Observation of charge-dependent azimuthal correlations and possible local strong parity violation in heavy ion collisions

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Rev.C 81 (2010) 054908, 2010.
Inspire Record 830676 DOI 10.17182/hepdata.98577

Parity-odd domains, corresponding to non-trivial topological solutions of the QCD vacuum, might be created during relativistic heavy-ion collisions. These domains are predicted to lead to charge separation of quarks along the orbital momentum of the system created in non-central collisions. To study this effect, we investigate a three particle mixed harmonics azimuthal correlator which is a \P-even observable, but directly sensitive to the charge separation effect. We report measurements of this observable using the STAR detector in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}$=200 and 62~GeV. The results are presented as a function of collision centrality, particle separation in rapidity, and particle transverse momentum. A signal consistent with several of the theoretical expectations is detected in all four data sets. We compare our results to the predictions of existing event generators, and discuss in detail possible contributions from other effects that are not related to parity violation.

19 data tables

$\langle cos(\phi_{\alpha}+\phi_{\beta}−2\phi_{c})\rangle$ as a function of reference multiplicity for different charge combinations, before corrections for acceptance effects. In the legend the signs indicate the charge of particles $\alpha$, $\beta$, and c. The results shown are for Au+Au collisions at 200 GeV obtained in the Reversed Full Field.

$\langle cos(\phi_{\alpha}+\phi_{\beta}−2\phi_{c})\rangle$ as a function of reference multiplicity for different charge combinations, before corrections for acceptance effects. In the legend the signs indicate the charge of particles $\alpha$, $\beta$, and c. The results shown are for Au+Au collisions at 200 GeV obtained in the Full Field.

$\langle cos(\phi_{\alpha}+\phi_{\beta}−2\phi_{c})\rangle$ as a function of reference multiplicity for different charge combinations, after corrections for acceptance effects. In the legend the signs indicate the charge of particles $\alpha$, $\beta$, and c. The results shown are for Au+Au collisions at 200 GeV obtained in the Reversed Full Field.

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Center of mass energy and system-size dependence of photon production at forward rapidity at RHIC

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Nucl.Phys.A 832 (2010) 134-147, 2010.
Inspire Record 822997 DOI 10.17182/hepdata.101347

We present the multiplicity and pseudorapidity distributions of photons produced in Au+Au and Cu+Cu collisions at \sqrt{s_NN} = 62.4 and 200 GeV. The photons are measured in the region -3.7 < \eta < -2.3 using the photon multiplicity detector in the STAR experiment at RHIC. The number of photons produced per average number of participating nucleon pairs increases with the beam energy and is independent of the collision centrality. For collisions with similar average numbers of participating nucleons the photon multiplicities are observed to be similar for Au+Au and Cu+Cu collisions at a given beam energy. The ratios of the number of charged particles to photons in the measured pseudorapidity range are found to be 1.4 +/- 0.1 and 1.2 +/- 0.1 for \sqrt{s_NN} = 62.4 GeV and 200 GeV, respectively. The energy dependence of this ratio could reflect varying contributions from baryons to charged particles, while mesons are the dominant contributors to photon production in the given kinematic region. The photon pseudorapidity distributions normalized by average number of participating nucleon pairs, when plotted as a function of \eta - ybeam, are found to follow a longitudinal scaling independent of centrality and colliding ion species at both beam energies.

14 data tables

Fig. 1. (Color online.) Top panel: Photon reconstruction efficiency $\left(\epsilon_{\gamma}\right)$ (solid symbols) and purity of photon sample $\left(f_{\mathrm{p}}\right)$ (open symbols) for PMD as a function of pseudorapidity $(\eta)$ for minimum bias $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Cu}+\mathrm{Cu}$ at $\sqrt{s_{\mathrm{NN}}}=$ $200 \mathrm{GeV}$. Bottom panel: Comparison between estimated $\epsilon_{\gamma}$ and $f_{\mathrm{p}}$ for PMD as a function of $\eta$ for minimum bias $\mathrm{Au}+\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=62.4 \mathrm{GeV}$ using HIJING and AMPT models. The error bars on the AMPT data are statistical and those for HIJING are within the symbol size. NOTE: For points with invisible error bars, the point size was considered as an absolute upper limit for the uncertainty.

