22 research outputs found
Angular and Current-Target Correlations in Deep Inelastic Scattering at HERA
Correlations between charged particles in deep inelastic ep scattering have
been studied in the Breit frame with the ZEUS detector at HERA using an
integrated luminosity of 6.4 pb-1. Short-range correlations are analysed in
terms of the angular separation between current-region particles within a cone
centred around the virtual photon axis. Long-range correlations between the
current and target regions have also been measured. The data support
predictions for the scaling behaviour of the angular correlations at high Q2
and for anti-correlations between the current and target regions over a large
range in Q2 and in the Bjorken scaling variable x. Analytic QCD calculations
and Monte Carlo models correctly describe the trends of the data at high Q2,
but show quantitative discrepancies. The data show differences between the
correlations in deep inelastic scattering and e+e- annihilation.Comment: 26 pages including 10 figures (submitted to Eur. J. Phys. C
Angular and Current-target Correlations in Deep Inelastic Scattering at HERA
Correlations between charged particles in deep inelastic e+ p scattering have been studied in the Breit frame with the ZEUS detector at HERA using an integrated luminosity of 6.4pb-1. Short-range correlations are analysed in terms of the angular separation between current-region particles within a cone centred around the virtual photon axis. Long-range correlations between the current and target regions have also been measured. The data support predictions for the scaling behaviour of the angular correlations at high Q2 and for anti-correlations between the current and target regions over a large range in Q2 and in the Bjorken scaling variable x. Analytic QCD calculations and Monte Carlo models correctly describe the trends of the data at high Q2, but show quantitative discrepancies. The data show differences between the correlations in deep inelastic scattering and e+e- annihilation
Kidney transplantation, bioengineering and regeneration: an originally immunology-based discipline destined to transition towards ad hoc organ manufacturing and repair
Measurement of D*+- production and the charm contribution to F(2) in deep inelastic scattering at HERA
The production of D*+-(2010) mesons in deep inelastic scattering has been
measured in the ZEUS detector at HERA using an integrated luminosity of 37
pb^-1. The decay channels D*+ -> D0 pi+(+c.c.), with D0 -> K- pi+ or D0 ->K-
pi- pi+ pi+, have been used to identify the D mesons. The e+p cross section for
inclusive D*+- production with 1<Q^2<600 GeV^2 and 0.02<y<0.7 is 8.31 +-
0.31(stat.) +0.30-0.50(syst.) nb in the kinematic region 1.5< pT(D*+-)<15 GeV
and |eta(D*+-)|<1.5. Differential cross sections are consistent with a
next-to-leading-order perturbative-QCD calculation when using
charm-fragmentation models which take into account the interaction of the charm
quark with the proton remnant.
The observed cross section is extrapolated to the full kinematic region in
pT(D*+-) and eta(D*+-) in order to determine the charm contribution,
F^ccbar_2(x,Q^2), to the proton structure function. The ratio
F^ccbar_2/F_2 rises from ~10% at Q^2 ~1.8 GeV^2 to ~30% at Q^2 ~130 GeV^2 for
x values in the range 10^-4 to 10-3.Comment: 35 pages, 9 figures. Correction 7/10/99: Figure 9 has been updated.
