Ricerche extra-SUSY a LHC

Ricerche extra-SUSY a LHC Incontri di Fisica delle Alte Energie (IFAE) Pavia, April 19th 2006 Lorenzo Menici Università “La Sapienza” di Roma Lorenzo Menici

Standard Model and beyond The Standard Model (SM) describes a all the accelerator based HEP data with great accuracy. On the other hand it is not fully theoretically satisfactory and there are hints for it to be the low energy limit of a more fundamental theory, e.g. • the hierarchy problem: no symmetry preventing the scalar masses (Higgs) from getting quadratic divergent radiative corrections at all perturbative orders • it does not include a quantum description of the gravity • it does not have a viable candidate for cold DM and cannot explain cosmological issues like baryon asymmetry and Lcosm • it does not take into account massive neutrinos • no exact unification of the gauge couplings through RG Lorenzo Menici

Outline The LHC will have an interesting potential already at the beginning: • √s: from 12 to 14 TeV before first shutdown • luminosity: from 1026 to 1033 in 1st phase. Then 1034 cm-2 s-1 • fraction of fb-1 collected in the first year even compared to the latest Tevatron • √s: 1.8 TeV • luminosity: latest peaks at 1.2·1032 Here we present the potential at start-upof ATLAS and CMS, the two multi-purpose detectors at LHC, concerning the possible detection of “non-SUSY” physics Beyond the Standard Model (BSM) together with the necessary integrated luminosity for the various channels. Lorenzo Menici

Outline Among the several on going analysis in the two collaborations, in this talk we chose to report on: • Extra gauge bosons (Z’, WR) and heavy Majorana neutrino N • Leptoquarks • Lepton Flavour Violation • Little Higgs • Split SUSY Other relevant signatures of non-SUSY physics BSM will have dedicated talks in this session • Long-lived Heavy Charged Particles (S. Viganò) • Extra Dimensions (F.L. Navarria) • New physics with Top events (M. Cobal) • New physics with Bottom events (S. Vecchi) Lorenzo Menici

E6 model LR model Z’ heavy neutral gauge bosons • Several models (GUT SO(10) and E6, SSM) predict an additional heavy neutral gauge boson, referred to as Z’. No prediction on mZ’ • Z & Z’: assuming they have the same coupling to fermions, they do not mix significantly (electroweak LEPI) • Most recent lower bounds from combined LEPII data, • mZ’ > 400-900 GeV/c2 , depending on the model • Tevatron RunII: expected to explore up to 800 GeV, depending on scenario Lorenzo Menici

Z’ψL=0.1 fb-1 Z’SMM L=10 fb-1 M(μ+ μ-) M(μ+ μ-) R. Cousins et al. CMS NOTE 2005/002 Z’ → μ+μ- • pp → Z’ → μ+μ- full simulation • Dominant irreducible background DY: pp →/Z0 → μ+μ- selection on single-μ OR double-μ L1 and HLT: μμ tracks originate from same vertex • Cuts to suppress reducible background could give small improvement (μ isolation, jet veto, μ’s be back to back) • No study of systematic errors yet, nor pile up discovery potential starting from 1 fb-1 • After discovery: how to determine the theoretical framework Z’ belongs to? Forward-backward asymmetry, study on going at CMS, done at ATLAS Lorenzo Menici

Z’: AFB model discrimination In all models, theZ’ production cross section as a function of cosθ* has the typical spin 1 behaviour. High mass dilepton events in pp collisions mainly from quark-antiquark annihilation. B. Trocme, ATL-PHYS-CONF-2005-014 • Incoming quark direction unknown, estimated with the reconstructed Z’ direction (see correlation) • The prob. ε of wrong quark direction (sea ) is energy dependent  AFB measured in bins of E around Z’ peak. • Wrong q direction cosθ*↔ -cosθ* spoils asymmetry, which can be corrected for a posteriori once is ε known reconstructed generated In each bin of cosθ*, from the observed AFB the corrected AFB is calculated using ε(cosθ*, E),100 fb-1 used. Results from achiavable with smaller statistics being investigated cosθ* (gen) cosθ* (reco) Lorenzo Menici