Fig. 1. (Color online.) Top panel: Photon reconstruction efficiency $\left(\epsilon_{\gamma}\right)$ (solid symbols) and purity of photon sample $\left(f_{\mathrm{p}}\right)$ (open symbols) for PMD as a function of pseudorapidity $(\eta)$ for minimum bias $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Cu}+\mathrm{Cu}$ at $\sqrt{s_{\mathrm{NN}}}=$ $200 \mathrm{GeV}$. Bottom panel: Comparison between estimated $\epsilon_{\gamma}$ and $f_{\mathrm{p}}$ for PMD as a function of $\eta$ for minimum bias $\mathrm{Au}+\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=62.4 \mathrm{GeV}$ using HIJING and AMPT models. The error bars on the AMPT data are statistical and those for HIJING are within the symbol size. NOTE: For points with invisible error bars, the point size was considered as an absolute upper limit for the uncertainty.

Fig. 2. (Color online.) Event-by-event photon multiplicity distributions (solid circles) for $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Cu}+\mathrm{Cu}$ at $\sqrt{s_{\mathrm{NN}}}=62.4$ and $200 \mathrm{GeV} .$ The distributions for top $0-5 \%$ central $\mathrm{Au}+$ Au collisions and top $0-10 \%$ central $\mathrm{Cu}+\mathrm{Cu}$ collisions are also shown (open circles). The photon multiplicity distributions for central collisions are observed to be Gaussian (solid line). Only statistical errors are shown. NOTE: For points with invisible error bars, the point size was considered as an absolute upper limit for the uncertainty.

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Pion Interferometry in Au+Au and Cu+Cu Collisions at RHIC

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Rev.C 80 (2009) 024905, 2009.
Inspire Record 814937 DOI 10.17182/hepdata.97124

We present a systematic analysis of two-pion interferometry in Au+Au collisions at $\sqrt{s_{\rm{NN}}}$ = 62.4 GeV and Cu+Cu collisions at $\sqrt{s_{\rm{NN}}}$ = 62.4 and 200 GeV using the STAR detector at RHIC. The multiplicity and transverse momentum dependences of the extracted femtoscopic radii are studied. The scaling of the apparent freeze-out volume with charged particle multiplicity is studied for the RHIC energy domain. The multiplicity scaling of the measured radii is found to be independent of colliding system and collision energy.

12 data tables

HBT parameters for all centralities of 62.4 GeV Au+Au

HBT parameters for 200 and 62.4 GeV Au+Au, 0-5%

Energy dependence of the pi- HBT parameters for central Au+Au, Pb+Pb, and Pb+Au collisions (AGS,SPS and RHIC) at midrapidity and k_T ~ 0.2-0.3 GeV/c.

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K/pi Fluctuations at Relativistic Energies

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Rev.Lett. 103 (2009) 092301, 2009.
Inspire Record 810902 DOI 10.17182/hepdata.98971

We report results for $K/\pi$ fluctuations from Au+Au collisions at $\sqrt{s_{NN}}$ = 19.6, 62.4, 130, and 200 GeV using the STAR detector at the Relativistic Heavy Ion Collider. Our results for $K/\pi$ fluctuations in central collisions show little dependence on the incident energies studied and are on the same order as results observed by NA49 at the Super Proton Synchrotron in central Pb+Pb collisions at $\sqrt{s_{NN}}$ = 12.3 and 17.3 GeV. We also report results for the collision centrality dependence of $K/\pi$ fluctuations as well as results for $K^{+}/\pi^{+}$, $K^{-}/\pi^{-}$, $K^{+}/\pi^{-}$, and $K^{-}/\pi^{+}$ fluctuations. We observe that the $K/\pi$ fluctuations scale with the multiplicity density, $dN/d\eta$, rather than the number of participating nucleons.

