Nicola Coppola - Academia.edu (original) (raw)

Papers by Nicola Coppola

Journal of Instrumentation, 2010

A precise and fast Fabry-Perot cavity polarimeter, installed in the HERA tunnel in the summer of ... more A precise and fast Fabry-Perot cavity polarimeter, installed in the HERA tunnel in the summer of 2003, was used to measure the longitudinal polarisation of the lepton beam. A complete theoretical model has been developed in order to control at the per mill level the degree of circular polarisation of the laser beam. The transport of this quantity within the whole optical setup has also been performed and controlled at the same level of precision. This is the first time that such a precision is achieved in the difficult, hostile and noisy environment of a particle collider.

Physics Letters B, 2003

Dijet angular distributions of photoproduction events in which a D * ± meson is produced in assoc... more Dijet angular distributions of photoproduction events in which a D * ± meson is produced in association with one of two energetic jets have been measured with the ZEUS detector at HERA, using an integrated luminosity of 120 pb −1. Differential cross sections as a function of the angle between the charm-jet and the proton-beam direction in the dijet rest frame have been measured for samples enriched in direct or resolved photon events. The results are compared with predictions from leading-order parton-shower Monte Carlo models and with next-toleading-order QCD calculations. The angular distributions show clear evidence for the existence of charm originating from the photon.

Physics Letters B, 2002

Searches in ep collisions for heavy excited fermions have been performed with the ZEUS detector a... more Searches in ep collisions for heavy excited fermions have been performed with the ZEUS detector at HERA. Excited states of electrons and quarks have been searched for in e + p collisions at a centre-of-mass energy of 300 GeV using an integrated luminosity of 47.7 pb −1. Excited electrons have been sought via the decays e * → eγ, e * → eZ and e * → νW. Excited quarks have been sought via the decays q * → qγ and q * → qW. A search for excited neutrinos decaying via ν * → νγ, ν * → νZ and ν * → eW is presented using e − p collisions at 318 GeV centre-of-mass energy, corresponding to an integrated luminosity of 16.7 pb −1. No evidence for any excited fermion is found, and limits on the characteristic couplings are derived for masses 250 GeV.

Physics Letters B, 2007

Bose-Einstein correlations of charged and neutral kaons have been measured in e ± p deep inelasti... more Bose-Einstein correlations of charged and neutral kaons have been measured in e ± p deep inelastic scattering with an integrated luminosity of 121 pb −1 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 12 = −(p 1 − p 2) 2 , 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.

Physics Letters B, 2012

The exclusive photoproduction reaction γ p → Υ(1S) p has been studied with the ZEUS detector in e... more The exclusive photoproduction reaction γ p → Υ(1S) p has been studied with the ZEUS detector in ep collisions at HERA using an integrated luminosity of 468 pb −1. The measurement covers the kinematic range 60 < W < 220 GeV and Q 2 < 1 GeV 2 , where W is the photon-proton centre-of-mass energy and Q 2 is the photon virtuality. The exponential slope, b, of the t dependence of the cross section, where t is the squared four-momentum transfer at the proton vertex, has been measured, yielding b = 4.3 +2.0 −1.3 (stat.) +0.5 −0.6 (syst.) GeV −2. This constitutes the first measurement of the t dependence of the γ p → Υ(1S) p cross section.

Physics Letters B, 2012

The production of isolated high-energy photons accompanied by jets has been measured in deep inel... more 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 −1. Measurements were made for exchanged photon virtualities, Q 2 , in the range 10 to 350 GeV 2. The photons were measured in the transverseenergy and pseudorapidity ranges 4 < E γ T < 15 GeV and −0.7 < η γ < 0.9, and the jets were measured in the transverse-energy and pseudorapidity ranges 2.5 < E jet T < 35 GeV and −1.5 < η jet < 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%.

