Approaching SUSY searches at CMS. Frédéric Ronga (ETH Zurich) LPHE seminar November 15, 2010

Transcription

1 Approaching SUSY searches at CMS Frédéric Ronga (ETH Zurich) LPHE seminar November 15, 20

2 Outline SUSY: what and why? The Compact Muon Solenoid SUSY searches at CMS Prospects F. Ronga (ETH Zurich) LPHE seminar November 15, 20 2

3 Supersymmetry in one slide Symmetry between bosons and fermions For example Each Standard Model multiplet is doubled in size this is the Minimal Supersymmetric Standard Model (MSSM) unbroken SUSY: all particles in a multiplet have same mass SUSY must be broken: SUSY particles are heavy also assume matter parity number of SUSY particles conserved Lightest superparticle (LSP) is stable F. Ronga (ETH Zurich) LPHE seminar November 15, 20 3

4 SUSY phenomenology MSSM still has 124 parameters Simplifying the model assume some SUSY breaking mechanism M0 = 200 GeV/c 2 M1/2 = 160 GeV/c 2 A0 = -400 GeV/c 2 tanβ = small number of parameters defined at the GUT scale generate mass spectrum and couplings at low scale by running renormalisation group evolution Example: CMSSM (msugra) gaugino mass M1/2 scalar mass M0 trilinear coupling A0 ratio of Higgs VEV: tanβ F. Ronga (ETH Zurich) LPHE seminar November 15, 20 4

5 SUSY phenomenology MSSM still has 124 parameters Simplifying the model assume some SUSY breaking mechanism M0 = 185 GeV/c 2 M1/2 = 350 GeV/c 2 A0 = 0 GeV tanβ = 35 small number of parameters defined at the GUT scale generate mass spectrum and couplings at low scale by running renormalisation group evolution Example: CMSSM (msugra) gaugino mass M1/2 scalar mass M0 trilinear coupling A0 ratio of Higgs VEV: tanβ F. Ronga (ETH Zurich) LPHE seminar November 15, 20 4

6 Why care about SUSY? Stability of the Higgs mass against higher-order corrections Unification of gauge couplings SM Provides a cold dark matter candidate MSSM F. Ronga (ETH Zurich) LPHE seminar November 15, 20 5

7 Why care about SUSY? Stability of the Higgs mass against higher-order corrections Unification of gauge couplings SM Provides a cold dark matter candidate MSSM It has been out there for too long: we (experimentalists) have a duty to bring theorists back to reality F. Ronga (ETH Zurich) LPHE seminar November 15, 20 5

8 Searching for SUSY at the LHC Topology of a SUSY event large energy release large number of jets low-pt leptons missing energy (MET) Searches rely on all aspects of the reconstruction electrons, photons and muons jets, total hadronic activity A typical SUSY event many jets, leptons and missing energy missing energy (especially tails) N.B. stay as model-independent as possible F. Ronga (ETH Zurich) LPHE seminar November 15, 20 6

9 CMS

10 The Compact Muon Solenoid Total weight Overall diameter Overall length t 15 m 21.6 m 66M channels for ~1 m 2 9.6M channels for ~2 m 2 76k PbWO4 crystals interleaved scintillator/brass redundant DT (CSC) and RPC 3.8T field F. Ronga (ETH Zurich) CHIPP annual plenary meeting August 23, 20 8

11 20 data sample 47/pb delivered 43/pb recorded 92% efficiency F. Ronga (ETH Zurich) CHIPP annual plenary meeting August 23, 20 9

12 20 data sample 47/pb delivered 43/pb recorded 92% efficiency Let s see what we got... F. Ronga (ETH Zurich) CHIPP annual plenary meeting August 23, 20 9

13 Muons... F. Ronga (ETH Zurich) CHIPP annual plenary meeting August 23, 20

14 Electrons! F. Ronga (ETH Zurich) CHIPP annual plenary meeting August 23, 20 11

15 Jets 4 complementary types of jet reconstruction CMS PAS JME CMS Preliminary - L = 0 µb Calorimeter jets from calorimeter deposits only Track jets Calo. jets Number of Events Data Pythia8 s=7tev Track jets from tracks only 500 Jet-plus-track jets subtract calorimeter response from CaloJet and replace with tracks Particle Flow (PF) jets cluster of particle flow objects: individual particle reconstruction by combining information from all sub-detectors JPT jets Δφ 12 PF jets Default clustering algo: anti-kt with R=0.5 F. Ronga (ETH Zurich) CHIPP annual plenary meeting August 23, 20 Δφ between two leading jets (used to select dijet sample) 12

