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JHEP09(2015)204 Springer July 18, 2015 : September 3, 2015 September 7, 2015 , September 29, 2015 : : : Received 10.1007/JHEP09(2015)204 Revised Accepted excess in the search for the Published doi: σ b,c Published for SISSA by [email protected] , and large missing transverse energy. Al- Z and Takahiro Terada b . 3 1506.07161 excess in minimal supersymmetric standard Satoshi Shirai The Authors. a c Phenomenology Z

Recently the ATLAS collaboration reported a 3 , [email protected] Tokyo 113-0033, Japan E-mail: [email protected] Berkeley Center for Theoretical Physics,and Department Theoretical Physics of Group, Physics, LawrenceUniversity Berkeley of National California, Laboratory, Berkeley, CADeutsches 94720, Elektronen-Synchrotron (DESY), U.S.A. 22607 Hamburg, Germany Department of Physics, University of Tokyo, b c a Open Access Article funded by SCOAP gsinos. We show that the excess can be explained by theKeywords: reasonable MSSM mass spectrum. ArXiv ePrint: events containing a dilepton pairthough from the excess a is not sufficientlyby significant yet, a it well-motivated is model quite tempting beyondity to the of explain standard this the excess model. minimal supersymmetric Infocus standard this on model paper the (MSSM) MSSM we for study spectrum this a where excess. possibil- the Especially, we are heavier than the and Hig- Abstract: Xiaochuan Lu, ATLAS model JHEP09(2015)204 6 2 . . 1 3 ± ± ]. The 2 6 . . 1 Z 3. In this , 2 (1) ≥ O jet n bosons are generically Z 225 GeV), and large scalar sum > excess in the search for the events with miss σ T E excess in the context of the SUSY SMs. excess. Z – 1 – σ 4 ], where the signal events are classified into MET 2 300 GeV) and the number of jets [ excess is not so statistically significant yet and might > Z ] get more severe. Possible solutions to overcome this Z 4 9 3 3 boson mass peak and large missing transverse energy (MET) [ Z 1 7 boson mass range, large MET ( ], general requirements in the SUSY SMs to explain the excess are studied, Z 3 = 100-200, 200-300 and 2. The two channels combine to give 29 observed events compared to 10 . 2 ± miss T 600 GeV) of the transverse momenta of all signal jets and the two leading . 4 E . > In ref. [ Although the present ATLAS On the other hand, the CMS collaboration has an analogous search for events with 2.1 Mass spectrum2.2 Decay of and T H in its decay chain. Ina the specific as case the of lightestnot the SUSY produced minimal enough SUSY (LSP), in standard it the modelincreasing SUSY is (MSSM) the cascade found production with decay that cross chain. section with Onefrom the can light the try to jets or compensate squarks, and this but MET the by constraints searches [ quite tempting to investigate whetherthe a signal. well-motivated model beyond TheSeveral the studies large SM are can MET devoted explain is to the a ATLAS typical signatureand of it the is supersymmetricproduction concluded (SUSY) cross that section SMs. the there order needs of colored to , be as well a as particle producing lighter than about 1.2 TeV, with large MET and abins dilepton ( pair on CMS counterpart search, no significant deviation from the SMeven expectation conflict is with found. the aforementioned counterpart search by the CMS collaboration, it is The observed events inwhereas the the expected dielectron numbers of andand the dimuon 6 channels (SM) are backgroundexpected events 16 are from 4 and the SM, 13 amounting respectively, to a 3 Recently the ATLAS collaboration has reported aa 3 dilepton pair on signal events should containmass a in same-flavor the opposite-sign( dilepton pair with its invariant 1 Introduction 3 LHC signals 4 Summary and discussion Contents 1 Introduction 2 SUSY spectrum JHEP09(2015)204 , W ], stop can be 4 Z ] can also 13 . Even if the ]. Combining bosons induce Z 14 Z , ] framework, but ]. There is also a 12 18 19 ]. In the light of the 33 – ] are severe and such an 2 28 ], where the first and second ]. Now the MSSM with split 5 40 ] seems to suggest the framework – excess. -jets searches [ 34 dilepton [ 21 Z b , Z 20 ]/Randall-Sundrum [ ]. The light sbottom scenario [ 17 14 – 2 – bosons may result in multi- events. Therefore our ] as well as CMS on- Z