Jets

Back to Physics Poster

Strong Coupling Constant alpha-s

    The value of the coupling constant alpha-s of the strong interactions was determined using jet measurements in deep inelastic lepton-proton scattering.  
The jets were selected in a frame of reference where the production mechanisms are the photon-gluon-fusion process and the QCD-Compton process. Both processes contain gluon-quark vertices and are therefore sensitive to alpha-s.  
    The quark and gluon distributions of the proton were taken from parameterizations based on structure function measurements.  
Inclusive jet cross sections were fitted and alpha-s was extracted using the jet transverse energy and alternatively the square root of the virtuality Q2 of the photon as the renormalization scale. The precision of the determined values are very competitive with the world average value as extracted by S.Bethke.  

Gluon Distribution of the Proton

    In a direct extraction of the gluon distribution of the proton, 2-jet events from deep inelastic positron-proton scattering were analysed. Apart from the photon-gluon-fusion process, which allows the gluon to be determined, the QCD Compton process contributes to this 2-jet production. In the latter process the scattered quark from the proton radiates a gluon that causes the second jet. In order to determine the gluon distribution of the proton, the contribution of the QCD Compton events is subtracted from the jet production using a simultaneous fit with the proton structure function data at a fixed value of the scale Q2. The value of the strong coupling constant was set to the world average value and was allowed to vary within the corresponding errors. 
The figure shows the gluon distribution of the proton. The jet measurement complements the gluon extraction from the proton structure function data alone and provides a measurement up to gluon momenta of x = 0.1. 
Homepage
Mission
Detector
Scientific Results
Organisation
Fast Navigator
framed version
last updated by H1 webmaster on 19/05/98