Improved $W$ boson Mass Measurement using $\sqrt{s}=7$ TeV Proton-Proton Collisions with the ATLAS Detector

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Improved $W$ boson Mass Measurement using $\sqrt{s}=7$ TeV Proton-Proton Collisions with the ATLAS Detector ATLAS-CONF-2023-004 22 March 2023
Main document (CDS record), Physics Briefing - internal	pdf from CDS
Figures Tables	-
Abstract
The $W$ boson mass is one of the most interesting fundamental parameters of the Standard Model of particle physics, as it allows for model-independent probes for effects of new physics. In this work, proton-proton data recorded by the ATLAS detector in 2011, at a center of mass energy of $7 \text{TeV}$, that were used for the first $W$ boson mass measurement at the LHC, have been reanalyzed with an advanced fitting technique based on a profile likelihood approach. This allows for a reduction of several systematic uncertainties. Advances in the modelling of the parton density functions of the proton in recent years have been taken into account and a more modern PDF set has been chosen as baseline. The updated measurement yields a preliminary value of $m_W = 80360 \pm 5 (\text{stat.}) \pm 15 (\text{syst.}) = 80360 \pm 16 \text{MeV}$, where the first uncertainty component is statistical and the second corresponds to the experimental and physics-modelling systematic uncertainty. This result is compatible with the published value and its uncertainty improved by 15%.
Figures
Figure 01a: Overview of the m_W fit results in all categories for the p_T^ℓ (left) and the m_T (right) distributions, with the CT10nnlo PDF set. The results are determined using a PLH approach and in comparison with a χ²-minimization approach using statistical uncertainties only, following the previous measurement [8]. Also shown is the result when using all categories simultaneously. png (169kB) eps (31kB)
Figure 01b: Overview of the m_W fit results in all categories for the p_T^ℓ (left) and the m_T (right) distributions, with the CT10nnlo PDF set. The results are determined using a PLH approach and in comparison with a χ²-minimization approach using statistical uncertainties only, following the previous measurement [8]. Also shown is the result when using all categories simultaneously. png (168kB) eps (31kB)
Figure 02a: Spread of m_W fit results for 1000 random variations of all sources of systematic uncertainty, using the p_T^ℓ distribution (left) and the m_T distribution (right), and the CT10nnlo PDF set. png (54kB) pdf (17kB)
Figure 02b: Spread of m_W fit results for 1000 random variations of all sources of systematic uncertainty, using the p_T^ℓ distribution (left) and the m_T distribution (right), and the CT10nnlo PDF set. png (54kB) pdf (17kB)
Figure 03a: Distribution of pull significances for all individual NPs in the combined PLH fits using the p_T^ℓ (left) and the m_T (right) distributions. png (52kB) pdf (16kB)
Figure 03b: Distribution of pull significances for all individual NPs in the combined PLH fits using the p_T^ℓ (left) and the m_T (right) distributions. png (52kB) pdf (16kB)
Figure 04a: Fitted m_W values for different PDF-Sets using the p_T^ℓ distribution (left) and m_T distribution (right). png (58kB) pdf (15kB)
Figure 04b: Fitted m_W values for different PDF-Sets using the p_T^ℓ distribution (left) and m_T distribution (right). png (58kB) pdf (15kB)
Figure 05a: Ranking of 10 nuisance parameters inducing the largest shift of the m_W central value in the combined PLH fits using the p_T^ℓ (left) and the m_T (right) distributions with the CT18 PDF set. The shifts are calculated by multiplying the post-fit pull value of a given NP with its pre-fit impact on the central value (pre-fit impact is calculated with no pull and a constraint of ± 1). png (66kB) pdf (15kB)
