cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.17182/hepdata.153487.v1/t22
title: "Table 9.1.2" of "The azimuthal correlation between the leading jet and the scattered lepton in deep inelastic scattering at HERA"

description: QED correction factors for $2.5 \;\mathrm{GeV} &lt; p_{T,jet}^{lead} &lt; 7 \;\mathrm{GeV}$ and $N_{jet} \geq 2$, as estimated with RAPGAP.
description: The azimuthal correlation angle, $\Delta\phi$, between the scattered lepton and the leading jet in deep inelastic $e^{\pm}p$ scattering at HERA has been studied using data collected with the ZEUS detector at a centre-of-mass energy of $\sqrt{s} = 318 \;\mathrm{GeV}$, corresponding to an integrated luminosity of $326 \;\mathrm{pb}^{-1}$.A measurement of jet cross sections in the laboratory frame was made in a fiducial region corresponding to photon virtuality $10 \;\mathrm{GeV}^{2} &lt; Q^{2} &lt; 350 \;\mathrm{GeV}^{2}$, inelasticity $0.04 &lt; y &lt; 0.7$, outgoing lepton energy $E_e &gt; 10 \;\mathrm{GeV}$, lepton polar angle $140^\circ &lt; \theta_e &lt; 180^\circ$, jet transverse momentum $2.5 \;\mathrm{GeV} &lt; p_\mathrm{T,jet} &lt; 30 \;\mathrm{GeV}$, and jet pseudorapidity $-1.5 &lt; \eta_\mathrm{jet} &lt; 1.8$.Jets were reconstructed using the $k_\mathrm{T}$ algorithm with the radius parameter $R = 1$.The leading jet in an event is defined as the jet that carries the highest $p_\mathrm{T,jet}$.Differential cross sections, $d\sigma/d\Delta\phi$, were measured as a function of the azimuthal correlation angle in various ranges of leading-jet transverse momentum, photon virtuality and jet multiplicity.Perturbative calculations at $\mathcal{O}(\alpha_{s}^2)$ accuracy successfully describe the data within the fiducial region, although a lower level of agreement is observed near $\Delta\phi \rightarrow \pi$ for events with high jet multiplicity, due to limitations of the perturbative approach in describing soft phenomena in QCD.The data are equally well described by Monte Carlo predictions that supplement leading-order matrix elements with parton showering.
DOI: 10.17182/hepdata.153487.v1/t23
title: "Table 9.1.3" of "The azimuthal correlation between the leading jet and the scattered lepton in deep inelastic scattering at HERA"

description: QED correction factors for $2.5 \;\mathrm{GeV} &lt; p_{T,jet}^{lead} &lt; 7 \;\mathrm{GeV}$ and $N_{jet} \geq 3$, as estimated with RAPGAP.
description: The azimuthal correlation angle, $\Delta\phi$, between the scattered lepton and the leading jet in deep inelastic $e^{\pm}p$ scattering at HERA has been studied using data collected with the ZEUS detector at a centre-of-mass energy of $\sqrt{s} = 318 \;\mathrm{GeV}$, corresponding to an integrated luminosity of $326 \;\mathrm{pb}^{-1}$.A measurement of jet cross sections in the laboratory frame was made in a fiducial region corresponding to photon virtuality $10 \;\mathrm{GeV}^{2} &lt; Q^{2} &lt; 350 \;\mathrm{GeV}^{2}$, inelasticity $0.04 &lt; y &lt; 0.7$, outgoing lepton energy $E_e &gt; 10 \;\mathrm{GeV}$, lepton polar angle $140^\circ &lt; \theta_e &lt; 180^\circ$, jet transverse momentum $2.5 \;\mathrm{GeV} &lt; p_\mathrm{T,jet} &lt; 30 \;\mathrm{GeV}$, and jet pseudorapidity $-1.5 &lt; \eta_\mathrm{jet} &lt; 1.8$.Jets were reconstructed using the $k_\mathrm{T}$ algorithm with the radius parameter $R = 1$.The leading jet in an event is defined as the jet that carries the highest $p_\mathrm{T,jet}$.Differential cross sections, $d\sigma/d\Delta\phi$, were measured as a function of the azimuthal correlation angle in various ranges of leading-jet transverse momentum, photon virtuality and jet multiplicity.Perturbative calculations at $\mathcal{O}(\alpha_{s}^2)$ accuracy successfully describe the data within the fiducial region, although a lower level of agreement is observed near $\Delta\phi \rightarrow \pi$ for events with high jet multiplicity, due to limitations of the perturbative approach in describing soft phenomena in QCD.The data are equally well described by Monte Carlo predictions that supplement leading-order matrix elements with parton showering.
DOI: 10.17182/hepdata.153487.v1/t24
title: "Table 9.2.1" of "The azimuthal correlation between the leading jet and the scattered lepton in deep inelastic scattering at HERA"

