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JHEP04(2016)154 = 14 TeV Springer s April 20, 2016 April 26, 2016 √ : : February 24, 2016 : Accepted Published , 10.1007/JHEP04(2016)154 Received and doi: 50) GeV in the a,c − (5 ∼ Published for SISSA by LSP m Sascha Caron − 9 GeV for DM masses between 40 and 140 GeV. a,b ∼ NLSP m m [email protected] = , m Wim Beenakker, d a . 3 [email protected] , 1602.00590 100 GeV bino-like dark . We find that these scenarios are The Authors. ∼ c Phenomenology

Global fit studies performed in the pMSSM and the excess signal orig- , [email protected] of data we expect the LHC experiments to be able to discover these supersymmet- 1 − E-mail: [email protected] Science Park 105, Amsterdam, TheInstitute Netherlands of Physics, UniversityScience of Park Amsterdam, 904, Amsterdam, TheInstituto Netherlands de Fisica Corpuscular,Calle IFIC-UV/CSIC, Jos´eBeltran 2, Catedr´atico Valencia, Spain Institute for Mathematics, AstrophysicsHeyendaalseweg and 135, Particle Nijmegen, Physics, The Radboud Netherlands UniversityNikhef, Nijmegen, b c d a Open Access Article funded by SCOAP pMSSM spectra. Keywords: ArXiv ePrint: run of the LHC. Counterintuitively, weenergy find increases that the the sensitivity requirement compared300 of fb to low the missing current transverse ATLAS andric CMS spectra searches. with mass With gapsWe down stress to the importance ∆ of a dedicated search strategy that targets precisely these favored not probed by traditionalto electroweak extend supersymmetry the searches ATLASstrategy at and for the CMS LHC. bino-like electroweak We darkproduction, supersymmetry propose matter, with searches a focusing with subsequent on decay anity into for chargino improved a pMSSM plus tri- scenarios next-to-lightest final with state. ∆ We explore the sensitiv- Abstract: inating from the Galactic Centerspectra seem with to a suggest compressed electroweak supersymmetric Melissa van Beekveld, Roberto Ruiz de Austri The case for 100 GeVLHC bino tri-lepton dark search matter: a dedicated JHEP04(2016)154 ]). 2 pairs 0 1 χ ]. 14 – 4 -parity conserving phenomenological R 8 17 : weak-scale (with masses around 2. In the – 1 – / ]). WIMPs can be detected directly and indirectly. 1 ), which is a DM candidate when it is the lightest 0 1 118 [ χ . WIMP miracle 9 5 = 0 7 2 h ]). These methods focus on locations of high DM density, such as the 3 13 1 15 ) state whose differs by 1 A theoretical framework for WIMPs can be provided by supersymmetry (SUSY). This sparticle 4.1 Reducible backgrounds version of the minimal supersymmetric standardnew model sparticles (pMSSM),the introduction can ofexample these provide the a solution lightestsupersymmetric neutralino to particle (˜ the (LSP). It hierarchy has recentlyin problem been the shown as that pMSSM the well framework annihilation as is of a ˜ WIMPs, possible for explanation for the Galactic Center (GC) photon center of the MilkyObservations Way or of dwarf the spheroidal centerthe satellite of Fermi our satellite, (dSphs) show of a with the photon the Milky excess Large Way. emanating from Areatheory this Telescope postulates region (LAT), for [ aboard each(or (SM) particle the existence of a the Planck collaboration (Ω Direct detection methods aim totween WIMPs measure and nuclear the recoils target material thatIndirect of originate the detection from detector methods (for collisions a try be- review,see to see for observe for instance instance annihilation ref. ref. [ products [ of WIMPs (for a review, The existence of darkmains unknown. matter (DM) The isparticles leading (WIMPs), widely i.e. theory accepted, particles is thatparticularly but have that favored no its DM due electromagnetic fundamental or consists to color nature100-1000 the of GeV) charge. can re- weakly WIMPs result are in interacting a massive DM relic density that is consistent with the value provided by 1 Introduction 5 LHC14 reach 6 Conclusion A Detailed discussion of the LHC14 reach 3 Background processes 4 Distinct kinematic features of the signal Contents 1 Introduction 2 Theoretical background JHEP04(2016)154 - ]. 16 WZ with 2 0 ˜ χ 1  χ contour of the most 10-25 GeV heavier σ ∼ ]. 22 , 21 ]. 19 ]. These studies are performed including all – 2 – 20 , ] and Tucana III [ 16 18 , 17 ]. 