cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.17182/hepdata.98962.v1/t4
title: "Figure 3 b" of "rho^0 Photoproduction in Ultra-Peripheral Relativistic Heavy Ion Collisions with STAR"

description: The invariant mass distribution for the coherently produced $\rho^{0}$ candidates obtained from the topology sample with the cut on the $\rho^{0}$ transverse momentum $p_{T}$ &lt; 150 MeV/c. The hatched area is the contribution from the combinatorial background. The solid line corresponds to Eq. 3 which encompasses the Breit-Wigner (dashed), the mass independent contribution from the direct $\pi^{+}\pi^{-}$ production (dash-dotted), and the interference term(dotted).
description: Photoproduction reactions occur when the electromagnetic field of a relativistic heavy ion interacts with another heavy ion. The STAR collaboration presents a measurement of $\rho^{0}$ and direct $\pi^{+}\pi^{-}$ photoproduction in ultra-peripheral relativistic heavy ion collisions at $\sqrt{s_{NN}}$=200 GeV. We observe both exclusive photoproduction and photoproduction accompanied by mutual Coulomb excitation. We find a coherent cross-section of $\sigma(AuAu \rightarrow Au^{*}Au^{*} \rho^{0})$ = 530 $\pm$ 19 (stat.) $\pm$ 57 (syst.) mb, in accord with theoretical calculations based on a Glauber approach, but considerably below the predictions of a color dipole model. The $\rho^{0}$ transverse momentum spectrum ( $p_{T}^{2}$ ) is fit by a double exponential curve including both coherent and incoherent coupling to the target nucleus; we find $\sigma_{inc}/\sigma_{coh}$ = 0.29 $\pm$ 0.03 (stat.) $pm$ 0.08 (syst.). The ratio of direct $\pi^{+}\pi^{-}$ to $\rho^{0}$ production is comparable to that observed in $\gamma p$ collisions at HERA, and appears to be independent of photon energy. Finally, the measured $\rho^{0}$ spin helicity matrix elements agree within errors with the expected s-channel helicity conservation.
DOI: 10.17182/hepdata.98962.v1/t5
title: "Figure 4" of "rho^0 Photoproduction in Ultra-Peripheral Relativistic Heavy Ion Collisions with STAR"

description: The ratio |B/A| as a function of $y_{\rho^{0}}$ for the minimum bias data, obtained by fitting Eq.3 to the invariant mass distributions in bins of $y_{\rho^{0}}$.
description: Photoproduction reactions occur when the electromagnetic field of a relativistic heavy ion interacts with another heavy ion. The STAR collaboration presents a measurement of $\rho^{0}$ and direct $\pi^{+}\pi^{-}$ photoproduction in ultra-peripheral relativistic heavy ion collisions at $\sqrt{s_{NN}}$=200 GeV. We observe both exclusive photoproduction and photoproduction accompanied by mutual Coulomb excitation. We find a coherent cross-section of $\sigma(AuAu \rightarrow Au^{*}Au^{*} \rho^{0})$ = 530 $\pm$ 19 (stat.) $\pm$ 57 (syst.) mb, in accord with theoretical calculations based on a Glauber approach, but considerably below the predictions of a color dipole model. The $\rho^{0}$ transverse momentum spectrum ( $p_{T}^{2}$ ) is fit by a double exponential curve including both coherent and incoherent coupling to the target nucleus; we find $\sigma_{inc}/\sigma_{coh}$ = 0.29 $\pm$ 0.03 (stat.) $pm$ 0.08 (syst.). The ratio of direct $\pi^{+}\pi^{-}$ to $\rho^{0}$ production is comparable to that observed in $\gamma p$ collisions at HERA, and appears to be independent of photon energy. Finally, the measured $\rho^{0}$ spin helicity matrix elements agree within errors with the expected s-channel helicity conservation.
DOI: 10.17182/hepdata.98962.v1/t6
title: "Figure 5" of "rho^0 Photoproduction in Ultra-Peripheral Relativistic Heavy Ion Collisions with STAR"

