CMS logoCMS event Hgg
Compact Muon Solenoid
LHC, CERN

CMS-PAS-SMP-15-001
Combination of results from the ATLAS and CMS experiments on anomalous triple gauge couplings from ${ZZ}$ production in ${pp}$ collisions at a center-of-mass energy of 7 TeV at the LHC
Abstract: A procedure is presented to combine data from the ATLAS and CMS experiments on $ZZ$ production to obtain constraints on anomalous neutral triple gauge boson couplings. Statistical and systematic uncertainties and their correlations are taken into account. Data from $pp$ collisions at a center-of-mass energy of 7 TeV delivered by the LHC are used. The datasets correspond to integrated luminosities of 4.6 and 5.0 fb$^{-1}$ for ATLAS and CMS, respectively. The combination is performed in the fully leptonic decay channels $ZZ \to \ell^+ \ell^- \nu \bar{\nu}$ (ATLAS) and $ZZ \to \ell^+ \ell^- \ell'^+ \ell'^-$ (ATLAS, CMS). Combined limits on the coupling parameters are $ -0.010 < f_4^\gamma < 0.011 $, $ -0.0087 < f_4^Z < 0.0091 $, $ -0.011 < f_5^\gamma < 0.010 $, and $ -0.0091 < f_5^Z < 0.0089 $ at 95% C.L., where all other parameters are fixed to the standard model values. These results represent the first combined limits of the ATLAS and CMS collaborations for anomalous gauge boson couplings.
Figures & Tables Summary References CMS Publications
Figures

png pdf
Figure 1:
One-parameter observed deltaNLL limits on aTGCs for $\Lambda = \infty $. All anomalous coupling parameters other than the measured one are set to their SM values.

png pdf
Figure 2-a:
Two-parameter expected and observed deltaNLL combined limits on aTGCs for $\Lambda = \infty $. All anomalous coupling parameters other than the measured one are set to their SM values.

png pdf
Figure 2-b:
Two-parameter expected and observed deltaNLL combined limits on aTGCs for $\Lambda = \infty $. All anomalous coupling parameters other than the measured one are set to their SM values.
Tables

png pdf
Table 1:
Observed and predicted event yields in bins of leading $Z$ ${p_{\mathrm {T}}}$ in the $ZZ \to \ell ^+ \ell ^- \ell '^+ \ell '^-$ channel for ATLAS. The first uncertainty is statistical while the second is systematic.

png pdf
Table 2:
Observed and predicted event yields in the $ZZ \to \ell ^+ \ell ^- \bar{\nu } \nu $ channel for ATLAS. The first uncertainty is statistical while the second is systematic.

png pdf
Table 3:
Summary of systematic uncertainties, as relative percentages of the correction factor $C_{ { {Z} {Z}} }$ or the acceptance $A_{ { {Z} {Z}} }$ of the fiducial region for ATLAS.

png pdf
Table 4:
Observed and predicted number of $ {Z} {Z}$ events for CMS.

png pdf
Table 5:
Relative systematic uncertainties in the $ZZ$ measurement for CMS.

png pdf
Table 6:
List of fully correlated uncertainties between experiments.

png pdf
Table 7:
List of uncorrelated uncertainties between experiments.

png pdf
Table 8:
Expected 95% confidence intervals from one-parameter fits for ATLAS, CMS and combined ATLAS and CMS experimental data inputs and for $\Lambda = \infty $. All anomalous coupling parameters other than the measured one are set to their SM values.

