Beyond the Standard Model at ATLAS

1
Beyond the Standard Modelat ATLAS

• Dan Tovey
• University of Sheffield

2
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.

3
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)
4
SUSY Signatures

• Q What do we expect SUSY events _at_ LHC to look
  like?
• A Look at typical decay chain

• 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.

5
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
• ee- mm- - em- - me-
• Position of edge measured with precision 0.5
• (30 fb-1).

DC1
ee- mm- - em- - me-
ee- mm-
5 fb-1 FULL SIM
Point 5
ATLAS
ATLAS
30 fb-1 atlfast
Modified Point 5 (tan(b) 6)
Physics TDR
6
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.

bbq edge
llq threshold
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
7
Sbottom/Gluino Mass
Gjelsten et al., ATL-PHYS-2004-007

• 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
300 fb-1
SPS1a
8
RH Squark Mass
Gjelsten et al., ATL-PHYS-2004-007

• Right handed squarks difficult as rarely decay
  via standard c02 chain
• Typically BR (qR g c01q) gt 99.
• Instead search for events with 2 hard jets and
  lots of ETmiss.
• Reconstruct mass using stransverse mass
  (Allanach et al.)
• mT22 min maxmT2(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
ATLAS
ATLAS
30 fb-1
100 fb-1
30 fb-1
Right squark
SPS1a
ATLAS
SPS1a
Right squark
SPS1a
Left slepton
Precision 3
9
Heavy Gaugino Measurements
Polesello, SN-ATLAS-2004-041

• 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
10
Model-Independent Masses
Rome
Allanach et al., ATL-PHYS-2002-005

• 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)
11
Measuring Model Parameters
Rome
Polesello et al., ATL-PHYS-2004-008

• 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.

12
SUSY Dark Matter
Rome
Polesello et al., ATL-PHYS-2004-008

• Can use parameter measurements for many purposes,
  e.g. estimate LSP Dark Matter properties (e.g.
  for 300 fb-1, SPS1a)
• Wch2 0.1921 ? 0.0053
• log10(scp/pb) -8.17 ? 0.04

Baer et al. hep-ph/0305191
LHC Point 5 gt5s error (300 fb-1)
SPS1a gt5s error (300 fb-1)
scp10-11 pb
Micromegas 1.1 (Belanger et al.) ISASUGRA 7.69
DarkSUSY 3.14.02 (Gondolo et al.) ISASUGRA 7.69
scp10-10 pb
Wch2
scp
scp10-9 pb
300 fb-1
300 fb-1
No REWSB
LEP 2
ATLAS
ATLAS
13
SUSY Dark Matter

• SUSY (e.g. mSUGRA) parameter space strongly
  constrained by cosmology (e.g. WMAP satellite)
  data.

mSUGRA A00, tan(b) 10, mgt0
Slepton Co-annihilation region LSP pure Bino.
Small slepton-LSP mass difference makes
measurements difficult.
Ellis et al. hep-ph/0303043
Disfavoured by BR (b ? s?) (3.2 ? 0.5) ?
10-4 (CLEO, BELLE)
'Bulk' region t-channel slepton exchange - LSP
mostly Bino. 'Bread and Butter' region for LHC
Expts.
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
14
Coannihilation Signatures
Comune, ATL-COM-PHYS-2004-052
DC2

• Small slepton-neutralino mass difference gives
  soft leptons
• Low electron/muon/tau energy thresholds crucial.
• Study point chosen within region
• m070 GeV m1/2350 GeV A00 tanß10 µgt0
• 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

• ETmissgt300 GeV
• 2 OSSF leptons PTgt10 GeV
• gt1 jet with PTgt150 GeV
• OSSF-OSOF subtraction applied

100 fb-1
ATLAS
Preliminary

• ETmissgt300 GeV
• 1 tau PTgt40 GeV1 tau PTlt25 GeV
• gt1 jet with PTgt100 GeV
• SS tau subtraction

100 fb-1
ATLAS
Preliminary
15
Focus Point Models
Lari, ATL-COM-PHYS-2004-048

• Large m0 ? sfermions are heavy
• Most useful signatures from heavy neutralino
  decay
• Study point chosen within focus point region
• m03000 GeV m1/2215 GeV A00 tanß10 µgt0
• Direct three-body decays c0n ? c01 ll
• Edges give m(c0n)-m(c01)

Rome








c03 ? c01 ll
c02 ? c01 ll
Z0 ? ll
ATLAS
ATLAS
30 fb-1
Preliminary
Preliminary
16
SUSY Spin Measurement
Barr, ATL-PHYS-2004-017

• 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

Point 5
ATLAS
150 fb -1
mlq
spin-0flat
150 fb -1
ATLAS
17
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
18
Littlest Higgs Model
Azuelos et al., SN-ATLAS-2004-038

