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What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
Discovery of The Higgs Boson
Dongwon ”DW” Han 1
Stony Brook University, USA
October 12th, 2015
1Local Expert: Professor John HobbsDongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
Outline
1 What is the Higgs Boson?
2 A Historical Account of the Higgs Boson
3 The ATLAS experiment
4 Production/ Decay Channels at the LHCH → ZZ ∗ → 4l ChannelH → γγ ChannelH →WW ∗ → lνlν Channel
5 Result : The ATLAS Experiment
6 Ongoing Research
7 Summary
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
What is the Higgs Boson?
Within the Standard Model (SM), electroweak symmetrybreaking is described by Brout-Englert-Higgs mechanism
BEH mechanism predicts the existence of a spin-0 scalarboson, known as the Higgs Boson, H.
Unfortunately, the SM does not predict the mass of the HiggsBoson, mH
Fortunately, given mH , we can calculate the production crosssections and the decay branching ratio
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
A Historical Account of the Higgs Boson I
In 1964, The Standard Model Higgs Boson was firstintroduced
Spontaneous breaking of the electroweak gauge symmetry.Proposed by three independent groups
Englert and Brout
Higgs
Guralnik, Hagen and Kibble
In 1967, the Higgs Boson got incorporated into the SM
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
A Historical Account of the Higgs Boson II
In the early 70s, its existence was only hypothetical.
Constraint on the Higgs mass: mH > 15MeV
”We should perhaps finish our paper with an apology and acaution. We apologize to experimentalists for having noidea what is the mass of the Higgs boson.”[Ellis et al., 1976]
Eventually, due to the stunning succes of the SM, a serioussearch for the Higgs Boson began
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
A Historical Account of the Higgs Boson III
Searches for the Higgs Boson at the LEP
ee+ collision experiment(LEP1) ee+ → Z → H + f f̄(LEP2) ee+ → Z + HIn 2000, Higgs-like events were observed aroundmH = 115GeV .The LEP was shut down at the end of 2000, leavingmH > 114.4GeV .
CDF and D0 experiments at Tevatron Collider
pp̄ collision experimentStudied H → bb and H →W+W−
Excluded the mass range 100GeV < mH < 103GeV and147GeV < mH < 180GeV
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
A Historical Account of the Higgs Boson IV
The LHC started operating in late 2009
pp collision experiment
(2011) 5fb−1 of data at 7 TeV in the center of mass
(2012) 7fb−1 of data at 8 TeV in the center of mass
On July 4th, 2012, CERN announced discovery of a newparticle consistent with the Higgs Boson predicted by theStandard Model at a mass of 125 GeV
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
A Historical Account of the Higgs Boson V
In 2013, Nobel prize in physics was awarded to Englert andHiggs ”for the theoretical discovery of a mechanism thatcontributes to our understanding of the origin of mass ofsubatomic particles, and which recently was confirmedthrough the discovery of the predicted fundamentalparticle, by the ATLAS and CMS experiments atCERN’s Large Hadron Collider.” [The Nobel Foundation, ]
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
The ATLAS experiment
ATLAS stands for AToroidal LHC Appartus
pp collision experiment
46 meters long, 25 meters ina diameter
3000 physicists from aroundthe globe are involved.
http://atlas.ch/
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
Production/ Decay Channels at the LHC I
Note: the table is for mH = 125.36GeV [Aad et al., 2015]
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
Production/ Decay Channels at the LHC II
https://twiki.cern.ch/twiki/bin/view/LHCPhysics/CrossSections#Higgs_cross_sections_and_decay_b
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
Production/ Decay Channels at the LHC III
http://lepewwg.web.cern.ch/LEPEWWG/
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
H → ZZ∗ → 4l Channel
H → ZZ ∗ → 4l Channel I
ZZ ∗ decays into two pairs of leptons with the same flavor andopposite charge.
Candidates: two pairs of isolated leptons
Leading pair: a pair with invariant mass closest to the Zboson mass.