Figure 05b: Ranking of 10 nuisance parameters inducing the largest shift of the m_W central value in the combined PLH fits using the p_T^ℓ (left) and the m_T (right) distributions with the CT18 PDF set. The shifts are calculated by multiplying the post-fit pull value of a given NP with its pre-fit impact on the central value (pre-fit impact is calculated with no pull and a constraint of ± 1). png (65kB) pdf (15kB)
Figure 06a: Post-fit distributions of p_T^ℓ (left) and m_T (right) with data and MC for W⁺→ e⁺ν_e (first row), W^-→ e^-ν_e (second row), W⁺→ μ⁺ν_μ (third row), W^-→ μ^-ν_μ (fourth row), inclusive over all η regions, and using the CT18 PDF set. The ratio indicates also the difference to the data before the fit. png (121kB) eps (2MB)
Figure 06b: Post-fit distributions of p_T^ℓ (left) and m_T (right) with data and MC for W⁺→ e⁺ν_e (first row), W^-→ e^-ν_e (second row), W⁺→ μ⁺ν_μ (third row), W^-→ μ^-ν_μ (fourth row), inclusive over all η regions, and using the CT18 PDF set. The ratio indicates also the difference to the data before the fit. png (123kB) eps (2MB)
Figure 06c: Post-fit distributions of p_T^ℓ (left) and m_T (right) with data and MC for W⁺→ e⁺ν_e (first row), W^-→ e^-ν_e (second row), W⁺→ μ⁺ν_μ (third row), W^-→ μ^-ν_μ (fourth row), inclusive over all η regions, and using the CT18 PDF set. The ratio indicates also the difference to the data before the fit. png (127kB) eps (2MB)
Figure 06d: Post-fit distributions of p_T^ℓ (left) and m_T (right) with data and MC for W⁺→ e⁺ν_e (first row), W^-→ e^-ν_e (second row), W⁺→ μ⁺ν_μ (third row), W^-→ μ^-ν_μ (fourth row), inclusive over all η regions, and using the CT18 PDF set. The ratio indicates also the difference to the data before the fit. png (129kB) eps (2MB)
Figure 06e: Post-fit distributions of p_T^ℓ (left) and m_T (right) with data and MC for W⁺→ e⁺ν_e (first row), W^-→ e^-ν_e (second row), W⁺→ μ⁺ν_μ (third row), W^-→ μ^-ν_μ (fourth row), inclusive over all η regions, and using the CT18 PDF set. The ratio indicates also the difference to the data before the fit. png (122kB) eps (2MB)
Figure 06f: Post-fit distributions of p_T^ℓ (left) and m_T (right) with data and MC for W⁺→ e⁺ν_e (first row), W^-→ e^-ν_e (second row), W⁺→ μ⁺ν_μ (third row), W^-→ μ^-ν_μ (fourth row), inclusive over all η regions, and using the CT18 PDF set. The ratio indicates also the difference to the data before the fit. png (122kB) eps (2MB)
Figure 06g: Post-fit distributions of p_T^ℓ (left) and m_T (right) with data and MC for W⁺→ e⁺ν_e (first row), W^-→ e^-ν_e (second row), W⁺→ μ⁺ν_μ (third row), W^-→ μ^-ν_μ (fourth row), inclusive over all η regions, and using the CT18 PDF set. The ratio indicates also the difference to the data before the fit. png (118kB) eps (2MB)
Figure 06h: Post-fit distributions of p_T^ℓ (left) and m_T (right) with data and MC for W⁺→ e⁺ν_e (first row), W^-→ e^-ν_e (second row), W⁺→ μ⁺ν_μ (third row), W^-→ μ^-ν_μ (fourth row), inclusive over all η regions, and using the CT18 PDF set. The ratio indicates also the difference to the data before the fit. png (121kB) eps (2MB)
Figure 07: The measured value of m_W is compared to SM prediction from the global electroweak fit [3], and to the combined values of m_W measured at LEP [5], Tevatron [6, 7] and the LHC [8, 9]. png (58kB) pdf (15kB)
Figure 08: The 68% and 95% confidence-level contours of the m_W and m_t indirect determinations from the global electroweak fit are compared to the 68% and 95% confidence-level contours of the ATLAS measurements of the top quark and W boson masses. png (154kB) pdf (23kB)
Figure 09a: Overview of the m_W fit results in all categories for the p_T^ℓ (left) and the m_T (right) distributions, with the CT10nnlo and CT18 PDF set. Also shown is the result when using all categories simultaneously. png (167kB) eps (30kB)
Figure 09b: Overview of the m_W fit results in all categories for the p_T^ℓ (left) and the m_T (right) distributions, with the CT10nnlo and CT18 PDF set. Also shown is the result when using all categories simultaneously. png (169kB) eps (30kB)
