Papers by Henk Uijterwaal
Routing Information Service R.I.S
Inclusive jet cross sections for events with a large rapidity gap with respect to the proton dire... more Inclusive jet cross sections for events with a large rapidity gap with respect to the proton direction from the reaction ep \rightarrow jet \; + \; X with quasi-real photons have been measured with the ZEUS detector. The cross sections refer to jets with transverse energies E_T^{jet}>8~GeV. The data show the characteristics of a diffractive process mediated by pomeron exchange. Assuming that the events are due to the exchange of a pomeron with partonic structure the qith, W H02
Construction and beam test of the ZEUS forward and rear calorimeter
Andresen, A.; Bamberger, A.; Bargende, A.; Barreiro, F.; Behrens, U.; Bentvelsen, S.; Brkic, M.; ... more Andresen, A.; Bamberger, A.; Bargende, A.; Barreiro, F.; Behrens, U.; Bentvelsen, S.; Brkic, M.; Burow, B.; Caldwell, A.; Cases, G.; Corriveau, F.; Crittenden, JA; Dake, A.; Dannemann, A.; Dawson, J.; Dierks, K.; Drews, G.; Engelen, J.; Fawcett, H.; Frisken, W.; Fürtjes, A.; ...
Physics Letters B, 1995
Photoproduction at HERA is studied in ep collisions, with the ZEUS detector, for yp centre-of-mas... more Photoproduction at HERA is studied in ep collisions, with the ZEUS detector, for yp centre-of-mass energies ranging from 130-270 GeV. A sample of events with two high-pr jets (or > 6 GeV, 77 < 1.6) and a third cluster in the approximate direction of the electron beam is isolated using a clustering algorithm. These events are mostly due to resolved photoproduction. The third cluster is identified as the photon remnant. Its properties, such as the transverse and longitudinal energy Rows around the axis of the cluster, are consistent with those commonly attributed to jets, and in particular with those found for the two jets in these events. The mean value of the photon remnant pr with respect to the beam axis is measured to be 2.1 f 0.2 GeV, which demonstrates substantial mean transverse momenta for the photon remnant.
Zeitschrift Fur Physik C-Particles and Fields, 1996
We present measurements of the structure function F 2 in e + p scattering at HERA in the range 3.... more We present measurements of the structure function F 2 in e + p scattering at HERA in the range 3.5 GeV 2 < Q 2 < 5000 GeV 2 . A new reconstruction method has allowed a significant improvement in the resolution of the kinematic variables and an extension of the kinematic region covered by the experiment. At Q 2 < 35 GeV 2 the range in x now spans 6.3 · 10 −5 < x < 0.08 providing overlap with measurements from fixed target experiments. At values of Q 2 above 1000 GeV 2 the x range extends to 0.5. Systematic errors below 5% have been achieved for most of the kinematic region. The structure function rises as x decreases; the rise becomes more pronounced as Q 2 increases. The behaviour of the structure function data is well described by next-to-leading order perturbative QCD as implemented in the DGLAP evolution equations.
Zeitschrift Fur Physik C-Particles and Fields, 1996
Zeitschrift Fur Physik C-Particles and Fields, 1996
A measurement of inclusive charged particle distributions in deep inelastic ep scattering for γ *... more A measurement of inclusive charged particle distributions in deep inelastic ep scattering for γ * p centre-of-mass energies 75 < W < 175 GeV and momentum transfer squared 10 < Q 2 < 160 GeV 2 from the ZEUS detector at HERA is presented. The differential charged particle rates in the γ * p centre-of-mass system as a function of the scaled longitudinal momentum, x F , and of the transverse momentum, p * t and <p * 2 t > , as a function of x F , W and Q 2 are given. Separate distributions are shown for events with (LRG) and without (NRG) a rapidity gap with respect to the proton direction. The data are compared with results from experiments at lower beam energies, with the naive quark parton model and with parton models including perturbative QCD corrections. The comparison shows the importance of the higher order QCD processes. Significant differences of the inclusive charged particle rates between NRG and LRG events at the same W are observed. The value of <p * 2 t > for LRG events with a hadronic mass M X , which excludes the forward produced baryonic system, is similar to the <p * 2 t > value observed in fixed target experiments at W ≈ M X .
