We present measurements from the PHENIX experiment of large parity-violating single spin asymmetries of high transverse momentum electrons and positrons from \(W^\pm/Z\) decays, produced in ...longitudinally polarized $p$$+$$p\( collisions at center of mass energies of \)\sqrt{s}\(=500 and 510~GeV. These asymmetries allow direct access to the anti-quark polarized parton distribution functions due to the parity-violating nature of the \)W\(-boson coupling to quarks and anti-quarks. The results presented are based on data collected in 2011, 2012, and 2013 with an integrated luminosity of 240 pb\)^{-1}\(, which exceeds previous PHENIX published results by a factor of more than 27. These high \)Q^2$ data provide an important addition to our understanding of anti-quark parton helicity distribution functions.
Measurements of the anisotropy parameter v(2) of identified hadrons (pions, kaons, and protons) as a function of centrality, transverse momentum p(T), and transverse kinetic energy KET at midrapidity ...(vertical bar eta vertical bar < 0.35) in Au + Au collisions at root s(N N) = 200 GeV are presented. Pions and protons are identified up to p(T) = 6 GeV/c, and kaons up to p(T) = 4 GeV/c, by combining information from time-of-flight and aerogel Cerenkov detectors in the PHENIX Experiment. The scaling of v(2) with the number of valence quarks (n(q)) has been studied in different centrality bins as a function of transverse momentum and transverse kinetic energy. A deviation from previously observed quark-number scaling is observed at large values of KET/n(q) in noncentral Au + Au collisions (20-60%), but this scaling remains valid in central collisions (0-10%).
Phys. Rev. C 95, 034904 (2017) 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.
Phys. Rev. C 95, 034910 (2017) We present the first measurements of long-range angular correlations and the
transverse momentum dependence of elliptic flow $v_2$ in high-multiplicity
$p$$+$Au ...collisions at $\sqrt{s_{_{NN}}}=200$ GeV. A comparison of these
results with previous measurements in high-multiplicity $d$$+$Au and $^3{\rm
He}$$+$Au collisions demonstrates a relation between $v_2$ and the initial
collision eccentricity $\varepsilon_2$, suggesting that the observed
momentum-space azimuthal anisotropies in these small systems have a collective
origin and reflect the initial geometry. Good agreement is observed between the
measured $v_2$ and hydrodynamic calculations for all systems, and an argument
disfavoring theoretical explanations based on momentum-space domain
correlations is presented. The set of measurements presented here allows us to
leverage the distinct intrinsic geometry of each of these systems to
distinguish between different theoretical descriptions of the long-range
correlations observed in small collision systems.
We describe directed searches for continuous gravitational waves in data from the sixth LIGO science data run. The targets were nine young supernova remnants not associated with pulsars; eight of the ...remnants are associated with non-pulsing suspected neutron stars. One target's parameters are uncertain enough to warrant two searches, for a total of ten. Each search covered a broad band of frequencies and first and second frequency derivatives for a fixed sky direction. The searches coherently integrated data from the two LIGO interferometers over time spans from 5.3-25.3 days using the matched-filtering F-statistic. We found no credible gravitational-wave signals. We set 95% confidence upper limits as strong (low) as 4×10−25 on intrinsic strain, 2×10−7 on fiducial ellipticity, and 4×10−5 on r-mode amplitude. These beat the indirect limits from energy conservation and are within the range of theoretical predictions for neutron-star ellipticities and r-mode amplitudes.