description: QED correction factors for $7 \;\mathrm{GeV} &lt; p_{T,jet}^{lead} &lt; 12 \;\mathrm{GeV}$ and $N_{jet} \geq 1$, as estimated with RAPGAP.
description: The azimuthal correlation angle, $\Delta\phi$, between the scattered lepton and the leading jet in deep inelastic $e^{\pm}p$ scattering at HERA has been studied using data collected with the ZEUS detector at a centre-of-mass energy of $\sqrt{s} = 318 \;\mathrm{GeV}$, corresponding to an integrated luminosity of $326 \;\mathrm{pb}^{-1}$.A measurement of jet cross sections in the laboratory frame was made in a fiducial region corresponding to photon virtuality $10 \;\mathrm{GeV}^{2} &lt; Q^{2} &lt; 350 \;\mathrm{GeV}^{2}$, inelasticity $0.04 &lt; y &lt; 0.7$, outgoing lepton energy $E_e &gt; 10 \;\mathrm{GeV}$, lepton polar angle $140^\circ &lt; \theta_e &lt; 180^\circ$, jet transverse momentum $2.5 \;\mathrm{GeV} &lt; p_\mathrm{T,jet} &lt; 30 \;\mathrm{GeV}$, and jet pseudorapidity $-1.5 &lt; \eta_\mathrm{jet} &lt; 1.8$.Jets were reconstructed using the $k_\mathrm{T}$ algorithm with the radius parameter $R = 1$.The leading jet in an event is defined as the jet that carries the highest $p_\mathrm{T,jet}$.Differential cross sections, $d\sigma/d\Delta\phi$, were measured as a function of the azimuthal correlation angle in various ranges of leading-jet transverse momentum, photon virtuality and jet multiplicity.Perturbative calculations at $\mathcal{O}(\alpha_{s}^2)$ accuracy successfully describe the data within the fiducial region, although a lower level of agreement is observed near $\Delta\phi \rightarrow \pi$ for events with high jet multiplicity, due to limitations of the perturbative approach in describing soft phenomena in QCD.The data are equally well described by Monte Carlo predictions that supplement leading-order matrix elements with parton showering.
DOI: 10.17182/hepdata.153487.v1/t25
title: "Table 9.2.2" of "The azimuthal correlation between the leading jet and the scattered lepton in deep inelastic scattering at HERA"

description: QED correction factors for $7 \;\mathrm{GeV} &lt; p_{T,jet}^{lead} &lt; 12 \;\mathrm{GeV}$ and $N_{jet} \geq 2$, as estimated with RAPGAP.
description: The azimuthal correlation angle, $\Delta\phi$, between the scattered lepton and the leading jet in deep inelastic $e^{\pm}p$ scattering at HERA has been studied using data collected with the ZEUS detector at a centre-of-mass energy of $\sqrt{s} = 318 \;\mathrm{GeV}$, corresponding to an integrated luminosity of $326 \;\mathrm{pb}^{-1}$.A measurement of jet cross sections in the laboratory frame was made in a fiducial region corresponding to photon virtuality $10 \;\mathrm{GeV}^{2} &lt; Q^{2} &lt; 350 \;\mathrm{GeV}^{2}$, inelasticity $0.04 &lt; y &lt; 0.7$, outgoing lepton energy $E_e &gt; 10 \;\mathrm{GeV}$, lepton polar angle $140^\circ &lt; \theta_e &lt; 180^\circ$, jet transverse momentum $2.5 \;\mathrm{GeV} &lt; p_\mathrm{T,jet} &lt; 30 \;\mathrm{GeV}$, and jet pseudorapidity $-1.5 &lt; \eta_\mathrm{jet} &lt; 1.8$.Jets were reconstructed using the $k_\mathrm{T}$ algorithm with the radius parameter $R = 1$.The leading jet in an event is defined as the jet that carries the highest $p_\mathrm{T,jet}$.Differential cross sections, $d\sigma/d\Delta\phi$, were measured as a function of the azimuthal correlation angle in various ranges of leading-jet transverse momentum, photon virtuality and jet multiplicity.Perturbative calculations at $\mathcal{O}(\alpha_{s}^2)$ accuracy successfully describe the data within the fiducial region, although a lower level of agreement is observed near $\Delta\phi \rightarrow \pi$ for events with high jet multiplicity, due to limitations of the perturbative approach in describing soft phenomena in QCD.The data are equally well described by Monte Carlo predictions that supplement leading-order matrix elements with parton showering.
DOI: 10.17182/hepdata.153487.v1/t26
title: "Table 9.2.3" of "The azimuthal correlation between the leading jet and the scattered lepton in deep inelastic scattering at HERA"

