18 July 2003L.Vacavant - Search for extra dimensions at LHC - EPS Aachen1 Search for extra dimensions at LHC Laurent Vacavant Lawrence Berkeley National

18 July 2003 L.Vacavant - Search for extra dimensions at LHC - EPS Aachen 1

Search for extra dimensions at LHC

Laurent Vacavant

Lawrence Berkeley National Laboratory

EPS Aachen / String theory and extra dimensions / 18 July 2003

on behalf of the ATLAS and CMS collaborations


Size of extra dimensions

Spectrum of Studies at LHC

Large Extra Dimensions• direct production of gravitons• virtual effects of gravitons

TeV-1-sized ED• Kaluza-Klein excitations ofgauge bosons

Warped ED• narrow resonance of graviton• radion

TransPlanckian physics:• elastic scattering• black holes (talk by G. Landsberg)

Other implications:• gauge coupling unification• singlet neutrino


LHC Studies

Objectives:

establish the sensitivity to the signals• start from Feynman rules derived by theorists• implement the partonic X-sections in a generator• use a fast simulation of detector

• acceptance• efficiency• resolution

• consider various physics & instrumental backgrounds

try to characterize the model• measurement of unique features• determination of the number of dimensions

parameters of underlying model ?


Detector Performance & Simulation

Fast simulation:• many aspects relevant to ED searches validated w/ full sim.:

• missing energy (cracks,….): OK for large ET

• mass resolution : thorough studies for H

Caveat:• systematic effects: linearity at TeV, instrumental bckgd, …

Detector Performance:• needed for first searches: missing ET, high-pT electron, photon, …• detectors already optimized for that (SUSY, Higgs)• example: resolution for electrons (ATLAS):

12% 24.5%0.7%

( ) T

E

E EE GeV

~ 0.8%m

m

(@ 500 GeV)


Large Extra Dimensions Kaluza-Klein Gravitons

ADD scenario: (cf. talk by I.Antoniadis)• gravity becomes strong at TeV size of ED 1 mm• SM confined in 4D, only gravity in the bulk• two parameters:

• number of extra (compactified) dimensions: • new fundamental mass scale MD:

Gravitons & Kaluza-Klein states:• in the bulk: gravitational interaction massless G• in 4D: KK states G(k), mk

2 = m02 + k2/RC

2

• coupling: universal & weak (1/MPl(4)), but large # of states

MD~ TeV RC ~ mm (for =2)

Constraints (experimental + astrophysics): talk by S.Mele


Large Extra DimensionsDirect Production of Kaluza-Klein Gravitons

Direct production at LHC:

Signatures: monojet + missing energy, (photon + missing energy)

ATLAS study:• partonic cross-sections from G.Giudice,R.Rattazzi, J.D.Wells Nucl.Phys. B54 3 (1999)• implemented in ISAJET• ATLAS fast-simulationBackground for jet signal:• jZ(), jW(), jW(e), jW()

Selection:• trigger: jet (||<5) + ET

miss

• lepton veto (||<2.5)• central jet (||<2.5)• large ET

miss

ATLAS: LV, I. Hinchliffe J.Phys. G:

Nucl. Part. Phys. 27 1839 (2001)



= 2 = 3 = 4

MDmax 9.1 TeV 7.0 TeV 6.0 TeV

R compact 8 m 2 Å 1 pm

MDmin ~ 4 TeV ~ 4.5 TeV ~ 5 TeV

= 2

MDmax 4.5 TeV

R compact 32 m

MDmin ~3.5 TeV

Missing energy: Sensitivity for 100 fb-1:

jet + G(k) signature:

photon + G(k) signature:

• S/B > 5• > 100 signal events• ET(jet) > 1 TeV

100 fb-1

(1 year @ 1034 cm-2s-1) discovery

confirm.

