# *Z* ^{′} at the LHC: interference and finite width effects in Drell-Yan

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## Abstract

The interference effects between an extra neutral spin-1 *Z* ^{′}-boson and the Standard Model background in the Drell-Yan channel at the LHC are studied in detail. The final state with two oppositely charged leptons is considered. The interference contribution to the new physics signal, currently not fully taken into account by experimental collaborations in *Z* ^{′}-searches and in the interpretation of the results, can be substantial. It may affect limits or discovery prospects of *Z* ^{′} at the LHC. As the *Z* ^{′}-boson interference is model-dependent, a proper treatment would a priori require a dedicated experimental analysis for each particular model. Doing so could potentially improve the sensitivity to new physics, but would require significantly more experimental effort.

At the same time, it is shown that one can define an invariant mass window, valid for a wide range of models, for which the contribution of the model-dependent interference to the Beyond the Standard Model signal is reduced to \( \mathcal{O} \)(10%), comparable to the level of the combined uncertainty from parton densities and higher order corrections. This quasi-model-independent “magic cut” does not scale with the mass of the *Z* ^{′}-boson and is approximately constant over a large range of masses. Such control of the interference effects relies on not-too-small branching ratios of *Z* ^{′} to leptons (typically of at least a few percent) which can be suppressed, however, by additional new decay channels of the *Z* ^{′}; a small width-to-mass ratio alone does *not* guarantee the interference to be small over an arbitrary kinematic range. Under the general assumption that these new decay channels of *Z* ^{′} are not dominant, one can perform quasi-model-independent analyses, preserving the current scheme used by the experimental collaborations for the *Z* ^{′}-boson search using the suggested invariant mass window cut.