description: QED correction factors for $7 \;\mathrm{GeV} &lt; p_{T,jet}^{lead} &lt; 12 \;\mathrm{GeV}$ and $N_{jet} \geq 3$, as estimated with RAPGAP.
description: The azimuthal correlation angle, $\Delta\phi$, between the scattered lepton and the leading jet in deep inelastic $e^{\pm}p$ scattering at HERA has been studied using data collected with the ZEUS detector at a centre-of-mass energy of $\sqrt{s} = 318 \;\mathrm{GeV}$, corresponding to an integrated luminosity of $326 \;\mathrm{pb}^{-1}$.A measurement of jet cross sections in the laboratory frame was made in a fiducial region corresponding to photon virtuality $10 \;\mathrm{GeV}^{2} &lt; Q^{2} &lt; 350 \;\mathrm{GeV}^{2}$, inelasticity $0.04 &lt; y &lt; 0.7$, outgoing lepton energy $E_e &gt; 10 \;\mathrm{GeV}$, lepton polar angle $140^\circ &lt; \theta_e &lt; 180^\circ$, jet transverse momentum $2.5 \;\mathrm{GeV} &lt; p_\mathrm{T,jet} &lt; 30 \;\mathrm{GeV}$, and jet pseudorapidity $-1.5 &lt; \eta_\mathrm{jet} &lt; 1.8$.Jets were reconstructed using the $k_\mathrm{T}$ algorithm with the radius parameter $R = 1$.The leading jet in an event is defined as the jet that carries the highest $p_\mathrm{T,jet}$.Differential cross sections, $d\sigma/d\Delta\phi$, were measured as a function of the azimuthal correlation angle in various ranges of leading-jet transverse momentum, photon virtuality and jet multiplicity.Perturbative calculations at $\mathcal{O}(\alpha_{s}^2)$ accuracy successfully describe the data within the fiducial region, although a lower level of agreement is observed near $\Delta\phi \rightarrow \pi$ for events with high jet multiplicity, due to limitations of the perturbative approach in describing soft phenomena in QCD.The data are equally well described by Monte Carlo predictions that supplement leading-order matrix elements with parton showering.
DOI: 10.17182/hepdata.153487.v1/t27
title: "Table 9.3.1" of "The azimuthal correlation between the leading jet and the scattered lepton in deep inelastic scattering at HERA"

