1. Jose E. Garcia presented by: Jose E. Garcia (IFIC-Valencia) on behalf of ATLAS Collaboration XXXIXth Rencontres de Moriond

2. Particle Spectrum Little Higgs searches at LHC 2  0,  +,  ++ W H, Z H T AHAH 1 TeV Z,W h  t M scalar sector gauge sector top sector v’   ’ 1 / 2 new couplings (+ scale f) J. E. Garcia Rencontres de Moriond – March 04 Littlest Higgs model SU(5)  SO(5) Gauge sector  [SU 2  U 1 ] 2 SM Higgs Arkani-Hamed et al., JHEP 207 (2002) 34 Phenomenology Han et al., Phys. Rev. D67 (2003) 95004 Burdman et al., hep-ph/0212228

3. qq annihilation   ( cot) 2 Wide range in cot  possible. e + e - & V h Z H  e + e - & W H  V H  V h (V is Z or W) Strategies at LHC 3 q’ q1q1 W+W+ q2q2 W+W+ 1 2  ++ VBF mechanism   ( v’) 2 v’ should be small W + W +  ++  W + W + q W b T q’ T Wb fusion   ( 1 ) 2 1 / 2  1 suppressed by b- quark PDF. bW, t Z, t h T  bW, t Z, t h q q’ VHVH VHVH Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

4. heavy top T 4 q W b T q’  (T) (fb) T T 1 / 2 = 1 Production mechanism = Wb fusion bW50 % T bW 50 % tZ25 % T tZ 25 % th25 % T th25 % BR 1, 2 Yukawa couplings of T and t  1 M 16   2 % 1 2   ( ) 2 Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

5. T  Wb 5 Cuts: - p T (jet) > 200 GeV - p T (lepton) > 100 GeV - E T > 100 GeV 1 b-tag required T  W b  b-jet + lepton + E T Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04 Backgrounds: tt, t, Wbb L = 3·10 5 pb -1 1 / 2 =1 Signal with 5  for M T < 2000 GeV

6. clear peak but poor statistics 6 T  Zt and T  ht h bb T t 1 TeV W b t T Z b + - W Signature: 3 leptons + 1 b-jet + E Tmiss Signature: 3 b-jets + 1 lepton + E Tmiss BKG tb Z, t Z, W Z tt, Wbb Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04 Not distinguishable peak BKG

7. T  Zt signal 7 Cuts: - 3 isolated leptons (2 of them with M  = M Z ) - 1 b –jet - E T > 100 GeV M T = 1 TeV L = 3·10 5 pb -1 1 / 2 =1 T  tZ  3 leptons + b-jet + E T +- Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04 Signal with 5  for M T < 1050 GeV

8. T  ht signal 8 Cuts: - p T (3-jets) > 130 GeV - p T (lepton) > 100 GeV - 110 < M h < 130 GeV At least 1 b-tag M( T ) (GeV) T  h t  3 b-jets + lepton + E T M T = 1.0 Bkg Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04 L = 3·10 5 pb -1 1 / 2 =1 M T = 1 TeV

9. Gauge Boson Z H 9 Once a mass is given, the only free parameter in the model is, .  (Z H ) (fb)   (cot  ) 2 cot  = 1 q q ZHZH  ( ) ~ (cot  ) 2  ( Zh ) ~ (cot 2  ) 2 Zh e + e - +  +  - +  +  - 12% BR cot  Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

10. Search for Z H 10 e + e - qq Z H e + e - slight improvement is reached using also  +  - M(Z H ) = 2 TeV L = 3·10 5 pb -1 Selection cuts: 2 isolated electrons with 2 isolated electrons with p T > 20 GeV and |  | 20 GeV and |  | < 2.5 minimum invariant mass minimum invariant mass equal to 800 GeV equal to 800 GeV Background: Drell-Yan ( e + e - ) Drell-Yan (qq  Z/  e + e - ) M( e + e - ) (GeV) N( e + e - ) bkg subtracted cot  = 1.0 S  5000 B  20 cot  = 0.2 S  100 B  8 Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

