A
bstract
We present a state-of-the-art computation for the production of dijets in proton-proton and proton-lead collisions at the LHC, in forward rapidity domains covered by the ATLAS calorimeter ...and the planned FoCal extension of the ALICE detector. We use the small-
x
improved TMD (ITMD) formalism, together with collinearly improved TMD gluon distributions and full
b
-space Sudakov resummation, and discuss nonperturbative corrections due to hadronization and showers using the Pythia event generator. We observe that the production of forward dijets in proton-nucleus collisions at moderately low
p
T
is an excellent probe of saturation effects, and demonstrate that the Sudakov resummation does not alter the suppression of the cross section.
We study 3-jet event topologies in proton-proton collisions at a centre-of-mass energy of
s
=
13
TeV
in a configuration, where one jet is present in the central pseudorapidity region (
|
η
|
<
2.0
) ...while two other jets are in a more forward (same hemisphere) area (
|
η
|
>
2.0
). We compare various parton level predictions using: collinear factorisation,
k
T
-factorisation with fully off-shell matrix elements and the hybrid framework. We study the influence of different parton distribution functions, initial state radiation, final state radiation, and hadronisation. We focus on differential cross sections as a function of azimuthal angle difference between the leading dijet system and the third jet, which is found to have excellent sensitivity to the physical effects under study.
Charged particle multiplicity distributions in positron-proton deep inelastic scattering at a centre-of-mass energy Formula omitted GeV are measured. The data are collected with the H1 detector at ...HERA corresponding to an integrated luminosity of 136 pb Formula omitted. Charged particle multiplicities are measured as a function of photon virtuality Formula omitted, inelasticity y and pseudorapidity Formula omitted in the laboratory and the hadronic centre-of-mass frames. Predictions from different Monte Carlo models are compared to the data. The first and second moments of the multiplicity distributions are determined and the KNO scaling behaviour is investigated. The multiplicity distributions as a function of Formula omitted and the Bjorken variable Formula omitted are converted to the hadron entropy Formula omitted, and predictions from a quantum entanglement model are tested.
The azimuthal correlation,
Δ
ϕ
12
, of high transverse momentum jets in pp collisions at
s
=
13
TeV is studied by applying PB-TMD distributions to NLO calculations via MCatNLO together with the ...PB-TMD parton shower. A very good description of the cross section as a function of
Δ
ϕ
12
is observed. In the back-to-back region of
Δ
ϕ
12
→
π
, a very good agreement is observed with the PB-TMD Set 2 distributions while significant deviations are obtained with the PB-TMD Set 1 distributions. Set 1 uses the evolution scale while Set 2 uses transverse momentum as an argument in
α
s
, and the above observation therefore confirms the importance of an appropriate soft-gluon coupling in angular ordered parton evolution. The total uncertainties of the predictions are dominated by the scale uncertainties of the matrix element, while the uncertainties coming from the PB-TMDs and the corresponding PB-TMD shower are very small. The
Δ
ϕ
12
measurements are also compared with predictions using MCatNLO together
Pythia
8, illustrating the importance of details of the parton shower evolution.
The determination of the strong coupling constant
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
α
s
(
m
Z
)
=
0.1166
(
19
)
exp
(
24
)
th
. Complementarily,
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
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.
The production of leading neutrons, where the neutron carries a large fraction
x
L
of the incoming proton’s longitudinal momentum, is studied in deep-inelastic positron-proton scattering at HERA. The ...data were taken with the H1 detector in the years 2006 and 2007 and correspond to an integrated luminosity of 122 pb
−1
. The semi-inclusive cross section is measured in the phase space defined by the photon virtuality 6<
Q
2
<100 GeV
2
, Bjorken scaling variable 1.5⋅10
−4
<
x
<3⋅10
−2
, longitudinal momentum fraction 0.32<
x
L
<0.95 and neutron transverse momentum
p
T
<0.2 GeV. The leading neutron structure function,
, and the fraction of deep-inelastic scattering events containing a leading neutron are studied as a function of
Q
2
,
x
and
x
L
. Assuming that the pion exchange mechanism dominates leading neutron production, the data provide constraints on the shape of the pion structure function.
The H1 very forward proton spectrometer at HERA Astvatsatourov, A.; Cerny, K.; Delvax, J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2014, Letnik:
736
Journal Article
Recenzirano
The very forward proton spectrometer, VFPS, is a component of the H1 detector at the HERA collider. Scattered protons emitted with a polar angle less than 1mrad and carrying a fractional energy 1−xP, ...0.008<xP≤0.028 of the incident proton beam energy can be detected by scintillating fiber detectors which are read out by position sensitive photo-multipliers. These detectors are contained in Roman pot stations which are moved close to the circulating proton beam. The structure, operation and performance of the two Roman pot stations located at about 220m from the H1 interaction point in the cryogenic section of the proton ring are described.
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