arXiv subjects

H. Niemi

Publications and source records attributed to H. Niemi.

45 records · Page 3Linked to original sources

arXiv2007

Elliptic flow from pQCD + saturation + hydro model

We have previously predicted multiplicities and transverse momentum spectra of hadrons for the most central LHC Pb+Pb collisions at $\sqrt{s_{NN}}=5.5$ TeV using initial state for hydrodynamic evolution from pQCD + final state saturation model. By considering binary collision and wounded nucleon profiles we extend these studies to non-central collisions, and predict the $p_{T}$ dependence of minimum bias $v_{2}$ for pions at the LHC. For protons we also show how the $p_{T}$ dependence of $v_2$ changes from RHIC to the LHC.

hep-ph↗

arXiv2007

Hadron multiplicities, pT-spectra and net-baryon number in central Pb+Pb collisions at the LHC

We compute the initial energy density and net baryon number density in 5% most central Pb+Pb collisions at $\sqrt s=5.5$ TeV from pQCD + (final state) saturation, and describe the evolution of the produced system with boost-invariant transversely expanding hydrodynamics. In addition to the total multiplicity at midrapidity, we give predictions for the multiplicity of charged hadrons, pions, kaons and (anti)protons, for the total transverse energy and net-baryon number, as well as for the $p_T$-spectrum of charged hadrons, pions and kaons. We also predict the region of applicability of hydrodynamics by comparing these results with high-$p_T$ hadron spectra computed from pQCD and energy losses.

hep-ph↗

arXiv2005

Transverse Spectra of Hadrons in Central $AA$ Collisions at RHIC and LHC from pQCD+Saturation+Hydrodynamics and from pQCD+Energy Losses

We study the transverse spectra of hadrons in nearly central $AA$ collisions at RHIC and LHC in a broad transverse momentum range Low-$p_T$ spectra are calculated by using boost-invariant hydrodynamics with initial energy and net-baryon densities from the EKRT pQCD+saturation model. High-$p_T$ spectra are obtained from pQCD jet calculation including the energy loss of the parton in the matter prior to its fragmentation to final hadrons.

hep-ph↗

arXiv2005

RHIC-tested predictions for low-$p_T$ and high-$p_T$ hadron spectra in nearly central Pb+Pb collisions at the LHC

We study the hadron spectra in nearly central $A$+$A$ collisions at RHIC and LHC in a broad transverse momentum range. We cover the low-$p_T$ spectra using longitudinally boost-invariant hydrodynamics with initial energy and net-baryon number densities from the perturbative QCD (pQCD)+saturation model. Build-up of the transverse flow and sensitivity of the spectra to a single decoupling temperature $\Tdec$ are studied. Comparison with RHIC data at $\ssNN=130$ and 200 GeV suggests a rather high value $\Tdec=150$ MeV. The high-$p_T$ spectra are computed using factorized pQCD cross sections, nuclear parton distributions, fragmentation functions, and describing partonic energy loss in the quark-gluon plasma by quenching weights. Overall normalization is fixed on the basis of p+$\bar{\rm p}$(p) data and the strength of energy loss is determined from RHIC Au+Au data. Uncertainties are discussed. With constraints from RHIC data, we predict the $p_T$ spectra of hadrons in 5 % most central Pb+Pb collisions at the LHC energy $\ssNN=5500$ GeV. Due to the closed framework for primary production, we can also predict the net-baryon number at midrapidity, as well as the strength of partonic energy losses at the LHC. Both at the LHC and RHIC, we recognize a rather narrow crossover region in the $p_T$ spectra, where the hydrodynamic and pQCD fragmentation components become of equal size. We argue that in this crossover region the two contributions are to a good approximation mutually independent. In particular, our results suggest a wider $p_T$-region of applicability for hydrodynamical models at the LHC than at RHIC.

hep-ph↗

arXiv2004

Photon Physics in Heavy Ion Collisions at the LHC

Various pion and photon production mechanisms in high-energy nuclear collisions at RHIC and LHC are discussed. Comparison with RHIC data is done whenever possible. The prospect of using electromagnetic probes to characterize quark-gluon plasma formation is assessed.

hep-ph↗

arXiv2003

Hard probes in heavy ion collisions at the LHC: heavy flavour physics

We present the results from the heavy quarks and quarkonia working group. This report gives benchmark heavy quark and quarkonium cross sections for $pp$ and $pA$ collisions at the LHC against which the $AA$ rates can be compared in the study of the quark-gluon plasma. We also provide an assessment of the theoretical uncertainties in these benchmarks. We then discuss some of the cold matter effects on quarkonia production, including nuclear absorption, scattering by produced hadrons, and energy loss in the medium. Hot matter effects that could reduce the observed quarkonium rates such as color screening and thermal activation are then discussed. Possible quarkonium enhancement through coalescence of uncorrelated heavy quarks and antiquarks is also described. Finally, we discuss the capabilities of the LHC detectors to measure heavy quarks and quarkonia as well as the Monte Carlo generators used in the data analysis.

hep-ph↗

arXiv2003

The Exact Evolution Equation of the Curvature Perturbation for Closed Universe

As is well known, the exact evolution equation of the curvature perturbation plays a very important role in investigation of the inflation power spectrum of the flat universe. However, its corresponding exact extension for the non-flat universes has not yet been given out clearly. The interest in the non-flat, specially closed, universes is being aroused recently. The need of this extension is pressing. We start with most elementary physical consideration and obtain finally this exact evolution equation of the curvature perturbation for the non-flat universes, as well as the evolutionary controlling parameter and the exact expression of the variable mass in this equation. We approximately do a primitive and immature analysis on the power spectrum of non-flat universes. This analysis shows that this exact evolution equation of the curvature perturbation for the non-flat universes is very complicated, and we need to do a lot of numerical and analytic work for this new equation in future in order to judge whether the universe is flat or closed by comparison between theories and observations.

astro-ph↗

arXiv2002

Dependence of hadron spectra on decoupling temperature and resonance contributions

Using equilibrium hydrodynamics with initial conditions for the energy and net baryon number densities from the perturbative QCD + saturation model, a good simultaneous description of the measured pion, kaon and (anti)proton spectra in central Au+Au collisions at $\sqrt s=130 A$GeV is found with a single decoupling temperature $\Tdec=150...160$ MeV. The interplay between the resonance content of the EoS and the development of the transverse flow leads to inverse slopes and $ $ of hadrons which increase with decreasing $\Tdec$. The origin of this result is discussed.

hep-ph↗

arXiv2002

Transverse spectra of hadrons at RHIC

We present results on spectra of pions, kaons and (anti)protons from a study of heavy ion collisions using the perturbative QCD + saturation model to calculate the production of initial (transverse) energy and baryon number followed by a hydrodynamic description of the expansion of produced matter. In particular, we study how the hadron spectra and multiplicities depend on the decoupling temperature $\Tdec$ when the low temperature phase contains all hadrons and and hadron resonances with mass below 2 GeV. We show that the spectra and multiplicities of pions, kaons and (anti)protons measured at RHIC in central Au+Au collisions with $\sqrt s=130$ GeV can be obtained with a single decoupling temperature 150$...$160 MeV, common for both the chemical and the kinetic freeze-out.

nucl-th↗