106 research outputs found
Measurements of Transverse Energy Flow in Deep-Inelastic Scattering at HERA
Measurements of transverse energy flow are presented for neutral current
deep-inelastic scattering events produced in positron-proton collisions at
HERA. The kinematic range covers squared momentum transfers Q^2 from 3.2 to
2,200 GeV^2, the Bjorken scaling variable x from 8.10^{-5} to 0.11 and the
hadronic mass W from 66 to 233 GeV. The transverse energy flow is measured in
the hadronic centre of mass frame and is studied as a function of Q^2, x, W and
pseudorapidity. A comparison is made with QCD based models. The behaviour of
the mean transverse energy in the central pseudorapidity region and an interval
corresponding to the photon fragmentation region are analysed as a function of
Q^2 and W.Comment: 26 pages, 8 figures, submitted to Eur. Phys.
Searches at HERA for Squarks in R-Parity Violating Supersymmetry
A search for squarks in R-parity violating supersymmetry is performed in e^+p
collisions at HERA at a centre of mass energy of 300 GeV, using H1 data
corresponding to an integrated luminosity of 37 pb^(-1). The direct production
of single squarks of any generation in positron-quark fusion via a Yukawa
coupling lambda' is considered, taking into account R-parity violating and
conserving decays of the squarks. No significant deviation from the Standard
Model expectation is found. The results are interpreted in terms of constraints
within the Minimal Supersymmetric Standard Model (MSSM), the constrained MSSM
and the minimal Supergravity model, and their sensitivity to the model
parameters is studied in detail. For a Yukawa coupling of electromagnetic
strength, squark masses below 260 GeV are excluded at 95% confidence level in a
large part of the parameter space. For a 100 times smaller coupling strength
masses up to 182 GeV are excluded.Comment: 32 pages, 14 figures, 3 table
Deep-Inelastic Inclusive ep Scattering at Low x and a Determination of alpha_s
A precise measurement of the inclusive deep-inelastic e^+p scattering cross
section is reported in the kinematic range 1.5<= Q^2 <=150 GeV^2 and
3*10^(-5)<= x <=0.2. The data were recorded with the H1 detector at HERA in
1996 and 1997, and correspond to an integrated luminosity of 20 pb^(-1). The
double differential cross section, from which the proton structure function
F_2(x,Q^2) and the longitudinal structure function F_L(x,Q^2) are extracted, is
measured with typically 1% statistical and 3% systematic uncertainties. The
measured partial derivative (dF_2(x,Q^2)/dln Q^2)_x is observed to rise
continuously towards small x for fixed Q^2. The cross section data are combined
with published H1 measurements at high Q^2 for a next-to-leading order DGLAP
QCD analysis.The H1 data determine the gluon momentum distribution in the range
3*10^(-4)<= x <=0.1 to within an experimental accuracy of about 3% for Q^2 =20
GeV^2. A fit of the H1 measurements and the mu p data of the BCDMS
collaboration allows the strong coupling constant alpha_s and the gluon
distribution to be simultaneously determined. A value of alpha
_s(M_Z^2)=0.1150+-0.0017 (exp) +0.0009-0.0005 (model) is obtained in NLO, with
an additional theoretical uncertainty of about +-0.005, mainly due to the
uncertainty of the renormalisation scale.Comment: 68 pages, 24 figures and 18 table
Inelastic photoproduction of J/Psi mesons at HERA
An analysis of inelastic photoproduction of J/Psi mesons is presented using data collected at the ep collider HERA corresponding to an integrated luminosity of above 80pb-1. Differential and double differential cross sections are measured in a wide kinematic region: 6
Inelastic Photoproduction of J/Psi Mesons at HERA
An analysis of inelastic photoproduction of J/Psi mesons is presented using
data collected at the ep collider HERA corresponding to an integrated
luminosity of above 80pb-1. Differential and double differential cross sections
are measured in a wide kinematic region: 60<W_gammap<260 GeV, 1<p_t^2< 60 GeV^2
and 0.05<z<0.9, where z is the fraction of the energy of the exchanged photon
transferred to the J/Psi meson in the rest frame of the target proton. Cross
sections at z<0.3 are presented for the first time. Theoretical calculations
within the Colour Singlet Model at NLO for direct photon processes are shown to
give a good description of the data in the medium z region (0.3<z<0.9) up to
the highest p_t^2 values. A calculation using a k_t factorisation approach in
LO in the Colour Singlet Model is also able to describe these data. The data in
the full z range are also compared to LO calculations within a non-relativistic
QCD framework including color octet and colour singlet contributions for direct
and resolved photons. It seems possible to reconcile data and theory with
modest contributions from colour octet processes. The polarisation of the J/Psi
meson is measured as a function of z and p_t,psi and is reasonably described by
the theoretical predictions.Comment: 30 pages, 11 figures, 11 table
Inelastic Leptoproduction of J/Psi Mesons at HERA
The leptoproduction of J/psi mesons is studied in inelastic reactions for
four momentum transfers 2<Q^2<100GeV^2. The data were taken with the H1
detector at the electron proton collider HERA and correspond to an integrated
luminosity of 77 pb-1. Single differential and double differential cross
sections are measured with increased precision compared with previous analyses.
New leading order calculations within the non-relativistic QCD factorisation
approach including colour octet and colour singlet contributions are compared
with the data and are found to give a reasonable description of most
distributions. An exception is the shape of the distribution in the J/psi
fractional energy, z, which deviates significantly from that of the data.
Comparisons with photoproduction are made and the polarisation of the produced
J/psi meson is analysed.Comment: 27 pages, 7 figures and 7 table
On the Rise of the Proton Structure Function F Towards Low x
A measurement of the derivative (d ln F_2 / d lnx)_(Q^2)= -lambda(x,Q^2) of the proton structure function F_2 is presented in the low x domain of deeply inelastic positron-proton scattering. For 5*10^(-5)=1.5 GeV^2, lambda(x,Q^2) is found to be independent of x and to increase linearly with ln(Q^2)
Feasibility study of an absolute energy calibration of imaging atmospheric Cherenkov telescopes by starlight
A new method is presented for an absolute energy calibration of imaging atmospheric Cherenkov
telescopes as a whole instrument at all relevant wavelengths. For this study the Cherenkov
telescope #1 of the HEGRA experiment was used. The
calibration was carried out by detecting the light of different selected stars during one
night. From the data a simple linear correlation was derived between the anode current of
the Cherenkov camera photomultiplier tubes and the incident photon flux. This result is
important for the imaging air Cherenkov technique in several aspects: The method enables to
determine the response function of Cherenkov telescopes in the energetic range of Cherenkov
light quickly and reliably. Therefore it can be used as an atmospheric calorimeter by
measuring the absolute integrated flux of Cherenkov photons. Moreover, the signal of a point
run can be predicted and a simulation of the apparatus response can be carried out more
reliably.
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