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Inclusive-jet and dijet cross sections in deep inelastic scattering at HERA
ZEUS Collaboration,Chekanov, S.,Derrick, M.,Magill, S.,Miglioranzi, S.,Musgrave, B.,Nicholass, D.,Repond, J.,Yoshida, R.,Mattingly, M.C.K.,Pavel, N.,Yagues Molina, A.G.,Antonelli, S.,Antonioli, P.,Bar Elsevier BV * North-Holland 2007 Nuclear Physics, Section B Vol.765 No.1-2
Inclusive-jet and dijet differential cross sections have been measured in neutral current deep inelastic ep scattering for exchanged boson virtualities Q<SUP>2</SUP>>125 GeV<SUP>2</SUP> with the ZEUS detector at HERA using an integrated luminosity of 82 pb<SUP>-1</SUP>. Jets were identified in the Breit frame using the k<SUB>T</SUB> cluster algorithm. Jet cross sections are presented as functions of several kinematic and jet variables. The results are also presented in different regions of Q<SUP>2</SUP>. Next-to-leading-order QCD calculations describe the measurements well. Regions of phase space where the theoretical uncertainties are small have been identified. Measurements in these regions have the potential to constrain the gluon density in the proton when used as inputs to global fits of the proton parton distribution functions.
Measurement of beauty production from dimuon events at HERA
IOP Publishing Ltd 2009 Journal of high energy physics Vol.2009 No.2
Beauty production in events containing two muons in the final state has been measured with the ZEUS detector at HERA using an integrated luminosity of 114 pb<SUP>−1</SUP>. A low transverse-momentum threshold for muon identification, in combination with the large rapidity coverage of the ZEUS muon system, gives access to almost the full phase space for beauty production. The total cross section for beauty production in <I>ep</I> collisions at (<I>s</I>)<SUP>1/2</SUP> = 318 GeV has been measured to be σ<SUB>tot</SUB>(<I>ep</I> &to; <I>b</I>&barb;<I>X</I>) = 13.9 ± 1.5(stat.)<SUP>+4.0</SUP><SUB>−4.3</SUB>(syst.) nb. Differential cross sections and a measurement of <I>b</I>&barb; correlations are also obtained, and compared to other beauty cross-section measurements, Monte Carlo models and next-to-leading-order QCD predictions.
Measurement of the longitudinal proton structure function at HERA
ZEUS Collaboration,Chekanov, S.,Derrick, M.,Magill, S.,Musgrave, B.,Nicholass, D.,Repond, J.,Yoshida, R.,Mattingly, M.C.K.,Antonioli, P.,Bari, G.,Bellagamba, L.,Boscherini, D.,Bruni, A.,Bruni, G.,Cind North-Holland Pub. Co 2009 Physics letters: B Vol.682 No.1
The reduced cross sections for ep deep inelastic scattering have been measured with the ZEUS detector at HERA at three different centre-of-mass energies, 318, 251 and 225 GeV. From the cross sections, measured double differentially in Bjorken x and the virtuality, Q<SUP>2</SUP>, the proton structure functions F<SUB>L</SUB> and F<SUB>2</SUB> have been extracted in the region 5x10<SUP>-4</SUP><x<0.007 and 20<Q<SUP>2</SUP><130 GeV<SUP>2</SUP>.
ZEUS Collaboration,Chekanov, S.,Derrick, M.,Magill, S.,Musgrave, B.,Nicholass, D.,Repond, J.,Yoshida, R.,Mattingly, M.C.K.,Antonioli, P.,Bari, G.,Bellagamba, L.,Boscherini, D.,Bruni, A.,Bruni, G.,Cind North-Holland Pub. Co 2009 Physics letters: B Vol.672 No.2
A search for events with an isolated high-energy lepton and large missing transverse momentum has been performed with the ZEUS detector at HERA using a total integrated luminosity of 504 pb<SUP>-1</SUP>. The results agree well with Standard Model predictions. The cross section for production of single W bosons in electron-proton collisions with unpolarised electrons is measured to be 0.89<SUB>-0.22</SUB><SUP>+0.25</SUP>(stat.)+/-0.10(syst.)pb.
Bose-Einstein correlations of charged and neutral kaons in deep inelastic scattering at HERA
ZEUS Collaboration,Chekanov, S.,Derrick, M.,Magill, S.,Musgrave, B.,Nicholass, D.,Repond, J.,Yoshida, R.,Mattingly, M.C.K.,Jechow, M.,Pavel, N.,Yagues Molina, A.G.,Antonelli, S.,Antonioli, P.,Bari, G. North-Holland Pub. Co 2007 Physics letters. Section B Vol.652 No.1
Bose-Einstein correlations of charged and neutral kaons have been measured in e<SUP>+</SUP>/-p deep inelastic scattering with an integrated luminosity of 121 pb<SUP>-1</SUP> using the ZEUS detector at HERA. The two-particle correlation function was studied as a function of the four-momentum difference of the kaon pairs, Q<SUB>12</SUB>=-(p<SUB>1</SUB>-p<SUB>2</SUB>)<SUP>2</SUP>, assuming a Gaussian shape for the particle source. The values of the radius of the production volume, r, and of the correlation strength, λ, were obtained for both neutral and charged kaons. The radii for charged and neutral kaons are similar and are consistent with those obtained at LEP.
