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The Higgs Boson: What is it? Have we found it? Michael Tuts Columbia University Cambridge/MIT Alumni December 4, 2012

The Higgs Boson - Dr Michael Tuts, Columbia University

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December 2012 Short Lecture to the Cantab NYC group by Dr Michael Tuts of Columbia University, organized by Susanna Goldfinger.

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Page 1: The Higgs Boson - Dr Michael Tuts, Columbia University

The  Higgs  Boson:  What  is  it?  

Have  we  found  it?  Michael  Tuts  

Columbia  University  Cambridge/MIT  Alumni  

December  4,  2012  

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1  meter  10-­‐1  meter  

A  person  A  hand  

A  Journey  to  the  Domain  of  Par=cle  Physics  

10-­‐2  meter  

Skin  

10-­‐3  meter  

Skin  pore  

10-­‐4  meter  

Skin  pore  micro-­‐organism  

10-­‐5  meter  

White  Blood  Cell  

10-­‐6  meter  

Cell  nucleus  DNA  strands  

10-­‐7  meter  10-­‐8  meter  

DNA  structure  

10-­‐9  meter  

DNA  molecules  

10-­‐10  meter  

Carbon  outer  electrons  

10-­‐11  meter  

Carbon  inner  electrons  

10-­‐12  meter  

Within  the  electron  cloud  

10-­‐13  meter  

Atomic  nucleus  

10-­‐14  meter  

Carbon  nucleus  detail  

10-­‐15  meter  

Proton’s  surface  

10-­‐16  meter  

3  colored  quarks  in  proton    

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“Colored”  Quarks  (not  to  scale!)  <0.0000000000000000001  meters  or  <10-­‐19  m  

Nucleus  0.000000000000001  meters  or  10-­‐15  m  

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The  “Standard  Model”  of  Par=cle  Physics  

Ordinary  maTer  (planets,  us!)    

is  made  of  this  first  generaYon  of  quarks  and  leptons  

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Very  light!  

Very  heavy!  

Massless!  

Very  heavy!  

Higgs  “mechanism”  provides  a  way  to  explain  why  the  elementary  par=cles  have  different  weights  (masses)…  How?  

But  our  simplest  theory  would  say  they  should  all  be  massless!    

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An  analogy…  

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How  can  we  answer  this  ques=on  –  does  the  Higgs  Boson  exist  and  can  we  prove  it?  

The  Tools  for  explora=on  1.  Create  a  Higgs  in  the  debris  of  par=cle  collisions  –  use  the  Large  Hadron  Collider    2.  Search  for  the  Higgs  in  that  debris  –  use  the  ATLAS  detector  as  a  microscope  to  explore  the  subatomic  world  

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Proton-­‐proton  collisions  at  7TeV  per  beam  At  the  CERN  lab  in  Geneva  Switzerland  

17mile  long  tunnel,  300  feet  underground,  1,200  magnets  

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The  ATLAS  Detector  is  big,  very  big  •  80  c  tall,  147  c  long,  7,000  tons,  100  Million  

channels  of  electronics  

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How  big  is  ATLAS?  …  very  

•  100  million  channels  of  electronics  

•  80  c  tall  •  140  c  long  •  7,000  tons  •  3,000  physicists  

(incl.  ~1,000  graduate  students)  

•  38  countries  •  175  ins=tu=ons  

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Think  of  the  ATLAS  detector  as  a  100  megapixel  digital  camera  •  100  million  channels  of  electronics  •  We  take  electronic  “pictures”  (called  

events)  •  We  take  40  million  “pictures”  per  second  •  We  analyze  these  “pictures”  using  a  

worldwide  network  of  50,000  computers  •  We  have  wrigen  already  ~40  PB  of  data  

(40,000,000  Gigabytes!)  

The  problem  •  A  total  1  billion  collisions  per  second  •  Most  are  “uninteres=ng”,  so  need  to  

decide  and  discard  quickly,  can  only  afford  to  save  200  per  second  

•  For  example,  Z  boson  –  15  per  second  •  For  example,  Higgs  boson  –  one  every  5  

seconds  

LHC  #6  by  Jonathan  Feldschuh  (2008)    

LHC  #26  by  Jonathan  Feldschuh  

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How  do  you  classify  “pictures”  as  interes=ng  or  less  interes=ng?  

Can  you  tell  the  difference  between  these  two?  

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An  ATLAS  “Picture”  …  maybe  a  Higgs?  

ZZ→e+e-­‐µ+µ-­‐          This  could  be  a  Higgs  event  …  or  more  mundane…  need  more  data  to  tell  for  sure  

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Another  possible  Higgs  candidate  events  the  Higgs  decaying  into  two  photons  H→  γγ    

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How  do  we  find  the  Higgs?    Is  one  enough?  

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So  what  do  we  see  in  the  actual  data?  Combine  the  2  photons  according  to  Einstein’s  equa=ons  to  tell  

us  the  weight  (mass)  of  the  parent  par=cle  

1015  (=1,000,000,000,000,000)“pictures”  taken  Around  the  “bump”  about  3,700  “pictures”  of  which  about  100  correspond  to  the  new  par=cle  

For  mH=126.5  ±  2  GeV:  observed:  3693  events  expected  from  B:  3635  expected  from  SM  Higgs:  100    Signal/Background  ~  3%  

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If  it  is  Higgs  –  do  we  see  it  produced  at  the  rate  we  expect  from  theory?  

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Are  we  done  –  is  this  the  end?  

