Wide Kinematic Range Research Articles

Probing the strange content of the proton with charm production in charged current at LHeC

We study charm production in charged-current deep-inelastic scattering (DIS) using the xFitter framework. Recent results from the LHC have focused renewed attention on the determination of the strange-quark parton distribution function (PDF), and the DIS charm process provides important complementary constraints on this quantity. We examine the current PDF uncertainty and use LHeC pseudodata to estimate the potential improvement from this proposed facility. As xFitter implements both fixed-flavor- and variable-flavor-number schemes, we can compare the impact of these different theoretical choices; this highlights some interesting aspects of multi-scale calculations. We find that the high-statistics LHeC data covering a wide kinematic range could substantially reduce the strange PDF uncertainty.

On the Possibility to Study Antiproton Production at the SPD Detector at NICA Collider for Dark Matter Search in Astrophysical Experiments

Dark matter is an important component of the Standard model of cosmology but its nature is still unknown. One of the most common explanations is that dark matter consists of Weakly Interacting Massive Particles (WIMPs), supposed to be cold thermal relics of the Big Bang and to build up the galactic dark halos. Indirect search of dark matter could be performed via the study of an anomalous antiproton component in cosmic rays originating from possible annihilation of dark matter pairs in the galactic halo, on top of the standard astrophysical production. The measurements performed by the AMS-02 and PAMELA spectrometers have shown that limited knowledge of antiproton-production cross sections in $pp$, $pD$, $pHe$ and $HeHe$ collisions is one of the main uncertainties of background subtraction. The planned SPD experiment at the NICA collider could provide a precision measurement of antiproton yield in wide kinematic range in $pp$ and $pD$ collisions at the energy scale from the threshold to $\sqrt{s}=26$ GeV/$c$.

Diffractive dijet production and Wigner distributions from the color glass condensate

Experimental processes that are sensitive to parton Wigner distributions provide a powerful tool to advance our understanding of proton structure. In this work, we compute gluon Wigner and Husimi distributions of protons within the Color Glass Condensate framework, which includes a spatially dependent McLerran-Venugopalan initial configuration and the explicit numerical solution of the JIMWLK equations. We determine the leading anisotropy of the Wigner and Husimi distributions as a function of the angle between impact parameter and transverse momentum. We study experimental signatures of these angular correlations at a proposed Electron Ion Collider by computing coherent diffractive dijet production cross sections in e+p collisions within the same framework. Specifically, we predict the elliptic modulation of the cross section as a function of the relative angle between nucleon recoil and dijet transverse momentum for a wide kinematical range. We further predict its dependence on collision energy, which is dominated by the growth of the proton with decreasing $x$.

Chronology-based architecture of descending circuits that underlie the development of locomotor repertoire after birth.

The emergence of new and increasingly sophisticated behaviors after birth is accompanied by dramatic increase of newly established synaptic connections in the nervous system. Little is known, however, of how nascent connections are organized to support such new behaviors alongside existing ones. To understand this, in the larval zebrafish we examined the development of spinal pathways from hindbrain V2a neurons and the role of these pathways in the development of locomotion. We found that new projections are continually layered laterally to existing neuropil, and give rise to distinct pathways that function in parallel to existing pathways. Across these chronologically layered pathways, the connectivity patterns and biophysical properties vary systematically to support a behavioral repertoire with a wide range of kinematics and dynamics. Such layering of new parallel circuits equipped with systematically changing properties may be central to the postnatal diversification and increasing sophistication of an animal's behavioral repertoire.

Measurement of the beam spin asymmetry of [formula omitted] in the deep-inelastic regime with CLAS

The beam spin asymmetry of the exclusive pseudoscalar channel e→p→e′p′η was measured for the first time in the deep-inelastic regime (W>2 GeV/c2 and Q2>1 GeV2/c2) using a longitudinally polarized 5.78 GeV electron beam at Jefferson Lab with the CEBAF Large Acceptance Spectrometer. The data were accumulated in 144 four-dimensional bins of Q2, xB, −t and ϕ over a wide kinematic range, where ϕ is the azimuthal angle between the lepton and hadron scattering planes, The measured azimuthal dependence with large amplitudes of the sin⁡ϕ moments is a clear indication of a substantial contribution to the polarized cross-section from transversely polarized virtual photons. In the framework of generalized parton distributions (GPDs) this contribution is expressed via longitudinal-transverse interference between chiral-even and chiral-odd GPDs. The experimental results are compared to the existing theoretical models demonstrating the sensitivity to the product of chiral-odd and chiral-even GPDs and provide new constraints to the existing GPD parameterizations.

