The production of photons at very small angles with respect to the proton beam direction is studied in deep-inelastic positron–proton scattering at HERA. The data are taken with the H1 detector in ...the years 2006 and 2007 and correspond to an integrated luminosity of 126 pb
−1
. The analysis covers the range of negative four momentum transfer squared at the positron vertex 6<
Q
2
<100 GeV
2
and inelasticity 0.05<
y
<0.6. Cross sections are measured for the most energetic photon with pseudorapidity
η
>7.9
as a function of its transverse momentum
and longitudinal momentum fraction of the incoming proton
. In addition, the cross sections are studied as a function of the sum of the longitudinal momentum fraction
of all photons in the pseudorapidity range
η
>7.9. The cross sections are normalised to the inclusive deep-inelastic scattering cross section and compared to the predictions of models of deep-inelastic scattering and models of the hadronic interactions of high energy cosmic rays.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A search for squarks in
R
-parity violating supersymmetry is performed in
e
±
p
collisions at HERA using the H1 detector. The full data sample taken at a centre-of-mass energy
GeV is used for the ...analysis, corresponding to an integrated luminosity of 255 pb
−1
of
e
+
p
and 183 pb
−1
of
e
−
p
collision data. The resonant production of squarks via a Yukawa coupling
λ
′ is considered, taking into account direct and indirect
R
-parity violating decay modes. Final states with jets and leptons are investigated. No evidence for squark production is found and mass dependent limits on
λ
′ are obtained in the framework of the Minimal Supersymmetric Standard Model and in the Minimal Supergravity Model. In the considered part of the parameter space, for a Yukawa coupling of electromagnetic strength
λ
′=0.3, squarks of all flavours are excluded up to masses of 275 GeV at 95% confidence level, with down-type squarks further excluded up to masses of 290 GeV.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Inclusive production of D super() mesons in deep-inelastic ep scattering at HERA is studied in the range 5<Q super(2)<100 GeV super(2) of the photon virtuality and 0.02<y<0.7 of the inelasticity of ...the scattering process. The observed phase space for the D super() meson is p sub( )TD super())>1.25 GeV and | eta (D super())|<1.8. The data sample corresponds to an integrated luminosity of 348 pb super(-1) collected with the H1 detector. Single and double differential cross sections are measured and the charm contribution ${F_{2}c\bar{c}}}$ to the proton structure function F sub(2) is determined. The results are compared to perturbative QCD predictions at next-to-leading order implementing different schemes for the charm mass treatment and with Monte Carlo models based on leading order matrix elements with parton showers.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A measurement is presented of the inclusive neutral current e super( plus or minus ) p scattering cross section using data collected by the H1 experiment at HERA during the years 2003 to 2007 with ...proton beam energies E sub( )pof 920, 575, and 460 GeV. The kinematic range of the measurement covers low absolute four-momentum transfers squared, 1.5 GeV super(2)<Q super(2)<120 GeV super(2), small values of Bjorken x, 2.910 super(-5)<x <0.01, and extends to high inelasticity up to y=0.85. The structure function F sub( )Lis measured by combining the new results with previously published H1 data at E sub( )p920 GeV and E sub( )p820 GeV. The new measurements are used to test several phenomenological and QCD models applicable in this low Q super(2) and low x kinematic domain.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The strong coupling constant $\alpha_s(M_Z)$ is determined from inclusive jet
and dijet cross sections in neutral-current deep-inelastic $ep$ scattering
(DIS) measured at HERA by the H1 collaboration ...using next-to-next-to-leading
order (NNLO) QCD predictions. The dependence of the NNLO predictions and of the
resulting value of $\alpha_s(M_Z)$ at the $Z$-boson mass $m_Z$ are studied as a
function of the choice of the renormalisation and factorisation scales. Using
inclusive jet and dijet data together, the strong coupling constant is
determined to be $\alpha_s(M_Z)=0.1166\,(19)_{\rm exp}\,(24)_{\rm th}$.
Complementary, $\alpha_s(M_Z)$ is determined together with parton distribution
functions of the proton (PDFs) from jet and inclusive DIS data measured by the
H1 experiment. The value $\alpha_s(M_Z)=0.1147\,(25)_{\rm tot}$ obtained is
consistent with the determination from jet data alone. The impact of the jet
data on the PDFs is studied. The running of the strong coupling is tested at
different values of the renormalisation scale and the results are found to be
in agreement with expectations.
The production of jets is studied in deep-inelastic e super(c)p scattering at large negative four momentum transfer squared 150<Q super(2)<15000 GeV super(2) using HERA data taken in 1999-2007, ...corresponding to an integrated luminosity of 395 pb super(− 1). Inclusive jet, 2-jet and 3-jet cross sections, normalised to the neutral current deep-inelastic scattering cross sections, are measured as functions of Q super(2), jet transverse momentum and proton momentum fraction. The measurements are well described by perturbative QCD calculations at next-to-leading order corrected for hadronisation effects. The strong coupling as determined from these measurements is (PDF).
