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Phenomenology of bulk scalar Phenomenology of bulk scalar production at the LHCproduction at the LHC
A PhD oral examinationA PhD oral examination
ByPierre-Hugues Beauchemin
A Small Title AnalysisA Small Title Analysis
Phenomenology: Phenomenology:
Study of the essential structure Study of the essential structure of nature that relates empirical of nature that relates empirical observations of phenomena to observations of phenomena to each other in a way which is each other in a way which is consistent with a fundamental consistent with a fundamental theory, but without being theory, but without being
directly derived from it.directly derived from it.
⇒
⇒
⇒
The structures (ingredients) of our theoretical framework is motivated by the more fundamental String Theory
Jargon:
Conceptual framework designed to relate Dark Energy measurement to possible High Energy physics observations
From this, physical predictions can be made for a specific experimental context
My work stand on the bridge between theory and observation
What kind of predictions are under What kind of predictions are under concern here?concern here?
Scalar production:Scalar production:
Controlled production or Controlled production or “creation” of a specific “creation” of a specific type of particle that type of particle that haven’t been observed haven’t been observed yet but is predicted by our yet but is predicted by our theoretical framework.theoretical framework.
⇒
Jargon
⇒
This scalar is gravitational interacting spinless particle
The physical predictions consist in deriving the Feynman rules of their coupling to ordinary field and to compute their cross section, ie their rate of production for a specific experiment
Part of my work consisted in using the theoretical framework to compute these quantities for scalar
direct production processes
At the LHCAt the LHC
The LHC is the The LHC is the experimental setup experimental setup which will provides the which will provides the empirical observations empirical observations that could reveal the that could reveal the phenomena under phenomena under study.study.
⇒
Jargon
The LHC is a Proton-Proton collider at 14 TeV so it can probe high mass and high PT states.
⇒
⇒
The LHC and Atlas detector design are optimized for new physics search
To “see” the collision products, 4 detectors will be build on the 27 km LHC ring.
The second part of my work consist in determine if the physics predictions that I computed from our theoretical framework can experimentally be tested with the ATLAS
detector at the LHC
However…However… There are already existing studies of the “phenomenology of There are already existing studies of the “phenomenology of
scalar production at the LHC”. scalar production at the LHC”.
e.g.: Higgs searche.g.: Higgs search
So what is new, different and interesting about what I So what is new, different and interesting about what I studied???studied???
⇒
ANSWER: BULK
Completely new theoretical framework, phenomena, set of predictions and
experimental signatures
⇔ Extra dimensions
Does it make sense to consider Does it make sense to consider that the world is 4+n dimensional?that the world is 4+n dimensional?
→
OF COURSE!
There are examples of everyday life of objects with more dimensions than we see.
What do we need to assert that the What do we need to assert that the fundamental structure of the Universe have fundamental structure of the Universe have
such a extra dimensions?such a extra dimensions?
Some theoretically motivated concept or Some theoretically motivated concept or mechanism that account for the fact that so far mechanism that account for the fact that so far precise particle physics experiment haven’t seen precise particle physics experiment haven’t seen such extra dimensions.such extra dimensions.
A way to justify that we can probe them.A way to justify that we can probe them.
The solution come from String Theory!
String Theory predicts the existence of branes
Our world as a 3-brane on which every SM fields are confined.
Gravity is not confined to such brane.
Moreover…Moreover… If we add supersymmetry to our framework, we will have the If we add supersymmetry to our framework, we will have the
ingredients to solve probably the most annoying problems of ingredients to solve probably the most annoying problems of fundamental physics:fundamental physics:
The cosmological constant problemThe cosmological constant problem
Recall the problem:Recall the problem:The vacuum energy predicted by quantum field The vacuum energy predicted by quantum field theory is much theory is much
bigger (10E60 times) than our Dark Energy measurement in the bigger (10E60 times) than our Dark Energy measurement in the c.m.b. anisotropy (WMAP)c.m.b. anisotropy (WMAP)
This new, well-motivated, rich and explanatory theoretical framework will be called the SUPERSYMMETRIC LARGE EXTRA DIMENSIONS (SLED) scenario
What is SLED involvesWhat is SLED involves?? In order to be able to solve the cosmological In order to be able to solve the cosmological
constant problem, SLED requires:constant problem, SLED requires:
Exactly 2 extra dimensions of Exactly 2 extra dimensions of OO(10(10m)m)SM particles stuck to a 3-braneSM particles stuck to a 3-braneN=2 SUperGRAvity in the bulkN=2 SUperGRAvity in the bulkSUSY strongly broken on the braneSUSY strongly broken on the braneBulk SUSY breaking scale of Bulk SUSY breaking scale of OO(10(10-3-3eV)eV)
We can use these structures to write down a low-energy 4D effective quantum field theory that generically couple the KK-states of a massless bulk scalar to the brane SM
fields and draw physical predictions from it!
MY WORK THUS CONSIST IN:MY WORK THUS CONSIST IN:
MMAAKKIINNGG TTHHEESSEE PPRREEDDIICCTTIIOONNSS
andand
USEUSE THEMTHEM TO TO SHOWSHOW HOWHOW SUCHSUCH THEORYTHEORY ISIS TESTABLETESTABLE
ATAT THETHE LHCLHC
Plan of the analysisPlan of the analysis Write the effective 4D low-energy Lagrangian Write the effective 4D low-energy Lagrangian
describing the coupling of a SLED bulk scalar to SM describing the coupling of a SLED bulk scalar to SM fieldfield
Concentrate on the lowest mass dimension Concentrate on the lowest mass dimension interaction term to:interaction term to:
Quarks and gluonsQuarks and gluons Higgs bosonsHiggs bosons
Evaluate the possibility to observe such scalar with Evaluate the possibility to observe such scalar with the ATLAS detector by studying:the ATLAS detector by studying:
Jet+Jet+ETTmissmiss:: Beauchemin et al. (J. Phys. G: Nucl. Part. Phys. Beauchemin et al. (J. Phys. G: Nucl. Part. Phys.
