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Polarization effects in slepton production at hadron colliders

Polarization effects in slepton production at hadron colliders. Giuseppe Bozzi Euro-GDR 2004 Frascati - November 25, 2004 in collaboration with B. Fuks and M. Klasen. Preprint submitted to arXiv : hep-ph/0411318. Introduction. SUSY : High energy extension of the Standard Model

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Polarization effects in slepton production at hadron colliders

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  1. Polarization effects in slepton production at hadron colliders Giuseppe Bozzi Euro-GDR 2004 Frascati - November 25, 2004 in collaboration with B. Fuks and M. Klasen Preprint submitted to arXiv : hep-ph/0411318

  2. Introduction • SUSY : • High energy extension of the Standard Model • Only non trivial extension of the Poincaré group • Symmetry between fermionic and bosonic degrees of freedom • Solving the hierarchy problem • Stabilization of the Higgs mass • Explanation of gauge coupling unification • MSSM : • One generator --> one SUSY particle for each SM particle • Renormalizability • B, L (--> R-parity) conservation

  3. Introduction • Phenomenology : • None of these partners has been discovered yet - Superpartner masses lie at a higher scale - SUSY must be broken • Hierarchy of scales must be maintained - Supersymmetry breaking through soft mass terms - Superpartner masses are no larger than a few TeV > Within the discovery reach of current and future hadron colliders (RHIC, Tevatron, LHC)

  4. Introduction • Purposes of this work : Processes studied : and • Unpolarised cross sections well known (both LO and NLO): - LO : S.Dawson, E.Eichten and C.Quigg, PRD 31 (1985) 1581 - LO : H.Baer, C.Chen, F.Paige and X.Tata, PRD 49 (1994) 3283 - NLO : H.Baer, B.W.Harris and M.H.Reno, PRD 57 (1998) 5871 - NLO : W.Beenakker, M.Klasen, M.Krämer, T.Plehn, M.Spira and P.M.Zerwas, PRL 83 (1999) 3780 (NLO enhances LO by ~ 35% at Tevatron and ~20% at LHC --> extended discovery reach) • Polarised cross sections - Old paper for old colliders: P.Chiappetta, J.Soffer and P.Taxil, PLB 162 (1985) 192 - No mixing (important, especially for the lightest slepton : ) - Discrimination between new physics signal and SM background • Verify and extend previous polarized calculations, including mixing effects relevant for third generation sleptons

  5. Cross sections • Feynman Diagrams : + • Electroweak couplings : • fermions • sfermions : multiplication by Sj1Si1* and Sj2Si2* after the introduction of the mixing matrix :

  6. Cross sections • Unpolarised partonic cross section • Remark : and are supposed degenerate in mass • Unpolarised hadronic cross section • Parton Distribution Function : GRV98LO M.Glück, E.Reya and A.Vogt, EPJ C5 (1998) 461

  7. Hadronic cross sections • and supposed degenerate in mass (no mixing here) • LHC : visible in the entire mass range • Tevatron : visible in a restricted mass range • RHIC : difficult ! • Background :  ~10 nb(3 to 6 orders of magnitude higher)

  8. Spin asymmetry • Cross sections • and • and (no photon contribution here) • Introduction of the mixing angle  (Mass eigenstates and ) • Polarised PDF used : GRSV2000LO (standard and valence) M. Glück, E. Reya, M. Stratmann and W. Vogelsang, PRD 63 (2001) 094005

  9. Spin Asymmetry, RHIC • RHIC : = 500 GeV (SUSY scenario with light , maybe visible) • GMSB scenario based on SPS 7 ( is the NLSP, after the gravitino) • Parameters : •  is varying (default: 40 TeV) • Mmes = 80 TeV • Nmes = 3 • tan  = 15 • µ > 0

  10. Spin Asymmetry, RHIC • Only a small area of interest : • Invisible cross section • Mass exclusion domain (LEP) • Physical constraints on SUSY parameters • Large PDF uncertainties (large Bjorken-x) • Sensitive to the mixing: constraints on SUSY parameters ? • Background : AL = – 0.1 … – 0.04(after invariant mass cut at ≈ 52 GeV) --> Discrimination SUSY/SM } 30%

  11. Spin Asymmetry, Tevatron • SUSY scenario based on SPS1a’( Standard choice ) • is the NLSP (after the neutralino), but slow decay • Parameters : • M1/2 = 250 GeV • M0 = 70 GeV (SPS 1a: 100 GeV) • A0 varying (default : 300 GeV; SPS 1a: -100 GeV) • tan  = 10 • µ > 0

  12. Spin Asymmetry, Tevatron • Physical constraints on SUSY parameters (cos  from 0.21 to 0.30) • Small PDF dependence(well known Bjorken-x range) • Sensitive to the mixing • Constraints on SUSY parameters ? • Background : AL = – 0.09 … – 0.08 (after invariant mass cut) --> Discrimination SUSY/SM } 5-6%

  13. Spin Asymmetry, LHC • SUSY scenario based on SPS 4(at LHC we can reach heavy masses --> SPS4) • Parameters : • M1/2 = 400 GeV (higher masses) • M0 = 300 GeV (higher masses) • A0 varying (default : 0) • tan  = 50 (large splitting) • µ > 0

  14. Spin Asymmetry, LHC } • Physical constraints on SUSY parameters (cos  is going from 0.29 to 0.40) • Large PDF uncertainties (small Bjorken-x) • Sensitive to the mixing • Constraints on SUSY parameters ? • Background : AL = – 0.025 … – 0.015 (after invariant mass cut) --> Discrimination SUSY/SM 20% } 10%

  15. Conclusions and outlook • Spin asymmetry measurements : • Differentiation of SM/SUSY processes for all 3 colliders. • More severe constraints on SUSY parameters ? • Tevatron : small PDF uncertainties --> reliable • LHC, RHIC : large PDF uncertainties --> more difficult • Outlook : • Better constraints on PDFs (from HERA, RHIC,…) are welcome! • Higher order calculations

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