No!  It  is  a  new  beginning!  This  is  not  “just”  a  new  par=cle  –  a  Higgs  would  be  unlike  any  we  have  ever  seen  before    

Is  it  a  Higgs  Boson?  Not  completely  sure  yet…  Is  it  produced  as  ocen  as  we  expect?  Does  it  decay  as  we  expect?  Are  its  other  proper=es,  like  “spin”,  as  predicted?  

So  far  looks  like  it  …  but  we  will  be  accumula=ng  even  more  data  

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It’s  not  just  Higgs!  The  stuff  we  are  made  of  –  the  Standard  Model  I  described  -­‐  makes  up  a  mere  4%  of  the  universe  

There  are  many  open  ques=ons  we  may  be  able  to  tackle…  What  is  dark  Mager?  Are  there  new  symmetries  and  par=cles?  What  is  the  nature  of  space-­‐=me  itself?  Something  we  never  thought  of?  

Exploring  this  new  energy  fron=er  is  like  Columbus  sesng  sail  across  the  Atlan=c  –  will  we  find  America,  India  or  a  new  con=nent?  

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•  People  –  38  countries    –  176  insYtuYons  (including  Cavendish,  

Cambridge  U)  –  3,054  authors  

•  In  the  U.S.  –  43  insYtutes:  Albany,  ANL,  Arizona,  UT  

Arlington,  Berkeley  LBL  and  UC,  Boston,  Brandeis,  BNL,  Chicago,  Columbia,  UT  Dallas,  Duke,  Fresno  State,  Hampton,  Harvard,  Indiana,  U  Iowa,  Iowa  State,  UC  Irvine,  Louisiana  Tech,    MassachuseTs,  MIT,  Michigan,  MSU,  New  Mexico,  NIU,  NYU,  Ohio  State,  Oklahoma,  Oklahoma  State,  Oregon,  Pennsylvania,  PiTsburgh,  UC  Santa  Cruz,  SLAC,  SMU,  South  Carolina,  SUNY  Stony  Brook,  Tuhs,  Illinois  Urbana,  Washington,  Wisconsin,  Yale  

–  592  authors  

Columbia  University  group  on  ATLAS  June  2012  

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The  Large  Hadron  Rap  –  abridged    (6M  hits  on  You  Tube)  

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•  If  you  are  in  kindergarten  or  beyond  we  will  need  you…become  a  parYcle  physicist  and  join  ATLAS!  

•  In  Geneva?  Come  visit  us  at  CERN  (hTp://outreach.web.cern.ch/outreach/visits/)  •  Follow  us  on  TwiTer  (twiTer.com/ATLASexperiment),  Facebook  (

facebook.com/group.php?v=wall&gid=23271817589),  You  Tube  (www.youtube.com/theATLASExperiment)  –  even  a  LHC  rap  video  (youtube.com/watch?v=j50ZssEojtM),  Blogs  (uslhc.us  and  atlas.ch/blog/)  

•  Watch  events  live  as  they  are  collected  (atlanYs.cern.ch/live/)  •  Want  to  learn  more?  Keep  your  ATLAS  pop-­‐up  book  handy  (

hTp://www.facebook.com/pages/Pop-­‐up-­‐Voyage-­‐to-­‐the-­‐Heart-­‐of-­‐MaTer/153102255147  )  as  you  navigate  the  ATLAS  website  www.atlas.ch      

•  Oh…and  we  even  have  a  line  of  ATLAS  clothing  and  cool  toys  –  caps,  fleeces,  Yes,  3D-­‐viewers,  puzzles,  cards,…  (atlas.ch/store.html)  

Come  join  us  on  this  journey!  

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…  but  the  Higgs  mechanism  leaves  us  another  puzzle    -­‐  why  is  the  Higgs  so  light?  (“Hierarchy  problem”)  

The  Fix:      -­‐  either  very  finely  tuned  cancella=on  (just  luck!)  OR    -­‐  introduce  a  new  idea  like  SUPERSYMMETRY  (SUSY)  

The  Price:      -­‐  double  the  number  of  elementary  par=cles,  none  of  which  have  been  seen!  

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The  Bonus:      -­‐  Besides  “fixing”  problems  with  SM    -­‐  It  might  be  that  the  lightest  SUSY  par=cle  is  dark  mager!    -­‐  String  theories  require  them!    

This  is  us  (the  standard  model)  

We  might  discover  this  at  the  LHC  

We  won’t  have  much  to  say  about  this  

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But  what  about  the  force  of  gravity?  …  It  wasn’t  in  our  Standard  Model    

The  Problem  –  We  know  how  it  behaves  at  large  distances  –  Einstein’s  Theory  of  

General  Rela=vity  tells  us  how  –  At  small  distances  quantum  theory  is  important  and  we  have  no  tested  

theory  of  quantum  gravity  (for  all  they  other  forces  we  do  have  a  quantum  theory)  

–  Why  is  it  so  weak?  (is  it  weak?  You  can  do  the  demo  at  home!)  The  Solu=on…perhaps  –  Maybe,  just  maybe,  String  Theory  or  string  theory  inspired  ideas  are  

the  answer  Our  experimental  problem    –  Do  we  have  any  hope  of  tes=ng  it?  

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An  analogy…  on  why  we  don’t  feel  those  other  dimensions  

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•  High-­‐energy  proton  collisions    •  Can  release  enough  energy  •  To  create  new,  heavy  par=cles  

'Children  learn  about  the  world  much  as  scienYsts  do-­‐-­‐smashing  things  to  smithereens,  staring  in  wonder  at  the  results  and  then  breaking  out  in  giggles’