Exclusive photoproduction of Formula omitted mesons is studied using the H1 detector at the ep collider HERA. A sample of about 900,000 events is used to measure single- and double-differential cross ...sections for the reaction Formula omitted. Reactions where the proton stays intact ( Formula omitted) are statistically separated from those where the proton dissociates to a low-mass hadronic system ( Formula omitted). The double-differential cross sections are measured as a function of the invariant mass Formula omitted of the decay pions and the squared 4-momentum transfer t at the proton vertex. The measurements are presented in various bins of the photon-proton collision energy Formula omitted. The phase space restrictions are Formula omitted, Formula omitted, and Formula omitted. Cross section measurements are presented for both elastic and proton-dissociative scattering. The observed cross section dependencies are described by analytic functions. Parametrising the Formula omitted dependence with resonant and non-resonant contributions added at the amplitude level leads to a measurement of the Formula omitted meson mass and width at Formula omitted and Formula omitted, respectively. The model is used to extract the Formula omitted contribution to the Formula omitted cross sections and measure it as a function of t and Formula omitted. In a Regge asymptotic limit in which one Regge trajectory Formula omitted dominates, the intercept Formula omitted and the slope Formula omitted of the t dependence are extracted for the case Formula omitted.
Measurements of Formula omitted meson production in diffractive deep inelastic scattering Formula omitted are presented which are based on HERA data recorded at a centre-of-mass energy Formula ...omitted with an integrated luminosity of 287 pb Formula omitted. The reaction Formula omitted is studied, where the system X, containing at least one Formula omitted meson, is separated from a leading low-mass proton dissociative system Y by a large rapidity gap. The kinematics of Formula omitted candidates are reconstructed in the Formula omitted decay channel. The measured cross sections compare favourably with next-to-leading order QCD predictions, where charm quarks are produced via boson-gluon fusion. The charm quarks are then independently fragmented to the Formula omitted mesons. The calculations rely on the collinear factorisation theorem and are based on diffractive parton densities previously obtained by H1 from fits to inclusive diffractive cross sections. The data are further used to determine the diffractive to inclusive Formula omitted production ratio in deep inelastic scattering.
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 Formula omitted, the inelasticity Formula omitted and the photon virtuality Formula omitted GeV Formula omitted. The search is performed using H1 data corresponding to an integrated luminosity of 351 pb Formula omitted. 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 and 6 pb, at Formula omitted 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 predictions.
A first measurement is presented of exclusive photoproduction of Formula omitted 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 Formula omitted GeV and correspond to an integrated luminosity of 1.16 pb Formula omitted. The Formula omitted mesons with transverse momenta Formula omitted GeV are reconstructed from their decays to charged pions, while leading neutrons carrying a large fraction of the incoming proton momentum, Formula omitted, are detected in the Forward Neutron Calorimeter. The phase space of the measurement is defined by the photon virtuality Formula omitted GeV Formula omitted, the total energy of the photon-proton system Formula omitted GeV and the polar angle of the leading neutron Formula omitted mrad. The cross section of the reaction Formula omitted 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 Formula omitted meson on the virtual pion. In the framework of one-pion-exchange dominance the elastic cross section of photon-pion scattering, Formula omitted, is extracted. The value of this cross section indicates significant absorptive corrections for the exclusive reaction Formula omitted.
Abstract
The determination of the strong coupling constant
$$\alpha _{\mathrm{s}} (m_{\mathrm{Z}})$$
α
s
(
m
Z
)
from H1 inclusive and dijet cross section data 1 exploits perturbative QCD predictions ...in next-to-next-to-leading order (NNLO) 2–4. An implementation error in the NNLO predictions was found 4 which changes the numerical values of the predictions and the resulting values of the fits. Using the corrected NNLO predictions together with inclusive jet and dijet data, the strong coupling constant is determined to be
$$\alpha _{\mathrm{s}} (m_{\mathrm{Z}}) =0.1166\,(19)_{\mathrm{exp}}\,(24)_{\mathrm{th}}$$
α
s
(
m
Z
)
=
0.1166
(
19
)
exp
(
24
)
th
. Complementarily,
$$\alpha _{\mathrm{s}} (m_{\mathrm{Z}})$$
α
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
$$\alpha _{\mathrm{s}} (m_{\mathrm{Z}}) =0.1147\,(25)_{\mathrm{tot}}$$
α
s
(
m
Z
)
=
0.1147
(
25
)
tot
obtained is consistent with the determination from jet data alone. Corrected figures and numerical results are provided and the discussion is adapted accordingly.
