presentatie freya blekman
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Managing the data of the Large Hadron ColliderTRANSCRIPT
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Managing the data of the Large Hadron Collider
(and other particle physics experiments)
Prof. Dr. Freya Blekman
Interuniversity Institute for High Energies Vrije Universiteit Brussel
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O
H C
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νe
u d
e ≈
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The “Standard Model”
§ Over the last ~100 years: The combination of Quantum Field Theory and discovery of many particles has led to
§ The Standard Model of Particle Physics § With a new “Periodic Table” of fundamental elements
Matter p
articles
Force particles
One of the greatest achievements of 20th Century Science
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The Standard Model!
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The Large Hadron Collider
General Purpose, pp, heavy ions
CMS
ATLAS
General Purpose: pp, heavy ions
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Compact Muon Solenoid (CMS)
Silicon
Pixels
c c c
µ+
e+
γ, πo
K-, π-,p,…
ν
Muon detectors
Hadron calorimeter
Crystal Electromagnetic
calorimeter
4 Tesla
Solenoid
All Silicon Strip
Tracker
Ko→ π+π-, …etc
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Quite a camera § CMS is like a camera with 90 Million pixels § But no ordinary camera § It can take up to 40 million pictures per second § The pictures are 3 dimensional § And at 15 million kilograms, it’s not very portable
§ LHC data challenge: The problem is that we cannot store all the pictures we can take so we have to choose the good ones fast!
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Experimental Challenges – Big Data in Particle Physics
§ Collisions are frequent § Beams cross ~ 16.5 million times per second at
present § About 20-‐30 pairs of protons collide each
crossing § Interesting collisions are rare -‐
§ less than 1 per 10 billion for some of the most interesting ones
§ We record only about 400 events per second.
§ We must pick the good ones and decide fast!
§ Decision (‘trigger’) levels § A first analysis is done in a few millionths of a
second and temporarily holds 100,000 pictures of the 16,500,000
§ A final analysis takes ~ 0.1 second and we use ~10000 computers
§ We still end up with lots of data – 1 GB per second!
Symmetry magazine’s summary infographic of LHC data volumes
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CERN
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Data distribution § Grid connects >100,000 processors in 34 countries
22 Petabytes in 2011
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CMS data in Belgium § In Flanders: CMS T2 hosted at VUB § Alternative T2 at UCL
§ Access to all CMS members all over the world § And main working node for all Flemish (+ ULB/UMons) particle physicists
§ Brussels Computing cluster (Tier 2 computer center): Consist of modular PCs 440 TB storage space (and growing) for Belgian users
2.2 PB storage space for CMS 19 TeraFLOPS (FLoating-‐point Operations Per Second) Funding agencies: FRS-‐FNRS (ULB, UMons) FWO-‐BigScience – Vlaams Supercomputing Centrum (VUB)
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Other CMS data
DBTA Workshop on Big Data, Cloud Data Management and NoSQL Big Data Management at CERN: The CMS Example
Other CMS Documents"
x 4000 people … for many decades
J.A. Coarasa (CERN) 25!
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Other CMS data
DBTA Workshop on Big Data, Cloud Data Management and NoSQL Big Data Management at CERN: The CMS Example
Other CMS Documents: Size"
A printed pile of all CMS documents that are already in a managed system
= 1.0 x (Empire State building)
Plus we have almost the same amount spread all over the place (PCs, afs, dfs,
various websites …)
J.A. Coarasa (CERN) 26!
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LHC open data? § LHC and CERN have very strict policies regarding publication of their results § ALL journal publications (including those in Nature/Science) are made public
§ Publishing in open access journals the norm
§ However, most of our data is only accessible to those in the collaboration
§ Exception: there are datasets available for education use § http://physicsmasterclasses.org/index.php
Secondary school student accessing public CMS data at Vrije Universiteit Brussel
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Open data in (astro) particle physics § The IceCube experiment is another particle physics experiment studying elementary particles of astrophysical origin
§ Based at the South Pole, IceCube includes Belgian scientists from VUB/ULB/UGent/Umons
§ IceCube data is analysed with the same cluster in Brussels as mentioned before
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Extreme High energy neutrinos § One of the most exciting IceCube results involves the observation of outrageously high-‐energy neutrinos from cosmic origin
§ Evidence for High-‐Energy Extraterrestrial Neutrinos at the IceCube Detector, IceCube Collaboration, Science 342, 1242856 (2013). DOI: 10.1126/science.1242856
§ After publication, the IceCube collaboration has made this data available to the scientific community
§ http://icecube.wisc.edu/science/data
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§ Working through 40 million collisions per second provides a daunting challenge processing huge amounts of data
§ Journal publications of LHC experiments all public
§ Other experiments such as IceCube also make some of their datasets public after publication
Outlook and Conclusion
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pp physics at the LHC corresponds to conditions around here
HI physics at the LHC corresponds to conditions around here
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Where the largest and smallest things meet
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The Dark Side § We now know that only ~5% of the energy in the universe is ordinary matter (remember E=mc2).
§ 25% is dark matter § SUSY theories can happily predict this amount
§ There are other possibilities but SUSY is a favorite § Provides great dark matter candidates (e.g. Neutralino or Gravitino)
§ Leads to remarkable unification of field strengths § And it fixes the Higgs mass problem
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How would we see the Higgs Boson ? Simulation – to predict and design detector – and to compare to what we actually see
NB: These old plots correspond to ~50 times more sensitivity than we have now (20x more data, 2x the energy)!
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§ all channels together: comb. significance: 4.9 σ
§ expected significance for SM Higgs: 5.9 σ
Characterization of excess near 125 GeV
26
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[GeV]4lm
Eve
nts
/ 3 G
eV
0
2
4
6
8
10
12
[GeV]4lm
Eve
nts
/ 3 G
eV
0
2
4
6
8
10
12 Data
Z+X
*,ZZaZ
=126 GeVHm
µ, 2e2µ7 TeV 4e, 4µ, 2e2µ8 TeV 4e, 4
CMS Preliminary -1 = 8 TeV, L = 5.26 fbs ; -1 = 7 TeV, L = 5.05 fbs
[GeV]4lm80 100 120 140 160 180
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Standard Model Higgs Decays
§ The SM Higgs is unstable § Decays “instantly” in a number of ways with very well known probabilities
(called Branching Fractions or Ratios that sum up to 1). § Branching ratios change with mass as seen here § Some decay modes are more easily seen than others Firstly if they end with electrons, muons, or photons
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Supersymmetry
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What made us so sure about the Higgs?
§ The Brout-‐Englert-‐Higgs theory has predictable consequences § It predicts very heavy force particles that carry the weak nuclear force known as the W+, W-‐ and Zo
§ The W+, W-‐ should both have a mass of 80.4 GeV Note that the proton has a mass of 1 GeV so these are very heavy fundamental particles!
§ The Zo should have a mass of 91.1 GeV § We find these predicted particles & measure their masses § For instance, the Zo should decay to two muons. We can measure their momenta and reconstruct the Zo mass.
§ If we do this for many Zo particles, a distribution of the mass values we get should have a very predictable shape.