Bosonul Higgs - vanatoarea unei particule

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Introducere in fizica particulelor elementare si in cautarea experimentala a particulei (bosonului) Higgs prezisa de teoria care explica originea masei particulelor elementare.

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  • Life, molecules, atoms, nuclei, protons and neutrons, quarks and electrons
  • But an ingredient is still missing … Think of what food is without salt. Salt gives all the flavor. What would be the equivalent of salt in particle physics, when describing the recipe of the Universe? It is the mass of the elementary particles. If there were no mass, all particles would be running in space of the speed of light. True, they would interact with each other, just as the four fundamental forces require, but there would be no structures being formed. No protons and neutrons, thus no nuclei, thus no atoms, thus no molecules and thus no life and thus no … us. So the question of the origin of mass is very very important.
  • But an ingredient is still missing … Think of what food is without salt. Salt gives all the flavor. What would be the equivalent of salt in particle physics, when describing the recipe of the Universe? It is the mass of the elementary particles. If there were no mass, all particles would be running in space of the speed of light. True, they would interact with each other, just as the four fundamental forces require, but there would be no structures being formed. No protons and neutrons, thus no nuclei, thus no atoms, thus no molecules and thus no life and thus no … us. So the question of the origin of mass is very very important.
  • But an ingredient is still missing … Think of what food is without salt. Salt gives all the flavor. What would be the equivalent of salt in particle physics, when describing the recipe of the Universe? It is the mass of the elementary particles. If there were no mass, all particles would be running in space of the speed of light. True, they would interact with each other, just as the four fundamental forces require, but there would be no structures being formed. No protons and neutrons, thus no nuclei, thus no atoms, thus no molecules and thus no life and thus no … us. So the question of the origin of mass is very very important.
  • In 1964, a solution was proposed to this puzzle. Peter Higgs, a Scottish theoretical physicist, came up with a theoretical mechanism that allows elementary particles to acquire mass. This was called the Higgs mechanism. It predicts the existence of a new elementary particle called the Higgs particle. If this particle is observed experimentally, it means his mechanism is correct and we understand the origin of mass. However, 45 years later, the particles has yet not been discovered. Not necessarily because it does not exist, but rather because our instruments have not become precise enough to search for this particle. As you will see, it’s like searching for a needed in a hay stack. But how exactly do scientists search for the Higgs particle?
  • In 1964, a solution was proposed to this puzzle. Peter Higgs, a Scottish theoretical physicist, came up with a theoretical mechanism that allows elementary particles to acquire mass. This was called the Higgs mechanism. It predicts the existence of a new elementary particle called the Higgs particle. If this particle is observed experimentally, it means his mechanism is correct and we understand the origin of mass. However, 45 years later, the particles has yet not been discovered. Not necessarily because it does not exist, but rather because our instruments have not become precise enough to search for this particle. As you will see, it’s like searching for a needed in a hay stack. But how exactly do scientists search for the Higgs particle?
