Beyond the Standard Model at ATLAS
Dan Tovey University of Sheffield 1 Beyond the Standard Model
Beyond the Standard Model physics one of the priorities of on-going physics studies (Data Challenges/full-sim + fast-sim). Huge variety of models being studied. In this talk will concentrate on a few topics mostly recent work. Cannot do justice to even these in 30 minutes. Will highlight models and techniques to be studied for Rome. Plans for physics commissioning studied (SUSY) described earlier this week (Saturday). Many thanks to Georges Azuelos, Samir Ferrag + members of SUSY & Exotics WGs. 2 Supersymmetry m1/2 (GeV) SUSY particularly well-motivated solution to gauge hierarchy problem, unification of couplings etc. Also often provides natural solution to Dark Matter problem of astrophysics/cosmology. Much work carried out historically by ATLAS (summarised in TDR). Work continuing to ensure ready to test new ideas in 2007. Universe Over-Closed m0 (GeV) 3 SUSY Signatures p c01 ~ c02 g q l
Q: What do we expect SUSY LHC to look like? A: Look at typical decay chain: l q g ~ c02 c01 p Strongly interacting sparticles (squarks, gluinos) dominate production. Heavier than sleptons, gauginos etc. g cascade decays to LSP. Long decay chains and large mass differences between SUSY states Many high pT objects observed (leptons, jets, b-jets). If R-Parity conserved LSP (lightest neutralino in mSUGRA) stable and sparticles pair produced. Large ETmiss signature (c.f. Wgln). Closest equivalent SM signature tgWb. 4 Dilepton Edge Measurements
When kinematically accessible c02 can undergo sequential two-body decay to c01 via a right-slepton (e.g. LHC Point 5). Results in sharp OS SF dilepton invariant mass edge sensitive to combination of masses of sparticles. Can perform SM & SUSY background subtraction using OF distribution e+e- + m+m- - e+m- - m+e- Position of edge measured with precision ~ 0.5% (30 fb-1). ~ ~ c02 c01 l ~ DC1 e+e- + m+m- - e+m- - m+e- e+e- + m+m- 5 fb-1 FULL SIM Point 5 ATLAS 30 fb-1 atlfast ATLAS Modified Point 5 (tan(b) = 6) Physics TDR 5 Measurements With Squarks
Dilepton edge starting point for reconstruction of decay chain. Make invariant mass combinations of leptons and jets. Gives multiple constraints on combinations of four masses. Sensitivity to individual sparticle masses. ~ c02 c01 l qL q ~ c02 c01 b h qL q llq edge 1% error (100 fb-1) lq edge 1% error (100 fb-1) llq threshold bbq edge 1% error (100 fb-1) 2% error (100 fb-1) TDR, Point 5 TDR, Point 5 TDR, Point 5 TDR, Point 5 ATLAS ATLAS ATLAS ATLAS 6 Sbottom/Gluino Mass l b g ~ lR c02 c01 p
Gjelsten et al., ATL-PHYS Following measurement of squark, slepton and neutralino masses move up decay chain and study alternative chains. One possibility: require b-tagged jet in addition to dileptons. Give sensitivity to sbottom mass (actually two peaks) and gluino mass. Problem with large error on input c01 mass remains g reconstruct difference of gluino and sbottom masses. Allows separation of b1 and b2 with 300 fb-1. ~ m(g)-0.99m(c01) = (500.0 6.4) GeV ~ 300 fb-1 ATLAS SPS1a ~ ~ ~ m(g)-m(b1) = (103.3 1.8) GeV ATLAS ~ ~ ~ ~ m(g)-m(b2) = (70.6 2.6) GeV l b g ~ lR c02 c01 p 300 fb-1 SPS1a 7 RH Squark Mass Gjelsten et al., ATL-PHYS ~ Right handed squarks difficult as rarely decay via standard c02 chain Typically BR (qR g c01q) > 99%. Instead search for events with 2 hard jets and lots of ETmiss. Reconstruct mass using stransverse mass (Allanach et al.): mT22 = min [max{mT2(pTj(1),qTc(1);mc),mT2(pTj(2),qTc(2);mc)}] Needs c01 mass measurement as input. Also works for sleptons. ~ ~ ~ qTc(1)+qTc(2)=ETmiss ~ c01 qR q ATLAS ATLAS 30 fb-1 30 fb-1 100 fb-1 Right squark ATLAS SPS1a SPS1a SPS1a Right squark Left slepton Precision ~ 3% 8 Heavy Gaugino Measurements