description: Coherent $\rho^{0}$ production cross-section for the minimum bias data set as a function of $y_{\rho^{0}}$ (black dots) overlaid by the $d\sigma/dy$ distribution predicted by the KN model [22] (solid line).
description: Photoproduction reactions occur when the electromagnetic field of a relativistic heavy ion interacts with another heavy ion. The STAR collaboration presents a measurement of $\rho^{0}$ and direct $\pi^{+}\pi^{-}$ photoproduction in ultra-peripheral relativistic heavy ion collisions at $\sqrt{s_{NN}}$=200 GeV. We observe both exclusive photoproduction and photoproduction accompanied by mutual Coulomb excitation. We find a coherent cross-section of $\sigma(AuAu \rightarrow Au^{*}Au^{*} \rho^{0})$ = 530 $\pm$ 19 (stat.) $\pm$ 57 (syst.) mb, in accord with theoretical calculations based on a Glauber approach, but considerably below the predictions of a color dipole model. The $\rho^{0}$ transverse momentum spectrum ( $p_{T}^{2}$ ) is fit by a double exponential curve including both coherent and incoherent coupling to the target nucleus; we find $\sigma_{inc}/\sigma_{coh}$ = 0.29 $\pm$ 0.03 (stat.) $pm$ 0.08 (syst.). The ratio of direct $\pi^{+}\pi^{-}$ to $\rho^{0}$ production is comparable to that observed in $\gamma p$ collisions at HERA, and appears to be independent of photon energy. Finally, the measured $\rho^{0}$ spin helicity matrix elements agree within errors with the expected s-channel helicity conservation.
DOI: 10.17182/hepdata.98962.v1/t7
title: "Figure 6" of "rho^0 Photoproduction in Ultra-Peripheral Relativistic Heavy Ion Collisions with STAR"

description: $\rho^{0}$ production cross-section as a function of the momentum transfer squared $t$, together with the fit of Eq. 5. The fit parameters are shown in Table I.
description: Photoproduction reactions occur when the electromagnetic field of a relativistic heavy ion interacts with another heavy ion. The STAR collaboration presents a measurement of $\rho^{0}$ and direct $\pi^{+}\pi^{-}$ photoproduction in ultra-peripheral relativistic heavy ion collisions at $\sqrt{s_{NN}}$=200 GeV. We observe both exclusive photoproduction and photoproduction accompanied by mutual Coulomb excitation. We find a coherent cross-section of $\sigma(AuAu \rightarrow Au^{*}Au^{*} \rho^{0})$ = 530 $\pm$ 19 (stat.) $\pm$ 57 (syst.) mb, in accord with theoretical calculations based on a Glauber approach, but considerably below the predictions of a color dipole model. The $\rho^{0}$ transverse momentum spectrum ( $p_{T}^{2}$ ) is fit by a double exponential curve including both coherent and incoherent coupling to the target nucleus; we find $\sigma_{inc}/\sigma_{coh}$ = 0.29 $\pm$ 0.03 (stat.) $pm$ 0.08 (syst.). The ratio of direct $\pi^{+}\pi^{-}$ to $\rho^{0}$ production is comparable to that observed in $\gamma p$ collisions at HERA, and appears to be independent of photon energy. Finally, the measured $\rho^{0}$ spin helicity matrix elements agree within errors with the expected s-channel helicity conservation.
DOI: 10.17182/hepdata.98962.v1/t8
title: "Figure 7" of "rho^0 Photoproduction in Ultra-Peripheral Relativistic Heavy Ion Collisions with STAR"

description: Comparison of theoretical predictions to the measured differential cross-section for coherent $\rho^{0}$ production. The statistical errors are shown by the solid vertical line at each data point. The sum of the statistical and systematic error bars is shown by the grey band.
description: Photoproduction reactions occur when the electromagnetic field of a relativistic heavy ion interacts with another heavy ion. The STAR collaboration presents a measurement of $\rho^{0}$ and direct $\pi^{+}\pi^{-}$ photoproduction in ultra-peripheral relativistic heavy ion collisions at $\sqrt{s_{NN}}$=200 GeV. We observe both exclusive photoproduction and photoproduction accompanied by mutual Coulomb excitation. We find a coherent cross-section of $\sigma(AuAu \rightarrow Au^{*}Au^{*} \rho^{0})$ = 530 $\pm$ 19 (stat.) $\pm$ 57 (syst.) mb, in accord with theoretical calculations based on a Glauber approach, but considerably below the predictions of a color dipole model. The $\rho^{0}$ transverse momentum spectrum ( $p_{T}^{2}$ ) is fit by a double exponential curve including both coherent and incoherent coupling to the target nucleus; we find $\sigma_{inc}/\sigma_{coh}$ = 0.29 $\pm$ 0.03 (stat.) $pm$ 0.08 (syst.). The ratio of direct $\pi^{+}\pi^{-}$ to $\rho^{0}$ production is comparable to that observed in $\gamma p$ collisions at HERA, and appears to be independent of photon energy. Finally, the measured $\rho^{0}$ spin helicity matrix elements agree within errors with the expected s-channel helicity conservation.
DOI: 10.17182/hepdata.98962.v1/t9
title: "Figure 8 a" of "rho^0 Photoproduction in Ultra-Peripheral Relativistic Heavy Ion Collisions with STAR"