Abstract We report on the measurement of the Central Exclusive Production of charged particle pairs h + h − (h = π, K, p) with the STAR detector at RHIC in proton-proton collisions at s $$ \sqrt{s} ...$$ = 200 GeV. The charged particle pairs produced in the reaction pp → p′ + h + h − + p′ are reconstructed from the tracks in the central detector and identified using the specific energy loss and the time of flight method, while the forward-scattered protons are measured in the Roman Pot system. Exclusivity of the event is guaranteed by requiring the transverse momentum balance of all four final-state particles. Differential cross sections are measured as functions of observables related to the central hadronic final state and to the forward-scattered protons. They are measured in a fiducial region corresponding to the acceptance of the STAR detector and determined by the central particles’ transverse momenta and pseudorapidities as well as by the forward-scattered protons’ momenta. This fiducial region roughly corresponds to the square of the four-momentum transfers at the proton vertices in the range 0.04 GeV2 < −t 1 , −t 2 < 0.2 GeV2, invariant masses of the charged particle pairs up to a few GeV and pseudorapidities of the centrally-produced hadrons in the range |η| < 0.7. The measured cross sections are compared to phenomenological predictions based on the Double Pomeron Exchange (DPE) model. Structures observed in the mass spectra of π + π − and K + K − pairs are consistent with the DPE model, while angular distributions of pions suggest a dominant spin-0 contribution to π + π − production. For π + π − production, the fiducial cross section is extrapolated to the Lorentz-invariant region, which allows decomposition of the invariant mass spectrum into continuum and resonant contributions. The extrapolated cross section is well described by the continuum production and at least three resonances, the f 0(980), f 2(1270) and f 0(1500), with a possible small contribution from the f 0(1370). Fits to the extrapolated differential cross section as a function of t 1 and t 2 enable extraction of the exponential slope parameters in several bins of the invariant mass of π + π − pairs. These parameters are sensitive to the size of the interaction region.
Phys. Rev. D 93, 011501 (2016) PHENIX measurements are presented for the cross section and double-helicity
asymmetry ($A_{LL}$) in inclusive $\pi^0$ production at midrapidity from
$p$$+$$p$ ...collisions at $\sqrt{s}=510$~GeV from data taken in 2012 and 2013 at
the Relativistic Heavy Ion Collider. The next-to-leading-order
perturbative-quantum-chromodynamics theory calculation is in excellent
agreement with the presented cross section results. The calculation utilized
parton-to-pion fragmentation functions from the recent DSS14 global analysis,
which prefer a smaller gluon-to-pion fragmentation function. The
$\pi^{0}A_{LL}$ results follow an increasingly positive asymmetry trend with
$p_T$ and $\sqrt{s}$ with respect to the predictions and are in excellent
agreement with the latest global analysis results. This analysis incorporated
earlier results on $\pi^0$ and jet $A_{LL}$, and suggested a positive
contribution of gluon polarization to the spin of the proton $\Delta G$ for the
gluon momentum fraction range $x>0.05$. The data presented here extend to a
currently unexplored region, down to $x\sim0.01$, and thus provide additional
constraints on the value of $\Delta G$. The results confirm the evidence for
nonzero $\Delta G$ using a different production channel in a complementary
kinematic region.
We present transverse momentum (p(T)) spectra of charged hadrons measured in deuteron-gold and nucleon-gold collisions at root s(NN)=200 GeV for four centrality classes. Nucleon-gold collisions were ...selected by tagging events in which a spectator nucleon was observed in one of two forward rapidity detectors. The spectra and yields were investigated as a function of the number of binary nucleon-nucleon collisions, nu, suffered by deuteron nucleons. A comparison of charged particle yields to those in p+p collisions show that yield per nucleon-nucleon collision saturates with nu for high momentum particles. We also present the charged hadron to neutral pion ratios as a function of p(T).
Phys. Rev. C 93, 024904 (2016) The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has
measured $\phi$ meson production and its nuclear modification in asymmetric
Cu$+$Au heavy-ion ...collisions at $\sqrt{s_{NN}}=200$ GeV at both forward
Cu-going direction ($1.2<y<2.2$) and backward Au-going direction
($-2.2<y<-1.2$), rapidities. The measurements are performed via the dimuon
decay channel and reported as a function of the number of participating
nucleons, rapidity, and transverse momentum. In the most central events,
0\%--20\% centrality, the $\phi$ meson yield integrated over $1<p_T<5$ GeV/$c$
prefers a smaller value, which means a larger nuclear modification, in the
Cu-going direction compared to the Au-going direction. Additionally, the
nuclear-modification factor in Cu$+$Au collisions averaged over all centrality
is measured to be similar to the previous PHENIX result in $d$$+$Au collisions
for these rapidities.
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