Polesello, SN-ATLAS Also possible to identify dilepton edges from decays of heavy gauginos. Requires high stats. Crucial input to reconstruction of MSSM neutralino mass matrix (independent of SUSY breaking scenario). ATLAS SPS1a ATLAS ATLAS ATLAS 100 fb-1 100 fb-1 100 fb-1 SPS1a 9 Model-Independent Masses
Rome Allanach et al., ATL-PHYS Combine measurements from edges from different jet/lepton combinations to obtain model-independent mass measurements. c01 ~ ~ lR ATLAS ATLAS Mass (GeV) Mass (GeV) ~ ~ c02 qL ATLAS ATLAS Mass (GeV) Mass (GeV) Sparticle Expected precision (100 fb-1) qL 3% 02 6% lR 9% 01 12% ~ 10 Measuring Model Parameters
Rome Polesello et al., ATL-PHYS Alternative use for SUSY observables (invariant mass end-points, thresholds etc.). Here assume mSUGRA/CMSSM model and perform global fit of model parameters to observables So far mostly private codes but e.g. SFITTER, FITTINO now on the market; c.f. global EW fits at LEP, ZFITTER, TOPAZ0 etc. Point m0m1/2A0 tan(b) sign(m) LHC Point SPS1a Parameter Expected precision (300 fb-1) m 2% m1/ 0.6% tan(b) 9% A0 16% 11 SUSY Dark Matter Rome Polesello et al., ATL-PHYS Can use parameter measurements for many purposes, e.g. estimate LSP Dark Matter properties (e.g. for 300 fb-1, SPS1a) Wch2 = log10(scp/pb) = 0.04 Baer et al. hep-ph/ LHC Point 5: >5s error (300 fb-1) SPS1a: >5s error (300 fb-1) Micromegas 1.1 (Belanger et al.) + ISASUGRA 7.69 DarkSUSY (Gondolo et al.) + ISASUGRA 7.69 scp=10-11 pb scp=10-10 pb Wch2 scp scp=10-9 pb 300 fb-1 300 fb-1 LEP 2 No REWSB ATLAS ATLAS 12 SUSY Dark Matter SUSY (e.g. mSUGRA) parameter space strongly constrained by cosmology (e.g. WMAP satellite) data. mSUGRA A0=0, tan(b) = 10, m>0 Slepton Co-annihilation region: LSP ~ pure Bino. Small slepton-LSP mass difference makes measurements difficult. 'Focus point' region: significant h component to LSP enhances annihilation to gauge bosons ~ Ellis et al. hep-ph/ DisfavouredbyBR (b s)= (3.2 0.5) (CLEO, BELLE) c01 t1 t g/Z/h ~ 'Bulk' region: t-channel slepton exchange - LSP mostly Bino. 'Bread and Butter' region for LHC Expts. c01 l lR ~ Also 'rapid annihilation funnel' at Higgs pole at high tan(b), stop co-annihilation region at large A0 0.094 h2 0.129 (WMAP) DC1 DC2 13 Coannihilation Signatures
Comune, ATL-COM-PHYS DC2 Small slepton-neutralino mass difference gives soft leptons Low electron/muon/tau energy thresholds crucial. Study point chosen within region: m0=70 GeV; m1/2=350 GeV; A0=0; tan=10 ; >0; Same model used for DC2 study. Decays of c02 to both lL and lR kinematically allowed. Double dilepton invariant mass edge structure; Edges expected at 57 / 101 GeV Stau channels enhanced (tanb) Soft tau signatures; Edge expected at 79 GeV; Less clear due to poor tau visible energy resolution. Rome 100 fb-1 ETmiss>300 GeV 2 OSSF leptons PT>10 GeV >1 jet with PT>150 GeV OSSF-OSOF subtraction applied ATLAS Preliminary ~ ~ ~ 100 fb-1 ETmiss>300 GeV 1 tau PT>40 GeV;1 tau PT1 jet with PT>100 GeV SS tau subtraction ATLAS Preliminary 14 Focus Point Models Large m0 sfermions are heavy
Lari, ATL-COM-PHYS Large m0 sfermions are heavy Most useful signatures from heavy neutralino decay Study point chosen within focus point region : m0=3000 GeV; m1/2=215 GeV; A0=0; tan=10 ; >0 Direct three-body decays c0n c01 ll Edges give m(c0n)-m(c01) Rome ~ ~ ~ ~ ~ ~ ~ ~ c02 c01 ll c03 c01 ll Z0 ll ATLAS ATLAS 30 fb-1 Preliminary Preliminary 15 SUSY Spin Measurement Barr, ATL-PHYS Q: How do we know that a SUSY signal is really due to SUSY? Other models (e.g. UED) can mimic SUSY mass spectrum A: Measure spin of new particles. One proposal (Barr) use standard two-body slepton decay chain charge asymmetry of lq pairs measures spin of c02 relies on valence quark contribution to pdf of proton (C asymmetry) shape of dilepton invariant mass spectrum measures slepton spin ~ Straight line distn (phase-space) Point 5 Spin-,mostly wino Spin-0 Spin- Spin-,mostly bino Polarise Measure Angle Point 5 ATLAS mlq 150 fb -1 spin-0=flat 150 fb -1 ATLAS 16 Little Higgs Models DC2 Rome
