Search for Exotica Search for Exotica (Preliminary Exotica results - PowerPoint PPT Presentation

Search for Exotica Search for Exotica (Preliminary Exotica results Exotica results up to up to √ √ s=209 s=209 GeV GeV from the from the LEP LEP (Preliminary experiments) experiments ) Javier Cuevas Javier Cuevas University of Oviedo University of Oviedo Topical Seminar on the Legacy of LEP and SLC Topical Seminar on the Legacy of LEP and SLC Siena, 8- -11 October 2001 11 October 2001 Siena, 8

Outline Outline � LEP LEP EXOTICA WG EXOTICA WG : Combination of all non : Combination of all non- -Higgs Higgs � and non- -SUSY searches at LEP2. SUSY searches at LEP2. and non � Technicolor Technicolor � � Excited leptons Excited leptons � � Single top production, FCNC Single top production, FCNC � � Leptoquarks Leptoquarks � � Gravity in extra dimensions Gravity in extra dimensions � � Data Samples used: Data Samples used: � 1 (~600 pb 1 per experiment) at – About 2.4 fb About 2.4 fb - (~600 pb - per experiment) at √ s √ s -1 -1 – =189- -209 209 GeV GeV =189 � Statistical procedure adopted for the combination of Statistical procedure adopted for the combination of � the different channels (same or different the different channels (same or different experiments), is the likelihood ratio method likelihood ratio method experiments), is the 2 Legacy of LEP/SLC J. Cuevas

Technicolor model Technicolor model � Technicolor Model Technicolor Model is an alternative to the Standard is an alternative to the Standard � Model Mechanism of Electroweak symmetry breaking. Model Mechanism of Electroweak symmetry breaking. � Role of Higgs boson is performed by bound states of Role of Higgs boson is performed by bound states of � new fundamental fermions, techniquarks techniquarks, which mix , which mix new fundamental fermions, with W and Z and generate their masses. with W and Z and generate their masses. � Minimal TC Minimal TC model with one doublet of TC model with one doublet of TC- -quarks is quarks is not not � confirmed by LEP1 and elsewhere precision by LEP1 and elsewhere precision confirmed measurements measurements � Extensions of TC Extensions of TC model with many doublets, model with many doublets, Walking Walking � Technicolor , overcome disagreement with experimental , overcome disagreement with experimental Technicolor results. A large number of doublets large number of doublets is required, which is required, which results. A generate huge number of bound states huge number of bound states. . generate 3 Legacy of LEP/SLC J. Cuevas

Technicolor model Technicolor model � These extensions call for a These extensions call for a large number N large number N D of D of � technidoublets (T (T U , T D ), with Q U =Q D +1 technidoublets U , T D ), with Q U =Q D +1 � Important simplification Important simplification: : “ “ Technicolor Straw Man Technicolor Straw Man � Model ” ” the lowest lying bound states of the lightest the lowest lying bound states of the lightest Model technifermion model model can be considered in isolation can be considered in isolation. . technifermion – Pseudoscalars Pseudoscalars: : Π Π T , Π Π T – T±, ±,0 0 , T’ ’ – Vectors: Vectors: ρ ρ T , ω ω T (nearly mass degenerate) – ±,0 0 , T (nearly mass degenerate) T±, � Scalar bound states are mixtures of Scalar bound states are mixtures of W W L , Z L , and ± , Z 0 , and L± L0 � the lightest mass mass- -eigenstate eigenstate technipions technipions π π T π T ± π 0 the lightest T± T0 | Π Π Τ > = = sin sin χ χ |W |W L > + cos cos χ χ | | π π T > | Τ > L > + T > � Mixing angle Mixing angle χ χ is related with the number of TC is related with the number of TC- - � χ =1/N doublets: sin sin 2 =1/N D doublets: 2 χ D 4 Legacy of LEP/SLC J. Cuevas

Decays of ρ ρ T Decays of T ρ T � The dominant decay modes of the The dominant decay modes of the ρ mediated by the TC T mediated by the TC � interaction are: interaction are: ρ → Π Π → π π χ 4 ( ~ c o s ) T T T T T → π χ χ 2 2 W ( ~ s in c o s ) L T → χ 4 W W ( ~ s in ) L L � In addition the In addition the ρ ρ T decays via the electroweak interaction via the electroweak interaction T decays � either into one one technipion technipion and a SM gauge boson and a SM gauge boson or into a or into a either into pair of SM fermions ( (becomes important if other decay becomes important if other decay pair of SM fermions channels are kinematically kinematically closed closed) ) channels are � Total width Total width depends on many parameters but does not depends on many parameters but does not � exceed ~15 ~15 GeV GeV for for m m ρ ≤ 200 200 GeV GeV . . exceed T ≤ ρ T 5 Legacy of LEP/SLC J. Cuevas

