Search for the chiral magnetic effect via charge-dependent azimuthal correlations relative to spectator and participant planes in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV
STAR Collaboration, M. S. Abdallah, J. Adam, L. Adamczyk, J. R. Adams, J. K. Adkins, G. Agakishiev, I. Aggarwal, M. M. Aggarwal, Z. Ahammed, I. Alekseev, D. M. … 展开作者
STAR Collaboration, M. S. Abdallah, J. Adam, L. Adamczyk, J. R. Adams, J. K. Adkins, G. Agakishiev, I. Aggarwal, M. M. Aggarwal, Z. Ahammed, I. Alekseev, D. M. Anderson, A. Aparin, E. C. Aschenauer, M. U. Ashraf, F. G. Atetalla, A. Attri, G. S. Averichev, V. Bairathi, W. Baker, J. G. Ball Cap, K. Barish, A. Behera, R. Bellwied, P. Bhagat, A. Bhasin, J. Bielcik, J. Bielcikova, I. G. Bordyuzhin, J. D. Brandenburg, A. V. Brandin, I. Bunzarov, J. Butterworth, X. Z. Cai, H. Caines, M. Calderón de la Barca Sánchez, D. Cebra, I. Chakaberia, P. Chaloupka, B. K. Chan, F-H. Chang, Z. Chang, N. Chankova-Bunzarova, A. Chatterjee, S. Chattopadhyay, D. Chen, J. Chen, J. H. Chen, X. Chen, Z. Chen, J. Cheng, M. Chevalier, S. Choudhury, W. Christie, X. Chu, H. J. Crawford, M. Csanád, M. Daugherity, T. G. Dedovich, I. M. Deppner, A. A. Derevschikov, A. Dhamija, L. Di Carlo, L. Didenko, X. Dong, J. L. Drachenberg, J. C. Dunlop, N. Elsey, J. Engelage, G. Eppley, S. Esumi, A. Ewigleben, O. Eyser, R. Fatemi, F. M. Fawzi, S. Fazio, P. Federic, J. Fedorisin, C. J. Feng, Y. Feng, P. Filip, E. Finch, Y. Fisyak, A. Francisco, C. Fu, L. Fulek, C. A. Gagliardi, T. Galatyuk, F. Geurts, N. Ghimire, A. Gibson, K. Gopal, X. Gou, D. Grosnick, A. Gupta, W. Guryn, A. I. Hamad, A. Hamed, Y. Han, S. Harabasz, M. D. Harasty, J. W. Harris, H. Harrison, S. He, W. He, X. H. He, Y. He, S. Heppelmann, S. Heppelmann, N. Herrmann, E. Hoffman, L. Holub, Y. Hu, H. Huang, H. Z. Huang, S. L. Huang, T. Huang, X. Huang, Y. Huang, T. J. Humanic, G. Igo, D. Isenhower, W. W. Jacobs, C. Jena, A. Jentsch, Y. Ji, J. Jia, K. Jiang, X. Ju, E. G. Judd, S. Kabana, M. L. Kabir, S. Kagamaster, D. Kalinkin, K. Kang, D. Kapukchyan, K. Kauder, H. W. Ke, D. Keane, A. Kechechyan, Y. V. Khyzhniak, D. P. Kikoła, C. Kim, B. Kimelman, D. Kincses, I. Kisel, A. Kiselev, A. G. Knospe, L. Kochenda, L. K. Kosarzewski, L. Kramarik, P. Kravtsov, L. Kumar, S. Kumar, R. Kunnawalkam Elayavalli, J. H. Kwasizur, S. Lan, J. M. Landgraf, J. Lauret, A. Lebedev, R. Lednicky, J. H. Lee, Y. H. Leung, C. Li, C. Li, W. Li, X. Li, Y. Li, X. Liang, Y. Liang, R. Licenik, T. Lin, Y. Lin, M. A. Lisa, F. Liu, H. Liu, H. Liu, P. Liu, T. Liu, X. Liu, Y. Liu, Z. Liu, T. Ljubicic, W. J. Llope, R. S. Longacre, E. Loyd, N. S. Lukow, X. Luo, L. Ma, R. Ma, Y. G. Ma, N. Magdy, R. Majka, D. Mallick, S. Margetis, C. Markert, H. S. Matis, J. A. Mazer, N. G. Minaev, S. Mioduszewski, B. Mohanty, M. M. Mondal, I. Mooney, D. A. Morozov, A. Mukherjee, M. Nagy, J. D. Nam, Md. Nasim, K. Nayak, D. Neff, J. M. Nelson, D. B. Nemes, M. Nie, G. Nigmatkulov, T. Niida, R. Nishitani, L. V. Nogach, T. Nonaka, A. S. Nunes, G. Odyniec, A. Ogawa, S. Oh, V. A. Okorokov, B. S. Page, R. Pak, A. Pandav, A. K. Pandey, Y. Panebratsev, P. Parfenov, B. Pawlik, D. Pawlowska, H. Pei, C. Perkins, L. Pinsky, R. L. Pintér, J. Pluta, B. R. Pokhrel, G. Ponimatkin, J. Porter, M. Posik, V. Prozorova, N. K. Pruthi, M. Przybycien, J. Putschke, H. Qiu, A. Quintero, C. Racz, S. K. Radhakrishnan, N. Raha, R. L. Ray, R. Reed, H. G. Ritter, M. Robotkova, O. V. Rogachevskiy, J. L. Romero, L. Ruan, J. Rusnak, N. R. Sahoo, H. Sako, S. Salur, J. Sandweiss, S. Sato, W. B. Schmidke, N. Schmitz, B. R. Schweid, F. Seck, J. Seger, M. Sergeeva, R. Seto, P. Seyboth, N. Shah, E. Shahaliev, P. V. Shanmuganathan, M. Shao, T. Shao, A. I. Sheikh, D. Shen, S. S. Shi, Y. Shi, Q. Y. Shou, E. P. Sichtermann, R. Sikora, M. Simko, J. Singh, S. Singha, M. J. Skoby, N. Smirnov, Y. Söhngen, W. Solyst, P. Sorensen, H. M. Spinka, B. Srivastava, T. D. S. Stanislaus, M. Stefaniak, D. J. Stewart, M. Strikhanov, B. Stringfellow, A. A. P. Suaide, M. Sumbera, B. Summa, X. M. Sun, X. Sun, Y. Sun, Y. Sun, B. Surrow, D. N. Svirida, Z. W. Sweger, P. Szymanski, A. H. Tang, Z. Tang, A. Taranenko, T. Tarnowsky, J. H. Thomas, A. R. Timmins, D. Tlusty, T. Todoroki, M. Tokarev, C. A. Tomkiel, S. Trentalange, R. E. Tribble, P. Tribedy, S. K. Tripathy, T. Truhlar, B. A. Trzeciak, O. D. Tsai, Z. Tu, T. Ullrich, D. G. Underwood, I. Upsal, G. Van Buren, J. Vanek, A. N. Vasiliev, I. Vassiliev, V. Verkest, F. Videbæk, S. Vokal, S. A. Voloshin, F. Wang, G. Wang, J. S. Wang, P. Wang, Y. Wang, Y. Wang, Z. Wang, J. C. Webb, P. C. Weidenkaff, L. Wen, G. D. Westfall, H. Wieman, S. W. Wissink, J. Wu, Y. Wu, B. Xi, Z. G. Xiao, G. Xie, W. Xie, H. Xu, N. Xu, Q. H. Xu, Y. Xu, Z. Xu, Z. Xu, C. Yang, Q. Yang, S. Yang, Y. Yang, Z. Ye, Z. Ye, L. Yi, K. Yip, Y. Yu, H. Zbroszczyk, W. Zha, C. Zhang, D. Zhang, S. Zhang, S. Zhang, X. P. Zhang, Y. Zhang, Y. Zhang, Y. Zhang, Z. J. Zhang, Z. Zhang, Z. Zhang, J. Zhao, C. Zhou, X. Zhu, Z. Zhu, M. Zurek, M. Zyzak
The chiral magnetic effect (CME) refers to charge separation along a strong magnetic field due to imbalanced chirality of quarks in local parity and charge-parity violating domains in quantum chromodynamics. The experimental measurement of the charge separation is made difficult by the presence of a major background from elliptic azimuthal anisotropy. This background and the CME signal have different sensitivities to the spectator and participant planes, and could thus be determined by measurements with respect to these planes. We report such measurements in Au+Au collisions at a nucleon-nucleon center-of-mass energy of 200 GeV at the Relativistic Heavy-Ion Collider. It is found that the charge separation, with the flow background removed, is consistent with zero in peripheral (large impact parameter) collisions. Some indication of finite CME signals is seen in mid-central (intermediate impact parameter) collisions. Significant residual background effects may, however, still be present.
