CMS-SMP-14-018

CMS-SMP-14-018 ; CERN-EP-2016-308
Measurement of the cross section for electroweak production of Z$\gamma$ in association with two jets and constraints on anomalous quartic gauge couplings in proton-proton collisions at $ \sqrt{s} = $ 8 TeV
CMS Collaboration
9 February 2017
Phys. Lett. B 770 (2017) 380
Abstract: A measurement is presented of the cross section for the electroweak production of a Z boson and a photon in association with two jets in proton-proton collisions at $ \sqrt{s} = $ 8 TeV. The Z bosons are identified through their decays to electron or muon pairs. The measurement is based on data collected with the CMS detector corresponding to an integrated luminosity of 19.7 fb$^{-1}$. The electroweak contribution has a significance of 3.0 standard deviations, and the measured fiducial cross section is 1.86$_{-0.75}^{+0.90}$ (stat)$_{-0.26}^{+0.34}$ (syst) $\pm$ 0.05 (lumi) fb, while the summed electroweak and quantum chromodynamic total cross section in the same region is observed to be 5.94$_{-1.35}^{+1.53}$ (stat)$_{-0.37}^{+0.43}$ (syst) $\pm$ 0.13 (lumi) fb. Both measurements are consistent with the leading-order standard model predictions. Limits on anomalous quartic gauge couplings are set based on the Z$\gamma$ mass distribution.
Links: e-print arXiv:1702.03025 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Representative diagrams for EW $\mathrm{ Z } \gamma {\mathrm {jj}} $ production at the LHC: (a) bremsstrahlung, (b) multiperipheral, (c,d) VBF with TGC, (e) VBS including QGC, and (f) Example diagram for the QCD $\mathrm{ Z } \gamma {\mathrm {jj}} $ production.
png pdf	Figure 2: The $M_{ {\mathrm {jj}} }$ distributions measured in (left) muon and (right) electron channels. The data (solid symbols with error bars representing the statistical uncertainties) are compared to a data-driven background estimate, combined with MC predictions for the signal contribution. The hashed bands represent the full uncertainty in the predictions, as described in Section 6. The last bin includes overflow events.
png pdf	Figure 2-a: The $M_{ {\mathrm {jj}} }$ distribution measured in the muon channel. The data (solid symbols with error bars representing the statistical uncertainties) are compared to a data-driven background estimate, combined with MC predictions for the signal contribution. The hashed bands represent the full uncertainty in the predictions, as described in Section 6. The last bin includes overflow events.
png pdf	Figure 2-b: The $M_{ {\mathrm {jj}} }$ distribution measured in the electron channel. The data (solid symbols with error bars representing the statistical uncertainties) are compared to a data-driven background estimate, combined with MC predictions for the signal contribution. The hashed bands represent the full uncertainty in the predictions, as described in Section 6. The last bin includes overflow events.
png pdf	Figure 3: The invariant mass distribution of the ${\mathrm{ Z } } \gamma $ system for events that pass the aQGC selection. The highest mass bin includes events with $M_{{\mathrm{ Z } } \gamma } > $ 420 GeV. Error bars represent the statistical uncertainty in the data, while the systematic uncertainties in the aQGC signal and background estimate are shown as hatched bands.

Tables
png pdf	Table 1: Summary of the three different event criteria: (1) selection for the EW signal measurement; (2) the cross section measurement; and (3) the selection for the aQGC search. ``j1" and ``j2" represent the jets that have the largest and second-largest $ {p_{\mathrm {T}}} $, ``$\ell 1$" and ``$\ell 2$" denote the lepton and antilepton from the decay of the Z boson, $y$ is the rapidity, $\Delta \phi _{{\mathrm{ Z } } \gamma , {\mathrm {jj}} }$ is the absolute difference between $\phi _{{\mathrm{ Z } } \gamma }$ and $\phi _{\mathrm {j1j2}}$, and the angular separation $\Delta R = \sqrt {\smash [b]{(\Delta \eta )^{2}+(\Delta \phi )^{2}}}$.
png pdf	Table 2: Summary of the major uncertainties.
png pdf	Table 3: Signal and background yields after the final selection for the SM measurement, for the two bins of 400 $ $ 800 GeV (lower). Only statistical uncertainties are reported.
png pdf	Table 4: Observed and expected shape-based exclusion limits for each aQGC parameter at 95% CL, without a form factor applied.

Summary

The measurement of the cross section for the electroweak production of a Z boson and a photon in association with two jets, where the Z boson decays into electron or muon pairs, was presented. The measurement is based on a sample of proton-proton collisions collected with the CMS detector at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.7 fb$^{-1}$. We find evidence for EW $\mathrm{ Z }\gamma{\mathrm{jj}} $ production with an observed (expected) significance of 3.0 (2.1) standard deviations. The fiducial cross section for EW $\mathrm{ Z }\gamma{\mathrm{jj}} $ production is measured to be 1.86$_{-0.75}^{+0.90}$ (stat)$_{-0.26}^{+0.34}$ (syst) $\pm$ 0.05 (lumi) fb, consistent with the theoretical prediction. The fiducial cross section for combined EW and QCD $\mathrm{ Z }\gamma{\mathrm{jj}} $ production is 5.94$_{-1.35}^{+1.53}$ (stat)$_{-0.37}^{+0.43}$ (syst) $\pm$ 0.13 (lumi) fb, which is also consistent with the leading-order theoretical prediction. In the framework of dimension-eight effective field theory operators, limits on the aQGC parameters $f_\mathrm{M0,1,2,3}$ and $f_\mathrm{T0,1,2,8,9}$ are set at 95% confidence level. This is the first constraints on the neutral aQGC parameters $f_\mathrm{T8}$.

