CMSPASHIN16017  
Charge asymmetry dependence of elliptic and triangular flow in pPb and PbPb collisions at $\sqrt{ s_{\text{NN}} } = $ 5.02 TeV  
CMS Collaboration  
February 2017  
Abstract: Charge dependent elliptic azimuthal anisotropy ($v_{\rm 2}$) in pPb and both $v_{\rm 2}$ and triangular azimuthal anisotropy ($v_{\rm 3}$) in PbPb collisions are measured at $\sqrt{ s_{\text{NN}} } = $ 5.02 TeV with the CMS detector at the LHC. The normalized difference of $v_{\rm 2}$ between positively and negatively charged particles, ($v_{\rm 2}^{}v_{\rm 2}^{+}$)/($v_{\rm 2}^{}+v_{\rm 2}^{+}$), shows a linear dependence with respect to the eventcharged asymmetry $A_{\rm ch}$, with comparable slopes observed for pPb and PbPb collisions at similar multiplicities. In PbPb collisions, the slopes are found to be the same for the $v_{\rm 2}$ and $v_{\rm 3}$ coefficients within uncertainties. These observations pose a challenge to the hypothesis that the charge asymmetry dependence of $v_{\rm 2}$ arises from a chiral magnetic wave. However, the results are in qualitative agreement with expectations based on local charge conservation.  
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These preliminary results are superseded in this paper, PRC 100 (2019) 064908. The superseded preliminary plots can be found here. 
Figures  
png pdf 
Figure 1:
Elliptic flow $v_2$ for positive and negativecharged particles as a function of charge asymmetry (left) and the normalized $v_{2}$ difference, $(v^{}_{2}  v^{+}_{2})/(v^{}_{2} + v^{+}_{2})$, as a function of corrected event charge asymmetry (right) for multiplicity range 185 $ \leq {N_\mathrm {trk}^\mathrm {offline}} < $ 220 in PbPb collisions at 5.02 TeV. Statistical uncertainties are indicated by the error bars. 
png pdf 
Figure 1a:
Elliptic flow $v_2$ for positive and negativecharged particles as a function of charge asymmetry (left) and the normalized $v_{2}$ difference, $(v^{}_{2}  v^{+}_{2})/(v^{}_{2} + v^{+}_{2})$, as a function of corrected event charge asymmetry (right) for multiplicity range 185 $ \leq {N_\mathrm {trk}^\mathrm {offline}} < $ 220 in pPb collisions at 5.02 TeV. Statistical uncertainties are indicated by the error bars. 
png pdf 
Figure 1b:
Elliptic flow $v_2$ for positive and negativecharged particles as a function of charge asymmetry (left) and the normalized $v_{2}$ difference, $(v^{}_{2}  v^{+}_{2})/(v^{}_{2} + v^{+}_{2})$, as a function of corrected event charge asymmetry (right) for multiplicity range 185 $ \leq {N_\mathrm {trk}^\mathrm {offline}} < $ 220 in PbPb collisions at 5.02 TeV. Statistical uncertainties are indicated by the error bars. 
png pdf 
Figure 2:
The eventaveraged $ {p_{\mathrm {T}}} $ value ($ < {p_{\mathrm {T}}} >$) for positive and negativecharged particles as a function of charge asymmetry (left) and the normalized $ < {p_{\mathrm {T}}} >$ difference, $( < {p_{\mathrm {T}}} >^{}  < {p_{\mathrm {T}}} >^{+})/( < {p_{\mathrm {T}}} >^{} + < {p_{\mathrm {T}}} >^{+})$, as a function of corrected event charge asymmetry (right) for multiplicity range 185 $ \leq {N_\mathrm {trk}^\mathrm {offline}} < $ 220 in pPb and PbPb collisions at 5.02 TeV. Statistical uncertainties are covered by the data points. 
