Rapidity Interval Research Articles

High-energy resummation in heavy-quark pair photoproduction

We present our predictions for the inclusive production of two heavy quark–antiquark pairs, separated by a large rapidity interval, in the collision of (quasi-)real photons at the energies of LEP2 and of some future electron–positron colliders. We include in our calculation the full resummation of leading logarithms in the center-of-mass energy and a partial resummation of the next-to-leading logarithms, within the Balitsky–Fadin–Kuraev–Lipatov (BFKL) approach.

Measurement of the B^{±} Meson Nuclear Modification Factor in Pb-Pb Collisions at sqrt[s_{NN}]=5.02 TeV.

The differential production cross sections of B^{±} mesons are measured via the exclusive decay channels B^{±}→J/ψK^{±}→μ^{+}μ^{-}K^{±} as a function of transverse momentum in pp and Pb-Pb collisions at a center-of-mass energy sqrt[s_{NN}]=5.02 TeV per nucleon pair with the CMS detector at the LHC. The pp(Pb-Pb) data set used for this analysis corresponds to an integrated luminosity of 28.0 pb^{-1} (351 μb^{-1}). The measurement is performed in the B^{±} meson transverse momentum range of 7 to 50 GeV/c, in the rapidity interval |y|<2.4. In this kinematic range, a strong suppression of the production cross section by about a factor of 2 is observed in the Pb-Pb system in comparison to the expectation from pp reference data. These results are found to be roughly compatible with theoretical calculations incorporating beauty quark diffusion and energy loss in a quark-gluon plasma.

Measurement of charmonium production in heavy-ion collisions with the ATLAS detector

The suppression of charmonium states in heavy-ion collisions is a phenomenon understood as a consequence of quark gluon plasma formation in the hot, dense system formed in heavy ion collisions at the LHC. In addition to hot matter effects in heavy-ion collisions, so-called cold nuclear effects that modify charmonium production are also present. Therefore, a full assessment requires detailed studies in both A+A and p+A collisions. Based on p+Pb data collected in 2013 and pp and Pb+Pb data collected in 2015 at the LHC, the ATLAS experiment has studied prompt and non-prompt J/ψ and ψ(2S) production via the dimuon decay final states. The production yields and excited-to-ground state yield ratios, measured in p+Pb and Pb+Pb with respect to that measured in pp collision data, are presented in intervals of transverse momentum, rapidity and centrality.

Coherent and incoherent Upsilon production in ultraperipheral collisions at the Large Hadron Collider

The exclusive photoproduction of $\Upsilon (nS)$ states were calculated in ultra-peripheral collisions for coherent and incoherent process in PbPb at $\sqrt{s_{NN}}$= 5.5 TeV. Different dipole models were compared in the theoretical framework of light-cone color dipole formalism. Moreover, it was calculated the differential cross section for the Upsilon states and their total cross section for two intervals of rapidity: $|y|\leq 4$ 4 and $ 2 \le$ y $\le 4.5$. A systematic study is done on the theoretical uncertainties associated to the production and predictions are presented for the first time for the incoherent cross section of the radially excited states.

Heavy flavor production in high-energyppcollisions: Color dipole description

We present a detailed study of open heavy flavor production in high-energy $pp$ collisions at the LHC in the color dipole framework. The transverse momentum distributions of produced $b$-jets, accounting for the jet energy loss, as well as produced open charm $D$ and bottom $B$ mesons in distinct rapidity intervals relevant for LHC measurements are computed. The dipole model results for the differential $b$-jet production cross section are compared to the recent ATLAS and CMS data while the results for $D$ and $B$ mesons production cross sections -- to the corresponding LHCb data. Several models for the phenomenological dipole cross section have been employed to estimate theoretical uncertainties of the dipole model predictions. We demonstrate that the primordial transverse momentum distribution of the projectile gluon significantly affects the meson spectra at low transverse momenta and contributes to the largest uncertainty of the dipole model predictions.