The ZEUS Leading Proton Spectrometer and its use in the measurement of elastic rho(0) photoproduction at HERA
Zeitschrift Fur Physik C-Particles and Fields, 1997
Page 1. Z. Phys. C 73, 253–268 (1997) ZEITSCHRIFT F¨UR PHYSIK C c© Springer-Verlag 1997 The ZEUS ... more Page 1. Z. Phys. C 73, 253–268 (1997) ZEITSCHRIFT F¨UR PHYSIK C c© Springer-Verlag 1997 The ZEUS Leading Proton Spectrometer and its use in the measurement of elastic ρ0 photoproduction at HERA The ZEUS Collaboration ...
Zeitschrift Fur Physik C-Particles and Fields, 1997
Diffractive dissociation of quasi-real photons at a photon-proton centre of mass energy of W ≈ 20... more Diffractive dissociation of quasi-real photons at a photon-proton centre of mass energy of W ≈ 200 GeV is studied with the ZEUS detector at HERA. The process under consideration is γp → XN , where X is the diffractively dissociated photon system of mass M X and N is either a proton or a nucleonic system with mass M N < 2 GeV. The cross section for this process in the interval 3 < M X < 24 GeV relative to the total photoproduction cross section was measured to be σ partial D /σ tot = 6.2 ± 0.2(stat) ± 1.4(syst)%. After extrapolating this result to the mass interval of m 2 φ < M 2 X < 0.05W 2 and correcting it for proton dissociation, the fraction of the total cross section attributed to single diffractive photon dissociation, γp → Xp, is found to be σ SD /σ tot = 13.3 ± 0.5(stat) ± 3.6(syst)%. The mass spectrum of the dissociated photon system in the interval 8 < M X < 24 GeV can be described by the triple pomeron (IP IP IP ) diagram with an effective pomeron intercept of α IP (0) = 1.12 ± 0.04(stat) ± 0.08(syst). The cross section for photon dissociation in the range 3 < M X < 8 GeV is significantly higher than that expected from the triple pomeron amplitude describing the region 8 < M X < 24 GeV. Assuming that this discrepancy is due to a pomeron-pomeronreggeon (IP IP IR) term, its contribution to the diffractive cross section in the interval 3 < M X < 24 GeV is estimated to be f IP IP IR = 26 ± 3(stat) ± 12(syst)%.
Physics Letters B, 1997
Charged particle production has been measured in deep inelastic scattering (DIS) events over a la... more Charged particle production has been measured in deep inelastic scattering (DIS) events over a large range of x and Q 2 using the ZEUS detector. The evolution of the scaled momentum, x p , with Q 2 , in the range 10 to 1280 GeV 2 , has been investigated in the current fragmentation region of the Breit frame. The results show clear evidence, in a single experiment, for scaling violations in scaled momenta as a function of Q 2 .
Measurement of elastic ρ 0 photoproduction at HERA
Page 1. Z. Phys. C 69, 39-54 (1995) ZEITSCHRIFT FOR PHYSIK C 9 Springer-Verlag 1995 Measurement o... more Page 1. Z. Phys. C 69, 39-54 (1995) ZEITSCHRIFT FOR PHYSIK C 9 Springer-Verlag 1995 Measurement of elastic p0 photoproduction at HERA ZEUS Collaboration M. Derrick, D. Krakauer, S. Magill, D. Mikunas, B. Musgrave ...
