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LHC &. Extra Dimensions. Dr Tracey Berry Royal Holloway University of London. LHC &. Extra Dimensions. Theoretical Motivations Extra Dimensional Models Considered Signatures Covered Search Facilities: ATLAS & CMS Uncertainties

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slide1

LHC &

Extra Dimensions

Dr Tracey Berry

Royal Holloway

University of London

Getting ready for the LHC, Madrid

Oct 23-27, 2006

slide2
LHC &

Extra Dimensions

  • Theoretical Motivations
  • Extra Dimensional Models Considered
  • Signatures Covered
  • Search Facilities: ATLAS & CMS
  • Uncertainties
  • Present Constraints and Discovery Limits for ED (ADD, RS, TeV-1, UED)
  • Summary of LHC Start-up Expectations
  • Conclusions

Getting ready for the LHC, Madrid

Oct 23-27, 2006

extra dimensions motivations
Extra Dimensions: Motivations

In the late 90’s Large Extra Dimensions (LED) were proposed as a solution to the hierarchy problem

MEW (1 TeV) << MPlanck (1019 GeV)?

Randall, Sundrum,Phys Rev Lett 83 (99)

Arkani-Hamed, Dimopoulos, Dvali,Phys Lett B429 (98)

RS

ADD

1 highly curved ED

Gravity localised in the ED

Many (d) large compactified EDs

In which G can propagate

Planck TeV brane

MPl2 ~ RdMPl(4+d)(2+d)

= Mple-kRc

~ TeV

 ifcompact space (Rd) is large

Effective MPl ~ 1TeV

if warp factorkRc ~11-12

Since then, new Extra Dimensional models have been developed and been used to solved other problems:

Dark Matter, Dark Energy, SUSY Breaking, etc

Some of these models can be/have been experimentally tested at high energy colliders

Getting ready for the LHC, Madrid

Oct 23-27, 2006

extra dimensional models

G

Extra Dimensional Models

Arkani-Hamed, Dimopoulos, Dvali,Phys Lett B429 (98)

ADD

  • (Many) Large flat Extra-Dimensions (LED) could be as large as a few m
  • In which G can propagate, SM particles restricted to 3D brane

Randall, Sundrum,Phys Rev Lett 83 (99)b

RS

Planck TeV brane

  • Small highly curved extra spatial dimension
  • (RS1 – two branes) Gravity localised in the ED

-1

Dienes, Dudas, Gherghetta,Nucl Phys B537 (99)

SM chiral

fermions

SM Gauge Bosons

W, Z, g, g

TeV

sized EDs

  • Bosons could also propagate in the bulk
  • Fermions are localized at the same (opposite) orbifold point: destructive (constructive) interference between SM gauge bosons and KK excitations

W, Z

UED

G

  • All SM particles propagate in “Universal” ED
  • often embedded in large ED

e, m

Getting ready for the LHC, Madrid

Oct 23-27, 2006

experimental signatures of

Exchange

ADD

RS

TeV-1

Experimental Signatures of

ED

Covered in this talk

  • Single jets/Single photons + missing ET
  • (direct graviton production in ADD)
  • Di-lepton, di-jet continuum modifications
  • (virtual graviton production in ADD)
  • Di-lepton, di-jet and di-photon resonances (new particles)in RS1-model (RS1-graviton) and TeV-1 ED model(ZKK)
  • Single leptons + missing ETin TeV-1 ED model (WKK)
  • Back-to-back energetic jets + missing ET (UED)
  • 4 jets + 4 leptons + missing ET(mUED)

Emission

ADD

Getting ready for the LHC, Madrid

Oct 23-27, 2006

present past ed search facilities
Present/Past ED Search Facilities

Tevatron, Fermilab, USA

LEP, CERN, Geneva

CERN: world's largest particle physics laboratory

CDF

p

e-

p

e+

D0

Tevatron: Highest energy collider operating in the world!

LEP I √s = 91 GeV

LEP II √s =136-208 GeV

Run I √s = 1.8 TeV

Run II √s = 1.96 TeV

Getting ready for the LHC, Madrid

Oct 23-27, 2006

slide7

Future ED Search Facilities!

Bigger & Better (?!)

Collider & Detectors!!

Higher CM of mass energy

LHC: √s = 14 TeV

Aim of Tev4LHC

use what has been learnt at the Tevatron to fully exploit LHC’s physics potential

Getting ready for the LHC, Madrid

Oct 23-27, 2006

atlas and cms experiments
ATLAS and CMS Experiments

Large general-purpose particle physics detectors

CMS

ATLAS

Total weight 7000 t

Overall diameter 25 m

Barrel toroid length 26 m

End-cap end-wall chamber span 46 m

Magnetic field 2 Tesla

Total weight 12 500 t

Overall diameter 15.00 m

Overall length 21.6 m

Magnetic field 4 Tesla

Detector subsystems are designed to measure:

energy and momentum of g ,e, m, jets, missing ET up to a few TeV

Getting ready for the LHC, Madrid

Oct 23-27, 2006

experimental uncertainties
Experimental Uncertainties

Systematic uncertainties associated with the detector measurements

  • Luminosity
  • Energy miscalibration which affects the performance of e/g/hadron energy reconstruction
  • Drift time and drift velocities uncertainties
  • Misalignment affects track and vertex reconstruction efficiency  increase of the mass residuals by around 30%
  • Magnetic and gravitational field effects  can cause a scale shift in a mass resolution by 5-10%
  • Pile-up  mass residuals increase by around 0.1-0.2%
  • Trigger and reconstruction acceptance uncertainties
  •  Affect the background and signal
  • Background uncertainties: variations of the bkgd shape  a drop of about 10-15% in the significance values