Solves hierarchy problem by cancelling loop corrections (top, W/Z, Higgs loops) to the Higgs mass with new states. New states derived from extended gauge group rather than new continuous symmetry (c.f. SUSY). Littlest Higgs model contains not too little, not too much, but just enough extra gauge symmetry : Electroweak singlet T quark (top loop) mixes with top; New gauge bosons WH, AH, ZH (W/Z loops); New SU(2)L triplet scalars, including neutral, singly charged, doubly charged f (Higgs loops). Requirement that these states protect Higgs from large corrections limits their masses: T quark ~ 1 TeV; WH, AH, ZH ~ 1 TeV; f0, f+/-, f+/-+/- ~ 10 TeV. t 17 Littlest Higgs Model Azuelos et al., SN-ATLAS Searches for/measurements of new particles studied. For T quark single production assumed. Yukawa couplings governed by 3 parameters (mt, mT, l1/l2) top mass eigenstate is mixture of t and T: Decays: DC2 Rome 18 Heavy Gauge Bosons DC2 Rome
Azuelos et al., SN-ATLAS Rome WH, ZH, AH arise from [SU(2) U(1)]2 symmetry 2 mixing angles (like qW):q for ZH, q for AH Branching Ratio 19 Z, W studies DC2 Rome M. Schaefer different models full sim. in progress O. Gaumer full simulation 20 Extra Dimensions M-theory/Strings g compactified Extra Dimensions (EDs) Q: Why is gravity weak compared to gauge fields (hierarchy)? A: It isnt, but gravity leaks into EDs. Possibility of Quantum Gravity effects at TeV scale colliders Variety of ED models studied by ATLAS (a few examples follow): Large (>> TeV-1) Only gravity propagates in the EDs, MeffPlanck~Mweak Signature: Direct or virtual production of Gravitons TeV-1 SM gauge fields also propagate in EDs Signature: 4D Kaluza-Klein excitations of gauge fields Warped Warped metric with 1 ED MeffPlanck~Mweak Signature: 4D KK excitations of Graviton (also Radion scalar) SM 4-brane SM 4-brane y=0 y = prc 21 Large Extra Dimensions
Vacavant et al., SN-ATLAS With d EDs of size R, observed Newton constant related to fundamental scale of gravity MD: GN-1=8pRdMD2+d Search for direct graviton production in jet(g) + ETmiss channel. DC2 Rome Gg g gG, qg g qG, qq g Gg Signal : graviton + 1 jet production Main background: Jet + Z(W) [Z g nn, W g ln] ATLAS 100 fb-1 ATLAS Single jet, 100 fb-1 q/g G MDmax (ET>1 TeV, 100 fb-1) = 9.1, 7.0, 6.0 TeV for d=2,3,4 22 TeV-1 Scale ED ATLAS Masses of KK modes given by: Mn2=(nMc)2+M02
Usual 4D + small (TeV-1) EDs + large EDs (>> TeV-1) SM fermions on 3-brane, SM gauge bosons on 4D+small EDs, gravitons everywhere. 4D Kaluza-Klein excitations of SM gauge bosons (here assume 1 small ED). Polesello et al., SN-ATLAS ATLAS 100 fb-1 Masses of KK modes given by: Mn2=(nMc)2+M02 for compactification scale Mc and SM mass M0 Look for l+l- decays of g and Z0 KK modes. Also ln decays (mT) of W+/- KK modes. Also g KK modes recently studied (in progress). 100 fb-1 ATLAS 5s reach for 100 fb-1 ~ 5.8 TeV (Z/g) ~ 6 TeV (W) For 300 fb-1 l+l- peak detected if Mc < 13.5 TeV (95% CL). 23 Warped Extra Dimensions
