Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Back-to-back relative-excess observable in search for the chiral
  magnetic effect   $\textbf{Background:}$ The chiral magnetic effect (CME) is extensively
studied in heavy-ion collisions at RHIC and LHC. In the commonly used reaction
plane (RP) dependent, charge dependent azimuthal correlator ($\Delta\gamma$),
both the close and back-to-back pairs are included. Many backgrounds contribute
to the close pairs (e.g. resonance decays, jet correlations), whereas the
back-to-back pairs are relatively free of those backgrounds.
  $\textbf{Purpose:}$ In order to reduce those backgrounds, we propose a new
observable which only focuses on the back-to-back pairs, namely, the relative
back-to-back opposite-sign (OS) over same-sign (SS) pair excess
($r_{\text{BB}}$) as a function of the pair azimuthal orientation with respect
to the RP ($\varphi_{\text{BB}}$).
  $\textbf{Methods:}$ We use analytical calculations and toy model simulations
to demonstrate the sensitivity of $r_{\text{BB}}(\varphi_{\text{BB}})$ to the
CME and its insensitivity to backgrounds.
  $\textbf{Results:}$ With finite CME, the $\varphi_{\text{BB}}$ distribution
of $r_{\text{BB}}$ shows a clear characteristic modulation. Its sensitivity to
background is significantly reduced compared to the previous $\Delta\gamma$
observable. The simulation results are consistent with our analytical
calculations.
  $\textbf{Conclusions:}$ Our studies demonstrate that the
$r_{\text{BB}}(\varphi_{\text{BB}})$ observable is sensitive to the CME signal
and rather insensitive to the resonance backgrounds.

25
The categories of this paper are: patt-sol
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The categories of this paper are: dg-ga
31
The categories of this paper are: ao-sci
4
The categories of this paper are: cond-mat
20
The categories of this paper are: acc-phys
18
The categories of this paper are: econ
35
The categories of this paper are: mtrl-th
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The categories of this paper are: solv-int
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The categories of this paper are: funct-an
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The categories of this paper are: comp-gas
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The categories of this paper are: adap-org
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The categories of this paper are: nlin
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The categories of this paper are: eess
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The categories of this paper are: math-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: q-fin