22 100 GeV bino-like DM particle and a ∼ 80-90 GeV and mostly - or wino-like next-to-lightest ], which coincide with the best global fit models obtained by [ 100 GeV [ ∼ 15 ∼ 0 1 0 1 ˜ χ ˜ χ m m ]. This limit is obtained using simplified models, where the NLSPs are assumed 23 ]. The best fit to the data corresponds to pMSSM models with mostly bino- The 95% confidence level exclusion limit on direct production of ˜ 16 , 15 To conclude, some signs coming from independent analyses justifies further studies In addition, global fit studies performed in the pMSSM with 15 parameters suggest likely pMSSM10 models havemore, a bino-like the LSP mass with differencestates a in between mass these around the models 100-200 LSP is GeV. and Further- 20 heavier GeV at neutralino moston and at pMSSM chargino low scenarios LSP NLSP with masses [ a a bino-like LSP with available accelerator, direct-detection andcess. cosmology An constraints analysis and of theincluding the constraints GC parameter from photon space the ex- of Higgsservables, mass, the the B- pMSSM DM observables, with relic electroweak 10 precision density parameters ob- and (pMSSM10), spin-independent DM scattering, shows that the most like LSPs with masses neutralino and chargino states (NLSPs)Furthermore, with these a same mass models closein are to the also the dwarf lightest consistent galaxy neutralino with Reticulum mass. a II small [ photon excess observed These models will notsection and have the NLSPs relevant branching that ratios.likely are pMSSM10 The 100% models shaded red from wino-like, area ref. which indicates [ the reduces 1 the production cross excess [ Figure 1. mediated decays [ to be 100% wino-like andfit relevant branching pMSSM ratios models are from set at ref. 100%. [ The star indicates the GC best JHEP04(2016)154 sig- T / E of data for 1 2, therefore / − ) for these pMSSM LSP contour of the most σ m σ − ], which coincide with the 15 NLSP m ] respectively. The red line indicates the current ]). The cuts used to create this figure are shown 45 46 – 3 – ). Standard searches for multi-lepton plus 20 GeV for the transverse momentum of a lepton. 1 > ) l ( ] and ref. [ ]. The shaded red area indicates the 1 T ]. p 43 16 22 discovery reach for the LHC at 14 TeV and with 300 fb σ ] is not included, because their analysis did not reach 5 44 ]. Previous searches for electroweak SUSY production at the LHC found no The expected 5 35 . Ref. [ – 1 24 )[ T / E significant excess. The LHC experimentsmasses, have but been the able existing to searchand constrain techniques the electroweak fail NLSPs sparticle become when too the smallnals mass (figure rely differences on between triggers the that LSP The require energy of the produced is roughly bounded by ( lider (LHC) for such weakly-interactingthe particles weak with scale. masses thatmulti-lepton could search Electroweak reside channels, SUSY where at searches the orcharginos leptons at near and originate . the from LHC Typical theor search decay are opposite-sign channels of typically di-leptons, look pair tri-leptons, produced for performed( four signatures using leptons that and include a same- large missing transverse energy models. The star indicatesbest the global GC fit best models fitlikely obtained pMSSM pMSSM10 by models models [ from from ref. ref. [ [ chargino and neutralino. This motivates a dedicated search at the Large Col- pMSSM models with a10%. bino-like LSP The and wino-like black NLSPs,indicate line the assuming indicates reach a obtained the background for uncertaintyreach reach ref. of for for [ the the ATLAS proposedin tri-lepton analysis. analysis table (ref. The [ blue line and green line Figure 2. JHEP04(2016)154 , 1 14b . We 1 − 90%), the ∼ 50 GeV. We 10 GeV − we will look at > 4 ) 2 µ ( ]) or a photon (e.g. T 14 GeV ). p 38 60 GeV – 14 GeV 2 > < 10(18) GeV ) 36 > 2 − > l ) e 2 + ( ) 10 GeV l 1 µ T ( µ p > ( T ) p T < M 2 18 GeV and p e ( > we will provide a brief overview of ) and T ) 1 p 1 ) and e 2 ( 1 µ 25 GeV ( T µ ( p T we will present our results. > T p p ) 5 1 l ( – 4 – T we will present the details of the Monte Carlo p 14(10) GeV and 25 GeV and = 14 TeV, which result in a tri-lepton plus missing 3 50) GeV. We will offer an improved search strategy ]). We investigated the sensitivity of these searches > > lepton pair with 12 s − ) ) 1 44 √ 1 1 – e e (5 ( ( trigger: 42 T T ∼ p p µ LSP and ) final state. We investigate the role of the missing transverse m T e / − E , the LHC experiments will not be sensitive to these very impor- 1 + − l ATLAS and CMS tri-lepton searches at 8 TeV signal selection at least one OSSF - (muon-electron) combi trigger: asymmetric di-electron trigger: symmetric di-electron trigger: asymmetric di-muon trigger: symmetric di-muon trigger: single NLSP channel, which extends the exclusion reach for the compressed pMSSM m T ≡ ] / E m 46 ]) has been suggested. The use of soft leptons in combination with a jet has + l 41 ). We therefore stress the importance of a dedicated search strategy that targets – 39 20 The paper is organized as follows. In section A lot of work has already been done to gain sensitivity in similar pMSSM scenarios. This paper addresses these pMSSM scenarios in wino-/higgsino-like chargino and neu- search ATLAS [ favored by the GC excess photon spectrum and globalthe fits theoretical (figure background.simulation In of section the signal anddiscriminating background parameters. processes Finally, considered. in In section section LSP production via vectortherefore