Fiducial distributions in Higgs and Drell-Yan production at N3LL+NNLO

The perturbative description of certain differential distributions across a wide kinematic range requires the matching of fixed-order perturbation theory with resummation of large logarithmic corrections to all orders. We present precise matched predictions for transverse-momentum distributions in Higgs boson (H) and Drell-Yan pair (DY) production as well as for the closely related ϕη* distribution at the LHC. The calculation is exclusive in the Born kinematics, and allows for arbitrary fiducial selection cuts on the decay products of the colour singlets, which is of primary relevance for experimental analyses. Our predictions feature very small residual scale uncertainties and display a good convergence of the perturbative series. A comparison of the predictions for DY observables to experimental data at 8 TeV shows a very good agreement within the quoted errors.

Global analysis of color fluctuation effects in proton– and deuteron–nucleus collisions at RHIC and the LHC

We test the hypothesis that configurations of a proton with a large-$x$ parton, $x_p \gtrsim 0.1$, have a smaller than average size. The QCD $Q^2$ evolution equations suggest that these small configurations also have a significantly smaller interaction strength, which has observable consequences in collisions with nuclei. We perform a global analysis of jet production data in proton- and deuteron-nucleus collisions at RHIC and the LHC. Using a model which takes a distribution of interaction strengths into account, we quantitatively extract the $x_p$-dependence of the average interaction strength, $\sigma(x_p)$, over a wide kinematic range. By comparing the RHIC and LHC results, our analysis finds that the interaction strength for small configurations, while suppressed, grows faster with collision energy than does that for average configurations. We check that this energy dependence is consistent with the results of a method which, given $\sigma(x_p)$ at one energy, can be used to quantitatively predict that at another. This finding further suggests that at even lower energies, nucleons with a large-$x_p$ parton should interact much more weakly than those in an average configuration, a phenomenon in line with explanations of the EMC effect for large-$x_p$ quarks in nuclei based on color screening.

Accessing the gluon Sivers function at a future electron-ion collider

In this work, we present a systematic study on the feasibility of probing the largely unexplored transverse momentum dependent gluon Sivers function (GSF) in open charm production, high p$_T$ charged di-hadron and di-jet production at a future high energy, high luminosity Electron-Ion Collider (EIC). The Sivers function is a measure for the anisotropy of the parton distributions in momentum space inside a transversely polarized nucleon. It is proposed that it can be studied through single spin asymmetries in the photon-gluon fusion subprocess in electron proton collisions at the EIC. Using a well tuned Monte Carlo model for deep inelastic scattering, we estimate the possible constraints of the GSF from the future EIC data. A comparison of all the accessible measurements illustrates that the di-jet channel is the most promising way to constrain the magnitude of the GSF over a wide kinematic range.

Quark-Hadron Duality of Spin Structure Functions in CLAS EG1b Data

The hypothesis of quark-hadron duality infers that physical observables of nucleons can be described by a complete set of basis states using either hadronic or quark degrees of freedom. In the EG1b experiment in Hall-B at Jefferson Lab, polarized electrons with energies of 1.6, 2.5, 4.2 and 5.7 GeV were scattered from proton and deuteron targets ( $$^{15}\hbox {NH}_3$$ and $$^{15}\hbox {ND}_3$$ dynamically polarized along the beam direction) and detected with CEBAF large acceptance spectrometer. Nucleon spin structure functions $$g_1$$ and $$g_2$$ were measured over a wide kinematic range ( $$0.05\,\hbox {GeV}^2< Q^2 <5\,\hbox {GeV}^2$$ and $$1.08\,\hbox {GeV}<{W}< 3\,\hbox {GeV}$$ ). These recently published data strongly constrain parametrization of world data in the resonance region, allowing comprehensive tests of Bloom–Gilman duality for polarized nucleons over a wide kinematic range.