Decays of π π T Decays of T � The The technipions technipions π π T π T decays, are induced mainly by ± π 0 decays, are induced mainly by T± T0 � ETC interactions which couples them to fermions ETC interactions which couples them to fermions − − π → Γ π → ∝ + 2 f f ; ( f f ) ( m m ) T i i T i i f ' f � The The π π T preferentially decay into the heaviest heaviest fermion fermion T preferentially decay into the � pairs allowed , main modes being: , main modes being: pairs allowed − → π ≈ ≈ τ ≈ bc ( 90% ), sc ( 5% ), v ( 5% ) τ T π → ≈ ≈ ττ ≈ 0 bb ( 90% ), cc ( 5% ), ( 5% ) T � Total width Total width < 1 < 1 GeV GeV for for M M π ~ 100 GeV GeV . . π ~ 100 � 6 Legacy of LEP/SLC J. Cuevas

Technicolor at LEP Technicolor at LEP � Although Although TC model TC model is rather complicated, the is rather complicated, the � phenomenology of the lightest bound states which it phenomenology of the lightest bound states which it predicts is relatively simple with few free with few free predicts is relatively simple parameters: parameters: � M M π π T mass of π π T T mass of � T � M M ρ ρ T mass of ρ ρ T T mass of � T χ =1/N � sin sin 2 2 χ =1/N D number of doublets , or D number of doublets , or � mixing angle of π π T and W L mixing angle of T and W L � For For ω ω T production and decay, a scale parameter and T production and decay, a scale parameter and � Q U +Q D must be specified. By analogy with QCD it is Q U +Q D must be specified. By analogy with QCD it is 0 ~ ρ T ω T π T π T supposed that M M ρ ~ M M ω , and M M π ~ M M π . supposed that T ~ T , and + . T0 T+ 7 Legacy of LEP/SLC J. Cuevas

Technicolor production at LEP Technicolor production at LEP 0 and can be produced at LEP in � ρ ρ T couples with γ γ and Z and Z 0 and can be produced at LEP in T couples with � s- -channel. channel. s � If If M M ρ ρ T < √ s, √ s, ρ ρ T can be produced in RR process produced in RR process and can and can T < T can be � be observed as a narrow resonance in s’ narrow resonance in s’ distribution. distribution. be observed as a � Technipions Technipions can be produced through virtual can be produced through virtual ρ ρ T � T exchange in pairs or in association with W L : exchange in pairs or in association with W L : + − → ρ → π π * e e T T T + − → ρ → π * e e W T T L � Production cross Production cross- -section of section of TC objects was expected to TC objects was expected to � be reasonably high reasonably high , which allowed search at LEP. , which allowed search at LEP. be 8 Legacy of LEP/SLC J. Cuevas

Expected cross- -section section Expected cross 10 Cross-section [ pb ] √ s = 200 GeV e + e - → ρ T γ M π =90 GeV GeV M T =90 π T N D =9 N D =9 1 - + π T M V =200 GeV GeV M V =200 * → π T (Q U +Q D )=4/3 γ (Q U +Q D )=4/3 0 T π e + e - → ρ T → -1 α ρ =2.91(3/N TC ) α ρ =2.91(3/N TC ) * T ω 10 , (TC coupling * (TC coupling T ρ → constant) constant) - e N TC =4 N TC =4 + e -2 10 150 200 250 300 M( ρ T ) [ GeV/c 2 ] 9 Legacy of LEP/SLC J. Cuevas

+ − → ρ → π π π * e e W , T T T T L � This process is searched for in This process is searched for in 4 jet 4 jet and in and in 2 jet+ 2 jet+ � lepton+neutrino final final states. states. lepton+neutrino � In both cases, a Neural Network is used which In both cases, a Neural Network is used which � combines topological variables topological variables and and b b- -tagging tagging combines π T most important background for π � The The most important background for search is T search is � e + e - → W W + W - . The main difference between W W + W - + e - → + W - . The main difference between + W - e - production is the presence of and π π + π - production is the presence of b b- -quark quark in the in the and + π π T decays of π . b b- -tagging is essential. tagging is essential. decays of T . � The mass is estimated after a The mass is estimated after a 5c 5c constrained fit constrained fit � imposing energy and momentum conservation and imposing energy and momentum conservation and equal masses of the two of the two fermion fermion objects ( objects (qq qq or or l l υ υ ). ). equal masses 10 Legacy of LEP/SLC J. Cuevas