Search for R-parity violating SUSY signatures with the ATLAS detector

Transcription

1 Search for R-parity violating SUSY signatures with the ATLAS detector SEARCH22, Maryland Shimpei Yamamoto (Univ. of Tokyo) on behalf of the ATLAS collaboration Outline. Introduction 2. RPV-SUSY searches at ATLAS 3. Summary

2 . Introduction

3 Unexpected SUSY? SUSY with R-parity ( (-) 3(B-L)+2S ) conservation (RPC) is really popular: - Provides elegant solutions to the dark matter and hierarchy problems. - Leads to natural GUT. But currently one can squeeze the parameter space: - No significant excess of events having large missing transverse momentum (Etmiss) at LHC searches. - Indication of mh~25gev. - Flavor constraints from b sγ, B τν, Bs μμ etc. - Constraints from dark matter direct detection experiments. Some viable RPC models still survive, but we certainly must all possibilities. 3

4 R-parity violating SUSY There s no reason why R-parity should be exactly conserved... R-parity violating (RPV) terms are allowed in the superpotential: W = W MSSM + ijk L i L j Ē k + ijkl i Q j Dk + apple i L i H u + D ijkūi j Dk Lepton number violating (LNV) Baryon number violating (BNV) If all terms appear, proton becomes unstable... p / M 2 SUSY p u d u B/ s L/ ū u π e + Part of them need not to be zero Proton still stable & rich phenomenology - Resonant/associated single SUSY particle production is possible. - The lightest SUSY particle (LSP) is no longer stable. - Etmiss is diluted (or absent!) R-parity has played some roles... advantages and disadvantages: - No dark matter candidate :-( - Could explain large mixing angles and hierarchical masses of neutrinos :-)) 4

5 RPV signatures So, what we re looking for is... Signature RPV scenario multileptons ( eeµµ ) LSP( ), LSP( ) multiple s LSP( ), like-sign dileptons LLĒ( ), LQ D( ) dilepton resonance ( ll ) LLĒ LQ D( late-decaying LSP( ), LSP( ) ) LSP( ) (LNV) Also for bilinear RPV( apple) and BNV ( ). 5

6 RPV signatures So, what we re looking for is... Signature RPV scenario multileptons ( eeµµ ) LSP( ), LSP( ) multiple s LSP( ), like-sign dileptons dilepton resonance ( ll ) LLĒ( ), LQ D( ) LLĒ LQ D( LSP( ) late-decaying but LSP( more ), coming LSP( ) soon... Also for bilinear RPV( apple) and BNV ( ). ) A handful of results today, (LNV) 6

7 NEW! 2 fb - ATLAS-CONF RPV-SUSY searches Multilepton final state

8 4-lepton search Very low SM background, high signal-to-background ration - Promising channel to find something new! - Interpretations using the results already reported (ATLAS-CONF-22-) Selection:. Single-lepton trigger followed by offline pt cut - >25GeV for electron - >2GeV for muon 2. 4 leptons with pt>gev 3. Etmiss > 5GeV 4. MSFOS(*)-MZ > GeV (Z-veto) (*) Same Flavor Opposite Sign Events / 2 GeV 3 2 s= 7 TeV (24 events before Etmiss cut) L dt = 2.6 fb ATLAS Preliminary - Data 2 Total SM tt tt V WZ ZZ llll ZZ other Z+jets SM + RPV BC SM + RPV m /2 =74 GeV, tanβ = 22 w/o Z-veto W/ Z-veto BG exp..7±.9.7±.8 Observed Limits on visible cross section of BSM: <3.5(.5) fb w(w/o) Z-veto miss E T 8