Getting ready for the LHC, Madrid

Oct 23-27, 2006

theoretical uncertainties
Theoretical Uncertainties
  • QCD and EW higher-order corrections (K-factors)
  • Parton Distribution Functions (PDF)
  • Hard process scale (Q2)
  • Differences between Next-to-Next-to-Leading Order (NNLO), NLO and LO calcalations

 affect signal and background magnitudes,

efficiency of the selection cuts,

significance computation…

Getting ready for the LHC, Madrid

Oct 23-27, 2006

pdf impact on sensitivity to ed

SM

2XD

4XD

6XD

PDF Impact on Sensitivity to ED
  • Extra dimensions affect the di-jet cross section through the running of as.

Parameterised by number of extra dimensions d and compactification scale Mc.

 So could potentially use s deviation to detect ED

Ferrag, hep-ph/0407303

MC= 2 TeV

MC= 2 TeV

MC= 6 TeV

PDF

uncertainties

  • PDF uncertainties (mainly due to high-x gluon) give an uncertainty “zone” on the SM cross sections
  • This reduces sensitivity to MC from 5 TeV to 2 (3) TeV for d= 4, 6 and for d=2 sensitivity is lost (MC<2 TeV)

Getting ready for the LHC, Madrid

Oct 23-27, 2006

model

MPl2 ~ RdMPl(4+d)(2+d)

G

Model

ADD

Arkani-Hamed, Dimopoulos, Dvali,Phys Lett B429 (98), Nuc.Phys.B544(1999)

    • (Many) Large flat Extra-Dimensions (LED),
    • could be as large as a few m
    • the maximum total number of dimensions is 3(our) + 6(extra)=9
    • G can propagate in ED
    • SM particles restricted to 3D brane
  • The fundamental scale is not planckian: MD= MPl(4+d) ~ TeV
  • Model parameters are:
  • d = number of ED
  • MPl(4+d) = Planck mass in the 4+d dimensions

For MPl ~ 1019 GeV and MPl(4+d) ~MEW R ~1032/d x10-17 cm

Getting ready for the LHC, Madrid

Oct 23-27, 2006

present constraints on the model

MPl2 ~ RdMPl(4+d)(2+d)

G

Present Constraints on the Model

ADD

For MPl ~ 1019 GeV and MPl(4+d) ~MEW  R ~1032/d x10-17 cm

  • d=1  R ~1013 cm, ruled out because deviations from Newtonian gravity over solar distances have not been observed
  • d=2  R ~1 mm, not likely because of cosmological arguments:

In particular graviton emission from Supernova 1987a* implies MD>50 TeV Closest allowed MPl(4+n) value for d=2 is ~30 TeV, out of reach at LHC

Run I

  • Can detect at collider detectors via:
    • graviton emission
    • Or graviton exchange

*Cullen, Perelstein Phys. Rev. Lett 83,268 (1999)

Getting ready for the LHC, Madrid

Oct 23-27, 2006

Gupta et. al. hep-ph/9904234

add collider signatures

G

g,q

jet,V

g,q

G

g,q

f,V

g,q

f,V

Broad increase in s due to closely spaced summed over KK towers

Run I

CDF Run I l=+1

Mll

ADD Collider Signatures
  • Real Gravitonemission in association with a vector-boson

Signature: jets + missing ET, V+missing ET

s depends on the number of ED

Jets+ missingET, γ+ missingET

  • Virtual Graviton exchange

Signature:

deviations in s and asymmetries of SM processes

e.g. qq l+l-,   & new processes e.g. gg  l+l-

Excess above di-lepton continuum

Getting ready for the LHC, Madrid

Oct 23-27, 2006

s independent of the number of ED* in Hewett convention

present constraints on the model1

MPl2 ~ RdMPl(4+d)(2+d)

G

Present Constraints on the Model

ADD

For MPl ~ 1019 GeV and MPl(4+d) ~MEW  R ~1032/d x10-17 cm

  • d=1  R ~1013 cm, ruled out because deviations from Newtonian gravity over solar distances have not been observed
  • d=2  R ~1 mm, not likely because of cosmological arguments:

In particular graviton emission from Supernova 1987a* implies MD>50 TeV Closest allowed MPl(4+n) value for d=2 is ~30 TeV, out of reach at LHC

  • LEP & Tevatron limits is MPl(4+d) ~> 1TeV
  • d>6 difficult to probe at LHC since cross-sections are very low

Run I

*Cullen, Perelstein Phys. Rev. Lett 83,268 (1999)

Getting ready for the LHC, Madrid

Oct 23-27, 2006

present add emission limits

q

q

q

qqgGKK

dominate sub-process for n>2

q

g

q

g

q

g

g

q

q

GKK

GKK

GKK

qggGKK

q

q

q

q

q

q

q

g

q

g

g

GKK

GKK

g

GKK

gggGKK

g

g

g

g

g

g

g

g

g

g

g

GKK

g

GKK

GKK

sfalls as 1/MDn+2 for all sub-processes

g

q

g

g

_

Gkk

g

Gkk

q

Present ADD Emission Limits

LEP and Tevatron results are complementary

For n>4:

