Strong Coupling Constant from the Photon Structure Function

TL;DR

The value of the strong coupling constant alpha(s) is extracted from a single-parameter pointlike fit to the photon structure function F(gamma)(2) at large x and Q(2) and from a first five-parameters full (pointlike and hadronic)fit to the complete F(Gamma)( 2) data set taken at PETRA, TRISTAN, and LEP.

Abstract

We extract the value of the strong coupling constant alpha_s from a single-parameter pointlike fit to the photon structure function F_2^gamma at large x and Q^2 and from a first five-parameter full (pointlike and hadronic) fit to the complete F_2^gamma data set taken at PETRA, TRISTAN, and LEP. In next-to-leading order and the MSbar renormalization and factorization schemes, we obtain alpha_s(m_Z)=0.1183 +/- 0.0050(exp.)^+0.0029_-0.0028(theor.) [pointlike] and alpha_s(m_Z)=0.1198 +/- 0.0028(exp.)^+0.0034_-0.0046(theor.) [pointlike and hadronic]. We demonstrate that the data taken at LEP have reduced the experimental error by about a factor of two, so that a competitive determination of alpha_s from F_2^gamma is now possible.

Figures (2)

• Figure 1: Single-parameter fits of the pointlike photon structure function, compared to PETRA Bartel:1984cg, TRISTAN Sahu:1995gjMuramatsu:1994rq, and LEP Barate:1999qyAcciarri:1998igAckerstaff:1997niAckerstaff:1997seAbbiendi:2002te data at large $Q^2$. The data points marked by open circles have not been used in the fits. Also shown is the hadronic contribution from a five-parameter NLO fit of the full photon structure function in the ${\rm DIS}_\gamma$ scheme.
• Figure 2: Five-parameter fits of the full photon structure function, compared to data from PETRA Berger:1984xt, TRISTAN Kojima:1997wgMuramatsu:1994rq, and LEP Barate:1999qyAbreu:1996xtAcciarri:1998igAckerstaff:1997niAbbiendi:2000cw at small $Q^2$. The data points marked by open circles refer to the second experiment and/or $Q^2$ value. Also shown are the hadronic and pointlike contributions to the NLO fit in the ${\rm DIS}_\gamma$ scheme.