Figure 10a: Ranking of 10 nuisance parameters with the largest post-fit impact on m_W in the combined PLH fits using the p_T^ℓ (left) and the m_T (right) distributions with the CT18 PDF set. png (75kB) pdf (15kB)
Figure 10b: Ranking of 10 nuisance parameters with the largest post-fit impact on m_W in the combined PLH fits using the p_T^ℓ (left) and the m_T (right) distributions with the CT18 PDF set. png (75kB) pdf (15kB)
Figure 11a: Overview of the global signal normalization factors obtained from the combined PLH fits using the p_T^ℓ (left) and the m_T (right) distributions with different PDF sets. The central values of the normalization factors without PDF profiling in the combined PLH fit are also indicated. png (62kB) pdf (15kB)
Figure 11b: Overview of the global signal normalization factors obtained from the combined PLH fits using the p_T^ℓ (left) and the m_T (right) distributions with different PDF sets. The central values of the normalization factors without PDF profiling in the combined PLH fit are also indicated. png (62kB) pdf (15kB)
Figure 12: Display of a candidate W→μν event using proton-proton collisions at 7 TeV center of mass energy at the LHC. Starting from the center of the ATLAS detector, the reconstructed tracks of the charged particles in the Inner Detector (ID) are shown as cyan lines. The energy deposits in the electromagnetic (the green layer) and hadronic (the red layer) calorimeters are shown as yellow boxes. The identified muon is shown with its reconstructed track (blue line) passing through the muon chambers (blue layers). The muon has a transverse momentum of p_T=36GeV, whereas the missing transverse energy (red arrow) is 35 GeV and corresponds to the muon neutrino energy. The transverse mass of the W boson candidate is 71 GeV. The view is in the transverse plane. png (215kB)
Figure 13: Display of a candidate W→μν event using proton-proton collisions at 7 TeV center of mass energy at the LHC. Starting from the center of the ATLAS detector, the reconstructed tracks of the charged particles in the Inner Detector (ID) are shown as cyan lines. The energy deposits in the electromagnetic (the green layer) and hadronic (the red layer) calorimeters are shown as yellow boxes. The identified muon is shown with its reconstructed track (blue line) passing through the muon chambers (blue layers). The muon has a transverse momentum of p_T=36 GeV, whereas the missing transverse energy (red arrow) is 35 GeV and corresponds to the muon neutrino energy. The transverse mass of the W boson candidate is 71 GeV. The view at the top shows the transverse plane, while the one at the bottom shows the longitudinal plane. In the longitudinal view, the arrow representing the missing transverse energy has been removed for clarity. png (518kB)
Figure 14: View of a candidate W→μν event using proton-proton collisions at 7 TeV center of mass energy at the LHC. Starting from the center of the ATLAS detector, the reconstructed tracks of the charged particles in the Inner Detector (ID) are shown as red lines. The energy deposits in the calorimeters are shown as yellow boxes. The identified muon is shown as a longer red dashed line. The missing transverse momentum is shown by a green dashed line. png (4MB)
Tables
Table 01: Summary of 28 categories and kinematic distributions used in the m_W measurement for the electron and muon decay channels. png (12kB) pdf (54kB)
Table 02: Overview of fitted values of the W boson mass for different PDF sets. The reported uncertainties are the total uncertainties. png (25kB) pdf (47kB)
Table 03: Impact of the different uncertainty categories on the total uncertainty of the W boson mass measurement using PLH and the CT18 PDF-Set. The impact of each group of systematic uncertainties is defined as the quadratic difference between the total fit uncertainty, and the fit uncertainty obtained excluding this group. png (14kB) pdf (40kB)

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2024-05-14 01:28:47