kaluza-klein gluon production at the lhc
DESCRIPTION
Kaluza-Klein gluon production at the LHC. Farvah Nazila MAHMOUDI. From Strings to LHC II – Bangalore – Dec. 20, 2007. Farvah Nazila Mahmoudi (Uppsala University - Sweden). in collaboration with M. Guchait and K. Sridhar. From Strings to LHC II – Bangalore – Dec. 20, 2007. - PowerPoint PPT PresentationTRANSCRIPT
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 ?
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 GeVsignificance = 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 results
LHC 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