350 research outputs found
Fine structure in the azimuthal transverse momentum correlations at GeV using the event shape analysis
The experimental results on transverse momentum azimuthal hadron correlations
at RHIC have opened a rich field for parton energy loss analysis in heavy-ion
collisions. Recently, a considerable amount of work has beendevoted to study
the shapes of the ``away-side'' jet which exhibit an interesting and unexpected
``double hump'' structure not observed in the analogous treatment of data.
Driven by the possibility that the latter result might just mean that such
structure exists already in the case of collisions, but that its relative
intensity could be small, here we use the Event Shape Analysis to show that it
is possible to identify and select well defined event topologies in
collisions, among which, a double hump structure for the away-side jet emerges.
Using two shape parameters, the sphericity in the transverse plane and the
recoil to analyze a sample of PYTHIA generated collisions at
GeV, we show that this structure corresponds to two jets
emitted in the backward hemisphere. Finally, we show that Q-PYTHIA
qualitatively reproduces the decrease in the yield of dijet events and the
increase of the double hump structure in the away side observed in heavy ion
collisions. The implications for the treatment of parton energy loss in
heavy-ion collisions are discussedComment: 6 pages, 7 fugures: One figure was changed, references were added.
This version will appear in Eur. Phys. J.
Search for Colour Singlet and Colour Reconnection Effects in Hadronic Z Decays at LEP
A search is performed in symmetric 3-jet hadronic Z decay events for evidence
of colour singlet production or colour reconnection effects. Asymmetries in the
angular separation of particles are found to be sensitive indicators of such
effects. Upper limits on the level of colour singlet production and colour
reconnection effects are established for a variety of models
Forward pi^0 Production and Associated Transverse Energy Flow in Deep-Inelastic Scattering at HERA
Deep-inelastic positron-proton interactions at low values of Bjorken-x down
to x \approx 4.10^-5 which give rise to high transverse momentum pi^0 mesons
are studied with the H1 experiment at HERA. The inclusive cross section for
pi^0 mesons produced at small angles with respect to the proton remnant (the
forward region) is presented as a function of the transverse momentum and
energy of the pi^0 and of the four-momentum transfer Q^2 and Bjorken-x.
Measurements are also presented of the transverse energy flow in events
containing a forward pi^0 meson. Hadronic final state calculations based on QCD
models implementing different parton evolution schemes are confronted with the
data.Comment: 27 pages, 8 figures and 3 table
Low Q^2 Jet Production at HERA and Virtual Photon Structure
The transition between photoproduction and deep-inelastic scattering is
investigated in jet production at the HERA ep collider, using data collected by
the H1 experiment. Measurements of the differential inclusive jet
cross-sections dsigep/dEt* and dsigmep/deta*, where Et* and eta* are the
transverse energy and the pseudorapidity of the jets in the virtual
photon-proton centre of mass frame, are presented for 0 < Q2 < 49 GeV2 and 0.3
< y < 0.6. The interpretation of the results in terms of the structure of the
virtual photon is discussed. The data are best described by QCD calculations
which include a partonic structure of the virtual photon that evolves with Q2.Comment: 20 pages, 5 Figure
Hadron Production in Diffractive Deep-Inelastic Scattering
Characteristics of hadron production in diffractive deep-inelastic
positron-proton scattering are studied using data collected in 1994 by the H1
experiment at HERA. The following distributions are measured in the
centre-of-mass frame of the photon dissociation system: the hadronic energy
flow, the Feynman-x (x_F) variable for charged particles, the squared
transverse momentum of charged particles (p_T^{*2}), and the mean p_T^{*2} as a
function of x_F. These distributions are compared with results in the gamma^* p
centre-of-mass frame from inclusive deep-inelastic scattering in the
fixed-target experiment EMC, and also with the predictions of several Monte
Carlo calculations. The data are consistent with a picture in which the
partonic structure of the diffractive exchange is dominated at low Q^2 by hard
gluons.Comment: 16 pages, 6 figures, submitted to Phys. Lett.
