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| CMS-HIN-16-022 ; CERN-EP-2017-220 | ||
| Observation of correlated azimuthal anisotropy Fourier harmonics in pp and pPb collisions at the LHC | ||
| CMS Collaboration | ||
| 26 September 2017 | ||
| Phys. Rev. Lett. 120 (2018) 092301 | ||
| Abstract: The azimuthal anisotropy Fourier coefficients ($v_n$) in 8.16 TeV pPb data are extracted via long-range two-particle correlations as a function of event multiplicity and compared to corresponding results in pp and PbPb collisions. Using a four-particle cumulant technique, $v_n$ correlations are measured for the first time in pp and pPb collisions. The $v_2$ and $v_4$ coefficients are found to be positively correlated in all collision systems. For high multiplicity pPb collisions an anticorrelation of $v_2$ and $v_3$ is observed, with a similar correlation strength as in PbPb data at the same multiplicity. The new correlation results strengthen the case for a common origin of the collectivity seen in pPb and PbPb collisions in the measured multiplicity range. | ||
| Links: e-print arXiv:1709.09189 [nucl-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
The $v_2$, $v_3$ [25], and $v_4$ coefficients from long-range two-particle correlations for 0.3 $ < {p_{\mathrm {T}}} < $ 3 GeV/$c$ as a function of ${N_\text {trk}^\text {offline}}$ in ${{\mathrm{p}} {\mathrm{p}}}$ at $ {\sqrt{\smash[b]{s}}} = $ 13 TeV (a), pPb at $ {\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 TeV [32] and 8.16 TeV (b), and PbPb at $ {\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 TeV collisions (c). The results corrected by low-multiplicity subtraction are denoted as $v_{n}^\text {sub}$. The lines show the $v_{n}$ results before subtraction of low-multiplicity correlations. The gray boxes represent systematic uncertainties. |
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Figure 2:
The SCs for the second and third coefficient (red points) and the second and fourth coefficient (blue points) as a function of ${N_\text {trk}^\text {offline}}$ in pp collisions at $ {\sqrt{\smash[b]{s}}} = $ 13 TeV (a), pPb collisions at $ {\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 and 8.16 TeV (b), and PbPb collisions at $ {\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 TeV (c). The gray boxes represent systematic uncertainties. |
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Figure 3:
The SCs for the second and third coefficients (left) and the second and fourth coefficients (right) normalized by $\left < v_2^{2}\right > \left < v_3^{2}\right > $ and $\left < v_2^{2}\right > \left < v_4^{2}\right > $ from two-particle correlations. The track ${p_{\mathrm {T}}}$ range is 0.3 $ < {p_{\mathrm {T}}} < $ 3 GeV/$c$ and the results are shown as a function of ${N_\text {trk}^\text {offline}}$ in pp collisions at $ {\sqrt{\smash[b]{s}}} = $ 13 TeV, pPb collisions at $ {\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 8.16 TeV, and PbPb collisions at $ {\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 TeV. |
| Summary |
| In summary, the first measurements of azimuthal anisotropy Fourier coefficients and correlations of different coefficients in pPb collisions at $\sqrt{\smash[b]{s_{_\mathrm{NN}}}} = $ 8.16 TeV are presented based on data collected by the CMS experiment at the LHC. The $v_2$, $v_3$, and $v_4$ Fourier coefficients are extracted from long-range two-particle correlations in classes of event multiplicity, and are found to be consistent with pPb data at $\sqrt{\smash[b]{s_{_\mathrm{NN}}}} = $ 5.02 TeV. The pPb results are compared to those in pp at $ \sqrt{\smash[b]{s}} = $13 TeV and PbPb at $\sqrt{\smash[b]{s_{_\mathrm{NN}}}} = $ 5.02 TeV. Using a four-particle cumulant technique, correlations of different coefficient orders are obtained, where a negative (positive) correlation is observed between $v_2$ and $v_3$ ($v_4$) in pPb collisions. This behavior is similar to what is observed in the PbPb system, where the result is attributed to the hydrodynamic flow of a strongly interacting medium. Normalized correlation coefficients for $v_2$ and $v_3$ are found to be quantitatively similar between pPb and PbPb, while for $v_2$ and $v_4$ the results are larger in PbPb than in PbPb. The corresponding result in pp collisions shows a similar trend at high multiplicity but the statistical uncertainties are too large to make a quantitative statement. The results presented in this Letter provide further evidence of a similar origin of collectivity observed in small and large hadronic systems and impose constraints on theoretical model calculations. |
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