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Detection of slepton non-universality effects at LHC

Detection of slepton non-universality effects at LHC. references: hep-ph/0405052, A. Barr hep-ph/0406317, Goto, Kawagoe, Nojiri. Electron/muon efficiency. It has aplication whenever exclusive studies

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Detection of slepton non-universality effects at LHC

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  1. Detection of slepton non-universality effects at LHC references: hep-ph/0405052, A. Barr hep-ph/0406317, Goto, Kawagoe, Nojiri

  2. Electron/muon efficiency • It has aplication whenever exclusive studies and leptonic signatures/endpoints are analysed, like for exmaple in the left squark cascade decay: when we study ll, llq and lq endpoints and apply subtraction: Correction factors for different efficiencies

  3. Outline • Left squark decay • Charge asymmetry • Left/right slepton mixing • Left squark decay, general case • Influence of mixings on charge asymmetry

  4. Left squark decay,charge asymmetrywhen slepton is purely right handed

  5. Left squark decay First emitted lepton (near) Final state: l+, l- , q, missing energy

  6. Decays of squark and slepton are spherically symmetric. Due to neutralino spin 1/2, if decay into followed by , the lepton favours going in the opposite direction to for ( and going in the same drection for the ). Angular distribution is not symmetric Invariant mass M(qlnear) is charge asymmetric. (decays to left and decays to right slepton have opposite asymmetries. ). If we can measure this asymmetry it is direct proof of neutralino spin.

  7. M(qlnear) Spin effects on Ideal distributions M(ql+) Events Spin correlations taken into account, M(ql+) Spin correlations taken into account, M(ql-) M(ql-) No spin correlations, no charge asymmetry, identical distributions of M(ql+)andM(ql-) M(ql)

  8. Charge asymmetry

  9. Selected mSUGRA point – LHCC 5 (nowexcluded by LEP): m0 =100 GeV m1/2 =300 GeV A0 =300 GeV tan(β) =2.1 sign(μ)=+ -second neutralino do not decay to left slepton -right squark never decay to second neutralino

  10. Monte Carlo • ISAJET, HERWIG, ATLFAST • Choice of parton distribution function is crucial • Necessary to include spin effects in HERWIG P. Richardson JHEP 11 (2001) 029 • Selection cuts to isolate left squark decay applied

  11. Asymmetry M(qlnear) quark antiquark ql+ ql- ql- ql+ Parton level distributions , can’t be measured by experiment

  12. Asymmetry M(qlfar) antiquark quark ql+ ql- ql- ql+ Parton level distributions, can’t be measured by experiment

  13. Problems • We do not know which is the first and which is the second emitted squark • Quark and antiquark are experimentally indistinguishable and have opposite asymmetries

  14. Solution • Study of M(l-q) and M(l+q) distributions • Each distribution contain contribution from both near and far lepton and contribution from both quark and antiquark LHC is pp collider → more quarks then antiquarks is going to be produced and asymmetry can be measured

  15. Asymmetry M(ql) Parton level distributions ql- ql+

  16. Asymmetryafter event selection and detector simulation M(ql) asymmetry L=500 fb-1 L=500 fb-1 After selection ql+ Parton level x 0.6 ql- No spin correlations asymmetry M(ll) L=150 fb-1

  17. Left squark decay andcharge asymmetrygeneral case

  18. Left/right slepton mixings • SELECTRONS: L/R mixing is negligible. Selectron mass eigenstates: • SMUONS: Smuon mass eigenstates: For large values tg(β) mixing can be observed • STAUS: Mixing is significant. Stau mass eigenstates: For “typical” mSUGRA point M1≈ 0.5 M2 , wino components dominate , bino component dominates , lighter slepton is dominantly , and the heavier one is dominantly

  19. Decay of second neutralinodepend on the mSUGRA point Dominant Allowed for some points, when m(02) > m(l2).

  20. Left squark decaygeneral case

  21. Effects of left/right mixings Left/right mixing affect - the charge asymmetry - decay width for l=µ,  • SELECTRONS: maximal asymmetry A(e) ≈ -1. • SMUONS: asymmetry smaller then in selectron case if there is L/R mixing significant. • STAUS: asymmetry opposite to selectron case

  22. Very important to choose point with: - large BR for left squark cascade decay in order to have large available statistics with small luminosity - large values of tg(β) if we want to study smuon mixing

  23. Some examples 1. If smuon mixing is not significant and decay of is open, then we have asymmetries from • Ifsmuon mixing is not significant and both decays of are open, then we have asymmetries from

  24. SPS1a: m0 =100 GeV m1/2 =250 GeV A0 =-100 GeV sign(μ)=+ tg(β)=10, 15, 20 SPS3: m0 =90 GeV m1/2 =400 GeV A0 =0 GeV sign(μ)=+ tg(β)=10 Decay is also open, and should show opposite charge asymmetry to that of Modified point effect of smuon mixing is significant

  25. SPS1a ( tg(β) = 10 ) theory SPS3 theory

  26. Plans • Start studies with SU3 point. All the necessary effects to be included in HERWIG and start private production. • First step would be to measure charge asymmetry, what would confirm neutralino spin. (Efficiencies would be included in mass distributions.) • Flavour workshop, CERN, 3-7 November

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