CDF limits best

jet+MET

g+MET

For n<4:

LEP limits best

Getting ready for the LHC, Madrid

Oct 23-27, 2006

add discovery limit g g emission
ADD Discovery Limit: g+G Emission

ppg+GKK

J. Weng et al. CMS NOTE 2006/129

  • G  high-pT photon + high missing ET
  • Main Bkgd: Zg  nng,
  • Signals generated with PYTHIA

(compared to SHERPA)

Bkgds: PYTHIA and compared to

SHERPA/CompHEP/Madgraph (B)

Using CTEQ6L

  • Full simulation & reconstruction
  • Theoretical uncert.

Real graviton production

At low pT the bkgd, particularly irreducible Zg  nng is too large require pT>400 GeV

Integrated Lum for a 5s significance discovery

Significance: S=2(√(S+B)-√B)>5

Also W e(m,t)n, Wg en, g+jets, QCD, di-g, Z0+jets

MD= 1– 1.5 TeV for 1 fb-1

2 - 2.5 TeV for 10 fb-1

3 - 3.5 TeV for 60 fb-1

Not considered by CMS analysis: Cosmic Rays at rate of 11 HZ: main background at CDF, also beam halo muons for pT> 400 GeV rate 1 HZ

Getting ready for the LHC, Madrid

Oct 23-27, 2006

add discovery limit g g emission1
ADD Discovery Limit: g+G Emission

ATLAS

L.Vacavant, I.Hinchcliffe

ATLAS-PHYS 2000-016

J. Phys., G 27 (2001) 1839-50

ppg+GKK :

qqgGKK

Rates for MD≥ 4TeV are very low

For d>2: No region where the model independent predictions can be made and where the rate is high enough to observe signal events over the background.

This gets worse as d increases

  • Better limits from the jet+G emission which has a higher production rate

This signature could be used as confirmation after the discovery in the jet channels

Getting ready for the LHC, Madrid

Oct 23-27, 2006

slide19

ADD Discovery Limit: jet+G Emission

ppjet+GKK

Real graviton production

gggG, qgqG & qqGg

Dominant subprocess

  • Signature: jet + G  jet with high transverse energy (ET>500 GeV)+ high missing ET (ETmiss>500 GeV),
  • vetos leptons: to reduce jet+W bkdg mainly
  • Bkgd.: irreducible jet+Z/W jet+ /jet+l jZ(nn) dominant bkgd, can be calibrated using ee and mm decays of Z.
  • ISAJET with CTEQ3L
  • Fast simulation/reco

Discovery limits

L.Vacavant, I.Hinchcliffe, ATLAS-PHYS 2000-016

J. Phys., G 27 (2001) 1839-50

Getting ready for the LHC, Madrid

Oct 23-27, 2006

J. Phys., G 27 (2001) 1839-50

MDMIN (TeV)

slide20

ADD Parameters: jet+G Emission

To characterise the model need to measure MD and d

Measuring s gives ambiguous results

(ppjet+GKK)

Use variation of s on √s

s at different √s almost independent of MD,varies with d

Run at two different √s

e.g. 10 TeV and 14 TeV, need 50 fb-1

Rates at 14 TeV of d=2 MD=6 TeV very similar to d=3 MD=5 TeV whereas

Rates at 10 TeV of (d=2 MD=6 TeV) and (d=3 MD=5 TeV) differ by ~ factor of 2

Getting ready for the LHC, Madrid

Oct 23-27, 2006

L.Vacavant, I.Hinchcliffe, ATLAS-PHYS 2000-016

J. Phys., G 27 (2001) 1839-50

tevatron add exchange limits

g

e+

e-

Tevatron ADD Exchange Limits

Both D0 and CDF have observed no significant excess

95% CL lower limits on fundamental Planck scale (Ms) in TeV, using different formalisms:

most stringent collider limits on LED to date!

D0 Run II: mm

D0 Run II: ee+gg

D0 Run I+II: ee+gg

CDF Run II: ee 200pb-1

1.11 1.32 1.11 1.00 0.93 0.88 0.96/0.99

D0 perform a 2D search in invariant mass & angular distribution

And to maximise reconstruction efficiency they perform combined ee+gg (diEM) search: reduces inefficiencies from

  • g ID requires no track, but g converts (ee)
  • e ID requires a track, but loose track due to imperfect track reconstruction/crack

Getting ready for the LHC, Madrid

Oct 23-27, 2006

slide22

ADD Discovery Limit: G Exchange

ppGKKmm

Virtual graviton production

  • Two opposite sign muons in the final state with Mmm>1 TeV
  • Irreducible background from Drell-Yan, also ZZ, WW, WW, tt (suppressed after selection cuts)
  • PYTHIA with ISR/FSR + CTEQ6L, LO + K=1.38
  • Full (GEANT-4) simulation/reco +

L1 + HLT(riger)

  • Theoretical uncert.
  • m and tracker misalignment, trigger and off-line recon. inefficiency, acceptance due to PDF

