Determination of the strong coupling constant $α_s(M_Z)$ in next-to-next-to-leading order QCD using H1 jet cross section measurements

Abstract

The strong coupling constant α s is determined from inclusive jet and dijet cross sections in neutral-current deep-inelastic ep scattering (DIS) measured at HERA by the H1 collaboration using next-to-next-to-leading order (NNLO) QCD predictions. The dependence of the NNLO predictions and of the resulting value of α s (m Z ) at the Z-boson mass m Z are studied as a function of the choice of the renormalisation and factorisation scales. Using inclusive jet and dijet data together, the strong coupling constant is determined to be α s (m Z ) = 0.1157 (20) exp (29) th . Complementary, α s (m Z ) is determined together with parton distribution functions of the proton (PDFs) from jet and inclusive DIS data measured by the H1 experiment. The value α s (m Z ) = 0.1142 (28) tot obtained is consistent with the determination from jet data alone. The impact of the jet data on the PDFs is studied. The running of the strong coupling is tested at different values of the renormalisation scale and the results are found to be in agreement with expectations.Dedicated to the memory of our dear friends and colleagues Vitaliy Dodonov and Yakov Vazdik.

NLO PDFs from the ABMP16 fit

“…Determinations of α s (M Z ) in DIS and including jet cross section measurements have been discussed in Ref. [8].…”

NNLO QCD corrections to jet production in charged current deep inelastic scattering

“…and diffractive DIS [15,16] and three-jet production in e + e − -annihilation [17], the process library was recently expanded to include Higgs production in vector boson fusion (VBF) in protonproton collisions [18], and single-jet production to N3LO QCD in NC DIS [19], using the method of Projection-To-Born (P2B). Results obtained within NNLOjet have already been used in phenomenological studies including the determination of α s (M Z ) from combined H1 jet data [20]. It is also worth mentioning that the known N3LO structure functions complemented by the presented fully differential NNLO calculation of CC di-jet production would allow for fully differential N3LO calculations of CC DIS to be perfomed using the method of P2B, as in [19], and that the calculations of leptonic CC DIS could equally be used for neutrino DIS studies.…”

PDF Dependence on Parameter Fits from Hadronic Data

“…Several recent determinations of α S based on hadronic data [20,22,23,24,21,25] implement the following procedure, which we shall dub Partial χ 2 :…”

“…1. Consider some experimental measurement of hadronic data, P. For example, t t production [20,24], Prompt photon events [22] jet production [23,21], and Z+jet production [25].…”

“…Two categories of determinations based on hadronic measurements enter the World Average: Those based on PDFs [16,17,18,19], which are essentially obtained by optimizing Eq 2 as a function of α S , and the t t production, currently including only the CMS measurement at 7 TeV [20], which is instead based on minimizing over a χ 2 function that considers explicitly the t t data only (we call this the partial χ 2 method ). We shall discuss the relation between these categories, and also try to elucidate the noticeable fact that determinations of α S based on an hadronic dataset, such as Ref [20] as well as more recent ones like Ref [21], give significatively different results from the determinations based on the PDFs that they use as input to compute the predictions in Eq. 1.…”