Search for SUSY R-Hadrons

Transcription

1 Search for SUSY R-Hadrons Morten Dam Jørensen (Niels Bohr Institute) on behalf of the ATLAS Collaboration Overview What are R-Hadrons Detection methods Latest results Rencontres de Moriond EW Youn Scientists Forum - Contact: mdj@nbi.dk

2 q What are R-Hadrons Coloured Massive Particles, i.e. luinos, squarks Assumed Lon-lived (in our searches) Predicted by numerous BSM models includin many SUSY scenarios Slow movin at LHC eneries β<1 Hadronises with liht SM quarks into bound states called R-Hadrons Electrically chared in specific bound states Nuclear scatterin of the liht quark system with detector causin electrical chare chane No interaction between detector and primary parton (σ 1/m 2 ) assumed q SMP LSP Scenario Conditions 1 01 MSSM 1 mass (determined by m 2 L,R, µ, tan,anda )closeto 01 mass. G GMSB Lare N, smallm,and/orlaretan. MSB No detailed phenomenoloy studies, see [23]. SUGRA Superravity with a ravitino LSP, see [24]. 1 MSSM Small m L,R and/or lare tan and/or very lare A. AMSB Small m 0,laretan. MSB Generic in minimal models. `i1 G GMSB 1 NLSP (see above). ẽ 1 and µ 1 co-nlsp and also SMP for small tan and µ. 1 MSB ẽ 1 and µ 1 co-lsp and also SMP when stau mixin small MSSM m + m 0 < m +. VerylareM > 1 1 1,2 2TeV µ (Hisino reion) or non-universal auino masses M > 1 4M 2, with the latter condition relaxed to M > 1 M 2 for M 2 µ. Natural in O-II models, where simultaneously also the can be lon-lived near GS = 3. AMSB SUSY SMP states arxiv:hep-ph/06140 M 1 >M 2 natural. m 0 not too small. See MSSM above. 01 MSSM Very lare m 2 q M 3,e..splitSUSY. G GMSB SUSY GUT extensions [25 27]. MSSM Very small M 3 M 1,2,O-IImodelsnear GS = 3. GMSB SUSY GUT extensions [25 29]. t 1 01 MSSM Non-universal squark and auino masses. Small m2 q and M 3,smalltan,lareA t. b1 Small m 2 q and M 3,laretan and/or lare A b A t. Table 1 Brief overview of possible SUSY SMP states considered in the literature. Classified by SMP, LSP, scenario, and typical conditions for this case to materialise in the iven scenario.

3 Fraction of candidates / 0.01 Fraction of candidates / ATLAS Ldt = 37 pb -1 Inclusive µ - data µ from Z µ µ - data µ from Z µ µ - mc ATLAS Ldt = 37 pb -1 Muon spec. ToF timin requirements of the trier electronics. The estimated trier efficiencies for GMSB slepton candidates are between 80% and 81%. The R-hadron search is much more adversely affected by the loss of trier efficiency for late candidates, since the reconstruction is seeded by the trier, and so even if an event is triered by another ob- R-Hadron ject, the candidate detection will be lost. For R-hadrons that could in ATLAS β (slepton search) Inclusive µ - data µ from Z µ µ - data µ from Z µ µ - mc β (R-hadron search) Fiure 1: Distribution of β for all candidates in data (points with error bars), muons from the decay Z µµ in data (full lines) and smeared Monte Carlo (dashed lines), in the estimation used in the slepton search arxiv: (upper) and in the estimation used in the R-hadron search (lower). Data ( Top EW QCD s 0 GeV 300 GeV 500 GeV = 7 TeV) BG stat uncertainty -1 ixel [MeV cm 2 ] Number of candidates / ATLAS -1 L dt = 34 pb Calo ToF arxiv: Data ( Top EW QCD s 0 GeV 300 GeV 500 GeV = 7 TeV) BG stat uncertainty β Tile nd Tile (riht) in data after the transverse momentum selection pt > 50 GeV. are plotted for comparison. The uncertainty shown on the backround is the e a relative de/dx Pixel resolution of about % in the asymptotic ckrounds further, the final selection requires that de/dx Pixel > xel 1.1MeV 1 cm 2 deposited by a MIP. In the tile calorimeter, an 1. orimeter provide independent measurements from which the mass ted. Makin requirements on both mass estimates is a powerful ividual distributions arisin from instrumental e ects. In Fiure 2 d on de/dx Pixel and Tile are shown after the 50 GeV transverse In contrast to the other fiures in this paper, the sinal distributions to illustrate the total expected spectra for the sinal+backround ta ( p s = 7 TeV) D 0 GeV 0 GeV 0 GeV stat uncertainty [GeV] m Pixel Number of candidates / 25 GeV ATLAS -1 L dt = 34 pb Data ( Top EW s = 7 TeV) QCD 0 GeV 300 GeV 500 GeV BG stat uncertainty TRT de/dx arxiv: m Tile [GeV] tor (left) and the tile calorimeter (riht). To obtain a mass estimate, a cut of the pixel detector distribution. This is a looser cut than used in the analysis nt is that Tile < 1. 4 from data, where the overwhelmin majority of candidates are muons. Therefore the trier trackin efficiency is estimated from Z µµ data, while the effects of timin are estimated from simulated R-hadron and GMSB events passin the level-1 trier simulation, which includes the be reconstructed because they are chared in the MS, the trier efficiencies rane between 55% for m =300GeV to 38% for m = 700 GeV. The estimated trier efficiency with respect to all R-hadrons produced in the scatterin model of Ref. [7] varies from 25% for m =300GeVto 17% for m =700GeV. Theeffect of the trier efficiencies can be seen in Tables 1 and 2 for the sinal and data in the slepton and R-hadron searches respectively Offline selection Collision events are selected by requirin a ood primary vertex with more than two ID tracks, and with z0 vtx < 150 mm (where z0 vtx is the z coordinate of the reconstructed primary vertex). Cosmic ray backround is rejected by removin tracks that do not pass close to the primary vertex in z. For candidates with an associated ID track, candidates with z0 trk z0 vtx > mm are removed, where z0 trk is the z coordinate at the distance of closest approach of the track to the oriin. If no ID track is associated with the candidate, then it is still rejected if z0 trk z0 vtx > 150 mm. Pairs of candidates with approximately opposite η and φ are also removed. The analysis searchin for sleptons requires two candidates in each event, because two sleptons are produced, and both have a hih probability to be observed in the MS. However, only one of them is required to pass the LLP selection. This requirement reduces backround from W production and QCD, but Z µµ decays remain. Any candidate that, when combined with a second muon, ives an invariant mass within GeV of the Z mass is rejected. In the R-hadron search, no requirement of two candidates per event is made, because R-hadrons may be neutral in Velocity as discriminator Time of fliht de/dx Specific Enery Loss No physics backround, only instrumental effects Estimate mass by velocity and momentum Can become neutral after hadronic interactions Unique chare flippin as sinature de/dx βγ vs. de/dx - LAr EM layer 1 technoloy βγ vs. de/dx - Tile layer 1 technoloy βγ βγ Calo de/dx - Chare flippin Pixel de/dx ATLAS-CONF cds.cern.ch: (thesis) mass hypothesis, the mean, µ, and Gaussian width,, of the mass etector and the tile calorimeter measurement. The sinal reion is Rencontres de Moriond EW Youn Scientists Forum