png pdf 
Figure 2a:
The eventaveraged $ {p_{\mathrm {T}}} $ value ($ < {p_{\mathrm {T}}} >$) for positive and negativecharged particles as a function of charge asymmetry (left) and the normalized $ < {p_{\mathrm {T}}} >$ difference, $( < {p_{\mathrm {T}}} >^{}  < {p_{\mathrm {T}}} >^{+})/( < {p_{\mathrm {T}}} >^{} + < {p_{\mathrm {T}}} >^{+})$, as a function of corrected event charge asymmetry (right) for multiplicity range 185 $ \leq {N_\mathrm {trk}^\mathrm {offline}} < $ 220 in pPb collisions at 5.02 TeV. Statistical uncertainties are covered by the data points. 
png pdf 
Figure 2b:
The eventaveraged $ {p_{\mathrm {T}}} $ value ($ < {p_{\mathrm {T}}} >$) for positive and negativecharged particles as a function of charge asymmetry (left) and the normalized $ < {p_{\mathrm {T}}} >$ difference, $( < {p_{\mathrm {T}}} >^{}  < {p_{\mathrm {T}}} >^{+})/( < {p_{\mathrm {T}}} >^{} + < {p_{\mathrm {T}}} >^{+})$, as a function of corrected event charge asymmetry (right) for multiplicity range 185 $ \leq {N_\mathrm {trk}^\mathrm {offline}} < $ 220 in PbPb collisions at 5.02 TeV. Statistical uncertainties are covered by the data points. 
png pdf 
Figure 3:
The linear slope for $v_2$ (left) and $ < {p_{\mathrm {T}}} >$ (right) parameters $r^{\rm norm}_{2}$ and $r^{\rm norm}_{ < {p_{\mathrm {T}}} >}$ as a function of event multiplicity in pPb and PbPb collisions at $ \sqrt{ s_{\text{NN}} } = $ 5.02 TeV. Statistical and systematic uncertainties are indicated by the error bars and shaded regions, respectively. 
png pdf 
Figure 3a:
The linear slope for $v_2$ parameter $r^{\rm norm}_{2}$ as a function of event multiplicity in pPb and PbPb collisions at $ \sqrt{ s_{\text{NN}} } = $ 5.02 TeV. Statistical and systematic uncertainties are indicated by the error bars and shaded regions, respectively. 
png pdf 
Figure 3b:
The linear slope for $ < {p_{\mathrm {T}}} >$ parameter $r^{\rm norm}_{ < {p_{\mathrm {T}}} >}$ as a function of event multiplicity in pPb and PbPb collisions at $ \sqrt{ s_{\text{NN}} } = $ 5.02 TeV. Statistical and systematic uncertainties are indicated by the error bars and shaded regions, respectively. 
png pdf 
Figure 4:
The triangular flow $v_3$ for positive and negativecharged particles (left) and the normalized difference in $v_{n}$, $(v^{}_{n}  v^{+}_{n})/(v^{}_{n} + v^{+}_{n})$, for $n=$ 2 and $n=$ 3 (right) as a function of corrected event charge asymmetry for 3040% centrality of PbPb collisions at $ \sqrt{ s_{\text{NN}} } = $ 5.02 TeV. Statistical uncertainties are covered by the data points. 
png pdf 
Figure 5:
The linear slope ($r^{\rm norm}_{n}$) parameter for elliptic ($n=$ 2) and triangular ($n=$ 3) flow as a function of centrality for PbPb collisions at $ \sqrt{ s_{\text{NN}} } = $ 5.02 TeV. Statistical and systematic uncertainties are indicated by the error bars and shaded regions, respectively. 
Summary 
The chargeddependent elliptic flow coefficients ($v_{2}$) in pPb and both $v_{2}$ and triangular flow coefficients ($v_{3}$) in PbPb have been measured as a function of eventcharged asymmetry at $ \sqrt{ s_{\text{NN}} } = $ 5.02 TeV. The normalized slope parameters of $v_{2}$ in pPb and PbPb collisions are found to be similar at the same eventcharged particle multiplicities. Moreover, the normalized slope parameters of the $v_{2}$ and $v_{3}$ coefficients show similar magnitudes in various centralities. These observations would not be expected if the charge dependence resulted from a Chiral Magnetic Wave mechanism. The data are qualitatively consistent with predictions from the local charge conservation mechanism. 
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