1. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 1 New particle searches with  at DELPHI Introduction  ID in searches Higgs search SUSY Excited leptons Technicolor F. Matorras IFCA, Santander, Spain DELPHI collaboration

2. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 2 A different point of view of tau physics widely used at LEP (as will be in LHC) –look for new particles that decay to tau(s) leptons rather than studying the tau decay In many models the most probable final state topologies include taus In other cases it is important for some region of the parameters Also used in other searches as complementary channel –when the new particle is expected to follow lepton universality or is accompanied by Z or W bosons –always significantly worst than  or ee channels! In general tau identification and reconstruction complicated –large variety of decays –hadronic decays –missing energy: lose mass information Good knowledge of  physics is important! –people in searches often ignores “basic” properties of the taus Introduction

3. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 3 Data sample DELPHI –multipurpose detector at LEP e  e  Collider at CERN –see more details in A.Andreazza and D.Dedovich talks First phase (LEP I) ‘89 to ‘95 –E cm ~Mz –>150 pb -1 –Mainly designed for Z physics –also for new particle searches –data was reanalyzed recently in view of new models From ‘95 until 2000 (LEP II) –gradual increase of energy up to 208 GeV –~ 700pb -1 above WW threshold –most searches rely on this data, especially the highest energy in 2000

4. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 4 Tau ID @ LEP2 Not too different from ID @LEP1 –see A.Andreazza and D.Dedovich talks –higher energy →higher particle multiplicity in the event→separation more complicated A  is typically seen as an isolated lepton or low multiplicity and narrow jet associated with missing energy –if lepton, its energy significantly smaller than that expected from a prompt lepton usually for any background channel with , there is the equivalent with e or  –but the lepton energy of prompt leptons is three times larger on average high boost → very narrow jet w.r.t. quark jets –often just one-prong events are used to, reduce background from gluon/hadron jets Different jet algorithms depending on the topology: Luclus, Durham, pure “geometrical”, mass clustering... –often refinements done to remove spurious tracks attached to the tau from quark jets based on energy, angle with the jet and mass of the jet

5. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 5 Tau event selection @ LEP2 Large variety of selection procedures and background processes depending on the topology, mass of the particle... Major background in most cases –qq(  g  for events containing jets very high cross section lost photons at low angle produce missing energy gluon jets or tracks unattached mimic a  basic to have a good  ID and good jet definition –radiative l  l  as above, a  looks like a acoplanarity, angle of missing momentum –two-photon events (e  e  ff) huge cross section missing energy in electrons/positrons at low angle transverse energy and transverse momentum Often WW or ZZ decays remain as almost irreducible background –mass information –specific variables in each case

6. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 6 Charged Higgs Eur. Phys. J. C34 (2004) Many extensions of SM predict the existence of the Charged Higgs –studied here in the framework of general 2 Higgs Doublet Models (2HDM) –produced in pairs H  H  at LEP energies –cross section only dependent on the E cm and mass Type II models –decay to heaviest fermions available cs or  BR free, but prejudice in favor of high  BR look for cscs, cs  and 

7. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 7 Charged Higgs (type II) Topology of these events: –in  : two acollinear , with additional missing energy –in cs  : two hadronic jets, with cs content and one  Remaining irreducible background, WW equivalent decays Mass of the parent boson –for purely leptonic decays at least 4 undetected, mass cannot be reconstructed some sensitivity remains in acoplanarity and P T –for semileptonic decays mass can be obtained from kinematical fits

8. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 8 Kinematical fits Widely used in channels with taus and/or neutrinos (also in others) Basic ideas and approximations: –treat primary neutrino momentum as unknown –treat E   as  unknown and tau direction as that of the resultant of the decay products (good approximation if boost is high) –use energy and momentum conservation –fit mass and all measured quantities (4C-fit) precise estimation of  Energy sometimes it becomes just a system –if applicable use additional constrain in mass (5C-fit) two particles of equal masses one of the jets with Z mass in other channels cs 

9. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 9 Charged Higgs (type II) Additional differences come from the spin of the parent boson: –differential polar angle cross-section –polarization of the produced  given the fixed helicity  from scalar H bosons have P   1  from vector W bosons have P   1  physics relevant for the search! simple  decay ID –e  n , others use “optimal polarization estimators” used to measure P   at LEP I build a likelihood function with that variables –firstly proposed by DELPHI

10. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 10 H  H  /W  W  separation in  These four variables are combined into a single likelihood function with significant WW discrimination

11. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 11 Charged Higgs (type I) Within type I models H  can also decay to W * A, if the pseudoscalar A is light –WAWA, WA , WAcs channels can be accessible –A decays to bb if kinematically allowed WA  topology similar to cs , but jets with bb content –Neural Nets used to optimize the separation tau ID vars b tagging vars kinematical vars –WW largely suppressed 5C-fit mass NN

12. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 12 Limits No excess from SM expectation was found, limits set on M H at 75-90 GeV depending on the model parameters (95% CL) limit for pure decay to 

13. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 13 Doubly Charged Higgs Phys. Lett. B522 (2003) Predicted in extensions of SM –left-right symmetric models –could be relatively light –produced in pairs H  H  at LEP –decay to pairs of leptons with the same charge not necessarily of the same flavor coupling H   the less bounded by indirect measurement 4  topologies searched for –no prompt –almost no background (only ZZ  4 , with good  ID) –despite having ≥4, mass reconstructed with high precision with 4C-fit –excluded below 99.1 GeV at 95% CL one candidate left with  mass compatible with the hypothesis of two equal mass charge 2 objects also compatible with ZZ with usual pairing!

14. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 14 Doubly Charged Higgs limits DELPHI extended the search to the case of couplings so small that the Higgs flies –taus produced far from the IP but inside the tracking system seen as “kinks” (described later in SUSY) –charged higgs reaching the calorimeter anomalous dE/dx Excluded for masses below 97.3 GeV for any assumption on the model h  >10  h  <10 

15. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 15 Neutral Higgs Eur. Phys. J. C32 (2004)/ Phys.Lett.B499(2001) SM/MSSM neutral Higgs –H decay to  is second highest BR at LEP mass range,  1/10 of BR(bb) –qq  in HZ (SM and MSSM) as a complementary channel –more important in MSSM, hA production (  1/5 or more) with at least 1  Good mass reconstruction with 4C/5C fit Final discrimination with a likelihood function No signal-like candidates at the highest energy  ID refined with likelihood Event likelihood radiative evt rejection

16. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 16 Neutral Higgs Eur. Phys. J. C32 (2004)/ Phys.Lett.B499(2001) SM/MSSM neutral Higgs –H decay to  is second highest BR at LEP mass range,  1/10 of BR(bb) –qq  in HZ (SM and MSSM) as a complementary channel –more important in MSSM, hA production (  1/5 or more) with at least 1  Good mass reconstruction with 4C/5C fit Final discrimination with a likelihood function No signal-like candidates at the highest energy

17. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 17 Neutral Higgs in extended models CERN-PH-EP 2003-061 (acc. by Eur. Phys. J. C) Decays with , even more interesting in the framework of general 2HDM –BR to  or bb is a free parameter –search for hA and hZ Search for 4  –identical to H  H  for high mass, except mass pairing (neutral bosons) –if one of the bosons is light, its boost is large and both  seen as a single jet, look for 3 jet topology –if both are light, 2 jets Reanalysis of LEP1 data to look for Yukawa production –“radiation” of a higgs from a ff final state –bb , 4  look for low mass radiated  or bb pair Limits set on a scale factor on the SM cross section

18. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 18 SUSY Eur. Phys. J. C31 (2003) Assume here MSSM with R-parity conservation –LSP (lightest supersymmetric particle) is stable –s-particles are produced in pairs –many scenarios depending on the model parameters In some scenarios, the stau is the lightest charged SUSY particle and the lightest neutralino is the LSP Other scenarios predict production of neutralino pairs, with cascade decays to several (≥2)  and a pair of LSP neutralino multilepton search  e 

19. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 19 Stau search Final state topology is two  and two neutralinos –neutralinos escape undetected –if neutralinos significantly lighter than staus (high  M ) the topology and analysis is identical to H  H  –Otherwise similar, but taking care of a slower  (smaller energy and smaller boost) Light stau at LEP1, data reanalyzed to exclude stau with suppressed couplings to Z No evidence of sparticles found Any mixing and any  M, 26.3 GeV<M<81.9 GeV excluded M>81.9 if  M>15 or MLSP<68

20. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 20 Extensions of MSSM Light gravitino Eur. Phys. J. C27 (2003) –gravitino is LSP –decays are not immediate and particles might fly –look for taus not produced in the IP R p is violated Eur. Phys. J. C32 (2004) –LSP can decay to fermions –many s-particle cascade decays include tau Stop, Sneutrino, Sleptons, gauginos... Anomaly Mediated SUSY Breaking Eur. Phys. J. C34 (2004) –results interpreted also in AMSB No excess found in any channel hadronic interaction fakes a decay at 20 cm

21. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 21 Excited leptons (Preliminary) Excited leptons expected in models with fermion substructure Produced in pairs (l * l * ) Or accompanied by a normal lepton (l * l) Expected decays: – l * →l  or lZ or W, (charged excited leptons) – * →  or lW or Z, (neutral excited leptons) –  present in many channels for    and   Cleaner signature in  channels –preselection based on  and  ID + kinematic cuts

22. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 22 Excited leptons In  * channels mass reconstructed with kinematical fits No evidence observed –m  * >102.7/101.0 GeV –m v* >94.2/101.9 GeV  *  * →  *→W*→W  *  → 

23. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 23 Limits on excited leptons Cross section and couplings limits

24. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 24 Technicolor models Eur. Phys. J. C22 (2001) DELPHI has studied the possibility to search for technimesons,  T,  T technirho decay to technipions or W technipions decay to bc or  search identical to H  H  in type I models –in fact search developed for this channel limits set over a wide range of parameter space

25. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 25 Conclusions DELPHI has searched a large variety of new physics/particles, whose decays included  leptons –charged and neutral Higgs –sleptons –excited leptons several new ideas proposed by DELPHI and adopted by other experiments extended the range of the search –many ideas taken from standard  physics contributed to this improvements Most results are final or hopefully become final in short term Unfortunately, no signal of new physics was found –limits set on many models for a large range of parameters model for most of the kinematically allowed mass range

26. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 26 charged higgs cross section limits

27. F.Matorras, IFCA, Spain New particles searches with  at DELPHI Nara, 17/09/2004 27 More limits on charged higgs