Physical Review D, 2002

Characteristics of the hadronic final state of diffractive deep inelastic scattering events, ep →... more Characteristics of the hadronic final state of diffractive deep inelastic scattering events, ep → eXp, were studied in the kinematic range 4 < M X < 35 GeV, 4 < Q 2 < 150 GeV 2 , 70 < W < 250 GeV and 0.0003 < x IP < 0.03 with the ZEUS detector at HERA using an integrated luminosity of 13.8 pb −1. The events were tagged by identifying the diffractively scattered proton using the leading proton spectrometer. The properties of the hadronic final state, X, were studied in its center-of-mass frame using thrust, thrust angle, sphericity, energy flow, transverse energy flow and "seagull" distributions. As the invariant mass of the system increases, the final state becomes more collimated, more aligned and more asymmetric in the average transverse momentum with respect to the direction of the virtual photon. Comparisons of the properties of the hadronic final state with predictions from various Monte Carlo model generators suggest that the final state is dominated by qqg states at the parton level.

The European Physical Journal C, 2004

The European Physical Journal C, 2006

The European Physical Journal C, 2002

The exclusive photoproduction of J/ψ mesons, γ p → J/ψ p, has been studied in ep collisions with ... more The exclusive photoproduction of J/ψ mesons, γ p → J/ψ p, has been studied in ep collisions with the ZEUS detector at HERA, in the kinematic range 20 < W < 290 GeV, where W is the photon-proton centre-of-mass energy. The J/ψ mesons were reconstructed in the muon and the electron decay channels using integrated luminosities of 38 pb −1 and 55 pb −1 , respectively. The helicity structure of J/ψ production shows that the hypothesis of s-channel helicity conservation is satisfied within two standard deviations. The total cross section and the differential cross-section dσ/dt, where t is the squared four-momentum transfer at the proton vertex, are presented as a function of W , for |t| < 1.8 GeV 2. The t distribution exhibits an exponential shape with a slope parameter increasing logarithmically with W with a value b = 4.15 ± 0.05(stat.) +0.30 −0.18 (syst.) GeV −2 at W = 90 GeV. The effective parameters of the Pomeron trajectory are α IP (0) = 1.200±0.009(stat.) +0.004 −0.010 (syst.) and α ′ IP = 0.115±0.018(stat.) +0.008 −0.015 (syst.) GeV −2 .

The European Physical Journal C, 2007

a * The variables x, Q 2 and y, which is used later on in the paper, are the three Lorentz-invari... more a * The variables x, Q 2 and y, which is used later on in the paper, are the three Lorentz-invariant quantities characterizing the DIS processes. Q 2 is the negative of the four-momentum-transfer squared, x the fraction of the proton momentum carried by the struck quark and y the inelasticity.

The European Physical Journal C - Particles and Fields, 2003

The production rates and substructure of jets have been studied in charged current deep inelastic... more The production rates and substructure of jets have been studied in charged current deep inelastic e + p scattering for Q 2 > 200 GeV 2 with the ZEUS detector at HERA using an integrated luminosity of 110.5 pb −1. Inclusive jet cross sections are presented for jets with transverse energies E jet T > 14 GeV and pseudorapidities in the range −1 < η jet < 2. Dijet cross sections are presented for events with a jet having E jet T > 14 GeV and a second jet having E jet T > 5 GeV. Measurements of the mean subjet multiplicity, n sbj , of the inclusive jet sample are presented. Predictions based on parton-shower Monte Carlo models and next-toleading-order QCD calculations are compared to the measurements. The value of α s (M Z), determined from n sbj at y cut = 10 −2 for jets with 25 < E jet T < 119 GeV, is α s (M Z) = 0.1202 ± 0.0052 (stat.) +0.0060 −0.0019 (syst.) +0.0065 −0.0053 (th.

The European Physical Journal C, 2007

Recent ZEUS measurements on dijet production in diffractive deep-inelastic scattering and diffrac... more Recent ZEUS measurements on dijet production in diffractive deep-inelastic scattering and diffractive photoproduction are reviewed. The measured cross sections are compared to next-to-leading order perturbative QCD calculations using recent diffractive parton densities. For diffractive photoproduction, where the factorisation theorem is not proven, such comparison serves as a test of QCD factorisation. No clear evidence of factorisation breaking was found.