11. Discovery region for Z H 11 L = 3·10 5 pb -1 S  B > 5 24 6 cot  (Z H ) decreases as M increases (Z H ) decreases as M increases (Z H )  (cot ) 2 (Z H )  (cot ) 2 BR( e + e - ) drops for cot  0 BR(Z H e + e - ) drops for cot   0 If Z H is found, cot  can be If Z H is found, cot  can be extracted from (Z H ) and (Z H ) extracted from (Z H ) and (Z H )M = [ 3.4(cot ) 2 +0.071 (cot 2) 2 ] % = [ 3.4 (cot ) 2 +0.071 (cot 2) 2 ] % M Z (TeV) H Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

12. Z H  Zh 12 q q cot  cot 2    (cot  cot 2  ) 2  (cot  )  (cot  = 0.5) m h = 120 GeV BR(h bb) = 66 % BR(h) = 0.2 % ZHZH hZ Ratio 0.5 Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04 m h = 200 GeV BR(h W + W - ) = 74 % BR(hZZ) = 26 %

13. Z H  Zh with h  bb 13 h ZHZH Z + - b b 2 TeV h bb ZHZH Z + - 1 TeV Cuts Background: Z + jets Cuts |  | < 2.5 (jets and leptons) P T (Z) > 250 GeV P T (h) > 250 GeV b-tagging |  | < 2.5 (jets and leptons) P T (Z) > 500 GeV P T (h) > 500 GeV b-tagging Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

14. Z H  Zh signal 14 b-tag:  b = 40%, R u = 100 Inside mass window: S = 15 S B = 8  B = 5 b-tag:  b = 50%, R u = 100 Inside mass window: S = 195 S B = 16  B = 50 M(Z H ) (GeV) M Z = 1 TeV H M(Z H ) (GeV) M Z = 2 TeV H L = 3·10 5 pb -1 cot  = 0.5 L = 3·10 5 pb -1 cot  = 0.5 Events Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

15. W H / Z H  W/Z h with h   15 h W H + Z H W+Z Cuts |  (  ) | < 2.5 P T (  ) > 25 GeV P T (h) > 400 GeV  -tagging,  (  ) = 80%   S(W H  Wh) = 64 S(Z H  Zh) = 33 B(h inclusive) = 8 B(  inclusive) = 5 97 13 S  B = 27 1 TeV WHWH ZHZH Bkg M Z = M W = 1 TeV H H L = 3·10 5 pb -1 cot  = 0.5 Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04 j j

16. Discovery region for V H 16 L = 3·10 5 pb -1 S/  B > 5 N > 10 M(V H ) (TeV) Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04 h(120)   h(120)  bb Z H  Zh  + - bb W H  Wh   bb Z H  Zh  jets  W H  Wh  jets  Z H  +  - W H   W H   V H to leptons

17. q’ New Higgs  ++ 17 Production: VBF mechanism (vector boson fusion) W + W +  ++  W + W + Decay: Events L = 3·10 5 pb -1 M(  ) = 1.5 TeV M(  ) = 2 TeV W + W +   ++  W + W + q1q1 W+W+ q2q2 q’ W+W+ 1 2  ++ v’ = 25 GeV   (v’) 2 SM Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04 Decay of  ++ to leptons is suppressed in this model

18.  ++  W + W + 18  ++  W + W +  + + Bkg: WWqq, WZ WZqq, W tt 2 forward jets (E > 100 GeV) 2 leptons (charge +) P T (lepton 1) > 150 GeV P T (lepton 2) > 20 GeV E T > 50 GeV m T > 500 GeV Main cuts: m T (  ) (GeV) Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04 L = 3·10 5 pb -1 m T = (E( 1 ) + E( 2 ) + | p T | ) 2 + (p( 1 ) + p( 2 ) + p T ) 2

19. Outlook and Summary 19 Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04 Searches for the new particles predicted by Littlest Higgs model at LHC have been performed. Heavy Top and new Gauge boson sector are observable over a large range of parameter. “Toy” model used for the study severely constrained by electro-weak measurements Little Higgs idea is realized in several different models: SU(5)/SO(5),SU(6)/SP(6), Minimal moose SU(3) 2 /SU(3) and general mooses SU(3) n /SU(3) k, etc. They have similar particle content and are less constrained. More detailed information on the ATLAS searches can be found in More detailed information on the ATLAS searches can be found in G. Azuelos et al., hep-ph/0402037

