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Measurements of Dielectron Production in Au$+$Au Collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV from the STAR Experiment

The STAR collaboration
Phys.Rev. C92 (2015) 024912, 2015

Abstract (data abstract)
BNL-RHIC. We report on measurements of dielectron ($e^+e^-$) production in Au$+$Au collisions at a center-of-mass energy of 200 GeV per nucleon-nucleon pair using the STAR detector at RHIC. Systematic measurements of the dielectron yield as a function of transverse momentum ($p_{\rm T}$) and collision centrality show an enhancement compared to a cocktail simulation of hadronic sources in the low invariant-mass region ($M_{ee}<$ 1 GeV/$c^2$). This enhancement cannot be reproduced by the $\rho$-meson vacuum spectral function. In minimum-bias collisions, in the invariant-mass range of 0.30 $-$ 0.76 GeV/$c^2$, integrated over the full $p_{\rm T}$ acceptance, the enhancement factor is 1.76 $\pm$ 0.06 (stat.) $\pm$ 0.26 (sys.) $\pm$ 0.29 (cocktail). The enhancement factor exhibits weak centrality and $p_{\rm T}$ dependence in STAR's accessible kinematic regions, while the excess yield in this invariant-mass region as a function of the number of participating nucleons follows a power-law shape with a power of 1.44 $\pm$ 0.10. Models that assume an in-medium broadening of the $\rho$ meson spectral function consistently describe the observed excess in these measurements. Additionally, we report on measurements of $\omega$ and $\phi$-meson production through their $e^+e^-$ decay channel. These measurements show good agreement with Tsallis Blast-Wave model predictions as well as, in the case of the $\phi$-meson, results through its $K^+K^-$ decay channel. In the intermediate invariant-mass region (1.1$<M_{ee}<$ 3 GeV/$c^2$), we investigate the spectral shapes from different collision centralities. Physics implications for possible in-medium modification of charmed hadron production and other physics sources are discussed.

  • Table 1

    Data from Figure 7

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    Estimated electron purity vs. momentum in 200 GeV Au + Au collisions.

  • Table 2

    Data from Figure 17

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    Acceptance correction factor for unlike-sign and like-sign pair difference from 200 GeV Au+Au minimum-bias collisions.

  • Table 3

    Data from Figure 18

    10.17182/hepdata.73504.v1/t3

    Ratio of the same-event like-sign to the mixed event unlike-sign distributions.

  • Table 4

    Data from Figure 20a

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    $e^+$ $e^-$ invariant mass pair distributions of signal pairs compared to the inclusive unlike sign and reconstructed background pairs in...

  • Table 5

    Data from Figure 20b

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    Signal-to-background ratios in minimum bias p+p and Au+Au collisions.

  • Table 6

    Data from Figure 20b

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    Signal-to-background ratios in central p+p and Au+Au collisions.

  • Table 7

    Data from Figure 28a

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    Invariant mass spectrum in the STAR acceptance ($p_T^e$ > 0.2 GeV/c, |$\eta^e$| < 1, and |$y_{ee}$|) from SQRT($s_{NN}$) = 200...

  • Table 8

    Data from Figure 28b

    10.17182/hepdata.73504.v1/t8

    Invariant mass spectrum in the STAR acceptance ($p_T^e$ > 0.2 GeV/c, |$\eta^e$| < 1, and |$y_{ee}$|) from SQRT($s_{NN}$) = 200...

  • Table 9

    Data from Figure 30

    10.17182/hepdata.73504.v1/t9

    Invariant mass spectra from SQRT($s_{NN}$ = 200 GeV Au+Au minimum-bias collisions in pT range 0 - 5 GeV/c. The ratio...

  • Table 10

    Data from Figure 30

    10.17182/hepdata.73504.v1/t10

    Invariant mass spectra from SQRT($s_{NN}$ = 200 GeV Au+Au minimum-bias collisions in pT range 5 - 10 GeV/c. The ratio...

  • Table 11

    Data from Figure 30

    10.17182/hepdata.73504.v1/t11

    Invariant mass spectra from SQRT($s_{NN}$ = 200 GeV Au+Au minimum-bias collisions in pT range 1 - 1.5 GeV/c. The ratio...