The radiation pattern within high energy quark- and gluon-initiated jets (jet substructure) is used extensively as a precision probe of the strong force as well as an environment for optimizing event ...generators with numerous applications in high energy particle and nuclear physics. Looking at electron-proton collisions is of particular interest as many of the complications present at hadron colliders are absent. A detailed study of modern jet substructure observables, jet angularities, in electron-proton collisions is presented using data recorded using the H1 detector at HERA. The measurement is unbinned and multi-dimensional, using machine learning to correct for detector effects. All of the available reconstructed object information of the respective jets is interpreted by a graph neural network, achieving superior precision on a selected set of jet angularities. Training these networks was enabled by the use of a large number of GPUs in the Perlmutter supercomputer at Berkeley Lab. The particle jets are reconstructed in the laboratory frame, using the \(k_{\mathrm{T}}\) jet clustering algorithm. Results are reported at high transverse momentum transfer \(Q^2>150\) GeV\({}^2\), and inelasticity \(0.2 < y < 0.7\). The analysis is also performed in sub-regions of \(Q^2\), thus probing scale dependencies of the substructure variables. The data are compared with a variety of predictions and point towards possible improvements of such models.
The strong coupling constant \(\alpha_s(M_Z)\) is determined from inclusive jet and dijet cross sections in neutral-current deep-inelastic \(ep\) scattering (DIS) measured at HERA by the H1 ...collaboration using next-to-next-to-leading order (NNLO) QCD predictions. The dependence of the NNLO predictions and of the resulting value of \(\alpha_s(M_Z)\) at the \(Z\)-boson mass \(m_Z\) are studied as a function of the choice of the renormalisation and factorisation scales. Using inclusive jet and dijet data together, the strong coupling constant is determined to be \(\alpha_s(M_Z)=0.1166\,(19)_{\rm exp}\,(24)_{\rm th}\). Complementary, \(\alpha_s(M_Z)\) is determined together with parton distribution functions of the proton (PDFs) from jet and inclusive DIS data measured by the H1 experiment. The value \(\alpha_s(M_Z)=0.1147\,(25)_{\rm tot}\) obtained is consistent with the determination from jet data alone. The impact of the jet data on the PDFs is studied. The running of the strong coupling is tested at different values of the renormalisation scale and the results are found to be in agreement with expectations.
Signals of QCD instanton-induced processes are searched for in neutral current deep-inelastic scattering at the electron-proton collider HERA in the kinematic region defined by the Bjorken-scaling ...variable $x > 10^{-3}$, the inelasticity $0.2< y < 0.7$ and the photon virtuality $150 < Q^2 < 15000$ GeV$^2$. The search is performed using H1 data corresponding to an integrated luminosity of ~$351$ pb$^{-1}$. No evidence for the production of QCD instanton-induced events is observed. Upper limits on the cross section for instanton-induced processes between $1.5$~pb and $6$~pb, at $95\%$~ confidence level, are obtained depending on the kinematic domain in which instantons could be produced. Compared to earlier publications, the limits are improved by an order of magnitude and for the first time are challenging theory predictions.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A first measurement is presented of exclusive photoproduction of $\rho^0$ mesons associated with leading neutrons at HERA. The data were taken with the H1 detector in the years $2006$ and $2007$ at a ...centre-of-mass energy of $\sqrt{s}=319$ GeV and correspond to an integrated luminosity of $1.16$ pb$^{-1}$. The $\rho^0$ mesons with transverse momenta $p_T<1$ GeV are reconstructed from their decays to charged pions, while leading neutrons carrying a large fraction of the incoming proton momentum, $x_L>0.35$, are detected in the Forward Neutron Calorimeter. The phase space of the measurement is defined by the photon virtuality $Q^2 < 2$ GeV$^2$, the total energy of the photon-proton system $20 < W_{\gamma p} < 100$ GeV and the polar angle of the leading neutron $\theta_n < 0.75$ mrad. The cross section of the reaction $\gamma p \to \rho^0 n \pi^+$ is measured as a function of several variables. The data are interpreted in terms of a double peripheral process, involving pion exchange at the proton vertex followed by elastic photoproduction of a $\rho^0$ meson on the virtual pion. In the framework of one-pion-exchange dominance the elastic cross section of photon-pion scattering, $\sigma^{\rm el}(\gamma\pi^+ \to \rho^0\pi^+)$, is extracted. The value of this cross section indicates significant absorptive corrections for the exclusive reaction $\gamma p\to\rho^0 n \pi^+$.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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