NB: effective theory, valid only for MD

minDMs ˆ



Characterization of the model: measure both MD and

Precise measurement of Xsection:• difficult: case (=2, MD= 5 TeV) very similar to the case (=4, MD= 4 TeV) for instance• not (yet) investigated in details

Run at a different CME:

(10 TeV) / (14 TeV)

• good discrimination if• 5% accuracy on (10)/(14)• > 50 fb-1 @ 10 TeV

• new CME close to 14 TeV(otherwise small overlap of regions allowed by eff. theory)


Large Extra DimensionsVirtual Exchange of Kaluza-Klein Gravitons

Virtual exchange of gravitons at LHC:

Signatures: deviations from SM in Drell-Yan X-sections, asymmetries (sensitivity mostly from interference terms, KK exchange Ms

-8)

ATLAS study:• partonic cross-sections • amplitude divergent for > 1: naive cut-off at Mll, < 0.9 MS

ATLAS: V. Kabachenko, A. Miagkov,

A. Zenin, ATL-PHYS-2001-012

K.Cheung hep-ph/0003306, J.L.Hewett hep-ph/9811356



dN

dpp

Meff = 4 TeVMeff = 4 TeV

Signatures: qq,gg , ll, (WW, tt, …)

• excess over DY events in di-lepton, di-photon mass distributions• some s-channel processes not present at tree-level in SM:

more central production for



PT > 800 GeVmgg > 1 TeV

Sensitivity for 100 fb-1:

5.1 TeV 6.6 TeV

Mostly a discovery channel:• no sensitivity on • w/o specifying UV theory, Ms cannot be related to MD


TeV-1-sized Extra DimensionsKaluza-Klein Gauge Bosons

Basics:• one extra dimension• compactified on a S1/Z2 orbifold• radius of compactification small enough gauge bosons in the bulk• fermions localized on:

• a fixed point (M1 model): invariance under y -y• opposite fixed points (M2 model): under y y + 2R

• Kaluza-Klein spectra for Z(k), W(k) : mk2 = m0

2 + k2MC2

• for MC = 4 TeV: m1 = 4 TeV, m2 = 8 TeV look for pp (1)/Z(1) l+l- on top of SM Drell-Yan

ATLAS study:• matrix elements from T.Rizzo• implemented in Pythia• ATLAS fast simulation

T. Rizzo, PRD 61 055005 (2000)

ATLAS: G.Azuelos, G.Polesello, Proc. Les Houches 2001

(cf. talk by I.Antoniadis)


TeV-1-sized Extra Dimensions (1)/Z(1) Kaluza-Klein Gauge Bosons

Signatures: (1)/Z(1) e+e-, +-

Mc = 4 TeV Mc = 4 TeV

SM

M2

M1

m(e+e-) m(l+l-)

e+e-

+-

• 2 TeV electron in ATLAS: E/E ~ 0.7 % (~20 % for a muon)• acceptance for leptons: || < 2.5


TeV-1-sized Extra Dimensions(1)/Z(1) Kaluza-Klein Gauge Bosons

Sensitivity from peak region:

for 100 fb-1, S/B > 5, S > 10 : MCmax = 5.8 TeV

Optimal reach (using interferences in tail region):

electrons e+

100 fb-1 200 fb-1 300 fb-1 300 fb-1

9.5 TeV 11 TeV 12 TeV 13.5 TeV

detailed study of systematics:• energy scale, calibration• higher order QCD & EW corrections• PDFs

likelihood fit analysis w/ MC experiments


TeV-1-sized Extra Dimensions (1)/Z(1) Kaluza-Klein Gauge Bosons

Characterization of the model:

M2

G*

Z’

M1

Z(1) or Z ‘ or RS graviton ??Forward-backward asymetries:

100 pb-1


TeV-1-sized Extra DimensionsW(1) Kaluza-Klein Gauge Bosons

Ditto for W(1):

Sensitivity for 100 fb-1:

from peak optimal

~ 6 TeV ~ 9 TeV

Discrimination from W ‘:

• more difficult• under study

ATLAS: G.Polesello, M. Prata, preliminary


Warped Extra DimensionRandall-Sundrum model: KK graviton narrow resonance

L

ELE

Golden channel: G(1) e+e-

• good acceptance• good energy resolution• good angular resolution• also G(1)

Main features to check:• universal couplings:G(1) +-, WW, ZZ, jj • spin 2• measure rc ?