9 BG breakdown Very high S/B ratio, but hard to estimate SM BG processes with very low rates. - BG estimation fully based on MC. - Validation regions to confirm that nothing goes wrong in the BG model. 4 leptons + Etmiss>5GeV + Z-veto ttbar.7±.4.3±. single t ±.4 ±.4 ttbar+v.48±.2.7±.4 ZZ.44±.9.9±.2 WZ.25±..9±.5 WW ±.5 ±.5 Zγ ±.5 ±.5 Z+LF-jets.33±.67.33±.67 Z+HFjets.24±.35.24±.35 Drell-Yan ±.5 ±.5 BG Total.7±.9.7±.8 Data 4 Validation samples ZZ: 4 leptons + low Etmiss(<5GeV) MC : 23±5 Data : 2 Top : 2 OFOS leptons + 2 fakes (reversed isolation) + b-tagged jet. MC : 8.4±.8 Data : 8 Z+light-flavor jets dominates and large uncertainty due the limited MC statistics. 9

10 Signal Model - BC-like tanβ-m/2 grid with -LSP (hep-ph/69263, arxiv:8.58v2) - m = A =, μ >, λ2 =.32 (at MGUT) - Production mode: - Strong, weak(, ± ), stau-pair, slepton-pair - Decay channel: Mass Channel BR Channel BR τ 48 τ µ ± e ( ) ν e 5.% τ e ± e ( ) ν µ 49.9% ẽ R 6 e ν µ 5.% µ ν e 5.% µ R 6 τ ± τ µ 99.9% χ 62 τ ± τ 99.6% m/2=4gev, tanβ=3 (BC benchmark) - Final state: - 2e ±, 2(e or mu), 2taus + Etmiss 4-body decay τ e τ χ ẽ ± R e ± (µ ± ) ( ) ν µ ( ( ) ν e )

11 Production process Not reviewed, for internal circulation only Weak prod. dominates for most of parameter space. Stau-pair prod. dominates at high-tanβ region. tachyonic stau tanβ tanβ LEP limit (mstau>8.9gev) Higgs bound Neutralino-LSP msugra/cmssm, msugra/cmssm, m = A = m GeV, = A = µ >, GeV, λ µ = >.32, λ at = m.32 at m 2 2 GUT GUT tanβ tanβ ATLAS ATLAS Preliminary Preliminary ATLAS ATLAS Preliminary Preliminary m /2 m /2 msugra/cmssm, msugra/cmssm, m = A = m GeV, = A = µ >, GeV, λ µ = >.32, λ at = m.32 at m 2 2 GUT GUT Strong m / m / Strong process event fraction τ pair production event fraction Strong process event fraction tanβ τ pair production event fraction tanβ msugra/cmssm, msugra/cmssm, m = A = m GeV, = A µ = >, GeV, λ µ = >.32, λ at = m.32 at m 2 2 GUT GUT tanβ ATLAS ATLAS Preliminary Preliminary ATLAS ATLAS Preliminary Preliminary msugra/cmssm, msugra/cmssm, m = A = m GeV, = A µ = >, GeV, λ µ = >.32, λ at = m.32 at m 2 2 GUT GUT Weak ` ` m / m /2 m / Gaugino event fraction Slepton production event fraction Gaugino event fraction Slepton production event fraction

12 Interpretation - Selection cuts with Z-veto. - Limits on BC-like grid: - m/2 < ~8GeV (corresponding gluino mass ~77GeV) for tanβ < 4 tan β 6 msugra/cmssm, m = A = GeV, µ ATLAS Preliminary >, int - λ =.32 at M GUT, L = 2.6 fb, 2 s=7 TeV n e,µ n obs miss 4, E T =, n exp =.7 ± > 5 GeV, Z Veto m(g ~ )=. TeV.8 m(g ~ )=.4 TeV m(g ~ )=.8 TeV m(τ )= GeV m(τ )=2 GeV m(g ~ )=2.2 TeV τ m( )=3 GeV m(g ~ )=2.4 TeV Observed 95% CL Expected 95% CL Expected ± σ Theoretical < 8 GeV m τ m h χ (LEP) LSP (Poor acceptance for tanβ>4 due to a small 4-body decay branch and a significant lifetime of stau.) m /2 2

