Measurement of Jet Production Cross Sections in Deep-inelastic ep Scattering at HERA

TL;DR

The study presents precision double-differential jet cross sections in neutral-current deep-inelastic $ep$ scattering at HERA, extending measurements to low $Q^2$ and low jet transverse momenta. It employs comprehensive detector-level unfolding with MC-driven corrections and compares results to state-of-the-art perturbative QCD predictions at NLO, aNNLO, and NNLO, including hadronisation corrections. The analysis yields a robust determination of the strong coupling constant $\,\alpha_s(M_Z)\,$ from normalised jet cross sections and tests the running of $\,\alpha_s\,$ across a wide renormalisation scale, with NNLO providing improved agreement and reduced scale uncertainty. The results also offer constraints on parton distribution functions at high $x$ and demonstrate the impact of higher-order QCD calculations on jet phenomenology in DIS.

Abstract

A precision measurement of jet cross sections in neutral current deep-inelastic scattering for photon virtualities $5.5<Q^2<80\,{\rm GeV}^2$ and inelasticities $0.2<y<0.6$ is presented, using data taken with the H1 detector at HERA, corresponding to an integrated luminosity of $290\,{\rm pb}^{-1}$. Double-differential inclusive jet, dijet and trijet cross sections are measured simultaneously and are presented as a function of jet transverse momentum observables and as a function of $Q^2$. Jet cross sections normalised to the inclusive neutral current DIS cross section in the respective $Q^2$-interval are also determined. Previous results of inclusive jet cross sections in the range $150<Q^2<15\,000\,{\rm GeV}^2$ are extended to low transverse jet momenta $5<P_{T}^{\rm jet}<7\,{\rm GeV}$. The data are compared to predictions from perturbative QCD in next-to-leading order in the strong coupling, in approximate next-to-next-to-leading order and in full next-to-next-to-leading order. Using also the recently published H1 jet data at high values of $Q^2$, the strong coupling constant $α_s(M_Z)$ is determined in next-to-leading order.

Figures (21)

• Figure 1: Deep-inelastic $ep$ scattering at different orders in $\alpha_s\xspace$: (a) Born contribution to inclusive NC DIS ($\mathcal{O}(\alpha_{\mathrm{em}}\xspace^2)$), (b) photon-gluon fusion ($\mathcal{O}(\alpha_{\mathrm{em}}\xspace^2 \alpha_s\xspace)$), (c) QCD Compton scattering ($\mathcal{O}(\alpha_{\mathrm{em}}\xspace^2 \alpha_s\xspace)$) and (d) a trijet process $\mathcal{O}(\alpha_{\mathrm{em}}\xspace^2 \alpha_s\xspace^2)$.
• Figure 2: Distributions of $Q^2$ and $y$ for the selected NC DIS data at detector level. The data are compared to predictions obtained from the Rapgap and Djangoh MC simulations, which are weighted to achieve a better description of the data (labelled as 'MC'). The non-weighted predictions of the generators are shown as thin lines. The background is obtained from simulated photoproduction events. The shaded areas indicate kinematic regions which are considered in the extended phase space of the unfolding procedure.
• Figure 3: Distributions of the inclusive jet multiplicity for the NC DIS data and the jet transverse momenta $P_{\rm T}^{\rm jet}$ of the inclusive jet measurement on detector level. Other details as in figure \ref{['figControlDIS']}.
• Figure 4: Distributions of $\langle P_{\mathrm{T}} \rangle_{2}$ of the dijet and $\langle P_{\mathrm{T}} \rangle_{3}$ of the trijet data on detector level for the measurement phase space. Other details as in figure \ref{['figControlDIS']}.
• Figure 5: Comparison of predictions obtained with different PDF sets for selected $Q^2$ bins of the inclusive jet, dijet and trijet cross sections. The ratios of predictions obtained using the CT14, MMHT, HERAPDF2.0 and ABMP16 to the NNPDF3.0 NNLO PDF set are displayed, where NLO matrix elements have been used in all cases. For comparison, also the ratio of NNPDF3.0 PDF set extracted at NLO precision to NNPDF3.0 NNLO is shown. The shaded area indicates the PDF uncertainty determined using NNPDF3.0 NNLO. The predictions based on ABMP16 shown here are valid only for five active flavours, and hence are shown only for $(Q^2 + P_{\rm T}\xspace^{2})/2>25\,\text{GeV}^2$.