Exclusive photoproduction of ρ0(770) mesons is studied using the H1 detector at the ep collider HERA. A sample of about 900,000 events is used to measure single- and double-differential cross ...sections for the reaction γp→π+π-Y. Reactions where the proton stays intact (mY=mp) are statistically separated from those where the proton dissociates to a low-mass hadronic system (mp<mY<10GeV). The double-differential cross sections are measured as a function of the invariant mass mππ of the decay pions and the squared 4-momentum transfer t at the proton vertex. The measurements are presented in various bins of the photon–proton collision energy Wγp. The phase space restrictions are 0.5≤mππ≤2.2GeV, |t|≤1.5GeV2, and 20≤Wγp≤80GeV. Cross section measurements are presented for both elastic and proton-dissociative scattering. The observed cross section dependencies are described by analytic functions. Parametrising the mππ dependence with resonant and non-resonant contributions added at the amplitude level leads to a measurement of the ρ0(770) meson mass and width at mρ=770.8-2.7+2.6(tot.)MeV and Γρ=151.3-3.6+2.7(tot.)MeV, respectively. The model is used to extract the ρ0(770) contribution to the π+π- cross sections and measure it as a function of t and Wγp. In a Regge asymptotic limit in which one Regge trajectory α(t) dominates, the intercept α(t=0)=1.0654-0.0067+0.0098(tot.) and the slope α′(t=0)=0.233-0.074+0.067(tot.)GeV-2 of the t dependence are extracted for the case mY=mp.
The strong coupling constant Formula omitted 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 Formula omitted at the Z-boson mass Formula omitted 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 Formula omitted. Complementary, Formula omitted is determined together with parton distribution functions of the proton (PDFs) from jet and inclusive DIS data measured by the H1 experiment. The value Formula omitted 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.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).A first measurement is presented of exclusive photoproduction of ... 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 ... GeV and correspond to an integrated luminosity of 1.16 pb... The ... mesons with transverse momenta ... GeV are reconstructed from their decays to charged pions, while leading neutrons carrying a large fraction of the incoming proton momentum, ..., are detected in the Forward Neutron Calorimeter. The phase space of the measurement is defined by the photon virtuality ... GeV..., the total energy of the photon-proton system ... GeV and the polar angle of the leading neutron ... mrad. The cross section of the reaction ... 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 ... meson on the virtual pion. In the framework of one-pion-exchange dominance the elastic cross section of photon-pion scattering, ..., is extracted. The value of this cross section indicates significant absorptive corrections for the exclusive reaction ...
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) A first measurement is presented of exclusive photoproduction of ... 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 ... GeV and correspond to an integrated luminosity of 1.16 pb... The ... mesons with transverse momenta ... GeV are reconstructed from their decays to charged pions, while leading neutrons carrying a large fraction of the incoming proton momentum, ..., are detected in the Forward Neutron Calorimeter. The phase space of the measurement is defined by the photon virtuality ... GeV..., the total energy of the photon-proton system ... GeV and the polar angle of the leading neutron ... mrad. The cross section of the reaction ... 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 ... meson on the virtual pion. In the framework of one-pion-exchange dominance the elastic cross section of photon-pion scattering, ..., is extracted. The value of this cross section indicates significant absorptive corrections for the exclusive reaction ...
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 $\gamma p\to\rho^0 n \pi^+$.
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