13 arviv: RPV-SUSY searches e µ resonance

14 RPV sneutrino - RPV tau sneutrino with LNV-decay: - Signature: e-μ resonance 3 6= && 32 6= - Excess expected in meμ distribution onstrained) - Low SM background. Electron: - pt > 25 GeV - η <.37 or.42< η < Isolated && shower shape requirements Muon: - pt > 25 GeV - η <2.4 - Reconstructed in Inner Detector&Muon Spectrometer. - Isolated Selection: Exactly one electron and one muon with opposite-sign charge No requirements on jets and Etmiss 4

15 BG estimate - SM background processes: - Z/γ * ( ττ), top, diboson - Estimated using MC - Instrumental background (jet/γ faking to a lepton) - W/Z+γ by MC QCD/W+jets background derived using a data-driven matrix method: N TT N TL N LT N LL = rr rf fr r( r) r( f ) f ( r) f ( f ) ( r)r ( r)f ( f )r ( f )f ( r)( r) ( r)( f ) ( f )( r) ( f )( f ) N RR N RF N FR N FF The efficiency r is measured using Z ll events selected with one tight (tag) and one loose (probe) leptons with 8<mll<GeV. The jet fake rate f is measured using QCD jet events; e.g. for electrons Select two same-sign electrons passing loose criteria but one fails tight (tag). Veto real lepton from Z: mee<7 or >GeV, Δφee>2 ) Define loose/tight lepton definitions apply on all events to get NTT,NTL,NLT and NLL. 2) Estimate efficiency (r) and fake rate (f) for a lepton that has passed the loose definition to also pass the tight definition. 3) Solve 4 4 matrix and obtain (RF,FR,FF) contributions to TT. 5

16 Results - Primary contributions to the systematic uncertainty on the BG estimation come from the theoretical cross section uncertainties. - 2% for top pair production (dominant BG) and 5-% for the others. ttbar 58 ± 7 Jet fake (QCD, W+jets) 75 ± 2 Z/γ * ( ττ) 75 ± 6 WW 38 ± 3 single t 54 ± 6 W/Z+γ 82 ± 3 WZ 22.4 ± 2.3 ZZ 2.48 ±.26 BG total 445 ± 25 Data 453 Result: no significant excess observed. (KS-test prob: 56%) 6

17 Interpretations - Limits on (pp! as a function of - ) BR(! eµ) m tau-sneutrino having a mass below.32(.45) TeV are excluded assuming 3 =.(.) and 32 =.5(.7) - Limits on coupling as a function of for various values of - sneutrino mass > 27GeV assuming 32 =.7 (most stringent limit to date) 3 m 32 7

18 arviv: RPV-SUSY searches Late-decaying -LSP

19 Neutralino-LSP decay could decay via non-zero λ, λ couplings: χ ũ u d LLĒ( ):! ll + LQ D( ): e, µ,! +2jets ± ~χ ~ µ χ λ 2ij q j q i µ ± The lifetime is proportional to (λ) -2, (λ ) -2 µ Decay prompt for λ, λ -5. If the RPV coupling is smaller than that (e.g. -7 ), a decay vertex with a significant distance from its production point can be seen. Perform a search using a displaced vertex (DV) reconstruction technique. The result presented today is based on 2 data, non-zero λ with muon final states. More to come using 2 full dataset covering variety of signatures: - Final states including e/tau 9

20 Displaced vertex Vertexing:. Select tracks with pt > GeV and d > 2mm wrt the primary vertices (PVs). 2. Make 2-track seed vertices. 3. Make all possible N-track combinations, then iteratively split, merge, remove tracks etc. until there are no tracks shared between vertices. Selection:. Vertex in z < 3mm and r < 8mm 2. Vertex χ 2 /DOF < 5 3. rdv rpv > 4mm 4. One muon with pt > 45GeV 5. Material veto (hadronic interactions, dominant background) Efficiency Vetoed regions (Beam pipe, Pixel layers) 2