Confidence limits for

1 fb-1: 3.9-5.5 ТеV for n=6..3

10 fb-1: 4.8-7.2 ТеV for n=6..3

100 fb-1: 5.7-8.3 ТеV for n=6..3

300 fb-1: 5.9-8.8 ТеV for n=6..3

Getting ready for the LHC, Madrid

Oct 23-27, 2006

Belotelov et al.,

CMS NOTE 2006/076, CMS PTDR 2006

slide23

ADD Discovery Limit: G Exchange

Virtual graviton production

CMS Confidence limits:

1 fb-1: 3.9-5.5 ТеV for n=6..3

10 fb-1: 4.8-7.2 ТеV for n=6..3

100 fb-1: 5.7-8.3 ТеV for n=6..3

300 fb-1:5.9-8.8 ТеV for n=6..3

V. Kabachenko et al.

ATL-PHYS-2001-012

Fast MC

Getting ready for the LHC, Madrid

Oct 23-27, 2006

Belotelov et al.,

CMS NOTE 2006/076, CMS PTDR 2006

experimental signature for model

Branching Fraction

10-2

10-4

10–6

10-8

g

W

u

Z

RS model

t

= Mple-kRc

Dilepton channel

H

Tevatron 700 GeV GKK

Experimental Signature for Model

RS

  • Model parameters:
  • Gravity Scale:
  • 1st graviton excitation mass: m1
  • = m1Mpl/kx1, & mn=kxnekrc(J1(xn)=0)
  • Coupling constant: c= k/MPl
  • 1 = m1 x12 (k/Mpl)2

5D curve space with AdS5 slice:

two 3(brane)+1(extra)+time!

Resonance

position

Coupling proportional to p-1 for KK levels above the fundamental level (n>=1) for n=0 graviton couples with the gravitational strenght

  • Couplings of each individual KK excitation are determined by the scale, = Mple-kRc ~ TeV massesmn = kxne-krc (J1(xn)=0)

width

Signature:Narrow, high-mass resonance states in dilepton/dijet/diboson channels

k = curvature, R = compactification radius

400 600 800 1000

K/MPl

Mll (GeV)

d/dM (pb/GeV)

10-2

10-4

10-6

10-8

10-10

KK excitations can be excited individually on resonance

700 GeV KK Graviton at the Tevatron

k/MPl = 1,0.7,0.5,0.3,0.2,0.1 from

top to bottom

1

0.5

0.1

0.05

0.01

At the LHC only the 1st excitations are likely to be seen at the LHC, since the other modes are suppressed by the falling parton distribution functions.

LHC

1500 GeV GKK and subsequent tower states

1000 3000 5000

Mll (GeV)

Allenach et al, JHEP 9 19 (2000), JHEP 0212 39 (2002)

Davoudiasl, Hewett, Rizzo hep-ph0006041

Getting ready for the LHC, Madrid

Oct 23-27, 2006

present rs constraints
Present RS Constraints

D0 performed combined ee+gg (diem search)

CDF performed ee & gg search, then combine

Present Experimental Limits

Theoretical Constraints

  • c>0.1 disfavoured as bulk curvature becomes to large (larger than the 5-dim Planck scale)
  • Theoretically preferred Lp<10TeV assures no new hierarchy appears between mEW and Lp

Getting ready for the LHC, Madrid

Oct 23-27, 2006

  • Theoretically preferred Lp<10TeV, otherwise the model would no longer be interesting for solving the hierarchy problem – assures no new hierarchy appears between mEW and Lp
slide26

RS1 Discovery Limit

100 fb-1

MG=1.5 TeV

  • Best channels to search in are G(1)e+e- and G(1)gg due to the energy and angular resolutions of the LHC detectors
  • G(1)e+e- best chance of discovery due to relatively small bkdg, from Drell-Yan*

Di-electron

  • HERWIG
  • Main Bkdg: Drell-Yan
  • Model-independent analysis
  • RS model with k/MPl=0.01 as a reference (pessimisitc scenario)
  • Fast Simulation

Sensitive at 5s up to 2080 GeV

*Reach goes up to 3.5 TeV for c=0.1 for a 20% measurement of the coupling.

Allenach et al, hep-ph0006114

Allenach et al, hep-ph0211205

*

Getting ready for the LHC, Madrid

Oct 23-27, 2006

slide27

RS1 Model Parameters

A resonance could be seen in many other channels: mm, gg, jj, bbbar, ttbar, WW, ZZ, hence allowing to check universality of its couplings:

e

Relative precision achievable (in %) for measurements of s.B in each channel for fixed points in the MG,Lp plane. Points with errors above 100% are not shown.

Also the size (R) of the ED could also be estimated from mass and cross-section measurements.

