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Spin Measurements in Supersymmetry at ATLAS

Spin Measurements in Supersymmetry at ATLAS. Christopher Lester Cavendish Laboratory, Cambridge (on behalf of the ATLAS collaboration). This talk is Backwards. not upside down !. Conclusions.

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Spin Measurements in Supersymmetry at ATLAS

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  1. Spin Measurements in Supersymmetry at ATLAS Christopher Lester Cavendish Laboratory, Cambridge (on behalf of the ATLAS collaboration)

  2. This talk is Backwards

  3. not upside down !

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

  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. The methods considered here Spins in “QLL chain” A.Barr hep-ph/0405052 ATL-PHYS-2004-017 Smillie et al hep-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. Other interesting methods Gluino chain spin Alvez, Eboli, Plehn hep-ph/0605067 MAOS method Cho, Kong, Kim, Park arXiv:0810.4853 Spins in chains with charginos Wang and Yavin hep-ph/0605296 Smillie hep-ph/0609296 Spins in chains radiating photons Ehrenfeld et al arXiv:0904.1293

  9. Spin Consistency Check

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

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

  12. Quark+NearLeptoninvariant mass distributions for: • hep-ph/0405052 L+L- and L+L- and ANTI-QUARKS QUARKS Back to backin 20 frame Back to backin 20 frame _ QL+ QL- Phase space (spin-0) Phase space (spin-0) Probability density Probability density _ _ QL- QL+ sin ½θ* sin ½θ* ATL-PHYS-2004-017

  13. Experimental problem Cannot reliably distinguish QUARKs from ANTI QUARKs In experiment, can only distinguishRED(QL+,_ L+) from BLUE(QL-,_L-) Can only distinguish lepton chargeRED(QL+,QL+) from BLUE(QL-,QL-)

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

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

  16. “Far” Lepton washout?(though compare with later comments Matchev arXiv:0808.2472) “NEAR” “FAR”

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

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

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

  20. Di-lepton mass spectra ATL-PHYS-PUB-2007-004 Biglietti et al SU1 – MC truth SU3 – MC truth M(LL) M(LL) Here at SU1 there are two sleptons (êL =255 GeV, êR=155 GeV) below chi2 =264 GeV. Chi1=137 GeV Here at SU3 there is only one accessible slepton below chi2 Chi2=219, êR=155, Chi1=118 GeV

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

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

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

  24. Fast simulation results ATL-PHYS-PUB-2007-004 Biglietti et al Note ... Flavour subtraction SU1 – ATLFAST SU3 – ATLFAST

  25. Fast simulation results ATL-PHYS-PUB-2007-004 Biglietti et al Note ... Flavour subtraction SU1 – ATLFAST SU3 – ATLFAST A A 100 /fb 30 /fb M(JL) M(JL) Sufficient power to eliminate null hypothesis

  26. Safety check ATL-PHYS-PUB-2007-004 Biglietti et al Expect to see NO ASYMMETRY in these OFOS lepton plots. Confirmed! SU1 – ATLFAST SU3 – ATLFAST 100 /fb 30 /fb M(JL) M(JL)

  27. Not all things that quack are ducks! QUACK ! UED SUSY QUACK !

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

  29. Jet + lepton asymmetry not good at distinguishing UED and SUSY either. Similar form, different magnitude Not detectable for UED masses UED masses SPS 1a masses

  30. “ANY-Spin” Determination (Smillie et.al.)Later fuller follow-up (Matchev, Kong, et al) F F F S F S F (SUSY) (UED) hep-ph/0605286 relative probability arXiv:0808.2472 M(JL)2 Cannot distinguish:

  31. 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

  32. Look at slepton production angle A.Barr hep-ph/0511115 ATL-PHYS-PUB-2005-023

  33. Have some access to desired angle A.Barr hep-ph/0511115 ATL-PHYS-PUB-2005-023 Distribution of is correlated with decay angle

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

  35. 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

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