1. 12 May 2004 Alan Barr UK ATLAS Physics SUSY Spin Measurements with ATLAS Alan Barr “What else could it possibly be?” “Don’t be so sure … ” hep-ph/0405052 “If it quacks like SUSY …” So … is it really supersymmetry?

2. 12 May 2004 Alan Barr UK ATLAS Physics Extended higgs sector (2 doublets) (S)particle reminder SMSUSY quarks (L&R) leptons (L&R) neutrinos (L&?) squarks (L&R) sleptons (L&R) sneutrinos (L&?)  Z 0 W ± gluon BW0BW0 h0H0A0H±h0H0A0H± H0H±H0H± 4 x neutralino 2 x chargino After Mixing gluino Spin-1/2 Spin-1 Spin-0 Spin-1/2 Spin-0 Bino Wino 0 Wino ± gluino ~ ~ “Left squark” = scalar SUSY partner of left quark

3. 12 May 2004 Alan Barr UK ATLAS Physics Sparticle decays generate: –Missing E T (LSP) –Jets (squarks/gluino) –Leptons (sleptons) “If we see these at LHC we have discovered SUSY” Not necessarily… Scalar mass term (GeV) Gaugino mass term (GeV) Plot by D. Tovey [RPC SUSY] 1-year low-lumi mSUGRA reach

4. 12 May 2004 Alan Barr UK ATLAS Physics Universal Extra Dimensions TeV-scale universal extra dimension model Kaluza-Klein states of SM particles –same QN’s as SM –m n 2 ≈ m 0 2 + n 2 /R 2 [+ boundary terms] –same spin as SM –KK parity Lightest KK state stable, and weakly interacting 1 st KK mode pair-produced First KK level looks a lot like SUSY hep-ph/0205314 Cheng, Matchev “How to get fooled at the LHC” Radius of extra dimension ~ TeV -1 KK tower of masses n=0,1,… Dubbed “Bosonic Supersymmetry”

5. 12 May 2004 Alan Barr UK ATLAS Physics UED KK spectrum 1 st excited KK level (example masses) Example decay spectrum Stable lightest KK particle (weakly interacting) hep-ph/0205314 Cheng, Matchev After adding boundary terms -> SUSY-like spectrum Need to measure spins!

6. 12 May 2004 Alan Barr UK ATLAS Physics SUSY decay chain Use mSUGRA LHC point 5 as example Well studied in context of sparticle masses Nice leptonic signal at LHC Spin-½, mostly wino Spin-0 Spin-½ Spin-0 Spin-½, mostly bino Final state = jet + l + + l - + E T ( + decay of other sparticle)

7. 12 May 2004 Alan Barr UK ATLAS Physics Spin projection factors In rest frame of with +ve z-axis aligned with q L Approximate SM particles as massless -> okay since m « p P S

8. 12 May 2004 Alan Barr UK ATLAS Physics Spin projection factors In rest frame of with +ve z-axis aligned with q L Approximate SM particles as massless -> okay since m « p P S S Σ=0 Spin-0

9. 12 May 2004 Alan Barr UK ATLAS Physics Spin projection factors In rest frame of with +ve z-axis aligned with q L Approximate SM particles as massless -> okay since m « p θ*θ* p S

10. 12 May 2004 Alan Barr UK ATLAS Physics Spin projection factors In rest frame of with +ve z-axis aligned with q L Approximate SM particles as massless -> okay since m « p θ*θ* p S P S S Spin projection factor Spin-0 m ql - measure Σ=0

11. 12 May 2004 Alan Barr UK ATLAS Physics l near q invariant mass (1) m/m max = sin ½ θ* Back to back in  2 0 frame θ*θ* quark near lepton χ20χ20 Phase space -> factor of sin ½ θ* Spin projection factor in |M| 2 : l + q -> sin 2 ½ θ* l - q -> cos 2 ½ θ* l+l+ l-l- Phase space Probability

12. 12 May 2004 Alan Barr UK ATLAS Physics l near q invariant mass (2) squark decay anti-squark decay l+l+ l+l+ l-l- l-l- (Lepton from  2 decay only – not directly measurable) Obvious asymmetry!Opposite asymmetry! -> if same # squarks as anti-squarks effect cancels 01 01

13. 12 May 2004 Alan Barr UK ATLAS Physics How to measure? l near q shows nice charge asymmetry –Excellent probe of spin of Experimental problems in measurement: –Can’t tell near lepton from far lepton Plot l + q and l – q instead -> contributions from both near and far –Can’t tell quark jet from anti-quark Sum of q and q-bar is measurable pp collider -> get squark asymmetry from PDFs

14. 12 May 2004 Alan Barr UK ATLAS Physics Production asymmetry Peak near 0.1, 0.1 Valence quarks Parton distribution function has more q than q-bar for Bjorken x ≈ 0.1 -> pp collider produces more squarks than anti-squarks x1 and x2 sampled by MC (Twice as much for our point) qg -> squark + gluino

15. 12 May 2004 Alan Barr UK ATLAS Physics l far q invariant mass (Lepton from slepton decay only – not directly measurable) l-l- l-l- l+l+ l+l+ squark decay anti-squark decay Some asymmetry inherited from boost of slepton in  2 0 rest frame

16. 12 May 2004 Alan Barr UK ATLAS Physics Parton Level difference/sum l+l+ l-l- Experimentally measurable -> q and q-bar -> near and far leptons Charge asymmetry Shape indicates that  2 0 is spin-½ spin-0=flat

17. 12 May 2004 Alan Barr UK ATLAS Physics After detector simulation (ATLFAST) l+l+ l-l- Change in shape due to charge- blind cuts parton-level * 0.6 -> Charge asymmetry survives detector sim -> Same shape as parton level (but with BG and smearing) detector-level Invariant mass Charge asymmetry, For cuts see C. Lester thesis spin-0 spin-½ Events

18. 12 May 2004 Alan Barr UK ATLAS Physics Cross-check No asymmetry if spin correlations turned off Monte Carlo is HERWIG (6.5) Can turn off spin correlations –distribution for “scalar  2 0 ” –consistent with flat –not consistent with spin-½  2 0 of previous page (linearly increasing) spin-½ -> spin-0 ->production asymmetry spin-0=flat

19. 12 May 2004 Alan Barr UK ATLAS Physics Further evidence - slepton spin Dilepton invariant mass. –“Right-handed” slepton –l + and l - are right handed –might expect pronounced spin effects (as for lq distributions) –none because slepton is scalar Scalar particle carrying lepton number –sounds like a slepton to me! Straight line dist n Shape after different-family subtraction Back-to-back in slepton frame (phase-space)

20. 12 May 2004 Alan Barr UK ATLAS Physics Conclusions Method for measuring spins of SUSY particles at the LHC Measure l ± q invariant mass distributions –equivalent to angular distributions in Look for lepton charge asymmetry Requires initial asymmetry in squark vs anti- squark production –valence quarks in PDFs at x ~ 0.1 Measure spin-½ nature of  2 0 Also spin-0 slepton from m ll Should be enough to kill “straw man” e.g. universal extra dimensions