5 data tables

(Color online) The event-by-event $K/\pi$ ratio for 200 GeV Au+Au central collisions (0-5%) compared with the same quantity calculated from mixed events. The inset shows the ratio of the distribution from real events to that from mixed events. The errors shown are statistical.

(Color online) The event-by-event $K/\pi$ ratio for 200 GeV Au+Au central collisions (0-5%) compared with the same quantity calculated from mixed events. The inset shows the ratio of the distribution from real events to that from mixed events. The errors shown are statistical.

(Color online) Measured dynamical $K/\pi$ fluctuations in terms of σdyn for central collisions (0 - 5%) of 19.6, 62.4, 130, and 200 GeV Au+Au compared with the central collisions (0 - 3.5%) of Pb+Pb from NA49 [7] and the statistical hadronization (SH) model of Ref. [14]. The solid line represents the relationship of the incident energy dependence of $\sigma_{dyn}$ in central collisions to the collision centrality dependence of $\nu_{dyn,K\pi}$ at higher energies. Both statistical (vertical line with horizontal bar) and systematic (no vertical line) error bars are shown for the experimental data.

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Energy and system size dependence of \phi meson production in Cu+Cu and Au+Au collisions

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Lett.B 673 (2009) 183-191, 2009.
Inspire Record 800796 DOI 10.17182/hepdata.101351

We study the beam-energy and system-size dependence of \phi meson production (using the hadronic decay mode \phi -- K+K-) by comparing the new results from Cu+Cu collisions and previously reported Au+Au collisions at \sqrt{s_NN} = 62.4 and 200 GeV measured in the STAR experiment at RHIC. Data presented are from mid-rapidity (|y|&lt;0.5) for 0.4 &lt; pT &lt; 5 GeV/c. At a given beam energy, the transverse momentum distributions for \phi mesons are observed to be similar in yield and shape for Cu+Cu and Au+Au colliding systems with similar average numbers of participating nucleons. The \phi meson yields in nucleus-nucleus collisions, normalised by the average number of participating nucleons, are found to be enhanced relative to those from p+p collisions with a different trend compared to strange baryons. The enhancement for \phi mesons is observed to be higher at \sqrt{s_NN} = 200 GeV compared to 62.4 GeV. These observations for the produced \phi(s\bar{s}) mesons clearly suggest that, at these collision energies, the source of enhancement of strange hadrons is related to the formation of a dense partonic medium in high energy nucleus-nucleus collisions and cannot be alone due to canonical suppression of their production in smaller systems.

8 data tables

Midrapidity $(|y| < 0.5)$ transverse momentum spectra of $\phi$ mesons for various collision centrality classes for $Cu+Cu$ collisions at $\sqrt{s_{NN}}=62.4$ and 200 GeV. To study the system size dependence, comparison of $40-50\%$ $Au+Au$ spectra to $10-20\%$ $Cu+Cu$ spectra at 200 GeV, and $40-60\%$ $Au+Au$ spectra to $20-30\%$ $Cu+Cu$ spectra at 62.4 GeV are shown. These centralities for the two colliding systems have similar $\langle N_{\scriptsize{\mbox{part}}}\rangle$ values as outlined in Table 2. The errors represent the statistical and systematic errors added in quadrature. They are found to be within the symbol size. The spectra are fitted to a Levy function discussed in the text.

Midrapidity $(|y| < 0.5)$ transverse momentum spectra of $\phi$ mesons for various collision centrality classes for $Cu+Cu$ collisions at $\sqrt{s_{NN}}=62.4$ and 200 GeV. To study the system size dependence, comparison of $40-50\%$ $Au+Au$ spectra to $10-20\%$ $Cu+Cu$ spectra at 200 GeV, and $40-60\%$ $Au+Au$ spectra to $20-30\%$ $Cu+Cu$ spectra at 62.4 GeV are shown. These centralities for the two colliding systems have similar $\langle N_{\scriptsize{\mbox{part}}}\rangle$ values as outlined in Table 2. The errors represent the statistical and systematic errors added in quadrature. They are found to be within the symbol size. The spectra are fitted to a Levy function discussed in the text.