  • Table 12

    Data from Figure 30

    10.17182/hepdata.73504.v1/t12

    Invariant mass spectra from SQRT($s_{NN}$ = 200 GeV Au+Au minimum-bias collisions in pT range 1.5 - 2 GeV/c. The ratio...

  • Table 13

    Data from Figure 30

    10.17182/hepdata.73504.v1/t13

    Invariant mass spectra from SQRT($s_{NN}$ = 200 GeV Au+Au minimum-bias collisions integrated. The ratio of dielectron yield over cocktail for...

  • Table 14

    Data from Figure 31

    10.17182/hepdata.73504.v1/t14

    The integrated dielectron yield as a function of pair pT in invariant mass range 0 - 0.15 GeV/c^2 compared with...

  • Table 15

    Data from Figure 31

    10.17182/hepdata.73504.v1/t15

    The integrated dielectron yield as a function of pair pT in invariant mass range 0.15 - 0.3 GeV/c^2 compared with...

  • Table 16

    Data from Figure 31

    10.17182/hepdata.73504.v1/t16

    The integrated dielectron yield as a function of pair pT in invariant mass range 0.3 - 0.76 GeV/c^2 compared with...

  • Table 17

    Data from Figure 31

    10.17182/hepdata.73504.v1/t17

    The integrated dielectron yield as a function of pair pT in invariant mass range 0.76 - 1.05 GeV/c^2 compared with...

  • Table 18

    Data from Figure 31

    10.17182/hepdata.73504.v1/t18

    The integrated dielectron yield as a function of pair pT in invariant mass range 1.05 - 1.8 GeV/c^2 compared with...

  • Table 19

    Data from Figure 31

    10.17182/hepdata.73504.v1/t19

    The integrated dielectron yield as a function of pair pT in invariant mass range 1.8 - 2.8 GeV/c^2 compared with...

  • Table 20

    Data from Figure 31

    10.17182/hepdata.73504.v1/t20

    The integrated dielectron yield as a function of pair pT in invariant mass range 2.8 to 3.5 GeV/c^2 compared with...

  • Table 21

    Data from Figure 32

    10.17182/hepdata.73504.v1/t21

    Invariant mass spectra from SQRT($s_{NN}$) = 200 GeV Au+Au collisions in different centralities. The ratio of dielectron yield over cocktail...

  • Table 22

    Data from Figure 32

    10.17182/hepdata.73504.v1/t22

    Invariant mass spectra from SQRT($s_{NN}$) = 200 GeV Au+Au collisions in different centralities. The ratio of dielectron yield over cocktail...

  • Table 23

    Data from Figure 32

    10.17182/hepdata.73504.v1/t23

    Invariant mass spectra from SQRT($s_{NN}$) = 200 GeV Au+Au collisions in different centralities. The ratio of dielectron yield over cocktail...

  • Table 24

    Data from Figure 32

    10.17182/hepdata.73504.v1/t24

    Invariant mass spectra from SQRT($s_{NN}$) = 200 GeV Au+Au collisions in different centralities. The ratio of dielectron yield over cocktail...

  • Table 25

    Data from Figure 33

    10.17182/hepdata.73504.v1/t25

    The integrated dielectron yield and ratio of dielectron yield over cocktail in different centralities for mass window 0 - 0.15...

  • Table 26

    Data from Figure 33

    10.17182/hepdata.73504.v1/t26

    The integrated dielectron yield and ratio of dielectron yield over cocktail in different centralities for mass window 0.15 - 0.3...

  • Table 27

    Data from Figure 33

    10.17182/hepdata.73504.v1/t27

    The integrated dielectron yield and ratio of dielectron yield over cocktail in different centralities for mass window 0.3 - 0.76...

  • Table 28

    Data from Figure 33

    10.17182/hepdata.73504.v1/t28

    The integrated dielectron yield and ratio of dielectron yield over cocktail in different centralities for mass window 0.76 - 1.05...

  • Table 29

    Data from Figure 33

    10.17182/hepdata.73504.v1/t29

    The integrated dielectron yield and ratio of dielectron yield over cocktail in different centralities for mass window 1.05 - 1.8...

