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Measurement of dijet $p_{\mathrm{T}}$ correlations in Pb+Pb and $pp$ collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV with the ATLAS detector ATLAS-CONF-2015-052 27 September 2015
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| Main document (CDS record) | pdf from CDS | |
| Figures and Auxiliary Material | - | |
| Abstract | ||
| Measurements of dijets in both Pb+Pb and $pp$ collisions at a nucleon--nucleon centre-of-mass energy of $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV are presented. The measurements were performed with the ATLAS detector at the LHC using data samples with integrated luminosities of 0.14 nb$^{-1}$ and 4.0 pb$^{-1}$ for the Pb+Pb and $pp$ data samples, respectively. Jets were reconstructed using the anti-$k_t$ algorithm with $R=0.4$. A background subtraction procedure was applied to correct the jet kinematics for the large underlying event present in Pb+Pb collisions. Measurements are reported of the normalized yields $\frac{1}{N}\frac{\mathrm{d}N}{\mathrm{d}x_{\mathrm{J}}}$, where $x_{\mathrm{J}}=p_{\mathrm{T}_{2}} / p_{\mathrm{T}_{1}}$ and $ p_{\mathrm{T}_{1}}$ and $p_{\mathrm{T}_{2}}$ are the leading and subleading jet transverse momenta, respectively. The results are presented as a function of $p_{\mathrm{T}_{1}}$ and collision centrality. The results were obtained by measuring the two-dimensional $p_{\mathrm{T}_{1}}-p_{\mathrm{T}_{2}}$ distributions and applying an unfolding procedure to account for experimental resolution in the measurement of both jets' transverse momenta simultaneously. The distributions are found to be similar in peripheral Pb+Pb collisions and $pp$ collisions, but highly modified in central Pb+Pb collisions. The results are consistent with expectations from partonic energy loss. | ||
| Figures | ||
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Figure 1: The symmetrised two-dimensional pT1-pT2 distributions for Pb+Pb data in the 0-10% (left) and 60-80% (center) centrality bins and for pp data (right). The dashed lines indicate the boundaries used in selecting the different triggers. The Pb+Pb data distributions have their combinatoric contribution subtracted. png (73kB), pdf (23kB) |
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Figure 2: The (1⁄N)dN⁄dxJ distributions for pairs with 100 < pT1 < 126 GeV for different collision centralities. The Pb+Pb data is shown in red, while the pp distribution is shown for comparison in blue, and is the same in all panels. Statistical uncertainties are indicated by the error bars while systematic uncertainties are shown with shaded boxes. png (48kB), pdf (30kB) |
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Figure 3: The (1⁄N)dN⁄dxJ distributions for different selections on pT1, shown for the 0-10% centrality bin (red) and for pp (blue). Statistical uncertainties are indicated by the error bars while systematic uncertainties are shown with shaded boxes. png (34kB), pdf (25kB) |
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| Auxiliary figures and tables | ||
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Figure 1: The (1⁄N)dN⁄dxJ distributions for pairs with 126 < pT1 < 158 GeV for different collision centralities. The Pb+Pb data is shown in red, while the pp distribution is shown for comparison in blue, and is the same in all panels. Statistical uncertainties are indicated by the error bars while systematic uncertainties are shown with shaded boxes. png (48kB), pdf (31kB) |
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Figure 2: The (1⁄N)dN⁄dxJ distributions for different selections on pT1, shown for the 20-30% centrality bin (red) and for pp (blue). Statistical uncertainties are indicated by the error bars while systematic uncertainties are shown with shaded boxes. png (34kB), pdf (25kB) |
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Figure 3: The (1⁄N)dN⁄dxJ distributions for different selections on pT1, shown for the 60-80% centrality bin (red) and for pp (blue). Statistical uncertainties are indicated by the error bars while systematic uncertainties are shown with shaded boxes. png (33kB), pdf (25kB) |
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Figure 4: The (1⁄N)dN⁄dxJ before (black) and after unfolding (red) shown for 100 < pT1 < 126 GeV, for 0-10% (left), 60-80% (center) Pb+Pb collisions and for pp collisions (right). Statistical uncertainties are indicated by the error bars while systematic uncertainties are shown for the unfolded results with shaded boxes. png (14kB), pdf (22kB) |
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