description: QED correction factors for $12 \;\mathrm{GeV} &lt; p_{T,jet}^{lead} &lt; 30 \;\mathrm{GeV}$ and $N_{jet} \geq 1$, as estimated with RAPGAP.
description: The azimuthal correlation angle, $\Delta\phi$, between the scattered lepton and the leading jet in deep inelastic $e^{\pm}p$ scattering at HERA has been studied using data collected with the ZEUS detector at a centre-of-mass energy of $\sqrt{s} = 318 \;\mathrm{GeV}$, corresponding to an integrated luminosity of $326 \;\mathrm{pb}^{-1}$.A measurement of jet cross sections in the laboratory frame was made in a fiducial region corresponding to photon virtuality $10 \;\mathrm{GeV}^{2} &lt; Q^{2} &lt; 350 \;\mathrm{GeV}^{2}$, inelasticity $0.04 &lt; y &lt; 0.7$, outgoing lepton energy $E_e &gt; 10 \;\mathrm{GeV}$, lepton polar angle $140^\circ &lt; \theta_e &lt; 180^\circ$, jet transverse momentum $2.5 \;\mathrm{GeV} &lt; p_\mathrm{T,jet} &lt; 30 \;\mathrm{GeV}$, and jet pseudorapidity $-1.5 &lt; \eta_\mathrm{jet} &lt; 1.8$.Jets were reconstructed using the $k_\mathrm{T}$ algorithm with the radius parameter $R = 1$.The leading jet in an event is defined as the jet that carries the highest $p_\mathrm{T,jet}$.Differential cross sections, $d\sigma/d\Delta\phi$, were measured as a function of the azimuthal correlation angle in various ranges of leading-jet transverse momentum, photon virtuality and jet multiplicity.Perturbative calculations at $\mathcal{O}(\alpha_{s}^2)$ accuracy successfully describe the data within the fiducial region, although a lower level of agreement is observed near $\Delta\phi \rightarrow \pi$ for events with high jet multiplicity, due to limitations of the perturbative approach in describing soft phenomena in QCD.The data are equally well described by Monte Carlo predictions that supplement leading-order matrix elements with parton showering.
DOI: 10.17182/hepdata.153487.v1/t28
title: "Table 9.3.2" of "The azimuthal correlation between the leading jet and the scattered lepton in deep inelastic scattering at HERA"

description: QED correction factors for $12 \;\mathrm{GeV} &lt; p_{T,jet}^{lead} &lt; 30 \;\mathrm{GeV}$ and $N_{jet} \geq 2$, as estimated with RAPGAP.
description: The azimuthal correlation angle, $\Delta\phi$, between the scattered lepton and the leading jet in deep inelastic $e^{\pm}p$ scattering at HERA has been studied using data collected with the ZEUS detector at a centre-of-mass energy of $\sqrt{s} = 318 \;\mathrm{GeV}$, corresponding to an integrated luminosity of $326 \;\mathrm{pb}^{-1}$.A measurement of jet cross sections in the laboratory frame was made in a fiducial region corresponding to photon virtuality $10 \;\mathrm{GeV}^{2} &lt; Q^{2} &lt; 350 \;\mathrm{GeV}^{2}$, inelasticity $0.04 &lt; y &lt; 0.7$, outgoing lepton energy $E_e &gt; 10 \;\mathrm{GeV}$, lepton polar angle $140^\circ &lt; \theta_e &lt; 180^\circ$, jet transverse momentum $2.5 \;\mathrm{GeV} &lt; p_\mathrm{T,jet} &lt; 30 \;\mathrm{GeV}$, and jet pseudorapidity $-1.5 &lt; \eta_\mathrm{jet} &lt; 1.8$.Jets were reconstructed using the $k_\mathrm{T}$ algorithm with the radius parameter $R = 1$.The leading jet in an event is defined as the jet that carries the highest $p_\mathrm{T,jet}$.Differential cross sections, $d\sigma/d\Delta\phi$, were measured as a function of the azimuthal correlation angle in various ranges of leading-jet transverse momentum, photon virtuality and jet multiplicity.Perturbative calculations at $\mathcal{O}(\alpha_{s}^2)$ accuracy successfully describe the data within the fiducial region, although a lower level of agreement is observed near $\Delta\phi \rightarrow \pi$ for events with high jet multiplicity, due to limitations of the perturbative approach in describing soft phenomena in QCD.The data are equally well described by Monte Carlo predictions that supplement leading-order matrix elements with parton showering.
DOI: 10.25549/ahf-ouc11399ernh
title: Hancock Photographs