  • Table 30

    Data from Figure 33

    10.17182/hepdata.73504.v1/t30

    The integrated dielectron yield and ratio of dielectron yield over cocktail in different centralities for mass window 1.8 - 2.8...

  • Table 31

    Data from Figure 33

    10.17182/hepdata.73504.v1/t31

    The integrated dielectron yield and ratio of dielectron yield over cocktail in different centralities for mass window 2.8 - 3.5...

  • Table 32

    Data from Figure 34

    10.17182/hepdata.73504.v1/t32

    Dielectron invariant mass spectra from minimum-bias.

  • Table 33

    Data from Figure 34

    10.17182/hepdata.73504.v1/t33

    Dielectron invariant mass spectra from the most central (0-10%) collisions that we are able to achieve most statistics at present.

  • Table 34

    Data from Figure 34

    10.17182/hepdata.73504.v1/t34

    The ratio of the Npart-scaled dielectron yield between minimum-bias and the most central collisions.

  • Table 35

    Data from Figure 35

    10.17182/hepdata.73504.v1/t35

    Mass spectrum of the excess (data - cocktail) in the low-mass region in Au+Au minimum-bias collisions compared to model calculations.

  • Table 36

    Data from Figure 36

    10.17182/hepdata.73504.v1/t36

    The yields scaled by Npart for the $\rho$-like region with the cocktail subtracted.

  • Table 37

    Data from Figure 36

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    The Omega-like region without cocktail subtraction as a function of Npart.

  • Table 38

    Data from Figure 36

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    The Phi-like region without cocktail subtraction as a function of Npart.

  • Table 39

    Data from Figure 37

    10.17182/hepdata.73504.v1/t39

    Correlated charm contributions to the dielectron mass spectra for different assumptions of the correlation strength.

  • Table 40

    Data from Figure 38

    10.17182/hepdata.73504.v1/t40

    Slope parameters Teff versus invariant mass for dielectrons from charm hadron decays.

  • Table 41

    Data from Figure 39a

    10.17182/hepdata.73504.v1/t41

    Omega meson invariant mass distribution from SQRT($s_{NN}$) = 200 GeV Au+Au minimum-bias collisions after subtraction of the combinatorial background using...

  • Table 42

    Data from Figure 39b

    10.17182/hepdata.73504.v1/t42

    Phi meson invariant mass distribution from SQRT($s_{NN}$) = 200 GeV Au+Au minimum-bias collisions after subtraction of the combinatorial background using...

  • Table 43

    Data from Figure 41_1

    10.17182/hepdata.73504.v1/t43

    The widths and mass positions of the omega signal from data compared to the values from the PDG and the...

  • Table 44

    Data from Figure 41_2

    10.17182/hepdata.73504.v1/t44

    The widths and mass positions of the phi signal from data compared to the values from the PDG and the...

  • Table 45

    Data from Figure 42

    10.17182/hepdata.73504.v1/t45

    The efficiency and acceptance correction factor as function of pT for mid-rapidity omega and phi mesons.

  • Table 46

    Data from Figure 43

    10.17182/hepdata.73504.v1/t46

    The pT distributions of the omega meson invariant yields from SQRT($s_{NN}$) = 200 GeV Au+Au minimum-bias collisions.

  • Table 47

    Data from Figure 43

    10.17182/hepdata.73504.v1/t47

    The pT distributions of the phi meson invariant yields from SQRT($s_{NN}$) = 200 GeV Au+Au minimum-bias collisions.

  • Table 48

    Data from Figure 46

    10.17182/hepdata.73504.v1/t48

    Unlike-sign/like-sign pair acceptance difference correction factor with the PHENIX phi acceptance compared with the full acceptance.

  • Table 49

    Data from Figure 47a

    10.17182/hepdata.73504.v1/t49

    Efficiency corrected invariant mass spectra calculated using the STAR data filtered with the PHENIX azimuthal angle acceptance. The data points...

  • Table 50

    Data from Figure 47b

    10.17182/hepdata.73504.v1/t50

    The same data points compared to theoretical model calculations of medium vector meson and QGP contributions.

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