Upper panels. $N_{\scriptsize{\mbox{part}}}$ scaled ($R^{N_{\scriptsize{\mbox{part}}}}_{AA}$) nuclear modification factors as a function of $p_{T}$ of $\phi$ mesons for $0-10\%$ and $20-30\%$ $Cu+Cu$ and $Au+Au$ collisions at $\sqrt{s_{NN}}=200$ GeV. Lower panel. Same as above for $N_{\scriptsize{\mbox{bin}}}$ scaled ($R^{N_{\scriptsize{\mbox{bin}}}}_{AA}$) nuclear modification factor. The error bars represent the statistical and systematic errors added in quadrature. The shaded band in upper panel around 1 at $p_{T}=4.5-5.5$ GeV/$c$ in the right side reflects the uncertainty in $N_{\scriptsize{\mbox{part}}}$ and that on the lower panel for $N_{\scriptsize{\mbox{bin}}}$ calculation for central $Au+Au$ collisions. The respective uncertainties for central $Cu+Cu$ collisions are of similar order.

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Measurements of $\phi$ meson production in relativistic heavy-ion collisions at RHIC

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Rev.C 79 (2009) 064903, 2009.
Inspire Record 797805 DOI 10.17182/hepdata.99047

We present results for the measurement of $\phi$ meson production via its charged kaon decay channel $\phi \to K^+K^-$ in Au+Au collisions at $\sqrt{s_{_{NN}}}=62.4$, 130, 200 GeV, and in p+p and d+Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV from the STAR experiment at RHIC. The mid-rapidity ($|y|<0.5$) $\phi$ meson spectra in central Au+Au collisions are found to be well described by a single exponential distribution. On the other hand, the spectra from p+p, d+Au and peripheral Au+Au collisions show power-law tails at intermediate and high transverse momenta ($p_{T}$) and are described better by Levy distributions. The constant $\phi/K^-$ yield ratio vs. beam species, collision centrality and colliding energy is in contradiction with expectations from models having kaon coalescence as the dominant mechanism for $\phi$ production at RHIC. The $\Omega/\phi$ yield ratio as a function of $p_{T}$ is consistent with a model based on the recombination of thermal $s$ quarks up to $p_{T}\sim 4$ GeV/c, but disagrees at higher transverse momenta. The measured nuclear modification factor, $R_{dAu}$, for the $\phi$ meson increases above unity at intermediate $p_{T}$, similar to that for pions and protons, while $R_{AA}$ is suppressed due to jet quenching in central Au+Au collisions. Number of constituent quark scaling of both $R_{cp}$ and $v_{2}$ for the $\phi$ meson with respect to other hadrons in Au+Au collisions at $\sqrt{s_{_{NN}}}$=200 GeV at intermediate $p_{T}$ is observed. These observations support quark coalescence as being the dominant mechanism of hadronization in the intermediate $p_{T}$ region at RHIC.

81 data tables

Background-subtracted invariant mass distributions at 0.4 < $p_{T}$ < 0.8 GeV/c in d + Au 200 GeV collisions (0–100%) with (solid points) and without (open points) the $\delta$-dipangle cut. The dashed curves show a Breit-Wigner (see the text for details) + linear background function fit to the case with the $\delta$-dip-angle cut.

Background-subtracted invariant mass distributions at 0.4 < $p_{T}$ < 0.8 GeV/c in d + Au 200 GeV collisions (0–100%) with (solid points) and without (open points) the $\delta$-dipangle cut. The dashed curves show a Breit-Wigner (see the text for details) + linear background function fit to the case with the $\delta$-dip-angle cut.