decided fusion, to but focus onlyan on 3 extra the events photon tri-lepton are or searcha expected channel. jet, at short the We found 300 production summary fb that cross istri-lepton by section given searches. demanding is of reduced We the by find cuts a that that factor these 10. are searches used In are in table not some sensitive of to the the pMSSM existing models or proposed for our models.standard Since mono-jet the and mono-photon consideredsensitive searches models (where due have two to a LSPs the are largemasses produced) are small bino all will production component set not cross ( at be channel the section is multi-TeV scale of suppressed in LSPs. due this to analysis, Furthermore, so high the the squark t-channel masses. squark exchange We also investigated the possibility of models tremendously. The use ofref. a [ hard initialbeen state, suggested as for well example (e.g. ref. a [ jet (e.g. ref. [ tralino production at the LHCtransverse with energy (3 energy and lepton transversesplittings momentum ∆ in thefor search the for 3 electroweak SUSY with mass find that, even withluminosity the of high-luminosity 3000 fb upgradetant of dark the matter scenarios LHCpage using resulting their in current an tri-leptonprecisely integrated search these strategies pMSSM (see spectra. figure searches start to lose sensitivity when the mass differences drop below 40 JHEP04(2016)154 . W θ s boson 5 . Z 2 and 10 GeV < W | > θ ) c ) j 2 is the ( l . The chargino leptons) η ( | β Z      T T p Z p M 50 GeV Z M − M ). These particles mix µ W 24 GeV 0 θ W and 75 GeV 30 40 GeV θ − c 20 and s > β β < < < β s ) > s − − − µ − l l l ) ( + + + 1 T l l l l Z 1000 GeV (50 GeV steps) ! are indicated by ( p Z T − M W 9 p 20 GeV . M W 30 GeV and within < M < M < M 0 µ W θ M 0 θ W < µ β > 300 − θ s < ) c c 50 GeV ) β ) µ 2 > β j c 1 ( ( c < ) j √ T 20 GeV (veto on higher − ( T 1 27 GeV or ) j p l T ( ( < Z W > Z < p T T ) /p , in increasing mass order. We demand that ) p M e 2 2 M T e , ( M ( 2 β  1 / W E T < p – 5 – M s 0 T θ W χ indicate the cosine and sine of θ M c p 2 c β < p β √ β s s c

and ˜ − 2 and . 4 0 , = Z 3 Z , 5 trigger: and < .  2 and 10 M , ˜ 2 χ M ) µ 1000 GeV and β 0 1 1 W 1 c 0 χ θ W j < − M θ ( M ) and the two Higgs doublets ( s 30 GeV 10 GeV 8 GeV ) s T β and 2 β c < > > e 50 GeV 50 GeV 300 60 GeV 50 GeV s , j /p ) − ) ) ) 1 3 wino 3 3 1 j > > > > > l l j l (      are the bino, wino and Higgsino masses. The ratio of the vacuum ( ( ( ( φ T T T T T boson mass. After diagonalization of these mass matrices, the mass T T T T = / / / / / µ p E soft tri-lepton searches (theory prospects) p E at least one OSSF lepton pair with 12 di-muon or di-electron or combination: single p ∆ E only allow for soft leptons 5 p E initial state radiation jet with at least one OSSF lepton pair with 12 exactly 3 leptons with 7 E at least one OSSF lepton pair with 12 exactly 3 leptons recorded with any of the ATLAS lepton triggers and 0 W ˜ χ ] ] ] and M Summary of cuts used/proposed in various tri-lepton searches at the LHC. 45 bino 2 44 43 is the M ] , 47 1 W M M Table 1. CMS [ 1312.7350 [ 1307.5952 [ 1511.05386 [ Opposite Sign Same Flavor. 1 where expectation values of themass. two Higgs The doublets cosine isFollowing denoted and the by sine same tan of notation, themass matrix weak is mixing given angle by: where eigenstates will be labeled as ˜ 2 Theoretical background Charginos and neutralinos are thegauge mass eigenstates ( of the superpartnersunder of the the influence electroweak of electroweakof symmetry the breaking. non-diagonal neutralino The mass neutral matrix: states mix as a result JHEP04(2016)154 ] 4 0 4 , Z ˜ χ 0 3 → 48 ˜ χ (2.1)  1 , m . The χ , m  2 ˜ 3 χ  2 ˜ χ m m 5%. . 1 ' 07 and BR(˜ 2 MeV. The latter ) . . T 3 production processes / E 0 50) GeV and < − ˜ χ l 50) GeV and ˜ ) = 0 χ − + 0 1 l − inv ˜ χ (5  → l − (5 we show the ATLAS limits l − ∼ + e 1 → ∼ l + m 0 2 -parity is conserved, and weakly e m ˜ χ , R → 0 1  1 , ∆ ˜ χ 0 2 χ , ∆  1 ˜ − χ χ  1 l ˜ ). We will assume that all squark and χ ). For the other configuration, higgsino- m + 2 l m | 0 1 ∼ M µ ˜ χ ∼ 3 , ν 0 2 0 2  ˜ ˜ χ  | χ l – 6 – |  ). If the mass difference between the interaction 2 m m µ µ boson decay width: Γ | → 0 2 Z < ˜ χ < M and 1  1 1 2 ˜ χ M M M , 1 45 GeV, unless the LSP has a very small coupling to the M NLSP respectively. ), mixing will be suppressed. In that case, simplified models [ & W 0 1 ˜ χ M m . We will consider two NLSP configurations. In one configuration, we  | higgsino µ | , 2 . The dominant production and decay channel is illustrated in figure 22, and the total branching ratio by BR(˜ . Chargino-neutralino production and decay to tri-lepton final states via gauge bosons in µ, e < M = 1 l ) = 0 NLSP and M 0 1 The LEP experiments searched for SUSY using the Slepton-mediated production processes and decays will be suppressed in these pMSSM In this