Measurement of D<sup>*+</sup>/- meson production in e<sup>+</sup>/-p scattering at low Q<sup>2</sup>
ZEUS Collaboration,Chekanov, S.,Derrick, M.,Magill, S.,Miglioranzi, S.,Musgrave, B.,Nicholass, D.,Repond, J.,Yoshida, R.,Mattingly, M.C.K.,Jechow, M.,Pavel, N.,Yagues Molina, A.G.,Antonelli, S.,Antoni North-Holland Pub. Co 2007 Physics letters: B Vol.649 No.2
The production of D<SUP>*+</SUP>/-(2010) mesons in e<SUP>+</SUP>/-p scattering in the range of exchanged photon virtuality 0.05<Q<SUP>2</SUP><0.7 GeV<SUP>2</SUP> has been measured with the ZEUS detector at HERA using an integrated luminosity of 82 pb<SUP>-1</SUP>. The decay channels D<SUP>*+</SUP>->D<SUP>0</SUP>π<SUP>+</SUP> with D<SUP>0</SUP>->K<SUP>-</SUP>π<SUP>+</SUP> and corresponding antiparticle decay were used to identify D<SUP>*</SUP> mesons and the ZEUS beampipe calorimeter was used to identify the scattered electron. Differential D<SUP>*</SUP> cross sections as functions of Q<SUP>2</SUP>, inelasticity, y, transverse momentum of the D<SUP>*</SUP> meson, p<SUB>T</SUB>(D<SUP>*</SUP>), and pseudorapidity of the D<SUP>*</SUP> meson, η(D<SUP>*</SUP>), have been measured in the kinematic region 0.02<y<0.85, 1.5<p<SUB>T</SUB>(D<SUP>*</SUP>)<9.0 GeV and |η(D<SUP>*</SUP>)|<1.5. The measured differential cross sections are in agreement with two different NLO QCD calculations. The cross sections are also compared to previous ZEUS measurements in the photoproduction and DIS regimes.
Inclusive-jet photoproduction at HERA and determination of α<sub>s</sub>
ZEUS Collaboration,Abramowicz, H.,Abt, I.,Adamczyk, L.,Adamus, M.,Aggarwal, R.,Antonelli, S.,Antonioli, P.,Antonov, A.,Arneodo, M.,Aushev, V.,Aushev, Y.,Bachynska, O.,Bamberger, A.,Barakbaev, A.N.,Bar North Holland 2012 Nuclear physics, B Vol.864 No.1
Inclusive-jet cross sections have been measured in the reaction ep->e+jet+X for photon virtuality Q<SUP>2</SUP><1 GeV<SUP>2</SUP> and γp centre-of-mass energies in the region 142<W<SUB>γ</SUB><SUB>p</SUB><293 GeV with the ZEUS detector at HERA using an integrated luminosity of 300 pb<SUP>-1</SUP>. Jets were identified using the k<SUB>T</SUB>, anti-k<SUB>T</SUB> or SIScone jet algorithms in the laboratory frame. Single-differential cross sections are presented as functions of the jet transverse energy, E<SUB>T</SUB><SUP>jet</SUP>, and pseudorapidity, η<SUP>jet</SUP>, for jets with E<SUB>T</SUB><SUP>jet</SUP>>17 GeV and -1<η<SUP>jet</SUP><2.5. In addition, measurements of double-differential inclusive-jet cross sections are presented as functions of E<SUB>T</SUB><SUP>jet</SUP> in different regions of η<SUP>jet</SUP>. Next-to-leading-order QCD calculations give a good description of the measurements, except for jets with low E<SUB>T</SUB><SUP>jet</SUP> and high η<SUP>jet</SUP>. The influence of non-perturbative effects not related to hadronisation was studied. Measurements of the ratios of cross sections using different jet algorithms are also presented; the measured ratios are well described by calculations including up to O(α<SUB>s</SUB><SUP>2</SUP>) terms. Values of α<SUB>s</SUB>(M<SUB>Z</SUB>) were extracted from the measurements and the energy-scale dependence of the coupling was determined. The value of α<SUB>s</SUB>(M<SUB>Z</SUB>) extracted from the measurements based on the k<SUB>T</SUB> jet algorithm is α<SUB>s</SUB>(M<SUB>Z</SUB>)=0.1206<SUB>-0.0022</SUB><SUP>+0.0023</SUP>(exp.)<SUB>-0.0035</SUB><SUP>+0.0042</SUP>(th.); the results from the anti-k<SUB>T</SUB> and SIScone algorithms are compatible with this value and have a similar precision.