Correction 3/04/00: Miss-prints in tables (1,2,3) and in Figure 5 have been
correcte
Angular and current-target correlations in deep inelastic scattering at HERA
Correlations between charged particles in deep inelastic e+ p scattering have been studied in the Breit frame with the ZEUS detector at HERA using an integrated luminosity of 6.4pb-1. Short-range correlations are analysed in terms of the angular separation between current-region particles within a cone centred around the virtual photon axis. Long-range correlations between the current and target regions have also been measured. The data support predictions for the scaling behaviour of the angular correlations at high Q2 and for anti-correlations between the current and target regions over a large range in Q2 and in the Bjorken scaling variable x. Analytic QCD calculations and Monte Carlo models correctly describe the trends of the data at high Q2, but show quantitative discrepancies. The data show differences between the correlations in deep inelastic scattering and e+e- annihilation
Measurement of the diffractive cross-section in deep inelastic scattering using ZEUS 1994 data
The DIS diffractive cross section, d sigma(gamma*p-->XN)(diff)/dM(X), has been measured in the mass range M(X) XN)(diff) (M(X), W, Q(2))/dM(X) proportional to W(adiff) with a(diff) = 0.507 +/- 0.034(stat)(-0.046)(+0.155) (syst) corresponding to a t-averaged pomeron trajectory of (P) = 1.127 +/- 0.009(stat)(-0.012)(+0.039) (syst) which is larger than (P) observed in hadron-hadron scattering The W dependence of the diffractive cross section is found to be the same as that of the total cross section for scattering of virtual photons on protons. The data are consistent with the assumption that the diffractive structure function F(2)(D(3)) factorizes according to x(P)F(2)(D(3))(x(p), beta, Q(2)) = (x(0)/x(P))(n)F(2)(D(2)) (beta, Q(2)). They are also consistent with QCD based models which incorporate factorization breaking. The rise of x(P)F(2)(D(3)) with decreasing x(P) and the weak dependence of F(2)(D(2)) On Q(2) suggest a substantial contribution from partonic interactions
Measurement of Dijet photoproduction at high transverse energies at HERA
The cross section for dijet photoproduction at high transverse energies is
presented as a function of the transverse energies and the pseudorapidities of
the jets. The measurement is performed using a sample of ep-interactions
corresponding to an integrated luminosity of 6.3 pb^(-1), recorded by the ZEUS
detector.Jets are defined by applying a k_T-clustering algorithm to the hadrons
observed in the final state. The measured cross sections are compared to
next-to-leading order QCD calculations. In a kinematic regime where theoretical
uncertainties are expected to be small, the measured cross sections are higher
than these calculations.Comment: 32 pages including 6 figure
ZEUS results on the measurement and phenomenology of F2 at low cursive greek chi and low Q2
Measurements of the proton structure function F2 for 0.6 < Q2 < 17 GeV2 and 1.2 × 10-5 < cursive Greek chi < 1.9 × 10 -3 from ZEUS 1995 shifted vertex data are presented. From ZEUS F2 data the slopes dF2/d ln Q2 at fixed cursive Greek chi and din F2/d ln(1/cursive Greek chi) for cursive Greek chi < 0.01 at fixed Q2 are derived. For the latter, E665 data are also used. The transition region in Q2 is explored using the simplest non-perturbative models and NLO QCD. The data at very low Q2 ≤ 0.65 GeV2 are described successfully by a combination of generalised vector meson dominance and Regge theory. From a NLO QCD fit to ZEUS data the gluon density in the proton is extracted in the range 3 × 10-5 < cursive Greek chi < 0.7. Data from NMC and BCDMS constrain the fit at large cursive Greek chi. Assuming the NLO QCD description to be valid down to Q2 ∼ 1 GeV2, it is found that the qq̄ sea distribution is still rising at small cursive Greek chi and the lowest Q2 values whereas the gluon distribution is strongly suppressed
Measurement of the spin-density matrix elements in exclusive electroproduction of ρ0 mesons at HERA
Exclusive electroproduction of ρ0 mesons has been measured using the ZEUS detector at HERA in two Q2 ranges, 0.25 < Q2 < 0.85 GeV2 and 3 < Q2 < 30 GeV2. The low-Q2 data span the range 20 < W < 90 GeV; the high-Q2 data cover the 40 < W < 120 GeV interval. Both samples extend up to four-momentum transfers of |t| = 0.6 GeV2. The distribution in the azimuthal angle between the positron scattering plane and the ρ0 production plane shows a small but significant violation of s-channel helicity conservation, corresponding to the production of longitudinally polarised (i.e. helicity zero) ρ0 mesons from transverse photons. Measurements of the 15 combinations of spin-density matrix elements which completely define the angular distributions are presented and discussed
Measurement of the spin density matrix elements in exclusive electroproduction of rho0 mesons at HERA
Exclusive electroproduction of rho^0 mesons has been measured using the ZEUS
detector at HERA in two Q^2 ranges, 0.25<Q^2<0.85 GeV^2 and 3<Q^2<30 GeV^2. The
low-Q^2 data span the range 20<W<90 GeV; the high-Q^2 data cover the 40<W<120
GeV interval. Both samples extend up to four-momentum transfers of |t|=0.6
GeV^2. The distribution in the azimuthal angle between the positron scattering
plane and the rho^0 production plane shows a small but significant violation of
s-channel helicity conservation, corresponding to the production of
longitudinally polarised (i.e. helicity zero) rho^0 mesons from transverse
photons. Measurements of the 15 combinations of spin-density matrix elements
which completely define the angular distributions are presented and discussed.Comment: 32 pages, 8 figures. This version has been accepted by The European
Physics Journal C and incorporates the referee's comment