analysis we will assume pMSSM models with a bino-like LSP (60-99 %), meaning The amount of bino, wino and higgsino mixing is controlled by the mass hierarchy of ˜ χ is the LSP. This particle is stable, provided that ν 0 1  ˜ corresponding branching ratios arel given by: BR(˜ and provided limits onimposes the a invisible limit of scenarios. The charginos and neutralinosbosons therefore as: predominantly decay via off-shell gauge where much heavier (corresponding to like NLSPs (70-90 %) aremuch assumed, heavier with (corresponding to slepton masses are atwino the multi-TeV scale. We will refer to these two configurations as obtained in these simplified models.are The set branching at ratios 100% for and the the indicated NLSPs decay are channels assumedthat to be 100% wino. assume wino-like NLSPs (80-99 %) with the interaction eigenstates ( eigenstates is big ( can be obtained,constraints which on have neutralino successfully and been chargino invoked masses. by the In LHC figure experiments to set Figure 3. the LHC. χ interacting, which makes it a WIMP candidate. JHEP04(2016)154 when 0 1 χ close to the − l search channel. + l T M / E decay, other leptons + )) branching ratio of at l 5 W , Υ mesons and − − l + 5 GeV, depending on the l . (10 J/ψ ]. We will use these limits M 103 final state is the production of ∼ O 50 with a mass close to ˜ , − bosons as well as . This T 0 2 9 49 . Z / χ E 91 + l & ˜ χ decay, a third may be faked by a photon. m Z – 7 – 10 GeV originating from decay and a third lepton may originate from a semi- . Z − l + l M leptons to and lighter leptons. τ this is the main irreducible background under consideration. This process : ∗ this process contains two leptons and missing transverse energy due to the and will therefore not be interesting for the considered 3 one lepton and missing energy originate from a leptonic two leptons arise from a leptonic two leptons arise from this process has two or four final state leptons. Missing transverse energy can − /γ l ∗ + : l -boson mass, and at 0 1 γ bosons that decay leptonically. All (irreducible and reducible) background processes 100 GeV. Scenarios where the LSP and the lightest chargino are wino-like and the ˜ χ Wt: may originate from a top decay orZ initial state radiation. There would be a minimal amount of missing energy in these events. originate from neutrinos (in theby case decays of of two final state leptons) or itZb: can be provided leptonic decay. low-mass Drell-Yan processes. WW: escaping neutrinos. A third lepton may beZZ: faked by initial state radiation (ISR). WZ includes all processes mediatedbackground by will on have or a off-shell resonanceZ in the distribution of ∼ Z We will not address pMSSM scenarios where the LSP is wino-like and the NLSPs • • • • • • 0 1 → + ˜ χ 0 2 ˜ 3 Background processes The dominant irreducible SMW background to the 3 that we consider are describedare below. considered. In all cases only leptonic decays of the gauge bosons χ Scenarios where the LSP andsection the NLSPs that are is higgsino-like much typically smaller have a than production in cross the case of the NLSPs being wino-like. section), in order tocompressed consider SUSY all scenarios regions from of a parameter particle space collider that point of mightare view. be higgsino-like interesting as for m these spectra donext-to-lightest not neutralino not is have bino-like a have a ˜ very small ( charginos and heavier neutralinosmass resulted difference in between thesein our particles SUSY and models. theDM detection We LSP do experiments [ or not astrophysicalDM demand experiments annihilation that (concerning cross our the section, models DM or relic satisfy spin-dependent density, limits and originating spin-independent from DM-nucleus cross boson (in that case, the LSP does not have a sizable higgsino component). Searches for JHEP04(2016)154 ] ¯ t t is, 55 T 3 [ / ]. We E due to 44 − closest to l + l − l . This makes + M l -boson decays. − l ], using Pythia decay or it may Delphes M is kinematically + l W b 51 − M l we see that the azimuth angle). + l φ 4b M 90 GeV. ∼ ]. We use 0 1 distribution shifts to higher 60 GeV) 54 ˜ χ ), as − l > m + l ]). Previous studies on tri-lepton 5a M ). In figure 56 T and / E 1.3 [ ∼ 4a , while wrongly selected pairs will usually m ] to avoid double counting. Jets are clustered 53 – 8 – boson. These processes will generally have small W . . The peak of the Z or m indicates the pseudorapidity and M Z . η Z M ) distribution (figure − l , we can reject events with large ( + Z (where l 2 M φ -factors for the background processes to be of order unity [ K ]) and must be accompanied by ISR or fake identified leptons to match algorithm as implemented in FastJet 3.1.3 [ = 20 GeV, 50 GeV and 100 GeV and one higgsino NLSP pMSSM model m < M mesons, Υ mesons and low-mass Drell-Yan processes. Usually this cut is + ∆ decays is rejected. We also need to introduce a lower cut on the invariant three leptons and three neutrinos will arise from leptonic T 27 12 GeV, and we will do the same in this analysis. 