Allenach et al, hep-ph0211205

Allenach et al, JHEP 9 19 (2000), JHEP 0212 39 (2002)

Getting ready for the LHC, Madrid

Oct 23-27, 2006

BR(G→) = 2 * BR(G→ee)

slide28

RS1 Model Determination

Spin-2 could be determined (spin-1 ruled out) with 90% C.L. up to MG = 1720 GeV

100 fb-1

MG=1.5 TeV 100 fb-1

e+e-

MC = 1.5 TeV

LHC

Note: acceptance at large pseudo-rapidities is essential for spin discrimination (1.5<|eta|<2.5)

Allanach et al, hep-ph 0006114

Getting ready for the LHC, Madrid

Oct 23-27, 2006

Stacked histograms

Spin-2 nature of the G(1) can be measured :

For masses up to 2.3 TeV (c=0.1) there is a 90 % chance that the spin-2 nature of the graviton can be determined with a 95 % C.L.

slide29

RS1 Discovery Limit

I. Belotelov et al.

CMS NOTE 2006/104

CMS PTDR 2006

Di-lepton states

G1μ+μ-

c=0.01

100 fb-1

c=0.1

100 fb-1

Solid lines = 5s discovery

Dashed = 1s uncert. on L

  • Two muons/electrons in the final state
  • Bckg: Drell-Yan/ZZ/WW/ZW/ttbar
  • PYTHIA/CTEQ6L
  • LO + K=1.30 both for signal and DY
  • Full (GEANT-4) and fast simulation/reco
  • Viable L1 + HLT(rigger) cuts
  • Theoretical uncert.
  • Misalignment, trigger and off-line reco
  • inefficiency, pile-up

Misalignment during 1st period when the momentum resolution will be reduced from 1-2% to 4-5%.

G1e+e-

B. Clerbaux et al.

CMS NOTE 2006/083

CMS PTDR 2006

Getting ready for the LHC, Madrid

Oct 23-27, 2006

Likelihood estimator based on event counting suited for small event samples: S=√(2[(S+B)log(1+S/B)-S])>5

slide30

RS1 Discovery Limit

Di-photon states

G1

  • Two photons in the final state
  • Bckg: prompt di-photons, QCD hadronic jets
  • and gamma+jet events, Drell-Yan e+e-
  • PYTHIA/CTEQ5L
  • LO for signal, LO + K-factors for bckg.
  • Fast simulation/reco + a few points with
  • full GEANT-4 MC
  • Viable L1 + HLT(rigger) cuts
  • Theoretical uncert.
  • Preselection inefficiency

M.-C. Lemaire et al.

CMS NOTE 2006/051

CMS PTDR 2006

c=0.1

Di-jet states

K. Gumus et al.

CMS NOTE 2006/070

CMS PTDR 2006

  • Bckg: QCD hadronic jets
  • L1 + HLT(rigger) cuts

5 Discovered Mass: 0.7-0.8 TeV/c2

Getting ready for the LHC, Madrid

Oct 23-27, 2006

cms rs discovery limits
CMS RS Discovery Limits

G1μ+μ-

G1

c>0.1 disfavoured as bulk curvature becomes to large (larger than the 5-dim Planck scale)

Theoretically preferred Lp<10TeV

G1e+e-

LHC completely covers the region of interest

Getting ready for the LHC, Madrid

Oct 23-27, 2006

slide32

TeV-1 Extra Dimension Model

  • I. Antoniadis, PLB246 377 (1990)
  • Multi-dimensional space with orbifolding
  • (5D in the simplest case, n=1)
  • The fundamental scale is not planckian:
  • MD ~ TeV
  • Gauge bosons can travel in the bulk
    •  Search for KK excitations of Z,g..
  • Fermion-gauge boson couplings
  • can be exponentially suppressed
  • for higher KK-modes
  • Fundamental fermions (quarks/leptons) can be
  • localized at the same (M1) or
  • opposite (M2) points of orbifold
  •  destructive (M1) or constructive (M2)
  • interference of the KK excitations
  • with SM model gauge bosons

New Parameters

R=MC-1 : size of the compact dimension

MC : corresponding compactification scale

M0 : mass of the SM gauge boson

Characteristic Signature: KK excitations of the gauge bosons appearing as resonances with masses : Mn = √(M02+n2/R2) where (n=1,2,…) & also interference effects!

G. Azuelos, G. Polesello

EPJ Direct 10.1140 (2004)

ppZ1KK/1KKe+e-

me+e- (GeV)

Getting ready for the LHC, Madrid

Oct 23-27, 2006

Mn = M0

In M1 case the KK gauge states couplings to SM fermions are the same as the SM ones but scaled by a factor of √2

present constraints on tev 1 ed
Present Constraints on TeV-1 ED

D0 performed the first dedicated experimental search for TeV-1 ED at a collider

Search for effects of virtual exchanges of the KK states of the Z and g

  • Search Signature: Signal has 2 distinct features:
  • enhancement at large masses (like LED)
  • negative interference between the 1st KK state of the Z/g and the SM Drell-Yan in between the Z mass and MC

diEM search 200 pb-1

Lower limit on the compactification scale of the longitudinal ED: MC>1.12 TeV at 95% C.L.

predicted background

L = 200pb-1

SM Drell-Yan

Better Limit: from precision electroweak data

TeV-1 ED signal hc=5.0 TeV-2

MC≥4 GeV

World Combined Limit MC>6.8 TeV at 95% C.L, dominated by LEP2 measurements

Getting ready for the LHC, Madrid

Oct 23-27, 2006

slide34

TeV-1 ED Discovery Limits

Di-electron states (ZKK decays)

  • Two high pT isolated electrons in the final state
  • Bckg: irreducible: Drell-Yan
  • Also ZZ/WW/ZW/ttabr
  • Signal and Bkgd: PYTHIA, CTEQ61M, PHOTOS used for inner bremsstrahlung production
  • LO + K=1.30 for signals,
  • LO + K-factors for bckg.
  • Full (GEANT-4) simulation/reco
  • with pile-up at low lum. (~1033cm-2s-1)
  • L1 + HLTrigger cuts
  • Theoretical uncert.

