Supersymmetry or Alternatives?

Transcription

1 Collider Physics at the Terascale, May 2007 Supersymmetry or Alternatives? Michael Krämer (RWTH Aachen) Michael Krämer Page 1 PeterFest 2007

2 Collider Physics at the Terascale, May 2007 Alternatives? Michael Krämer (RWTH Aachen) Michael Krämer Page 2 PeterFest 2007

3 Alternatives? Michael Krämer Page 3 PeterFest 2007

4 Alternatives... Excited quarks and leptons Leptoquarks Michael Krämer Page 4 PeterFest 2007

5 Excited quarks and leptons Jugendsünde... Excited leptons?? Experimental Consequences of Quark - Structure G.B. West & P.M. Zerwas, Phys.Rev.D10:2130,1974. Excited Quarks And Leptons J.H. Kühn & P.M. Zerwas, Phys.Lett.B147:189,1984. Signals Of Excited Quarks And Leptons J.H. Kühn, H.D. Tholl & P.M. Zerwas, Phys.Lett.B158:270,1985. Excited Quark And Lepton Production At Hadron Colliders U. Baur, M. Spira, & P.M. Zerwas, Phys.Rev.D42: ,1990. Bounds on radii and magnetic dipole moments of quarks and leptons from LEP, SLC and HERA G. Köpp, D. Schaile, M. Spira & P.M. Zerwas, Z.Phys.C65: ,1995 Michael Krämer Page 5 PeterFest 2007

6 Excited quarks and leptons Proliferation of quarks and leptons substructure with compositness scale Λ 1 TeV? Consider simple model where excited fermion has spin and isospin equal to 1/2 Couplings to gauge bosons and fermions [ ] L = 1 2Λ f Rσ µν λ a g s f s 2 Ga µ + gf τ 2 W µ + g f Y 2 B µ f L + h.c. and contact interactions for ŝ Λ L = g2 Λ jµ j µ with j µ = η L fl γ µ f L + η L f Lγ µ f L + η L f Lγ µ f L + h.c. + (L R) Michael Krämer Page 6 PeterFest 2007

7 Excited quarks Focus on hadron collider phenomenology with production processes Promising channel is production via qg fusion in s-channel: qg q and decay via gauge interactions: q qg, qγ, qz, q W Michael Krämer Page 7 PeterFest 2007

8 Excited quarks: Experimental search CDF analysis (Phys.Rev.Lett.72: ,1994) Exclusion 80 GeV m 540 GeV Michael Krämer Page 8 PeterFest 2007

9 Excited leptons Production via contact interactions: q q l l, l l, l l and decay via gauge interactions l lγ, lz, νw Michael Krämer Page 9 PeterFest 2007

10 Excited leptons: Experimental search recent D0 analysis: p p ee eeγ (5349-CONF) Michael Krämer Page 10 PeterFest 2007

11 Excited leptons: Experimental search recent D0 analysis: p p ee eeγ (5349-CONF) BF (qq e*e) [pb] σ σ CI (Λ = m e* ) (GM decay only) D Run II Preliminary 1.0 fb (Λ = m e* ) σ CI σ CI σ CI σ CI σ CI σ CI (Λ = 1 TeV) (Λ = 2 TeV) (Λ = 3 TeV) (Λ = 4 TeV) (Λ = 5 TeV) theor. uncert. obs. limit (95% CL) exp. limit (95% CL) [GeV] m e* Michael Krämer Page 11 PeterFest 2007

12 Excited leptons: Experimental search recent D0 analysis: p p ee eeγ (5349-CONF) Λ [TeV] 6-1 D Run II Preliminary 1.0 fb excluded 95% CL [GeV] m e* Michael Krämer Page 12 PeterFest 2007

13 Excited leptons: Prospects at the LHC eg. pp ee eez (ATLAS ) LHC reach: M < 4 TeV for Λ = 6 TeV Michael Krämer Page 13 PeterFest 2007

14 Leptoquarks Atom smasher hurls particle theory into chaos! (Daily Telegraph 20 February 1997) The accepted perception of the universe was called into question again yesterday by results from an international atom smasher experiment. Remember? I believed it too! Michael Krämer Page 14 PeterFest 2007

