Polarization effects in slepton production at hadron colliders Benjamin Fuks in collaboration with G. Bozzi and M. Klasen Preprint submitted to arXiv : hep-ph/0411318 November 22, 2004

Table of contents Introduction Cross sections Spin asymmetry Conclusions November 22, 2004

Introduction SUSY : MSSM : High energy extension to 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 : 1 generator  one SUSY particle for each SM elementary particle Renormalizability B, L and R-parity conservation November 22, 2004

Introduction Phenomenology : None of these partners has been discovered yet  SUSY must be broken  Masses of the superpartners at a higher scale. Hierarchy of scales must be maintained  Supersymmetry breaking is soft  Superpartner masses are no larger than a few TeV  Interest for hadron colliders (RHIC, Tevatron, LHC)  Exploration of the TeV mass range November 22, 2004

Introduction Purposes of this work : Processes studied : and (production of scalar leptons) Unpolarised cross sections well known : 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 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  Spin asymmetries in longitudinally polarized hadron colliders November 22, 2004

Table of contents Introduction Cross sections Spin asymmetry Conclusions November 22, 2004

Cross sections + Feynman Diagrams : Electroweak couplings : fermions sfermions : multiplication by Sj1Si1* and Sj2Si2*  Introduction of the mixing matrix : November 22, 2004

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 November 22, 2004

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 : σ ~10 nb  3 to 6 orders of magnitude higher November 22, 2004

Table of contents Introduction Cross sections Spin asymmetry Conclusions November 22, 2004

Spin asymmetry Cross sections and and (no photon contribution here) Introduction of the mixing angle θ Mass eigenstates and Polarised PDF used : GRSV2000LO (standard and valence) M. Glück, E. Reya, M. Stratmann and W. Vogelsang, PRD 63 (2001) 094005 The lightest slepton November 22, 2004

Spin Asymmetry, RHIC RHIC : = 500 GeV  SUSY scenario with light  Maybe it will be visible GMSB scenario based on SPS 7  is the NLSP (after the gravitino) Parameters : Λ is varying (default : 40 TeV) Mmes = 80 TeV Nmes = 3 tan β = 15 µ > 0 November 22, 2004

} Spin Asymmetry, RHIC  Constraints on SUSY param. ? 30% 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 param. ? Background : AL = – 0.1 … – 0.04 (after invariant mass cut at ≈ 52 GeV)  Discrimination SUSY/SM } 30% November 22, 2004

Spin Asymmetry, Tevatron SUSY scenario based on SPS 1a’  Standard choice is the NLSP (after the neutralino), but slow decay Parameters : M1/2 = 250 GeV M0 = 70 GeV (100 GeV for SPS 1a) A0 varying (default : −300 GeV; -100 GeV for SPS 1a) tan β = 10 µ > 0 November 22, 2004

Spin Asymmetry, Tevatron Physical constraints on SUSY parameters  cos(θ) is going from 0.21 to 0.30 Small PDF dependence (well known Bjorken-x range) Sensitive to the mixing  Constraints on SUSY param. ? Background : AL = – 0.09 … – 0.08 (after invariant mass cut)  Discrimination SUSY/SM } 5-6% November 22, 2004

Spin Asymmetry, LHC SUSY scenario based on SPS 4 LHC : = 14 TeV  We can reach heavy masses  SPS 4 allows heavy Parameters : M1/2 = 400 GeV ( higher masses) M0 = 300 GeV ( higher masses) A0 varying (default : 0 GeV) tan β = 50 (large  large splitting) µ > 0 November 22, 2004

} } Spin Asymmetry, LHC  Constraints on SUSY param. ? 20% Physical constraints on SUSY parameters  cos(θ) is going from 0.29 to 0.40 Large PDF uncertainties (small Bjorken-x) Sensitive to the mixing  Constraints on SUSY param. ? Background : AL = – 0.025 … – 0.015 (after invariant mass cut) Discrimination SUSY/SM } 20% } 10% November 22, 2004

Table of contents Introduction Cross sections Spin asymmetry Conclusions November 22, 2004

Conclusions Spin asymmetry measurements : Differentiation of SM/SUSY processes for all 3 colliders. More severe constraints on SUSY parameters ? Tevatron : small PDF uncertainties  certainly LHC, RHIC : large PDF uncertainties  more difficult Outlook : Better constraints on PDFs can help (HERA, RHIC,…) NLO calculations November 22, 2004