References
1	ATLAS Collaboration	Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC	PLB 716 (2012) 1	1207.7214
2	CMS Collaboration	Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC	PLB 716 (2012) 30	CMS-HIG-12-028 1207.7235
3	CMS Collaboration	A search for $ WW\gamma $ and $ WZ\gamma $ production and constraints on anomalous quartic gauge couplings in pp collisions at $ \sqrt{s} = $ 8 TeV	PRD 90 (2014) 032008	CMS-SMP-13-009 1404.4619
4	ATLAS Collaboration	Evidence of $ W\gamma\gamma $ production in pp collisions at $ \sqrt{s} = $ 8 TeV and limits on anomalous quartic gauge couplings with the ATLAS detector	PRL 115 (2015) 031802	1503.03243
5	ATLAS Collaboration	Measurements of $ Z\gamma $ and $ Z\gamma\gamma $ production in pp collisions at $ \sqrt{s}= $ 8 TeV with the ATLAS detector	PRD 93 (2016) 112002	1604.05232
6	CMS Collaboration	Measurements of the pp$ \to\mathrm{W}^{\pm}\gamma\gamma $ and pp$ \to\mathrm{Z}\gamma\gamma $ cross sections and limits on dimension-8 effective anomalous gauge couplings at $ \sqrt{s} = $ 8 TeV	CMS-PAS-SMP-15-008	CMS-PAS-SMP-15-008
7	ATLAS Collaboration	Evidence for electroweak production of $ W^{\pm}W^{\pm} $jj in $ pp $ collisions at $ \sqrt{s} = $ 8 TeV with the ATLAS detector	PRL 113 (2014) 141803	1405.6241
8	ATLAS Collaboration	Measurement of $ W^{\pm}W^{\pm} $ vector-boson scattering and limits on anomalous quartic gauge couplings with the ATLAS detector		1611.02428
9	CMS Collaboration	Study of vector boson scattering and search for new physics in events with two same-sign leptons and two jets	PRL 114 (2014) 051801	CMS-SMP-13-015 1410.6315
10	CMS Collaboration	Evidence for exclusive $ \gamma\gamma $ to $ W^{+}W^{-} $ production and constraints on anomalous quartic gauge couplings at $ \sqrt{s} = $ 7 and 8 TeV	JHEP 08 (2016) 119	CMS-FSQ-13-008 1604.04464
11	CMS Collaboration	Measurement of electroweak-induced production of W gamma with two jets in pp collisions at $ \sqrt{s} = $ 8 TeV and constraints on anomalous quartic gauge couplings		CMS-SMP-14-011 1612.09256
12	ATLAS Collaboration	Measurements of $ W^\pm Z $ production cross sections in $ pp $ collisions at $ \sqrt{s} = $ 8 TeV with the ATLAS detector and limits on anomalous gauge boson self-couplings	PRD 93 (2016) 092004	1603.02151
13	CMS Collaboration	Measurement of the hadronic activity in events with a Z and two jets and extraction of the cross section for the electroweak production of a Z with two jets in pp collisions at $ \sqrt{s} = $ 7 TeV	JHEP 10 (2013) 062	CMS-FSQ-12-019 1305.7389
14	CMS Collaboration	Measurement of electroweak production of two jets in association with a Z boson in proton-proton collisions at $ \sqrt{s} = $ 8 TeV	EPJC 75 (2014) 2	CMS-FSQ-12-035 1410.3153
15	ATLAS Collaboration	Measurement of the electroweak production of dijets in association with a $ Z $-boson and distributions sensitive to vector boson fusion in proton-proton collisions at $ \sqrt{s} = $ 8 TeV using the ATLAS detector	JHEP 04 (2013) 031	1401.7610
16	CMS Collaboration	Measurement of electroweak production of a W boson and two forward jets in proton-proton collisions at $ \sqrt{s}= $ 8 TeV	JHEP 11 (2016) 147	CMS-SMP-13-012 1607.06975
17	CMS Collaboration	Particle--flow event reconstruction in CMS and performance for jets, taus, and $ E_{\mathrm{T}}^{\text{miss}} $	CMS-PAS-PFT-09-001
18	CMS Collaboration	Commissioning of the particle-flow event reconstruction with the first LHC collisions recorded in the CMS detector	CMS-PAS-PFT-10-001
19	CMS Collaboration	Performance of photon reconstruction and identification with the CMS detector in proton-proton collisions at $ \sqrt{s} = $ 8 TeV	JINST 10 (2015) P08010	CMS-EGM-14-001 1502.02702
20	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004	CMS-00-001
