447 Search Results

Here, we report the first evidence of spin interference in exclusive 𝐽/𝜓 → 𝑒⁺⁢𝑒⁻ photoproduction in ultraperipheral heavy-ion collisions at STAR at $$\sqrt{𝑠_{𝑁⁢𝑁}}$$ = 200  GeV. In Au + Au collisions, a negative cos⁡(2⁢𝜙) modulation is found for 𝑝_𝑇 < 120  MeV/𝑐 with a significance of 3.2⁢𝜎, while the isobar data (Ru + Ru, Zr + Zr) show a consistent negative modulation with a significance of 1.9⁢𝜎, opposite in sign to that in 𝜌⁰ → 𝜋⁺⁢𝜋⁻ photoproduction. This establishes for the first time that the interference sign is controlled by the spin structure of the final-state daughters, resolving the ambiguity present inmore » the all-boson 𝜌⁰ channel. The compact 𝐽/𝜓 probes gluon distributions at perturbative scales, resulting in a weaker modulation and providing stringent constraints on color glass condensate calculations. These findings demonstrate that spin-dependent interference in heavy vector mesons provides a new, experimentally accessible handle on gluon structure beyond traditional cross-section measurements.« less

We present a catalog of 500 galaxy cluster candidates in the SPT-Deep field: a 100 deg$$^{2}$$ field that combines data from the SPT-3G and SPTpol surveys to reach noise levels of 3.0, 2.2, and 9.0 μK-arcmin at 95, 150, and 220 GHz, respectively. Candidates are selected via the thermal Sunyaev–Zel’dovich (SZ) effect with a minimum significance of ξ = 4.0, resulting in a catalog of purity ∼89%. Optical data from the Dark Energy Survey and infrared data from the Spitzer Space Telescope are used to confirm 442 cluster candidates. The clusters span 0.12 < z ≲ 1.8 and 1.0 × 10$$^{14}$$M$$_{⊙}$$/h$$_{70}$$ < M$$_{500c}$$ < 8.7 × 10$$^{14}$$M$$_{⊙}$$/h$$_{70}$$. The sample’s median redshift is 0.74, and themore » median mass is 1.7 × 10$$^{14}$$M$$_{⊙}$$/h$$_{70}$$; these are the lowest median mass and highest median redshift of any SZ-selected sample to date. We assess the effect of infrared emission from cluster member galaxies on cluster selection by performing a joint fit to the infrared dust and tSZ signals by combining measurements from SPT and overlapping submillimeter data from Herschel/SPIRE. We find that at high redshift (z > 1), the tSZ signal is reduced by 17.9−3.2+3.8%(3.8−0.7+0.9%) at 150 GHz (95 GHz) due to dust contamination. We repeat our cluster finding method on dust-nulled SPT maps and find the resulting catalog is consistent with the nominal SPT-Deep catalog, suggesting dust contamination does not significantly impact the SPT-Deep selection function; we attribute this lack of bias to the inclusion of the SPT 220 GHz band.« less

We present a measurement of the full shape of the power spectrum of the thermal Sunyaev–Zel’dovich (tSZ) effect down to arcminute scales using cosmic microwave background (CMB) data from the South Pole Telescope (SPT) over a roughly 100 deg² field. The analysis incorporates data from the 2019–2020 seasons of the SPT-3G survey in bands centered at 95, 150, and 220 GHz; from the full SPTpol dataset at 150 GHz; and from the Herschel–SPIRE survey in bands centered at 600 and 857 GHz. We combine data from all the above bands using linear combination (LC) techniques to produce a tSZ ormore » Compton-y map. We modify the LC weights to produce multiple versions of the Compton-y map, including minimum-variance (MV) and foreground-minimized (-min) maps. We measure the auto- and cross-power spectra of a subset of these maps in the range ℓ ∈ [500, 5000]. While this power spectrum includes contributions from signals other than tSZ, we present numerous checks to show that the most challenging foreground signal, the cosmic infrared background (CIB), is much lower than the desired tSZ signal in the scales of interest in this work. The final tSZ power spectrum is measured at 9.3σ with both the MV and CIB-min maps. Our results are consistent with those reported in other CMB surveys across the literature. Using the difference in the tSZ power spectrum from the MV and CIB-min maps, we reconstruct the scale-dependent tSZ–CIB cross correlation $$ρ^{\textrm{tSZ}}_{ℓ}$$ x CIB, finding 3.1σ evidence for a nonzero correlation coefficient that is positive on large scales and approaches zero for ℓ > 2500. This result represents the deepest tSZ maps ever produced and provides new constraints that can help refine astrophysical feedback mechanisms and models of the intracluster medium.« less

