# LHC searches for Dark Matter in compressed mass scenarios: challenges in the forward proton mode

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## Abstract

We analyze in detail the LHC prospects at the center-of-mass enery of \( \sqrt{s} \) = 14 TeV for charged electroweakino searches, decaying to leptons, in compressed supersymmetry scenarios, via exclusive photon-initiated pair production. This provides a potentially increased sensitivity in comparison to inclusive channels, where the background is often overwhelming. We pay particular attention to the challenges that such searches would face in the hostile high pile-up environment of the LHC, giving close consideration to the backgrounds that will be present. The signal we focus on is the exclusive production of same-flavour muon and electron pairs, with missing energy in the final state, and with two outgoing intact protons registered by the dedicated forward proton detectors installed in association with ATLAS and CMS. We present results for slepton masses of 120–300 GeV and slepton-neutralino mass splitting of 10–20 GeV, and find that the relevant backgrounds can be controlled to the level of the expected signal yields. The most significant such backgrounds are due to semi-exclusive lepton pair production at lower masses, with a proton produced in the initial proton dissociation system registering in the forward detectors, and from the coincidence of forward protons produced in pile-up events with an inclusive central event that mimics the signal. We also outline a range of potential methods to further suppress these backgrounds as well as to enlarge the signal yields.

## Keywords

Supersymmetry Phenomenology QCD Phenomenology## Notes

### **Open Access**

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## References

- [1]H.E. Haber and G.L. Kane,
*The search for supersymmetry: probing physics beyond the standard model*,*Phys. Rept.***117**(1985) 75 [INSPIRE].ADSCrossRefGoogle Scholar - [2]
- [3]MSSM Working Group collaboration,
*The minimal supersymmetric standard model: group summary report*, talk given at the*GDR (Groupement De Recherche)*—*Supersymetrie*, April 15–17, Montpellier, France (1998), hep-ph/9901246 [INSPIRE]. - [4]H. Baer and X. Tata,
*Weak scale supersymmetry: from superfields to scattering events*, Cambridge University Press, Cambridge U.K. (2006).CrossRefzbMATHGoogle Scholar - [5]H. Goldberg,
*Constraint on the photino mass from cosmology*,*Phys. Rev. Lett.***50**(1983) 1419 [*Erratum ibid.***103**(2009) 099905] [INSPIRE]. - [6]J.R. Ellis et al.,
*Supersymmetric relics from the Big Bang*,*Nucl. Phys.***B 238**(1984) 453 [INSPIRE].ADSCrossRefGoogle Scholar - [7]T.J. LeCompte and S.P. Martin,
*Large Hadron Collider reach for supersymmetric models with compressed mass spectra*,*Phys. Rev.***D 84**(2011) 015004 [arXiv:1105.4304] [INSPIRE].ADSGoogle Scholar - [8]H. Baer et al.,
*Physics at a Higgsino factory*,*JHEP***06**(2014) 172 [arXiv:1404.7510] [INSPIRE].ADSCrossRefGoogle Scholar - [9]A. Arbey et al.,
*Physics at the e*^{+}*e*^{−}*linear collider*,*Eur. Phys. J.***C 75**(2015) 371 [arXiv:1504.01726] [INSPIRE].ADSGoogle Scholar - [10]CMS collaboration,
*Search for dark matter and supersymmetry with a compressed mass spectrum in the vector boson fusion topology in proton-proton collisions at*\( \sqrt{s} \) = 8*TeV*,*Phys. Rev. Lett.***118**(2017) 021802 [arXiv:1605.09305] [INSPIRE]. - [11]CMS collaboration,
*Search for new physics in the compressed mass spectra scenario using events with two soft opposite-sign leptons and missing transverse momentum at*\( \sqrt{s} \) = 13 TeV, CMS-PAS-SUS-16-025 (2016). - [12]T. Golling et al.,