5 discovery limit of

ppZ1KK/1KKe+e-

(M1 model)

With L=30/80 fb-1 CMS will be able to detect a peak in the e+e- invar. mass distribution if MC<5.5/6 TeV.

B. Clerbaux et al.

CMS NOTE 2006/083

CMS PTDR 2006b

Getting ready for the LHC, Madrid

Oct 23-27, 2006

Saturation for E>1.7TeV in the barrel and 3TeV in the end-caps

EM energy corrected for energy leakage in the HAD cal. and for ECAL electronics saturation: (above)

slide35

TeV-1 ED Discovery Limits

ATLAS expectations for e and μ:

PYTHIA + Fast simu/paramaterizedreco + Theor. uncert.

In ee channel experimental resolution is smaller than the natural width of the Z(1), in mm channel exp. momentum resol. dominates the width

g(1)/Z(1)→e+e-/m+m-

Worse resolution for m

2 TeV e in ATLFAST:

DE/E~0.7 %

~20% for m

  • Requiring >10 events above a given mll and S= (N-NB)/√NB > 5

With 100 fb-1 ATLAS will be able to detect resonance if MC (R-1)<5.8 TeV (ee+mm)

  • Acceptance for leptons: |h|<2.5

Even for lowest resonances of MC (4 TeV), no events would be observed for the n=2 resonances of Z and g at 8 TeV (Mn = √(M02+n2/R2)), which would have been the most striking signature for this kind of model.

G. Azuelos, G. Polesello

EPJ Direct 10.1140 (2004)

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Oct 23-27, 2006

G. Azuelos, G. Polesello (Les Houches 2001 Workshop Proceedings), Physics at TeV Colliders, 210-228 (2001)

slide36

TeV-1 ED Discovery Limits

ATLAS expectations for e and μ:

PYTHIA + Fast simu/paramaterizedreco + Theor. uncert.

In ee channel experimental resolution is smaller than the natural width of the Z(1), in mm channel exp. momentum dominates the width

ATLAS Mc=4 TeV

g(1)/Z(1)→e+e-/m+m-

Worse resolution for m

2 TeV e in ATLFAST:

DE/E~0.7 %

~20% for m

  • Requiring >10 events above a given mll and and S= (N-NB)/√NB > 5

With 100 fb-1 ATLAS will be able to detect resonance if MC (R-1)<5.8 TeV (ee+mm)

  • Using a maximum likelihood method to fit the reconstructed distributions describing the kinematics of the event:

G. Azuelos, G. Polesello

EPJ Direct 10.1140 (2004)

With 300 fb-1 can reach 13.5 TeV (ee+mm)

Getting ready for the LHC, Madrid

Oct 23-27, 2006

G. Azuelos, G. Polesello (Les Houches 2001 Workshop Proceedings), Physics at TeV Colliders, 210-228 (2001)

distinguishing z 1 from z rs g
Distinguishing Z(1) from Z’, RS G
  • Spin 1 Z(1) signal can be distinguished from a spin-2 narrow graviton resonance using the angular distribution of its decay products.
  • Z(1) can also be distinguished from a Z’ with SM-like couplings using the distribution of the forward-backward asymmetry: due to contributions of the higher lying states, the interference terms and the additional √2 factor in its coupling to SM fermions.

The Z(1) can be discriminated for masses up to about 5 TeV with L=300fb-1.

4 TeV resonances

Z(1) or Z’ or RS Graviton?

ATLAS

G. Azuelos, G. Polesello

EPJ Direct 10.1140 (2004)

Getting ready for the LHC, Madrid

Oct 23-27, 2006

G. Azuelos, G. Polesello

EPJ Direct 10.1140 (2004)

slide38

TeV-1 ED Discovery Limits

WKK decays

W1  e

  • Isolated high-pT lepton + missing ET
  • Invmass (l,n) > 1 TeV, veto jets
  • Bckg: irreducible bkdg: Wen,

Also pairs: WW, WZ, ZZ, ttbar

  • Fast simulation/reco

R-1=4 TeV

R-1=5 TeV

R-1=6 TeV

Sum over 2 lepton flavours

For L=100 fb-1 a peak in the lepton-neutrino transverse invariant mass (mTln) will be detected if the compactification scale (MC= R-1) is < 6 TeV

SM

SM

mTen (GeV)

If a peak is detected, a measurement of the couplings of the boson to the leptons and quarks can be performed for MC up to ~ 5 TeV.

G. Polesello, M. Patra

EPJ Direct, ATLAS 2003-023

G. Polesello, M. Patra

EPJ Direct C 32 Sup.2 (2004) pp.55-67

Getting ready for the LHC, Madrid

Oct 23-27, 2006

slide39

TeV-1 ED Discovery Limits

WKK decays

W1  e

If no signal is observed with100 fb-1 a limit of MC > 11.7 TeV can be obtained from studying the mTendistribution below the peak:

R-1=4 TeV

R-1=5 TeV

Here: suppression in s

R-1=6 TeV

- due to –ve interference (M1) between SM gauge bosons and the whole tower of KK excitations

SM

- sizable even for MC above the ones accessible to a direct detection of the mass peak.

