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Managing the data of the Large Hadron Collider

Managing the data of the Large Hadron Collider

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  • 1. 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  
  • 2. O H C
  • 3. νe u d e ≈  
  • 4. 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  particles   Force  particles   One  of  the  greatest   achievements  of  20th   Century  Science      
  • 5. The  Standard  Model!      
  • 6. The  Large  Hadron  Collider   General  Purpose,   pp,  heavy  ions   CMS ATLAS   General  Purpose:   pp,  heavy  ions  
  • 7. Compact  Muon  Solenoid  (CMS)   Silicon Pixels ccc 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
  • 8. 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!    
  • 9. 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  
  • 10. CERN  
  • 11. Data  distribution   §  Grid  connects  >100,000  processors  in  34  countries   22  Petabytes  in  2011  
  • 12. 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)    
  • 13. Other  CMS  data   DBTA Workshop on Big Data, Cloud Data Management and NoSQLBig Data Management at CERN: The CMS Example Other CMS Documents" x    4000  people      …  for  many  decades J.A. Coarasa (CERN) 25!
  • 14. Other  CMS  data   DBTA Workshop on Big Data, Cloud Data Management and NoSQLBig 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!
  • 15. 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  
  • 16. 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  
  • 17. 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    
  • 18. §  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  
  • 19. pp physics at the LHC corresponds to conditions around here HI physics at the LHC corresponds to conditions around here
  • 20. Where  the  largest  and  smallest  things  meet  
  • 21. 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  
  • 22. 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)!  
  • 23. §  all  channels  together:                       comb.  significance:  4.9  σ   §  expected  significance     for  SM  Higgs:  5.9  σ       Characterization  of  excess  near  125  GeV   26
  • 24. [GeV]4lm Events/3GeV 0 2 4 6 8 10 12 [GeV]4lm Events/3GeV 0 2 4 6 8 10 12 Data Z+X *,ZZZ =126 GeVHm µ, 2e2µ7 TeV 4e, 4 µ, 2e2µ8 TeV 4e, 4 CMS Preliminary -1 = 8 TeV, L = 5.26 fbs;-1 = 7 TeV, L = 5.05 fbs [GeV]4lm 80 100 120 140 160 180
  • 25. 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  
  • 26. Supersymmetry  
  • 27. 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.  

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