RFMirTarget: A Random Forest Classifier for Human miRNA Target Gene Prediction
Abstract. MicroRNAs (miRNAs) are key regulators of eukaryotic gene expression whose fundamental role has been already identified in many cell pathways. The correct identification of miRNAs targets is a major challenge in bioinformatics. So far, machine learning-based methods for miRNA-target prediction have shown the best results in terms of specificity and sensitivity. However, despite its well-known efficiency in other classifying tasks, the random forest algorithm has not been employed in this problem. Therefore, in this work we present RFMirTarget, an efficient random forest miRNA-target prediction system. Our tool analyzes the alignment between a candidate miRNA-target pair and extracts a set of structural, thermodynamics, alignment and position-based features. Experiments have shown that RFMirTarget achieves a Matthew’s correlation coefficient nearly 48 % greater than the performance reported for the MultiMiTar, which was trained upon the same data set. In addition, tests performed with RFMirTarget reinforce the importance of the seed region for target prediction accuracy
Measurement of D* Meson Cross Sections at HERA and Determination of the Gluon Density in the Proton using NLO QCD
With the H1 detector at the ep collider HERA, D* meson production cross
sections have been measured in deep inelastic scattering with four-momentum
transfers Q^2>2 GeV2 and in photoproduction at energies around W(gamma p)~ 88
GeV and 194 GeV. Next-to-Leading Order QCD calculations are found to describe
the differential cross sections within theoretical and experimental
uncertainties. Using these calculations, the NLO gluon momentum distribution in
the proton, x_g g(x_g), has been extracted in the momentum fraction range
7.5x10^{-4}< x_g <4x10^{-2} at average scales mu^2 =25 to 50 GeV2. The gluon
momentum fraction x_g has been obtained from the measured kinematics of the
scattered electron and the D* meson in the final state. The results compare
well with the gluon distribution obtained from the analysis of scaling
violations of the proton structure function F_2.Comment: 27 pages, 9 figures, 2 tables, submitted to Nucl. Phys.
Measurement of Leading Proton and Neutron Production in Deep Inelastic Scattering at HERA
Deep--inelastic scattering events with a leading baryon have been detected by
the H1 experiment at HERA using a forward proton spectrometer and a forward
neutron calorimeter. Semi--inclusive cross sections have been measured in the
kinematic region 2 <= Q^2 <= 50 GeV^2, 6.10^-5 <= x <= 6.10^-3 and baryon p_T
<= MeV, for events with a final state proton with energy 580 <= E' <= 740 GeV,
or a neutron with energy E' >= 160 GeV. The measurements are used to test
production models and factorization hypotheses. A Regge model of leading baryon
production which consists of pion, pomeron and secondary reggeon exchanges
gives an acceptable description of both semi-inclusive cross sections in the
region 0.7 <= E'/E_p <= 0.9, where E_p is the proton beam energy. The leading
neutron data are used to estimate for the first time the structure function of
the pion at small Bjorken--x.Comment: 30 pages, 9 figures, 2 tables, submitted to Eur. Phys.
Search for Doubly-Charged Higgs Boson Production at HERA
A search for the single production of doubly-charged Higgs bosons H^{\pm \pm}
in ep collisions is presented. The signal is searched for via the Higgs decays
into a high mass pair of same charge leptons, one of them being an electron.
The analysis uses up to 118 pb^{-1} of ep data collected by the H1 experiment
at HERA. No evidence for doubly-charged Higgs production is observed and mass
dependent upper limits are derived on the Yukawa couplings h_{el} of the Higgs
boson to an electron-lepton pair. Assuming that the doubly-charged Higgs only
decays into an electron and a muon via a coupling of electromagnetic strength
h_{e \mu} = \sqrt{4 \pi \alpha_{em}} = 0.3, a lower limit of 141 GeV on the
H^{\pm\pm} mass is obtained at the 95% confidence level. For a doubly-charged
Higgs decaying only into an electron and a tau and a coupling h_{e\tau} = 0.3,
masses below 112 GeV are ruled out.Comment: 15 pages, 3 figures, 1 tabl
Z Boson Pair-Production at LEP
Events stemming from the pair-production of Z bosons in e^+e^- collisions are
studied using 217.4 pb^-1 of data collected with the L3 detector at
centre-of-mass energies from 200 GeV up to 209 GeV. The special case of events
with b quarks is also investigated.
Combining these events with those collected at lower centre-of-mass energies,
the Standard Model predictions for the production mechanism are verified. In
addition, limits are set on anomalous couplings of neutral gauge bosons and on
effects of extra space dimensions
- …