Transcript Document 7741658

Search for extra dimensions at LHC
Laurent Vacavant
Lawrence Berkeley National Laboratory
on behalf of the ATLAS and CMS collaborations
EPS Aachen / String theory and extra dimensions / 18 July 2003
18 July 2003
L.Vacavant - Search for extra dimensions at LHC - EPS Aachen
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Spectrum of Studies at LHC
Large Extra Dimensions
• direct production of gravitons
• virtual effects of gravitons
TeV-1-sized ED
• Kaluza-Klein excitations of
gauge bosons
Warped ED
• narrow resonance of graviton
• radion
TransPlanckian physics:
• elastic scattering
• black holes (talk by G. Landsberg)
18 July 2003
Other implications:
• gauge coupling unification
• singlet neutrino
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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 ?
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Detector Performance & Simulation
Detector Performance:
• needed for first searches: missing ET, high-pT electron, photon, …
• detectors already optimized for that (SUSY, Higgs)
• example: resolution for electrons (ATLAS):
E

E
m
m
12%
E (GeV )
~ 0.8%

24.5%
 0.7%
ET
(@ 500 GeV)
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, …
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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:
MD~ TeV  RC ~ mm (for =2)
Constraints (experimental + astrophysics): talk by S.Mele
Gravitons & Kaluza-Klein states:
• in the bulk: gravitational interaction  massless G
• in 4D: KK states G(k), mk2 = m02 + k2/RC2
• coupling: universal & weak (1/MPl(4)), but large # of states
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Large Extra Dimensions
Direct 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-simulation
Background for jet signal:
• jZ(), jW(), jW(e), jW()
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Selection:
• trigger: jet (||<5) + ETmiss
• lepton veto (||<2.5)
• central jet (||<2.5)
• large ETmiss
ATLAS: LV, I. Hinchliffe J.Phys. G:
Nucl. Part. Phys. 27 1839 (2001)
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Large Extra Dimensions
Direct Production of Kaluza-Klein Gravitons
Missing energy:
Sensitivity for 100 fb-1:
• S/B > 5
100 fb-1
(1 year @
1034 cm-2s-1)
• > 100 signal events
• ET(jet) > 1 TeV
 jet + G(k) signature:
discovery
=2
=3
=4
MDmax
9.1 TeV
7.0 TeV
6.0 TeV
R compact
8 m
2Å
1 pm
MDmin
~ 4 TeV
~ 4.5 TeV
~ 5 TeV
 photon + G(k) signature: confirm.
=2
NB: effective theory, valid only
for
sˆ  M D  MDmin
18 July 2003
MDmax
4.5 TeV
R compact
32 m
MDmin
~3.5 TeV
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Large Extra Dimensions
Direct Production of Kaluza-Klein Gravitons
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)
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Large Extra Dimensions
Virtual 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 K.Cheung hep-ph/0003306, J.L.Hewett hep-ph/9811356
• amplitude divergent for  > 1:
naive cut-off at Mll, < 0.9 MS
ATLAS: V. Kabachenko, A. Miagkov,
A. Zenin, ATL-PHYS-2001-012
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Large Extra Dimensions
Virtual Exchange of Kaluza-Klein Gravitons
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 
dN
d
Meff = 4 TeV
pp
Meff = 4 TeV