31)31) H+EH+ETT
missmiss:: Beauchemin et al. (J. Phys. G: Nucl. Part. Phys. Beauchemin et al. (J. Phys. G: Nucl. Part. Phys. 30)30)
LAGRANGIANLAGRANGIAN
This formal object summarize all the structures contained in SLED and describe the dominant coupling of a bulk scalar with the SM fields.
Coupling to quarks and gluons:
Coupling to Higgs bosons:
Cross sectionsCross sectionsFrom this we can predict the distributions for all the experimental observables: PT, , ET
miss, etc.
Extra dimensions phase space factor:
Jet+E Tmiss
Where we followed the conventions of [hep-ph/9912459]:
After having compute these differential cross section, I wrote Monte Carlo programs using PYTHIA to perform the integrations numerically and to generate the events used to simulate ATLAS
detector’s outcomes.
+E Tmiss
Jet+EJet+ETTmissmiss Experimental Analysis Experimental Analysis
The main standard background (ie. known events that leave The main standard background (ie. known events that leave the same jet+Ethe same jet+ETT
missmiss signature signature inin the detector) are the detector) are pppp→jet+Z(→→jet+Z(→) ) (277.6 fb)(277.6 fb) pp→jet+W(→epp→jet+W(→eee) (364.2fb)) (364.2fb)
pp→jet+W(→pp→jet+W(→) (363.7 fb)) (363.7 fb)
pp→jet+W(→pp→jet+W(→) (363.3 fb)) (363.3 fb)
PTjet ≥ 500 GeV
Proc.:Proc.:
Jet+…Jet+…
ZZ→→ WW→→ee WW→→ WW→→nn Bulk Bulk scalarscalar
TotalTotal 2776027760 3642036420 3637036370 3633036330 3096030960
No No leptonlepton
2710027100 52245224 957957 2460024600 3009030090
j1-j1-j2j2|
≤≤2.832.83
2494024940 14301430 866866 94599459 2772027720
ResultsResultsDiscovery criteria:
⇔ 99.99994% certainty that it is not a statistical
fluctuation
With the 36700 background events (PT≥500 GeV), it is required that:
S ≥ 970 events σ(pp→jet+φ) ≥ 10.9 fb
1-2
23
TeV 101.7
TeV 101.5−
−−
×=
×=
g
c2n
22
DD M and M ggccn
==+
where
⇒ To be valid and testable at the LHC, any model of bulkscalar must satisfy the following inequalities that show the ATLAS sensitivity to this new physics:
22
2 )M(1 and )M(1 minD
(n)obs
minD
(n)obs
+
≥≥≥≥nn
ccgg
+E+ETTmissmiss Experimental Analysis Experimental Analysis
The main standard background are:The main standard background are: qqqq→→ (56.2 pb)(56.2 pb) gg→gg→ (49.0 pb)(49.0 pb) QCD jet-jet QCD jet-jet ( 7.0 pb)( 7.0 pb) QCD QCD -jet-jet (15.0 pb)(15.0 pb) qq→hZ→qq→hZ→ (1.22E-3 pb)(1.22E-3 pb) qq→tth (h→qq→tth (h→)) (1.28E-3 pb)(1.28E-3 pb)
After applying standard cuts for h→ search:
SPECIFIC
TO SLED
But looking to these graphs, we can see that we can get aBetter sensitivity of we also apply a cut on ET
miss
ConclusionConclusion SLED scenario offers a fundamentally new SLED scenario offers a fundamentally new
understanding of high energy physics and thus deserves understanding of high energy physics and thus deserves to be carefully studiedto be carefully studied
SLED has a rich phenomenology. In particular, it predicts SLED has a rich phenomenology. In particular, it predicts coupling of bulk scalars to SM particles.coupling of bulk scalars to SM particles.
I computed physical predictions for fairly generic bulk-I computed physical predictions for fairly generic bulk-scalar and bulk scalar-Higgs interactionsscalar and bulk scalar-Higgs interactions
I then showed that this theory can be tested at the LHCI then showed that this theory can be tested at the LHC
Using cut on ETmiss, I evaluate ATLAS sensitivity to:Using cut on ETmiss, I evaluate ATLAS sensitivity to:
qqqq: 0.26 : 0.26 ≲g≲≲g≲11gggg: 0.06: 0.06≲c≲≲c≲11hhhh: 0.09: 0.09≲a≲≲a≲11
What do gain from these considerations?What do gain from these considerations?
This brane technology allows for extra This brane technology allows for extra dimensions as big as dimensions as big as OO(10(10m) across.m) across.
Explain why gravity is so weak.Explain why gravity is so weak.
⇒ Experimental test of the Newton law (classical) at distance scales smaller than the radius R of the extra dimensions.
The D-dimensional Planck scale will be: MRM2n
D
n2
Pl
+≈
TeVMmeV1Rm10R D-1 ≈→≈→≈
We can study quantum gravity in colliders!