A measurement of the Higgs boson mass and width via its decay to two Z bosons
is presented. Proton-proton collision data collected by the CMS experiment, corresponding to an integrated luminosity of 138 fb^−1
at a center-of-mass energy of 13 TeV,
is used. The invariant mass distribution of four leptons in the on-shell Higgs boson
decay is used to measure its mass and constrain its width. This yields the most precise
single measurement of the Higgs boson mass to date, 125.04
± 0.12 GeV, and an upper
limit on the width
Γ
H
< 330 MeV at 95% confidence level. A combination of the on-and off-shell Higgs boson production decaying to four leptons is used to determine
the Higgs boson width, assuming that no new virtual particles affect the production, a premise that is tested by adding new heavy particles in the gluon fusion loop
model. This result is combined with a previous CMS analysis of the off-shell Higgs
boson production with decay to two leptons and two neutrinos, giving a measured
Higgs boson width of 3.0
+2.0, −1.5 MeV, in agreement with the standard model prediction
of 4.1 MeV. The strength of the off-shell Higgs boson production is also reported.
The scenario of no off-shell Higgs boson production is excluded at a confidence level
corresponding to 3.8 standard deviations.
Higgs boson mass and width measurements with on-shell production
The Higgs boson mass and width are measured, using on-shell production, by fitting the m4â„“ distribution in the mass range 105 < m4â„“ < 140 GeV. The results have been determined using the CMS statistical analysis tool
COMBINE, which is based on the ROOFIT and ROOSTATS frameworks.
Table 1 shows the mass measurements obtained from the 1D approach, where no further assumptions have been made. In comparison to the 1D model, the 1D′BS model reduces the uncertainty by about 15%. Implementing the δm4â„“/m4â„“ categorization
then gives the N –1D′BS model, which leads to an additional 10% improvement. Finally, using
the D kin, bkg discriminant to reduce the background produces the N –2D′BS model with another
4% improvement. Table 5 shows the resulting m4â„“ measurements using this last model. All the measured m4â„“ values from the different fits are statistically compatible, given their uncertainties and correlations. Figure 1 displays the observed 1D likelihood scans as functions of
mH, from the fits for the different 4â„“ categories and combined. Combining all the m4â„“ final
states and data-taking years, our final result is mH = 125.04 ± 0.11 (stat) ± 0.05 (syst) =
125.04 ± 0.12 GeV. The largest systematic uncertainty is from the lepton momentum scale and
equals 0.03 and 0.04 GeV for final states with muons and electrons, respectively.
Table 1: Best fit values for the mass of the Higgs boson measured in the inclusive 4â„“ final state and separately for different flavor categories using the 1D approach. Uncertainties are separated into statistical and systematic uncertainties. Expected uncertainties are also given assuming mH = 125.38 GeV
Table 2: Best fit values for the mass of the Higgs boson measured in the inclusive 4â„“ final state and separately for different flavor categories, using the final fit configuration (N –2D’BS). Uncertainties are separated into statistical and systematic uncertainties. Expected uncertainties are also given assuming mH = 125.38 GeV.
As a check on the analysis technique and the systematic uncertainty from this method, the
1D′BS model is applied to Z → 4â„“ events in the m4â„“ range 70–105 GeV. The signal shape is
obtained using a convolution of a Breit–Wigner function and a double-sided Crystal Ball function. The fitted values of mZ in different subchannels are m4µ
Z = 91.02 ± 0.14 GeV, m4e
Z =
91.18 ± 0.45 GeV, m2e2µ
Z = 91.40 ± 0.29 GeV, and m2e2µ Z = 91.40 ± 0.37 GeV, leading to a combined value of mZ = 91.17 ± 0.12 GeV, consistent with the world-average Z boson mass and with the uncertainty in agreement with the expected value of ± 0.12 GeV from simulation.
The results from this analysis are combined with those extracted using data recorded with the
CMS detector during Run 1 at √
s = 7 and 8 TeV. Since this analysis uses an improved
method to extract the systematic uncertainties affecting lepton momentum, the lepton energy
scales and resolution uncertainties are considered uncorrelated between the two runs. The combined observed result from both data-taking periods is mH = 125.08 ± 0.12 GeV = 125.08 ±
0.10 (stat)±0.05 (syst) GeV. The corresponding expected statistical and systematic uncertainties
are ±0.10 and ±0.05 GeV, respectively. Figure 2 presents a summary of the Higgs boson mass
measurements by the CMS Collaboration in the four-lepton decay channel.
