Kaluza-Klein gluon production at the LHC

Farvah Nazila Mahmoudi(Uppsala University -

Sweden)

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

From Strings to LHC II – Bangalore – Dec. 20, 2007

in collaboration with M. Guchait and K. Sridhar

Randall-Sundrum Model RS1

Modified RS1

Collider search

Kaluza-Klein gluon

Tevatron constraints

LHC constraints

Conclusion

Contents

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

Idea:

We are confined on 3-brane

Graviton lives in the bulk

Brane world scenarios

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

SM fields

graviton

Typical scenarios:

Large (flat) Extra Dimensions

(Arkani-Hamed-Dimopoulos-Dvali,’98)

Warped (small) Extra Dimensions

(Randall-Sundrum,’99)

Setup:

Five-dimensional theory

Warped extra dimension

A slice of anti-de Sitter spacetime in five dimensions (AdS5)

Fifth dimension compactified on a S1

/Z2 orbifold

The compactification radius Rc is of the order of

Two branes: at orbifold fixed points = 0 and =

Randall-Sundrum Model (RS1)

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

Two D3-branes:

Randall-Sundrum Model (RS1)

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

5 dimensional metric:

Warp factor

UV/Planck brane

bulk

Planck

=0

UV/Planck brane

bulk

Planck

=0

IR/TeV brane

SM particle

=

= extra-dimension coordinate

K = mass scale

Rc = (modest-sized) radius

The warp factor acts as a conformal factor for the fields localized on the brane

Mass factors get rescaled by this factor

Randall-Sundrum Model (RS1)

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

Solve the hierarchy!

Randall-Sundrum Model (RS1)

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

Brane separation stabilized by a bulk scalar field

Discrete KK-spectrum with masses given by a common mass factor

multiplied by the zeroes of the Bessel function.

Interesting collider phenomenology

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

AdS/CFT correspondence RS model is dual to a 4-d effective theory incorporating

gravity

The dual theory is conformally invariant from the Planck scale down to the TeV scale

The KK excitations as well as the fields localized on the TeV brane are TeV-scale composites

The original RS theory is dual to a theory of TeV-scale compositeness of the entire SM

Deformation of the original scenario

unviable

Modifying the model:

Simplest possibility: modify the model so that only the Higgs field is localized on the TeV

brane while the rest of the SM fields are in the bulk

only the Higgs is composite

makes sense because only the scalar sector is natural

guiding principles:

flavour hierarchy,

consistency with electroweak precision tests

avoidance of flavour-changing neutral currents

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

Bulk Randall-Sundrum

The location of the fermions in the bulk:

To get a large Yukawa coupling (overlap with the Higgs) one needs to localize the fermion close to

the TeV brane

The fermions close to the Planck brane will have small Yukawa couplings

top sector:

Large Yukawa of the top proximity to the TeV brane

(t, b)L cannot be close to the TeV brane

tR needs to be localized close to the TeV brane

Bulk Randall-Sundrum

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

To avoid huge effects of FCNCs,

To be consistent with precision tests of the electroweak

sector:

the masses of the KK modes of the gauge bosons have

to be strongly constrained

bosons are found to be in the region of 2-3TeV

Bulk Randall-Sundrum

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

The best signal for this scenario is probably:

production of KK gluons

gluon KK modes near the TeV brane

Orthonormality of profiles of gluons and KK gluons

suppressed coupling

gg at a hadron collider cannot produce the KK gluon at leading order

KK gluon can, therefore, be produced by annihilation of light quarks

Production of Kaluza-Klein gluons

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

Large BR into right-handed top/anti-top pairs

g = gauge coupling

Non universal couplings to the SM particles

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

Kaluza-Klein gluon

What is the direct, model-independent bound that existing collider data can

provide ?

What is the direct, model-independent bound that existing collider data can

provide ?

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

Constraint from Tevatron

KK gluon with a mass just a little above the threshold: large branching into top pairs: about 92.5%

To this: add the central value of the SM production cross-section:

for mt = 175GeV

Tevatron Run II1.96 TeV in the center of mass

Experimental value:

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

Constraint from Tevatron

Direct bound!

95 C.L.

M. Guchait, F.M. and K. Sridhar, JHEP 0705, 103

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

Constraint from Tevatron

CTEQ4M

PDFLIB

Direct bound!

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

KK gluon at the LHC

Agashe et al., hep-ph/0612015

Production mechanism:

and annihilation

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

KK gluon at the LHC

Agashe et al., hep-ph/0612015

Discovery of the KK Gluon with M < 4 TeV

For 100 f b

-1 :

: produced from both gg and initial states through the usual QCD processes

KK gluon: radiated from one of the heavy-quark legs

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

Associate production with ttbar

Interesting:

gg initial state contributes to the associated production process

the process directly probes the coupling of the gKK to the tops which is an important feature

of the new dynamics.

The produced gKK decays into a pair

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

Associate production at the LHC

Background:

two non-resonant pairs coming from QCD processes

computed using ALPGEN

from gKK : large momenta

other : more moderate momenta

enhanced (signal / QCD background)

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

Associate production at the LHC

14 TeV in the center of massAssuming 100 fb-1 integrated luminosity

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

Signal kinematics: standard three-jet production

all three final-state particles in our case are massive

lower cut of 300 GeV on the pT of the t and the tbar coming from the decay of the gKK

and

a cut of 50 GeV on the each of the other pair

Associate production at the LHC

background cross section: 0.33

fb

Cuts

from gKK : pT > 300 GeV

other : pT > 50 GeV

significance = 5 M = 2790

GeV

M. Guchait, F.M. and K. Sridhar, arXiv:0710.2234

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

KK Gluon at the LHC

Mass obtained for a significance of 5 in

function of pT

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

M. Guchait, F.M. and K. Sridhar, arXiv:0710.2234

KK Gluon at the LHC

2 GMS1 results:

GMS1:

Using Tevatron data: First direct constraints on the KK gluon massThe lower bound is obtained to be about 770 GeV

GMS2:

Associate production process at the LHC: promising resultsLHC will probe masses in the range 2.8-2.9 TeVnext steps: hadron level MC, study of polarizations,…

From Strings to LHC II – Bangalore – Dec. 20, 2007Farvah Nazila MAHMOUDI

Conclusions

1 Guchait, Mahmoudi, Sridhar

Interesting phenomenology from the Bulk Randall-Sundrum model

Striking prediction: existence of KK gluons

with large decay to top/anti-top pair