Polarization effects in slepton production at hadron colliders

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 --gt one SUSY particle for each SM
  particle
• Renormalizability
• B, L (--gt 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
• gt 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 --gt 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 gt 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)
• --gt 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 gt 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)
• --gt Discrimination SUSY/SM

5-6
13
Spin Asymmetry, LHC

• SUSY scenario based on SPS 4(at LHC we can reach
  heavy masses --gt SPS4)
• Parameters
• M1/2 400 GeV (higher masses)
• M0 300 GeV (higher masses)
• A0 varying (default 0)
• tan ? 50 (large splitting)
• µ gt 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)
• --gt 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 --gt reliable
• LHC, RHIC large PDF uncertainties --gt more
  difficult
• Outlook
• Better constraints on PDFs (from HERA, RHIC,)
  are welcome!
• Higher order calculations