CMS-EXO-12-011

CMS-EXO-12-011 ; CERN-PH-EP-2015-190
Search for W' decaying to tau lepton and neutrino in proton-proton collisions at $ \sqrt{s} = $ 8 TeV
CMS Collaboration
18 August 2015
Phys. Lett. B 755 (2016) 196
Abstract: The first search for a heavy charged vector boson in the final state with a tau lepton and a neutrino is reported, using 19.7 fb$^{-1}$ of LHC data at $\sqrt{s} = $ 8 TeV. A signal would appear as an excess of events with high transverse mass, where the standard model background is low. No excess is observed. Limits are set on a model in which the W' decays preferentially to fermions of the third generation. These results substantially extend previous constraints on this model. Masses below 2.0 to 2.7 TeV are excluded, depending on the model parameters. In addition, the existence of a W' boson with universal fermion couplings is excluded at 95% confidence level, for W' masses below 2.7 TeV. For further reinterpretation a model-independent limit on potential signals for various transverse mass thresholds is also presented.
Links: e-print arXiv:1508.04308 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; Public twiki page ; CADI line (restricted) ;

Figures	Summary	Additional Figures	References	CMS Publications

Figures
png pdf	Figure 1: Branching fractions (left-hand scale and solid lines) and total width (right-hand scale and dotted lines) for W' decays in the NUGIM, as calculated in Refs. [11,12,2]. For $\cot{\theta _E} = $ 1 the values are the same as those in the SSM, rescaled to accommodate the WH decay channel.
png pdf	Figure 2: The $ {M_{\mathrm {T}}} $ distribution after the final selection. Data points with error bars show LHC data. The horizontal error bar on each point indicates the width of the bin, which is 25 GeV for the first three bins and 50 GeV for all other bins. The filled histogram shows the background estimate discussed in the text, and the hatched area the uncertainty in this estimate. The signal shapes for different SSM W' boson masses are shown as open histograms. The cross section for SSM $M_{\mathrm{W}' } = $ 500 GeV is scaled by 0.2. In the ratio plot the bin-width is increased where needed to have at least one expected background event in each bin.
png pdf	Figure 3: Limits on the product of cross section and branching fraction into $\tau \nu $ for a SSM W' boson. The solid line shows the limit observed with 19.7 fb$^{-1}$ of data while the dashed line corresponds to the expected limit. The shaded bands indicate the 68% and 95% confidence intervals of the expected limit. The dotted and the long-dashed lines show the cross section prediction in the SSM as a function of the W' boson mass, in NNLO and LO, respectively.
png pdf	Figure 4: Limits on the NUGIM parameter space are shown from various analyses. The solid line refers to this analysis. The non-LHC limits (CKM and Lepton flavor violation) are calculated in Ref. [11]. The W' results are from Ref. [13] for the tb final state and Ref. [9] for $\mathrm{ e } \nu $ as reinterpreted in Ref. [12]. The lines correspond to 95% CL limits.
png pdf	Figure 5: Model independent limits, on the effective cross section for a W'-like signal above a threshold value $ { {M_{\mathrm {T}}} ^\text {min}} $, for different $ { {M_{\mathrm {T}}} ^\text {min}} $. The solid line shows the limit observed with 19.7 fb$^{-1}$ of data while the dashed line corresponds to the expected limit. The shaded bands indicate the 68% and 95% confidence intervals of the expected limit. The region above the curve is excluded.

Summary

In summary, the first search for an excess in the transverse mass distribution of the $\tau{+}E_{\mathrm{T}}^{\text{miss}}$ channel has been performed. The data sample was collected with the CMS detector in proton-proton collisions at $ \sqrt{s} = $ 8 TeV, and corresponds to an integrated luminosity of 19.7 fb$^{-1}$. No significant excess beyond the SM expectation is observed. An SSM W' boson is excluded in the mass range 0.3 TeV $ < M_{\mathrm{ W}'} < $ 2.7 TeV at 95% confidence level. Within the NUGIM the lower limit on the W'-boson mass depends on the coupling constant $\cot \theta_E$ and varies from 2.0 to 2.7 TeV at 95% confidence level. In summary, the first search for an excess in the transverse mass distribution of the tau+$ E_{\mathrm{T}}^{\text{miss}} $ channel has been performed. The data sample was collected with the CMS detector in proton-proton collisions at $ \sqrt{s} =$ 8 TeV, and corresponds to an integrated luminosity of 19.7 fb$^{-1}$. No significant excess beyond the SM expectation is observed. An SSM W' boson is excluded in the mass range 0.3 TeV $ < M_{\mathrm{W}'} <$ 2.7 TeV at 95% confidence level. Within the NUGIM the lower limit on the W'-boson mass depends on the coupling constant $ \cot { \theta_E} $ and varies from 2.0 to 2.7 TeV at 95% confidence level.

Additional Figures
png pdf	Additional Figure 1: Sketch of the ABCD method. Region A is used to obtain a QCD template sample, region C and D is used to determine the normalization and region B is the signal region. The variable to distinguish the signal and QCD region is $p_{\mathrm{T}}/ E_{\mathrm {T}}^{\text {miss}}$.
png pdf	Additional Figure 2: Tight-to-loose ratio split in the various tau decay signatures.
png pdf	Additional Figure 3: Relative systematic uncertainties on the number of background events.
png pdf	Additional Figure 4: The simulated backgrounds are shown for the kinematic distributions $\Delta \phi (\tau, E_{\mathrm {T}}^{\text {miss}} )$.
png pdf	Additional Figure 5: The simulated backgrounds are shown for the kinematic distributions $ {p_{\mathrm {T}}}^{\tau }/ {E_{\mathrm {T}}^{\text {miss}}} $.
png pdf	Additional Figure 6: The simulated backgrounds are shown for the kinematic distributions $ {M_\mathrm {T}}$.
png pdf	Additional Figure 7: Distribution of the transverse mass $ {M_\mathrm {T}}$ at generator and reconstruction level for various $ { {\mathrm {W}} ^{\prime }}$ masses.
png pdf	Additional Figure 8: Distribution of the transverse mass $ {M_\mathrm {T}}$ at generator level for various $\cot{\theta _{E}}$.
png pdf	Additional Figure 9: Distribution of the invariant mass $ {M_{\tau \nu}}$ at generator level for various $\cot{\theta _{E}}$.
png pdf	Additional Figure 10: Signal efficiencies for various $ { {\mathrm {W}} ^{\prime } }$ masses. The blue rectangles denote the trigger efficiency. The red dots denote the efficiency to tigger an event and reconstruct exactly one isolated $\tau $ in the event. The green rectangles denote the two previous efficiencies times the efficiency of the kinematic selection. All efficiencies are given with respect all $ { {\mathrm {W}} ^{\prime } } \rightarrow \tau \nu $ decays.
png pdf	Additional Figure 11: Event display for the event with the highest $ {M_\mathrm {T}} $.

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