excess, the MSSM mass spectrum will at least satisfy the . h 10 Z ]. , 9 11 ], the NMSSM scenario can reduce the significance of the excess ], where the SUSY are around TeV scale and the SUSY ], where the branching fraction of neutralino NLSP into 15 27 , ] or singlino-like in the next-to-MSSM (NMSSM) [ 7 – , ] in the composite Higgs [ with a mass of around 125 GeV [ 4 6 13 , 22 h 16 2 in the next step of the decay chain. In the case of the GGM with a light boson can be efficient. An important requirement here is to ensure that ]. When the mass difference between the neutralino LSP and the neutralino Z Z 14 – ] or multi-lepton [ 8 12 boson. Another type of spectrum is studied in ref. [ Z To explain the ATLAS In this paper, we revisit the possibility of explaining the excess in the MSSM, in On the other hand, compressed spectra are utilized in other attempts to explain the The spectrum with the light LSP is realized in the so-called general , or the -rich decay chains are realized at the LHC, the non-leptonic decays of the condition that the SUSY cascade decayZ chain has large branching fractionsignals to of multi-jets plus METmultiple with leptonic zero decays lepton, of which are the goal severely is constrained. to Moreover, find the mass spectra which satisfy the conditions: split SUSY is quiteHiggs compatible discovery, with this the framework observed isSUSY-like Higgs intensively spectrum mass studied is [ [ one ofinteresting to the study most this convincing and model viable in models. light of Therefore the it ATLAS is very particular in the well-motivated splitattractive candidates SUSY-like of spectrum. models beyond The theof MSSM standard the model. is Higgs boson one Especially the of recentof the discovery the most split SUSY [ scalars are heavier than TeV scale.scale MSSM, This framework such can as overcome SUSY weak points flavor/CP of and the cosmological weak- problems. Most importantly, the like neutralinos, and hencenon-SUSY is study severely [ constrained by this also has bottom-rich signatures. gravitino, this requirement isIn satisfied the because heavy the LSP gravitinowith scenarios, LSP light sbottom the is [ very LSP weakly isother coupled. constraints taken [ to beonly a in Bino-like a small neutralino region inreduce in the the the significance, parameter MSSM but space sbottom [ produces bottom when it decays into Higgsino- excess [ NLSP is less thanLSP the plus Higgs a massthe (125 GeV), parent the particle two-body (gluinocan decay produce or of squark) the NLSP decays into mainly the into the NLSP so that the NLSP mediation (GGM) [ close to one. However,search constraints [ from other SUSYexplanation searches is such not as viable jets+MET [ [ light gravitino LSP, in which theand neutralino next-to-LSP (NLSP) decaysgeneration into squarks the decay gravitino into aZ Bino followed by the Bino decaying into Higgsinos and difficulty are discussed, including use of a compressed spectrum or a spectrum with the JHEP09(2015)204 ). 2 , and 0 1 boson. χ 100 GeV Z ∼ ˜ B boson with a ] (see figure m Z 44 − – ˜ H 41 ) can well account for m 1 r ˜ t and a Higgsino-like Sfermions 3 , 0 2 χ – 3 – Z -rich. Z ˜ ˜ B H g . Schematic picture of the present MSSM spectrum. , the above conditions can be simultaneously satisfied. As we will t ˜ g m 2 Figure 1 − , when the stop is heavy and the spectrum is sufficiently compressed, the excess. If the mass spectrum is compressed enough, ˜ g 2 Z m . , we reduce essential features of the MSSM spectrum to a simplified model, and 3 4 & ˜ H SUSY cascade decay chain is Less constrained byjets+MET. searches other than the dilepton channel, such as multi- m Because of the renormalization group effects, the right-handed stop is expected to In this paper, we point out that a simple mass spectrum (figure as the NLSPs. For simplicity, we take the Wino heavier than the gluino. • • ± 1 ˜ the squarks, gluino branchingchannel fraction becomes shows the an top-stop-loop-induced interestinggluon process for feature: suitable into the mass a splitting dominantThis Higgsino-like between decay neutralino reduces gluino and and the the a dominantly branching neutralinos decays [ fraction into a of neutral gluino Higgsino three-body with a decay . modes, and the gluino