Background: dominated by tt̄ and Z+ jets
Provide good sensitivity over a wide mass range (110-600GeV), because of the high momentum resolution
Leptons are very well measured at the LHC detector, so youcan reconstruct mH
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
H → ZZ∗ → 4l Channel
H → ZZ ∗ → 4l Channel II
[Aad et al., 2012]
[Aad et al., 2012]
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
H → γγ Channel
H → γγ Channel I
Mass Range between 110GeV and 150 GeV
Triggers: Energetic photonpairs
Et > 20GeV for eachcluster (7 TeV data)Et > 35GeV on theleading cluster and 25GeV on the subleadingcluster(8 TeV data)
Dominant background: theSM γγ production
mH can be reconstructed [Aad et al., 2012]
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
H → WW∗ → lνlν Channel
H → WW ∗ → lνlν Channel I
Signature: two oppositecharge leptons with largetransverse momentum and alarge momentum imbalance
Because the outgoingneutrinos can’t be observedat the LHC detector, mH
can’t be reconstructed inthis case.
The background and itscomposition depends on thejet multiplicity
[Aad et al., 2012]
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
H → WW∗ → lνlν Channel
H → WW ∗ → lνlν Channel II
[Aad et al., 2012]
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
Result : The ATLAS Experiment I
[Aad et al., 2012]
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
Result : The ATLAS Experiment II
[Aad et al., 2012]
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
Result : The ATLAS Experiment III
[Aad et al., 2012][Aad et al., 2012]
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
Result : The ATLAS Experiment IV
[Aad et al., 2012]
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
Ongoing Research
Is it a spin 0 particle?
Spin 1 is ruled out. We still need to check spin n > 2 cases
Is it a scalar or pseudoscalar?
In the SM, there is only one scalar Higgs Boson. However,other theories, such as SUSY, predicts the existence of a familyof Higgs Boson, which at least one of them is pseduscalar
Does this new particle couple to other particles in proportionto their masses?
If it is the case, it strongly suggests that this new particle giverises to particle massesIn order to test this, we need to observe other decay channelswhich haven’t been observed yet.
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
Summary
A Higgs-like particle was discovered in 2012.
This new particle is the SM Higgs Boson beyond anyreasonable doubt.
So far, the properties of the Higgs Boson is consistent withthe prediction of the Standard Model.
Further studies will tell us whether there is any deviation fromthe SM.
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
Bibliography I
Aad, G. et al. (2012).
Observation of a new particle in the search for the Standard Model Higgsboson with the ATLAS detector at the LHC.
Phys. Lett., B716:1–29.
Aad, G. et al. (2015).
Measurements of the Higgs boson production and decay rates andcoupling strengths using pp collision data at
√s = 7 and 8 TeV in the
ATLAS experiment.
ATLAS Experiment.
What is ATLAS?
Accessed October 10, 2015.
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
Bibliography II
Ellis, J., Gaillard, M. K., and Nanopoulos, D. (1976).
A Phenomenological Profile of the Higgs Boson.
Nuclear Physics B, 106:292 – 340.
Schott, M.
Standard Model at the LHC.
Accessed October 08, 2015.
TANEDO, F.
Why do we expect a Higgs boson? Part I: Electroweak SymmetryBreaking.
Accessed October 10, 2015.
The CDF Collaboration, the D0 Collaboration, the Tevatron New Physics,Higgs Working Group (2012).
Updated Combination of CDF and D0 Searches for Standard Model HiggsBoson Production with up to 10.0 fb−1 of Data.
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
What is the Higgs Boson? A Historical Account of the Higgs Boson The ATLAS experiment Production/ Decay Channels at the LHC Result : The ATLAS Experiment Ongoing Research Summary
Bibliography III
The Nobel Foundation.
The Nobel Prize in Physics 2013.
Accessed October 10, 2015.
Dongwon ”DW” Han Stony Brook University, USA
Discovery of The Higgs Boson
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