118327970
Universal O(N) scaling and the chiral critical line in (2+1)-flavor QCD with small chemical potentials
We show that for small values of the chemical potential the curvature of the phase transition line can be deduced from an analysis of scaling properties of the chiral condensate and its susceptibilities. We make use of a recent analysis of the magnetic equation of state in (2+1)-flavor QCD where a connection between the QCD parameters and the universal scaling fields could be established. The remaining dependence of the reduced temperature on the chemical potential can be fixed by an analysis of a mixed susceptibility, obtained from a derivative with respect to quark mass and chemical potential. We extract this dependence which describes the curvature of the phase transition line, at two values of the cut-off, $aT=1/4$ and $1/8$. We find that cut-off effects are small for the curvature parameter and determine the transition line in the chiral limit to leading order in the light quark chemical potential. We obtain $T_c(\mu_B)/T_c(0) = 1 - 0.00656(66) (\mu_B/T)^2 +{\cal O}(\mu_B^4)$.
119188644
QCD bulk thermodynamics and conserved charge fluctuations with HISQ fermions
After briefly reviewing recent progress by the HotQCD collaboration in studying the 2+1 flavor QCD equation of state, we will focus on results on fluctuations of conserved charges by the BNL-Bielefeld and HotQCD collaborations. Higher order cumulants of the net-charge distributions are increasingly dominated by a universal scaling behavior, which arises due to a critical point of QCD in the chiral limit. Considering cumulants up to the 6^{th} order, we observe that they generically behave as expected from universal scaling laws, which is quite different from cumulants calculated within the hadron resonance gas model. Taking ratios of these cumulants, we obtain volume independent results that can be compared to the experimental measurements. We will argue that the freeze-out chemical potentials and the freeze-out temperature, usually obtained by a HRG model fit to the measured hadronic yields, can also be obtained in a model independent way from ab-initio lattice QCD calculations by utilizing observables related to conserved charge fluctuations. Further, we will show that the freeze-out strangeness and electric charge chemical potentials can be fixed by imposing strangeness neutrality and isospin asymmetry constraints in the lattice QCD calculations, in order to accommodate conditions met in heavy ion collisions. All results have been obtained with the highly improved staggered quark action (HISQ) and almost physical quark masses on lattices with temporal extent of N_\tau=6,8,10,12. 
After briefly reviewing recent progress by the HotQCD collaboration in studying the 2+1 flavor QCD equation of state, we will focus on results on fluctuations of conserved charges by the BNL-Bielefeld and HotQCD collaborations. Higher order cumulants of the net-charge distributions are increasingly dominated by a universal scaling behavior, which arises due to a critical point of QCD in the chiral limit. Considering cumulants up to the 6(th) order, we observe that they generically behave as expected from universal scaling laws, which is quite different from cumulants calculated within the hadron resonance gas model. Taking ratios of these cumulants, we obtain volume independent results that can be compared to the experimental measurements. We will argue that the freeze-out chemical potentials and the freeze-out temperature, usually obtained by a HRG model fit to the measured hadronic yields, can also be obtained in a model independent way from ab-initio lattice QCD calculations by utilizing observables related to conserved charge fluctuations. Further, we will show that the freeze-out strangeness and electric charge chemical potentials can be fixed by imposing strangeness neutrality and isospin asymmetry constraints in the lattice QCD calculations, in order to accommodate conditions met in heavy ion collisions. All results have been obtained with the highly improved staggered quark action (HISQ) and almost physical quark masses on lattices with temporal extent of N(τ) = 6, 8, 10, 12.
67814332
An efficient method to compute the residual phase on a Lefschetz thimble
We propose an efficient method to compute the so-called residual phase that appears when performing Monte Carlo calculations on a Lefschetz thimble. The method is stochastic and its cost scales linearly with the physical volume, linearly with the number of stochastic estimators and quadratically with the length of the extra dimension along the gradient flow. This is a drastic improvement over previous estimates of the cost of computing the residual phase. We also report on basic tests of correctness and scaling of the code.