16 Missing Transverse Energy Three types of MET roughly corresponding to calo. jet, JPT jet and PF jet reconstruction No significant MET expected in minimum bias CMS PAS JME--004 MET cleaning low-level clean-up from noise crucial for many searches very effective cleaning (tails compatible with MC) MET resolution vs PF Σ(ET) much gain in combining subdetector information as expected from MC F. Ronga (ETH Zurich) CHIPP annual plenary meeting August 23, 20 ) (GeV) x,y "(Calibrated E type2 caloe T (Data) type2 caloe T (MC) tce T (Data) tce T (MC) pfe T (Data) pfe T (MC) MET resolution Calo. MET T. c. MET PF MET s = 7 TeV CMS preliminary Calibrated pf!e T (GeV) 13

17 One more thing... double b-jet candidate F. Ronga (ETH Zurich) LPHE seminar November 15, 20 14

18 b-tagging at CMS Secondary vertices are built from tracks inside jets relies on hits in the pixel detector primary vertex built from all good quality tracks in the event and compatible with vertex candidate candidate with highest ΣpT 2 is selected I.P. most powerful variable Note: b-tagging also crucial for searches (many b-jets) F. Ronga (ETH Zurich) LPHE seminar November 15, 20 15

19 b-tagging performance CMS PAS BTV--001 CMS Preliminary 20, s = 7 TeV, L = 15 nb Data Sim.(light) Sim.(charm) Sim.(bottom) Entries/ Data/Sim Track 3D IP significance 3D impact parameter significance Comparison between data and simulation Track counting algorithm Comparison between data and simulation For fixed N, tag jets with Nth track with IP significance greater than S F. Ronga (ETH Zurich) LPHE seminar November 15, 20 16

20 (early) SUSY searches

21 SUSY searches at CMS Reminder large energy release Hadronic searches CMS PAS SUS--001 Leptonic searches large number of jets # leptons SS 2 OS 3 low-pt leptons missing energy (MET) Dominant backgrounds QCD ttbar W+jets ttbar W+jets QCD fakes (ttbar) ttbar Z+jets fake (ttbar) Strategy suppress Standard Model processes ( background ) different strategies depending on final state (different bkgds) estimate remainder data-driven techniques developed New Physics will manifest itself as an excess F. Ronga (ETH Zurich) LPHE seminar November 15, 20 18

22 Hadronic searches: prospects 95% exclusion limits for searches with jets and missing energy expressed in the msugra parameter space assumes 50% syst. uncertainty on backgrounds F. Ronga (ETH Zurich) LPHE seminar November 15, 20 19

23 Hadronic searches: αt variable Exclusive n-jet searches (n 2) Construct distribution of CMS PAS SUS--001 αt=0.5 for perfectly balanced di-jet event αt<0.5 if one jet mis-measured Multi-jet extension bring back to (pseudo) di-jet system by grouping jets together jets below threshold lead to αt>0.5 study αt as a function of energy release: HT = sum of jet pt F. Ronga (ETH Zurich) LPHE seminar November 15, 20 20

24 Suppressing QCD with αt CMS PAS SUS--001 Dijet αt with low HT selection Dijet αt with high HT selection Impressive drop of 4 orders of magnitude as expected from Monte Carlo simulations F. Ronga (ETH Zurich) LPHE seminar November 15, 20 21

25 Estimating QCD with αt Study fraction of events failing αt<0.55 steep fall, increasing with HT emulate jet loss (5- times expected) flattens decrease Exploit centrality of SUSY Use low-ht distribution to estimate bkgd at high HT background distribution flat in η of leading jet even if emulate jet removal normalise in high-η bin F. Ronga (ETH Zurich) LPHE seminar November 15, 20 22

26 Estimating QCD with αt Study fraction of events failing αt<0.55 steep fall, increasing with HT emulate jet loss (5- times expected) flattens decrease Exploit centrality of SUSY Use low-ht distribution to estimate bkgd at high HT background distribution flat in η of leading jet even if emulate jet removal normalise in high-η bin F. Ronga (ETH Zurich) LPHE seminar November 15, 20 > 0.55) f(" T H T H T > 160 GeV > 160 GeV: removed jets CMS preliminary -1 s = 7 TeV, 54 nb ! leading jet 22

