arXiv subjects

M. S. Daugherity

Publications and source records attributed to M. S. Daugherity.

At least 91 records · Page 5Linked to original sources

arXiv2016

Measurement of parity-violating spin asymmetries in W$^{\pm}$ production at midrapidity in longitudinally polarized $p$$+$$p$ collisions

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.

hep-ex↗

arXiv2016

Centrality-dependent modification of jet-production rates in deuteron-gold collisions at $\sqrt{s_{NN}}$=200 GeV

Jet production rates are measured in $p$$+$$p$ and $d$$+$Au collisions at $\sqrt{s_{NN}}$=200 GeV recorded in 2008 with the PHENIX detector at the Relativistic Heavy Ion Collider. Jets are reconstructed using the $R=0.3$ anti-$k_{t}$ algorithm from energy deposits in the electromagnetic calorimeter and charged tracks in multi-wire proportional chambers, and the jet transverse momentum ($p_T$) spectra are corrected for the detector response. Spectra are reported for jets with $12<p_T<50$ GeV/$c$, within a pseudorapidity acceptance of $\left|η\right|<0.3$. The nuclear-modification factor ($R_{d{\rm Au}}$) values for 0\%--100\% $d$$+$Au events are found to be consistent with unity, constraining the role of initial state effects on jet production. However, the centrality-selected $R_{d{\rm Au}}$ values and central-to-peripheral ratios ($R_{\rm CP}$) show large, $p_T$-dependent deviations from unity, which challenge the conventional models that relate hard-process rates and soft-particle production in collisions involving nuclei.

nucl-ex↗

arXiv2016

Scaling properties of fractional momentum loss of high-pT hadrons in nucleus-nucleus collisions at $\sqrt{s_{_{NN}}}$ from 62.4 GeV to 2.76 TeV

Measurements of the fractional momentum loss ($S_{\rm loss}\equivδp_T/p_T$) of high-transverse-momentum-identified hadrons in heavy ion collisions are presented. Using $π^0$ in Au$+$Au and Cu$+$Cu collisions at $\sqrt{s_{_{NN}}}=62.4$ and 200 GeV measured by the PHENIX experiment at the Relativistic Heavy Ion Collider and and charged hadrons in Pb$+$Pb collisions measured by the ALICE experiment at the Large Hadron Collider, we studied the scaling properties of $S_{\rm loss}$ as a function of a number of variables: the number of participants, $N_{\rm part}$, the number of quark participants, $N_{\rm qp}$, the charged-particle density, $dN_{\rm ch}/dη$, and the Bjorken energy density times the equilibration time, $\varepsilon_{\rm Bj}τ_{0}$. We find that the $p_T$ where $S_{\rm loss}$ has its maximum, varies both with centrality and collision energy. Above the maximum, $S_{\rm loss}$ tends to follow a power-law function with all four scaling variables. The data at $\sqrt{s_{_{NN}}}$=200 GeV and 2.76 TeV, for sufficiently high particle densities, have a common scaling of $S_{\rm loss}$ with $dN_{\rm ch}/dη$ and $\varepsilon_{\rm Bj}τ_{0}$, lending insight on the physics of parton energy loss.

nucl-ex↗

arXiv2016

$ϕ$ meson production in the forward/backward rapidity region in Cu$+$Au collisions at $\sqrt{s_{NN}}=200$ GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has measured $ϕ$ 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 $ϕ$ 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.

nucl-ex↗

arXiv2016

Measurement of higher cumulants of net-charge multiplicity distributions in Au$+$Au collisions at $\sqrt{s_{_{NN}}}=7.7-200$ GeV

