A new measurement of the proton structure function F_2(x,Q^2) is reported for momentum transfers squared Q^2 between 1.5~GeV^2 and 5000~GeV^2 and for Bjorken x between 3\cdot 10^{-5} and 0.32 using ...data collected by the HERA experiment H1 in 1994. The data represent an increase in statistics by a factor of ten with respect to the analysis of the 1993 data. Substantial extension of the kinematic range towards low Q^2 and x has been achieved using dedicated data samples and events with initial state photon radiation. The structure function is found to increase significantly with decreasing x, even in the lowest accessible Q^2 region. The data are well described by a Next to Leading Order QCD fit and the gluon density is extracted.
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IJS, IMTLJ, KILJ, KISLJ, NUK, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Inclusive D*± production is measured in deep-inelastic ep scattering at HERA with the H1 detector. In addition, the production of dijets in events with a D*± meson is investigated. The analysis ...covers values of photon virtuality 2 ≤ Q2 ≤ 100 GeV2 and of inelasticity 0.05 ≤ y ≤ 0.7. Differential cross sections are measured as a function of Q2 and x and of various D*± meson and jet observables. Within the experimental and theoretical uncertainties all measured cross sections are found to be adequately described by next-to-leading order (NLO) QCD calculations, based on the photon-gluon fusion process and DGLAP evolution, without the need for an additional resolved component of the photon beyond what is included at NLO. A reasonable description of the data is also achieved by a prediction based on the CCFM evolution of partons involving the kT-unintegrated gluon distribution of the proton.
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DOBA, FZAB, GEOZS, IJS, IMTLJ, IZUM, KILJ, KISLJ, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Excitation functions of the differential cross sections
dσ
dgw
, analyzing powers
A
N
and spin correlation parameters
A
NN
,
A
SS
and
A
SL
have been measured with internal targets at the Cooler ...Synchrotron COSY. Data were taken continously during the acceleration and deceleration of the internal beam for kinetic energies between 450 and 2500 MeV and scattering angles 30° ⩽ σ
cm
⩽ 90°. Details of the experimental method are presented. The results provide excitation functions and angular distributions of high precision and internal consistency. No evidence for narrow structures are found. Upper limits on the coupling of narrow resonances to elastic scattering in the mass range √
s = 2.2…2.8 GeV are deduced. The data have significant impact on phase shift solutions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Measurements are presented of inclusive charm and beauty cross sections in e$^+$p collisions at HERA for values of photon virtuality Q$^2$ > 150 GeV$^2$ and of inelasticity 0.1 < y < 0.7. The charm ...and beauty fractions are determined using a method based on the impact parameter, in the transverse plane, of tracks to the primary vertex, as measured by the H1 vertex detector. The data are divided into four regions in Q$^2$ and Bjorken x, and values for the structure functions $F_2^{c\overline{c}}$ and $F_2^{b\overline{b}}$ are obtained. The results are found to be compatible with the predictions of perturbative quantum chromodynamics.
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DOBA, FZAB, GEOZS, IJS, IMTLJ, IZUM, KILJ, KISLJ, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
This Letter of Intent describes LUXE (Laser Und XFEL Experiment), an experiment that aims to use the high-quality and high-energy electron beam of the European XFEL and a powerful laser. The ...scientific objective of the experiment is to study quantum electrodynamics processes in the regime of strong fields. High-energy electrons, accelerated by the European XFEL linear accelerator, and high-energy photons, produced via Bremsstrahlung of those beam electrons, colliding with a laser beam shall experience an electric field up to three times larger than the Schwinger critical field (the field at which the vacuum itself is expected to become unstable and spark with spontaneous creation of electron-positron pairs) and access a new regime of quantum physics. The processes to be investigated, which include nonlinear Compton scattering and nonlinear Breit-Wheeler pair production, are relevant to a variety of phenomena in Nature, e.g. in the areas of astrophysics and collider physics and complement recent results in atomic physics. The setup requires in particular the extraction of a minute fraction of the electron bunches from the European XFEL accelerator, the installation of a powerful laser with sophisticated diagnostics, and an array of precision detectors optimised to measure electrons, positrons and photons. Physics sensitivity projections based on simulations are also provided.
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