Upper panels: same-event (full points) and mixed-event (solid line) $K^{+}K^{-}$ invariant mass distributions at 0.6 < $p_{T}$ < 1.4 GeV/c in p + p 200 GeV collisions (a), 0.8 < $p_{T}$ < 1.2 GeV/c in Au + Au 62.4 GeV collisions (60–80%) (c), and 0.8 < $p_{T}$ < 1.2 GeV/c in Au + Au 200 GeV collisions (0–10%) (e). Lower panels: the corresponding $\phi$ meson mass peaks after subtracting the background. Dashed curves show a Breit-Wigner + linear background function fit in (b), (d). In (f), both linear and quadratic backgrounds are shown as dashed and dot-dashed lines, respectively.

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Beam-Energy and System-Size Dependence of Dynamical Net Charge Fluctuations

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Rev.C 79 (2009) 024906, 2009.
Inspire Record 791177 DOI 10.17182/hepdata.98972

We present measurements of net charge fluctuations in $Au + Au$ collisions at $\sqrt{s_{NN}} = $ 19.6, 62.4, 130, and 200 GeV, $Cu + Cu$ collisions at $\sqrt{s_{NN}} = $ 62.4, 200 GeV, and $p + p$ collisions at $\sqrt{s} = $ 200 GeV using the dynamical net charge fluctuations measure $\nu_{+-{\rm,dyn}}$. We observe that the dynamical fluctuations are non-zero at all energies and exhibit a modest dependence on beam energy. A weak system size dependence is also observed. We examine the collision centrality dependence of the net charge fluctuations and find that dynamical net charge fluctuations violate $1/N_{ch}$ scaling, but display approximate $1/N_{part}$ scaling. We also study the azimuthal and rapidity dependence of the net charge correlation strength and observe strong dependence on the azimuthal angular range and pseudorapidity widths integrated to measure the correlation.

10 data tables

(Color online) Dynamical net charge fluctuations, $\nu_{+−,dyn}$, of particles produced within pseudorapidity $|\eta|$ < 0.5, as function of the number of participating nucleons.

(Color online) Corrected values of dynamical net charge fluctuations ($\nu^{corr}_{+−,dyn}$) as a function of $\sqrt{s_{NN}}$. See text for details.

(Color online) Dynamical net charge fluctuations, $\nu_{+−,dyn}$, of particles produced with pseudorapidity $|\eta|$ < 0.5 scaled by (a) the multiplicity, $dN_{ch}/d\eta$. The dashed line corresponds to charge conservation effect and the solid line to the prediction for a resonance gas, (b) the number of participants, and (c) the number of binary collisions.

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System-size independence of directed flow at the Relativistic Heavy-Ion Collider

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Rev.Lett. 101 (2008) 252301, 2008.
Inspire Record 790350 DOI 10.17182/hepdata.102949

We measure directed flow ($v_1$) for charged particles in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}} =$ 200 GeV and 62.4 GeV, as a function of pseudorapidity ($\eta$), transverse momentum ($p_t$) and collision centrality, based on data from the STAR experiment. We find that the directed flow depends on the incident energy but, contrary to all existing models, not on the size of the colliding system at a given centrality. We extend the validity of the limiting fragmentation concept to different collision systems, and investigate possible explanations for the observed sign change in $v_1(p_t)$.

11 data tables

Charged particle $v_1(\eta)$ for 0-5 % centrality in Au+Au collisions at 200 GeV.

$<P_x>/<P_t>$ of charged particles as a function of pseudorapidity, for centrality 0-5% in Au+Au collisions at 200 GeV.

Charged particle $v_1(\eta)$ for 5-40 % centrality in Au+Au collisions at 200 GeV.

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Version 2
Global polarization measurement in Au+Au collisions

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Rev.C 76 (2007) 024915, 2007.
Inspire Record 750410 DOI 10.17182/hepdata.98581

The system created in non-central relativistic nucleus-nucleus collisions possesses large orbital angular momentum. Due to spin-orbit coupling, particles produced in such a system could become globally polarized along the direction of the system angular momentum. We present the results of Lambda and anti-Lambda hyperon global polarization measurements in Au+Au collisions at sqrt{s_NN}=62.4 GeV and 200 GeV performed with the STAR detector at RHIC. The observed global polarization of Lambda and anti-Lambda hyperons in the STAR acceptance is consistent with zero within the precision of the measurements. The obtained upper limit, |P_{Lambda,anti-Lambda}| <= 0.02, is compared to the theoretical values discussed recently in the literature.