We report the measurement of cumulants ($C_n, n=1\ldots4$) of the net-charge distributions measured within pseudorapidity ($|η|<0.35$) in Au$+$Au collisions at $\sqrt{s_{_{NN}}}=7.7-200$ GeV with the PHENIX experiment at the Relativistic Heavy Ion Collider. The ratios of cumulants (e.g. $C_1/C_2$, $C_3/C_1$) of the net-charge distributions, which can be related to volume independent susceptibility ratios, are studied as a function of centrality and energy. These quantities are important to understand the quantum-chromodynamics phase diagram and possible existence of a critical end point. The measured values are very well described by expectation from negative binomial distributions. We do not observe any nonmonotonic behavior in the ratios of the cumulants as a function of collision energy. The measured values of $C_1/C_2 = μ/σ^2$ and $C_3/C_1 = Sσ^3/μ$ can be directly compared to lattice quantum-chromodynamics calculations and thus allow extraction of both the chemical freeze-out temperature and the baryon chemical potential at each center-of-mass energy.

nucl-ex↗

arXiv2015

Dielectron production in Au$+$Au collisions at $\sqrt{s_{NN}}$=200 GeV

We present measurements of $e^+e^-$ production at midrapidity in Au$+$Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV. The invariant yield is studied within the PHENIX detector acceptance over a wide range of mass ($m_{ee} <$ 5 GeV/$c^2$) and pair transverse momentum ($p_T$ $<$ 5 GeV/$c$), for minimum bias and for five centrality classes. The \ee yield is compared to the expectations from known sources. In the low-mass region ($m_{ee}=0.30$--0.76 GeV/$c^2$) there is an enhancement that increases with centrality and is distributed over the entire pair \pt range measured. It is significantly smaller than previously reported by the PHENIX experiment and amounts to $2.3\pm0.4({\rm stat})\pm0.4({\rm syst})\pm0.2^{\rm model}$ or to $1.7\pm0.3({\rm stat})\pm0.3({\rm syst})\pm0.2^{\rm model}$ for minimum bias collisions when the open-heavy-flavor contribution is calculated with {\sc pythia} or {\sc mc@nlo}, respectively. The inclusive mass and $p_T$ distributions as well as the centrality dependence are well reproduced by model calculations where the enhancement mainly originates from the melting of the $ρ$ meson resonance as the system approaches chiral symmetry restoration. In the intermediate-mass region ($m_{ee}$ = 1.2--2.8 GeV/$c^2$), the data hint at a significant contribution in addition to the yield from the semileptonic decays of heavy-flavor mesons.

nucl-ex↗

arXiv2015

Inclusive cross section and double-helicity asymmetry for $π^{0}$ production at midrapidity in $p$$+$$p$ collisions at $\sqrt{s}=510$ GeV

PHENIX measurements are presented for the cross section and double-helicity asymmetry ($A_{LL}$) in inclusive $π^0$ 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 $π^{0}A_{LL}$ 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 $π^0$ and jet $A_{LL}$, and suggested a positive contribution of gluon polarization to the spin of the proton $ΔG$ 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 $ΔG$. The results confirm the evidence for nonzero $ΔG$ using a different production channel in a complementary kinematic region.

hep-ex↗

arXiv2015

$ϕ$ meson production in $d$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV

The PHENIX experiment has measured $ϕ$ meson production in $d$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV using the dimuon and dielectron decay channels. The $ϕ$ meson is measured in the forward (backward) $d$-going (Au-going) direction, $1.2<y<2.2$ ($-2.2<y<-1.2$) in the transverse-momentum ($p_T$) range from 1--7 GeV/$c$, and at midrapidity $|y|<0.35$ in the $p_T$ range below 7 GeV/$c$. The $ϕ$ meson invariant yields and nuclear-modification factors as a function of $p_T$, rapidity, and centrality are reported. An enhancement of $ϕ$ meson production is observed in the Au-going direction, while suppression is seen in the $d$-going direction, and no modification is observed at midrapidity relative to the yield in $p$$+$$p$ collisions scaled by the number of binary collisions. Similar behavior was previously observed for inclusive charged hadrons and open heavy flavor indicating similar cold-nuclear-matter effects.

