Kari J. Eskola

EPS09: A New Generation of NLO and LO Nuclear Parton Distribution Functions

We present a next-to-leading order (NLO) global DGLAP analysis of nuclear parton distribution functions (nPDFs) and their uncertainties. Carrying out an NLO nPDF analysis for the first time with three different types of experimental input — deep inelastic l+A scattering, Drell-Yan dilepton production in p+A collisions, and inclusive pion production in d+Au and p+p collisions at RHIC — we find that these data can well be described in a conventional collinear factorization framework. Although the pion production has not been traditionally included in the global analyses, we find that the shape of the nuclear modification factor RdAu of the pion pT-spectrum at midrapidity retains sensitivity to the gluon distributions, providing evidence for shadowing and EMC-effect in the nuclear gluons. We use the Hessian method to quantify the nPDF uncertainties which originate from the uncertainties in the data. In this method the sensitivity of χ2 to the variations of the fitting parameters is mapped out to orthogonal error sets which provide a user-friendly way to calculate how the nPDF uncertainties propagate to any factorizable nuclear cross-section. The obtained NLO and LO nPDFs and the corresponding error sets are collected in our new release called family EPS09. These results should find applications in precision analyses of the signatures and properties of QCD matter at the LHC and RHIC.

Scaling of transverse energies and multiplicities with atomic number and energy in ultrarelativistic nuclear collisions

Abstract We compute how the initial energy density and produced gluon, quark and antiquark numbers scale with atomic number and beam energy in ultrarelativistic heavy ion collisions. The computation is based on the argument that the effect of all momentum scales can be estimated by performing the computation at one transverse momentum scale, the saturation momentum. The initial numbers are converted to final ones by assuming kinetic thermalization and adiabatic expansion. The main emphasis of the study is at LHC and RHIC energies but it is observed that even at SPS energies this approach leads to results which are not unreasonable: what is usually described as a completely soft non-perturbative process can also be described in terms of gluons and quarks. The key element is the use of the saturation scale.

THE FRAGILITY OF HIGH-pT HADRON SPECTRA AS A HARD PROBE

Abstract We study the suppression of high- p T hadron spectra in nuclear collisions, supplementing the perturbative QCD factorized formalism with radiative parton energy loss. We find that the nuclear modification factor R A A ( p T ) , which quantifies the degree of suppression, is almost p T -independent both for RHIC (in agreement with data) and for the LHC. This is a consequence of the shape of the partonic p T -spectrum in elementary collisions which implies that for the same value of R A A at higher p T , an increasingly smaller fraction of parton energy loss is needed. When the values of the time-averaged transport coefficient q ˆ exceed 5 GeV 2 / fm , R A A ( p T ) gradually loses its sensitivity to the corresponding produced energy density. This is due to particle production in the outer corona of the medium, which remains almost unsuppressed even for extreme densities. Thus, even for the highest experimentally accessible transverse momentum at the LHC and in contrast to jets, the measurement of leading partons via leading hadrons is not a penetrating probe of the dense matter, but a rather fragile probe which fragments for the opacities reached below the skin of the medium. Relating the transport coefficient to the energy density produced in the collision region, we find and discuss a phenomenon reminiscent of the opacity problem of elliptic flow: namely, the interaction of the hard parent parton with the medium appears to be much stronger than that expected for perturbative interactions of the hard parton with an ideal quark–gluon plasma.

Gas-filled recoil separator for studies of heavy elements☆

Abstract A gas-filled recoil separator for the study of heavy elements has been constructed. The separator is of type QDQQ with the first, vertically focusing, quadrupole providing improved matching to the acceptance of the dipole magnet. The separator has been designed also for use in vacuum mode in which case a mass resolving power of ≈ 100 is estimated. The deflection angle is 25° and the radius of curvature is 1850 mm. Maximum beam rigidity is 2.2 T m. In the first experiments, new isotopes in the region Z = 85–90 have been synthesized.