*Physics at a*100*TeV pp collider: beyond the Standard Model phenomena*,*CERN Yellow Report*(2017) 441 [arXiv:1606.00947] [INSPIRE]. - [13]ILD concept group collaboration,
*Naturalness and light Higgsinos: why ILC is the right machine for SUSY discovery*,*PoS***EPS-HEP2017**(2017) 306 [arXiv:1710.02406] [INSPIRE]. - [14]V.V. Khoze, A.D. Plascencia and K. Sakurai,
*Simplified models of dark matter with a long-lived co-annihilation partner*,*JHEP***06**(2017) 041 [arXiv:1702.00750] [INSPIRE].ADSCrossRefzbMATHGoogle Scholar - [15]ATLAS collaboration,
*Search for electroweak production of supersymmetric states in scenarios with compressed mass spectra at*\( \sqrt{s} \) = 13*TeV with the ATLAS detector*,*Phys. Rev.***D 97**(2018) 052010 [arXiv:1712.08119] [INSPIRE]. - [16]CMS collaboration,
*Searches for pair production of charginos and top squarks in final states with two oppositely charged leptons in proton-proton collisions at*\( \sqrt{s} \) = 13*TeV*,*JHEP***11**(2018) 079 [arXiv:1807.07799] [INSPIRE]. - [17]CMS collaboration,
*Search for electroweak production of charginos and neutralinos in multilepton final states in proton-proton collisions at*\( \sqrt{s} \) = 13*TeV*,*JHEP***03**(2018) 166 [arXiv:1709.05406] [INSPIRE]. - [18]CMS collaboration,
*Search for new physics in events with two soft oppositely charged leptons and missing transverse momentum in proton-proton collisions at*\( \sqrt{s} \) = 13*TeV*,*Phys. Lett.***B 782**(2018) 440 [arXiv:1801.01846] [INSPIRE]. - [19]E. Bagnaschi et al.,
*Likelihood analysis of the pMSSM11 in Light of LHC*13*TeV data*,*Eur. Phys. J.***C 78**(2018) 256 [arXiv:1710.11091] [INSPIRE].ADSCrossRefGoogle Scholar - [20]R. Barbieri and G.F. Giudice,
*Upper bounds on supersymmetric particle masses*,*Nucl. Phys.***B 306**(1988) 63 [INSPIRE].ADSCrossRefGoogle Scholar - [21]B. de Carlos and J.A. Casas,
*One loop analysis of the electroweak breaking in supersymmetric models and the fine tuning problem*,*Phys. Lett.***B 309**(1993) 320 [hep-ph/9303291] [INSPIRE]. - [22]G.F. Giudice, T. Han, K. Wang and L.-T. Wang,
*Nearly degenerate gauginos and dark matter at the LHC*,*Phys. Rev.***D 81**(2010) 115011 [arXiv:1004.4902] [INSPIRE].ADSGoogle Scholar - [23]C. Han et al.,
*Probing light higgsinos in natural SUSY from monojet signals at the LHC*,*JHEP***02**(2014) 049 [arXiv:1310.4274] [INSPIRE].ADSCrossRefGoogle Scholar - [24]P. Schwaller and J. Zurita,
*Compressed electroweakino spectra at the LHC*,*JHEP***03**(2014) 060 [arXiv:1312.7350] [INSPIRE].ADSCrossRefGoogle Scholar - [25]M.A. Ajaib et al.,
*Neutralinos and sleptons at the LHC in light of muon*(*g*− 2)_{μ},*Phys. Rev.***D 92**(2015) 075033 [arXiv:1505.05896] [INSPIRE].ADSGoogle Scholar - [26]T. Ghosh,
*Neutralinos and sleptons at the LHC in Light of Muon Anomalous magnetic moment*, Ph.D. thesis, Texas A-M, U.S.A. (2016).Google Scholar - [27]A. Kobakhidze, M. Talia and L. Wu,
*Probing the MSSM explanation of the muon g-2 anomaly in dark matter experiments and at a*100*TeV pp collider*,*Phys. Rev.***D 95**(2017) 055023 [arXiv:1608.03641] [INSPIRE].ADSGoogle Scholar - [28]M. Endo, K. Hamaguchi, S. Iwamoto and K. Yanagi,
*Probing minimal SUSY scenarios in the light of muon g*− 2*and dark matter*,*JHEP***06**(2017) 031 [arXiv:1704.05287] [INSPIRE].ADSCrossRefGoogle Scholar - [29]K. Griest and D. Seckel,
*Three exceptions in the calculation of relic abundances*,*Phys. Rev.***D 43**(1991) 3191 [INSPIRE].ADSGoogle Scholar - [30]M.J. Baker et al.,
*The coannihilation codex*,*JHEP***12**(2015) 120 [arXiv:1510.03434] [INSPIRE].ADSGoogle Scholar - [31]J. Edsjo and P. Gondolo,
*Neutralino relic density including coannihilations*,*Phys. Rev.***D 56**(1997) 1879 [hep-ph/9704361] [INSPIRE]. - [32]ATLAS collaboration, https://twiki.cern.ch/twiki/bin/view/AtlasPublic/SupersymmetryPublicResults.