4 Inner detector only search ATLAS-CONF Most recent result (2.06 fb -1 ) Pixel de/dx Estimator Calibrated on slow SM particles Missin Enery Trier MET > 70 GeV Offline MET > 85 GeV p > 0 GeV Pixel de/dx > 1.8 MeV -1 cm 2 Distance to nearest track > 0.25 Distance to nearest jet > Pixel mass (ID+Calo) Proton mass run stability Sinal de/dx response Sinal mass estimates

5 Results Increased statistics No sinificant deviation from the Standard Model Upper limit: <0.1 pb (CLs method 95% CL) Gluino mass exclusion up to 8 GeV for Split-SUSY models (ID+Calo 20 Limit: 580 GeV)

6 Conclusion Nearly all sub detectors in ATLAS have R-Hadron discrimination capabilities New limit from ATLAS on inner detector only searches for R- Hadrons. Many other searches onoin We try to avoid heavy model dependence (beyond nuclear scatterin) but input from theorists is welcomed!

7 Backup slides Rencontres de Moriond EW Youn Scientists Forum - Contact: mdj@nbi.dk

8 Pixel countin tables Sinal Gluino 400 GeV Gluino 700 GeV Gluino 00 GeV Cut level Cut Eff. Total Eff. Cut Eff. Total Eff. Cut Eff. Total Eff. Trier Offline ET miss Primary vtx Hih-p T Isolation Hih-p ionization Data Cut level #Events Cut Eff. Total Eff. Trier 2,413,863 Offline ET miss 1,421, Primary vtx 1,368, Hih-p T 212, Isolation 32, Hih-p 21, E-03 ionization E-04 Rencontres de Moriond EW Youn Scientists Forum - Contact: mdj@nbi.dk

9 20 Inner detector & Calorimeter 20 Muon Spectrometer, 20 Rencontres de Moriond EW Youn Scientists Forum - Contact: mdj@nbi.dk

10 Detection methods Time of Fliht Velocity as discriminator Time of fliht Specific Enery Loss No physics backround, only instrumental effects Estimate mass by velocity and momentum Can become neutral after hadronic interactions Unique chare flippin as sinature m = p p 1 2 Specific Enery Loss?? m = p de dx = Kz 2 Z A apple ln 2m ec T max 2 ( ) I

11 Search strateies in ATLAS Multiple searches with variation of sub detectors to maximise model coverae General selection Trier (MET or Muons) Momentum cut Isolation (from pollutin tracks, jets) Data driven backround estimation Search specific selection Short lifetime, Hih hadronic interaction probability ID only: Pixel de/dx Intermediate lifetimes, moderate hadronic interaction ID+Calo: Pixel de/dx and Calo ToF Lon lifetime, low mass MS only: Candidates that where neutral in ID but became chared by interactions. rane lifetime # estimators MS Had Calo EM Calo TRT SCT Pixel Inner detector ID and Calo MS only ATLAS combined Inclusive, maximum detector acceptance ID+Calo+MS: Require a minimum of compatible estimates, semi-multivariate methodoloy Rencontres de Moriond EW Youn Scientists Forum

12 SUSY limits (dec 2011)

13 Theoretical predictions Split-SUSY -like predictions Cross sections calculated with Prospino 2.1 Decoupled mass scales, emulatin infinite life-time by decay suppression cross section [pb] Theoretical Prediction CTEQ 6.6 Split SUSY, other masses: TeV Prospino 2.1 Th. Uncertainty Sbottom Stop Gluino Squark Mass (GeV) (pb) Sbottom Mass [GeV] Assumptions Prospino 2.1 NLO SUSY Splittin scale TeV s = 7 TeV CTEQ 6.6 & MSTW 2008 Th. uncertainty represents K-factor variation

14 Limit

15 Mass distribution

16 Pixel de/dx mass estimator - proton mass stability