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| CMS-PAS-FSQ-16-009 | ||
| Measurement of double parton scattering in same-sign WW production in p-p collisions at $\sqrt{s}= $ 13 TeV with the CMS experiment | ||
| CMS Collaboration | ||
| March 2017 | ||
| Abstract: Same-sign $\mathrm{ W^{\pm} W^{\pm} }$ production in which the bosons originate from two distinct parton-parton interactions within the same proton-proton collision is studied in the $\mu^{\pm}\mu^{\pm}$ and $\mathrm{e}^{\pm}\mu^{\pm}$ final states. A data set of 35.9 fb$^{-1}$ of proton-proton collisions at $\sqrt{s}= $ 13 TeV, recorded with the CMS detector at the LHC in 2016, is used. A multivariate classifier is trained to distinguish the signal process from the main background components. A measurement of the double-parton scattering process WW is performed on these data. A cross section of 1.09$^{+0.50}_{-0.49}$ pb is extracted for the inclusive WW double parton scattering process, which is compatible with the Monte-Carlo prediction of 1.64 pb. | ||
| Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Schematic diagram of the $\mathrm{ W^{\pm }W^{\pm } }$ DPS process (left) and the leading Feynman diagrams of the corresponding SPS process $\mathrm{ W^{\pm }W^{\pm }jj }$ (right). |
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Figure 1-a:
Schematic diagram of the $\mathrm{ W^{\pm }W^{\pm } }$ DPS process. |
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Figure 1-b:
Leading Feynman diagrams of the corresponding SPS process $\mathrm{ W^{\pm }W^{\pm }jj }$. |
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Figure 2:
Input variables to the BDT training. All backgrounds and the signal are shown in colored histograms with the data shown in black markers. The statistical (dark blue), and systematic (light blue) uncertainty bands are shown in the ratio below the distributions. The variables are from left to right and top to bottom: $p_{\mathrm{T,1}}$, $p_{\mathrm{T,2}}$, ${E_{\mathrm {T}}^{\text {miss}}} $, $\eta _1 \times \eta _2$, $|\eta _1 + \eta _2|$, $M_{\mathrm{T2}}^{\ell \ell }$ , $M_{\mathrm{T},(\ell _1, {E_{\mathrm {T}}^{\text {miss}}} )}$, $M_{\mathrm{T},(\ell _1,\ell _2)}$, $|\Delta \phi _{(\ell _1,\ell _2)}|$, $|\Delta \phi _{(\ell \ell ,\ell _2)}|$, $|\Delta \phi _{(\ell _2, {E_{\mathrm {T}}^{\text {miss}}} )}|$, and the BDT discriminator output distribution. |
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Figure 2-a:
The $p_{\mathrm{T,1}}$ distribution. All backgrounds and the signal are shown in colored histograms with the data shown in black markers. The statistical (dark blue), and systematic (light blue) uncertainty bands are shown in the ratio below the distributions. |
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Figure 2-b:
The $p_{\mathrm{T,2}}$ distribution. All backgrounds and the signal are shown in colored histograms with the data shown in black markers. The statistical (dark blue), and systematic (light blue) uncertainty bands are shown in the ratio below the distributions. |
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Figure 2-c:
The ${E_{\mathrm {T}}^{\text {miss}}} $ distribution. All backgrounds and the signal are shown in colored histograms with the data shown in black markers. The statistical (dark blue), and systematic (light blue) uncertainty bands are shown in the ratio below the distributions. |
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Figure 2-d:
The $\eta _1 \times \eta _2$ distribution. All backgrounds and the signal are shown in colored histograms with the data shown in black markers. The statistical (dark blue), and systematic (light blue) uncertainty bands are shown in the ratio below the distributions. |
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Figure 2-e:
The $|\eta _1 + \eta _2|$ distribution. All backgrounds and the signal are shown in colored histograms with the data shown in black markers. The statistical (dark blue), and systematic (light blue) uncertainty bands are shown in the ratio below the distributions. |
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Figure 2-f:
The $M_{\mathrm{T2}}^{\ell \ell }$ distribution. All backgrounds and the signal are shown in colored histograms with the data shown in black markers. The statistical (dark blue), and systematic (light blue) uncertainty bands are shown in the ratio below the distributions. |
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Figure 2-g:
The $M_{\mathrm{T},(\ell _1, {E_{\mathrm {T}}^{\text {miss}}} )}$ distribution. All backgrounds and the signal are shown in colored histograms with the data shown in black markers. The statistical (dark blue), and systematic (light blue) uncertainty bands are shown in the ratio below the distributions. |
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Figure 2-h:
The $M_{\mathrm{T},(\ell _1,\ell _2)}$ distribution. All backgrounds and the signal are shown in colored histograms with the data shown in black markers. The statistical (dark blue), and systematic (light blue) uncertainty bands are shown in the ratio below the distributions. |
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Figure 2-i:
The $|\Delta \phi _{(\ell _1,\ell _2)}|$ distribution. All backgrounds and the signal are shown in colored histograms with the data shown in black markers. The statistical (dark blue), and systematic (light blue) uncertainty bands are shown in the ratio below the distributions. |
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Figure 2-j:
The $|\Delta \phi _{(\ell \ell ,\ell _2)}|$ distribution. All backgrounds and the signal are shown in colored histograms with the data shown in black markers. The statistical (dark blue), and systematic (light blue) uncertainty bands are shown in the ratio below the distributions. |
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Figure 2-k:
The $|\Delta \phi _{(\ell _2, {E_{\mathrm {T}}^{\text {miss}}} )}|$ distribution. All backgrounds and the signal are shown in colored histograms with the data shown in black markers. The statistical (dark blue), and systematic (light blue) uncertainty bands are shown in the ratio below the distributions. |
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Figure 2-l:
The BDT discriminator output |
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Figure 3:
Final BDT classifier output with all background estimations in place for $\mathrm{e}\mu $ in the two charges in the top row and $\mu \mu $ in the bottom row. Observed data are shown in black markers with the signal pre-fit expectation as a red histogram and separately imposed as a red line to show the behavior of the signal in the BDT classifier. All backgrounds are shown with their post-fit values and uncertainties in the other colored histograms. Each plot features a ratio histogram showing the data compared to the background expectation with post-fit uncertainties. |
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Figure 3-a:
Final BDT classifier output with all background estimations in place for $\mathrm{e}^{-}\mu^{-} $. Observed data are shown in black markers with the signal pre-fit expectation as a red histogram and separately imposed as a red line to show the behavior of the signal in the BDT classifier. All backgrounds are shown with their post-fit values and uncertainties in the other colored histograms. Each plot features a ratio histogram showing the data compared to the background expectation with post-fit uncertainties. |
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Figure 3-b:
Final BDT classifier output with all background estimations in place for $\mathrm{e}^{+}\mu^{+} $. Observed data are shown in black markers with the signal pre-fit expectation as a red histogram and separately imposed as a red line to show the behavior of the signal in the BDT classifier. All backgrounds are shown with their post-fit values and uncertainties in the other colored histograms. Each plot features a ratio histogram showing the data compared to the background expectation with post-fit uncertainties. |
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Figure 3-c:
Final BDT classifier output with all background estimations in place for $\mu^{-} \mu^{-} $. Observed data are shown in black markers with the signal pre-fit expectation as a red histogram and separately imposed as a red line to show the behavior of the signal in the BDT classifier. All backgrounds are shown with their post-fit values and uncertainties in the other colored histograms. Each plot features a ratio histogram showing the data compared to the background expectation with post-fit uncertainties. |
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Figure 3-d:
Final BDT classifier output with all background estimations in place for $\mu^{+} \mu^{+} $. Observed data are shown in black markers with the signal pre-fit expectation as a red histogram and separately imposed as a red line to show the behavior of the signal in the BDT classifier. All backgrounds are shown with their post-fit values and uncertainties in the other colored histograms. Each plot features a ratio histogram showing the data compared to the background expectation with post-fit uncertainties. |
| Tables | |
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Table 1:
Kinematic event selection requirements. |
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Table 2:
Summary of pre-fit systematic uncertainties for all background (and signal) components. |
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Table 3:
Expected background and signal yields and, observed event counts in the four charge and flavor combinations. |
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Table 4:
Results obtained from a constrained fit to the BDT classifier. |
| Summary |
|
The observed yield of the DPS WW signal process is lower than the expectation. Although from the PYTHIA-8 cross section of 1.64 pb a significance of 3.27 is expected, the measured cross section is below that value at 1.09$^{+0.50}_{-0.49}$ pb with a significance of 2.23$\sigma$. Conversely, applying the factorization approach with an expected cross section of 0.87 pb, and an expected significance of 1.81$\sigma$ results in a larger than expected cross section. The upper limit on the cross section in the absence of signal is expected to be $<$ 0.97 pb and measured to be $<$ 1.94 pb. This result presents the most precise measurement of the DPS WW process to date. |
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