scalar superparticles are heavy,which and decays we into consider neutralinos productionthere and of are . the nearly degenerate relatively The two lightχ Higgsino-like LSP gluino, neutralinos is ˜ a Bino-like neutralino ˜ be typically lighter than the other squarks. If the right-handed stop is lighter among 2 SUSY spectrum 2.1 Mass spectrum We take the split SUSY-like spectrum, where the gauginos and Higgsinos are light whereas gluino decay channel.branching The fraction Higgsino-like close to neutralino 1. canIn Together, this then section gives decay rise to into anstudy efficient LHC production of signals ofin the section model and its constraints. Summary and discussions are given the ATLAS and see in section gluino radiative decay into a Higgsino-like neutralino and a gluon becomes the dominant JHEP09(2015)204 . h – 3 , → 0 2 m 41 0 i χ χ . 0 1 boson if ˜ χ BF(˜ m 3 W , − 3 =2 and less than , i 0 2 ˜ χ Z P boson, efficiently m Z < m boson in the present Z W u m in the case of the light 100 GeV. ˜ 0 3 H χ -term, but ' µ 0 1 g varies substantially in the case ˜ χ excess. The gluino decay into a h and ˜ m is greater than Z 0 2 − or 3 χ , 3 , 0 2 Z 0 2 ˜ χ χ m and ˜ 0 1 boson, and into a chargino with a χ H ˜ t – 4 – 5 in the limit of large mass difference between h . 0 or t compared to other channels: (i) gluon and Bino, (ii) ' Z 2 2 / )) ) t h 0 1 /m ˜ χ ˜ t m First, we consider the neutralino decay. A neutralino may decay → 1. Once the Higgs channel becomes kinematically available, the 0 i ˜ g bosons in the gluino decay chain efficiently, χ ' . Diagrams of the gluino decay into a Higgsino and gluon. boson is the complex partner of the Higgs, whereas the transverse Next, let us move on to the gluino decay. As studied in refs. [ Z ) Z Z BF(˜ 0 1 3 ˜ , χ boson. Thanks to the log enhancement, this decay mode dominates over =2 Z i Figure 2 → depending on the phases of parameters such as . This can be understood in the Nambu-Goldstone picture: the longitudinal 3 P , 3 , β 0 2 0 2 χ ' χ 2 / ) is Higgsino-like, so it is approximately degenerate with Higgsino-like neutralinos ˜ and ˜ , BF(˜ bosons per gluino decay is enhanced. In this case, the constraints from other SUSY Z ], the partial decay rate of gluino into a gluon and an (up-type) Higgsino is relatively h 0 1 0 1 1 ± ˜ ˜ ˜ Higgsino-like neutralino, followed by theproduces decay of the the neutralino intothe a other channels forZ wide parameter space andsearches, the such as expectation multi-jets value and of leptons the signals, can number be of relaxed. Another advantage of this 44 enhanced by a factorneutralino, (log ( and antiquark,gluino and efficiently (iii) chargino, produces quarkgluino Higgsino-like and and neutralinos antiquark. heavy (but Therefore, ˜ relativelythe the lighter gluino among has the some squarks) advantages to stop. explain This the radiative ATLAS decay of equally contained in theorder to two produce mass the eigenstatesis of required. Higgsino-like In neutralinos. the following Therefore analysis, in weDecay assume of gluino. χ χ component of the components are unimportant indecays the into limit. the Taking up-type the Higgsino average in is justified our because spectrum gluino (see below), and it is approximately This means that neutralinos cannotspectrum. decay into the If chargino the withm a mass difference betweenbranching ˜ ratio of each Higgsino-likeof neutralino into low tan SUSY spectrum and a simplified model studiedDecay in of the neutralinos. next section. into a lighter neutralinoeach emitting channel a is kinematically allowed.χ In the present mass spectrum, the lightest chargino 2.2 Decay of neutralinosWe and study gluino neutralino and gluino decays in this subsection to motivate the present split JHEP09(2015)204 ), at (2.4) (2.5) (2.1) (2.2) (2.3) is not. c R,j u ˜ B 7 . By using µν C + 100 GeV parameter, t ]. For this σ 1 y , and several µ 42 . L,i M µν and Q   = u u , )( 33 u | 33 , , HG ˜ ˜ ˜ ˜ g H H 2 5 µ H 2 ) ! | ˜ g C O µν C Ri σ ˜ µν 2 d   1 u ], we set the weak scale σ ˜ m ! u H 45 2 ( t ˜ same as squark masses. To H y + ( ≡ A t Ri ≡ u y + 3 m ˜ 2 u 2 ,ij s ˜ H 2 u 2 s g m ˜ g H 5 2 O . O , squark masses, Higgs − 14 2 ! − , R Li M ˜ 2 t ˜ 2 q 1 2 1 t ! y m m R 3 2 ˜ 2 t about 100 GeV, we fix t 1 and

