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 : MSSM : 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

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)

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

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

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

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)

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

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

} Spin Asymmetry, RHIC --> Discrimination SUSY/SM 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 parameters ? Background : AL = – 0.1 … – 0.04 (after invariant mass cut at ≈ 52 GeV) --> Discrimination SUSY/SM } 30%

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

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%

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

} } Spin Asymmetry, LHC 20% --> Discrimination SUSY/SM 10% 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%

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