16120128
Bulk thermodynamics and charge fluctuations at non-vanishing baryon density
We present results on bulk thermodynamic quantities as well as net baryon number, strangeness and electric charge fluctuations in QCD at non-zero density and temperature obtained from lattice calculations with almost physical quark masses for two values of the lattice cut-off aT = 1/4 and 1/6. We show that with our improved p4fa3-action the cut-off effects are under control when using lattices with a temporal extent of 6 or larger and that the contribution to the equation of state, which is due to a finite chemical potential is small for {mu}{sub q}/T < 1. Moreover, at vanishing chemical potential, i.e. under conditions almost realized at RHIC and the LHC, quartic fluctuations of net baryon number and strangeness are large in a narrow temperature interval characterizing the transition region from the low to high temperature phase. At non-zero baryon number density, strangeness fluctuations are enhanced and correlated to fluctuations of the net baryon number. If strangeness is furthermore forced to vanish, as it may be the case in systems created in heavy ion collisions, strangeness fluctuations are significantly smaller than baryon number fluctuations.
15858058
Non-zero density QCD by the Taylor expansion method: The isentropic equation of state, hadronic fluctuations and more
We discuss the Taylor expansion approach to non-zero baryon chemical potential ($\mu_B$) and present results on expanion coefficients of the pressure and energy density up to the 6-th order in $\mu_B$. Calculations have been performed with (2+1)-flavor of improved staggerd fermions (p4fat3) and almost physical masses on lattices with temporal extent of four and six time slices. We use the expansion coefficients to construct the isentropic equation of state on lines of constant entropy per baryon number and various different hadronic fluctuations. Furthermore, we estimate the radius of convegence of our expansion, which can be seen as a method to analyze the structure of the QCD phase diagram.
117478307
Chiral restoration and deconfinement in two-color QCD with two flavors of staggered quarks
In preparation of lattice studies of the two-color QCD phase diagram we studychiral restoration and deconfinement at finite temperature with two flavors ofstaggered quarks using an RHMC algorithm on GPUs. We first study unquenchingeffects in local Polyakov loop distributions, and the Polyakov loop potentialobtained via Legendre transformation, in a fixed-scale approach for heavierquarks. We also present the chiral condensate and the correspondingsusceptibility over the lattice coupling across the chiral transition forlighter quarks. Using Ferrenberg-Swendsen reweighting we extract the maxima ofthe chiral susceptibility in order to determine pseudo-critical couplings onvarious lattices suitable for chiral extrapolations. These are then used to fixthe relation between coupling and temperature in the chiral limit.
119331939
Chiral perturbation theory for lattice QCD with a twisted mass term
Quantum chromodynamics on a lattice with Wilson fermions and a chirally twisted mass term for two degenerate quark flavours is considered in the framework of chiral perturbation theory. The pion mass and decay constant are calculated in next-to-leading order including terms linear in the lattice spacing a.
17272111
Effects of fermion localization in Higgsless theories and electroweak constraints
Abstract Extra-dimensional Higgsless models with electroweak symmetry breaking through boundary conditions generically have difficulties with electroweak precision constraints, when the fermions are localized to the “branes” in the fifth dimension. In this Letter we show that these constraints can be relaxed by allowing the light fermions to have a finite extent into the bulk of the fifth dimension. The T and U electroweak parameters can be naturally suppressed by a custodial symmetry, while the S parameter can be made to vanish through a cancellation, if the leakage into the bulk of the light gauge fields and the light left-handed fermion fields are of the same size. This cancellation is possible while allowing realistic values for the first two generations of fermion masses, although special treatment is probably required for the top quark. We present this idea here in the context of a specific continuum theory-space model; however, it can be applied to any five-dimensional Higgsless model, either with a flat or a warped background.
123963830
Diphoton production at the LHC
118496607
Antiproton cooling in the Fermilab Recycler Ring
The 8.9‐GeV/c Recycler antiproton storage ring is equipped with both stochastic and electron cooling systems. These cooling systems are designed to assist accumulation of antiprotons for the Tevatron collider operations. In this paper we report on an experimental demonstration of electron cooling of high‐energy antiprotons. At the time of writing this report, the Recycler electron cooling system is routinely used in collider operations. It has helped to set recent peak luminosity records.
109569741
Historical perspective of the H− ion source symposia
The International Symposium on the Production and Neutralization of Negative Hydrogen Ions and Beams is entering its third decade of providing a forum for the H− ion source community. The first meeting was held at Brookhaven National Laboratory in 1977 and has returned there every three years to 1995. This is the eighth meeting in this series and for the first time is in Europe, hosted by CEA/Center de Cadarache. Since this Symposium is meeting in Europe many new people have had an opportunity to attend and many of these are of a younger generation. On the 20th anniversary of the First Symposium it seems fitting that a historical review should be given. The Symposium meetings and its archiving of information has been a valuable asset to this community. I hope to briefly describe the early H− source work and provide some insight into the success of the H− source effort.