]. Following ref. [ + y + m 1 = 3 TeV, and ± 1 s 3 i 44 2 s g L χ 2 – X ˜ + M g 2 q = 800 GeV is taken unless otherwise stated. To 1 4 – 5 – , ˜ ) , 3 3 M 3 ˜ g 37 m 42 , ˜ ˜ B L B 7 0 2 ˜ 2 q 1 m −

χ m C m , where the branching fractions of gluino are plotted.

2 s β 2 − g 2 3

π . For simplicity, we neglect mixing among squarks, and ˜ g π and ˜ sin 14 1 β β 2 t 16 m 2 0 1 y 16 − ( and diagonalize the neutralino (and chargino) mass matrix t 2 π χ s 2 y 0 1 2 g s = = π g 2 sin g √ 2 M s ˜ B 7 √   g 32 384 4 C u u 33 , ˜ , and tan ˜ H = 10 TeV. The black line represents the branching fraction of the µ 5 H 2 = = = A , dimension six dipole operator C r d C ln ˜ t ˜ u B m u 7 µν 33 . At the mass scale, these Wilson coefficients are given by ˜ , d H   ˜ 5 m H 2 C axis in the figure G u 33 , five dominant branching fractions of gluino are shown with the right- C , ) µ ˜ C H 2 ˜ g d ln O LSP µν d 3(a) m ˜ Bσ ) factor, otherwise, the two body decay rate is overestimated [ t ( , and positive. We vary , Bino and Wino mass parameters u ≡ ˜ g 1 ˜ /m H 5 ˜ t ˜ B m 7 is logarithmically enhanced through the operator mixing with M O In figure In the calculation of gluino branching fractions, the relevant parameters are gluino In the estimation of gluino branching fractions, we need resummation of the m O , u ˜ ˜ B H 7 5 make mass difference betweenwith ˜ to show the handed stop mass mass CP odd Higgs mass we take a universalthree mass times for larger squarks than except thereduce for latter, the the and number right-handed of stop. parameters, we The fix former is set C Thus, the radiative decay rateheavier of sfermions. the We gluino evaluate into the thegluino gluino Higgsino mass decay are rates scale. relatively with enhanced these ForYukawa with and details, Wilson gauge coefficients see at coupling refs. the parameters. [ Here we take into account only the top Yukawa and strong couplings. The Wilson coefficient Here we neglect sfermion flavor violationthe and renormalization the group Yukawa couplings equations other than (RGEs)the of gluino the mass Wilson scale. coefficients, The we evolve RGEs down of to interest are written as, four-Fermi operators which include athe gluino spinor sfermion e.g., mass scale.O The operators relevant for the radiative decay of the gluino are are severely constrained by LHC searches even for thelog compressed ( mass spectrum. resummation, we first evaluate thetor Wilson coefficients of the dimension five dipole opera- radiative decay is that we can suppress the branching fractions into heavy-flavor jets, which JHEP09(2015)204 1 − M = 2. ) 700 3 ) = β , 0 2 µ ˜ χ and g µ 600 10) 10) , plane , 100) 100) → 100), respec- 2 , , , 2 50 2 , g , , , − 2 − − ( ( (+ , LSP = 2, sgn( = 800 GeV, and 500 . The solid black, . The branching m - β ˜ r g TeV) = ( ˜ t ˜ g / r ˜ t m for various choices of m m [GeV] 3 and (+ β, m 600 GeV, and tan 3(b) , 400 0 2 , LSP tan − . The solid black, long- ˜ , χ ) on ) m 0 1 µ g 3 ˜ , χ = 0 2 100) ˜ m µ χ (sgn( , 300 g 2 , = → − ( g , 1. 200 plane. We set tan LSP − 10) m , LSP = 500 GeV, 50 (d) BF(˜ ) = 100