Allanach et al., ATL-PHYS Search for gg(qq) g G(1) g e+e-. Study using test model with k/MPl=0.01 (narrow resonance). Signal seen for mass in range [0.5,2.08] TeV for k/MPl=0.01. Measure spin (distinguish from Z) using polar angle distribution of e+e-. Measure shape with likelihood technique. Can distinguish spin 2 vs. spin 1 at 90% CL for mass up to 1.72 TeV. DC2 Rome m1 = 1.5 TeV 100 fb-1 100 fb-1 ATLAS Experimental resolution ATLAS m1 = 1.5 TeV 100 fb-1 100 fb-1 ATLAS ATLAS 24 Black Hole Signatures Tanaka et al.,ATL-PHYS In large ED (ADD) scenario, when impact parameter smaller than Schwartzschild radius Black Hole produced with potentially large x-sec (~100 pb). Decays democratically through spherical Black Body radiation of SM states Boltzmann energy distribution. Rome w/o pile-up ATLAS - select spherical events - Reconstruct MBH for each event- Reconstruct MP from ds/dMBH - Reconstruct TH from distribution of MBH - Deduce n from TH, MBH and MP Discovery potential Mp < ~4 TeV< ~ 1 day Mp < ~6 TeV< ~ 1 year Mp=1TeV, n=2, MBH = 6.1TeV 25 Other Topics for Rome Exotics group also studying variety of other models using full-sim for Rome: Doubly charge Higgs Sequential heavy leptons Excited leptons 26 Summary Much work on Beyond the Standard Model Physics being carried out. Lots of input from both theorists (new ideas) and experimentalists (new techniques). Exotics and SUSY WGs contributing fully to Data Challenges Validating software Performing new studies reliant on detector performance Plan for extensive set of full-sim studies for Rome. Big effort ramping up now to understand how to exploit first data in timely fashion Calibrations Background rejection Background estimation Tools Lots of scope for new people/groups to get involved. 27 BACK-UP SLIDES 28 Inclusive Searches Use 'golden' Jets + n leptons + ETmiss discovery channel. Map statistical discovery reach in mSUGRA m0-m1/2 parameter space. Sensitivity only weakly dependent on A0, tan(b) and sign(m). Syst.+ stat. reach harder to assess: focus of current & future work. 5s 5s ATLAS ATLAS 29 SUSY Mass Scale First measured SUSY parameter likely to be mass scale:
Defined as weighted mean of masses of initial sparticles. Calculate distribution of 'effective mass' variable defined as scalar sum of masses of all jets (or four hardest) and ETmiss: Meff=S|pTi| + ETmiss. Distribution peaked at ~ twice SUSY mass scale for signal events. Pseudo 'model-independent' measurement. Typical measurement error (syst+stat) ~10% for mSUGRA models for 10 fb-1. Jets + ETmiss + 0 leptons ATLAS 10 fb-1 10 fb-1 ATLAS 30 Exclusive Studies l q g ~ lR c02 c01 p
With more data will attempt to measure weak scale SUSY parameters (masses etc.) using exclusive channels. Different philosophy to TeV Run II (better S/B, longer decay chains) g aim to use model-independent measures. Two neutral LSPs escape from each event Impossible to measure mass of each sparticle using one channel alone Use kinematic end-points to measure combinations of masses. Old technique used many times before (n mass from b decay spectrum, W (transverse) mass in Wgln). Difference here is we don't know mass of neutral final state particles. l q g ~ lR c02 c01 p 31 Mass Relation Method Nojiri et al., ATL-PHYS Hot off the press: new idea for reconstructing SUSY masses! Impossible to measure mass of each sparticle using one channel alone (Page 8). Should have added caveat: Only if done event-by-event! Remove ambiguities by combining different events analytically g mass relation method (Nojiri et al.). Also allows all events to be used, not just those passing hard cuts (useful if background small, buts stats limited e.g. high scale SUSY). Preliminary ATLAS ATLAS SPS1a 32 Chargino Mass Measurement