15 Leptoquarks: HERA excess of high Q 2 events Leptoquark search at HERA e + µ +, τ + LQ λ ei λ lj q i q j p X p HERA excess of events at Q 2 > GeV 2 (1997) y e H1 Q 2 =15000GeV 2 Q 2 =10000GeV 2 Q 2 =2500GeV M e (GeV) H1 observed 12 events (SM expectation 4.71 ± 0.76) ZEUS observed 12 events (SM expectation 8.66 ± 0.66) Michael Krämer Page 15 PeterFest 2007

16 Leptoquarks Leptoquarks and diquarks in e+ e- collisions up to 2-TeV. D. Schaile & P.M. Zerwas, La Thuile Workshop 1987 Virtual Leptoquark Effects On The Drell-Yan Process R. Rückl & P.M. Zerwas, La Thuile Workshop 1987 (e b), (e t) type leptoquarks C. Berger, J. Tutas, M. Spira & P.M. Zerwas, DESY HERA Workshop 1987 Single leptoquark production at hadron colliders J. Ohnemus, S. Rudaz, T.F. Walsh & P.M. Zerwas, Phys.Lett.B334: ,1994 Leptoquark / squark interpretation of HERA events: Virtual effects in e+ e- annihilation to hadrons J. Kalinowski, R. Rückl, H. Spiesberger & P.M. Zerwas, Z.Phys.C74: ,1997 Formation and decay of scalar leptoquarks / squarks in e p collisions T. Plehn, H. Spiesberger, M. Spira, & P.M. Zerwas, Z.Phys.C74: ,1997 Pair production of scalar leptoquarks at the Tevatron M. Krämer, T. Plehn, M. Spira & P.M. Zerwas, Phys.Rev.Lett.79: ,1997 Pair production of scalar leptoquarks at the LHC M. Krämer, T. Plehn, M. Spira & P.M. Zerwas, Phys.Rev.D71:057503,2005 Michael Krämer Page 16 PeterFest 2007

17 Leptoquarks: Hadroproduction potentially large hadron collider cross section: cross section prediction depends only on m LQ : ˆσ LO [ q q LQ + LQ ] = α2 s π ŝ ˆσ LO [ gg LQ + LQ ] = α2 s π 96ŝ 2 27 β3 [ β ( 41 31β 2) + ( 18β 2 β 4 17 ) log 1 + β 1 β ] where β = 1 4m LQ /ŝ Cross section coincides with squark-pair production for m g σ(p p t t) m g 4- q-coupling 0 σ(p p LQ LQ) Michael Krämer Page 17 PeterFest 2007

18 Leptoquarks: Hadroproduction at NLO Reduction of scale uncertainty at NLO LO NLO σ tot [pb]: pp LQ+LQ+X s=1.8 TeV M LQ =200 GeV 1 µ/m 10 LQ Michael Krämer Page 18 PeterFest 2007

19 Leptoquarks: Hadroproduction at NLO Improved mass bounds at NLO 1 σ tot [pb]: pp LQ+LQ+X s=1.8 TeV 10-1 NLO LO : : µ=m LQ µ=[m LQ /2, 2M LQ ] µ=m LQ {α s,q/g: LO} LO : µ= ŝ {α s,q/g: NLO} M LQ [GeV] Michael Krämer Page 19 PeterFest 2007

20 Leptoquarks: Experimental searches Improved mass bounds at NLO First Generation Scalar LQ Search 2 σ(pb) Q=2*M LQ LO 95% cross section limit syst. uncert.=15% β = 1 Theor. σ LQ (NLO - CTEQ4M) Kraemer et al., CERN-TH/97-67 Q=M LQ / M LQ (GeV/c 2 ) Michael Krämer Page 20 PeterFest 2007

21 Leptoquarks: Experimental searches Current status (D0 Fermilab-Pub E) BR(LQ eq) DØ -1 Run II: ~250pb -1 Run I: ~120pb eνjj eejj Run II Combined Limit Runs I & II Combined Scalar Leptoquark Mass (GeV/c Limit ) Michael Krämer Page 21 PeterFest 2007

22 Leptoquarks: Prospects for the LHC [Abdullin, Charles] LHC reach: m LQ < 1.5 TeV for β = 1 Michael Krämer Page 22 PeterFest 2007

23 In Summa Democrit was right! Michael Krämer Page 23 PeterFest 2007