21 V Number of vertices ertices / 2 mm BG validation Vertex mass Nvtx trk and rdv in control region (no material veto) data 2 Dijet MC W,Z MC ttbar MC ATLAS data 2 Dijet MC W,Z MC ttbar MC Ldt = 33 pb Number of tracks in vertex ATLAS Ldt = 33 pb - - Vertices / 2 mm without applying any trigger requirements or the muon selection criteria. Multiplying this number by the proba bility for each MC event type to satisfy the muon-trigge and the o ine muon-selection criteria yields the expected background for each sample. The W! µ µ sample yields no selected vertices, but has high e ciency for sat isfying the muon requirements. As a result, for this back ground we find the highest upper limit of all the othe samples. Given observed W! µ µ MC events and the luminosities of the data and of the MC sample, we find the expected W! µ µ background yield to be 3 N bgd <.3 events at 9% data confidence 2 level. The expected background yield fromdijet Z, t t, MCand dijetatlas events is at leas an order of magnitude W,Z smaller. MC - 2 ttbar MC Ldt = 33 pb We validate the use of MC to estimate the background by comparing displaced-vertex yields in a sample of non di ractive MC events and data collected with minimum bias triggers. For this study, we select vertices with m DV < GeV and reject vertices with m DV correspond ing to KS or decays or to photon conversions, in or der to increase the purity of material-interaction vertice with high position resolution. From MC, we determine R int (r DV ), the radius-dependent fraction of vertices tha are - due to particle interactions with material. This frac tion is close to unity in detector material and much smalle Vertex r DV [mm] than unity in gap regions between material layers, which are filled with N 2 gas. Using R int (r DV ) and the number o 2-track Comparison vertices of in the a pixel m DV layer (top), and NDV trk in (center), the adjacent and r gap DV we determine an e ective pixel-layer-to-gas mass-density ratio. GeV. From Other, than R the material veto and the NDV trk 4 int (r DV ), and the number of NDV trk > 2 vertices seen in DV and each r pixel layer, we predict the expected DV distributions include a veto on KS number of such vertices in the adjacent gap. Comparing 2 Data/MC reasonably agree. Materials are well described in MC. Figure 5: (bottom) distributions of data and MC events in the control region m DV < and m DV > GeV requirements, all selection criteria are applied. In addition, the N trk decays. The MC histograms are normalized to the integrated luminosity of the data, with the MC cross-section given by PYTHIA [].