2 m k η Z > J/ψ ∆ two leptons come from semi-leptonic decays of the top . An additional − boson decays peaks at l p = 20 GeV. In each model, the LSP has a mass of + l Z : = m ¯ t ] for parton showering. We allow up to one additional parton in the hard matrix ele- M lepton can enter from variousbe processes faked like by initial a state jet. radiation, WWW: t background. We define these benchmark SUSY models as: three wino NLSP pMSSM R Although the LSPs carry away most of the energy of the NLSPs, this does not nec- The selection of the OSSF lepton pair becomes complicated when there is more than As long as ∆ The mass gap is clearly visible in the invariant mass of the opposite sign same flavor We model all signal and background processes using MadGraph5 [ is taken. We select the OSSF lepton pair as the lepton pair that has a minimal distance 52 • • Z -factors from next-to-leading order corrections ( essarily mean that there is a large missing energy ( M in ∆ Because correctly selected pairschoice have ensures an that invariant we mass have that ahave is clearer a edge kinematically mass at limited, that ∆ this is closer to from on shell mass distribution, as theevents background with has an accumulationset of at events at low one possible OSSF lepton pair. In the ATLAS search, the lepton pair with suppressed for values larger thanenergies ∆ when the masson gap shell increases. The invariant mass of thesure OSSF a lepton large pair from signal acceptance remains, while a large fraction of the background arising WZ models with ∆ with ∆ (OSSF) lepton pair ( 4 Distinct kinematic featuresTo of evaluate the which signal kinematicbackground, features we can will be first invoked consider to four distinguish ‘benchmark’ between pMSSM signal models and and the irreducible using the anti- as a fast detector simulation.K The SUSY processes that arechannels considered reported typically have small adopt a conservative approach by not considering the NLO corrections. production in association with a cross sections ([ the signal topology. 8.1 [ ment and adopt the MLM matching scheme [ Background processes that we do not consider include other tri-boson processes and JHEP04(2016)154 . > ) j 7a ( T p 110 GeV, '  1 ˜ χ m ' 50 GeV or 0 2 ˜ χ > m ) j , as shown in figure ( (b) (b) T − background process. This l p + l M WZ 20 GeV, the yellow curve represents ' ) before detector simulation. All three ) before detector simulation. The blue m 100 GeV. The curves are normalized to a ' right right ( ( m T T / / E E – 9 – ) background, the red curve represents the wino NLSP originating from the ) and ) and WZ ). The only significant remaining background is then background, a jet veto with T left left ¯ t / E ( ( t 6b − − l l + + 20 GeV. All events are normalized to a cross section of 1 pb. l l ). M M ' m 5b (a) (a) Distribution for Distribution for 50 GeV and the purple curve represents ∆ 90 GeV such that ∆ ' ' 0 1 , which can be rejected efficiently by the requirement on ˜ χ m 4.1 Reducible backgrounds To get rid of a large fraction30 GeV of the can be introducedZb (figure counterintuitively, lower than the is due to themass fact gaps, the that final the stateThis leptons two causes get LSPs the more are LSPs energy, causingtransverse often to them energy be produced to (figure produced back-to-back. recoil less against the With back-to-back, LSP. which increasing results in a higher missing Figure 5. curves represent a wino NLSP,∆ the red curve representscross ∆ section of 1 pb. Figure 4. curve represents the irreducible diboson ( scenario and the green curve them higgsino NLSP scenario. In both scenarios, JHEP04(2016)154 ) will W , l T originating will now be / E ) (transverse ( W T l φ W . 100 GeV. Events l / ) remains. We do E ( ∼ T W π 0 1 p and are correlated in a , l ˜ χ = T T T m φ / E / / E E and ( (b) φ T )) will be smaller for the 1 ∆ / l E 5. bosons, the distribution will ( . 2 T ) and p , W ) < W l | of reducible backgrounds will be ( W ) l 50 GeV. T 1 ) after detector simulation and before ( T . We therefore can also veto events j p T ( < / E p η ) | lepton ( 6a e right ( vs T T )( p T 1 , the -decay) for background events than for the j / E ( < p T W 7b p – 10 – , for any events containing ) j . . ( π 1 T = 20 GeV wino NLSP model with ) and − 8b = m left φ 50 or 30 GeV and , p )( 0 (at least one OSSF lepton pair). ) > 1 l l ( ) ( > 60 GeV. 1 T T j ) p ( < − l T ) 50 GeV and 10 GeV p ). The signal events for low + , p l − ) l ( < (a) − + 8a ) l l N ( µ + ( l ( T ). As can be seen in figure l M < M ( < p T Distribution for ) is peaked towards ∆ p boson decay. If we then allow for a boost of the ) = 3 and W l ( , l W T Veto on jets with N 5 GeV 12 GeV / To conclude, we now have 5 observables that we can use to discriminate signal from Based on the features just discussed, we use the following cuts to optimize the analysis: In the rest frame of a particle decaying in two other particles, the decay particles The transverse momentum of the highest E • • • • ( φ background: get smeared out to othernot values expect as well, the although samethe a topology sum small for of peak three at the components: ∆ be signal uniformly two events. LSPs distributed This and forgenerated a is the events, . because as signal We the shown events. expect in that This figure ∆ is also observed in the Monte Carlo funnel-like shape. We will use this feature to discriminatewill signal be from produced background. back-to-back.