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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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      

The  Standard  Model!      

The  Large  Hadron  Collider  

General  Purpose,  pp,  heavy  ions  

CMS

ATLAS  

General  Purpose:  pp,  heavy  ions  

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

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!    

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  

CERN  

Data  distribution  §  Grid  connects  >100,000  processors  in  34  countries  

22  Petabytes  in  2011  

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)    

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!

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!

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  

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  

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  

 

§  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  

pp physics at the LHC corresponds to conditions around here

HI physics at the LHC corresponds to conditions around here

Where  the  largest  and  smallest  things  meet  

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  

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)!  

§  all  channels  together:                      comb.  significance:  4.9  σ  

§  expected  significance    for  SM  Higgs:  5.9  σ    

 

Characterization  of  excess  near  125  GeV  

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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

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  

Supersymmetry  

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.