description: Projections of the two dimensional efficiency corrected $\Phi_{h}$ vs $cos(\Theta_{h})$ distributions obtained with the minimum bias data set. The solid line shows the result of the two-dimensional fit to the data with Eq. 6 and the coefficients given in Tab. III.
description: Photoproduction reactions occur when the electromagnetic field of a relativistic heavy ion interacts with another heavy ion. The STAR collaboration presents a measurement of $\rho^{0}$ and direct $\pi^{+}\pi^{-}$ photoproduction in ultra-peripheral relativistic heavy ion collisions at $\sqrt{s_{NN}}$=200 GeV. We observe both exclusive photoproduction and photoproduction accompanied by mutual Coulomb excitation. We find a coherent cross-section of $\sigma(AuAu \rightarrow Au^{*}Au^{*} \rho^{0})$ = 530 $\pm$ 19 (stat.) $\pm$ 57 (syst.) mb, in accord with theoretical calculations based on a Glauber approach, but considerably below the predictions of a color dipole model. The $\rho^{0}$ transverse momentum spectrum ( $p_{T}^{2}$ ) is fit by a double exponential curve including both coherent and incoherent coupling to the target nucleus; we find $\sigma_{inc}/\sigma_{coh}$ = 0.29 $\pm$ 0.03 (stat.) $pm$ 0.08 (syst.). The ratio of direct $\pi^{+}\pi^{-}$ to $\rho^{0}$ production is comparable to that observed in $\gamma p$ collisions at HERA, and appears to be independent of photon energy. Finally, the measured $\rho^{0}$ spin helicity matrix elements agree within errors with the expected s-channel helicity conservation.
DOI: 10.3535/s73-ca9-nje
title: Clerodendrum L.

description: Digital Specimen for the physical specimen hosted at Botanic Garden and Botanical Museum Berlin.
DOI: 10.17182/hepdata.98962.v1/t10
title: "Figure 8 b" of "rho^0 Photoproduction in Ultra-Peripheral Relativistic Heavy Ion Collisions with STAR"

description: Projections of the two dimensional efficiency corrected $\Phi_{h}$ vs $cos(\Theta_{h})$ distributions obtained with the minimum bias data set. The solid line shows the result of the two-dimensional fit to the data with Eq. 6 and the coefficients given in Tab. III.
description: Photoproduction reactions occur when the electromagnetic field of a relativistic heavy ion interacts with another heavy ion. The STAR collaboration presents a measurement of $\rho^{0}$ and direct $\pi^{+}\pi^{-}$ photoproduction in ultra-peripheral relativistic heavy ion collisions at $\sqrt{s_{NN}}$=200 GeV. We observe both exclusive photoproduction and photoproduction accompanied by mutual Coulomb excitation. We find a coherent cross-section of $\sigma(AuAu \rightarrow Au^{*}Au^{*} \rho^{0})$ = 530 $\pm$ 19 (stat.) $\pm$ 57 (syst.) mb, in accord with theoretical calculations based on a Glauber approach, but considerably below the predictions of a color dipole model. The $\rho^{0}$ transverse momentum spectrum ( $p_{T}^{2}$ ) is fit by a double exponential curve including both coherent and incoherent coupling to the target nucleus; we find $\sigma_{inc}/\sigma_{coh}$ = 0.29 $\pm$ 0.03 (stat.) $pm$ 0.08 (syst.). The ratio of direct $\pi^{+}\pi^{-}$ to $\rho^{0}$ production is comparable to that observed in $\gamma p$ collisions at HERA, and appears to be independent of photon energy. Finally, the measured $\rho^{0}$ spin helicity matrix elements agree within errors with the expected s-channel helicity conservation.
DOI: 10.17182/hepdata.98963.v1/t1
title: "Figure 2" of "Observation of pi^+pi^-pi^+pi^- Photoproduction in Ultra-Peripheral Heavy Ion Collisions at STAR"