Coherent J/ψ photoproduction in ultra-peripheral PbPb collisions at [formula omitted] with the CMS experiment

The cross section for coherent J/ψ photoproduction accompanied by at least one neutron on one side of the interaction point and no neutron activity on the other side, Xn0n, is measured with the CMS experiment in ultra-peripheral PbPb collisions at sNN=2.76TeV. The analysis is based on a data sample corresponding to an integrated luminosity of 159μb−1, collected during the 2011 PbPb run. The J/ψ mesons are reconstructed in the dimuon decay channel, while neutrons are detected using zero degree calorimeters. The measured cross section is dσXn0ncoh/dy(J/ψ)=0.36±0.04(stat)±0.04(syst) mb in the rapidity interval 1.8<|y|<2.3. Using a model for the relative rate of coherent photoproduction processes, this Xn0n measurement gives a total coherent photoproduction cross section of dσcoh/dy(J/ψ)=1.82±0.22(stat)±0.20(syst)±0.19(theo) mb. The data strongly disfavor the impulse approximation model prediction, indicating that nuclear effects are needed to describe coherent J/ψ photoproduction in γ+Pb interactions. The data are found to be consistent with the leading twist approximation, which includes nuclear gluon shadowing.

Unprecedented warming revealed from multi-proxy reconstruction of temperature in southern China for the past 160 years

Using the southern limit of snowfall recorded in Chinese documents, chronologies of tree-ring width, and tree-ring stable oxygen isotope (δ18O), the annual temperature anomaly in southern China during 1850–2009 is reconstructed using the method of signal decomposition and synthesis. The results show that the linear trend was 0.47°C (100 yr)−1 over 1871–2009, and the two most rapid warming intervals occurred in 1877–1938 and 1968–2007, at rates of 0.125°C (10 yr)−1 and 0.258°C (10 yr)−1, respectively. The decadal variation shows that the temperature in the moderate warm interval of the 1910s–1930s was notably lower than that of the 1980s–2000s, which suggests that the warming since the 1980s was unprecedented for the past 160 years, though a warming hiatus existed in the 2000s. Additionally, there was a rapid cooling starting from the 1860s, followed by a cold interval until the early 1890s, with the coldest years in 1892 and 1893. A slight temperature decline was also found from the 1940s to the late 1960s. This study provides an independent case to validate the global warming for the past 160 years and its hiatus recently, because the proxy data are not affected by urbanization.

Demography and climate in Late Eneolithic Ukraine, Moldova, and Romania: Multiproxy evidence and pollen-based regional corroboration

Attempts to correlate macro-scale climate dynamics with anomalies in local and regional archaeological data sets should account for differences in geographic scale and effect size. Using the modern analogue technique, this paper reconstructs temperature, precipitation, and growing degree-day trends in Ukraine, Moldova, and Romania from a set of 20 pollen cores in order to explicate the regional impact of the 6.0–5.0ka BP rapid climate change interval observed in the GISP2 K+ glacio-chemical sequence. Results are compared against a model of regional demographic development covering the time span of 6000–3000BCE. This study indicates that, while macro-scale trends are discernible in Eastern Europe, climatic instability during the fourth millennium BCE was regionally variable and resultant demographic responses were highly targeted and heterogeneous in nature. A period of cooling ca. 3825–3650calBCE resulted in the fracturing of Eneolithic complexes in Romania and generally spurred adaptation to more mobile systems of settlement and subsistence. However, a contemporaneous alternative response involved large-scale migrations to peripheral regions, including the establishment of the Tripolye giant-settlements in Central Ukraine. The methods used illustrate the need for obtaining more proximate confirmation when applying large-scale climate processes to explanations of local and regional archaeological contexts.

Dynamical evolution of critical fluctuations and its observation in heavy ion collisions

We study time evolution of critical fluctuations of conserved charges near the QCD critical point in the context of relativistic heavy ion collisions. A stochastic diffusion equation is employed in order to describe the diffusion property of the critical fluctuation arising from the coupling of the order parameter field to conserved charges. We show that the diffusion property gives rise to a possibility of probing the early time fluctuations through the rapidity window dependence of the second-order cumulant and correlation function of conserved charges. It is pointed out that their non-monotonic behaviors as functions of the rapidity interval are robust experimental signals for the existence of the critical enhancement around the QCD critical point.