The European Physical Journal C, 1998

Optics Express, 2012

The resolution of single-shot coherent diffractive imaging at X-ray free-electron laser facilitie... more The resolution of single-shot coherent diffractive imaging at X-ray free-electron laser facilities is limited by the low signal-to-noise level of diffraction data at high scattering angles. The iterative reconstruction methods, which phase a continuous diffraction pattern to produce an image, must be able to extract information from these weak signals to obtain the best quality images. Here we show how to modify iterative reconstruction methods to improve tolerance to noise. The method is demonstrated with the hybrid input-output method on both simulated data and single-shot diffraction patterns taken at the Linac Coherent Light Source.

High Energy Physics, 2005

A detailed study of vector meson production (φ and J/ψ) in e ± p collisions at HERA with the ZEUS... more A detailed study of vector meson production (φ and J/ψ) in e ± p collisions at HERA with the ZEUS and H1 detector has been performed. The cross sections are measured as a function of Q 2 , W and t. In this contribution, the results are summarised, compared to theoretical calculations and the dynamical picture emerging in perturbative QCD is highlighted. The measurement of the hadronic component of the photon light-cone wave function in the exclusive production of di-pions, ep → eπ + π − p is also reported.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2007

The Global Tracking Trigger (GTT) of the ZEUS experiment is described. The GTT is data driven at ... more The Global Tracking Trigger (GTT) of the ZEUS experiment is described. The GTT is data driven at the ZEUS first level trigger rate of ≤600 Hz and performs event based track finding on data from the experiment's Central Tracking Detector (CTD), silicon Micro Vertex Detector (MVD) and Straw Tube Tracker(STT) forward detectors. The resulting track based trigger quantities calculated (track multiplicity, verticies, vector meson masses, background event probabilities, etc.) are available within ∼9 ms and are used in the experiment's second level trigger to improve the selection of physics events. Detector information is pushed to the PC farm of the GTT using PowerPC VME board computers which are either embedded within the detector's frontend readout system (MVD) or are parasitically attached to them via multiple serial transputer links (CTD and STT). Data flow and control is performed via point-to-point Fast and Giga ethernet switched network connections using the TCP protocol. The principal design challenges were: integrating new and interfacing to existing frontend systems, providing a useful trigger result, satisfying the rate and latency requirements, and not interfering with ongoing data taking during commissioning. These aims have been achieved. The GTT has been actively used in the ZEUS trigger since 2004 when an initial CTD-only algorithm was used, in 2005 this was upgraded to use MVD information which significantly improves track and primary vertex resolutions. Commissioning problems delayed the STT implementation and its use in the GTT has only been tested.

Journal of High Energy Physics, 2009

Beauty photoproduction in dijet events has been measured at HERA with the ZEUS detector using an ... more Beauty photoproduction in dijet events has been measured at HERA with the ZEUS detector using an integrated luminosity of 126 pb −1. Beauty was identified in events with a muon in the final state by using the transverse momentum of the muon relative to the closest jet. Lifetime information from the silicon vertex detector was also used; the impact parameter of the muon with respect to the primary vertex was exploited to discriminate between signal and background. Cross sections for beauty production as a function of the muon and the jet variables as well as dijet correlations are compared to QCD predictions and to previous measurements. The data are well described by predictions from next-to-leading-order QCD.

Journal of High Energy Physics, 2013

The cross sections for inelastic photoproduction of J/ψ and ψ′ mesons have been measured in ep co... more The cross sections for inelastic photoproduction of J/ψ and ψ′ mesons have been measured in ep collisions with the ZEUS detector at HERA, using an integrated luminosity of 468 pb−1 collected in the period 1996–2007. The ψ′ to J/ψ cross section ratio was measured in the range 0.55 < z < 0.9 and 60 < W < 190 GeV as a function of W, z and p T . Here W denotes the photon-proton centre-of-mass energy, z is the fraction of the incident photon energy carried by the meson and p T is the transverse momentum of the meson with respect to the beam axis. The J/ψ cross sections were measured for 0.1 < z < 0.9, 60 < W < 240 GeV and p T > 1 GeV. Theoretical predictions within the non-relativistic QCD framework including NLO colour-singlet and colour-octet contributions were compared to the data, as were predictions based on the k T -factorisation approach.