## Keywords

Phenomenological Models Hadronic Colliders## References

- [1]S. Drell and T.-M. Yan,
*Massive Lepton Pair Production in Hadron-Hadron Collisions at High-Energies*,*Phys. Rev. Lett.***25**(1970) 316 [*Erratum ibid.***25**(1970) 902] [INSPIRE].ADSCrossRefGoogle Scholar - [2]UA1 collaboration, G. Arnison et al.,
*Experimental Observation of Isolated Large Transverse Energy Electrons with Associated Missing Energy at*\( \sqrt{s}=540 \)*GeV*,*Phys. Lett.***B 122**(1983)103 [INSPIRE].ADSCrossRefGoogle Scholar - [3]UA2 collaboration, M. Banner et al.,
*Observation of Single Isolated Electrons of High Transverse Momentum in Events with Missing Transverse Energy at the CERN pp Collider*,*Phys. Lett.***B 122**(1983) 476 [INSPIRE].ADSCrossRefGoogle Scholar - [4]UA1 collaboration, G. Arnison et al.,
*Experimental Observation of Lepton Pairs of Invariant Mass Around 95 GeV/c*^{2}*at the CERN SPS Collider*,*Phys. Lett.***B 126**(1983) 398 [INSPIRE].ADSCrossRefGoogle Scholar - [5]UA2 collaboration, P. Bagnaia et al.,
*Evidence for Z*^{0}→*e*^{+}*e*^{−}*at the CERN*\( \overline{p}p \)*Collider*,*Phys. Lett.***B 129**(1983) 130 [INSPIRE].ADSCrossRefGoogle Scholar - [6]M. Dittmar,
*Neutral current interference in the TeV region: the experimental sensitivity at the LHC*,*Phys. Rev.***D 55**(1997) 161 [hep-ex/9606002] [INSPIRE].ADSGoogle Scholar - [7]T.G. Rizzo,
*The determination of the helicity of W*^{′}*boson couplings at the LHC*,*JHEP***05**(2007)037 [arXiv:0704.0235] [INSPIRE].ADSCrossRefGoogle Scholar - [8]F. Petriello and S. Quackenbush,
*Measuring Z*^{′}*couplings at the CERN LHC*,*Phys. Rev.***D 77**(2008)115004 [arXiv:0801.4389] [INSPIRE].ADSGoogle Scholar - [9]A. Papaefstathiou and O. Latunde-Dada,
*NLO production of W*^{′}*bosons at hadron colliders using the MC@NLO and POWHEG methods*,*JHEP***07**(2009) 044 [arXiv:0901.3685] [INSPIRE].ADSCrossRefGoogle Scholar - [10]T.G. Rizzo,
*Indirect searches for Z-prime-like resonances at the LHC*,*JHEP***08**(2009) 082 [arXiv:0904.2534] [INSPIRE].ADSCrossRefGoogle Scholar - [11]C.-W. Chiang, N.D. Christensen, G.-J. Ding and T. Han,
*Discovery in Drell-Yan Processes at the LHC*,*Phys. Rev.***D 85**(2012) 015023 [arXiv:1107.5830] [INSPIRE].ADSGoogle Scholar - [12]E. Accomando et al.,
*Interference effects in heavy W*’*-boson searches at the LHC*,*Phys. Rev.***D 85**(2012) 115017 [arXiv:1110.0713] [INSPIRE].ADSGoogle Scholar - [13]D. Choudhury, R.M. Godbole and P. Saha,
*Dijet resonances, widths and all that*,*JHEP***01**(2012)155 [arXiv:1111.1054] [INSPIRE].ADSCrossRefGoogle Scholar - [14]A. Leike,
*The phenomenology of extra neutral gauge bosons*,*Phys. Rept.***317**(1999) 143 [hep-ph/9805494] [INSPIRE].ADSCrossRefGoogle Scholar - [15]CDF collaboration,
*Search for a New Heavy Gauge Boson W*^{′}*with Electron + missing ET Event Signature in*\( p\overline{p} \)*collisions at*\( \sqrt{s}=1.96 \)*TeV*,*Phys. Rev.***D 83**(2011) 031102 [arXiv:1012.5145] [INSPIRE].Google Scholar - [16]CDF collaboration,
*A search for high-mass resonances decaying to dimuons at CDF*,*Phys. Rev. Lett.***102**(2009) 091805 [arXiv:0811.0053] [INSPIRE].CrossRefGoogle Scholar - [17]D0 collaboration, V. Abazov et al.,
*Search for W*^{′}*bosons decaying to an electron and a neutrino with the D0 detector*,*Phys. Rev. Lett.***100**(2008) 031804 [arXiv:0710.2966] [INSPIRE].ADSCrossRefGoogle Scholar - [18]D0 collaboration, V.M. Abazov et al.,
*Search for a heavy neutral gauge boson in the dielectron channel with 5.4 fb*^{−1}*of*\( p\overline{p} \)*collisions at*\( \sqrt{s}=1.96 \)*TeV*,*Phys. Lett.***B 695**(2011) 88 [arXiv:1008.2023] [INSPIRE].ADSCrossRefGoogle Scholar - [19]ATLAS collaboration,
*ATLAS search for a heavy gauge boson decaying to a charged lepton and a neutrino in pp collisions at*\( \sqrt{s}=7 \)*TeV*,*Eur. Phys. J.***C 72**(2012) 2241 [arXiv:1209.4446] [INSPIRE].ADSCrossRefGoogle Scholar - [20]ATLAS collaboration,
*Search for high-mass dilepton resonances in 20 f b*^{−1}*of pp collisions at*\( \sqrt{s}=8 \)*TeV with the ATLAS experiment*,ATLAS-CONF-2013-017(2013). - [21]CMS collaboration,