27 Estimating QCD with αt Study fraction of events failing αt<0.55 steep fall, increasing with HT emulate jet loss (5- times expected) flattens decrease Exploit centrality of SUSY Use low-ht distribution to estimate bkgd at high HT background distribution flat in η of leading jet even if emulate jet removal normalise in high-η bin F. Ronga (ETH Zurich) LPHE seminar November 15, 20 > 0.55) f(" T H T H T > 160 GeV SUSY > 160 GeV: removed jets CMS preliminary -1 s = 7 TeV, 54 nb ! leading jet 22

28 QCD contribution to MET QCD also affects single-lepton searches mis-measurement of multi-jet events produces instrumental MET need to predict this instrumental MET component MET templates pool of templates from multi-jet events in bins of HT and number of jets for each candidate event pick template sum up templates to get instr. MET prediction < H T < 300 GeV! 4 N J MET (GeV) -1 0 < H T < 200 GeV = 3 N J MET (GeV) -1-1 CMS Preliminary, 65 nb, 300 < H T < 350! 4 N J 200 < H T < 250 = 3 N J < H T < 400! 4 N J MET (GeV) < H T < 300 = 3 N J s = 7 TeV < H T < 500! 4 N J MET (GeV) < H T < 400 = 3 N J < H T < 00! 4 N J MET (GeV) < H T < 00 = 3 N J MET (GeV) MET (GeV) MET (GeV) Legend MET (GeV) MET (GeV) F. Ronga (ETH Zurich) LPHE seminar November 15, 20 23

29 MET templates closure test Validation of method in photon+jets events photon is well measured only expected MET comes from jet mis-measurement Events / 5 GeV 1-1 CMS preliminary, 65 nb " +! at 7 TeV 3 jets data Template prediction Prediction and observation agree MET > 15 GeV: 12.5 predicted 11 observed MET (GeV) MET observed and predicted in γ+jets events F. Ronga (ETH Zurich) LPHE seminar November 15, 20 24

30 SS dileptons: prospects Event selection 2 good and isolated same-sign leptons (ee,eµ,µµ) ) 2 (GeV/c m 1/ CMS Preliminary, s = 7 TeV -1 Observe 1 event in 0 pb -1 Observe 4 event in 1 fb -1 CDF Preliminary 3l (3.2 fb ) -1 D0 observed limit (2.3 fb ) 3 jets, HT > 200 GeV 350 LEP excluded regions msugra: tanβ = 3, A 0 = 0, (µ) > 0 missing energy 300 Very clean signature only SM background: W ± W ± /pb 1/fb dominated by fake leptons, mainly from top-antitop: one lepton from W, another from b decay normally caught by isolation requirement measure isolation efficiency in b-bbar m 0 (GeV/c ) 95% CL limits, msugra isolation = energy deposited in a cone around the particle F. Ronga (ETH Zurich) LPHE seminar November 15, 20 25

31 SS dileptons: ttbar µ fake rate tag-and-probe method tag with b-jet on one side study isolation of muon on other side reweight to account for different pt and jet multiplicity in QCD and ttbar Events(Normalized)/ CMS Preliminary, Jet N -1 s=7 TeV, 51 nb! 2 data QCD MC Events(Normalized)/0.6 Reweight CMS Preliminary, -1 s=7 TeV, 51 nb data QCD MC tt MC Relative Isolation Relative Isolation F. Ronga (ETH Zurich) LPHE seminar November 15, 20 26

32 Wrapping up the SUSY searches The search has begun in various channels all hadronic, 1, 2 and more leptons Data-driven (SM) background estimation methods are in place Stay tune for new results very soon In the meanwhile: what can we expect?... F. Ronga (ETH Zurich) LPHE seminar November 15, 20 27

33 Global SUSY fits and a quick look at the future

34 Global fits? Confronting a model to data combine measurements compare with predictions constrain the parameters or exclude the model... Global SUSY fits there is more than direct searches: Flavour Physics (in particular B Physics...) low energy (g-2) Precision Electro-weak data Cosmological data exploit them to constrain SUSY A famous example of global fit The ingredients a consistent set of measurements state-of-the-art predictions F. Ronga (ETH Zurich) LPHE seminar November 15, 20 and a combination of the two 29

