1. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 1 Spin Measurements in Supersymmetry at the LHC Christopher Lester Cavendish Laboratory, Cambridge (on behalf of the ATLAS collaboration)

2. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 2 This talk is Backwards

3. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 3 not upside down !

4. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 4 Conclusions ATLAS does not yet know the circumstances (models, masses, integrated luminosities) in which the spins of supersymmetric particles will be unambiguously measurable There are lots of good and promising ideas – both within ATLAS and outside some are partly tested some are un-tested plenty of work remains to be done!

5. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 5 What is “Discovering SUSY” ? What makes Supersymmetry different to Universal Extra Dimensional (UED) models? One part of the answer: SPIN

6. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 6 We will see two important themes: Mass measurements will precede ( * ) spin determinations “Spin measurement” ( ** ) should not be confused with “sensitivity to spin” (*) or will at best be simultaneous with (**) Here “spin measurement” means “determining unambiguously the correct nature (scalar, fermion, vector) of one or more particles in a decay chain or model

7. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 7 The methods considered here Spins in “QLL chain” A.Barrhep-ph/0405052 ATL-PHYS-2004-017 Smillie et alhep-ph/0605286 (including ATLAS member) Biglietti et al ATL-PHYS-PUB-2007-004 (Study of second lightest neutralino spin measurement with ATLAS detector at LHC Matchev et al arXiv:0808.2472 Slepton Spin (pair production) A.Barr hep-ph/0511115 ATL-PHYS-PUB-2005-023

8. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 8 Other interesting methods Gluino chain spin Alvez, Eboli, Plehnhep-ph/0605067 MAOS method Cho, Kong, Kim, Park arXiv:0810.4853 Spins in chains with charginos Wang and Yavinhep-ph/0605296 Smillie hep-ph/0609296 Spins in chains radiating photons Ehrenfeld et alarXiv:0904.1293

9. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 9 Spin Consistency Check

10. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 10 Spin Consistency Check Di-Lepton Invariant Mass (GeV) Relative Frequency Straight line Consistent with: Phase-space Scalar slepton (SFSF) Fermion KK lepton (FVFV)

11. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 11 QL Spin Determination (A.Barr) “NEAR” “FAR” How can we tell from ? 2 problems : How can we distinguish the ‘near’ lepton from the ‘far’ lepton? hep-ph/0405052 ATL-PHYS-2004-017

12. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 12 Quark+NearLepton invariant mass distributions for: sin ½ θ* Back to back in  2 0 frame QL + QL - Phase space (spin-0) Probability density QUARKS L+ L- and sin ½ θ* Back to back in  2 0 frame QL - QL + Phase space (spin-0) Probability density ANTI -QUARKS L+ L- and __ _ hep-ph/0405052 ATL-PHYS-2004-017

13. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 13 Experimental problem Cannot reliably distinguish QUARKs from ANTI QUARKs In experiment, can only distinguish RED(QL+,_ L+) from BLUE(QL-,_L-) Can only distinguish lepton charge RED(QL+,QL+) from BLUE(QL-,QL-)

14. Expect QUARK and ANTI-QUARK contributions to cancel: QL + _ QL - _ SUM jL + SUM jL -

15. But LHC is Proton-Proton machine More Quarks than Anti-Quarks! So get: QL + _ QL - _ SUM jL + jL - Asymmetry! hep-ph/0405052 ATL-PHYS-2004-017

16. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 16 “Far” Lepton washout? (though compare with later comments Matchev arXiv:0808.2472) “NEAR” “FAR”

17. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 17 jL + So define m jL +, m jL - asymmetry parton-level detector-level Asymmetry “A” spin-0 Spin-½ M jL / GeV  sin ½ θ* where jL - hep-ph/0405052 ATL-PHYS-2004-017 500 fb-1 M(QL)

18. Charge asymmetry at detector level Susy spins compared only with no spin (i.e. with phase space) Points are for 500 fb -1 detector level no spin parton level x 0.6 Barr hep-ph/0405052 ATL-PHYS-2004-017 (similar to SU3) M(QL)

19. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 19 Tested further in ATLAS ATL-PHYS-PUB-2007-004 Biglietti et al Preselection cuts Dilepton selection cuts Parametrised Simulation (ATLFAST)

20. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 20 Di-lepton mass spectra ATL-PHYS-PUB-2007-004 Biglietti et al SU1 – MC truth SU3 – MC truth Here at SU1 there are two sleptons (ê L =255 GeV, ê R =155 GeV) below chi 2 =264 GeV. Chi 1 =137 GeV Here at SU3 there is only one accessible slepton below chi2 Chi 2 =219, ê R =155, Chi 1 =118 GeV M(LL)

21. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 21 Jet-lepton mass spectra ATL-PHYS-PUB-2007-004 Biglietti et al SU1 – MC truth SU3 – MC truth M(QL)

22. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 22 Truth Asymmetry ATL-PHYS-PUB-2007-004 Biglietti et al where A SU3 – MC truth 30 /fb M(QL)

23. Truth Asymmetry ATL-PHYS-PUB-2007-004 Biglietti et al SU1 – MC truth Near lepton Left slepton Near lepton Right slepton Far lepton Right slepton Far lepton Left slepton A A A A 220 /fb M(QL) Shows asymmetry depends on particle identities

24. Backgrounds ATL-PHYS-PUB-2007-004 Biglietti et al Main background is SUSY Mostly defeated by flavour subtraction Main Standard Model backgrounds are Di-top + jets W / Z + jets

25. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 25 Fast simulation results ATL-PHYS-PUB-2007-004 Biglietti et al SU1 – ATLFAST SU3 – ATLFAST Note... Flavour subtraction

26. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 26 Fast simulation results ATL-PHYS-PUB-2007-004 Biglietti et al AA SU1 – ATLFAST SU3 – ATLFAST Note... Flavour subtraction 30 /fb100 /fb Sufficient power to eliminate null hypothesis M(JL)

27. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 27 Safety check ATL-PHYS-PUB-2007-004 Biglietti et al SU1 – ATLFAST SU3 – ATLFAST Expect to see NO ASYMMETRY in these OFOS lepton plots. Confirmed! 30 /fb100 /fb M(JL)

28. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 28 QUACK ! SUSY UED Not all things that quack are ducks!

29. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 29 UED SUSY SPS1a masses UED type masses UED and SUSY not distinguished by dilepton mass spectrun hep-ph/0605286 Compare ratios of dilepton invariant mass distributions for different spin configurations (SUSY is horizontal) : M(LL) 2

30. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 30 Jet + lepton asymmetry not good at distingusihing UED and SUSY either UED massesSPS 1a masses Not resolvable for UED masses, maybe for SUSY Charge asymmetry due to quark vs antiquark excess

31. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 31 UED massesSPS 1a masses Similar form, different magnitude Not detectable for UED masses Jet + lepton asymmetry not good at distinguishing UED and SUSY either.

32. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 32 “ANY-Spin” Determination (Smillie et.al.) Later fuller follow-up (Matchev, Kong, et al) F FFF SFS hep-ph/0605286 arXiv:0808.2472 M(JL) 2 (SUSY) (UED) relative probability Cannot distinguish:

33. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 33 Direct di-slepton production A.Barr hep-ph/0511115 ATL-PHYS-PUB-2005-023 Event selection: two single leptons transverse missing energy > 100 GeV no jets with pT> 100 GeV no b-jets mT2(l+, l-) < 100 GeV Mll< 150 GeV |missing pT+ pT(l+), pT(l-)| <100 GeV Lepton pT(l1) > 40 GeV, pT(l2) > 30 GeV

34. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 34 Look at slepton production angle A.Barr hep-ph/0511115 ATL-PHYS-PUB-2005-023

35. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 35 Have some access to desired angle Distribution of is correlated with decay angle A.Barr hep-ph/0511115 ATL-PHYS-PUB-2005-023

36. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 36 Fast simulation plot Outer error bars: after SUSY & SM background subtraction Significance strongly dependent on mass spectrum A.Barr hep-ph/0511115 ATL-PHYS-PUB-2005-023

37. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 37 End Notes QLL chain Some spin “sensitivity” – but no strong UED/SUSY separation Reduced discriminatory power when considering general couplings (Matchev/Kong). Di-slepton production Better chance of separating UED/SUSY Still model dependent Both require large cross sections

38. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 38 Backup slides

39. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 39 M T2 -assisted spin determination assign 4-momenta SUSY UED Cho, Choi,Kim,Park, 0810.4853

40. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 40 Cross sections imply spins Datta, Kane, Toharia hep- ph/0510204 Higher spins mean higher cross sections (for given masses)

41. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 41 SU1 (stau co-annihilation) point

42. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 42 SU3 bulk point

43. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 43 SU3 bulk point

44. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 44 Helicity dependence Process 1 (SUSY) Process 1 (UED, transverse Z*: P /P = 2x) Both prefer highinvariant mass TL

45. LHC SUSY SPIN MEASUREMENTS SPIN PRAHA 2009 45 Example mass spectra SPS1a mass spectrum: (GeV) UED-type mass spectrum: (GeV) (R -1 ~ 800 GeV)