20. Jose E. Garcia presented by: Jose E. Garcia (IFIC-Valencia) on behalf of ATLAS Collaboration XXXIXth Rencontres de Moriond

21. The Littlest Higgs model 21 SU(5) dim 24 S0(5) dim 10 contains [SU(2)U(1)] 2 SU(2)U(1) Standard model U(1) QED 24 - 10 = 14 massless Goldstone bosons 4 GB used to give mass to Z H, W H, A H 4 GB used to give mass to Z,W, and h 10 GB6 GB  0,  +,  ++ broken at scale   1 TeV broken at scale  244 GeV broken at scale   1 TeV mass through radiative corrections   Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

22. Motivation : Quadratic divergences : Higgs fields : electroweak Planck hierarchy and fine-tuning problems bosons fermions gauge bosons new quarks new gauge bosons quarks cancellations SUSY : Little Higgs : electroweak Planck Goldstone bosons pseudo-Goldstone bosons symmetry breaking "light" mass massless The Littlest Higgs model 22 Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

23. Corrections 23 t t t (4m t – 2M w – 4M z – m h ) 2 2 2 2 2  m h = 8  8  2 2 2 3  Minimum needed to cancel all loops T heavy top new EW singlet W H, Z H heavy gauge bosons new SU(2)  U(1) symmetry  heavy higgs bosons many new Goldstone bosons EW triplet (  0,  +,  ++ ) Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

24. Mass Range Upper limits: to avoid fine tuning scale f < 1 TeV· 24 T M < 2 TeV· m h = 120 GeV M < 0.2 TeV m h = 200 GeV M < 2 TeV W H, Z H, A H M < 6 TeV· m h = 120 GeV M < 2.2 TeV m h = 200 GeV M < 6 TeV  M < 10 TeV ± Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

25. Top quark sector 25 Little Higgs t and  will mix  standard top t, heavy top T v = electroweak scale = 244 GeV  = heavy scale  1 TeV 1, 2 = Yukawa couplings O(1)  2 new free parameters, , 1 2 can be eliminated using SM top mass  > 1 TeV (EW data!) but if M T is too large  fine tuning  = 1 TeV Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

26. Littlest Higgs: particle content and couplings 26 new particlescouplingsmass New constants:scale  and 1, ,  ’, ’ - No relations between these new constants - A H couplings not fixed by the model - EW data  ƒ  fine tuning 2 TeV < ƒ < 4 TeV weakness of the model Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

27. Expectations for Z H 27 M(Z H )  m W (f/v) [cot  + 1/cot  ] f = scale for new physics v = Fermi scale (244 GeV) Avoid fine tuning  M < 2.2 TeV (assuming m h = 120 GeV) M expected in 1-2 TeV region with wide range of cot  parameter. Agree with EW data  f > 2 TeV Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

28. b-tagging 28 = 220 GeV = 800 GeV 115 0.5 M Z = 1 TeV H M Z = 2 TeV H ~ 100 0.4 Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

29. W H W h with h bb h bb WHWH W 1 TeV Cuts Background: W + jet, tt |  | < 2.5 (jets and leptons) assume colinear to l for W H reconstruction P T (Z) > 250 GeV P T (h) > 250 GeV b-tagging 120 GeV b-tag:  b = 50%, R u = 100 Inside mass window: S = 1499 S B = 471  B = 69 l ± ± ± ± ± M W = 1 TeV H 29 Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

30. Deductions for A H  W H /Z H not background for A H M(A H ) (GeV).BR(A H Z h) min. .BR(A H  Z h) min. fb region excluded at 95 % CL if we see nothing deduced only from study deduced only from study Z H  Z h with h   can combine other studies can combine other studies theorical uncertainties (strong model-dependency) for A H theorical uncertainties (strong model-dependency) for A H can deduce limits on.BR(A H Z h) from results for Z H (same decays) can deduce limits on .BR(A H  Z h) from results for Z H (same decays) hypothesis : favorable cases where M(W H /Z H ) and M(A H ) are distant for each M(A H ) (resolution of M(W H /Z H ) being 45  80 GeV) hypothesis : favorable cases where M(W H /Z H ) and M(A H ) are distant for each M(A H ) (resolution of M(W H /Z H ) being 45  80 GeV) 30 Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04