35 Today s constraints F. Ronga (ETH Zurich) LPHE seminar November 15, 20 + constraints on mass spectrum 30

36 Performing the fit Multi-parameter χ 2 variable Ci experimental constraints Pi predicted value for a given parameter set Fitting for all model parameters, e.g., CMSSM M0, M1/2, A0, tanβ (sign(µ)=1) including relevant SM uncertainties mtop, mz, ΓZ, Δαhad... and existing constraints on sparticle masses LEP and Tevatron searches produce Markov Chain Monte Carlo with 25 million points F. Ronga (ETH Zurich) Dark Matter in the Sky and Underground September 23, 20 31

37 Prospects for the LHC Today s data seems to favour low-mass SUSY SUSY could be around the corner! (or the end of CMSSM...) M1/2 [GeV] τ LSP 1 tanβ =, A 0 = 0, μ > 0 CMS preliminary s=7 TeV Hadronic search, 95% C.L. curves L = 00/pb L = 0/pb CMS-NOTE full CMSSM parameter space 68% C.L. 95% C.L. Eur.Phys.J.C64: ,2009 NO EWSB M0 [GeV] F. Ronga (ETH Zurich) Dark Matter in the Sky and Underground September 23, 20 32

38 And with some luck... After discovery of a dilepton edge (m 2 ll) edge = (m2 χ m 0 2 lr )(m 2 lr m 2 χ ) m 2 lr χ 0 1 l Dilepton edge measurement at CMS 0/pb integrated 14 TeV M1/2 [GeV] !" LSP arxiv: [hep-ph] CMSSM today s data 68% C.L. 95% C.L. CMSSM 0/pb LHC data 68% C.L. 95% C.L. NO EWSB M0 [GeV] F. Ronga (ETH Zurich) Dark Matter in the Sky and Underground September 23, 20 33

39 An aside A special type of SUSY search

40 Heavy Stable Charged Particles In some models of SUSY (e.g., Split SUSY) CMS PAS EXO--004 gluinos are light, squarks are heavy gluino decay is suppressed: gluino is stable gluino hadronizes to R-hadrons R-mesons: (gluino,quark,anti-quark) R ±,R 0 R-baryons: (gluino + 3 quarks) R ++,R ±,R 0 R-gluinoballs: (gluino + gluon) R 0 If the lifetime is long enough: track as it moves through detector high energy loss, low momentum The role of the gluino can also be taken by a squark or a slepton e.g., stop or stau F. Ronga (ETH Zurich) CHIPP annual plenary meeting August 23, 20 35

41 HSCP search at CMS Identify HSCP as it moves through the detector CMS PAS EXO--004 tracks with high pt, high de/dx tracker-only (silicon strip detector) additional selection: muon ID track+muon search Reconstruct mass from de/dx Perform search counting experiment in masses GeV/c 2 data-driven prediction using side-bands de/dx B A D C F. Ronga (ETH Zurich) CHIPP annual plenary meeting August 23, 20 pt 36

42 HSCP search at CMS Identify HSCP as it moves through the detector CMS PAS EXO--004 tracks with high pt, high de/dx tracker-only (silicon strip detector) additional selection: muon ID track+muon search Reconstruct mass from de/dx Perform search counting experiment in masses GeV/c 2 data-driven prediction using side-bands de/dx B A D C F. Ronga (ETH Zurich) CHIPP annual plenary meeting August 23, 20 pt 36

43 HSCP cross-section limits Exclusion gluino Prediction gluino Tracker only Cross-check prediction in backgroundenhanced region (loose selection) No event observed in signal region 95% CL upper limits exclude mgluino < 271 GeV/c 95% CL (tracker-only) exclude mgluino < 284 GeV/c 95% CL(tracker+muon) F. Ronga (ETH Zurich) CHIPP annual plenary meeting August 23, 20 37

44 Summary

45 Conclusion LHC has performed extremely well in last few months More than 40/pb collected by the LHC experiments CMS is keeping up and shows very good performance The search for SUSY is on, in all topologies Prospects for next year are very good! F. Ronga (ETH Zurich) LPHE seminar November 15, 20 39