An interpretation of the charge dependent correlations sensitive to the Chiral Magnetic Effect (CME) -- the separation of the electric charges along the system magnetic field (across the reaction plane) -- is ambiguous due to a possible large background (non-CME) effects. The background contribution is proportional to the elliptic flow $v_2$; it is the largest in measurements relative to the participant plane, and is smaller in measurements relative to the flow plane determined by spectators, where the CME signal, on opposite, is likely larger. In this note I discuss a possible strategy for co…
Correlation measurements with respect to the spectator and participant planes in relativistic heavy ion collisions were proposed to extract the chiral magnetic effect (CME) from background dominated azimuthal correlators. This paper investigates the effects of two- and three-particle nonflow correlations on the extracted CME signal fraction, $f_{\text{CME}}$. It is found, guided by a multiphase transport (AMPT) model and the heavy ion jet interaction generator (HIJING) together with experimental data, that the nonflow effects amount to approximately $(4\pm5)$% and $(-5\pm3)$% without and with …
Difference between signal and background of the chiral magnetic effect relative to spectator and participant planes in isobar collisions at $\sqrt{s_{_{\rm NN}}} = 200$ GeV
We present a method to select events with specific initial configuration, namely body-tip, in heavy-ion collisions using deformed Uranium nuclei. We propose to use asymmetry in spectator neutron numbers to filter out these body-tip events from the unbiased configurations in U+U collisions. We have used a variable S_eta to differentiate between the body-tip and unbiased configurations. We have calculated the second order azimuthal anisotropy, namely elliptic flow (v2), for this body-tip configuration in the framework of a transport model and found it to be consistently lower compared to that in…
Spectator fragments resulting from relativistic heavy ion collisions, consisting of single protons and neutrons along with groups of stable nuclear fragments up to Nitrogen (Z=7), are measured in PHOBOS. These fragments are observed in Au+Au (sqrt(sNN)=19.6 GeV) and Cu+Cu (22.4 GeV) collisions at high pseudorapidity ($η$). The dominant multiply-charged fragment is the tightly bound Helium ($α$), with Lithium, Beryllium, and Boron all clearly seen as a function of collision centrality and pseudorapidity. We observe that in Cu+Cu collisions, it becomes much more favorable for the $α$ fragments t…
We report a new measurement of negatively charged pion directed flow $v_1$ relative to the spectator plane for Pb+Pb collisions at the beam energy 40A GeV recorded by the NA49 experiment at CERN. $v_1$ is reported as a function of rapidity and transverse momentum in different classes of collision centrality. The projectile spectator plane is estimated using transverse segmentation of the NA49 forward hadron calorimeter. The new results extend the NA49 data for $v_1$, which was previously measured only relative to the participant plane, and complement recent preliminary data by the NA61/SHINE c…
A Multi-Phase Transport (AMPT) model is used to study the elliptic flow fluctuations of identified particles using participant and spectator event planes. The elliptic flow measured using the first order spectator event plane is expected to give the elliptic flow relative to the true reaction plane which suppresses the flow fluctuations. However, the elliptic flow measured using the second-order participant plane is expected to capture the elliptic flow fluctuations. Our study shows that the first order spectator event plane could be used to study the elliptic flow fluctuations of the identifi…
Limits on the chiral magnetic effect from the event shape engineering and participant-spectator correlation techniques in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV
I show that the average transverse momentum, $\langle p_t \rangle$, of the hadrons emitted in relativistic nuclear collisions can be used as a ``knob'' to control the strength of the magnetic field induced by the spectator and the participant protons over the overlap region. I thus argue that any observable sensitive to this magnetic field is nontrivially correlated with $\langle p_t \rangle$ at a given collision centrality.