description: The Hancock Foundation Archive consists of correspondence, reports, clippings, photographs, sound recordings, film, and other materials, 1823-2005, documenting the activities and history of the Hancock Foundation at the University of Southern California, its founder G. Allan Hancock, and the Hancock family. Included are records of the Foundation's scientific and research activities in marine biology and zoology; the Foundation's Library; the Hancock Museum, housed in the Foundation building on the USC campus; and the research vessel Velero IV, the second of Captain Hancock's ships put into service for research purposes. Also included are historical documents regarding the Hancock family's land interests in Los Angeles, and material documenting the non-scientific interests of Captain Hancock. Specifically this digital collection includes: • Allan Hancock Foundation publications. • Sound recordings produced by the Allan Hancock Foundation for radio broadcast in the 1930's and 1940's. Many of the recordings are of the Hancock Ensemble whose 'cellist was Allan Hancock. Digitized thanks to generous support from the Association for Recorded Sound Collections (ARSC) (https://www.arsc-audio.org/index.php), Lance Bowling and Cambria Music, Kenneth Hayashida MD (USC ’89) • Films and photographs from the Allan Hancock Foundation mostly from the expeditions of the research vessels Velero II, III, and IV. The digitization efforts for the Hancock collection have been financed (in part) with Federal funds from the National Park Service Maritime Heritage grant program (https://www.nps.gov/maritime/grants/apply.htm), administered by the National Park Service, U.S. Department of the Interior. However, the contents and opinions contained herein do not necessarily reflect the views or policies of the Department of the Interior, nor does the mention of trade names or commercial products constitute endorsement or recommendation by the Department of the Interior. The project received Federal financial assistance for preservation of historic maritime resources and for increasing public awareness and appreciation for the maritime heritage of the United States. Under Title VI of the Civil Rights Act of 1964, Section 504 of the Rehabilitation Act of 1973, and the Age Discrimination Act of 1975, as amended, the U.S. Department of the Interior prohibits discrimination on the basis of race, color, national origin, disability or age in its federally funded assisted programs. If you believe you have been discriminated again in any program, activity, or facility as described above, or if you desire further information, please write to: Office of Equal Opportunity National Park Service 1849 C Street, NW Washington, DC 20240. • Station logs from the research vessel Velero IV.
DOI: 10.17182/hepdata.153487.v1/t29
title: "Table 9.3.3" of "The azimuthal correlation between the leading jet and the scattered lepton in deep inelastic scattering at HERA"

description: QED correction factors for $12 \;\mathrm{GeV} &lt; p_{T,jet}^{lead} &lt; 30 \;\mathrm{GeV}$ and $N_{jet} \geq 3$, as estimated with RAPGAP.
description: The azimuthal correlation angle, $\Delta\phi$, between the scattered lepton and the leading jet in deep inelastic $e^{\pm}p$ scattering at HERA has been studied using data collected with the ZEUS detector at a centre-of-mass energy of $\sqrt{s} = 318 \;\mathrm{GeV}$, corresponding to an integrated luminosity of $326 \;\mathrm{pb}^{-1}$.A measurement of jet cross sections in the laboratory frame was made in a fiducial region corresponding to photon virtuality $10 \;\mathrm{GeV}^{2} &lt; Q^{2} &lt; 350 \;\mathrm{GeV}^{2}$, inelasticity $0.04 &lt; y &lt; 0.7$, outgoing lepton energy $E_e &gt; 10 \;\mathrm{GeV}$, lepton polar angle $140^\circ &lt; \theta_e &lt; 180^\circ$, jet transverse momentum $2.5 \;\mathrm{GeV} &lt; p_\mathrm{T,jet} &lt; 30 \;\mathrm{GeV}$, and jet pseudorapidity $-1.5 &lt; \eta_\mathrm{jet} &lt; 1.8$.Jets were reconstructed using the $k_\mathrm{T}$ algorithm with the radius parameter $R = 1$.The leading jet in an event is defined as the jet that carries the highest $p_\mathrm{T,jet}$.Differential cross sections, $d\sigma/d\Delta\phi$, were measured as a function of the azimuthal correlation angle in various ranges of leading-jet transverse momentum, photon virtuality and jet multiplicity.Perturbative calculations at $\mathcal{O}(\alpha_{s}^2)$ accuracy successfully describe the data within the fiducial region, although a lower level of agreement is observed near $\Delta\phi \rightarrow \pi$ for events with high jet multiplicity, due to limitations of the perturbative approach in describing soft phenomena in QCD.The data are equally well described by Monte Carlo predictions that supplement leading-order matrix elements with parton showering.
DOI: 10.17182/hepdata.153487.v1/t30
title: "Table 10.1.1" of "The azimuthal correlation between the leading jet and the scattered lepton in deep inelastic scattering at HERA"

