20160124 겨울가속기스쿨 high1home.kias.re.kr/MKG/upload/Collider16/seongchanpark.pdf ·...
Transcript of 20160124 겨울가속기스쿨 high1home.kias.re.kr/MKG/upload/Collider16/seongchanpark.pdf ·...
LHC Physics
SeongchanParkYonsei&KIAS
Colloquium for 2016 Winter School on Collider PhysicsHigh-1 Resort, 24-30 Jan, 2016
from ‘God particle’
LHC is here
We are at the very front of human intelligence
What we are doing is something GREAT.
Be proud of what you are doing!
Plan
• A theorist’s introduction to LHC physics
• Physics learned from the LHC so far
• Some speculations about BSM
• Conclusion
LHC: Large Hadron Collider
Q. Why large?
Actually proton.Q. Why not electron?
LHC in Seoul
google “LHC MAP”
Tevatron in Seoul
FCC in Seoul
FCC in Seoul
available Energy/momentum
distance one can probe
The uncertainty principle
GeV
★~1970 reached strong scale 10-13cm≈(1/M) e-2pi/as b0 ★~1900 reached atomic scale 10-8cm≈1/(α2me)
eV
★~2011 reach weak scale 10-17cm ⇐LHC here!
TeV
Why large?
Why hadron?
lighter, more efficient!
Q. Why proton rather than electron?
Power of radiation:[Larmor’s formula]
(see Jackson)
Proton• proton is NOT an
elementary particle but a composite state of many colored particles
• p={u,d,s,g,ubar, dbar…}
• It is highly dynamical!
• Q. Is this good or bad?F. Bissey et.al. Phys. Rev. D 76, 114512 (2007)
Only a fraction of the proton energy is actually participating the scattering processes ..
Parton Distribution Function (PDF)
• First introduced by Feynman (1969) in Parton model.• i=u,d,s,c,b,t,g, and anti-quarks (Parton id =[-6,6])• Q=scale of the interactions • scale dependence determined by Alterelli-Parisi equation
from Lattice calculations, fits to the data (and AdS/QCD)
LO, NLO, NNLO…
(more in SJLee, MHPark’s lectures)
PDFs in MarketCTEQ fortran code and grids
CTEQ-Jefferson Lab (CJ) the CJ12 PDF sets
GRV/GJR fortran code and grids
MRST fortran code and grids, C++ code
MSTW fortran, C++ and Mathematica codes + grids etc.
ALEKHIN fortran,C++,Mathematica code, and grids
ZEUS ZEUS 2002 PDFs, ZEUS 2005 jet fit PDFs
HERAPDF Combined H1/ZEUS page, HERAPDF1.0 paper
H1 H1 2000
BBG BBG06_NS
NNPDF Non Singlet PDF code - hep-ph/0701127
CTEQ6, Q=100 GeV
gluon
up
http://hepdata.cedar.ac.uk/pdf/pdf3.htmlOn-line PDF plotter
Hadron Collider=Infinitely many colliders with different CM energies
Useful when you want to search for something unknown!For precision measurements, you’d better have e-e+
machine.
but complicated…..
Q. Assuming that ~20% energy of proton energy is contributing to a hard collision, how small distance scale can be probed at LHC14?
Answer:
Q. why can we use hbar=c=1?
LHC~TeV ~10-17 cm
What’s Physics of 10-17 cm?
• The distance scale for electroweak symmetry breaking… (Q. what is EWSB?)
• In the SM, the Higgs mechanism is responsible for EWSB …(Q. any other idea?)
• => excitation of Higgs field (=Higgs particle) can be seen.
• The LHC discovered a Higgs boson!
누가 “힉스 입자”라는 이름을 붙였나?
P. Higgs “My life as a boson” (2010)
누가 “힉스 입자”라는 이름을 붙였나?
S. Weinberg (2012) The New York Book Review
Steven Weinberg 曰
Refs in S. Weinberg [Model of Leptons] 1967
잘못 된 순서
…
힉스입자 발견의 숨은 의미(1)
• The first discovered spin-0 elementary particle The mechanism of Electroweak symmetry breaking
but theoretically problematic (Q. what’s the problem?)
Note) there were many spin-0 particles discovered but they are all composite states of quarks. (mesons: q-qbar)
힉스 입자 발견의 숨은 의미(2)
• Completion of the SM All elementary particles are now discovered! (Q. what are they?)
All free parameters in the SM are now measured! (Q. how many?)
but it does not mean that particle physics ends.. (later more)
표준모형(1)• 양자 역학 + 상대성 이론 =
• 시공간 차원 수 =
• 시공간 대칭성 =
• 게이지 대칭성 =
• 기본 입자 =
• +게이지 대칭성의 붕괴 메커니즘
표준모형(2) • QFT with Lorentz invariance, local gauge invariance
• spacetime = 4D Minkowski (gravity ignored. why?)
• gauge symmetries: G=SU(3)CXSU(2)LXU(1)Y, Y=T3-Qe
• Matter s=½: Weyl spinors (not Dirac? Why?) (Where are neutrinos?)
• [Q~(3,2,yQ), u~(3,1,yu), d~(3,1,yd), L~(1,2,yL), e~(1,1,ye) ]X3 gen
• Complex scalar s=0: H~(1,2,yH) with negative mass term for EWSB (why not fermion for EWSB?)
from wikipedia
Quiz: 표준모형의 자유계수는 몇 개인가?