Transverse momentum distribution of primary charged particles in p–Pb interactions at forward pseudorapidity at LHC energies

Transverse momentum distributions of primary charged particles have been studied using simulated data from the HIJING 1.0 event generator in the minimum bias p–Pb collisions at [Formula: see text] = 0.9, 1.8, 2.76 and 5.02[Formula: see text], in the two forward pseudorapidity ([Formula: see text]) regions: [Formula: see text] and [Formula: see text] and in the transverse momentum range of [Formula: see text]. The simulated data in the pseudorapidity region of [Formula: see text] at 5.02[Formula: see text] depicts some differences in the region of [Formula: see text] [Formula: see text] 2[Formula: see text] when compared with CMS data. Model shows systematically higher values than the experimental measurements pointing out absorption effect for the experimental data. It is also observed that with increasing rapidity interval from [Formula: see text] to [Formula: see text] observed differences for the behavior of the transverse momentum distributions are shifted to high transverse momentum region. The nuclear modification factor as a function of transverse momentum is constructed using the HIJING 1.0 code. With incident energy, the values of nuclear modification factor increase, for 0.9 and 1.8 [Formula: see text], the distributions seem to increase, but for 2.76 and 5.02 [Formula: see text], the distributions look flat. Numerically, the value of nuclear modification factor increases with the increase in the number of jets. This result shows that for the considered more forward pseudorapidiry area, the influence of the incident energy dominates and this is the reason that main results in the areas are connected with the leading particles.

Cross-modal attention influences auditory contrast sensitivity: Decreasing visual load improves auditory thresholds for amplitude- and frequency-modulated sounds.

We used a cross-modal dual task to examine how changing visual-task demands influenced auditory processing, namely auditory thresholds for amplitude- and frequency-modulated sounds. Observers had to attend to two consecutive intervals of sounds and report which interval contained the auditory stimulus that was modulated in amplitude (Experiment 1) or frequency (Experiment 2). During auditory-stimulus presentation, observers simultaneously attended to a rapid sequential visual presentation-two consecutive intervals of streams of visual letters-and had to report which interval contained a particular color (low load, demanding less attentional resources) or, in separate blocks of trials, which interval contained more of a target letter (high load, demanding more attentional resources). We hypothesized that if attention is a shared resource across vision and audition, an easier visual task should free up more attentional resources for auditory processing on an unrelated task, hence improving auditory thresholds. Auditory detection thresholds were lower-that is, auditory sensitivity was improved-for both amplitude- and frequency-modulated sounds when observers engaged in a less demanding (compared to a more demanding) visual task. In accord with previous work, our findings suggest that visual-task demands can influence the processing of auditory information on an unrelated concurrent task, providing support for shared attentional resources. More importantly, our results suggest that attending to information in a different modality, cross-modal attention, can influence basic auditory contrast sensitivity functions, highlighting potential similarities between basic mechanisms for visual and auditory attention.

Measurement of the relative yields of ψ(2S) to ψ(1S) mesons produced at forward and backward rapidity in p+p , p+Al , p+Au , and He3+Au collisions at sNN=200 GeV

The PHENIX Collaboration has measured the ratio of the yields of $\psi(2S)$ to $\psi(1S)$ mesons produced in $p$$+$$p$, $p$$+$Al, $p$$+$Au, and $^{3}$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV over the forward and backward rapidity intervals $1.2<|y|<2.2$. We find that the ratio in $p$$+$$p$ collisions is consistent with measurements at other collision energies. In collisions with nuclei, we find that in the forward ($p$-going or $^{3}$He-going) direction, the relative yield of $\psi(2S)$ mesons to $\psi(1S)$ mesons is consistent with the value measured in \pp collisions. However, in the backward (nucleus-going) direction, the $\psi(2S)$ is preferentially suppressed by a factor of $\sim$2. This suppression is attributed in some models to breakup of the weakly-bound $\psi(2S)$ through final state interactions with comoving particles, which have a higher density in the nucleus-going direction. These breakup effects may compete with color screening in a deconfined quark-gluon plasma to produce sequential suppression of excited quarkonia states.