Journal of Instrumentation, 2010

A precise and fast Fabry-Perot cavity polarimeter, installed in the HERA tunnel in the summer of ... more A precise and fast Fabry-Perot cavity polarimeter, installed in the HERA tunnel in the summer of 2003, was used to measure the longitudinal polarisation of the lepton beam. A complete theoretical model has been developed in order to control at the per mill level the degree of circular polarisation of the laser beam. The transport of this quantity within the whole optical setup has also been performed and controlled at the same level of precision. This is the first time that such a precision is achieved in the difficult, hostile and noisy environment of a particle collider.

Physics Letters B, 2003

Dijet angular distributions of photoproduction events in which a D * ± meson is produced in assoc... more Dijet angular distributions of photoproduction events in which a D * ± meson is produced in association with one of two energetic jets have been measured with the ZEUS detector at HERA, using an integrated luminosity of 120 pb −1. Differential cross sections as a function of the angle between the charm-jet and the proton-beam direction in the dijet rest frame have been measured for samples enriched in direct or resolved photon events. The results are compared with predictions from leading-order parton-shower Monte Carlo models and with next-toleading-order QCD calculations. The angular distributions show clear evidence for the existence of charm originating from the photon.

Physics Letters B, 2002

Searches in ep collisions for heavy excited fermions have been performed with the ZEUS detector a... more Searches in ep collisions for heavy excited fermions have been performed with the ZEUS detector at HERA. Excited states of electrons and quarks have been searched for in e + p collisions at a centre-of-mass energy of 300 GeV using an integrated luminosity of 47.7 pb −1. Excited electrons have been sought via the decays e * → eγ, e * → eZ and e * → νW. Excited quarks have been sought via the decays q * → qγ and q * → qW. A search for excited neutrinos decaying via ν * → νγ, ν * → νZ and ν * → eW is presented using e − p collisions at 318 GeV centre-of-mass energy, corresponding to an integrated luminosity of 16.7 pb −1. No evidence for any excited fermion is found, and limits on the characteristic couplings are derived for masses 250 GeV.

Physics Letters B, 2007

Bose-Einstein correlations of charged and neutral kaons have been measured in e ± p deep inelasti... more Bose-Einstein correlations of charged and neutral kaons have been measured in e ± p deep inelastic scattering with an integrated luminosity of 121 pb −1 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 12 = −(p 1 − p 2) 2 , 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.

Physics Letters B, 2012

The exclusive photoproduction reaction γ p → Υ(1S) p has been studied with the ZEUS detector in e... more The exclusive photoproduction reaction γ p → Υ(1S) p has been studied with the ZEUS detector in ep collisions at HERA using an integrated luminosity of 468 pb −1. The measurement covers the kinematic range 60 < W < 220 GeV and Q 2 < 1 GeV 2 , where W is the photon-proton centre-of-mass energy and Q 2 is the photon virtuality. The exponential slope, b, of the t dependence of the cross section, where t is the squared four-momentum transfer at the proton vertex, has been measured, yielding b = 4.3 +2.0 −1.3 (stat.) +0.5 −0.6 (syst.) GeV −2. This constitutes the first measurement of the t dependence of the γ p → Υ(1S) p cross section.

Physics Letters B, 2012

The production of isolated high-energy photons accompanied by jets has been measured in deep inel... more 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 −1. Measurements were made for exchanged photon virtualities, Q 2 , in the range 10 to 350 GeV 2. The photons were measured in the transverseenergy and pseudorapidity ranges 4 < E γ T < 15 GeV and −0.7 < η γ < 0.9, and the jets were measured in the transverse-energy and pseudorapidity ranges 2.5 < E jet T < 35 GeV and −1.5 < η jet < 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%.