nucl-ex↗

arXiv2015

Systematic study of charged-pion and kaon femtoscopy in Au$+$Au collisions at $\sqrt{s_{_{NN}}}$=200 GeV

We present a systematic study of charged pion and kaon interferometry in Au$+$Au collisions at $\sqrt{s_{_{NN}}}$=200 GeV. The kaon mean source radii are found to be larger than pion radii in the outward and longitudinal directions for the same transverse mass; this difference increases for more central collisions. The azimuthal-angle dependence of the radii was measured with respect to the second-order event plane and similar oscillations of the source radii were found for pions and kaons. Hydrodynamic models qualitatively describe the similar oscillations of the mean source radii for pions and kaons, but they do not fully describe the transverse-mass dependence of the oscillations.

nucl-ex↗

arXiv2015

Cross Section and Transverse Single-Spin Asymmetry of $η$ Mesons in $p^{\uparrow}+p$ Collisions at $\sqrt{s}=200$ GeV at Forward Rapidity

We present a measurement of the cross section and transverse single-spin asymmetry ($A_N$) for $η$ mesons at large pseudorapidity from $\sqrt{s}=200$~GeV $p^{\uparrow}+p$ collisions. The measured cross section for $0.5<p_T<5.0$~GeV/$c$ and $3.0<|η|<3.8$ is well described by a next-to-leading-order perturbative-quantum-chromodynamics calculation. The asymmetries $A_N$ have been measured as a function of Feynman-$x$ ($x_F$) from $0.2<|x_{F}|<0.7$, as well as transverse momentum ($p_T$) from $1.0<p_T<4.5$~GeV/$c$. The asymmetry averaged over positive $x_F$ is $\langle{A_{N}}\rangle=0.061{\pm}0.014$. The results are consistent with prior transverse single-spin measurements of forward $η$ and $π^{0}$ mesons at various energies in overlapping $x_F$ ranges. Comparison of different particle species can help to determine the origin of the large observed asymmetries in $p^{\uparrow}+p$ collisions.

hep-ex↗

arXiv2015

Centrality dependence of low-momentum direct-photon production in Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV

The PHENIX experiment at RHIC has measured the centrality dependence of the direct photon yield from Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV down to $p_T=0.4$ GeV/$c$. Photons are detected via photon conversions to $e^+e^-$ pairs and an improved technique is applied that minimizes the systematic uncertainties that usually limit direct photon measurements, in particular at low $p_T$. We find an excess of direct photons above the $N_{\rm coll}$-scaled yield measured in $p$$+$$p$ collisions. This excess yield is well described by an exponential distribution with an inverse slope of about 240 MeV/$c$ in the $p_T$ range from 0.6--2.0 GeV/$c$. While the shape of the $p_T$ distribution is independent of centrality within the experimental uncertainties, the yield increases rapidly with increasing centrality, scaling approximately with $N_{\rm part}^α$, where $α=1.48{\pm}0.08({\rm stat}){\pm}0.04({\rm syst})$.

nucl-ex↗

arXiv2015

Measurement of $Υ$(1S+2S+3S) production in $p$$+$$p$ and Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV

Measurements of bottomonium production in heavy ion and $p$$+$$p$ collisions at the Relativistic Heavy Ion Collider (RHIC) are presented. The inclusive yield of the three $Υ$ states, $Υ(1S+2S+3S)$, was measured in the PHENIX experiment via electron-positron decay pairs at midrapidity for Au$+$Au and $p$$+$$p$ collisions at $\sqrt{s_{_{NN}}}=200$ GeV. The $Υ(1S+2S+3S)\rightarrow e^+e^-$ differential cross section at midrapidity was found to be $B_{\rm ee} dσ/dy =$ 108 $\pm$ 38 (stat) $\pm$ 15(syst) $\pm$ 11 (luminosity) pb in $p$$+$$p$ collisions. The nuclear modification factor in the 30\% most central Au$+$Au collisions indicates a suppression of the total $Υ$ state yield relative to the extrapolation from $p$$+$$p$ collision data. The suppression is consistent with measurements made by STAR at RHIC and at higher energies by the CMS experiment at the Large Hadron Collider.