The directed flow of charged particles at mid-rapidity is measured in Pb-Pb collisions at $\sqrt{s_\rm{NN}}=2.76$ TeV relative to the collision symmetry plane defined by the spectator nucleons. A negative slope of the rapidity-odd directed flow component with approximately 3 times smaller magnitude than found at the highest RHIC energy is observed. This suggests a smaller longitudinal tilt of the initial system and disfavors the strong fireball rotation predicted for the LHC energies. The rapidity-even directed flow component is measured for the first time with spectators and found to be indep…
A significant excess of J/$ψ$ yield at very low transverse momentum ($p_T < 0.3$ GeV/c) was observed by the ALICE and STAR collaborations in peripheral A+A collisions, which points to evidence of coherent photoproduction of J/$ψ$ in violent hadronic interactions. Theoretically, the photoproduction of J$/ψ$ in hadronic collisions raises questions about how spectator and non-spectator nucleons participate in the coherent reaction. For the first time, we argue that the strong interactions in the overlapping region of incoming nuclei may disturb the coherent production, leaving room for different …
The chiral magnetic effect (CME) refers to charge separation along a strong magnetic field between left- and right-handed quarks, caused by interactions with topological gluon fields from QCD vacuum fluctuations. We present two approaches to handle the dominant elliptic flow ($v_2$) background in the three-particle correlator ($Δγ_{112}$), sensitive to CME. In the first approach, we present the $Δγ_{112}$ and $Δγ_{123}$ measurements in U+U and Au+Au collisions. While hydrodynamic simulations including resonance decays and local charge conservation predict that $Δγ_{112}$ scaled by $N_{\rm part…
System-size dependence of dihadron azimuthal correlations in ultra-relativistic heavy ion collision is simulated by a multi-phase transport model. The structure of correlation functions and yields of associated particles show clear participant path-length dependences in collision systems with a partonic phase. The splitting parameter and root-mean-square width of away-side correlation functions increase with collision system size from $^{14}$N+$^{14}$N to $^{197}$Au+$^{197}$Au collisions. The double-peak structure of away-side correlation functions can only be formed in sufficient "large" coll…
Recent data from p+p and p+Pb collisions at the Large Hadron Collider (LHC), and d+Au and $^3$He+Au collisions at the Relativistic Heavy Ion Collider (RHIC) reveal patterns that---when observed in the collision of heavy nuclei---are commonly interpreted as indicators of a locally equilibrated system in collective motion. The comparison of these data sets, including the forthcoming results from p+Au and p+Al collisions at RHIC, will help to elucidate the geometric dependence of such patterns. It has recently been shown that A-Multi-Phase-Transport-Model (AMPT) can describe some of these feature…
We propose a novel method to search for the chiral magnetic effect (CME) in heavy ion collisions. We argue that the relative strength of the magnetic field (mainly from spectator protons and responsible for the CME) with respect to the reaction plane and the participant plane is opposite to that of the elliptic flow background arising from the fluctuating participant geometry. This opposite behavior in a single collision system, hence with small systematic uncertainties, can be exploited to extract the possible CME signal from the flow background. The method is applied to the existing data at …
Using two novel methods, pair invariant mass ($m_{inv}$) and comparative measurements with respect to reaction plane ($Ψ_{\rm RP}$) and participant plane ($Ψ_{\rm PP}$), we isolate the possible chiral magnetic effect (CME) from backgrounds in 200 GeV Au+Au collisions at STAR. The invariant mass method identifies the resonance background contributions, coupled with the elliptic flow ($v_{2}$), to the charge correlator CME observable ($Δγ$). At high mass ($m_{inv}>1.5$ GeV/$c^{2}$) where resonance contribution is small, we obtain the average $Δγ$ magnitude. In the low mass region ($m_{inv}<1.5$ …
We calculate the electromagnetic fields generated in small systems by using a multiphase transport (AMPT) model. Compared to $A+A$ collisions, we find that the absolute electric and magnetic fields are not small in $p$+Au and $d$+Au collisions at energies available at the BNL Relativistic Heavy Ion Collider and in $p$+Pb collisions at energies available at the CERN Large Hadron Collider. We study the centrality dependencies and the spatial distributions of electromagnetic fields. We further investigate the azimuthal fluctuations of the magnetic field and its correlation with the fluctuating ge…