∆ We therefore expect thatfrom the a background distribution for signal than for thewith background, high as shown inmostly figure larger than themomentum one of of the the signal. leptonsignal originating We events from expect (figure a higher Figure 6. imposing any cuts. Shown aredistributions all we reducible would and expect irreducible forare background a normalized distributions, ∆ to as a well as luminosity the of 300 fb JHEP04(2016)154 funnel cut 100 GeV. ∼ 0 1 100 GeV. Events and ˜ χ ∼ m 0 1 ˜ χ m (b) 150 GeV (b) < T / E < ) after detector simulation and before ), the number of events are weighted by W , l right T ( ) 5 GeV / E 50 GeV ( T ). The dotted black line indicates the φ 8a / E < W l ( T – 11 – T / = 20 GeV wino NLSP model with E p 6 . . ) and m 1 = 20 GeV wino NLSP model with − left m ( ) + 0 against − W l l T + ( l / E T distribution for ∆ M p 20 GeV. < Right: ) (a) (a) 2. W ). l 50 GeV: ( < (dotted black line in figure . T ) < 4.1 p 2 scatter plot of W T / , l E Distribution for T if else: Left: / E ( – – φ ∆ Funnel cut: • • The cut flow diagram for theis background processes given and in the table four benchmark SUSY scenarios figures are made afterthe demanding distributions exactly we 3 would expect leptons for and a at ∆ least one OSSF lepton pair. We show Figure 8. (defined in section their cross section and the histogram is normalized to 1 (for background and signal separately). Both Figure 7. imposing any cuts. Shown aredistributions all we reducible would and expect irreducible forare background a normalized distributions, ∆ to as a well as luminosity the of 300 fb

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ZZ W W Z W W W W t t Zγ t W Zb ¯ JHEP04(2016)154 . m 9a 30 GeV > 1.15. Further- ]) as the signifi- ∼ ), using a jet veto . This is because, ) and LSP masses 57 value measures the 1 N 10a 10b boson are set at 100% Z value of 2). In figure W for mass gaps N σ Z 2 and > Z = 10%. The σ contour of the most likely pMSSM10 mod- value (as defined in ref. [ triggers for its discovery. In contrast, using σ (and therefore a decays to the N T σ / Z E  1 – 13 – χ or T and ˜ p 0 2 . A detailed discussion is presented in the appendix. χ 1 − 50 GeV if the NLSPs are wino-like (figure − 9 20 GeV if the NLSPs are higgsino-like (figure for the wino NLSP and higgsino NLSP scenarios and an integrated ∼ . We find that the 14 TeV LHC can probe LSP masses up to 140 GeV & 1 10 100 GeV for the wino NLSP pMSSM models. Note that this does not − m ) we present the significance as a color code for the ATLAS and CMS reach < ], which was found for wino NLSP models. The higgsino NLSP production 9d 30 GeV. The reduced production cross section is the limiting factor for higher 22 < and ) ). The dotted red line indicates the 1 j 9b ( 1 ( T p However, using the proposed search strategy with 10% background uncertainty, the 9c gap SUSY scenarios for heavystrategy. have Studies large suggest repercussions that on thesecannot the models rely LHC are SUSY on most search the likely standard tothe high be proposed jet realized search in strategy nature,an it but integrated we is luminosity even of possible 30 to fb probe the discussed SUSY scenarios at ison is given in figure luminosity of 300 fb for mass gaps between up to 95 GeV for ∆ with LSP and NLSP masses for both pMSSM scenarios. Evidently, these special small-mass- which reduces the neutralino-chargino productionmore, cross section the branching by ratios a for factor in the the ˜ simplified models, whereas in our models thesesensitivity would branching be ratios greatly are enhanced not compared 100%. to the standard LHC searches. A compar- significance. We observe that theThe sensitivity for sensitivity ATLAS and using CMS the increasesand for ATLAS LSP higher search masses ∆ strategy reaches exactly resemble the ATLAS limit indicatedin contrast by with the ATLAS, purple we line do in not figure use simplified models where the NLSPs are 100% wino, and for the wino (higgsino) NLSPin scenarios table using their current tri-leptonels searches (as from indicated ref. [ cross section is smaller than the wino NLSP production cross section, which reduces the To evaluate our sensitivity, we willcance and use assume the a systematicdifference background between the error outcome of of ain pMSSM units model and of the the outcomeCL, standard of the which deviation. Standard corresponds Model Typically, to the a exclusion significance reach of is 2 indicated by the 95% 5 LHC14 reach JHEP04(2016)154 and 10% systematic ]. The dotted red line 1 − ] (only for wino NLSP). 