Vadym Zhuravlov

1. Vadym Zhuravlov SUSY in ATLAS ATLAS MDT seminar 30 Jan 2007

2. Contents: • Introduction: what is SUSY and why SUSY • Models, points, spectra • Production and decay of SUSY particles in ATLAS • Inclusive searches – missing Et sigmature • SUSY spectroscopy • Spin measurement • Stransverse mass • Conclusion

3. Why SUSY? • A symmetry which relates bosons and fernions and represented by operator • Q |BOSON> = |FERMION> and Q |FERMION> = |BOSON> • Q does not change the particle quantum numbers • 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) Why SUSY? • 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 • Anomaly mediation: SUSY is broken in another brane. BULK Hidden sector Our brane superfields

9. Particle Spectra GeV

10. SUGRA: DM favored regions • Bulk region: light susy particles. cc → ffbar t-channel slepton exchange • Stau coannihilation region: masses of stau and neutralino are almost degenerate. Neutralono-stau co-annihilation ct → t* → tg • Focus point: heavy squarks and sleptons and light neutralino (almost higgsino) cc → WW, ZZ, qqbar • Funnel region: mA=2mc. Resonant annihilation cc → A(H) → ffbar

11. 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

12. Production @ LHC Annihilation Quark- gluon Fusion

13. Decays

14. Decays

15. Cross-sections

16. Inclusive search • Signature: • High missing energy (LSP is undetected) • High-Pt jets and leptons 1-lepton mode MET > 100 GeV 2 jet with Pt>100 GeV 4 jets with pt>50 GeV Transv. Spher. > 0.2 m or e pt>10 GeV 2-lepton mode MET > 100 GeV 2 jet with Pt>100 GeV 4 jets with pt>50 GeV 2 m or e pt>20 GeV 0-lepton mode MET > 100 GeV 1 jet with Pt>100 GeV 4 jets with pt>50 GeV Transv. Spher. > 0.2

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

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

19. No lepton mode General idea: no-lepton estimates from tagged lepton samples Z  : - Z  l+l- : easy, but suffers from statistics - W  l with l+ into pseudo-missing-ET - MC based estimates W  l: - W  l with lepton tagged - W + 1 jet (pure), extrapolation to >= 4 jets with MC reweighting and Z+jets samples - MC based estimates ttbar: bbqql with lepton tagged why lepton missed: 60% tau 35% e, acceptance 5% isolation

20. 1 lepton SUSY Background: ttbar -> lnln (one l is missing) and ttbar -> qqbar ln W -> ln

21. General ideas: other variable SUSY signal plus bg bg A D B C bg bg Missing ET Bg in D = A x C/B normalize to data

22. decay resimulation Select pure ttbar sample, reconstruct kinematics Resimulate W decay and replace in original event quark u - d antiquark

23. Now have bbll event

24. decay resimulation: • Goal is to model complex background events using samples of tagged SM events. • Initially we will know: • a lot about decays of SM particles (e.g. W, Z) • a reasonable amount about the (gaussian) performance of the detector. • rather little about PDFs, the hard process and Underlying Events. • Philosophy • Tag ‘seed’ events containing Z/W/top • Reconstruct 4-momentum of Z/W/top (x2 if e.g. ttbar) • Decay/hadronise with e.g. Pythia • Simulate decay products with atlfast or fullsim • Remove original decay products from seed event • Merge new decay products with seed event (inc. ETmiss) • Perform standard SUSY analysis on merged event

25. 2 lepton SUSY Background: ttbar->bblnln Bbqqln with second lepton from b/c decay

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

27. SUSY spectroscopy • Inclusive searches: Meff = Sjets|Pt| + Etmiss correlated to MSUSY=SMisi / Ssi MeffSUSY = MSUSY-Mc2/MSUSY SUGRA: excelent correlation, MSSM: acceptable 10% measurement @ 100fb-1

28. p p ~ c01 ~ ~ ~ q ~ c02 l g q q l l SUSY spectroscopy • Due to R-parity conservation all SUSY events contain 2 neutralino which escape the detector. • Since neutralino are not detected, one can measure the kinematic end-points rather then mass-peaks.

29. p p ~ c01 ~ ~ ~ q ~ c02 l g q q l l SUSY spectroscopy (2) Minv Di-lepton invariant mass: e+e- + µ+µ- - e±µ± ATLAS Preliminary • Event selection: Electrons and muons with PT ≥ 20 GeV • Separate leptons from jets by ΔR > 0.4 • Fitted endpoint: 100.25 ± 1.14 GeV which is consistent with the expected value within the error

30. p p ~ c01 ~ ~ ~ q ~ c02 l g q q l l lq edge llq edge 1% error (100 fb1) 1% error (100 fb-1) SUSY spectroscopy (3) – more endpoints

31. p p ~ c01 ~ ~ ~ q Sparticle Expected precision (100 fb-1) qL 3% 02 6% lR 9% 01 12% ~ c02 l g ~ q ~ ~ ~ q l l SUSY spectroscopy (3) – mass peaks The 4-momentum of the c02 can be reconstructed from the approximate relation p(c02) = ( 1-m(c01)/m(ll) ) pll valid when m(ll) near the edge. The c02 can be combined with b-jets to reconstruct the gluino and sbottom mass peaks from g→bb→bbc02

32. 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

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

34. 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

35. Right-Handed Squark Mass • Determine the mass of right-handed squarks from: • The signal is two hard jets plus large ETmiss • Event selection: ETmiss > 200 GeV • Two jets with ET >150 GeV • No reconstructed electrons or muons • Calculate the stransverse mass of the two hard • jets. The endpoint gives the mass of right-handed • squarks

36. Other topics: • R-hadrons • Tau-signatures • Gaugino direct production • Study of gauge-mediated SUSY • R-parity violating processes • 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