, 1 1 0 2 8 6 4 2

m 1 . . . . .

1 0 → 0 0 0

3 , 2

BF ˜ χ g g (˜ ) (b) LSP mass dependence of BF(˜ − 0 M ( − , respectively. We take , ˜ g ± 1 µ/M ˜ χ m 10) tb , – 6 – 2 as a function of the stop mass , ) 3 700 3 1000 , − , 0 2 0 2

˜ on the

χ

1 ˜

χ ˜ , and

χ g 0 g and sgn( 3 0 1 g , ˜ 0 2 χ β 600 → ˜ χ tt g g , TeV) = ( 1 0 10). (b): the branching fraction into / → ˜ , χ r 2 100 500 g ˜ 3 t , g , 0 2 ˜ χ , g 3 , 2 0 β, m [GeV] [TeV] ˜ χ

400

r 1 =

˜ t r

LSP

tt

t ˜ m tan m

, , /m

˜ q ) ± 1 3

,

χ˜ m 5 . µ 2 0

tb TeV) = (+

10 1 for other choices of parameters are shown in figure

300 2 ˜ / χ r 3 g ˜ , t 3 ,

0 0 2 2 χ˜ ˜

tt χ g 200 β, m

is relatively inefficient for the gluon channel. The branching fraction of the 3 . Various dependencies of branching fractions of the gluino. (a): the branching frac- 0 1 ˜ χ = 100 TeV. It is greater than 0.7 and 0.9 in the red and blue regions, respectively. tan tt , r 1 ˜ ) t 100 3(a)

1 2 8 7 6 5 4 3 9 4 2 8 6 0 1

......