Physical Review D, 2002

Characteristics of the hadronic final state of diffractive deep inelastic scattering events, ep →... more Characteristics of the hadronic final state of diffractive deep inelastic scattering events, ep → eXp, were studied in the kinematic range 4 < M X < 35 GeV, 4 < Q 2 < 150 GeV 2 , 70 < W < 250 GeV and 0.0003 < x IP < 0.03 with the ZEUS detector at HERA using an integrated luminosity of 13.8 pb −1. The events were tagged by identifying the diffractively scattered proton using the leading proton spectrometer. The properties of the hadronic final state, X, were studied in its center-of-mass frame using thrust, thrust angle, sphericity, energy flow, transverse energy flow and "seagull" distributions. As the invariant mass of the system increases, the final state becomes more collimated, more aligned and more asymmetric in the average transverse momentum with respect to the direction of the virtual photon. Comparisons of the properties of the hadronic final state with predictions from various Monte Carlo model generators suggest that the final state is dominated by qqg states at the parton level.

The European Physical Journal C, 2004

The European Physical Journal C, 2006

The European Physical Journal C, 2002

The exclusive photoproduction of J/ψ mesons, γ p → J/ψ p, has been studied in ep collisions with ... more The exclusive photoproduction of J/ψ mesons, γ p → J/ψ p, has been studied in ep collisions with the ZEUS detector at HERA, in the kinematic range 20 < W < 290 GeV, where W is the photon-proton centre-of-mass energy. The J/ψ mesons were reconstructed in the muon and the electron decay channels using integrated luminosities of 38 pb −1 and 55 pb −1 , respectively. The helicity structure of J/ψ production shows that the hypothesis of s-channel helicity conservation is satisfied within two standard deviations. The total cross section and the differential cross-section dσ/dt, where t is the squared four-momentum transfer at the proton vertex, are presented as a function of W , for |t| < 1.8 GeV 2. The t distribution exhibits an exponential shape with a slope parameter increasing logarithmically with W with a value b = 4.15 ± 0.05(stat.) +0.30 −0.18 (syst.) GeV −2 at W = 90 GeV. The effective parameters of the Pomeron trajectory are α IP (0) = 1.200±0.009(stat.) +0.004 −0.010 (syst.) and α ′ IP = 0.115±0.018(stat.) +0.008 −0.015 (syst.) GeV −2 .

The European Physical Journal C, 2007

a * The variables x, Q 2 and y, which is used later on in the paper, are the three Lorentz-invari... more a * The variables x, Q 2 and y, which is used later on in the paper, are the three Lorentz-invariant quantities characterizing the DIS processes. Q 2 is the negative of the four-momentum-transfer squared, x the fraction of the proton momentum carried by the struck quark and y the inelasticity.

The European Physical Journal C - Particles and Fields, 2003

The production rates and substructure of jets have been studied in charged current deep inelastic... more The production rates and substructure of jets have been studied in charged current deep inelastic e + p scattering for Q 2 > 200 GeV 2 with the ZEUS detector at HERA using an integrated luminosity of 110.5 pb −1. Inclusive jet cross sections are presented for jets with transverse energies E jet T > 14 GeV and pseudorapidities in the range −1 < η jet < 2. Dijet cross sections are presented for events with a jet having E jet T > 14 GeV and a second jet having E jet T > 5 GeV. Measurements of the mean subjet multiplicity, n sbj , of the inclusive jet sample are presented. Predictions based on parton-shower Monte Carlo models and next-toleading-order QCD calculations are compared to the measurements. The value of α s (M Z), determined from n sbj at y cut = 10 −2 for jets with 25 < E jet T < 119 GeV, is α s (M Z) = 0.1202 ± 0.0052 (stat.) +0.0060 −0.0019 (syst.) +0.0065 −0.0053 (th.

The European Physical Journal C, 2007

Recent ZEUS measurements on dijet production in diffractive deep-inelastic scattering and diffrac... more Recent ZEUS measurements on dijet production in diffractive deep-inelastic scattering and diffractive photoproduction are reviewed. The measured cross sections are compared to next-to-leading order perturbative QCD calculations using recent diffractive parton densities. For diffractive photoproduction, where the factorisation theorem is not proven, such comparison serves as a test of QCD factorisation. No clear evidence of factorisation breaking was found.