Figure 1: The profile likelihood from the mH fit using the N –2D′BS model for each of the 4â„“ categories and combined. The change in likelihood corresponding to 68 and 95% CLs are shown
by the dashed horizontal lines. Both statistical and systematic uncertainties are included in the
fits.
Figure 2: Summary of the CMS Higgs boson mass measurements using the four-lepton final
state. The red vertical line and the gray column represent the best fit value and the total uncertainty, respectively, as measured by combining the Runs 1 and 2 data. The yellow band and
horizontal black bars show the statistical and total uncertainties in each measurement, respectively. The value of each measurement is given, along with the total and statistical only (in
parentheses) uncertainties.
Higgs boson width measurement with off-shell production
Table 3: Summary of the total Higgs boson width ΓH measurement, showing the 68% CL (central values with uncertainties) and 95% CL (in square brackets) intervals for the H → ZZ → 4â„“
channel alone and in combination with the off-shell H → ZZ → 2â„“2ν channel.
Figure 3: Observed (solid) and expected (dashed) profile likelihood projections from the Higgs
boson width fit using on- and off-shell production from this analysis. The analysis of the offshell H → ZZ → 4â„“ channel combined with the on-shell H → ZZ → 4â„“ channel is shown
in black. The full combination of H → ZZ → 4â„“ with the off-shell H → ZZ → 2â„“2ν is
given in red. The black horizontal dashed lines show the 68 and 95% CL values.
The observed limits on ΓH are stronger than the average expected values from simulation.
This is supported by the upper left, where the number of observed events in the
sensitive region of m4â„“ > 340 GeV and Dbkg > 0.6 in the Untagged category is below the expected value, but still consistent with it. The smaller number of events in this region favors the
hypothesis of negative interference between the signal and background contributions, which
dominates over the pure signal contributions for ΓH values near the SM value. Therefore, large
and very small values of ΓH are disfavored.
A measurement of the Higgs boson mass (mH) and width (ΓH) using the decays to two Z
bosons is presented. The data sample comes from proton-proton collisions at the LHC recorded
by the CMS experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated
luminosity of 138 fb−1
. On-shell Higgs boson production with the H → 4â„“ decay (â„“ = e, µ) is
used to measure its mass and constrain its width. The mass measurement yields mH = 125.04±
25.
Table 4: Measured values of the signal strengths µ off-shell
, µ
off-shell, F
, and µ
off-shell, V
, and their 68%
and 95% (in square brackets) CL intervals from the combined fit to the off-shell H → ZZ → 4â„“
and 2ℓ2ν channels.
Figure 4: Observed 2D profile likelihood projection of the off-shell signal strength parameters
(µ off-shell, F , and µ off-shell, V ) from the fit to the combined off-shell H → ZZ → 4â„“ and 2â„“2ν channels. The
best fit value is shown by the black cross and the SM prediction by the red x. The 68 and 95%
CL contours are given by the dashed and solid curves, respectively. The color scale to the right
of the plot relates the quantitative values.
0.11 (stat) ± 0.05 (syst) GeV = 125.04 ± 0.12 GeV, in agreement with the expected precision of
±0.12 GeV. From on-shell production events, an upper limit of ΓH < 330 MeV is set at 95%
confidence level. The mass measurement is further improved by combining data from Runs
1 and 2, leading to the most precise single measurement of the mass to date in this channel,
mH = 125.08 ± 0.10 (stat) ± 0.05 (syst) GeV = 125.08 ± 0.12 GeV. Using on- and off-shell Higgs
boson production with the decay to four leptons, and combining them with a separate analysis
with Higgs boson decay to two leptons plus two neutrinos, we measure ΓH = 3.0+2.0, −1.5 MeV,
consistent with the standard model prediction of 4.1 MeV. These results are summarized in
Table 5. The strength of the off-shell Higgs boson production is also reported, and the scenario
of no off-shell Higgs boson production is excluded at a confidence level corresponding to 3.8
standard deviations. Results of the measurements are tabulated in the HEPData record for this
analysis.
Table 5: Summary of the Higgs boson mass and total width ΓH measurements, showing the
allowed 68% CL (central values with uncertainties) and 95% CL (in square brackets) intervals.
Uncertainties are reported as a combination of statistical and systematic uncertainties. The first
two rows display the outcomes of the analysis conducted within the on-shell H → ZZ → 4â„“
region, where the width is restricted to be positive. The third row incorporates results from the
off-shell H → ZZ → 4â„“ region combined with the on-shell H → ZZ → 4â„“ and off-shell
H → ZZ → 2â„“2ν.
====== Physics =======
Read more:
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