  • Sensitivity and limits Combine results from two experiments
  • Bosonul Higgs - vanatoarea unei particule

    1. 1. Cautand originea masei (Cautand bosonul Higgs) Adrian Buzatu Departmentul de Fizica & AstronomieUniversitatea din Glagsow, Regatul Unit
    2. 2. De la mare la mic …02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 2
    3. 3. Universul ca o prajitura Tava: spatiu-timp Ingrediente: ~ 20 particule elementare Reteta: 4 forte (interactii) elementare02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 3
    4. 4. Particule si forte elementare Forta electromagnetica Forta tare Forta slaba Forta slaba02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 4
    5. 5. O mare varietate de mase Masa reprezentata de suprafata02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 5
    6. 6. Masa particulelor elementare Leptoni Cuarci Purtatori de forta Unele masive cat atomi masivi!02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 6
    7. 7. Fotonul si bosonul Z Forta electroslaba = forta electromagnetica + forta slaba Fotonul == Bosonul Z Apoi, spontan, simetria este rupta! Fotonul != Bosonul Z Fotonul ramane fara masa; Bosonul Z primeste masa.02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 7
    8. 8. Ingredientul lipsa, bosonul Higgs Masa reprezentata de suprafata Care este originea masei particulelor elementare? Teoria propune atunci: Inca un pas la reteta: mecanismul Higgs Inca un ingredient fundamental: campul Higgs format din bosoni Higgs02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 8
    9. 9. Campul scalar Higgs Peste tot in univers exista un … numar Un camp scalar … … cunoscut de catre public ca si campul Higgs, … dar corect trebuie numit campul Englert–Brout–Higgs–Guralnik–Hagen–Kibble Particulele elementare simt o frecare (vascozitate) cu acest camp Higgs chiar si in vid, astfel incetinesc de la viteza luminii. Astfel, ele primesc masa!02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 9
    10. 10. Particula scalara: bosonul Higgs In stiinta, experimentul == judecatorul unei teorii Trebuie confirmari experimentale pentru TOATE predictiile acestei teorii Dar aceasta teorie are o SINGURA predictie … … existenta unei noi particule elementare … scalara, numerele cuantice zero (ca vidul), probabilitatea de interactie fixata atunci cand masa sa este fixata … Dar masa particulei nu este fixata de teorie! Este tocmai bosonul Higgs!02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 10
    11. 11. Peter Higgs02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 11
    12. 12. Analogia cu padurea Aceeasi energie Padure Cine strabate Ciocnire de copaci padurea primul?Unul slabutUnul grasut Cel mai slabut ajunge primul. A fost incetinit mai putin, caci s-a ciocnit cu mai putini copaci. Padurea: campul scalar Higgs Un singur copac: o particula scalara (bosonul Higgs) Ciocniri cu bosonii Higgs => frecare cu campul scalar Higgs => viteza scade fata de viteza luminii => particula primeste masa diferita de zero02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 12
    13. 13. Teorie si experiment Predictie teoretica Predictie teoretica Cine : Urbain Le Verrier Cine : Peter Higgs + ceilalti Ce : prezice planeta Neptun Ce : prezice noua particula Unde : Franta Unde : Scotia Cand : August 1846 Cand : 1964 (acum 49 de ani!) Cum : mate/teorie Cum : mate/teorie Pt ce : ciudata orbita a lui Uranus Pt ce : particulele primesc masa Aici contribuim noi Verificare experimentala Verificare experimentala Cine : Johann Gottfried Galle Cine : laboratoarele CERN Ce : a discoperit-o! Ce : a discoperit-o! Unde : Germania Unde : Elvetia Cand : Septembrie 1846 Cand : 2012-2013 Cum : telescop/experiment Cum : accelerator/detector/experiment Pt ce : experimentul = judecator! Pt ce : experimentul = judecator! 1 zi doar: telescopul sau era 49 de ani: ne imbunatateam mereu suficient de precis! “microscopul”02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 13
    14. 14. Fermilab, langa Chicago, SUA02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 14
    15. 15. Collider Detector at Fermilab02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 15
    16. 16. Particulele interactioneaza diferit02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 16
    17. 17. Masa bosonului Higgs - Iulie 2011 Cu 95% incredere, masa sa poate fi doar in intervalul 114.4 - 149 GeV/c2, adica 123 – 160 unitati atomice de masa02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 17
    18. 18. CERN, Geneva, Elvetia02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 18
    19. 19. ATLAS detector02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 19
    20. 20. ATLAS detector02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 20
    21. 21. ATLAS detector02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 21
    22. 22. Masa bosonului Higgs - Martie 2012 Cu 95% incredere, masa sa poate fi doar in intervalul 115.5 - 127 GeV/c2, adica 124 – 136 unitati atomice de masa02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 22