Left-Right symmetric model Left-Right (LR) symmetric models explains the origin of the parity violation in weak interactions (as a result of the spontaneously broken parity) and predicts the existence of additional gauge bosons WR and Z’. In addition, heavy right-handed Majorana neutrino states N arise naturally within LR symmetric model. The Ns could be partners of light neutrino states, related to their non-zero masses through the see-saw mechanism. These reasons make the LR symmetric model very attractive and the search of WR, Z’ and N an important challenge for LHC. Lorenzo Menici

Heavy Majorana neutrino search S. N. Gnimenko et al. CMS IN 2005/040 We can study two kind of processes with WR and Nl: • pp  WR  l + Nl + X • pp  Z’  Nl + Nl + X followed by the decay Nl l + j1 + j2 Lorenzo Menici

Heavy Majorana neutrino search Suppose a WR mass of 2000 GeV and a Ne mass of 500 GeV. We require events with two isolated electrons and at least two jets selected and, using the 4-momenta of jets and electrons, we calculate Mejj = MN and Meejj = MWR. Background from ZW, , Z+jets, ZH and WH production. 5σ discovery With 30 fb-1 Ne and WR can be discovered at CMS for masses up to 2.4 TeV and 4 TeV respectively. Lorenzo Menici

Leptoquarks Leptoquarks (LQs) are an interesting category of exotic colour triplets with couplings to quarks and leptons. • They are predicted by GUTs, composite models, technicolor schemes, E6 models, SUSY models with R-parity violation,… • Inter-generational mixing is not allowed • There exist 14 species of LQs, differing by spin (scalar/vector), fermion number F = 3B+L, isospin and chirality of the coupling • They have fractional electric charge (±5/3, ±4/3, ±2/3 and ±1/3) • Two possible decay modes: • The LQ branching fractions β≡ B(LQ  lq) depends on the model Consider now the pair production of scalar LQs, which proceeds through gg fusion and annihilation. Tevatron+LEP+HERA current limit on the mass of the first LQ generation: MLQ > 242 GeV. Lorenzo Menici

(LQ)(LQ)  lljj Benekos et al. com-phys-2004-071 Pair production of scalar LQs of the first two generations (i.e. only eejj and μμjj final states are considered here). Topology of the final state: two high-pT leptons and two high-ET jets. Bounds in LQ mass for the cases β=1 and β=0.5. The main background arise from QCD processes, eliminated requiring • isolation of high-pT leptons • same-flavour and opposite sign leptons with pT > 100 GeV and |η| < 2.5 • at least two jets with ET > 70 GeV, ΣETcalo > 570 GeVand ETmiss/ΣETcalo < 0.05 • selecting events with high lepton-jet reconstructed invariant mass mlj (LQ)(LQ)  eejj 30 fb-1 of int. lum. Selection with |mej-MLQ < 100 GeV| Lorenzo Menici

(LQ)(LQ) ννjj Benekos et al. com-phys-2004-071 Pair production of scalar LQs of the third generation (i.e. ντντjj final state), otherwise huge Z( νν)+jets irreducible background fot the first two generations. In contrast, for a third generation LQ  ντb, ATLAS b-tagging allows s/b separation. Topology of the final state: large ETmiss and two high-ET jets. Again β=1 and β=0.5 cases. Other background from W+jets (lνbb, τνbb), (lνblνb, τνbτνb), ZZ (ννbb), ZW (bblν, bbτν, ννjj) and WW (lνjj, τνjj), eliminated requiring (besides b-tagging) • lepton veto • azimuthal constraints on jets (because of back-to-back LQ production) • at least two jets from b-quarks with ET > 70 GeV and |η| < 5 • ETmiss > 400 GeVand mlj > 180 GeV (LQ)(LQ)  ννjj 30 fb-1 of int. lum. Lorenzo Menici