21	CMS Collaboration	Performance of CMS muon reconstruction in pp collision events at $ \sqrt{s} = $ 7 TeV	JINST 7 (2012) P10002	CMS-MUO-10-004 1206.4071
22	CMS Collaboration	Measurement of the Z$ \gamma $ production cross section in pp collisions at 8 TeV and search for anomalous triple gauge boson couplings	JHEP 04 (2015) 164	CMS-SMP-13-014 1502.05664
23	CMS Collaboration	Energy calibration and resolution of the CMS electromagnetic calorimeter in pp collision at $ \sqrt{s}= $ 7 TeV	JINST 8 (2013) P09009	CMS-EGM-11-001 1306.2016
24	CMS Collaboration	Measurement of the Inclusive W and Z Production Cross Sections in pp Collisions at $ \sqrt{s} = $ 7 TeV	JHEP 10 (2011) 132	CMS-EWK-10-005 1107.4789
25	CMS Collaboration	Performance of electron reconstruction and selection with the CMS detector in proton-proton collisions at $ \sqrt{s} = $ 8 TeV	JINST 10 (2015) P06005	CMS-EGM-13-001 1502.02701
26	M. Cacciari, G. P. Salam, and G. Soyez	FastJet user manual	EPJC 72 (2012) 1896	1111.6097
27	M. Cacciari, G. P. Salam, and G. Soyez	The anti-$ {k_{\mathrm{T}}} $ jet clustering algorithm	JHEP 04 (2008) 063	0802.1189
28	CMS Collaboration	Determination of jet energy calibration and transverse momentum resolution in CMS	JINST 6 (2011) P11002	CMS-JME-10-011 1107.4277
29	CMS Collaboration	Jet performance in pp collisions at $ \sqrt{s} = $ 7 tev	CMS-PAS-JME-10-003
30	F. Campanario, M. Kerner, L. D. Ninh, and D. Zeppenfeld	$ Z\gamma $ production in association with two jets at next-to-leading order QCD	EPJC 74 (2014), no. 9	1407.7857
31	M. L. Mangano, M. Moretti, F. Piccinini, and M. Treccani	Matching matrix elements and shower evolution for top-quark production in hadronic collisions	JHEP 01 (2007) 013	hep-ph/0611129
32	J. Alwall et al.	Comparative study of various algorithms for the merging of parton showers and matrix elements in hadronic collisions	EPJC 53 (2008) 473	0706.2569
33	J. Alwall et al.	MadGraph 5: going beyond	JHEP 06 (2011) 128	1106.0522
34	T. Sjostrand, S. Mrenna, and P. Skands	PYTHIA 6.4 physics and manual	JHEP 05 (2006) 026	hep-ph/0603175
35	J. Pumplin et al.	New generation of parton distributions with uncertainties from global QCD analysis	JHEP 07 (2002) 012	hep-ph/0201195
36	GEANT4 Collaboration	GEANT4 --- a simulation toolkit	NIMA 506 (2003) 250
37	CMS Collaboration	Measurement of $ W\gamma $ and $ Z\gamma $ production in pp collisions at $ \sqrt{s} = $ 7 TeV	PLB 701 (2011) 535	CMS-EWK-10-008 1105.2758
38	CMS Collaboration	CMS Luminosity Based on Pixel Cluster Counting --- Summer 2013 Update	CMS-PAS-LUM-13-001	CMS-PAS-LUM-13-001
39	M. Guzzi et al.	CT10 parton distributions and other developments in the global QCD analysis		1101.0561
40	A. D. Martin, W. J. Stirling, R. S. Thorne, and G. Watt	Parton distributions for the LHC	EPJC 63 (2009) 189	0901.0002
41	H.-L. Lai et al.	Uncertainty induced by QCD coupling in the CTEQ global analysis of parton distributions	PRD 82 (2010) 054021	1004.4624
42	A. L. Read	Presentation of search results: the $ CL_s $ technique	JPG 28 (2002) 2693
43	T. Junk	Confidence level computation for combining searches with small statistics	NIMA 434 (1999) 435	hep-ex/9902006
44	O. J. P. Eboli, M. C. Gonzalez-Garcia, and J. K. Mizukoshi	$ pp\rightarrow jj e^\pm \mu^\pm \nu\nu $ and $ jje^\pm\mu^\mp\nu\nu $ at $ \cal $ o($ \alpha^6_{\rm em} $) and $ \cal $ o($ \alpha_{em}^4 \alpha_s^2 $) for the study of the quartic electroweak gauge boson vertex at CERN LHC	PRD 74 (2006) 073005	hep-ph/0606118
45	S. S. Wilks	The large-sample distribution of the likelihood ratio for testing composite hypotheses	Ann. Math. Statist. 9 (1938) 60
46	G. J. Gounaris, J. Layssac, and F. M. Renard	Unitarity constraints for transverse gauge bosons at LEP and supercolliders	PLB 332 (1994) 146	hep-ph/9311370
47	J. Baglio et al.	Release Note ---- VBFNLO 2.7.0		1404.3940