Measurement of isolated photons accompanied by jets in deep inelastic ep scattering
ZEUS Collaboration,Abramowicz, H.,Abt, I.,Adamczyk, L.,Adamus, M.,Aggarwal, R.,Antonelli, S.,Antonioli, P.,Antonov, A.,Arneodo, M.,Arslan, O.,Aushev, V.,Aushev, Y.,Bachynska, O.,Bamberger, A.,Barakbae North-Holland Pub. Co 2012 Physics letters: B Vol.715 No.1
The production of isolated high-energy photons accompanied by jets has been measured in deep inelastic ep scattering with the ZEUS detector at HERA, using an integrated luminosity of 326 pb<SUP>-1</SUP>. Measurements were made for exchanged photon virtualities, Q<SUP>2</SUP>, in the range 10 to 350 GeV<SUP>2</SUP>. The photons were measured in the transverse-energy and pseudorapidity ranges 4<E<SUB>T</SUB><SUP>γ</SUP><15 GeV and -0.7<η<SUP>γ</SUP><0.9, and the jets were measured in the transverse-energy and pseudorapidity ranges 2.5<E<SUB>T</SUB><SUP>jet</SUP><35 GeV and -1.5<η<SUP>jet</SUP><1.8. Differential cross sections are presented as functions of these quantities. Perturbative QCD predictions give a reasonable description of the shape of the measured cross sections over most of the kinematic range, but the absolute normalisation is typically in disagreement by 20-30%.
Multijet production at low x<sub>Bj</sub> in deep inelastic scattering at HERA
ZEUS Collaboration,Chekanov, S.,Derrick, M.,Magill, S.,Musgrave, B.,Nicholass, D.,Repond, J.,Yoshida, R.,Mattingly, M.C.K.,Jechow, M.,Pavel, N.,Yagues Molina, A.G.,Antonelli, S.,Antonioli, P.,Bari, G. North Holland 2007 Nuclear Physics, Section B Vol.786 No.1
Inclusive dijet and trijet production in deep inelastic ep scattering has been measured for 10<Q<SUP>2</SUP><100 GeV<SUP>2</SUP> and low Bjorken x, 10<SUP>-4</SUP><x<SUB>Bj</SUB><10<SUP>-2</SUP>. The data were taken at the HERA ep collider with centre-of-mass energy s=318 GeV using the ZEUS detector and correspond to an integrated luminosity of 82 pb<SUP>-1</SUP>. Jets were identified in the hadronic centre-of-mass (HCM) frame using the k<SUB>T</SUB> cluster algorithm in the longitudinally invariant inclusive mode. Measurements of dijet and trijet differential cross sections are presented as functions of Q<SUP>2</SUP>, x<SUB>Bj</SUB>, jet transverse energy, and jet pseudorapidity. As a further examination of low-x<SUB>Bj</SUB> dynamics, multi-differential cross sections as functions of the jet correlations in transverse momenta, azimuthal angles, and pseudorapidity are also presented. Calculations at O(α<SUB>s</SUB><SUP>3</SUP>) generally describe the trijet data well and improve the description of the dijet data compared to the calculation at O(α<SUB>s</SUB><SUP>2</SUP>).
Measurement of the energy dependence of the total photon-proton cross section at HERA
ZEUS Collaboration,Abramowicz, H.,Abt, I.,Adamczyk, L.,Adamus, M.,Aggarwal, R.,Antonelli, S.,Antonioli, P.,Antonov, A.,Arneodo, M.,Aushev, V.,Aushev, Y.,Bachynska, O.,Bamberger, A.,Barakbaev, A.N.,Bar North-Holland Pub. Co 2011 Physics letters: B Vol.697 No.3
The energy dependence of the photon-proton total cross section, σ<SUB>tot</SUB><SUP>γ</SUP><SUP>p</SUP>, was determined from e<SUP>+</SUP>p scattering data collected with the ZEUS detector at HERA at three values of the center-of-mass energy, W, of the γp system in the range 194<W<296 GeV. This is the first determination of the W dependence of σ<SUB>tot</SUB><SUP>γ</SUP><SUP>p</SUP> from a single experiment at high W. Parameterizing σ<SUB>tot</SUB><SUP>γ</SUP><SUP>p</SUP>≃W<SUP>2ε</SUP>, ε=0.111+/-0.009(stat.)+/-0.036(syst.) was obtained.