- [33]CMS collaboration, https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsSUS.
- [34]J. Ohnemus, T.F. Walsh and P.M. Zerwas,
*γγ production of nonstrongly interacting SUSY particles at hadron colliders*,*Phys. Lett.***B 328**(1994) 369 [hep-ph/9402302] [INSPIRE]. - [35]K. Piotrzkowski,
*Tagging two photon production at the CERN LHC*,*Phys. Rev.***D 63**(2001) 071502 [hep-ex/0009065] [INSPIRE]. - [36]N. Schul and K. Piotrzkowski,
*Detection of two-photon exclusive production of supersymmetric pairs at the LHC*,*Nucl. Phys. Proc. Suppl.***179-180**(2008) 289 [arXiv:0806.1097] [INSPIRE]. - [37]V.A. Khoze, A.D. Martin, M.G. Ryskin and A.G. Shuvaev,
*A new window at the LHC: BSM signals using tagged protons*,*Eur. Phys. J.***C 68**(2010) 125 [arXiv:1002.2857] [INSPIRE].ADSCrossRefGoogle Scholar - [38]L.A. Harland-Lang, C.H. Kom, K. Sakurai and W.J. Stirling,
*Measuring the masses of a pair of semi-invisibly decaying particles in central exclusive production with forward proton tagging*,*Eur. Phys. J.***C 72**(2012) 1969 [arXiv:1110.4320] [INSPIRE].ADSCrossRefGoogle Scholar - [39]FP420 R&D collaboration,
*The FP420 & project: Higgs and new physics with forward protons at the LHC*, 2009*JINST***4**T10001 [arXiv:0806.0302] [INSPIRE]. - [40]LHC Forward Physics Working Group collaboration,
*LHC forward physics*,*J. Phys.***G 43**(2016) 110201 [arXiv:1611.05079] [INSPIRE]. - [41]O. Kepka and C. Royon,
*Anomalous WWγ coupling in photon-induced processes using forward detectors at the LHC*,*Phys. Rev.***D 78**(2008) 073005 [arXiv:0808.0322] [INSPIRE].ADSGoogle Scholar - [42]C. Royon,
*Forward physics at the LHC: from the structure of the Pomeron to the search for γ-induced resonances*,*Acta Phys. Polon.***B 47**(2016) 1781 [arXiv:1606.07675] [INSPIRE].ADSCrossRefGoogle Scholar - [43]L.A. Harland-Lang, V.A. Khoze and M.G. Ryskin,
*Photon-initiated processes at high mass*,*Phys. Rev.***D 94**(2016) 074008 [arXiv:1607.04635] [INSPIRE].ADSGoogle Scholar - [44]V.A. Khoze, A.D. Martin and M.G. Ryskin,
*Can invisible objects be*‘*seen*’*via forward proton detectors at the LHC?*,*J. Phys.***G 44**(2017) 055002 [arXiv:1702.05023] [INSPIRE].ADSCrossRefGoogle Scholar - [45]C. Baldenegro, S. Fichet, G. von Gersdorff and C. Royon,
*Searching for axion-like particles with proton tagging at the LHC*,*JHEP***06**(2018) 131 [arXiv:1803.10835] [INSPIRE].ADSCrossRefGoogle Scholar - [46]L.A. Harland-Lang, V.A. Khoze and M.G. Ryskin,
*Exclusive physics at the LHC with SuperChic 2*,*Eur. Phys. J.***C 76**(2016) 9 [arXiv:1508.02718] [INSPIRE].ADSCrossRefGoogle Scholar - [47]L.A. Harland-Lang, V.A. Khoze and M.G. Ryskin,
*Exclusive LHC physics with heavy ions: SuperChic 3*,*Eur. Phys. J.***C 79**(2019) 39 [arXiv:1810.06567] [INSPIRE].ADSCrossRefGoogle Scholar - [48]SuperCHIC code and documentation, http://projects.hepforge.org/superchic/ (2019).
