The largely unknown parton distribution functions of nuclei and the similarities observed between high-multiplicity pp and pPb events compared to PbPb, often described by means of hydrodynamics, are ...the main motivations for an extended pPb data taking program during LHC Run 3 and Run 4. The future increase in luminosity combined with the LHCb unique detector capabilities will allow to perform new and precise measurements. Moreover, an upgraded internal gas target is going to be installed for the LHCb Run 3, allowing a wider choice of target gas species and an increase of the gas density by up to two orders of magnitude. Prospects will be presented on both the LHCb collider and fixed target programs.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
Particle identification at high-energy physics experiments typically relies on classifiers combining different experimental observables. In this document, an innovative approach employing ...machine learning techniques to describe their dependence from the relevant features is presented. The proposed method is applied to the fixed-target programme at the LHCb experiment, where the sample size of the particle identification calibration channels affects the experimental performance. It is demonstrated to perform better than a model based on the LHCb detailed simulation and to be fast and suitable to a large variety of use cases.
Abstract
Particle identification in large high-energy physics experiments typically relies on
classifiers obtained by combining many experimental observables. Predicting the probability density ...function (
pdf
) of such classifiers in the multivariate space covering the relevant experimental features is usually challenging.
The detailed simulation of the detector response from first principles
cannot provide the reliability needed for the most precise physics measurements.
Data-driven modelling is usually preferred, though sometimes limited by the available data size and different coverage of the feature space by the control channels.
In this paper, we discuss a novel approach to the modelling of particle
identification classifiers using machine-learning techniques. The marginal
pdf
of the classifiers is described with a Gaussian Mixture Model, whose parameters are predicted by Multi Layer Perceptrons trained on calibration data. As a proof of principle, the method is applied to the data acquired by the LHCb experiment in its fixed-target configuration. The model is trained on a data sample of proton-neon collisions and applied to smaller data samples of proton-helium and proton-argon collisions collected at different centre-of-mass energies. The method is shown to perform better than a detailed simulation-based approach, to be fast and suitable to be applied to a large variety of use cases.
A
bstract
A comprehensive set of azimuthal single-spin and double-spin asymmetries in semi-inclusive leptoproduction of pions, charged kaons, protons, and antiprotons from transversely polarized ...protons is presented. These asymmetries include the previously published HERMES results on Collins and Sivers asymmetries, the analysis of which has been extended to include protons and antiprotons and also to an extraction in a three-dimensional kinematic binning and enlarged phase space. They are complemented by corresponding results for the remaining four single-spin and four double-spin asymmetries allowed in the one-photon-exchange approximation of the semi-inclusive deep-inelastic scattering process for target-polarization orientation perpendicular to the direction of the incoming lepton beam. Among those results, significant non-vanishing cos (
ϕ−ϕ
S
) modulations provide evidence for a sizable worm-gear (II) distribution,
g
1
T
q
x
p
T
2
. Most of the other modulations are found to be consistent with zero with the notable exception of large sin (
ϕ
S
) modulations for charged pions and
K
+
.
The LHCspin project Santimaria, Marco; Carassiti, Vittore; Ciullo, Giuseppe ...
SciPost physics proceedings,
07/2022
8
Journal Article
Peer reviewed
Open access
Broad and unexplored kinematic regions can be accessed at the LHC
with fixed-target
pp
p
p
,
pA
p
A
and
PbA
P
b
A
collisions at
\sqrt{s_{NN}}
s
N
N
=72-115 GeV. The LHCb detector is a ...fully-instrumented
forward spectrometer able to run in fixed-target mode, and currently
hosts a target gas cell to take data in the upcoming Run 3. The LHCspin
project aims at extending this physics program to Run 4 and to bring
polarised physics at the LHC. An overview of the physics potential and a
description of the LHCspin experimental setup are presented.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Hard exclusive electroproduction of ... mesons is studied with the HERMES spectrometer at the DESY laboratory by scattering ...27.6 GeV positron and electron beams off a transversely polarized hydrogen target. The amplitudes of five azimuthal modulations of the single-spin asymmetry of the cross section with respect to the transverse proton polarization are measured. They are determined in the entire kinematic region as well as for two bins in photon virtuality and momentum transfer to the nucleon. Also, a separation of asymmetry amplitudes into longitudinal and transverse components is done. These results are compared to a phenomenological model that includes the pion pole contribution. Within this model, the data favor a positive ... transition form factor.
Full text
Available for:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).Exclusive electroproduction of ... mesons on unpolarized hydrogen and deuterium targets is studied in the kinematic region ...of ... GeV..., 3.0 GeV ... 6.3 GeV, and ... GeV... Results on the angular distribution of the ... meson, including its decay products, are presented. The data were accumulated with the HERMES forward spectrometer during the 1996-2007 running period using the 27.6 GeV longitudinally polarized electron or positron beam of HERA. The determination of the virtual-photon longitudinal-to-transverse cross-section ratio reveals that a considerable part of the cross section arises from transversely polarized photons. Spin density matrix elements are presented in projections of ... or ... Violation of ...-channel helicity conservation is observed for some of these elements. A sizable contribution from unnatural-parity-exchange amplitudes is found and the phase shift between those amplitudes that describe transverse ... production by longitudinal and transverse virtual photons, ... and ..., is determined for the first time. A hierarchy of helicity amplitudes is established, which mainly means that the unnatural-parity-exchange amplitude describing the ... transition dominates over the two natural-parity-exchange amplitudes describing the ... and ... transitions, with the latter two being of similar magnitude. Good agreement is found between the HERMES proton data and results of a pQCD-inspired phenomenological model that includes pion-pole contributions, which are of unnatural parity.
Full text
Available for:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The influence of the cold nuclear medium effects on hadron multiplicities in semiinclusive deepinelastic scattering was studied extensively. A series of measurements on deuterium, helium, neon, ...krypton and xenon target has been performed in order to study hadronization. Hadron multiplicities on nucleus A relative to those on deuteron are presented for various hadrons together with the first direct measurement of pt-broadening effects in lepto production. The data have been accumulated by the Hermes experiment at the Desy laboratory using a 27.6 GeV positron or electron beam. These analysis provide precious information concerning the spacetime evolution of hadronization.
Single-spin asymmetries for semi-inclusive electroproduction of charged pions in deep-inelastic scattering of positrons are measured for the first time with transverse target polarization. The ...asymmetry depends on the azimuthal angles of both the pion (phi) and the target spin axis (phi(S)) about the virtual-photon direction and relative to the lepton scattering plane. The extracted Fourier component sin((phi+phi(S))(pi)(UT) is a signal of the previously unmeasured quark transversity distribution, in conjunction with the Collins fragmentation function, also unknown. The component sin((phi-phi(S)(pi)(UT) arises from a correlation between the transverse polarization of the target nucleon and the intrinsic transverse momentum of quarks, as represented by the previously unmeasured Sivers distribution function. Evidence for both signals is observed, but the Sivers asymmetry may be affected by exclusive vector meson production.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
PDF