nucl-ex↗

arXiv2015

Heavy-quark production and elliptic flow in Au$+$Au collisions at $\sqrt{s_{_{NN}}}=62.4$ GeV

We present measurements of electrons and positrons from the semileptonic decays of heavy-flavor hadrons at midrapidity ($|y|<$ 0.35) in Au$+$Au collisions at $\sqrt{s_{_{NN}}}=62.4$ GeV. The data were collected in 2010 by the PHENIX experiment that included the new hadron-blind detector. The invariant yield of electrons from heavy-flavor decays is measured as a function of transverse momentum in the range $1<p_T^e<5$ GeV/$c$. The invariant yield per binary collision is slightly enhanced above the $p$$+$$p$ reference in Au$+$Au 0%--20%, 20%--40% and 40%--60% centralities at a comparable level. This may be a result of the interplay between initial-state Cronin effects, final-state flow, and energy loss for heavy-quark production at this low beam energy. The $v_2$ of electrons from heavy-flavor decays is nonzero when averaged between $1.3<p_T^e<2.5$ GeV/$c$ from $0<{\rm centrality}<40$% collisions at $\sqrt{s_{_{NN}}}=62.4$ GeV. For 20%--40% centrality collisions, the $v_2$ at $\sqrt{s_{_{NN}}}=62.4$ GeV is smaller than that for heavy flavor decays at $\sqrt{s_{_{NN}}}=200$ GeV. The $v_2$ of the electrons from heavy-flavor decay at the lower beam energy is also smaller than $v_2$ for pions. Both results indicate that the heavy-quarks interact with the medium formed in these collisions, but they may not be at the same level of thermalization with the medium as observed at $\sqrt{s_{_{NN}}}=200$ GeV.

nucl-ex↗

arXiv2015

Search for dark photons from neutral meson decays in $p$$+$$p$ and $d$$+$Au collisions at $\sqrt{s_{_{NN}}}$=200 GeV

The standard model (SM) of particle physics is spectacularly successful, yet the measured value of the muon anomalous magnetic moment $(g-2)_μ$ deviates from SM calculations by 3.6$σ$. Several theoretical models attribute this to the existence of a "dark photon," an additional U(1) gauge boson, which is weakly coupled to ordinary photons. The PHENIX experiment at the Relativistic Heavy Ion Collider has searched for a dark photon, $U$, in $π^0,η\rightarrow γe^+e^-$ decays and obtained upper limits of $\mathcal{O}(2\times10^{-6})$ on $U$-$γ$ mixing at 90% CL for the mass range $30<m_U<90$ MeV/$c^2$. Combined with other experimental limits, the remaining region in the $U$-$γ$ mixing parameter space that can explain the $(g-2)_μ$ deviation from its SM value is nearly completely excluded at the 90% confidence level, with only a small region of $29<m_U<32$ MeV/$c^2$ remaining.

nucl-ex↗

arXiv2015

An Upgrade Proposal from the PHENIX Collaboration

In this document the PHENIX collaboration proposes a major upgrade to the PHENIX detector at the Relativistic Heavy Ion Collider. This upgrade, sPHENIX, enables an extremely rich jet and beauty quarkonia physics program addressing fundamental questions about the nature of the strongly coupled quark-gluon plasma (QGP), discovered experimentally at RHIC to be a perfect fluid. The startling dynamics of the QGP on fluid-like length scales is an emergent property of quantum chromodynamics (QCD), seemingly implicit in the Lagrangian but stubbornly hidden from view. QCD is an asymptotically free theory, but how QCD manifests as a strongly coupled fluid with specific shear viscosity near $T_C$, as low as allowed by the uncertainty principle, is as fundamental an issue as that of how confinement itself arises.