• 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
19
Heavy Gauge Bosons
DC2
Azuelos et al., SN-ATLAS-2004-038
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
20
Z, W studies
DC2
Rome
M. Schaeferdifferent modelsfull sim. in progress
O. Gaumerfull simulation
21
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 (gtgt TeV-1)
• Only gravity propagates in the EDs,
  MeffPlanckMweak
• 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
• MeffPlanckMweak
• Signature 4D KK excitations of Graviton (also
  Radion scalar)

22
Large Extra Dimensions
Vacavant et al., SN-ATLAS-2001-005

• With d EDs of size R, observed Newton constant
  related to fundamental scale of gravity MD
• GN-18pRdMD2d
• 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
MDmax (ETgt1 TeV, 100 fb-1) 9.1, 7.0, 6.0 TeV
for d2,3,4
23
TeV-1 Scale ED
Polesello et al., SN-ATLAS-2003-036

• Usual 4D small (TeV-1) EDs large EDs
• (gtgt TeV-1)
• SM fermions on 3-brane, SM gauge bosons on
  4Dsmall EDs, gravitons everywhere.
• 4D Kaluza-Klein excitations of SM gauge bosons
  (here assume 1 small ED).

ATLAS
100 fb-1

• Masses of KK modes given by
• Mn2(nMc)2M02
• for compactification scale Mc and SM mass M0
• Look for ll- 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 ll- peak detected if
• Mc lt 13.5 TeV (95 CL).

24
Warped Extra Dimensions
Allanach et al., ATL-PHYS-2002-031

• Search for gg(qq) g G(1) g ee-. Study using test
  model with k/MPl0.01 (narrow resonance).
• Signal seen for mass in range 0.5,2.08 TeV for
  k/MPl0.01.
• Measure spin (distinguish from Z) using polar
  angle distribution of ee-.
• 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
100 fb-1
m1 1.5 TeV
100 fb-1
ATLAS
ATLAS
25
Black Hole Signatures
Tanaka et al., ATL-PHYS-2003-037

• 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
ATLAS
w/o pile-up
- 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 lt 4 TeV ? lt 1 day
• Mp lt 6 TeV ? lt 1 year

Mp1TeV, n2, MBH 6.1TeV
26
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

27
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.

28

• BACK-UP SLIDES

29
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
30
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
• MeffSpTi ETmiss.
• Distribution peaked at twice SUSY mass scale
  for signal events.
• Pseudo 'model-independent' measurement.
• Typical measurement error (syststat) 10 for
  mSUGRA models for 10 fb-1.

Jets ETmiss 0 leptons
ATLAS
10 fb-1
10 fb-1
ATLAS
31
Exclusive Studies

• 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.

32
Mass Relation Method
Nojiri et al., ATL-PHYS-2003-039

• 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
33
Chargino Mass Measurement

c1
Nojiri et al., ATL-PHYS-2003-040

q

q
c01

• Mass of lightest chargino very difficult to
  measure as does not participate in standard
  dilepton SUSY decay chain.
• Decay process via nslepton gives too many extra
  degrees of freedom - concentrate instead on decay
  c1 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


c01
W

c02
p
lR
q

q
q
g

q
q
l
q
l
PRELIMINARY


Modified LHCC Point 5 m0100 GeV m1/2300 GeV
A0300 GeV tanß6 µgt0

100 fb-1
34
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
• m070 GeV m1/2350 GeV A00 tanß10 µgt0
• Same model to be used for DC2 SUSY study.

35
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(gll-) 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

36
Little Higgs
Introduce scalar fields
SU(5)
global
local subgroup
Littlest Higgs model
broken ( Higgs mechanism)
broken
massive gaugevector bosons
Massless Goldstone bosons
4
14 Goldstone bosons
Higgs is a gauge boson !
10
37
Littlest Higgs Model
To cancel the top loop, introduce SU(2)L singlet
quark TL, and TR
38
Higgs-Gauge Boson Couplings
Azuelos et al., SN-ATLAS-2004-038

• Measurement of ZHZh and WHWh couplings needed
  to test model

B-tagging at high energy needed
high energy
39
Heavy Leptons

• Extra heavy leptons present in many extended
  gauge models.
• Study ll-4j channel.
• Backgrounds from ttbar, WZ, WW, ZZ.
• Also 6 lepton channel.

Alexa et al., ATL-PHYS-2003-014
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
40
Excited Quarks
O. Çakir, C. Leroy, R. Mehdiyev,ATL-PHYS-2002-014
DC2
Rome
41
Excited Leptons
Experimental considerations - high energy e, g
- Z ? jj, W ? jj
DC2
Rome
L 300 fb-1, L 6 TeV
42
Black Hole Production

• Theoretical Uncertainties
• 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 phaseCM Harris, P. Richardson
  and BR Webber, JHEP 0308 (2003) 033
  (hep-ph/0307305)
• Characteristics
• temperature depends on the mass
• black body radiation emission of particles
• high multiplicity
• democratic emission
• spherical distribution

Rome