description: Distribution of the $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ transverse momentum $p_{T} = |\sum_{i=1}^{4}\overrightarrow{p}_{T,i}|$􏰇: The filled circles are the measured 􏰇points with the statistical errors. The hatched filled histogram shows the expected distribution from simulation of coherent photoproduction (cf. section III). The strong enhancement at low transverse momenta is due to coherently produced $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$. This unique signature is used in the event selection which requires $p_{T}$ &lt; 150 MeV/c (arrow). The remaining background is estimated from +2 or −2 charged four-prong combinations, by normalizing (factor = 1.186 $\pm$ 0.054) their $p_{T}$ distribution (gray filled histogram) to that of the neutral four-prongs in the region of $p_{T}$ &gt; 250 MeV/c (vertical line) yielding the unfilled histogram (see section IV).
description: We present a measurement of $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ photonuclear production in ultra-peripheral Au-Au collisions at $\sqrt{s_{NN}}$ = 200 GeV from the STAR experiment. The $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ final states are observed at low transverse momentum and are accompanied by mutual nuclear excitation of the beam particles. The strong enhancement of the production cross section at low transverse momentum is consistent with coherent photoproduction. The $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ invariant mass spectrum of the coherent events exhibits a broad peak around 1540 $\pm$ 40 MeV/$c^{2}$ with a width of 570 $\pm$ 60 MeV/$c^{2}$, in agreement with the photoproduction data for the $\rho^{0}$(1700). We do not observe a corresponding peak in the $\pi^{+}\pi^{-}$ final state and measure an upper limit for the ratio of the branching fractions of the $\rho^{0}$(1700) to $\pi^{+}\pi^{-}$ and $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ of 2.5 % at 90 % confidence level. The ratio of $\rho^{0}$(1700) and $\rho^{0}$(770) coherent production cross sections is measured to be 13.4 $\pm$ 0.8 (stat.) $\pm$ 4.4 (syst.) %.
DOI: 10.17182/hepdata.98963.v1/t2
title: "Figure 3" of "Observation of pi^+pi^-pi^+pi^- Photoproduction in Ultra-Peripheral Heavy Ion Collisions at STAR"

description: Invariant Mass distribution of two-pion subsystems: The filled circles show the measured $\pi^{+}\pi^{-}$ invariant mass spectrum for the selected four-prong sample (four entries per event) with statistical errors. The open circles represent the mass spectrum of the like-sign pion pairs (two entries per event). The unlike-sign mass distribution exhibits an enhancement with respect to the like-sign pairs in the $\rho^{0}$(770) region. The solid line histograms show the prediction from simulation assuming the relative S-wave decay $\rho`\rightarrow\rho^{0}$(770) $f_{0}$(600).
description: We present a measurement of $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ photonuclear production in ultra-peripheral Au-Au collisions at $\sqrt{s_{NN}}$ = 200 GeV from the STAR experiment. The $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ final states are observed at low transverse momentum and are accompanied by mutual nuclear excitation of the beam particles. The strong enhancement of the production cross section at low transverse momentum is consistent with coherent photoproduction. The $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ invariant mass spectrum of the coherent events exhibits a broad peak around 1540 $\pm$ 40 MeV/$c^{2}$ with a width of 570 $\pm$ 60 MeV/$c^{2}$, in agreement with the photoproduction data for the $\rho^{0}$(1700). We do not observe a corresponding peak in the $\pi^{+}\pi^{-}$ final state and measure an upper limit for the ratio of the branching fractions of the $\rho^{0}$(1700) to $\pi^{+}\pi^{-}$ and $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ of 2.5 % at 90 % confidence level. The ratio of $\rho^{0}$(1700) and $\rho^{0}$(770) coherent production cross sections is measured to be 13.4 $\pm$ 0.8 (stat.) $\pm$ 4.4 (syst.) %.
DOI: 10.17182/hepdata.98963.v1/t3
title: "Figure 4" of "Observation of pi^+pi^-pi^+pi^- Photoproduction in Ultra-Peripheral Heavy Ion Collisions at STAR"