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Large Extra Dimensions
Virtual Exchange of Kaluza-Klein Gravitons
Sensitivity for 100 fb-1:
PT > 800 GeV
5.1 TeV
mgg > 1 TeV
6.6 TeV
Mostly a discovery channel:
• no sensitivity on 
• w/o specifying UV theory, Ms cannot be related to MD
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TeV-1-sized Extra Dimensions
Kaluza-Klein Gauge Bosons
Basics: (cf. talk by I.Antoniadis)
• 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 + 2R
• Kaluza-Klein spectra for Z(k), W(k) : mk2 = m02 + 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
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TeV-1-sized Extra Dimensions
(1)/Z(1) Kaluza-Klein Gauge Bosons
Signatures: (1)/Z(1)  e+e-, +• 2 TeV electron in ATLAS: E/E ~ 0.7 % (~20 % for a muon)
• acceptance for leptons: || < 2.5
Mc = 4 TeV
Mc = 4 TeV
M2
+-
M1
e+e-
SM
m(e+e-)
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m(l+l-)
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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):
likelihood fit analysis w/ MC experiments
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
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TeV-1-sized Extra Dimensions
(1)/Z(1) Kaluza-Klein Gauge Bosons
Characterization of the model:
Z(1)
or Z ‘ or RS graviton ??
Forward-backward asymetries:
M2
G*
Z’
M1
100 pb-1
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TeV-1-sized Extra Dimensions
W(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
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Warped Extra Dimension
Randall-Sundrum model: KK graviton narrow resonance
Golden channel: G(1)  e+eL
L
E
E
Planck brane
SM brane
KK graviton excitations
(cf. talk by I.Antoniadis)
•
•
•
•
G(k)
•
•
•
•
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 ?
scale 
coupling & width: c = k/MPl
0.01 < k/MPl < 0.1
ATLAS: B.C. Allanach, K.Odigari, A. Parker, B. Webber
mass spectrum:
JHEP 9 19 (2000), ditto + M.J.Palmer, A. Sabetfakhri
mn = k xn exp(-krc)
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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
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Warped Extra Dimension
Randall-Sundrum model: KK graviton narrow resonance
Signature: G(1)  e+eATLAS, e+emG= 1.5 TeV, c = 0.01
discovery
CMS, e+emG= 1.5 TeV, c = 0.01
CMS, e+emG= 4 TeV, c = 0.1
100 fb-1
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Warped Extra Dimension
Randall-Sundrum model: KK graviton narrow resonance
c = k/MPl
Sensitivity:
CMS, 100 fb-1
mG (GeV)
 LHC covers completely the interesting region
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Warped Extra Dimension
Randall-Sundrum model: KK graviton narrow resonance
Spin determination:
ATLAS, e+e-, 100 fb-1
mG= 1.5 TeV, c = 0.01
Signal:
• from gluon fusion
1 – cos4*
• from quark annihilation
1 – 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
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Warped Extra Dimension
Randall-Sundrum model: KK graviton narrow resonance
c = k/MPl
Spin-1 hypothesis rejection:
CMS, 100 fb-1
mG (GeV)
 large fraction of interesting region covered by LHC.
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Warped Extra Dimension
Randall-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) W.D. Goldberger, M.B. Wise, PRL 83 4922 (1999)
Radion phenomenology:
G.Giudice, R.Rattazzi, J.D.Wells, hep-ph/0002178
• coupling similar to Higgs, mixes with Higgs ( parameter)
• enhanced coupling to gluons
ATLAS: G.Azuelos, D.Cavalli, H.Przysiezniak,LV
• narrow width
Eur.Phys.J direct C4 16 (2002)
Higgs
Radion =0
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Radion =1/6
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Warped Extra Dimension
Randall-Sundrum model: the radion
Reinterpretation of Higgs signals:
SM Higgs
100 fb-1
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Warped Extra Dimension
Randall-Sundrum model: the radion
Decay in two Higgses:   hh   bb
• clean signature
• good kinematical constraints
• small background
Luminosity (fb-1) required
for 5 discovery:


(TeV)
m=300
GeV
m=600
GeV
0
1
4
43
0
10
333
-
1/6
1
2
57
1/6
10
250
-
Reach in  with 30 fb-1:
max = 2.2 TeV (m=300 GeV)
Complementary channel:
  hh  bb 
max = 1.0 TeV (m=600 GeV)
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Higgs doublet & right-handed neutrino
Model:
• gives  small masses w/o see-saw
• singlet neutrino  in the bulk
•  ~ R , coupling reduced by R
ATLAS: K.Assamagan, A.Deandrea,
Phys. Rev D 65 076006 (2002)
Study:
•
•
•
•
charged Higss (2HDM-II)
MSSM: only H    R
 in bulk: H    R   L
asymmetry to discriminate:
100 fb-1
H    L
MSSM
( H    L )  ( H    R )
A
( H    L )  ( H    R )
 measure polarization asymmetries
 use hadronic  decays
ph E   jet
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Other studies (in a jumble)
Studies not covered in this talk:
Gauge coupling unification:
• di-jet cross-sections
G.Balazs, B.Laforge
hep-ph/0110217
On-going studies:
Black holes: MC Herwig + simulation (cf. talk by G.Landsberg)
TransPlanckian elastic scattering
Large Extra Dimensions:
• direct production of graviscalars (stringy effects)
Next (see Les Houches 2003):
Universal ED scenario: faking SUSY ?
Disentangling radion and Higgs: coupling measurements
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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
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