png pdf
Table 9:
Observed 95% confidence intervals from one-parameter fits for ATLAS, CMS and combined ATLAS and CMS experimental data inputs and for $\Lambda = \infty $. All anomalous coupling parameters other than the measured one are set to their SM values.
Summary
The combination of anomalous TGC limits from ATLAS and CMS using the $ZZ$ production channel in $pp$ collisions at a center-of-mass energy of 7 TeV at the LHC is presented. The datasets correspond to integrated luminosities of $4.6$ and 5.0 fb$^{-1}$ for ATLAS and CMS, respectively. Combined 95% C.L. limits from one-parameter fits on aTGC parameters are: $ -0.010 < f_4^\gamma < 0.011$, $ -0.0087 < f_4^Z < 0.0091$, $ -0.011 < f_5^\gamma < 0.010$, $-0.0091 < f_5^Z < 0.0089 $. The combination improves the sensitivity to aTGC parameters by about 20% relative to the sensitivity of a single experiment. Negligible is the effect of the systematic uncertainties on the limits on aTGC parameters. These results represent the first combined limits of the ATLAS and CMS collaborations for anomalous gauge boson couplings. Nevertheless, they are not competitive with respect to recent results using 8 TeV data from the LHC [21] because of the larger data-set with four times the integrated luminosity compared to 7 TeV data-set. This analysis outlines a combination procedure that can serve as guidance for future combinations of aTGC parameters at the LHC.
References
1 ATLAS Collaboration Measurement of $ ZZ $ production in $ pp $ collisions at $ \sqrt{s}=7 $ TeV and limits on anomalous $ ZZZ $ and $ ZZ\gamma $ couplings with the ATLAS detector JHEP 1303 (2013) 128 1211.6096
2 M. Cacciari, G. P. Salam, and G. Soyez The Anti-k(t) jet clustering algorithm JHEP 0804 (2008) 063 0802.1189
3 ATLAS Collaboration Measurement of the top quark pair cross section with ATLAS in pp collisions at $ \sqrt(s) = 7 $ TeV using final states with an electron or a muon and a hadronically decaying $ \tau $ lepton PLB717 (2012) 89--108 1205.2067
4 ATLAS Collaboration Improved luminosity determination in pp collisions at sqrt(s) = 7 TeV using the ATLAS detector at the LHC EPJC73 (2013), no. 8 1302.4393
5 ATLAS Collaboration Luminosity Determination in $ pp $ Collisions at $ \sqrt{s}=7 $ TeV Using the ATLAS Detector at the LHC EPJC71 (2011) 1630 1101.2185
6 CMS Collaboration Measurement of the $ ZZ $ production cross section and search for anomalous couplings in 2l2l ' final states in $ pp $ collisions at $ \sqrt{s}=7 $ TeV JHEP 1301 (2013) 063 CMS-SMP-12-007
1211.4890
7 CMS Collaboration Collaboration Absolute Calibration of the Luminosity Measurement at CMS: Winter 2012 Update Technical Report CMS-PAS-SMP-12-008, CERN, Geneva
8 K. Hagiwara et al. Probing the weak boson sector in $ \text{e}^+\text{e}^- \rightarrow W^+W^- $ Nucl. Phys. B 282 (1987) 253
9 U. Baur and D. L. Rainwater Probing neutral gauge boson selfinteractions in $ ZZ $ production at the Tevatron Int. J. Mod. Phys. A16S1A (2001) 315--317 hep-ph/0011016
10 T. Gleisberg et al. Event generation with SHERPA 1.1 JHEP 02 (2009) 007 0811.4622
11 G. Cowan, K. Cranmer, E. Gross, and O. Vitells Asymptotic formulae for likelihood-based tests of new physics EPJC71 (2011) 1554, , [Erratum: Eur. Phys. J.C73,2501(2013)] 1007.1727
12 G. J. Feldman and R. D. Cousins A Unified approach to the classical statistical analysis of small signals PRD57 (1998) 3873--3889 physics/9711021
13 T. Junk Confidence level computation for combining searches with small statistics NIMA434 (1999) 435--443 hep-ex/9902006
14 A. L. Read Presentation of search results: the CL s technique Journal of Physics G: Nuclear and Particle Physics 28 (2002), no. 10
15 The ATLAS Collaboration, The CMS Collaboration, The LHC Higgs Combination Group Collaboration Procedure for the LHC Higgs boson search combination in Summer 2011 CMS-NOTE-2011-005
16 S. M. Lee and G. A. Young Parametric bootstrapping with nuisance parameters Statistics and Probability Letters 71 (2005), no. 2, 143 -- 153
17 B. Efron Bootstrap Methods: Another Look at the Jackknife Ann. Statist. 7 (01, 1979) 1--26
18 H.-L. Lai et al. New parton distributions for collider physics PRD 82 (2010) 074024 1007.2241
19 A. Martin, W. Stirling, R. Thorne, and G. Watt Parton distributions for the LHC EPJC 63 (2009) 189 0901.0002
20 M. Botje et al. The PDF4LHC Working Group Interim Recommendations 1101.0538
21 CMS Collaboration Measurement of the $ pp \to ZZ $ production cross section and constraints on anomalous triple gauge couplings in four-lepton final states at $ \sqrt s= $8 TeV PLB740 (2015) 250--272 CMS-SMP-13-005
1406.0113
Compact Muon Solenoid
LHC, CERN