자유 계수(free parameter) = ??
Free parameter
=parameter in theory determined only by experiments not by theory
자유 계수: 소금 한 큰 술 …
125 GeV
Free parameters in the SM
NEW!
(NOTE) Flavor problem
• Most of free parameters in the SM are about Fermion masses and mixings.
• How can we understand those parameters? Any underlying principle?
• More in Prof. Y. J. Kwon’s talk in this school.
CMS PAS HIG-14-009
ATLAS arXiv:1406.3827
PDG new
Current status of Higgs mass measurement
CMS PAS HIG-14-009
Decay pattern is consistent with the SM!
• The Higgs in the SM plays two main roles: EWSB (or gauge boson masses) and fermion masses. Both have been experimentally checked!
The Higgs potential
The most generalrenormalizablepotential with
Tachyonic mass
NOTE: 2 free parameters in the entire Higgs sector.
VEV of the Higgs
known since 1970s
Higgs quartic coupling
(2012)
4제곱항의 계수
Higgs potential
Now, all the parameters in the Higgs sector are experimentally measured!
Ultimate confirmation of the SM!
h-h-h h-h-h-h
Indeed, these are main motivations for future colliders
At large field limit
Quantum effective coupling
RG running of lambda
Top quark Yukawa coupling
self gauge
Top massCMS+ATLAS arXiv:1512.02244
2-loop effective coupling
criticality
arXiv:1405.4781
[Hamada, Kawai, Oda, SCP, PRL 2014]
Higgs potential with Quantum corrections
Higgs potential near criticality
Hamada, Kawai, Oda, SCP (2014, 2015)
% of woman science major
Intriguing implication
• The Higgs potential at high scale becomes flat.
• That may contribute to the accelerated expansion of the Universe in early time…
sol: Higgs inflation
A big beautiful hierarchical
structure
SM:
what’s wrong with this?
A big hierarchical
structuretends to collapse
unless there is a mechanism protecting the
structure
But keep in mind hierarchy exists in nature
Solar Eclipse: angular size of the sun is the same as the angular size of the moon within 2.5% (pure coincidence!)
Politics: Florida recount, 136/2,913,144 =1.000061 (!!)
Numerology: 987654321/123456789 =8.000000073 (!!!)
(Food for thought: is it really numerology?)
The hierarchy problem
• We don’t understand why the Higgs mass is so much lighter than the UV scale of the physics
★ We DO understand why the gauge boson’s are much lighter than the UV scale
★ We DO understand why the electron is much lighter than the UV scale
The 1-loop Higgs mass
bare parameter (in Lagrangian) cutoffphysical
~17 digits tuned
~natural!
The 1-loop Higgs mass in dimensional regularization
only sees “log divergence” not “power divergence”
Q. where is the quadratic divergence?
Criticality
scattering at E*:
for scalar mass:
Why so small?
BSM at TeV
• Many BSM models have been proposed …Low scale SUSY, extra dimensions (= new strong dynamics, technicolor), no-Higgs models…
• Most of them predicted new particles at around TeV
SM
Exotica
Higgs
CMS publications
SUSYTop
Bottom
http://cms-results.web.cern.ch/cms-results/public-results/publications-vs-time/
but no new physics seen so far @ LHC
• Impressive progress in NP searches..
• but no NP is seen yet (diphoton @ 750 GeV???)
Interpretation-1• New physics is just around the corner, once again… LHC13
and LHC14 will see new particles! Q. why LHC7/LHC8 didn’t see anything other than the Higgs boson?
• Maybe the new physics scale is still too high to be seen in LHC8…Q. why the new scale is at least O(10-100) bigger than the EW scale if the new physics is responsible for the hierarchy problem? (little hierarchy problem)
• Maybe the new physics has so degenerate spectrum so that the LHC detector could not identify the soft signals.. (e.g. stop/top degeneracy) Q. Why so degenerate? Is it simply due to that GOD is cruel to us?
Interpretation-2• “The hierarchy problem” may be just an artifact generated by
trouble-making theorists?
• If one takes the Higgs mass problem serious, what about the cosmological constant problem, which is a way more serious …
• (Mp/Mw)2 vs (Mp/cc)4 ~(Mp/Mν)4
• Can anthropic argument be the (only possible) solution to the CC problem ?
• Maybe we have not reached to the proper level of understanding these problems?
clues for BSM• Dark matter : no candidate for CDM exist in the
SM => indicating ~TeV physics
• Baryon asymmetry: CKM picture does not provide enough CP violation
• Neutrino oscillations : may need RH neutrinos?
• …many more…(Q. what’s yours?)
Interplay with astrophysics
• New generation of astrophysical observations based on cosmic-ray detection and CMBR measurement started to give us new data about our universe..
• IceCube (neutrino), Fermi-Lat(photon), Planck (CMBR) etc..
• Very interestingly, newly obtained data often suggests that what we know is only a small fraction of the whole story
• (Energy of unknown source)/(Energy of known source)~ (95%)/(5%) …the SM is only responsible for this 5%!
• New source for cosmic ray may call for our attention..
http://xkcd.com
So
• There are many more new discoveries waiting for us!
• Let’s be optimistic
• Let’s be prepared!
9th planet could have seen only by who were looking for
Hurt (IPAC) [Diagram was created using WorldWide Telescope.] See more at: http://m.caltech.edu/news/caltech-researchers-find-evidence-real-ninth-planet-49523#sthash.2XiwckxI.dpuf