. . . . µ

→ 0 0 0 0 0 0 0 0

0 0 0 0 m (a) Branching fraction of each decay mode

3 , 2 BF ˜ χ g g (˜ ) rnhn Fraction Branching 0 (c) Squark mass dependence of BF(˜ figure gluino into fraction becomes largenegative. in This particular is when because thecancellation we up-type in take Higgsino the the component case in relative of the low sign LSP tan decreases between by partial gluino to the Higgsino-likefigure neutralinos for and the gluon. kinematicalor reason. chargino It As and diminishes the gluino inemitting mass increase the a splittings (to right quark-antiquark between the pair side the left become relevant of of neutralino non-negligible. the the figure), The the choice three-body of decay the channels parameters in correspond to (sgn( tively. (c): the branchinglong-dashed fraction red, into short-dashed blue,and and 3 dotted times green larger lines than(d): the correspond lighter to the stop squarks mass. branching masses fraction Weand set 1, of 1.5, ˜ 2, Figure 3 tions of thedashed gluino red, decay medium-dashed blue, asing short-dashed functions green, fractions and of to dot-dashed the(sgn( pink LSP lines show mass theparameters. branch- The solid black, long-dashed red, medium-dashed blue, and short-dashed green lines JHEP09(2015)204 is on r ] in- 3 ˜ t , (2.6) 0 2 ˜ excess. χ 48 ]). The bosons, /m , g ˜ 600 GeV q Z Z 47 52 − m , → = . We assume g 51 0 1 (1) mm from being real and µ ˜ χ O 1 Z M ), due to the large → 3 , . 0 2 (100) TeV to produce 0 2 4 χ ˜ O χ  g = 500 GeV, and ˜ ] are used. The gluino pro- r → 2 and 3. If the ˜ t 1 0 2 100), with , 100 GeV, can lead to efficient 54 , ˜ m χ 5 g M . 2 bosons. Therefore, constraints g ' , , 1 100 TeV ˜ q , excess. On the other hand, the 0 1 Z ˜ → χ  m 100 3 Z g m = 1 − ≡ − − 3 1  r ˜ L t 3 ˜ , q M 0 2 ] should place severe constraints on it. In ˜ χ m 2 − /m NLSP ˜ q m = m m ] (which has FastJet incorporated [ 2 , – 7 – 1 − 50 ˜ g 300 GeV L,R ˜ q m TeV) = ( / m  r ˜ t m 1. µ 300 GeV and β, m ' . ) (10) 0 1 3 , tan ˜ O 0 2 χ , ˜ χ ] and Delphes 3 [ (1) TeV can realize the favoured gluino decay, which may leave ∼ gZ m ˜ g , heavier stop can increase the BF(˜ O 49 GeV − cτ → ˜ g = ] is applied with a scale parameter set to a quarter of the gluino mass. µ/ g m 3(c) r , we also vary the gluino mass as well as the LSP mass, showing the region , we show the dependence of the gluino branching fraction of ˜ 53 ˜ t m ]. 3(c) 3(d) = 100 GeV and take the branching fraction of each decay as 1 for simplicity. = 2. We show the cases that 46 0 1 ˜ χ β m bosons. Single lepton+MET channels are expected to be less important due to the − To study the fitting region and various constraints, we generate this simplified model As discussed before, this simplified model can produce sufficient amount of In figure In figure 0 2 Z production, BF(˜ ˜ χ (1) mm, severer constraints will be imposed even in the case of the compressed mass with up to one extraterfaced parton to in Pythia the 6.4 [ matrix elementMLM using matching MADGRAPH [ 5 v2.1.2 [ The parton distribution functionsduction (PDFs) cross from sections CTEQ6L1 are [ calculated at next-to-leading order (NLO) in the strong coupling by the gluino decayby and multi-jets+MET the channels could hadronicfour-lepton+MET potentially decay analyses be modes could important. of also Dilepton+Dijet+METof be and relevant due to thesecond (semi-)leptonic lepton decay veto. modes m which we expectcounterpart to search be by consistent the CMSaddition, with this collaboration the simplified [ model ATLAS can easily produce up to six jets due to the produced 3 LHC signals The essential features ofreduced the into a present simplified mass model spectrum with the discussed decay in chain: the ˜ last section can be where the branching fractionhigh. of Here the we gluino set ( intopositive. a We Higgsino-like see, neutralino andZ a gluon is The standard trackingthe system primary assumes vertex. the Thereforethe gluino the standard decay stop MET mass occurs and/orO should jets within be and/or less leptons than signals.spectrum [ If the decay length is larger than log enhancement. Notemass increases: that, however, the gluino decay length gets larger as the stop the squark masses. Hereand we assume tan large enough, the possibility that theAs relatively seen “natural” SUSY in can figure account for the ATLAS JHEP09(2015)204 ] 10 2) for excess . 