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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.

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kaluza klein gluon production at the lhc

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

contents

Farvah Nazila MAHMOUDI

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

Contents
  • Randall-Sundrum Model RS1
  • Modified RS1
  • Collider search
  • Kaluza-Klein gluon
  • Tevatron constraints
  • LHC constraints
  • Conclusion
slide3

SM fields

graviton

Farvah Nazila MAHMOUDI

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

Brane world scenarios

  • Idea:
    • We are confined on 3-brane
    • Graviton lives in the bulk
  • Typical scenarios:
    • Large (flat) Extra Dimensions

(Arkani-Hamed-Dimopoulos-Dvali,’98)

    • Warped (small) Extra Dimensions

(Randall-Sundrum,’99)

slide4

Farvah Nazila MAHMOUDI

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

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  = 
slide5

Planck

Planck

bulk

bulk

 =0

 =0

SM particle

UV/Planck brane

UV/Planck brane

IR/TeV brane

 =

Farvah Nazila MAHMOUDI

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

Randall-Sundrum Model (RS1)

Two D3-branes:

 = extra-dimension coordinate

Rc = (modest-sized) radius

5 dimensional metric:

Warp factor

K = mass scale

slide6

Farvah Nazila MAHMOUDI

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

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!

slide7

Farvah Nazila MAHMOUDI

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

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

slide8

Farvah Nazila MAHMOUDI

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

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

slide9

Farvah Nazila MAHMOUDI

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

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
slide10

Farvah Nazila MAHMOUDI

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

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

slide11

Farvah Nazila MAHMOUDI

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

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
slide12

Farvah Nazila MAHMOUDI

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

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
slide13

Farvah Nazila MAHMOUDI

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

Kaluza-Klein gluon

Non universal couplings to the SM particles

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

g = gauge coupling

slide14

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

Farvah Nazila MAHMOUDI

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

Constraint from Tevatron

  • What is the direct, model-independent bound that existing collider data can provide ?
slide15

Farvah Nazila MAHMOUDI

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

Constraint from Tevatron

  • Tevatron Run II
  • 1.96 TeV in the center of mass
  • Experimental value:
slide16

CTEQ4M

PDFLIB

95 C.L.

Farvah Nazila MAHMOUDI

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

Constraint from Tevatron

  • Direct bound!

Direct bound!

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

slide17

Farvah Nazila MAHMOUDI

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

KK gluon at the LHC

Production mechanism:

and annihilation

Agashe et al., hep-ph/0612015

slide18

Farvah Nazila MAHMOUDI

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

KK gluon at the LHC

For 100 fb-1 :

Discovery of the KK Gluon with M < 4 TeV

Agashe et al., hep-ph/0612015

slide19

Farvah Nazila MAHMOUDI

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

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
slide20

Farvah Nazila MAHMOUDI

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

Associate production at the LHC

slide21

Farvah Nazila MAHMOUDI

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

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)
slide22

Farvah Nazila MAHMOUDI

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

Associate production at the LHC

  • 14 TeV in the center of mass
  • Assuming 100 fb-1 integrated luminosity

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

slide23

Farvah Nazila MAHMOUDI

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

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:0710.2234

slide24

Farvah Nazila MAHMOUDI

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

KK Gluon at the LHC

Mass obtained for a significance of 5 in function of pT

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

slide25

Farvah Nazila MAHMOUDI

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

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 2.8-2.9 TeV
  • next steps: hadron level MC, study of polarizations,…

1Guchait, Mahmoudi, Sridhar