*Search for new physics in final states with a lepton and missing transverse energy in pp collisions at the LHC*,*Phys. Rev.***D 87**(2013) 072005 [arXiv:1302.2812] [INSPIRE].ADSGoogle Scholar - [22]CMS collaboration,
*Search for heavy narrow dilepton resonances in pp collisions at*\( \sqrt{s}=7 \)*TeV and*\( \sqrt{s}=8 \)*TeV*,*Phys. Lett.***B 720**(2013)63[arXiv:1212.6175][INSPIRE].ADSGoogle Scholar - [23]CMS collaboration,
*Search for leptonic decays of W*^{′}*bosons in pp collisions at*\( \sqrt{s}=7 \)*TeV*,*JHEP***08**(2012) 023 [arXiv:1204.4764] [INSPIRE].ADSGoogle Scholar - [24]ATLAS collaboration,
*Search for high-mass resonances decaying to dilepton final states in pp collisions at*\( \sqrt{s}=7 \)*TeV with the ATLAS detector*,*JHEP***11**(2012) 138 [arXiv:1209.2535] [INSPIRE].ADSGoogle Scholar - [25]G. Bella et al.,
*A search for heavy Kaluza-Klein electroweak gauge bosons at the LHC*,*JHEP***09**(2010) 025 [arXiv:1004.2432] [INSPIRE].ADSCrossRefGoogle Scholar - [26]E. Boos, V. Bunichev, L. Dudko and M. Perfilov,
*Interference between W*^{′}*and W in single-top quark production processes*,*Phys. Lett.***B 655**(2007) 245 [hep-ph/0610080] [INSPIRE].ADSCrossRefGoogle Scholar - [27]D0 collaboration, V. Abazov et al.,
*Search for W*^{′}*boson resonances decaying to a top quark and a bottom quark*,*Phys. Rev. Lett.***100**(2008) 211803 [arXiv:0803.3256] [INSPIRE].ADSCrossRefGoogle Scholar - [28]D0 collaboration, V.M. Abazov et al.,
*Search for W*^{′}→*tb resonances with left- and right-handed couplings to fermions*,*Phys. Lett.***B 699**(2011) 145 [arXiv:1101.0806] [INSPIRE].ADSCrossRefGoogle Scholar - [29]CMS collaboration,
*Search for a W*^{′}*boson decaying to a bottom quark and a top quark in pp collisions at*\( \sqrt{s}=7 \)*TeV*,*Phys. Lett.***B 718**(2013) 1229 [arXiv:1208.0956] [INSPIRE].ADSGoogle Scholar - [30]D. Berdine, N. Kauer and D. Rainwater,
*Breakdown of the narrow width approximation for new physics*,*Phys. Rev. Lett.***99**(2007) 111601 [hep-ph/0703058] [INSPIRE].ADSCrossRefGoogle Scholar - [31]N. Kauer,
*Narrow-width approximation limitations*,*Phys. Lett.***B 649**(2007) 413 [hep-ph/0703077] [INSPIRE].ADSCrossRefGoogle Scholar - [32]C. Uhlemann and N. Kauer,
*Narrow-width approximation accuracy*,*Nucl. Phys.***B 814**(2009)195 [arXiv:0807.4112] [INSPIRE].ADSCrossRefGoogle Scholar - [33]E. Accomando, A. Belyaev, L. Fedeli, S.F. King and C. Shepherd-Themistocleous,
*Z*^{′}*physics with early LHC data*,*Phys. Rev.***D 83**(2011) 075012 [arXiv:1010.6058] [INSPIRE].ADSGoogle Scholar - [34]M.S. Carena, A. Daleo, B.A. Dobrescu and T.M. Tait,
*Z*^{′}*gauge bosons at the Tevatron*,*Phys. Rev.***D 70**(2004) 093009 [hep-ph/0408098] [INSPIRE].ADSGoogle Scholar - [35]G. Altarelli, B. Mele and M. Ruiz-Altaba,
*Searching for new heavy vector bosons in*\( p\overline{p} \)*colliders*,*Z. Phys.***C 45**(1989) 109 [*Erratum ibid.***C 47**(1990) 676] [INSPIRE].Google Scholar - [36]C. Prescott et al.,
*Parity nonconservation in inelastic electron scattering*,*Phys. Lett.***B 77**(1978)347 [INSPIRE].ADSCrossRefGoogle Scholar - [37]S.L. Wu,
*e*^{+}*e*^{−}*physics at PETRA: the first 5-Years*,*Phys. Rept.***107**(1984) 59 [INSPIRE].ADSCrossRefGoogle Scholar - [38]P. Langacker,
*The physics of heavy Z*^{′}*gauge bosons*,*Rev. Mod. Phys.***81**(2009) 1199 [arXiv:0801.1345] [INSPIRE].ADSCrossRefGoogle Scholar - [39]H.-L. Lai et al.,
*New parton distributions for collider physics*,*Phys. Rev.***D 82**(2010) 074024 [arXiv:1007.2241] [INSPIRE].ADSGoogle Scholar - [40]J.M. Campbell, J. Huston and W. Stirling,
*Hard interactions of quarks and gluons: a primer for LHC physics*,*Rept. Prog. Phys.***70**(2007) 89 [hep-ph/0611148] [INSPIRE].ADSCrossRefGoogle Scholar - [41]Wolfram Research, Inc.,
*Mathematica*, version 7.0, Champaign U.S.A. (2008).Google Scholar - [42]A. Belyaev, N.D. Christensen and A. Pukhov,
*CalcHEP 3.4 for collider physics within and beyond the Standard Model*,*Comput. Phys. Commun.***184**(2013) 1729 [arXiv:1207.6082] [INSPIRE].ADSCrossRefGoogle Scholar