2 2.3 and Z < ± ], ATLAS 2 2 4 . χ ] and CMS [ 9 6 (6 . 1 ± +MET constraint; and channel exclusion line 2 . Z parameter estimation from +MET data [ ZZ Z σ fitting regions in the figure. σ and 2 σ and 2 ] and show ]. 600 GeV) of the transverse momenta variable. The regions ∆ σ 60 59 2 > – χ T 55 H – 8 – constraint including the ATLAS four lepton, CMS four parameter estimations from the ATLAS 101 GeV), two jets, and MET larger than 225 GeV. +dijet+MET [ ZZ σ < Z ] and four-lepton+MET data by ATLAS [ ll 4 and 2 < m ]. Then we estimate the exclusion curves at the 95% confidence σ 60 prescription. We use the SM background estimations and its channel. ] and CMS s Z 4) between each of the leading two jets and the MET direction. . 10 0 CL + dijet channels. The red regions show 1 > Z ) , we show 1 4 miss T +dijet+MET [ ,E ] and CMS [ Z . Constraints at the 95% CL of the simplified model. The black solid line shows the 2 9 , 1 ]. For this fitting, we estimate the number of SUSY signal events for the ATLAS mass range (81 GeV 1 Similarly, we also estimate the signal strength of the CMS In figure (jet Z φ level, by usinguncertainties the provided by each reference. Regardingsearches, the we ATLAS choose multi-jets (2-6 a jets)+MET channeleach parameter which point is among expected 15 toATLAS signal [ give regions. the We most combine the stringent four-lepton+MET constraints data on by 6.0, corresponding to 68thdegrees and of 95th freedom, respectively, percentile are of referred the to as Chi-Squared 1 distributionmulti-jets with (2-6 jets)+MET two data [ and CMS the Additional cuts include theof large scalar all sum signal ( (∆ jets and theWith two the leading observed leptons, number 16the and (13) dielectron large and (dimuon) the azimuthal channel, SM angular we expectation construct separations value a 4 constant, adding the resummationaccuracy (NLO+NLL) of by soft using NLL-fast gluon v2.1 emission [ at next-to-leading-logarithmic data [ cut, which requires a same-flavor opposite-sign dilepton pair with its invariant mass in ATLAS multi-jets+MET constraints; the blue dashedthe line green shows dotted the line CMS showslepton, a and combined CMS the ATLAS excess of the Figure 4 JHEP09(2015)204 ] 15 are can 3 t , excess 0 2 m +MET χ 2 Z Z − ˜ g excess in the m ) is of our true t +MET signals. Z & m Z 2 . NLSP m NLSP m . In this model, while the 0 u − ˜ ˜ g H g m +MET search by the CMS, which in the signal region of the ATLAS → Z T g H – 9 – excess and not excluded by the various constraints, Z excess and the CMS counterpart exclusion limit. Z ] are found less important. ), and hence justifies our use of this simplified model. We see , and the present simplified model well describes the realistic 61 excess without conflicting with other SUSY searches, apart 3 3 Z +MET counterpart search. There is even a small parameter region +MET excess. Z Z +MET search. In such a region the gluino radiative decays into Z +dijet+MET [ , the relatively small mass splitting region ( Z 4 . Other constraints such as ATLAS large jet multiplicities (7-10 jets)+MET [ ], the compressed mass spectrum can well fit the observed distributions of MET 4 12 and the scalar sum of transverse momenta However there is a subtlety when we consider the Moreover the present MSSM mass spectrum has another advantage. As pointed out In figure miss +MET search. This feature is also the case for the present MSSM model. The mass T the ATLAS excess can beexclusion explained limit and and the the CMS ATLASboth constraint best searches is can fit evaded. be region consistent However within is the thisof CMS very model, our close, taking into and fast account possible it simulations.more uncertainties is precise hard A constraints. to more conclude detailed the detector simulation will be needed to estimate seems to exclude aAlthough the large ATLAS and portion CMS searches of