1. Kaluza-Klein gluon production at the LHC
Farvah Nazila Mahmoudi
(Uppsala University - Sweden)
in collaboration with M. Guchait and K. Sridhar
From Strings to LHC II – Bangalore – Dec. 20, 2007
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI

2. Contents Randall-Sundrum Model RS1 Modified RS1 Collider search
Kaluza-Klein gluon
Tevatron constraints
LHC constraints
Conclusion
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI

3. Brane world scenarios Idea: Typical scenarios:
We are confined on 3-brane
Graviton lives in the bulk
SM fields
graviton
Typical scenarios:
Large (flat) Extra Dimensions
(Arkani-Hamed-Dimopoulos-Dvali,’98)
Warped (small) Extra Dimensions
(Randall-Sundrum,’99)
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI

4. Randall-Sundrum Model (RS1)
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  = 
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI

5. Randall-Sundrum Model (RS1)
UV/Planck brane
bulk
Planck
 =0
IR/TeV brane
SM particle
 =
Two D3-branes:
 = extra-dimension coordinate
Rc = (modest-sized) radius
5 dimensional metric:
Warp factor
K = mass scale
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI

6. Randall-Sundrum Model (RS1)
The warp factor acts as a conformal factor for the fields localized on the brane
 Mass factors get rescaled by this factor
Solve the hierarchy!
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI

7. Randall-Sundrum Model (RS1)
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, 2007
Farvah Nazila MAHMOUDI

8. Deformation of the original scenario
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
unviable
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI

9. makes sense because only the scalar sector is natural
Bulk Randall-Sundrum
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, 2007
Farvah Nazila MAHMOUDI

10. Bulk Randall-Sundrum top sector:
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
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI

11. Bulk Randall-Sundrum  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
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI

12. Production of Kaluza-Klein gluons
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
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI

13. Kaluza-Klein gluon Non universal couplings to the SM particles
g = gauge coupling
Large BR into right-handed top/anti-top pairs
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI

14. Constraint from Tevatron
What is the direct, model-independent bound that existing collider data can provide ?
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
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI

15. Constraint from Tevatron
Tevatron Run II
1.96 TeV in the center of mass
Experimental value:
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI

16. Constraint from Tevatron
95 C.L.
CTEQ4M
PDFLIB
Direct bound!
Direct bound!
M. Guchait, F.M. and K. Sridhar, JHEP 0705, 103
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI

17. KK gluon at the LHC Production mechanism: and annihilation
Agashe et al., hep-ph/
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI

18. Discovery of the KK Gluon with M < 4 TeV
KK gluon at the LHC
For 100 f b-1 :
Discovery of the KK Gluon with M < 4 TeV
Agashe et al., hep-ph/
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI

19. Associate production with ttbar
: produced from both gg and initial states
through the usual QCD processes
KK gluon: radiated from one of the heavy-quark legs
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, 2007
Farvah Nazila MAHMOUDI

20. Associate production at the LHC
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI

21. two non-resonant pairs coming from QCD processes
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, 2007
Farvah Nazila MAHMOUDI

22. Associate production at the LHC
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
14 TeV in the center of mass
Assuming 100 fb-1 integrated luminosity
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI

23. background cross section: 0.33 fb
KK Gluon at the LHC
Cuts
from gKK : pT > 300 GeV
other : pT > 50 GeV
significance = 5  M = 2790 GeV
background cross section: 0.33 fb
M. Guchait, F.M. and K. Sridhar, arXiv:
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI

24. Mass obtained for a significance of 5 in function of pT
KK Gluon at the LHC
Mass obtained for a significance of 5 in function of pT
M. Guchait, F.M. and K. Sridhar, arXiv:
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI

25. Conclusions
Interesting phenomenology from the Bulk Randall-Sundrum model
Striking prediction: existence of KK gluons
with large decay to top/anti-top pair
2 GMS1 results:
GMS1:
Using Tevatron data:
First direct constraints on the KK gluon mass
The 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 TeV
next steps: hadron level MC, study of polarizations,…
1 Guchait, Mahmoudi, Sridhar
From Strings to LHC II – Bangalore – Dec. 20, 2007
Farvah Nazila MAHMOUDI