattering a 160 GeV muon beam off a longitudinally polarised NH
3 target, cover a range of the Bjorken variable
x between 0.004 and 0.7. A leading order evaluation of the helicity distributions for the three lightest quarks and antiquark flavours derived from these asymmetries and from our previous deuteron data is presented. The resulting values of the sea quark distributions are small and do not show any sizable dependence on
x in the range of the measurements. No significant difference is observed between the strange and antistrange helicity distributions, both compatible with zero. The integrated value of the flavour asymmetry of the helicity distribution of the light-quark sea,
Δ
u
¯
−
Δ
d
¯
, is found to be slightly positive, about 1.5 standard deviations away from zero.
A search for supersymmetry or other new physics resulting in similar final states is presented using a data sample of 4.73 inverse femtobarns of pp collisions collected at sqrt(s)=7 TeV with the CMS ...detector at the LHC. Fully hadronic final states are selected based on the variable MT2, an extension of the transverse mass in events with two invisible particles. Two complementary studies are performed. The first targets the region of parameter space with medium to high squark and gluino masses, in which the signal can be separated from the standard model backgrounds by a tight requirement on MT2. The second is optimized to be sensitive to events with a light gluino and heavy squarks. In this case, the MT2 requirement is relaxed, but a higher jet multiplicity and at least one b-tagged jet are required. No significant excess of events over the standard model expectations is observed. Exclusion limits are derived for the parameter space of the constrained minimal supersymmetric extension of the standard model, as well as on a variety of simplified model spectra.
The inclusive double-spin asymmetry, MathML equation, has been measured at COMPASS in deep-inelastic polarised muon scattering off a large polarised NH sub(3) target. The data, collected in the year ...2007, cover the range MathML equation, 0.004<x<0.7 and improve the statistical precision of MathML equation by a factor of two in the region x<0.02. The new proton asymmetries are combined with those previously published for the deuteron to extract the non-singlet spin-dependent structure function MathML equation. The isovector quark density, Delta q sub(3)(x,Q super(2)), is evaluated from a NLO QCD fit of MathML equation. The first moment of Delta q sub(3) is in good agreement with the value predicted by the Bjorken sum rule and corresponds to a ratio of the axial and vector coupling constants MathML equation.
The longitudinal polarisation transfer from muons to and $\bar{\varLambda}$ hyperons, $D_{\varLambda(\bar{\varLambda})}$ , has been studied in deep-inelastic scattering off an unpolarised isoscalar ...target at the COMPASS experiment at CERN. The spin transfers to and $\bar{\varLambda}$ produced in the current fragmentation region exhibit different behaviours as a function of x and x sub(F ). The measured x and x sub(F )dependences of D sub(LL ) super( )are compatible with zero, while $D_{\bar{\varLambda}}$ tends to increase with x sub(F ), reaching values of 0.4-0.5. The resulting average values are D sub(LL ) super( )= -0.012c0.047c0.024 and $D_{\bar{\varLambda}}$ = 0.249c0.056c0.049. These results are discussed in the frame of recent model calculations.
The longitudinal double spin asymmetry A1ρ for exclusive leptoproduction of ρ0 mesons, μ+N→μ+N+ρ, is studied using the COMPASS 2002 and 2003 data. The measured reaction is incoherent exclusive ρ0 ...production on polarised deuterons. The Q2 and x dependence of A1ρ is presented in a wide kinematical range, 3×10-3<Q2< 7 (GeV/c)2 and 5×10-5<x<0.05. The results presented are the first measurements of A1ρ at small Q2 (Q2< 0.1 (GeV/c)2) and small x (x<3×10-3). The asymmetry is in general compatible with zero in the whole kinematical range.
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