Deep inelastic charged-current reactions have been studied in e + p and e − p collisions at a cen... more Deep inelastic charged-current reactions have been studied in e + p and e − p collisions at a center of mass energy of about 300 GeV in the kinematic region Q 2 >200 GeV 2 and x>0.006 using the ZEUS detector at HERA. The integrated cross sections for Q 2 >200 GeV 2 are found to be σ e + p→νX = 30.3 +5.5 −4.2 +1.6 −2.6 pb and σ e − p→νX = 54.7 +15.9 − 9.8 +2.8 −3.4 pb. Differential cross sections have been measured as functions of the variables x, y and Q 2 . From the measured differential cross sections dσ/dQ 2 , the W boson mass is determined to be M W = 79 +8 −7 +4
Physics Letters B, 1995
Inclusive jet differential cross sections for the reaction ep ~ jet + X at Q2 below 4 GeV 2 have ... more Inclusive jet differential cross sections for the reaction ep ~ jet + X at Q2 below 4 GeV 2 have been measured with the ZEUS detector at HERA using an integrated luminosity of 0.55 pb -t. These cross sections are given in the kinematic region 0.2 < y < 0.85, for jet pseudorapidities in the ep-laboratory range -1 < ~t < 2 and refer to jets at the hadron level with a cone radius of one unit in the 7/-~b plane. These results correspond to quasi-real photoproduction at centre-of-mass energies in the range 130-270 GeV and, approximately, for jet pseudorapidities in the interval -3 < r/~t(yp CMS) < 0. These measurements cover a new kinematic regime of the partonic structure of the photon, at typical scales up to ,-~300 GeV 2 and photon fractional momenta down to x~, ,-, 10 -2. Leading logarithm parton shower Monte Carlo calculations, which include both resolved and direct processes and use the predictions of currently available parametrisations of the photon patton distributions, describe in general the shape and magnitude of the measured ~et and E~ t distributions.
Physics Letters B, 1994
Jets in photoproduction events have been studied with the ZEUS detector for yp centre-of-mass ene... more Jets in photoproduction events have been studied with the ZEUS detector for yp centre-of-mass energies ranging from 130 to 250 GeV. The inclusive jet distributions give evidence for the dominance of resolved photon interactions. In the di-jet sample the direct processes are for the first time clearly isolated. Di-jet cross sections for the resolved and direct processes are given in a restricted kinematic range.
Physics Letters B, 1995
Inclusive jet cross sections for events with a large rapidity gap with respect to the proton dire... more Inclusive jet cross sections for events with a large rapidity gap with respect to the proton direction from the reaction ep -+ jet + X with quasi-real photons have been measured with the ZEUS detector. The cross sections refer to jets with transverse energies EF' > 8 GeV. The data show the characteristics of a diffractive process mediated by pomeron exchange. Assuming that the events are due to the. exchange of a pomeron with partonic structure, the quark and gluon content of the pomeron is probed at a scale N ( EFt)'. A comparison of the measurements with model predictions based on QCD plus Regge phenomenology requires a contribution of partons with a hard momentum density in the pomeron. A combined analysis of the jet cross sections and recent ZEUS measurements of the diffractive structure function in deep inelastic scattering gives the first experimental evidence for the gluon content of the pomeron in diffractive hard scattering processes. The data indicate that between 30% and 80% of the momentum of the pomeron carried by partons is due to hard gluons.
Physics Letters B, 1996
at a median Q2 of 10P4 GeV2 has been studied with the ZEUS detector at HERA. The differential 4 p... more at a median Q2 of 10P4 GeV2 has been studied with the ZEUS detector at HERA. The differential 4 photoproduction cross section du/dt has an exponential shape and has been determined in the kinematic range 0.1 < it/ < 0.5 GeV' and 60 < W < 80 GeV. An integrated cross section of flYI' _-Q,, = 0.96 f O.l9~~:;~,k pb has been obtained by extrapolating to t = 0. When compared to lower energy data, the results show a weak energy dependence of both u,~+$~ and the slope of the t distribution. The C$ decay angular distributions are consistent with s-channel helicity conservation. From lower energies to HERA energies, the features of q5 photoproduction are compatible with those of a soft diffractive process.
Physics Letters B, 1996
Jet photoproduction, where the two highest transverse energy (E jet T ) jets have E jet T above 6... more Jet photoproduction, where the two highest transverse energy (E jet T ) jets have E jet T above 6 GeV and a jet-jet invariant mass above 23 GeV, has been studied with the ZEUS detector at the HERA ep collider. Resolved and direct photoproduction samples have been separated. The cross section as a function of the angle between the jet-jet axis and the beam direction in the dijet rest frame has been measured for the two samples. The measured angular distributions differ markedly from each other. They agree with the predictions of QCD calculations, where the different angular distributions reflect the different spins of the quark and gluon exchanged in the hard subprocess.
Uploads
Papers by Henk Uijterwaal