description: QED correction factors for $10 \;\mathrm{GeV}^{2} &lt; Q^{2} &lt; 50 \;\mathrm{GeV}^{2}$ and $N_{jet} \geq 1$, as estimated with RAPGAP.
description: The azimuthal correlation angle, $\Delta\phi$, between the scattered lepton and the leading jet in deep inelastic $e^{\pm}p$ scattering at HERA has been studied using data collected with the ZEUS detector at a centre-of-mass energy of $\sqrt{s} = 318 \;\mathrm{GeV}$, corresponding to an integrated luminosity of $326 \;\mathrm{pb}^{-1}$.A measurement of jet cross sections in the laboratory frame was made in a fiducial region corresponding to photon virtuality $10 \;\mathrm{GeV}^{2} &lt; Q^{2} &lt; 350 \;\mathrm{GeV}^{2}$, inelasticity $0.04 &lt; y &lt; 0.7$, outgoing lepton energy $E_e &gt; 10 \;\mathrm{GeV}$, lepton polar angle $140^\circ &lt; \theta_e &lt; 180^\circ$, jet transverse momentum $2.5 \;\mathrm{GeV} &lt; p_\mathrm{T,jet} &lt; 30 \;\mathrm{GeV}$, and jet pseudorapidity $-1.5 &lt; \eta_\mathrm{jet} &lt; 1.8$.Jets were reconstructed using the $k_\mathrm{T}$ algorithm with the radius parameter $R = 1$.The leading jet in an event is defined as the jet that carries the highest $p_\mathrm{T,jet}$.Differential cross sections, $d\sigma/d\Delta\phi$, were measured as a function of the azimuthal correlation angle in various ranges of leading-jet transverse momentum, photon virtuality and jet multiplicity.Perturbative calculations at $\mathcal{O}(\alpha_{s}^2)$ accuracy successfully describe the data within the fiducial region, although a lower level of agreement is observed near $\Delta\phi \rightarrow \pi$ for events with high jet multiplicity, due to limitations of the perturbative approach in describing soft phenomena in QCD.The data are equally well described by Monte Carlo predictions that supplement leading-order matrix elements with parton showering.
DOI: 10.17182/hepdata.153487.v1/t31
title: "Table 10.1.2" of "The azimuthal correlation between the leading jet and the scattered lepton in deep inelastic scattering at HERA"

description: QED correction factors for $10 \;\mathrm{GeV}^{2} &lt; Q^{2} &lt; 50 \;\mathrm{GeV}^{2}$ and $N_{jet} \geq 2$, as estimated with RAPGAP.
description: The azimuthal correlation angle, $\Delta\phi$, between the scattered lepton and the leading jet in deep inelastic $e^{\pm}p$ scattering at HERA has been studied using data collected with the ZEUS detector at a centre-of-mass energy of $\sqrt{s} = 318 \;\mathrm{GeV}$, corresponding to an integrated luminosity of $326 \;\mathrm{pb}^{-1}$.A measurement of jet cross sections in the laboratory frame was made in a fiducial region corresponding to photon virtuality $10 \;\mathrm{GeV}^{2} &lt; Q^{2} &lt; 350 \;\mathrm{GeV}^{2}$, inelasticity $0.04 &lt; y &lt; 0.7$, outgoing lepton energy $E_e &gt; 10 \;\mathrm{GeV}$, lepton polar angle $140^\circ &lt; \theta_e &lt; 180^\circ$, jet transverse momentum $2.5 \;\mathrm{GeV} &lt; p_\mathrm{T,jet} &lt; 30 \;\mathrm{GeV}$, and jet pseudorapidity $-1.5 &lt; \eta_\mathrm{jet} &lt; 1.8$.Jets were reconstructed using the $k_\mathrm{T}$ algorithm with the radius parameter $R = 1$.The leading jet in an event is defined as the jet that carries the highest $p_\mathrm{T,jet}$.Differential cross sections, $d\sigma/d\Delta\phi$, were measured as a function of the azimuthal correlation angle in various ranges of leading-jet transverse momentum, photon virtuality and jet multiplicity.Perturbative calculations at $\mathcal{O}(\alpha_{s}^2)$ accuracy successfully describe the data within the fiducial region, although a lower level of agreement is observed near $\Delta\phi \rightarrow \pi$ for events with high jet multiplicity, due to limitations of the perturbative approach in describing soft phenomena in QCD.The data are equally well described by Monte Carlo predictions that supplement leading-order matrix elements with parton showering.