- [49]ATLAS collaboration,
*Technical design report for the ATLAS forward proton detector*, CERN-LHCC-2015-009 (2015). - [50]ATLAS collaboration,
*Status of the AFP project in the ATLAS experiment*,*AIP Conf. Proc.***1654**(2015) 090001 [INSPIRE]. - [51]M. Albrow et al.,
*CMS-TOTEM precision proton spectrometer*, CERN-LHCC-2014-021 (2014). - [52]V.A. Khoze,
*Photon-photon collisions at the LHC*, invited talk at the*International Conference Photon-2017*, May 22–27, CERN, Geneva Switzerland (2017).Google Scholar - [53]V.A. Khoze,
*Challenges in searches for dark matter at the LHC in forward proton mode*, invited talk at the*Workshop on Diffraction and Low-x Physics*, August 26–September 1, Reggio Calabria, Italy (2018).Google Scholar - [54]V. A. Khoze,
*Challenges in searches for dark matter at the LHC in forward proton mode*, invited talk at the*Workshop on QCD and Diffraction: Various Faces of QCD*, November 15–17, Cracow, Pooland (2018).Google Scholar - [55]M. Tasevsky,
*Future physics measurements with AFP*, invited talk at the*LHC Working Group on Forward Physics and Diffraction*, December 7–8, Geneva, Switzerland (2017).Google Scholar - [56]L. Beresford and J. Liu,
*Photon collider search strategy for sleptons and dark matter at the LHC*, arXiv:1811.06465 [INSPIRE]. - [57]CMS collaboration,
*Search for chargino pair production and top squark pair production in final states with two leptons in proton-proton collisions at*\( \sqrt{s} \) = 13*TeV*, CMS-PAS-SUS-17-010 (2017). - [58]ATLAS collaboration,
*Technical design report for the ATLAS inner tracker strip detector*, CERN-LHCC-2017-005 (2017). - [59]CMS collaboration,
*The phase-2 upgrade of the CMS tracker*, CERN-LHCC-2017-009 (2017). - [60]
*HL/HE-LHC physics workshop report*, in preparation (2019).Google Scholar - [61]ATLAS collaboration,
*Measurement of the exclusive γγ*→*μ*^{+}*μ*^{−}*process in proton-proton collisions at*\( \sqrt{s} \) = 13*TeV with the ATLAS detector*,*Phys. Lett.***B 777**(2018) 303 [arXiv:1708.04053] [INSPIRE]. - [62]ATLAS collaboration,
*Measurement of exclusive γγ*→*W*^{+}*W*^{−}*production and search for exclusive Higgs boson production in pp collisions at*\( \sqrt{s} \) = 8*TeV using the ATLAS detector*,*Phys. Rev.***D 94**(2016) 032011 [arXiv:1607.03745] [INSPIRE]. - [63]CMS, TOTEM collaboration,
*Observation of proton-tagged, central (semi)exclusive production of high-mass lepton pairs in pp collisions at 13 TeV with the CMS-TOTEM precision proton spectrometer*,*JHEP***07**(2018) 153 [arXiv:1803.04496] [INSPIRE]. - [64]DELPHES 3 collaboration,
*DELPHES 3, a modular framework for fast simulation of a generic collider experiment*,*JHEP***02**(2014) 057 [arXiv:1307.6346] [INSPIRE]. - [65]T. Sjöstrand et al.,