22 Result & interpretation Signal region: - m DV > GeV - # of tracks in DV 4 SM MC background expectation - N BG <.3 No signal observed. Vertex mass 2 Signal region ATLAS Number of tracks in vertex Ldt = 33 pb - Data 2 Signal MC - Figure 7: Vertex mass (m DV )vs. vertextrackmultiplicity(n trk ) tions with respect to the PV. This distribution is convolved with a Gaussian representing the z distribution of the PV, and then multiplied by the 2-dimensional e ciency map for vertices in that signal MC sample, obtaining the expected distribution of r DV vs. z DV. This distribution is generated separately for two cases. In the first case the reconstructed DV and muon originate from the same neutralino, and in the second they originate from di erent neutralinos. This allows us to correctly account for the muon-reconstruction CL e ciency for the desired value of c, despite the fact that the signal MC is produced with a different lifetime, Interpretation c MC. Integrating over (λ 2ij ): the r DV vs. z DV distributions, we obtain the total e ciency for reconstructing at least one vertex and one muon in the event given our selection criteria - and the value of c. From the e ciency and luminosity, we Limits obtain the on expected average lifetime signal-event yield for any value of the signal production cross-section. The expected background yield is taken to be zero with a conservative uncertainty of.3 events, which is the 9% CL upper 3limit on the background (see Section 6). The upper limit on B is then calculated using the CL s method [8], where signal-only and 7 GeV signal-plus-background ~ q, 494 GeV χ p-values are evaluated 2 using pseudo-experiments 7 GeV ~ q, 8 GeV χ generated from distributions based on counting.5 TeV ~ q, statistics. 494 GeV χ The uncertainties on luminosity, e ciency, 5 GeV and ~ q, 8 background GeV χ are treated as nuisance parameters. PROSPINO: σ(m ~ = 5 GeV) q The systematic uncertainty on PROSPINO: the track-reconstruction σ(m ~ = 7 GeV) q e ciency is taken into account in the limit calculation by use of the alternative e ciency functions described in Section 7. All other e ciency systematic uncertainties are used when converting the limit on the number of signal events to the limit - on B. The resulting limits are shown in Figure 8, with the PROSPINO-calculated cross-sections for squark masses of 5 GeV and 7-2 GeV. Since no background is expected, the expected and observed limits are indistinguishable. 2 In addition, based on the observation of no signal events in cτ a data sample of 33 pb, we set a 95% confidence-level upper limit of.9 pb on the cross-section times the detector acceptance times the reconstruction e ciency for any Exclude ε σdv - m(squark)=5gev excluded. Cross-section x B.F. [pb] Figure 8: ATLAS Ldt = 33 pb - [mm] Upper limits at 95% CL on the production cross-section 3 Foundat IN2P3-C BMBF, many; G Benoziyo Japan; C RCN, N tugal; M ROSATO MSSR, S South A Foundat and Gen STFC, t Kingdom The c ners is a and the NDGF ( KIT/Gri (Netherl and BNL 22

23 arviv: RPV-SUSY searches LNV with bilinear terms

24 Bilinear RPV Bilinear RPV (brpv) terms introduce neutrino masses and mixings. - Currently constrained by neutrino oscillation experiments. brpv terms can be embedded in any RPC-SUSY model: - brpv in msugra: - Same cascades as in RPC scenarios - LSP may decay, but results in lepton+etmiss+jets final states (most of LSP decays involve leptons/taus/neutrinos). - brpv parameters are motivated by the neutrino oscillation parameters. χ decays ττν 29.8 other.8 µw.3 τw Zν brpv interpretation based on the -lepton analysis result with fb -. τµν 4.8 τeν 4.8 bbν

25 SR & BG estimate - Signal region: - Exactly one isolated muon with pt>2gev 5 - (electrons are highly suppressed in the 4 model) jets with pt>4gev2 - leading jet with pt>6gev - - Δφ(jets, Etmiss) >.2-2 MT > GeV - Etmiss > 2GeV - ATLAS Data 2 ( s=7 TeV) Standard Model Etmiss/Meff multijets > (data.5 estimate) L dt =.4 fb - W+jets Z+jets 4 4 Electron Channel tt single top Meff > 5GeV Dibosons 3 MSUGRA m =5 m /2 =33 3 4J W+jets Control Region Data/MC overflow = /. Events / 5 GeV Data / SM Events Events / / 5 5 GeV GeV 2 2 ATLAS L dt =.4 fb ATLAS ATLAS L dt =.4 fb L dt =.4 fb Electron Channel Electron Muon Channel Channel - BG estimation: - W+jets, top - Normalize MC to data in background specific control regions (WR,TR). Data 2 ( s=7 TeV) Standard Model multijets (data estimate) W+jets Z+jets tt single top Dibosons MSUGRA m =5 m /2 =33 4J W+jets Control Region - QCD m eff by the matrix method. m eff Data 2 ( s=7 TeV) Data Standard 2 ( Model s=7 TeV) Standard multijets Model (data estimate) multijets W+jets(data estimate) W+jets Z+jets Z+jets tt tt single top single top Dibosons Dibosons MSUGRA m =5 m /2 =33 MSUGRA m =5 m /2 =33 4J W+jets Control Region 4J Top Control Region Data/MC overflow = /. - - Extrapolate to Signal Regions using MC 2 shapes Data/MC overflow = /.2 Data/MC overflow = /.3 WR Events / 5 GeV N(b-jet)= Data / SM 5-4 < MT L dt =.4 < 8GeV fb 4 Muon Channel 3 < 3 Etmiss < 8GeV Events / 5 GeV ATLAS Data 2 ( s=7 TeV) Standard Model multijets (data estimate) W+jets Z+jets tt single top Dibosons MSUGRA m =5 m /2 =33 4J W+jets Control Region ATLAS L dt =.4 fb - Muon Channel TR Δφ(jets, Etmiss) >.2 2 Meff > 3GeV N(b-jet) Data 2 ( s=7 TeV) Standard Model multijets (data estimate) W+jets Z+jets tt single top Dibosons MSUGRA m =5 m /2 =33 4J Top Control Region Data/MC overflow = /.3 Data/MC overflow = /. 9 Data Data / SM SM m eff m eff Data / SM m eff ev 5 ATLAS Data 2 ( s=7 TeV) FIG. 4: ev Distributions ATLAS for events in the lepton Data 2 ( plus s =7 TeV) four jets control regions for the electron channel (left column) and muon 25