SM

mTen (GeV)

- Can’t get such a limit with Wmn since momentum spread - can’t do optimised fit which uses peak edge

G. Polesello, M. Patra

EPJ Direct, ATLAS 2003-023

G. Polesello, M. Patra

EPJ Direct C 32 Sup.2 (2004) pp.55-67

Getting ready for the LHC, Madrid

Oct 23-27, 2006

slide40

TeV-1 ED g* Discovery Limits

This is more challenging than Z/W which have leptonic decay modes

Detect KK gluon excitations (g*) by reconstructing their hadronic decays (no leptonic decays).

Detect g* by (1) deviation in dijet s

(2) analysing its decays into heavy quarks

SM

SM

Coupling of g* to quarks = √2 * SM couplings

 g*  wide resonances decaying into pairs of quarks

Getting ready for the LHC, Madrid

Oct 23-27, 2006

slide41

TeV-1 ED g* Discovery Limits

Reconstructed mass peaks

Gluon excitation decays

M=1 TeV

  • bbar or ttbar jets
  • For ttbar one t is forced to decay leptonically
  • Bckg: SM continuum bbar,

ttbar, 2 jets, W +jets

  • PYTHIA
  • Fast simulation/reco

M=1 TeV± 200 GeV

Width expected to be

G(g*) = 2 asM where M=g* mass

 G(g*) ~ 200 GeV for M=1 TeV

SM

M=1 TeV

For M=1 TeV natural width ~= experimental effects (fragmentation and detector resolution)

Getting ready for the LHC, Madrid

Oct 23-27, 2006

L. March, E. Ros, B. Salvachua,

ATL-PHYS-PUB-2006-002

slide42

TeV-1 ED g* Discovery Limits

Reconstructed mass peaks

M=1 TeV

Mass windows used to evaluate the significance

M=2 TeV

M=1 TeV± 200 GeV

M=3 TeV± 600 GeV

3 years at HL running

With 300 fb-1 Significance of 5 achieved for:

ttbar channel: R-1 = 3.3 TeV

bbar channel: R-1 = 2.7 TeV

Getting ready for the LHC, Madrid

Oct 23-27, 2006

L. March, E. Ros, B. Salvachua,

ATL-PHYS-PUB-2006-002

slide43

TeV-1 ED g* Discovery Limits

M=1 TeV

M=2 TeV

Although with 300 fb-1 Significance of 5 achieved for:

bbar channel: R-1 = 2.7 TeV

However, it is not in general possible to obtain a mass peak well separated from the bkdg.  it is unlikely that an excess of events in the g*bbar channel could be used as evidence of the g* resonance, since there are large uncertainties in the calculations of the bkdgs. For M=1TeV the peak displacements could be used as evidence for new physics if the b-jet energy scale can be accurately computed.

Getting ready for the LHC, Madrid

Oct 23-27, 2006

L. March, E. Ros, B. Salvachua,

ATL-PHYS-PUB-2006-002

slide44

TeV-1 ED g* Discovery Limits

But in g*ttbar, the bkdg is mainly irreducible and not so large. g* resonance can be detected in this decay channel if the tt-bar s can be computed in a reliable way.

M=1 TeV± 200 GeV

M=3 TeV± 600 GeV

Conclusion:

g* decays into b-quarks are difficult to detect, decays into t-quarks might yield a significant signal for g* mass below 3.3 TeV.

This could be used to confirm the presence of g* in the case that an excess in the dijet s is observed.

Getting ready for the LHC, Madrid

Oct 23-27, 2006

L. March, E. Ros, B. Salvachua,

ATL-PHYS-PUB-2006-002

slide45

600

570

g1

1

Q1

Z1

L1

Universal Extra Dimensions

Standard/Minimal UED

  • All particles can travel into the bulk, so each SM particle has an infinite tower of KK partners
  • Spin of the KK particles is the same as their SM partners
  • In minimal UED: 1 ED compactified in an orbifold (S1/Z2) of size R
    • KK parity conservation  the lightest massive KK particle (LKP) is stable (dark matter candidate).
    • Level one KK states must be pair produced
  • Mass degeneration except if radiative corrections included

The model parameters: compactificaton radius R, cut-off scale , mh

Thick/Fat brane

  • SM brane is endowed with a finite thickness in the ED
  • Gravity-matter interactions break KK number conservation:
  • ● 1st level KK states decay to G+SM.
  • ● If radiative corrections  mass degeneracy is broken and  and leptons are produced.

Getting ready for the LHC, Madrid

Oct 23-27, 2006

slide46

Present Constraints on UED

Bounds to the compactification scale:

  • Precision EWK data measurements set a lower bound of R-1 > 300 GeV
  • Dark matter constraints imply that 600 < R-1 <1050 GeV

Phys. Rev. D64, 035002 (2001) Appelquist, Cheung, Dobrescu

Servant , Tait, Nucl. Phys. B650,391 (2003)

Getting ready for the LHC, Madrid

Oct 23-27, 2006

slide47

l

l

1

Z1

p

p

q

L1

q

Q1

Geo accep

L1,HLT

2 OSSF

4 ISO

b-tag veto

pTl<

ETmiss

Z veto

600

g1

g1

q

Q1

570

q

L1

1

Z1

l

l

g1

1

Z1

Q1

L1

UEDDiscovery Limit

Standard UED

Final State:

4 low-pT isolated leptons (2 pairs of opposite sign, same flavour leptons) + n jets + missing ET (from 2 undetected g1)

Getting ready for the LHC, Madrid

Oct 23-27, 2006

Used a possion stat method

slide48

UEDDiscovery Limit

Standard UED

  • 4 leptons in the final state + missing pT
  • Irreducible Bckg: ttbar + n jets (n = 0,1,2), 4 b-quarks, ZZ, Zbbar
  • To improve bkdg rejection over signal: apply b-tagging and Z-tagging vetoes
  • CompHEP for signal and CompHEP, PYTHIA, Alpgen for bckg. with CTEQ5L
  • Full simulation/reco + L1 + HLT(rigger) cuts
  • Theoretical and experimental uncert.