description: Invariant Mass distribution of two-pion subsystems: The open circles show the measured invariant mass spectrum of the lightest $\pi^{+}\pi^{-}$ pair in the event with the bars indicating the statistical errors. The filled circles represent the invariant mass distribution of the $\pi^{+}\pi^{-}$ that is recoiling against the lightest pair. The spectrum exhibits a clear peak in the $\rho^{0}$(770) region. The solid line histograms show the prediction from simulation assuming the relative S-wave decay $\rho`\rightarrow\rho^{0}$(770) $f_{0}$(600).
description: We present a measurement of $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ photonuclear production in ultra-peripheral Au-Au collisions at $\sqrt{s_{NN}}$ = 200 GeV from the STAR experiment. The $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ final states are observed at low transverse momentum and are accompanied by mutual nuclear excitation of the beam particles. The strong enhancement of the production cross section at low transverse momentum is consistent with coherent photoproduction. The $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ invariant mass spectrum of the coherent events exhibits a broad peak around 1540 $\pm$ 40 MeV/$c^{2}$ with a width of 570 $\pm$ 60 MeV/$c^{2}$, in agreement with the photoproduction data for the $\rho^{0}$(1700). We do not observe a corresponding peak in the $\pi^{+}\pi^{-}$ final state and measure an upper limit for the ratio of the branching fractions of the $\rho^{0}$(1700) to $\pi^{+}\pi^{-}$ and $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ of 2.5 % at 90 % confidence level. The ratio of $\rho^{0}$(1700) and $\rho^{0}$(770) coherent production cross sections is measured to be 13.4 $\pm$ 0.8 (stat.) $\pm$ 4.4 (syst.) %.
DOI: 10.25549/vercoutere-ouc110610700
title: Nude man sitting under a tree in a garden

description: One nude pink male sitting in a garden under a tree with a large black and gray bird flying by; garden has rows of crops as well as flowers, grass, plants,and fence. Primaily pinks and green. See description of 001 for OT notes.
DOI: 10.3535/6hl-jfw-b68
title: Maesa perlaria (Lour.) Merr.

description: Digital Specimen for the physical specimen hosted at Botanic Garden and Botanical Museum Berlin.
DOI: 10.3535/sfk-vpq-xfr
title: Acanthus hirsutus Boiss.

description: Digital Specimen for the physical specimen hosted at Botanic Garden and Botanical Museum Berlin.
DOI: 10.17182/hepdata.98963.v1/t4
title: "Figure 5" of "Observation of pi^+pi^-pi^+pi^- Photoproduction in Ultra-Peripheral Heavy Ion Collisions at STAR"

description: (Color online) Invariant mass distribution of coherently produced $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$: The filled circles are the measured points with the statistical errors, the gray filled histogram is the background estimated from charged four-prongs (cf. Fig. 2). The thick black line shows the fit of a modified $S$-wave Breit-Wigner on top of a second order polynomial background (thin black line; cf. Eq. (5)) taking into account the detector acceptance in the region $|y| &lt; 1$ (rising dashed line). The dotted curve represents the signal curve without background.
description: We present a measurement of $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ photonuclear production in ultra-peripheral Au-Au collisions at $\sqrt{s_{NN}}$ = 200 GeV from the STAR experiment. The $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ final states are observed at low transverse momentum and are accompanied by mutual nuclear excitation of the beam particles. The strong enhancement of the production cross section at low transverse momentum is consistent with coherent photoproduction. The $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ invariant mass spectrum of the coherent events exhibits a broad peak around 1540 $\pm$ 40 MeV/$c^{2}$ with a width of 570 $\pm$ 60 MeV/$c^{2}$, in agreement with the photoproduction data for the $\rho^{0}$(1700). We do not observe a corresponding peak in the $\pi^{+}\pi^{-}$ final state and measure an upper limit for the ratio of the branching fractions of the $\rho^{0}$(1700) to $\pi^{+}\pi^{-}$ and $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ of 2.5 % at 90 % confidence level. The ratio of $\rho^{0}$(1700) and $\rho^{0}$(770) coherent production cross sections is measured to be 13.4 $\pm$ 0.8 (stat.) $\pm$ 4.4 (syst.) %.
DOI: 10.17182/hepdata.98963.v1/t5
title: "Figure 6" of "Observation of pi^+pi^-pi^+pi^- Photoproduction in Ultra-Peripheral Heavy Ion Collisions at STAR"