11 data tables

(Color online) Invariant mass distribution for the $\Lambda$ (filled circles) and $\overline{\Lambda}$ (open squares) candidates after the quality cuts for Au+Au collisions at $\sqrt{s_{NN}}$=62.4 GeV (centrality region 0-80%).

(Color online) Global polarization of $\Lambda$–hyperons as a function of $\Lambda$ transverse momentum $p^{\Lambda}_{t}$. Filled circles show the results for Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV (centrality region 20-70%) and open squares indicate the results for Au+Au collisions at $\sqrt{s_{NN}}$=62.4 GeV (centrality region 0-80%). Only statistical uncertainties are shown.

(Color online) Global polarization of $\Lambda$–hyperons as a function of $\Lambda$ pseudorapidity $\eta^{\Lambda}$. Filled circles show the results for Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV (centrality region 20-70%). A constant line fit to these data points yields $P_{\Lambda}=(2.8\pm 9.6)\times 10^{-3}$ with $\chi^{2}/ndf=6.5/10$. Open squares show the results for Au+Au collisions at $\sqrt{s_{NN}}$=62.4 GeV (centrality region 0-80%). A constant line fit gives $P_{\Lambda}=(1.9\pm 8.0)\times 10^{-3}$ with $\chi^{2}/ndf=14.3/10$. Only statistical uncertainties are shown.

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Energy dependence of $\pi^{\pm}$, $p$ and $\bar{p}$ transverse momentum spectrafor Au+Au collisions at $\sqrt{s_{\mathrm {NN}}}$~=~62.4 and 200 GeV

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Lett.B 655 (2007) 104-113, 2007.
Inspire Record 747299 DOI 10.17182/hepdata.100592

We study the energy dependence of the transverse momentum (pT) spectra for charged pions, protons and anti-protons for Au+Au collisions at \sqrt{s_NN} = 62.4 and 200 GeV. Data are presented at mid-rapidity (|y| &lt; 0.5) for 0.2 &lt; pT &lt; 12 GeV/c. In the intermediate pT region (2 &lt; pT &lt; 6 GeV/c), the nuclear modification factor is higher at 62.4 GeV than at 200 GeV, while at higher pT (pT >7 GeV/c) the modification is similar for both energies. The p/pi+ and pbar/pi- ratios for central collisions at \sqrt{s_NN} = 62.4 GeV peak at pT ~ 2 GeV/c. In the pT range where recombination is expected to dominate, the p/pi+ ratios at 62.4 GeV are larger than at 200 GeV, while the pbar/pi- ratios are smaller. For pT > 2 GeV/c, the pbar/pi- ratios at the two beam energies are independent of pT and centrality indicating that the dependence of the pbar/pi- ratio on pT does not change between 62.4 and 200 GeV. These findings challenge various models incorporating jet quenching and/or constituent quark coalescence.

5 data tables

Midrapidity (|y| < 0.5) transverse momentum spectra for pions, protons, anti-protons for various event centrality classes for Au+Au at sqrt(sNN) = 62.4 GeV. Also shown to study the energy dependence are the central 0-12% pion, proton, anti-proton spectra for Au+Au at sqrt(sNN) = 200 GeV.

The insets show pi−/pi+ ratios at sqrt(sNN) = 62.4 GeV and anti-proton/proton ratios at sqrt(sNN) = 62.4 (0-10%) and 200 GeV (0-12%).

The minimum bias data shown here were extracted from the figures by xyscan. Hence, the dataset is not full (especially in the lower pT range where it is hard to distinguish points), and the statistical errors shown here are an upper limit of the statistical uncertainty based on the marker sizes.

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