Vadym Zhuravlov

1. Vadym Zhuravlov SUSY in ATLAS ATLAS MDT seminar 27 Nov 2007

2. Contents: • Introduction: what is SUSY and why SUSY • Models, points, spectra • Quasi-stable NLSP • Missing Et signature • Background • Spin measurement • Conclusion

3. Why SUSY? • A symmetry which relates bosons and fernions and represented by operator • Q |BOSON> = |FERMION> and Q |FERMION> = |BOSON> • Generalization of Poincare algebra links together representation with different spin • {QQ} = 2σ P • Q does not change the particle quantum numbers, except spin • Even if there is no “WHY” still there is a question: • why there are two classes of • particles in nature – • bosons and fermions • Invented more then 30 years ago and still not discovered • ( Higgs also)

4. Provides unification of gauge coulings: • (requires SUSY masses below few TeV) • Provides a good candidate for Dark Matter – lightest neutralino (R-parity is conserved)

5. Why SUSY? • Solves “hierarchy” problem • SM is effective theory at • E<<Λ (~1019 GeV) • MHiggs(tree level) ~ 1038 GeV • Fine tuning needed! • “Not natural…” ΔMHiggs ~ Λ ΔMHiggs ~ Λ2 ΔMHiggs ~ log Λ SUSY: = 0

6. Barnett Newman “Broken Obelisk”

7. SUSY fields and particles • SM: 28 bosonic and 96 fermionic DOF – highly non-supersymmetric! • Fields -> superfields • 2 complex Higgs fields: h, H, A, H+, H- • tanb = V1/V2 • MSSM – 124 parameters.

8. SUSY is a broken symmetry. HOW? • Non of MSSM fields can develop non-zero VEV to break SUSY. Hidden sector where SUSY is broken. • Messenger: transmit broken SUSY to visible sector. • Gravity mediated SUSY breaking: gravitino mass ~ EW mass • mSUGRA parameters: m0, m1/2, A0, tanb, sign(m) • Gauge mediated SUSY breaking: messinger sector consists of particles with SU(3)xSU(2)xU(1) quantum numbers • Gaugino mediation: SUSY is broken in another brane. BULK Hidden sector Our brane gaugino

9. R-parity R = (-1)3(B-L)+2s “+” for ordinary particles “-” for supersymmetrical partners If R-parity is conserved, SUSY-particles are created in pairs, LSP is stable Under R-parity the lepton and barion numbers are conserved Rule to create SUSY Feynman vertex: take SM vertex and replace 2 legs by super-legs

10. Renorm. Group Equations Particle Spectra GeV

11. SUSY Dark Matter Slepton Co-annihilation region: LSP ~ pure Bino. Small slepton-LSP mass difference makes measurements difficult. tanβ=10, μ>0 'Focus point' region: significant h component to LSP enhances annihilation to gauge bosons excluded by LEP Ellis et al. hep-ph/0303043 New constrain 0.094 < Ώh2 < 0.129 'Bulk' region: t-channel slepton exchange - LSP mostly Bino. 'Bread and Butter' region for LHC Expts. Old constrain 0.1 < Ώh2 < 0.3 Favorite by g-2 STAU is NLSP excluded by b→sγ

12. Quasi- stable STAU Production: • Experimental signatures: • Lifetime > 10-8 : slow muon-like particle • 10-10 < Lifetime < 10-8 : kink tracks • Lifetime < 10-10 : muons with large impact parameter A.Gladyshev hep-ph/0509168 10 fb-1 Mτ = 160 GeV tanβ=10 340 STAUs

13. S. Bressler ATLAS TOF - MDT Hit radius reconstruction in the MDT – m • A charged particle passing the MDT will leave clusters of ionized atoms • The electrons drift to the wire in the center of each tube • The radius from which the electrons drift to the wire is calculated from a time measurement • t0 is estimated for a muon traveling at the speed of light • The segment is tangent to the radii • Some hits from “noise” are ignored tdrift t0 R=R(tdrift)=R(tmeasured-t0) tmeasured=t0+tdrift Segment reconstruction

14. S. Bressler ATLAS TOF - MDT Radius reconstruction in the MDT –slow particle • The long time window of the MDT guarantees that data of low b particles will be saved. • The measured hit radius is incorrect • We want to estimate t • Larger radii result in • Badly fitted segment • Wrong direction of segment t0(slow particle) =t0+t tdrift Rmeasured=R(tmeasured-t0) = R(tdrift+t) > R tmeasured=t0+t+tdrift Segment reconstruction

15. S. Bressler ATLAS TOF - MDT A b reconstruction algorithm (1) • Relies on long time window of MDT and BCID from ID • Identify penetrating particle by associating muon hits and segments with extrapolated ID track • Loop over possible t • Change MDT digits’ time and hence radii • Create MDT segments from the re-timed digits • Estimate t0 (TOF) from the Dt that minimizes the c2 • Include information from segmentsin trigger chambers • RPC tof • TGC direction • Calculate b and M

16. misal1_mc12.005414.GMSB5_jimmy.susy.digit.RDO.v12000502 part of MuGirl Hiroshi Nomoto M=P/βγ

17. Golden channel: jets+MET

18. Decays

19. Cross-sections

20. Inclusive search no interaction with detector  ET,miss 1-lepton mode MET > 100 GeV 1 jet with Pt>100 GeV 4 jets with pt>50 GeV Transv. Spher. > 0.2 m or e pt > 20 GeV 2-lepton mode MET > 100 GeV 1 jet with Pt>100 GeV 4 jets with pt>50 GeV 2 m or e pt>20 GeV Transv. Spher. > 0.2 0-lepton mode MET > 100 GeV 1 jet with Pt>100 GeV 4 jets with pt>50 GeV Transv. Spher. > 0.2 TDR cuts – 10 years old!!!