Effects of next-to-leading order DGLAP evolution on generalized parton distributions of the proton and deeply virtual Compton scattering at high energy

We studied the effects of NLO Q^2 evolution of generalized parton distributions (GPDs) using the aligned-jet model for the singlet quark and gluon GPDs at an initial evolution scale. We found that the skewness ratio for quarks is a slow logarithmic function of Q^2, reaching r^mathrm{S}=1.5{-}2 at Q^2=100 GeV^2 and r^mathrm{g} approx 1 for gluons in a wide range of Q^2. Using the resulting GPDs, we calculated the DVCS cross section on the proton in NLO pQCD and found that this model in conjunction with modern parameterizations of proton PDFs (CJ15 and CT14) provides a good description of the available H1 and ZEUS data in a wide kinematic range.

Charmonium production in pPb and PbPb collisions at 5.02 TeV with CMS

Charmonium states, such as the J/ψ and ψ(2S) mesons, are excellent probes of the deconfined state of matter, the Quark-Gluon Plasma (QGP) created in heavy ion collisions. In addition, the measurements in pPb collisions allow to study the cold nuclear matter effects, being crucial to disentangle these from the QGP-related effects in PbPb collisions. In this talk the new nuclear modification factor RAA of prompt and nonprompt J/ψ in PbPb collisions at [see formula in PDF] = 5.02 TeV were presented over a wide kinematic range (3 &lt; pT &lt; 50 GeV/c, |y| &lt; 2.4), and fine event-centrality intervals. The results were compared to those at 2.76 TeV over a similar kinematic range. In addition, new prompt ψ(2S) RAA results at 5.02 TeV were reported. Finally the final prompt and nonprompt J/ψ results, as well as preliminary ψ(2S) results, in pPb collisions at 5.02 TeV, were discussed.

Determination of the proton spin structure functions for 0.05&lt;Q2&lt;5GeV2 using CLAS

We present the results of our final analysis of the full data set of g_1^p(Q^2), the spin structure function of the proton, collected using CLAS at Jefferson Lab in 2000-2001. Polarized electrons with energies of 1.6, 2.5, 4.2 and 5.7 GeV were scattered from proton targets (15^NH_3 dynamically polarized along the beam direction) and detected with CLAS. From the measured double spin asymmetries, we extracted virtual photon asymmetries A_1^p and A_2^p and spin structure functions g_1^p and g_2^p over a wide kinematic range (0.05 GeV^2 < Q^2 < 5 GeV^2 and 1.08 GeV < W < 3 GeV), and calculated moments of g_1^p. We compare our final results with various theoretical models and expectations, as well as with parameterizations of the world data. Our data, with their precision and dense kinematic coverage, are able to constrain fits of polarized parton distributions, test pQCD predictions for quark polarizations at large x, offer a better understanding of quark-hadron duality, and provide more precise values of higher-twist matrix elements in the framework of the Operator Product Expansion.

Gas kinematics, morphology and angular momentum in the FIRE simulations

We study the z=0 gas kinematics, morphology, and angular momentum content of isolated galaxies in a suite of cosmological zoom-in simulations from the FIRE project spanning $M_{\star}=10^{6-11}M_{\odot}$. Gas becomes increasingly rotationally supported with increasing galaxy mass. In the lowest-mass galaxies ($M_{\star}<10^{8}M_{\odot}$), gas fails to form a morphological disk and is primarily dispersion and pressure supported. At intermediate masses ($M_{\star}=10^{8-10}M_{\odot}$), galaxies display a wide range of gas kinematics and morphologies, from thin, rotating disks, to irregular spheroids with negligible net rotation. All the high-mass ($M_{\star}=10^{10-11}M_{\odot}$) galaxies form rotationally supported gas disks. Many of the halos whose galaxies fail to form disks harbor high angular momentum gas in their circumgalactic medium. The ratio of the specific angular momentum of gas in the central galaxy to that of the dark-matter halo increases significantly with galaxy mass, from $j_{\rm gas}/j_{\rm DM}\sim0.1$ at $M_{\star}=10^{6-7}M_{\odot}$ to $j_{\rm gas}/j_{\rm DM}\sim2$ at $M_{\star}=10^{10-11}M_{\odot}$. The reduced rotational support in the lowest-mass galaxies owes to (a) stellar feedback and the UV background suppressing the accretion of high-angular momentum gas at late times, and (b) stellar feedback driving large non-circular gas motions. We broadly reproduce the observed scaling relations between galaxy mass, gas rotation velocity, size, and angular momentum, but may somewhat underpredict the incidence of disky, high-angular momentum galaxies at the lowest observed masses ($M_{\star}=(10^{6}-2\times10^{7})M_{\odot}$). In our simulations, stars are uniformly less rotationally supported than gas. The common assumption that stars follow the same rotation curve as gas thus substantially overestimates galaxies' stellar angular momentum, particularly at low masses.