description: (Color online) Invariant mass distribution of coherently produced $\pi^{+}\pi^{-}$ pairs. The filled circles are the measured points with statistical errors. The thick black line shows the fit taking into account the detector acceptance in the region $|y| &lt; 1$. The non-interfering combinatorial background is represented by the thin black line, which is a fit to the like-sign invariant mass distribution scaled by a factor estimated from the $p_{T}$ distribution (gray filled histogram). The dotted curve shows the Breit-Wigner without background, the dashed line the interfering background component that is assumed to be mass-independent. The dash-dotted curve is the Söding interference term of the two [31].
description: We present a measurement of $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ photonuclear production in ultra-peripheral Au-Au collisions at $\sqrt{s_{NN}}$ = 200 GeV from the STAR experiment. The $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ final states are observed at low transverse momentum and are accompanied by mutual nuclear excitation of the beam particles. The strong enhancement of the production cross section at low transverse momentum is consistent with coherent photoproduction. The $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ invariant mass spectrum of the coherent events exhibits a broad peak around 1540 $\pm$ 40 MeV/$c^{2}$ with a width of 570 $\pm$ 60 MeV/$c^{2}$, in agreement with the photoproduction data for the $\rho^{0}$(1700). We do not observe a corresponding peak in the $\pi^{+}\pi^{-}$ final state and measure an upper limit for the ratio of the branching fractions of the $\rho^{0}$(1700) to $\pi^{+}\pi^{-}$ and $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ of 2.5 % at 90 % confidence level. The ratio of $\rho^{0}$(1700) and $\rho^{0}$(770) coherent production cross sections is measured to be 13.4 $\pm$ 0.8 (stat.) $\pm$ 4.4 (syst.) %.
DOI: 10.17182/hepdata.98963.v1/t6
title: "Figure 7" of "Observation of pi^+pi^-pi^+pi^- Photoproduction in Ultra-Peripheral Heavy Ion Collisions at STAR"

description: (Color online) High mass region of the $m_{\pi^{+}\pi^{-}}$ spectrum with tighter cuts applied in order to suppress background: The filled circles are the measured values with statistical errors. No significant enhancement is seen in the region around 1540 MeV/$c^{2}$ where the $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ invariant mass spectrum exhibits a peak. The thick solid line shows the fit of a modified $S$-wave Breit-Wigner (cf. Eq. (5)) with parameters fixed to the values extracted from the fit of the $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ invariant mass distribution on top of an $S$-wave Breit-Wigner that describes the tail of the $\rho^{0}$(770) (thin solid line) taking into account the detector acceptance. The dashed curve represents the signal curve without the $\rho^{0}$ tail.
description: We present a measurement of $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ photonuclear production in ultra-peripheral Au-Au collisions at $\sqrt{s_{NN}}$ = 200 GeV from the STAR experiment. The $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ final states are observed at low transverse momentum and are accompanied by mutual nuclear excitation of the beam particles. The strong enhancement of the production cross section at low transverse momentum is consistent with coherent photoproduction. The $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ invariant mass spectrum of the coherent events exhibits a broad peak around 1540 $\pm$ 40 MeV/$c^{2}$ with a width of 570 $\pm$ 60 MeV/$c^{2}$, in agreement with the photoproduction data for the $\rho^{0}$(1700). We do not observe a corresponding peak in the $\pi^{+}\pi^{-}$ final state and measure an upper limit for the ratio of the branching fractions of the $\rho^{0}$(1700) to $\pi^{+}\pi^{-}$ and $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ of 2.5 % at 90 % confidence level. The ratio of $\rho^{0}$(1700) and $\rho^{0}$(770) coherent production cross sections is measured to be 13.4 $\pm$ 0.8 (stat.) $\pm$ 4.4 (syst.) %.