26 Interpretation - brpv interpretations were done in -lepton + Etmiss RPC-SUSY search. - Observed: 7 - BG exp.: 6±2.7 m /2 --- brpv msugra with neutralino with cτ<5mm brpv MSUGRA: tanβ =, A =, µ> int - ATLAS L =.4 fb, s=7 TeV Observed CL S 95% CL muon, 4 jets, tight SR Expected CL S Expected CL S ±σ 4 ~ q (9 GeV) ~ g (9 GeV) 35 ~ q (7 GeV) 3 ~ g (7 GeV) cτ = 3 mm 25 cτ = 7 mm cτ = 5 mm m 26

27 Summary No sign of RPC SUSY yet... unexpected SUSY could be there. R-parity is conserved or violated? Pros and cons on both. RPC-SUSY parameter space is being squeezed... all possibilities should be considered. ATLAS is trying to cover possible RPV signatures: 4 results were presented in context of LLE, LQD and bilinear RPV (LNV) SUSY. Many analyses are being performed. More to come in coming months (BNV, variety of signatures...) Also keep a close eye on 8TeV collision data to find something unexpected!! 27

28 Backup

29 MSFOF - Before applying Etmiss cut, 24 events remain. Events / 2 GeV 3 2 s= 7 TeV L dt = 2.6 fb ATLAS Preliminary - (c) Data 2 Total SM tt tt V WZ ZZ llll ZZ other Z+jets SM + RPV SM + DGwSL Events / 5 GeV 2 s= AT M SFOS e µ 29

30 RPV stau re 4: Characteristics of the m /2 -tan β plane in the BC scenario. The shaded regions include: etically forbidden region producing tachyons, a region with a χ LSP, a region excluded by LE s bounds, and a region with m τ below the 8 GeV threshold considered in this analysis. - Branching ratio of stau 4-body decay and lifetime. m /2 msugra/cmssm, msugra/cmssm, m = Am = = A = GeV, µ >, λ =.32 at m GeV, µ >, λ =.32 2 at m GUT 2 GUT tanβ ATLAS ATLAS Preliminary Preliminary m /2 m / τ 4 body branching fraction τ 4 body branching fraction tanβ msugra/cmssm, msugra/cmssm, m = A m= = A = GeV, µ >, λ =.32 at m GeV, µ >, λ =.32 2 at m GUT 2 GUT tanβ ATLAS ATLAS Preliminary Preliminary m /2 m /2 τ lifetime [ps] igure 5: Branching 5: ratio ratio of the of τ the four-body τ four-body decay decay (left) (left) and and the τ the lifetime τ lifetime (right) (right) as a as function a function of mo nd an β. tanthe β. The solid solid shaded shaded areas areas excluded are excluded from from this this analysis, analysis, see Figure see Figure 4 for4 details. for details. 3