*An introduction to PYTHIA 8.2*,*Comput. Phys. Commun.***191**(2015) 159 [arXiv:1410.3012] [INSPIRE]. - [66]L.A. Harland-Lang, V.A. Khoze and M.G. Ryskin,
*The photon PDF in events with rapidity gaps*,*Eur. Phys. J.***C 76**(2016) 255 [arXiv:1601.03772] [INSPIRE].ADSCrossRefGoogle Scholar - [67]V.A. Khoze, A.D. Martin and M.G. Ryskin,
*The extraction of the bare triple-Pomeron vertex: a crucial ingredient for diffraction*,*Phys. Lett.***B 643**(2006) 93 [hep-ph/0609312] [INSPIRE]. - [68]P. Bolzoni and G. Kramer,
*Inclusive lepton production from heavy-hadron decay in pp collisions at the LHC*,*Nucl. Phys.***B 872**(2013) 253 [*Erratum ibid.***B 876**(2013) 334] [arXiv:1212.4356] [INSPIRE]. - [69]
- [70]M. Bahr et al.,
*HERWIG++ physics and manual*,*Eur. Phys. J.***C 58**(2008) 639 [arXiv:0803.0883] [INSPIRE].ADSCrossRefGoogle Scholar - [71]J. Bellm et al.,
*HERWIG 7.0/HERWIG++ 3.0 release note*,*Eur. Phys. J.***C 76**(2016) 196 [arXiv:1512.01178] [INSPIRE]. - [72]M. Tasevsky,
*Review of central exclusive production of the Higgs boson beyond the standard model*,*Int. J. Mod. Phys.***A 29**(2014) 1446012 [arXiv:1407.8332] [INSPIRE].ADSCrossRefGoogle Scholar - [73]B.E. Cox, F.K. Loebinger and A.D. Pilkington,
*Detecting Higgs bosons in the bb decay channel using forward proton tagging at the LHC*,*JHEP***10**(2007) 090 [arXiv:0709.3035] [INSPIRE].ADSCrossRefGoogle Scholar - [74]K.A. Goulianos and J. Montanha,
*Factorization and scaling in hadronic diffraction*,*Phys. Rev.***D 59**(1999) 114017 [hep-ph/9805496] [INSPIRE]. - [75]A.B. Kaidalov et al.,
*On determination of the triple pomeron coupling from the ISR data*,*Phys. Lett.***B 45**(1973) 493.ADSCrossRefGoogle Scholar - [76]R.B. Appleby et al.,
*The practical Pomeron for high energy proton collimation*,*Eur. Phys. J.***C 76**(2016) 520 [arXiv:1604.07327] [INSPIRE].ADSCrossRefGoogle Scholar - [77]V.A. Khoze et al.,
*Diffraction and correlations at the LHC: definitions and observables*,*Eur. Phys. J.***C 69**(2010) 85 [arXiv:1005.4839] [INSPIRE].ADSCrossRefGoogle Scholar - [78]ATLAS collaboration,
*Reconstruction of primary vertices at the ATLAS experiment in Run 1 proton-proton collisions at the LHC*,*Eur. Phys. J.***C 77**(2017) 332 [arXiv:1611.10235] [INSPIRE]. - [79]CMS collaboration,
*Technical proposal for a MIP timing detector in the CMS experiment phase 2 upgrade*, CERN-LHCC-2017-027 (2017). - [80]ATLAS collaboration,
*A High-Granularity Timing Detector (HGTD) in ATLAS: performance at the HL-LHC*, ATL-LARG-PROC-2018-003 (2018). - [81]M.J. Murray,
*private communication*.Google Scholar - [82]A. Manohar, P. Nason, G.P. Salam and G. Zanderighi,
*How bright is the proton? A precise determination of the photon parton distribution function*,*Phys. Rev. Lett.***117**(2016) 242002 [arXiv:1607.04266] [INSPIRE].ADSCrossRefGoogle Scholar