The European Physical Journal C, 1998

Optics Express, 2012

The resolution of single-shot coherent diffractive imaging at X-ray free-electron laser facilitie... more The resolution of single-shot coherent diffractive imaging at X-ray free-electron laser facilities is limited by the low signal-to-noise level of diffraction data at high scattering angles. The iterative reconstruction methods, which phase a continuous diffraction pattern to produce an image, must be able to extract information from these weak signals to obtain the best quality images. Here we show how to modify iterative reconstruction methods to improve tolerance to noise. The method is demonstrated with the hybrid input-output method on both simulated data and single-shot diffraction patterns taken at the Linac Coherent Light Source.

High Energy Physics, 2005

A detailed study of vector meson production (φ and J/ψ) in e ± p collisions at HERA with the ZEUS... more A detailed study of vector meson production (φ and J/ψ) in e ± p collisions at HERA with the ZEUS and H1 detector has been performed. The cross sections are measured as a function of Q 2 , W and t. In this contribution, the results are summarised, compared to theoretical calculations and the dynamical picture emerging in perturbative QCD is highlighted. The measurement of the hadronic component of the photon light-cone wave function in the exclusive production of di-pions, ep → eπ + π − p is also reported.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2007

The Global Tracking Trigger (GTT) of the ZEUS experiment is described. The GTT is data driven at ... more The Global Tracking Trigger (GTT) of the ZEUS experiment is described. The GTT is data driven at the ZEUS first level trigger rate of ≤600 Hz and performs event based track finding on data from the experiment's Central Tracking Detector (CTD), silicon Micro Vertex Detector (MVD) and Straw Tube Tracker(STT) forward detectors. The resulting track based trigger quantities calculated (track multiplicity, verticies, vector meson masses, background event probabilities, etc.) are available within ∼9 ms and are used in the experiment's second level trigger to improve the selection of physics events. Detector information is pushed to the PC farm of the GTT using PowerPC VME board computers which are either embedded within the detector's frontend readout system (MVD) or are parasitically attached to them via multiple serial transputer links (CTD and STT). Data flow and control is performed via point-to-point Fast and Giga ethernet switched network connections using the TCP protocol. The principal design challenges were: integrating new and interfacing to existing frontend systems, providing a useful trigger result, satisfying the rate and latency requirements, and not interfering with ongoing data taking during commissioning. These aims have been achieved. The GTT has been actively used in the ZEUS trigger since 2004 when an initial CTD-only algorithm was used, in 2005 this was upgraded to use MVD information which significantly improves track and primary vertex resolutions. Commissioning problems delayed the STT implementation and its use in the GTT has only been tested.

Journal of High Energy Physics, 2009

Beauty photoproduction in dijet events has been measured at HERA with the ZEUS detector using an ... more Beauty photoproduction in dijet events has been measured at HERA with the ZEUS detector using an integrated luminosity of 126 pb −1. Beauty was identified in events with a muon in the final state by using the transverse momentum of the muon relative to the closest jet. Lifetime information from the silicon vertex detector was also used; the impact parameter of the muon with respect to the primary vertex was exploited to discriminate between signal and background. Cross sections for beauty production as a function of the muon and the jet variables as well as dijet correlations are compared to QCD predictions and to previous measurements. The data are well described by predictions from next-to-leading-order QCD.

Journal of High Energy Physics, 2013

The cross sections for inelastic photoproduction of J/ψ and ψ′ mesons have been measured in ep co... more The cross sections for inelastic photoproduction of J/ψ and ψ′ mesons have been measured in ep collisions with the ZEUS detector at HERA, using an integrated luminosity of 468 pb−1 collected in the period 1996–2007. The ψ′ to J/ψ cross section ratio was measured in the range 0.55 < z < 0.9 and 60 < W < 190 GeV as a function of W, z and p T . Here W denotes the photon-proton centre-of-mass energy, z is the fraction of the incident photon energy carried by the meson and p T is the transverse momentum of the meson with respect to the beam axis. The J/ψ cross sections were measured for 0.1 < z < 0.9, 60 < W < 240 GeV and p T > 1 GeV. Theoretical predictions within the non-relativistic QCD framework including NLO colour-singlet and colour-octet contributions were compared to the data, as were predictions based on the k T -factorisation approach.