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/

2. 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

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)

9. Spin Asymmetry, RHIC
RHIC : = 500 GeV (SUSY scenario with light , maybe visible)
GMSB scenario based on SPS ( 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 --> 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%

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 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 = – … – (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