The correlation between the mean transverse momentum, [p_T], and the squared anisotropic flow, $$v^2_n$$, on an event-by-event basis has been suggested to be influenced by the initial conditions in heavy-ion collisions. We present measurements of the variances and covariance of [p_T] and $$v^2_n$$, along with their dimensionless ratio, for Au+Au collisions at various beam energies: $$\sqrt{s_{NN}}$$ = 14.6, 19.6, 27, 54.4, and 200 GeV. Our measurements reveal a distinct energy-dependent behavior in the variances and covariances. In addition, the dimensionless ratio displays a similar behavior across different beam energies. We compare our measurements with hydrodynamic models and similar measurements frommore » Pb+Pb collisions at the Large Hadron Collider (LHC). These findings provide valuable insights into the beam energy dependence of the specific shear viscosity (η/s) and initial-state effects, allowing for differentiating between different initial-state models.« less

Rapidity-odd directed flow v₁ measurements are presented for $K^±$ and $$K^0_S$$ in Au + Au collisions for $$\sqrt{s_{NN}}$$ from 3.0 to 3.9 GeV with the STAR experiment. For comparison, v₁ of π^±, protons, and Λ from the same collisions are also discussed. The mid-rapidity v₁ slope dv₁/dy|_y=0 for protons and Λ is positive in these collisions. On the other hand, v₁ slope of kaons exhibits a strong dependence: negative at p_T < 0.6 GeV/c and positive at higher p_T. A similar p_T dependence is also evident for the v₁ slope of charged pions. Compared to the spectator-removed calculations in Au+Aumore » collisions at $$\sqrt{s_{NN}}$$ = 3.0–3.9 GeV, the JAM model demonstrates a pronounced shift of the v₁ slopes of mesons towards the negative direction. It suggests that the shadowing effect of the spectators plays an important role in the observed kaon anti-flow at low p_T in the high baryon density region of non-central collisions.« less

We report measurements of charmonium sequential suppression in Ru+Ru and Zr+Zr collisions at $$\sqrt{s_{NN}}$$ =200  GeV with the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The inclusive yield ratio of 𝜓⁡(2⁢S) to J/𝜓 as a function of transverse momentum is reported, along with the centrality dependence of the double ratio, defined as the 𝜓⁡(2⁢S) to J/𝜓 ratio in heavy-ion collisions relative to that in 𝑝 +𝑝 collisions. In the 0–80% centrality class, the double ratio is found to be 0.41±0.10 (stat)±0.03 (syst)±0.02 (ref), lower than unity with a significance of 5.6 standard deviations. This provides experimental evidence that 𝜓⁡(2⁢S) is significantly moremore » suppressed than J/𝜓 in heavy-ion collisions at RHIC. This sequential suppression pattern seems to increase from peripheral to central collisions, but with no significant dependence on the transverse momentum.« less

The vacuum is now understood to have a rich and complex structure, characterized by fluctuating energy fields and a condensate of virtual quark–antiquark pairs. The spontaneous breaking of the approximate chiral symmetry, signalled by the nonvanishing quark condensate $$\langle$$$$q\bar{q}$$$$\rangle$$, is dynamically generated through topologically nontrivial gauge configurations such as instantons. The precise mechanism linking the chiral symmetry breaking to the mass generation associated with quark confinement remains a profound open question in quantum chromodynamics (QCD)—the fundamental theory of strong interaction. High-energy proton–proton collisions could liberate virtual quark–antiquark pairs from the vacuum that subsequently undergo confinement to form hadrons, whose propertiesmore » could serve as probes into QCD confinement and the quark condensate. Here we report evidence of spin correlations in $$Λ\bar{Λ}$$ hyperon pairs inherited from spin-correlated strange quark–antiquark virtual pairs. Measurements by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory reveal a relative polarization signal of (18 ± 4)% that links the virtual spin-correlated quark pairs from the QCD vacuum to their final-state hadron counterparts. Crucially, this correlation vanishes when the hyperon pairs are widely separated in angle, consistent with the decoherence of the quantum system. Our findings provide a new experimental model for exploring the dynamics and interplay of quark confinement and entanglement.« less