KK graviton excitations G(k)

(cf. talk by I.Antoniadis)

• scale

• coupling & width: c = k/MPl

• 0.01 < k/MPl < 0.1• mass spectrum:

mn = k xn exp(-krc)

ATLAS: B.C. Allanach, K.Odigari, A. Parker, B. Webber JHEP 9 19 (2000), ditto + M.J.Palmer, A. Sabetfakhri hep-ph/0211205

CMS: C.Collard, M.-C. Lemaire, P.Traczyk, G.Wrochna hep-ex/0207061; I. Golutvin, P.Moissenz, V.Palichik, M.Savina, S.Shmatov

Planck brane SM brane



Signature: G(1) e+e-

ATLAS, e+e-

mG= 1.5 TeV, c = 0.01CMS, e+e-

mG= 1.5 TeV, c = 0.01CMS, e+e-

mG= 4 TeV, c = 0.1

100 fb-1

discovery



Sensitivity:

LHC covers completely the

c =

k/M

Pl

mG (GeV)

CMS, 100 fb-1

interesting region



Spin determination:ATLAS, e+e-, 100 fb-1

mG= 1.5 TeV, c = 0.01

Signal:• from gluon fusion 1 – cos4*

• from quark annihilation1 – 3cos2* + 4cos4*

Spin-1 (Z ‘): 1 + cos2*

Drell-Yan SM

NB: acceptance at large • coverage to 2.4-2.5 is essential• almost no discrimination spin 1/spin 2 for || < 1.5



Spin-1 hypothesis rejection:

large fraction of

c =

k/M

Pl

mG (GeV)

CMS, 100 fb-1

interesting regioncovered by LHC.


Warped Extra DimensionRandall-Sundrum model: the radion

The RS radion:• fluctuations of distance between branes• solving hierarchy problem requires krc~12• dynamical mechanism to do so, gives a mass to the radion, possibly lighter than G(1)

Radion phenomenology:• coupling similar to Higgs, mixes with Higgs ( parameter)• enhanced coupling to gluons• narrow width

W.D. Goldberger, M.B. Wise, PRL 83 4922 (1999)

G.Giudice, R.Rattazzi, J.D.Wells, hep-ph/0002178

Higgs

Radion =0Radion =1/6

ATLAS: G.Azuelos, D.Cavalli, H.Przysiezniak,LVEur.Phys.J direct C4 16 (2002)



Reinterpretation of Higgs signals:

100 fb-1

SM Higgs



Decay in two Higgses: hh bb

(TeV)

m=300 GeV

m=600GeV

0 1 4 43

0 10 333 -

1/6 1 2 57

1/6 10 250 -

Luminosity (fb-1) requiredfor 5 discovery:

Reach in with 30 fb-1:

• clean signature• good kinematical constraints• small background

max = 2.2 TeV (m=300 GeV)

Complementary channel: hh bb

max = 1.0 TeV (m=600 GeV)


Higgs doublet & right-handed neutrino

Model:• gives small masses w/o see-saw• singlet neutrino in the bulk• ~ R , coupling reduced by R

jethp E

MSSM

LH 100 fb-1

Study:• charged Higss (2HDM-II)• MSSM: only • in bulk: • asymmetry to discriminate:

measure polarization asymmetries use hadronic decays

ATLAS: K.Assamagan, A.Deandrea, Phys. Rev D 65 076006 (2002)

RH

R LH

( ) ( )

( ) ( )L R

L R

H HA

H H


Other studies (in a jumble)

Gauge coupling unification:• di-jet cross-sections

G.Balazs, B.Laforgehep-ph/0110217

Large Extra Dimensions:• direct production of graviscalars (stringy effects)

TransPlanckian elastic scattering

Universal ED scenario: faking SUSY ?Disentangling radion and Higgs: coupling measurements

Studies not covered in this talk:

On-going studies:

Next (see Les Houches 2003):

Black holes: MC Herwig + simulation (cf. talk by G.Landsberg)


Conclusion

A lot of models, with very rich and various phenomenology !

LHC experiments have studied/are studying many of them

The LHC will be able to probe the relevant region of the parameter space for most of the models studied so far

Thanks to my colleagues in ATLAS and CMS.Special thanks to: G. Azuelos, F. Gianotti, L. Pape, L. Poggioli, G. Polesello, S. Shmatov, P. Traczyk, G. Wrochna

Documents

18 July 2003L.Vacavant - Search for extra dimensions at LHC - EPS Aachen1 Search for extra dimensions at LHC Laurent Vacavant Lawrence Berkeley National