arerelatively similar the more to account best-fit each other, of region the theLHC ATLAS for search constraints hadronic makes between the activity. the ATLAS This ATLAS and difference CMS leads searches. to Then there slightly is different a tiny region where in ref. [ E Z spectrum of our interest, thus, canwithout account conflicting for with not only the theof major number the of SUSY excess. the searches ATLAS but also the more detailed behaviours from the CMS dominated, as seen in figure gluino decay chains.explain Therefore the ATLAS we can conclude the very simple MSSM spectrum may can relatively enhanceLSP the is radiative Bino-like gluino neutralino,Motivated the decay by direct this ˜ feature, gluino we decay exploredexcess. into the simplified the We model LSP found to is that explain thewell the relatively ATLAS suppressed. gluino explain mass the around ATLAS 800-1000 GeV and In this paper, weMSSM study spectrum. the We possibility studyare of the heavier explaining gluino than the and thethat recent neutralino the gluino, ATLAS decays small assuming in mass the the difference Bino between case the LSP that gluino sfermions and and the neutralinos and/or Higgsino large NLSP. stop We mass show space that is consistent withapart ATLAS from the CMS consistent with both the ATLAS 4 Summary and discussion and ATLAS interest, because in this regionbe the very close gluino to decay 1 branchingfrom (see fraction the figure in figure the that split within MSSM the can justified parameter region, there is a substantial parameter in figure JHEP09(2015)204 pp 177 ] TeV (2015) 124 ]. = 8 04 s √ SPIRE IN [ JHEP , arXiv:1503.03290 , and its detailed study [ β TeV TeV –proton collision = 8 Prog. Theor. Phys. Suppl. = 8 s , s The ATLAS Z + MET excess in √ √ (2015) 318 ]. arXiv:1503.04184 = 13 TeV will be around 100 with the , C 75 SPIRE s IN √ ][ collisions at pp – 10 – ]. ]. Eur. Phys. J. General gauge mediation , SPIRE SPIRE 10619. IN IN · [ ]. ][ ), which permits any use, distribution and reproduction in production and its number is estimated to be around 50. arXiv:1405.7875 ¯ t t [ SPIRE Search for squarks and gluinos with the ATLAS detector in final Search for supersymmetry in events containing a same-flavour IN METing SUSY on the Z peak Search for physics beyond the standard model in events with two leptons, ][ or more excess will be observed. Thus, the LHC Run II will provide CC-BY 4.0 σ (2014) 176 This article is distributed under the terms of the Creative Commons and the center-of-mass energy 09 arXiv:0801.3278 arXiv:1506.05799 1 [ , − collaboration, collaboration, ]. collaboration, JHEP , SPIRE = 10 fb arXiv:1502.06031 IN the MSSM states with jets anddata missing transverse momentum using (2009) 143 CMS jets and missing transverse[ momentum in ATLAS ATLAS opposite-sign dilepton pair, jetscollisions and with large missing the transverse ATLAS[ momentum detector in In this study, we assume the split SUSY-like spectrum in which the scalar tops play It will be worth noting that this mass spectrum may provide a good Bino-like dark The LHC Run II will provide more obvious test for this model. The production M. Cahill-Rowley, J.L. Hewett, A. Ismail and T.G. Rizzo, P. Meade, N. Seiberg and D. Shih, G. Barenboim et al., dt L [5] [6] [2] [3] [4] [1] References Aid for Scientific Research No. 26 Open Access. Attribution License ( any medium, provided the original author(s) and source are credited. more generic types of MSSM spectra, and it willAcknowledgments be done elsewhere. The work of T.T. is supported by a Grant-in-Aid for JSPS Fellows, and a JSPS Grant-in- the other parameters, such asis the beyond Wino the mass, scope CP of phases and the tan present paper. a dominant role inrespectively. the gluino Although decay, this and assumption the is Bino well and motivated, Higgsino it are is the LSP interesting and to NLSP, investigate SM background comes from Assuming the systematic uncertainty ofthe the 8 background TeV estimation result, is a 30% 5 a as very in clear the case test of of the present SUSY model. candidate. 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