High-energy, heavy-ion collisions can create local domains of chirality-imbalanced quarks, reflecting the topological features of quantum chromodynamics. The chiral magnetic effect (CME) predicts an electric charge separation of quarks in such topological domains along the magnetic field ($$\vec{B}$$) generated by the passing of two high-Z nuclei. Here, we use a correlation observable Δ⁢𝛾$$^{112}$$ between charged meson pairs to detect the CME-induced charge separation and a novel event shape selection (ESS) method to mitigate the background effects related to elliptic flow (𝑣₂). The ESS method classifies events based on the emission pattern of final-state particles and determines Δ⁢𝛾$$^{112}_{ESS}$$ from the zero-flowmore » limit. We reconstruct the $$\vec{B}$$ field direction from the spectator nucleons, which minimizes backgrounds unrelated to the collective motion of the system. In this work, we report the measurements of Δ⁢𝛾$$^{112}$$ and a background indicator Δ⁢𝛾$$^{132}$$ in Au+Au collisions from the Brookhaven National Laboratory Relativistic Heavy Ion Collider (RHIC) Beam Energy Scan phase II and at the top RHIC energy. After background suppression, Δ⁢𝛾$$^{132}_{ESS}$$ aligns with zero, and Δ⁢𝛾$$^{112}_{ESS}$$ is reduced to no more than 20% of Δ⁢𝛾$$^{112}$$. We observe a finite residual charge separation with 2.5⁢𝜎, 3⁢𝜎, and 3.2⁢𝜎 significance in the 20–50% centrality range of Au + Au collisions at 11.5, 14.6, and 19.6 GeV. The results at 17.3 and 27 GeV also show positive values but with a lower significance of 1.3⁢𝜎 and 1.1⁢𝜎, respectively. The corresponding Δ⁢𝛾$$^{112}_{ESS}$$ values at 7.7, 9.2, and 200 GeV are consistent with zero within uncertainties.« less

In the originally published version of this article, several errors were identified in the author list and acknowledgements section. These have now been corrected as follows: Corrections to the Author List: Barrera has been corrected to Barresi. Copello (affiliation 18) has been corrected to Copello (affiliation 19). F. De Domizio has been corrected to S. Di Domizio. Figueros-Feliciamo has been corrected to Figueroa-Feliciano. Mancarella (affiliations 8, 17) has been corrected to Mancarella (affiliations 8, 18). Manenti (affiliations 18, 19) has been corrected to Manenti (affiliations 19, 20). Mayer (affiliations 3, 20, 31) has been corrected to Mayer (affiliations 3, 21,more » 31). Pagot has been corrected to Pageot. Puranam (affiliation 20) has been corrected to Puranam (affiliation 21). O. Penek has been corrected to Ö. Penek. L. Pettinacci has been corrected to V. Pettinacci. P. Pirro has been corrected to S. Pirro. Previtale has been corrected to Previtali. Rappoldi (affiliation 18) has been corrected to Rappoldi (affiliation 19). Raselli (affiliation 18) has been corrected to Raselli (affiliation 19). Rizzoli (affiliations 8, 17) has been corrected to Rizzoli (affiliations 8, 18). Rossella (affiliation 18) has been corrected to Rossella (affiliation 19). Correction to the Acknowledgements Section: The following grant numbers were missing and have now been added: This work was supported by NSF-PHY-2412377 and NSF-PHY-1913374. Additionally, on page 11, Section 5, second line, the chemical formula was incorrectly given as Li₂MO₄. The correct formula is Li₂MoO₄. The original article has been updated to reflect these corrections. The publisher apologizes for the inconvenience.« less

The STAR Collaboration reports measurements of acoplanarity using semi-inclusive distributions of charged-particle jets recoiling from direct photon and 𝜋⁰ triggers, in central Au–Au and 𝑝⁢𝑝 collisions at $$\sqrt{s_{NN}}$$ = 200 GeV. Significant medium-induced acoplanarity broadening is observed for large but not small recoil jet resolution parameter, corresponding to recoil jet yield enhancement up to a factor of ≈ 20 for trigger-recoil azimuthal separation far from 𝜋. This phenomenology is indicative of the response of the quark-gluon plasma to excitation, but not the scattering of jets off of its quasiparticles. As a result, the measurements are not well described by currentmore » theoretical models which incorporate jet quenching.« less