16 22 (d) (b) ). This is due to the reduced cross sections and 1 = 110 GeV) indicate the GC best fit pMSSM models – 14 –  1 ˜ χ m (a) (c) . Stars (located around contour of the most likely pMSSM10 models from ref. [  1 ˜ σ χ m ], which coincide with the best global fit models obtained by [ Standard ATLAS and CMS tri-lepton search sensitivities for wino NLSP (figures a and = 15 0 1 ˜ χ m limit from ref. [ indicates the 1 Figure 9. c), and higgsino NLSPerror. (figures b Note and thatsimplified d) the SUSY pMSSM models significance models (as (indicatedbranching assuming ratios indicated by in 300 fb in comparison the with figure the color simplified SUSY scale) models. is The somewhat dashed gray lower line indicates than the for the JHEP04(2016)154 100 GeV and a cut ∼ ]. The dotted red 16 funnel cut ] (only for wino NLSP). 22 (b) integrated luminosity could 1 − = 110 GeV) indicate the GC best fit pMSSM  1 ˜ χ m – 15 – final state searches at the LHC for precisely these pMSSM T / E + . Stars (located around l  1 ˜ χ (a) missing transverse energy increases the sensitivity to these pMSSM m contour of the most likely pMSSM10 models from ref. [ ], which coincide with the best global fit models obtained by [ = σ 0 1 low 15 ˜ χ m Significance (indicated by the color scale) for wino NLSP (a) and higgsino NLSP (b) . Contrary to what is required in most searches for SUSY, we find that the Zb Using the proposed strategy, the 14 TeV LHC with 300 fb , where the bosons decay leptonically. The main reducible background processes are and ¯ t channel and could goof down to a mass dedicated splittings SUSYLSP, as as search low these that as pMSSM 9 targets scenarios GeV.spectrum are compressed observed We favored for stress pMSSM by the the Galactic global scenarios Center. importance fit with Via studies the a and introduction by bino-like of the the photon excess WZ t requirement of models compared to the current electroweak SUSY searches. probe bino-like DM with masses up to 140 GeV using the chargino-neutralino production these models due to thecurrent large LHC bino component electroweak of SUSY the searchfavored lightest strategies neutralino. pMSSM are We not models. found and that willthe the We not sensitivity therefore be of sensitive propose the toscenarios. an 3 these improved The search main strategy irreducible to background enhance for this search channel is the production of 6 Conclusion Global pMSSM fits and thebino-like pMSSM lightest solution neutralino of as the GC aneutralino photon viable that excess WIMP suggest are candidate, a accompanied 10-25 GeV by a heavier. chargino and Standard mono-jet searches are not sensitive to Figure 10. pMSSM models assuming a backgroundcates the systematic limit uncertainty of 10%.models from The ref. dashed [ gray lineline indi- indicates the 1 JHEP04(2016)154 of data 1 − decay, the sensitivity Z contour of the most likely σ (b) ], which coincide with the best 15 30 GeV, using a background uncertainty of 10% < – 16 – . ) j ( 11 T p ]. The shaded red area indicates the 1 exclusion reach for the LHC at 14 TeV and with 300 fb ] (only for wino NLSP). 16 σ 22 (a) The expected 2 der the grant MULTIDARK CSD2209-00064,PEOPLE-2011-ITN, the PITN-GA-2011-289442-INVISIBLES Invisibles and European thede ITN “SOM la project Sabor Materia” (FP7- y (FPA2011-29678)alla and origen del the “Fenomenologia Modelo y Estandar17747) Cosmologia e MEC de lmplicaciones projects. la Experimentales Fisica en mas la era del LHC” (FPA2010- Acknowledgments R. RdA, is supportedthanks by the the support Ram´ony Cajal of program the of Spanish the MICINN’s Spanish Consolider-Ingenio MICINN and 2010 also Programme un- on the invariant mass offor the these scenarios lepton is pair increased originatingtri-lepton tremendously from searches, as leptonic as compared to shown the in current figure ATLAS and CMS (5%). Stars indicateglobal the fit GC points best obtained fitpMSSM10 by pMSSM models [ models from ref. from [ ref. [ Figure 11. for the wino NLSPindicated by (a) the and blue and higgsino(5%). red NLSP solid The (dotted) solid (b) line, (dotted) models. usingmomentum black a line cuts systematic The indicates background with uncertainty the current of the limit CMS 10% obtained requirement and using the ATLAS default reach lepton is transverse JHEP04(2016)154 1 10 − ). 