Jet Fragmentation in pp, p + Pb and Pb + Pb collisions in the ATLAS detector

Jets are an important tool to study the hot, dense matter produced in Pb+Pb collisions at the LHC. Jet rates have been found to be reduced by approximately a factor of two, in the most central events and over a wide kinematic range. In order to understand precisely how the jets are modified, it is important to measure how the jet momentum is carried by its fragmentation products. In this proceedings, we present the status of fragmentation function measurements at 5.02 TeV for p+Pb and Pb+Pb collisions as well as measurement for Pb+Pb and pp collisions at 2.76 TeV.

Measurement of prompt and nonprompt mathrm{J}/{psi } production in mathrm {p}mathrm {p} and mathrm {p}mathrm {Pb} collisions at sqrt{s_{mathrm {NN}}} =5.02,text {TeV}

This paper reports the measurement of mathrm{J}/{psi } meson production in proton–proton (mathrm {p}mathrm {p}) and proton–lead (mathrm {p}mathrm {Pb}) collisions at a center-of-mass energy per nucleon pair of 5.02,text {TeV} by the CMS experiment at the LHC. The data samples used in the analysis correspond to integrated luminosities of 28,text {pb}^{-1} and 35,text {nb}^{-1} for mathrm {p}mathrm {p} and mathrm {p}mathrm {Pb} collisions, respectively. Prompt and nonprompt mathrm{J}/{psi } mesons, the latter produced in the decay of {mathrm {B}} hadrons, are measured in their dimuon decay channels. Differential cross sections are measured in the transverse momentum range of 2<p_{mathrm {T}} <30{,text {GeV}/{c}} , and center-of-mass rapidity ranges of |y_mathrm{{CM}} |<2.4 (mathrm {p}mathrm {p}) and -2.87<y_mathrm{{CM}}<1.93 (mathrm {p}mathrm {Pb}). The nuclear modification factor, R_{mathrm {p}mathrm {Pb}}, is measured as a function of both p_{mathrm {T}} and y_mathrm{{CM}}. Small modifications to the mathrm{J}/{psi } cross sections are observed in mathrm {p}mathrm {Pb} relative to mathrm {p}mathrm {p} collisions. The ratio of mathrm{J}/{psi } production cross sections in mathrm {p}-going and Pb-going directions, R_mathrm{{FB}}, studied as functions of p_{mathrm {T}} and y_mathrm{{CM}}, shows a significant decrease for increasing transverse energy deposited at large pseudorapidities. These results, which cover a wide kinematic range, provide new insight on the role of cold nuclear matter effects on prompt and nonprompt mathrm{J}/{psi } production.

Neutral pion and eta meson measurements with the ALICE detector

The ALICE experiment at the LHC is optimized to study the quark-gluon plasma (QGP), created in heavy-ion collisions. The medium-induced energy loss of particles can be investigated via the measurement of neutral meson spectra in heavy-ion collisions as well as via neutral meson-hadron correlations. Neutral mesons are identified from decay photon pairs via the invariant mass technique. Photons are measured in ALICE directly in the two electromagnetic calorimeters (PHOS and EMCal), as well as via the method of photon conversion (PCM) into electron-positon pairs, where the latter are measured in the inner tracking system (ITS) and the time projection chamber (TPC). Results obtained from EMCal, PHOS and PCM are consistent and allow measurements of spectra with high precision over a wide kinematical range. Suppression of the high-pT meson production is observed through the mesasurement of nuclear modification factor (RAA), which decreases with increasing the centrality of the collision. The suppression of the per-trigger yield on the away side in high-pT π0 hadron correlations as measured by the modification factor (IAA) also shows evidence for parton energy loss in the medium.