Asymptotic behavior of the correlation coefficients of transverse momenta in the model with string fusion

In the framework of the model with fusion of quark–gluon strings on the transverse lattice, we find the asymptotic behavior of the correlation coefficients between observables in separated rapidity intervals with a high string density in a realistic case with an inhomogeneous distribution of strings in the impact parameter plane. We calculate the asymptotic forms for three types of correlations: between the average transverse momenta of particles with rapidity in these intervals, between the average transverse momentum of particles in one rapidity interval and the multiplicity of particles in another, and also between the multiplicities of charged particles in these intervals. We show that the previously found independence of the asymptotic form of the correlation coefficient between the average transverse momenta from the variance in the number of particles produced in string fragmentation holds only in the case of a uniform distribution of strings in the transverse plane. We also show that the found general expressions for the long-range correlation coefficients in the particular case with a uniform distribution of strings in the transverse plane become the formulas previously obtained by another method applicable only in this simple case.

Charged particle production in p+Pb collisions measured by the ATLAS detector

Per-event charged particle spectra and nuclear modification factors are measured with the ATLAS detector at the LHC in p+Pb interactions at √sNN = 5.02 TeV. Results are presented as a function of transverse momentum, rapidity, and in different intervals of collision centrality, which is characterised in p+Pb collisions by the total transverse energy measured over the pseudorapidity interval −3.2 < η < −4.9 in the direction of the lead beam. Three different calculations of the number of nucleons participating in p+Pb collisions have been performed, assuming the Glauber model and its Glauber-Gribov Colour Fluctuation extensions. The results using different models are compared with each other, as well as with other measurements made under the same conditions and also with centrality definition based on different rapidity intervals.

Forward-backward correlations between intensive observables

We demonstrate that the investigations of the forward-backward correlations between intensive observables enable to obtain more clear signal about the initial stage of hadronic interaction, e.g. about the process of string fusion, compared to usual forward-backward multiplicity correlations. As an example, the correlation between mean-event transverse momenta of charged particles in separated rapidity intervals is considered. We performed calculations in the framework of dipole-based Monte Carlo string fusion model. We obtained the dependence of the correlation strength on the collision centrality for different initial energies and colliding systems. It is shown that the dependence reveals the decline of the correlation coefficient for most central Pb-Pb collisions at LHC energy. We compare the results both with the ones obtained in alternative models and with the ones obtained by us using various MC generators.

Long-range rapidity correlations between mean transverse momenta

The forward-backward correlation strength between event-mean transverse momenta of particles produced in separated rapidity intervals in high energy hadronic collisions is analyzed in the simple model with the string fusion on a transverse lattice. The coefficient of long-range rapidity p t - p t correlation is obtained using the negative binomial distribution for the number of strings, which is closer to reality than the poissonian one. The results demonstrate good agreement with the asymptotes of the correlation coefficient analytically calculated earlier at large string density. It is observed that at LHC energy the p t - p t correlation coefficient reveals the drop for most central collisions. The model calculations show that the physical reason for this decrease is the attenuation of color field fluctuations due to the string fusion at large string density, whereas at RHIC energy the string density is not enough to provide a decline of the correlation coefficient for most central collisions.

Rapid Analysis and Time Interval Deconvolution for Comprehensive Fuel Compound Group Classification and Speciation Using Gas Chromatography-Vacuum Ultraviolet Spectroscopy.

A time interval deconvolution (TID) method was devised to integrate a gas chromatography-vacuum ultraviolet (GC-VUV) data set in order to provide bulk characterization and speciation of finished gasoline samples. The method was demonstrated using a commercially available standard and tested on a series of ASTM gasoline proficiency samples. Very good correlation (R2 ∼ 0.97-0.99) between GC-VUV and measurements using various ASTM methods was achieved. A key advantage of the TID method applied to GC-VUV data sets is that a large number of coelution events can be tolerated, resulting in significantly easier and faster separations, approximately 30 min in the case of gasoline. Methods for determining relative response factors, VUV reference libraries, and generalization to other types of complex samples are also discussed.