Lepton Flavour Violation Lepton Flavour Violation (LFV) is predicted by different models of physics BSM (GUT, Technicolor, String Theory with Esymmetry, leptoquarks, forth generation neutrino models, SUSY with broken R-parity, MSSM with non-universal parameters at the GUT scale…) and it could be important in order to give an explanation to the recent important indications of neutrino oscillations (mixing also in the lepton sector?). At the moment no evidence of LFV from the experimental search of the most important LFV processes (such as τμγ,τμμμ, Z  μτ,…). LHC is going to detect LFV processes or to further lower their possible BRs. Lorenzo Menici

τ μμμ M. Biasini et al. CMS NOTE 2002/0037 Main background (see CMS NOTE1997/096) from D & B mesons production Feynman diagrams giving τ μμμ in mSUGRA Lorenzo Menici

Little Higgs Little Higgs (LH) is possible way of solving the hierarchy problem: the Higgs boson is a pseudo-Goldstone boson arising from some global symmetry breaking at the TeV scale (usually exploiting non-linear sigma models). Several implementation of LH model exist (different symmetry groups broken) and they all have in common a set of new particles. For the “Littlest Higgs” case: • One heavy top particle T with charge 2/3 • Three scalars Φ++, Φ+ and Φ0 • Four gauge bosons WH±, ZHand AH T produced at LHC via bq  Tq’ small cross section because of the low b-quark content in a proton. The scalar sector is not so favorable because of the SM background, expecially for the Φ++ case. Extra gauge bosons are the most promising channels for a first evidence of LH at work in nature. Lorenzo Menici

ZH e+e- AH and ZH could be revealed searching for a peak in the invariant mass distribution of e+e- and μ+μ-. Consider now ZH: its cross section is proportional to (cotθ)2, the mixing angle θ being the only free parameter of the theory once the ZHmass is fixed. Here an example of ZH e+e-search (with SM Drell-Yan background) G. Azuelos et al. Eur.Phys.J.C39S2 ZH  e+e- 100 fb-1 300 fb-1 Lorenzo Menici

WH eν Also WH production cross section depends oncotθ. WH lνis the decay to detect (isolated charged lepton + missing ET). Consider the WH eνcase: event selected requiring an isolated electron with pT > 200 GeV, |η| <2.5and ETmiss > 400 GeV. The main background arises from eνproduction via a virtual W. G. Azuelos et al. Eur.Phys.J.C39S2 WH  eν 100 fb-1 300 fb-1 Lorenzo Menici

Split SUSY Observation: if we (at the moment) are forced to accept the fine-tuning of the vacuum energy without explanation, the fine-tuning of the electroweak scale is much less problematic! Moreover, also in SUSY theories some fine-tunings at work (absence of large FCNC effects due to sfermions non-observation of light Higgs or charginos at LEP). Split SUSY (SpS) solves these SUSY problems giving up electroweak naturalness and featuring • heavysfermions • a light Higgs boson (mH < 200 GeV) • long-lived gluino • four neutralinos and two charginos At the LHC, the experimental challenge would be the observation of R-hadrons (meta-stable color-singlet bound states of the long-lived gluino with quarks or gluons), in addition to the search of direct production on charginos and neutralinos (identifying their gaugino/Higgsino components and their Higgs Yukawa couplings) Lorenzo Menici

R-hadrons detection R-hadrons can be considered stable from a detector point of view. Particularly interesting the case of charged R-hadrons that behave like slow muon-like particles and could be detected using Time Of Flight (TOF) methods (see Viganò’s talk). The ATLAS detector would allow the discovery of R-hadrons with a mass reach of at least 1300 GeV with few fb-1. For higher masses we have to face both low production cross section and trigger problems. A. C. Kraan et al. hep-ex/0511014 Triggered R-hadrons and Background fot 1 fb-1 Ratio S/√B for different R-hadron masses for 1 fb-1 Lorenzo Menici

Conclusions • The subject of this talk is an overview of some of the most interesting channels on non-SUSY physics BSM at LHC • Many of these signatures (if exist) could be revealed with 10-30 fb-1 at ATLAS and/or CMS (but also LHCb could play a relevant role in searching for new physics!) • Other important channels (Extra Dimensions, Top/Bottom physics BSM, long-lived heavy charged particles) will be discussed afterward in this session • Other channels have not been discussed due to lack of time but are equally important Lorenzo Menici

Ricerche extra-SUSY a LHC