Light-Meson Spectroscopy at Compass

The goal of the COMPASS experiment at CERN is to study the structure and spectroscopy of hadrons. The two-stage spectrometer has large acceptance and covers a wide kinematic range for charged as well as neutral particles allowing to access a wide range of reactions. Light mesons are studied with negative (mostly $\pi^-$) and positive ($p$, $\pi^+$) hadron beams with a momentum of $190\,\text{GeV}/c$. The light-meson spectrum is measured in different final states produced in diffractive dissociation reactions with squared four-momentum transfer $t$ to the target between $0.1$ and $1.0\,(\text{GeV}/c)^2$. The flagship channel is the $\pi^-\pi^+\pi^-$ final state, for which COMPASS has recorded the currently world's largest data sample. These data not only allow us to measure the properties of known resonances with high precision, but also to search for new states. Among these is a new axial-vector signal, the $a_1(1420)$, with unusual properties. The findings are confirmed by the analysis of the $\pi^-\pi^0\pi^0$ final state.

Measurement of top quark pair differential cross sections in the dilepton channel in pp collisions at s=7 and 8 TeV with ATLAS

Measurements of normalized differential cross-sections of top quark pair ($t\bar t$) production are presented as a function of the mass, the transverse momentum and the rapidity of the $t\bar t$ system in proton-proton collisions at center-of-mass energies of $\sqrt{s}$ = 7 TeV and 8 TeV. The dataset corresponds to an integrated luminosity of 4.6 fb$^{-1}$ at 7 TeV and 20.2 fb$^{-1}$ at 8 TeV, recorded with the ATLAS detector at the Large Hadron Collider. Events with top quark pair signatures are selected in the dilepton final state, requiring exactly two charged leptons and at least two jets with at least one of the jets identified as likely to contain a $b$-hadron. The measured distributions are corrected for detector effects and selection efficiency to cross-sections at the parton level. The differential cross-sections are compared with different Monte Carlo generators and theoretical calculations of $t\bar t$ production. The results are consistent with the majority of predictions in a wide kinematic range.

Measurements of top-quark pair differential cross-sections in the lepton+jets channel in pp collisions at [Formula: see text] using the ATLAS detector.

Measurements of normalized differential cross-sections of top-quark pair production are presented as a function of the top-quark, tbar{t} system and event-level kinematic observables in proton–proton collisions at a centre-of-mass energy of sqrt{s}=8,mathrm{TeV}. The observables have been chosen to emphasize the tbar{t} production process and to be sensitive to effects of initial- and final-state radiation, to the different parton distribution functions, and to non-resonant processes and higher-order corrections. The dataset corresponds to an integrated luminosity of 20.3 fb^{-1}, recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider. Events are selected in the lepton+jets channel, requiring exactly one charged lepton and at least four jets with at least two of the jets tagged as originating from a b-quark. The measured spectra are corrected for detector effects and are compared to several Monte Carlo simulations. The results are in fair agreement with the predictions over a wide kinematic range. Nevertheless, most generators predict a harder top-quark transverse momentum distribution at high values than what is observed in the data. Predictions beyond NLO accuracy improve the agreement with data at high top-quark transverse momenta. Using the current settings and parton distribution functions, the rapidity distributions are not well modelled by any generator under consideration. However, the level of agreement is improved when more recent sets of parton distribution functions are used.

Prompt and non-prompt J/ψ production in pPb collisions with CMS

The mechanisms of charmonium production in the high-density medium created in heavy ion collisions are still not quantitatively understood. In order to disentangle among different mechanisms which changes the charmonium cross section, a multi-dimensional analysis is needed in a wide kinematic range and in various collision systems (pp, pA and AA). This paper will present the first measurement of the prompt and non-prompt J/ψ production with the CMS detector from the pPb collisions at sNN=5.02 TeV with an integrated luminosity of 34.6 nb−1 in 2013. The ratio of the forward and backward production yields is measured in bins of pT and rapidity of J/ψ, as well as the event activity.