nucl-ex↗

arXiv2014

Beam-energy and system-size dependence of the space-time extent of the pion emission source produced in heavy ion collisions

Two-pion interferometry measurements are used to extract the Gaussian radii $R_{\rm out}$, $R_{\rm side}$, and $R_{\rm long}$, of the pion emission sources produced in Cu$+$Cu and Au$+$Au collisions at several beam collision energies $\sqrt{s_{_{NN}}}$ at PHENIX. The extracted radii, which are compared to recent STAR and ALICE data, show characteristic scaling patterns as a function of the initial transverse size $\bar{R}$ of the collision systems and the transverse mass $m_T$ of the emitted pion pairs, consistent with hydrodynamiclike expansion. Specific combinations of the three-dimensional radii that are sensitive to the medium expansion velocity and lifetime, and the pion emission time duration show nonmonotonic $\sqrt{s_{_{NN}}}$ dependencies. The nonmonotonic behaviors exhibited by these quantities point to a softening of the equation of state that may coincide with the critical end point in the phase diagram for nuclear matter.

nucl-ex↗

arXiv2014

Low-mass vector-meson production at forward rapidity in $p$$+$$p$ collisions at $\sqrt{s}=200$ GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured low mass vector meson, $ω$, $ρ$, and $ϕ$, production through the dimuon decay channel at forward rapidity ($1.2<|y|<2.2$) in $p$$+$$p$ collisions at $\sqrt{s}=200$ GeV. The differential cross sections for these mesons are measured as a function of both $p_T$ and rapidity. We also report the integrated differential cross sections over $1<p_T<7$ GeV/$c$ and $1.2<|y|<2.2$: $dσ/dy(ω+ρ\rightarrowμμ) = 80 \pm 6 \mbox{(stat)} \pm 12 \mbox{(syst)}$ nb and $dσ/dy(ϕ\rightarrowμμ) = 27 \pm 3 \mbox{(stat)} \pm 4 \mbox{(syst)}$ nb. These results are compared with midrapidity measurements and calculations.

hep-ex↗

arXiv2014

Measurement of $K_S^0$ and $K^{*0}$ in $p$$+$$p$, $d$$+$Au, and Cu$+$Cu collisions at $\sqrt{s_{_{NN}}}=200$ GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider has performed a systematic study of $K_S^0$ and $K^{*0}$ meson production at midrapidity in $p$$+$$p$, $d$$+$Au, and Cu$+$Cu collisions at $\sqrt{s_{_{NN}}}=200$ GeV. The $K_S^0$ and $K^{*0}$ mesons are reconstructed via their $K_S^0 \rightarrow π^0(\rightarrow γγ)π^0(\rightarrowγγ)$ and $K^{*0} \rightarrow K^{\pm}π^{\mp}$ decay modes, respectively. The measured transverse-momentum spectra are used to determine the nuclear modification factor of $K_S^0$ and $K^{*0}$ mesons in $d$$+$Au and Cu$+$Cu collisions at different centralities. In the $d$$+$Au collisions, the nuclear modification factor of $K_S^0$ and $K^{*0}$ mesons is almost constant as a function of transverse momentum and is consistent with unity showing that cold-nuclear-matter effects do not play a significant role in the measured kinematic range. In Cu$+$Cu collisions, within the uncertainties no nuclear modification is registered in peripheral collisions. In central collisions, both mesons show suppression relative to the expectations from the $p$$+$$p$ yield scaled by the number of binary nucleon-nucleon collisions in the Cu$+$Cu system. In the $p_T$ range 2--5 GeV/$c$, the strange mesons ($K_S^0$, $K^{*0}$) similarly to the $ϕ$ meson with hidden strangeness, show an intermediate suppression between the more suppressed light quark mesons ($π^0$) and the nonsuppressed baryons ($p$, $\bar{p}$). At higher transverse momentum, $p_T>5$ GeV/$c$, production of all particles is similarly suppressed by a factor of $\approx$ 2.

nucl-ex↗