Metastable domains of fluctuating topological charges can change the chirality of quarks and induce local parity violation in quantum chromodynamics. This can lead to observable charge separation along the direction of the strong magnetic field produced by spectator protons in relativistic heavy-ion collisions, a phenomenon called the chiral magnetic effect (CME). A major background source for CME measurements using the charge-dependent azimuthal correlator ($Δγ$) is the intrinsic particle correlations (such as resonance decays) coupled with the azimuthal elliptical anisotropy ($v_{2}$). In he…
In collisions of identical nuclei at a given impact parameter, the number of nucleons participating in the overlap region of each nucleus can be unequal due to nuclear density fluctuations. The asymmetry due to the unequal number of participating nucleons, referred to as longitudinal asymmetry, causes a shift in the center of mass rapidity of the participant zone. The information of the event asymmetry allows us to isolate and study the effect of longitudinal asymmetry on rapidity distribution of final state particles. In a Monte Carlo Glauber model the average rapidity-shift is found to be al…
The beam energy dependence of $v_4$ (the quadrupole moment of the transverse radial flow) is sensitive to the nuclear equation of state (EoS) in mid-central Au + Au collisions at the energy range of $3 < \sqrt{s_{NN}} < 30$ GeV, which is investigated within the hadronic transport model JAM. Different equations of state, namely, a free hadron gas, a first-order phase transition and a crossover are compared. An enhancement of $v_4$ at $\sqrt{s_{NN}}\approx 6$ GeV is predicted for an EoS with a first-order phase transition. This enhanced $v_4$ flow is driven by both the enhancement of $v_2$ as we…
Probing initial geometrical anisotropy and final azimuthal anisotropy in heavy-ion collisions at Large Hadron Collider energies through event-shape engineering
The hard proton knock-out by the proton from the deuteron at relativistic energies is considered with a focus on the color transparency (CT) effect which influences the initial and final state interactions. The calculations are performed in the framework of the generalized eikonal approximation supplemented by the quantum diffusion model of CT. The main results of the previous calculations [1] at the beam momentum below 20 GeV/c are confirmed, including the dependence of the nuclear transparency on the transverse momentum of the spectator neutron, $p_{st}$, and on the relative azimuthal angle …
Through $^{12}$C + $^{197}$Au collisions at $\sqrt{s_{NN}} =$ 200 GeV using a multiphase transport (AMPT) model, the azimuthal angle dependences of the Hanbury Brown-Twiss (HBT) radii relative to the second- and third-order participant plane from $π$-$π$ correlations are discussed. Three initial geometric configurations of $^{12}$C, namely three-$α$-cluster triangle, three-$α$-cluster chain and Woods-Saxon distribution of nucleons, are taken into account, and their effects on the correlations are investigated. The ratio of the third- to the second-order HBT radii $R_{o(s),3}^2/R_{o(s),2}^2$ is…
The hot and dense medium produced in relativistic heavy-ion collisions has been conjectured to be accompanied by an axial charge asymmetry that may lead to a separation of electric charges in the direction of the extremely strong magnetic field, also known as the Chiral Magnetic Effect (CME). The measurement of azimuthal correlator ($Δγ$) with respect to the spectator plane, gives us an opportunity to measure the possible CME fraction beyond the flow background. Preliminary results using this approach with combined Au+Au collisions at $\sqrt{s_{NN}} =$ 200 GeV and U+U at $\sqrt{s_{NN}} =$ 193 …
Momentum-space azimuthal harmonic event planes (EP) are constructed from final-state midrapidity particles binned in transverse momentum (pT ) in sqrt(s_NN) = 200 GeV Au+Au collisions in a multi-phase transport (AMPT) model. The EP correlations between pT bins, corrected by EP resolutions, are smaller than unity. This indicates that the EP's decorrelate over pT in AMPT, qualitatively consistent with data and hydrodynamic calculations. It is further found that the EP correlations approximately factorize into single pT-bin EP correlations to a common plane. This common plane appears to be the mo…
We investigate the properties of electromagnetic fields in isobaric $_{44}^{96}\textrm{Ru}+\,_{44}^{96}\textrm{Ru}$ and $_{40}^{96}\textrm{Zr}+\,_{40}^{96}\textrm{Zr}$ collisions at $\sqrt{s}$ = 200 GeV by using a multiphase transport model, with special emphasis on the correlation between magnetic field direction and participant plane angle $Ψ_{2}$ (or spectator plane angle $Ψ_{2}^{\rm SP}$), i.e. $\langle{\rm cos}\ 2(Ψ_B - Ψ_{2})\rangle$ [or $\langle{\rm cos}\ 2(Ψ_B - Ψ_{2}^{\rm SP})\rangle$]. We confirm that the magnetic fields of $_{44}^{96}\textrm{Ru}+\,_{44}^{96}\textrm{Ru}$ collisions a…