~ ~ c+1 Nojiri et al., ATL-PHYS ~ q c01 q Mass of lightest chargino very difficult to measure as does not participate in standard dilepton SUSY decay chain. Decay process via n+slepton gives too many extra degrees of freedom - concentrate instead on decay c+1 g W c01. Require dilepton c02 decay chain on other leg of event and use kinematics to calculate chargino mass analytically. Using sideband subtraction technique obtain clear peak at true chargino mass (218 GeV). ~ 3 s significance for 100 fb-1. ~ g p ~ W ~ ~ c01 q p c02 ~ lR q q g ~ q q q l l PRELIMINARY ~ ~ ~ Modified LHCC Point 5: m0=100 GeV; m1/2=300 GeV; A0=300 GeV; tan=6 ; >0 100 fb-1 33 Coannihilation Models
Small slepton-neutralino mass difference gives soft leptons from decay Low electron/muon/tau energy thresholds crucial. At high tan(b) stau decay channel dominates. Need to be able to ID soft taus (good jet rejection). Study started within ATLAS examining signatures of these models. Study point chosen within coannihilation region : m0=70 GeV; m1/2=350 GeV; A0=0; tan=10 ; >0 Same model to be used for DC2 SUSY study. l q g ~ lR c02 c01 p 34 Physics Commissioning
(See also talk during Commissioning Workshop earlier in week) Preparations needed to ensure efficient/reliable searches for/measurements of SUSY particles in timely manner: Initial calibrations (energy scales, resolutions, efficiencies etc.); Minimisation of poorly estimated SM backgrounds; Estimation of remaining SM backgrounds; Development of useful tools. Many issues will be common with other WG, esp: Standard Model (W (gln) + n jet, Z(gll) + n jet) from Z(gl+l-) + n jet); Top (full reconstruction of semi-leptonic ttbar events); Higgs (Estimation of high ETmiss backgrounds) Jet/ETmiss (Estimation of fake ETmiss QCD backgrounds, jet energy scale etc.); Combined Performance groups (calibration of energy scales, resolutions and efficiencies). Should work together to develop common tools and analysis strategies wherever possible 35 Little Higgs Littlest Higgs model Higgs is a gauge boson !
Introduce scalar fields gauge symmetry SU(5) global local subgroup Littlest Higgs model broken( Higgs mechanism) broken Massless Goldstonebosons massive gauge vector bosons 4 14 Goldstone bosons Higgs is a gauge boson ! 10 36 Littlest Higgs Model vev for h
triggers EW symm. breaking mass to Z, W, h massless 1-loop gauge interactions: acquires mass from one-loop gauge interactions vev for h t To cancel the top loop,introduce SU(2)L singlet quark TL, and TR 37 Higgs-Gauge Boson Couplings
Azuelos et al., SN-ATLAS Measurement of ZHZh and WHWh couplings needed to test model B-tagging at high energy needed high energy 38 Heavy Leptons Extra heavy leptons present in many extended gauge models. Study l+l-+4j channel. Backgrounds from ttbar, WZ, WW, ZZ. Also 6 lepton channel. Alexa et al., ATL-PHYS Experimental considerations: - high energy leptons, jets Systematics: - large NLO corrections conclusion: ATLAS can discover sequential charged heavy leptons up to ML = 0.9 / 1.0 TeV (low/high luminosity) DC2 Rome 39 Excited Quarks DC2 Rome ATL-PHYS-99-002 40
O. akir, C. Leroy, R. Mehdiyev, ATL-PHYS ATL-PHYS ATL-PHYS DC2 Rome 40 Excited Leptons DC2 Rome
Experimental considerations:- high energy e, g- Z jj, W jj DC2 Rome L = 300 fb-1, L = 6 TeV 41 Black Hole Production Theoretical Uncertainties Rome Characteristics
production cross section disintegration emission of gravitational radiation (balding phase) main phase ?= Hawking radiation, or evaporation spin-down phase: loss of angular momentum Schwarzschild phase: emission of particles quantum numbers conserved? Planck phase: impossible to calculate CHARYBDIS generator: time evolution, grey-body factors, Planck phase CM Harris, P. Richardson and BR Webber, JHEP 0308 (2003) 033 (hep-ph/ ) Characteristics temperature: depends on the mass black body radiation: emission of particles high multiplicity democratic emission spherical distribution Rome 42