Measurement of jet activity in top quark events using the eμ final state with two b-tagged jets in pp collisions at s = 8 $$ \sqrt{s}=8 $$ TeV with the ATLAS detector

Measurements of the jet activity in $t\bar{t}$ events produced in proton--proton collisions at $\sqrt{s}=8$ TeV are presented, using $20.3\,$fb$^{-1}$ of data collected by the ATLAS experiment at the Large Hadron Collider. The events were selected in the dilepton $e\mu$ decay channel with two identified $b$-jets. The numbers of additional jets for various jet transverse momentum ($p_T$) thresholds, and the normalised differential cross-sections as a function of $p_T$ for the five highest-$p_T$ additional jets, were measured in the jet pseudorapidity range $|\eta|<4.5$. The gap fraction, the fraction of events which do not contain an additional jet in a central rapidity region, was measured for several rapidity intervals as a function of the minimum $p_T$ of a single jet or the scalar sum of $p_T$ of all additional jets. These fractions were also measured in different regions of the invariant mass of the $e\mu b\bar{b}$ system. All measurements were corrected for detector effects, and found to be mostly well-described by predictions from next-to-leading-order and leading-order $t\bar{t}$ event generators with appropriate parameter choices. The results can be used to further optimise the parameters used in such generators.

High energy resummation in dihadron production at the LHC

We propose to study at the Large Hadron Collider (LHC) the inclusive production of a pair of hadrons (a "di-hadron" system) in a kinematics where two detected hadrons with high transverse momenta are separated by a large interval of rapidity. This process has much in common with the widely discussed Mueller-Navelet jet production and can also be used to access the dynamics of hard proton-parton interactions in the Regge limit. For both processes large contributions enhanced by logarithms of energy can be resummed in perturbation theory within the Balitsky-Fadin-Kuraev-Lipatov (BFKL) formalism with next-to-leading logarithmic accuracy (NLA). The experimental study of di-hadron production would provide with an additional clear channel to test the BFKL dynamics. We present here the first theoretical predictions for cross sections and azimuthal angle correlations of the di-hadrons produced with LHC kinematics.

Multi-strange baryon production in p Pb collisions at sNN=5.02 TeV

The multi-strange baryon yields in Pb--Pb collisions have been shown to exhibit an enhancement relative to pp reactions. In this work, $\Xi$ and $\Omega$ production rates have been measured with the ALICE experiment as a function of transverse momentum, ${p_{\rm T}}$, in p-Pb collisions at a centre-of-mass energy of ${\sqrt{s_{\rm NN}}}$ = 5.02 TeV. The results cover the kinematic ranges 0.6 GeV/$c<{p_{\rm T}} <$7.2 GeV/$c$ and 0.8 GeV/$c<{p_{\rm T}}<$ 5 GeV/$c$, for $\Xi$ and $\Omega$ respectively, in the common rapidity interval -0.5 $<{y_{\rm CMS}}<$ 0. Multi-strange baryons have been identified by reconstructing their weak decays into charged particles. The ${p_{\rm T}}$ spectra are analysed as a function of event charged-particle multiplicity, which in p-Pb collisions ranges over one order of magnitude and lies between those observed in pp and Pb-Pb collisions. The measured ${p_{\rm T}}$ distributions are compared to the expectations from a Blast-Wave model. The parameters which describe the production of lighter hadron species also describe the hyperon spectra in high multiplicity p-Pb. The yield of hyperons relative to charged pions is studied and compared with results from pp and Pb-Pb collisions. A statistical model is employed, which describes the change in the ratios with volume using a canonical suppression mechanism, in which the small volume causes a species-dependent relative reduction of hadron production. The calculations, in which the magnitude of the effect depends on the strangeness content, show good qualitative agreement with the data.