12a & 20 GeV 10 GeV 15a 10 GeV. m & & & and m m 14a ), the sensitivity 170 (110) GeV with requirements, we can 13b 50 GeV for . > T < p and ) e ( 50 GeV is used (figures T 13a < ) < p j ( T , the proposed analysis can exclude p 1 − ) for the wino (higgsino) NLSP region. The 1 – 17 – , while the ATLAS and CMS experiments with 1 − of data or reducing the systematic error on the standard ). Using the proposed cuts and assuming a systematic 1 ). − 13d 15b 50 GeV for and 10 GeV and and < ) ) we show the reached significance using the current ATLAS lepton 13c µ 14b ( T 12d ( 6 (15) GeV can be realized for the wino (higgsino) NLSP pMSSM models. In < p & requirements (as indicated in table (figures 12c 30 GeV is used. Using this cut, the LHC operating at 14 TeV and with 300 fb T 1 ), the LHC can probe LSP masses up to 135 GeV (85 GeV) for ∆ p − 50 GeV if the NLSPs are wino-like and LSP masses up to 95 GeV for ∆ < ) We therefore conclude that an updated search strategy is needed. Even in the most Even using an integrated luminosity of 30 fb If the systematic error could be reduced to 5% (figure In the standard analysis, the requirements on the transverse momentum of the leptons − 12b j ( 9 T model background to 5%) thenot current sensitive tri-lepton to search the strategies discussed of favored ATLAS regions and of CMS the are pMSSM parameter space. with an integrated luminositytheir of current 30 tri-lepton fb searches3000 fb are not even sensitive with anoptimistic integrated cases luminosity (using of 3000 fb contrast, the ATLAS and CMSare experiments in with that their case current still tri-lepton not search able strategies to probethe the wino favored (higgsino) pMSSM regions NLSP(25) (figure scenarios GeV for (figures LSPbackground masses uncertainty up of 10%, to we 135 can (85) be GeV sensitive to and the ∆ 100 GeV bino-like DM particle Therefore, if it is possiblethis would to be lower the worth to lepton pursue. transverse momentum trigger requirements, would be greatly enhanced.mass In gaps that case, exclusion of LSP masses In figure trigger significance is somewhat reduced comparedthe to lepton the transverse significance momenta. using lower Usingexclude requirements wino the on pMSSM ATLAS trigger scenarios lepton with LSP masses up to 135 GeV and mass gaps if the NLSPs areand higgsino-like. If(25 GeV) a for jet the wino veto (higgsino) with NLSP region. are 5 GeV In this appendix we show whaterror happens and if different the assumptions integrated onp the luminosity cuts, are the systematic made.of In integrated the luminosity standard∼ can analysis, probe a jet LSP veto masses with up to 140 GeV for mass gaps between A Detailed discussion of the LHC14 reach JHEP04(2016)154 ]. The dotted ) and higgsino ] (only for wino 16 left 22 (d) (b) . of 50 GeV. Figures (c) and (d) using 1 T p = 110 GeV) indicate the GC best fit pMSSM  1 ˜ χ m – 18 – requirements as shown in table T p contour of the most likely pMSSM10 models from ref. [ (c) (a) σ ). Stars (located around ], which coincide with the best global fit models obtained by [ 15 right Significance (indicated by the color scale) for wino NLSP models ( NLSP). Figures (a) andthe (b) ATLAS are trigger made lepton using a minimal jet Figure 12. NLSP models ( models from ref. [ red line indicates the 1 JHEP04(2016)154 ]. The dotted ) and higgsino ] (only for wino 16 left 22 (d) (b) . 1 − = 110 GeV) indicate the GC best fit pMSSM  1 ˜ χ m – 19 – contour of the most likely pMSSM10 models from ref. [ (c) (a) σ ). Stars (located around ], which coincide with the best global fit models obtained by [ 15 right Significance (indicated by the color scale) for wino NLSP models ( NLSP). Figures (a) and (b)(c) are made and assuming (d) a are systematic background made uncertainty assuming of an 5%. integrated Figures luminosity of 30 fb Figure 13. NLSP models ( models from ref. [ red line indicates the 1 JHEP04(2016)154 1 − contour of σ . Stars (located ], which coincide  1 ˜ χ 15 m = 0 1 ˜ χ m and 5% systematic error and (b) 3000 fb 1 − ]. The dotted red line indicates the 1 (a) (b) ]. – 20 – 16 22 = 110 GeV) indicate the GC best fit pMSSM models from ref. [ Standard ATLAS and CMS tri-lepton search significances (indicated by the color scale)  1 ˜ χ m around with the best globalthe fit most models likely pMSSM10 obtained models by from [ ref. [ Figure 14. for wino NLSP pMSSMand models 10% assuming systematic (a) error. 300 fb The dashed gray line indicates the limit JHEP04(2016)154 1 − . Stars (located ], which coincide  1 ˜ χ 15 m = 0 1 ˜ χ m and 5% systematic error and (b) 3000 fb 1 − (a) (b) ]. – 21 – 16 = 110 GeV) indicate the GC best fit pMSSM models from ref. [ Standard ATLAS and CMS tri-lepton search sensitivities (indicated by the color scale)  1 ˜ χ m around with the best global fit models obtained by [ Figure 15. for higgsino NLSP pMSSM models assumingand (a) 10% 300 fb systematic error. The dashed gray line indicates the limit JHEP04(2016)154 ] Phys. -ray ] ] D 90 D 89 γ , ] J. Phys. ]. , (2013) 129902] SPIRE IN Phys. Rev. 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