Quark and gluon production in high energy nucleus-nucleus collisions

Abstract The transverse energy spectrum d σ /d E T in very high energy nucleus-nucleus collisions is considered by including both hard and soft processes. The production of hard gluons and quarks is computed in perturbative QCD and the soft component is taken from the recent CERN heavy ion experiments. We conclude that while hard processes carry less than 5% of the total E T at the energies √ s = 20 GeV of the CERN experiments, their share grows rapidly with energy so that it is about a half at RHIC energies, √ s = 200 GeV, and clearly dominant at Tevatron energies, √ s = 2000 GeV.

Predictions for

Predictions for charged hadron, identified light hadron, quarkonium, photon, jet and gauge bosons in p+Pb collisions at sqrt s_NN = 5 TeV are compiled and compared. When test run data are available, they are compared to the model predictions.

p+

Predictions for charged hadron, identified light hadron, quarkonium, photon, jet and gauge bosons in p+Pb collisions at sqrt s_NN = 5 TeV are compiled and compared. When test run data are available, they are compared to the model predictions.

Pb Collisions at sqrt s_NN = 5 TeV

We present an improved leading-order global DGLAP analysis of nuclear parton distribution functions (nPDFs), supplementing the traditionally used data from deep inelastic lepton-nucleus scattering and Drell-Yan dilepton production in proton-nucleus collisions, with inclusive high-pT hadron production data measured at RHIC in d+Au collisions. With the help of an extended definition of the χ2 function, we now can more efficiently exploit the constraints the different data sets offer, for gluon shadowing in particular, and account for the overall data normalization uncertainties during the automated χ2 minimization. The very good simultaneous fit to the nuclear hard process data used demonstrates the feasibility of a universal set of nPDFs, but also limitations become visible. The high-pT forward-rapidity hadron data of BRAHMS add a new crucial constraint into the analysis by offering a direct probe for the nuclear gluon distributions—a sector in the nPDFs which has traditionally been very badly constrained. We obtain a strikingly stronger gluon shadowing than what has been estimated in previous global analyses. The obtained nPDFs are released as a parametrization called EPS08.

PREDICTIONS FOR p+Pb COLLISIONS AT

A long-standing prediction of nuclear models is the emergence of a region of long-lived, or even stable, superheavy elements beyond the actinides. These nuclei owe their enhanced stability to closed shells in the structure of both protons and neutrons. However, theoretical approaches to date do not yield consistent predictions of the precise limits of the ‘island of stability’; experimental studies are therefore crucial. The bulk of experimental effort so far has been focused on the direct creation of superheavy elements in heavy ion fusion reactions, leading to the production of elements up to proton number Z = 118 (refs 4, 5). Recently, it has become possible to make detailed spectroscopic studies of nuclei beyond fermium (Z = 100), with the aim of understanding the underlying single-particle structure of superheavy elements. Here we report such a study of the nobelium isotope 254No, with 102 protons and 152 neutrons—the heaviest nucleus studied in this manner to date. We find three excited structures, two of which are isomeric (metastable). One of these structures is firmly assigned to a two-proton excitation. These states are highly significant as their location is sensitive to single-particle levels above the gap in shell energies predicted at Z = 114, and thus provide a microscopic benchmark for nuclear models of the superheavy elements.

\sqrt{s_{_{\it NN}}} = 5

A bstractWe determine the spatial (impact parameter) dependence of nuclear parton distribution functions (nPDFs) using the A-dependence of the spatially independent (averaged) global fits EPS09 and EKS98. We work under the assumption that the spatial dependence can be formulated as a power series of the nuclear thickness functions TA. To reproduce the A-dependence over the entire x range we need terms up to [TA]4. As an outcome, we release two sets, EPS09s (LO, NLO, error sets) and EKS98s, of spatially dependent nPDFs for public use. We also discuss the implementation of these into the existing calculations. With our results, the centrality dependence of nuclear hard-process observables can be studied consistently with the globally fitted nPDFs for the first time. As an application, we first calculate the LO nuclear modification factor