21. No lepton mode Meff = Sjjets|Pt| + Et miss correlated to MSUSY MSUSY = SMisi / Ssi

22. ATLAS TDR Background No lepton mode S/B = 2 S/B = 10 Matrix Element calculation VS Parton Showering

23. Estimate background from data Bad knowledge of: • Underlined Event • Cross-sections • Parton Distribution Functions • Detector Calibration (jets, MET) • statistics of Monte Carlo

24. QCD Background • Two main sources: • fake ETmiss (gaps in acceptance, dead/hot cells, non-gaussian tails etc.) • real ETmiss (neutrinos from b/c quark decays) • Simulations require detailed understanding of detector performance (not easy with little data). • Huge cross-section – need of Fast Shower Simulation • Estimate background using data: jet smearing function Pythia dijets SUSY SU3

25. jets MET QCD Background • Step 1: Measure jet smearing function from data • Select events: ETmiss > 100 GeV, Df(ETmiss, jet) < 0.1 • Estimate pT of jet closest to EtMiss as pTtrue-est = pTjet + ETMiss • Step 2: Smear low ETmiss multijet events with measured smearing function fluctuating jet Njets >= 4, pT(j1,j2) >100GeV, pT(j3,j4) > 50GeV ATLAS ATLAS NB: error bars expected errors on background. Preliminary Preliminary ETmiss

26. No lepton channel: Z→νν background • Get Z from Zee, what are the steps : • Take Zee events • Correct for electron identification efficiency (measured with real data) • Correct for acceptance cuts (with MC) • Get Z distributions • Below is the formula summarizing the different steps : 20.00% 3.36% Correct for kinematics cuts (PT(lept) > 20 GeV/c) from MC 20% Correct for fiducial cuts (|(lept)| < 2.5) from MC 15% # branching ratios from PDG Factor 6 Z MET distribution Correct for electron id efficiency (measured with data) factor 2

27. 1 lepton SUSY Background: ttbar -> lnln (one l is missing) and ttbar -> qqbar ln

28. How to get rid of semi-leptonic ttbar background? W mass bbqql bbll MT (GeV) MT (GeV) Transverse mass: Minv(Missing Pt and PtLepon)

29. di-leptonic ttbar: decay resimulation • Select pure biased di-leptonic ttbar sample: small MET (no susy signal) – seed events • Reconstruct kinematics. How? → coming soon • resimulate top decay (as many times as needed) and count events with large MET with susy no susy

30. 2 lepton SUSY Background: ttbar->bblnln Bbqqln with second lepton from b/c decay

31. dileptonic ttbar background: clean bb lνlν sample Clean di-leptonic ttbar sample

32. N_pairs > 0 B C A D N_pairs = 0 ttbar background for 2 lepton search Number of pairs background + SUSY Missing ET No strong correlation between MET and N_pairs Background in D = A x C/B

33. 1 lepton search: main background – dileptonic top. • Why one lepton is missing? • it is tau. Take one of the leptons of clean di-leptonic ttbar sample and replace it by tau. Decay tau and see what happens – change of MET, Njets, nLeptons. • it miss-identified. Drop on the two leptons of clean di-leptonic sample, re-weight events by miss-identification efficiency

34. Inclusive reach in mSUGRA parameter space Reach sensitivity only weakly depends on tanb, A0 and m

35. Measure Angle Spin-0 Spin-½ Polarise Spin-½, mostly wino Spin-0 Spin-½, mostly bino SUSY spin measurement • If SUSY signals are observed at the LHC, it will be vital to measure the spins of the new particles to demonstrate that they are indeed the predicted super-partners • Angular distributions in sparticle decays lead to charge asymmetry in lepton-jet invariant mass distributions. The size of the asymmetry is proportional to the primary production asymmetry between squarks and anti-squarks • charge asymmetry of lq pairs measures spin of c02 • shape of dilepton invariant mass spectrum measures slepton spin Spin-0 flat

36. stransverse mass Transverse mass Mt– endpoint is a mass of decaying particle (W) Stransverse mass Mt2– endpoint is a mass of c

37. stransverse mass – direct slepton production Signature: two opposite sign same flavor leptons and missing Et Endpoint of stransverse mass is a function of mass difference of slepton and LSP MT2

38. Other topics: • R-hadrons • Tau-signatures • Gaugino direct production • Study of gauge-mediated SUSY • R-parity violating processes • Spectroscopy • Conclusion: • LHC is last chance to discover SUSY • SM uncertainties in the BG estimation is a limiting factor • Many models, parameters, preferable points: lot of work

39. Backup slides

40. “SUSY was invented more then 30 years ago and still not discovered” • but • Electron was invented more then 2 500 years before • Vision of Ezekiel • … et a lumbis eius et sursum quasi aspectus splendoris ut visio electri