Discovery sensitivity

Studied for low lum run ~2x1033cm-2s-1

Getting ready for the LHC, Madrid

Oct 23-27, 2006

Used a possion stat method

slide49

G

jet

p

p

q1,g1

jet

q1,g1

G

5

UEDDiscovery Limit

Thick brane in UED with TeV-1 size

Significance vs Mass of 1st KK excitation

S

100 fb-1

~2.7 TeV

  • 2 back-to back jets + missing ET (>775 GeV)
  • Irreducible Bckg: Z() jj, W(l) jj
  • PYTHIA/CTEQ5L + SHERPA for bckgr.
  • Fast simulation/reco

5s discovery possible at ATLAS with 100 fb-1 if first KK excitation mass < 2.7 TeV

Getting ready for the LHC, Madrid

Oct 23-27, 2006

P. H. Beauchemin, G. Azuelos

ATL-PHYS-PUB-2005-003

slide50

LHC Start-up Expectations

Getting ready for the LHC, Madrid

Oct 23-27, 2006

conclusions
Conclusions
  • The discovery potential of both experiments makes it possible to investigate if extra dimensions really exist within various ED scenarios at a few TeV scale:
      • Large Extra-Dimensions (ADD model)
      • Randall-Sundrum (RS1)
      • TeV-1 Extra dimension Model
      • Universal Extra Dimensions
  • Reaches in different channels depend on the performance of detector systems: proper energy, momentum, angular reconstruction for high-energy leptons and jets, Et measurement, b-tagging and identification of prompt photons
  • New results have been predicted with data collected in the start-up LHC weeks (integrated luminosity<1 fb-1)

For methods to disentangle new physics from SM physics, see lectures by M. Mangano.

For Gravitaton/Black Holes see talk by: B. Webber.

Getting ready for the LHC, Madrid

Oct 23-27, 2006

slide52
The End!

Backup slides…

Getting ready for the LHC, Madrid

Oct 23-27, 2006

present add emission limits1

q

q

q

qqgGKK

dominate sub-process for n>2

q

g

q

g

q

g

g

q

q

GKK

GKK

GKK

qggGKK

q

q

q

q

q

q

q

g

q

g

g

GKK

GKK

g

GKK

gggGKK

g

g

g

g

g

g

g

g

g

g

g

GKK

g

GKK

GKK

sfalls as 1/MDn+2 for all sub-processes

g

g

q

q

g

g

g

g

_

_

Gkk

Gkk

g

g

Gkk

Gkk

q

q

Present ADD Emission Limits

LEP and Tevatron results are complementary

For n>4:

CDF limits best

jet+MET

For n<4:

LEP limits best

Tevatron better at large values of n,

because of the higher energy, which is a bigger effect at larger values of n.  

sa total number of possible modes in the KK tower NKK

s a NKK a √(s-hat)

But this is true for each ED, so s a (√(s-hat))n

the difference in energy is a bigger effect for n=6 than n=2

g+MET

g+MET at LEP is cleaner & has lower backgrounds than jet+MET (Tevatron), so the precision of their experiments wins out for lower values of n

Getting ready for the LHC, Madrid

Oct 23-27, 2006

add g exchange

Dilepton Channel

Z/

l-

SM events expected

to be distributed

uniformly

in cosq*

l+

l+

l+

l-

l-

l-

Signal events are accumulated

at low cosq* &

high mass

ADD: G Exchange?

Search for spin-2 broad σ change

 study deviations in invariant mass & angular distribution from SM processes

Search Signature

Deviations in (ee, mm, gg) cross sections () and angular distributions from SM processes

SM

ED

Diphoton Channel

low mass, high cosq*

SM

ED

Getting ready for the LHC, Madrid

Oct 23-27, 2006

  • Clean experimental signature (ee,mm) even in a hadron collider
  • Low backgrounds & Z0 peak used as a calibration point (ee,mm)
slide55

Angular distributions

Spin-1/Spin-2 Discrimination

Spin-1 States:Z from extended gauge models, ZKK

Spin-2 States:RS1-graviton

Method: unbinned likelihood ratio statistics incorporating the angles in of the decay products the Collins-Soper farme (R.Cousins et al. JHEP11 (2005) 046). The statististical technique has been applied to fully simu/reco events.

Z’ vs RS1-graviton

I. Belotelov et al.

CMS NOTE 2006/104

CMS PTDR 2006

Older results on spin discrimination from ATLAS can be found

B.C. Allanach et al, JHEP 09 (2000) 019; ATL-PHYS-2000-029

Getting ready for the LHC, Madrid

Oct 23-27, 2006