    23. 23. Masa bosonului Higgs – 04 Iulie 2012 O noua particula elementara “ca un boson Higgs” (in acord cu bosonul Higgs din Modelul Standard) a fost observata in intervalul de mase 125 – 127 GeV/c 2, adica 135 – 136 unitati atomice de masa02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 23
    24. 24. Descoperirea noii particule02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 24
    25. 25. Masa particulelor elementare Leptoni Cuarci Purtatori de forta Unele masive cat atomi masivi!02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 25
    26. 26. 04 Iulie 2012 – ca un boson Higgs Toate proprietatile masurate sunt in acord cu cele ale bosonului Higgs Dar mai erau doua proprietati de masurat (spinul si si paritatea), plus cat de des este produsa particula Bosonul Higgs are spinul zero si paritate pozitiva Odata stiuta masa, in Modelul Standard se prezice exact cat de des este produsa particula02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 26
    27. 27. Fabiola Gianotti, liderul ATLAS02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 27
    28. 28. 14 Martie 2013 – un boson Higgs Cele doua noi proprietati au fost masurate si coincid cu cele ale teoriei Avem asadar “un boson Higgs” De ce nu “bosonul Higgs?” Existe teorii noi care prezic mai multi bosoni Higgs Fizicenii spera sa descopere si ceva nou02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 28
    29. 29. Concluzii Introdus notiunile de particule elementare si interactiile dintre ele ca ingredientele si reteta materiei din Univers Descrierea naturii este incompleta fara originea masei particulelor Acum 49 de ani o teorie a fost propusa sa explice asta Era nevoie de o confirmare sau infirmare experimentala De atunci, fizicenii si-au imbunatatit constant “microscopul” 4 Iulie 2012: O noua particula elementara, este “ca un boson Higgs” 14 Martie 2013: Noi proprietati masurate, este “un boson Higgs” 10 Decembrie 2013: Peter Higgs va lua Premiul Nobel? 2015-2016: doar unul sau mai multi bosoni Higgs?02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 29
    30. 30. Adrian Buzatu si Peter Higgs02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 30
    31. 31. Adrian Buzatu02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 31
    32. 32. Adrian Buzatu02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 32
    33. 33. Multumesc! Intrebari? Sugestii?http://adrianbuzatu.ro
    34. 34. Backup slides02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 34
    35. 35. The Recipe for the Universe Light, radio, radar Nuclear stability Radioactivity02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 35
    36. 36. The Scientists’ Room Analogy02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 36
    37. 37. The Tevatron Accelerator Fermilab, near Chicago, USA Complex of particle accelerators Collides matter and antimatter (protons and antiprotons) 150 m/s less than the speed of light (300 million m/s) 2.5 million collisions per second 2 collision locations: CDF and DZero02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 37
    38. 38. Collider Detector at Fermilab Central Cal Muon Detectors Plug Cal Silicon Central Tracker Tracker A particle detector (3D digital camera) As big as a huge room Layers of subdetectors Measuring particle type, direction of movement, energy and momentum02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 38
    39. 39. The WH Associated Production Our search: a W boson + a Higgs boson The W boson decays to an electron (muon) + neutrino It helps us a lot that we can indentify well electrons and muons in the detector Our search (WH) Colliding Virtual Decay products particles particles in detector Higgs Particle (H)02/04/13 Elementary particle 39 Adrian Buzatu - Povestea descoperirii unui boson Higgsas massive as heavy atoms
    40. 40. My Improvement Charged lepton (Electron or Muon) My contribution to improve the search: More charged leptons, which means More W bosons, which means More WH events, which means More signal selected, which means More precise “microscope”! We introduce a new method to reconstruct electrons and muons that would normally be lost in the non instrumented regions of the detector02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 40
    41. 41. Charged Lepton Improvement Cylindrical detector rolled on a plane Y axis: 0-2Pi X axis – 0 for half heightDark blue, Green – muonsLight blue – electronsRed – muons or electrons thatwould be lost in the noninstrumented regions of thedetector, but we recover Adrian Buzatu, Conferinta Diasporei 2012
    42. 42. Key Analyses Variables Mass of hypothetical particle decaying to two bottom quarks Output of trained artificial neural network with background peaking at 0 and signal at 1 Red: WH Signal multiplied by 5 times!02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 42
    43. 43. My PhD Result – 3 August 2011 Dotted line: how precise our “microscope” is Solid line: what we actually measure with our “microscope” Name of the game: drive the solid line below 1 to exclude the Higgs boson! Black: the WH analysis before my contribution Red: with the addition of my original PhD contribution, the WH analysis improves both the Y axis: Measurement precision of the “microscope” divided by theory prediction and the actual measurement02/04/13 Adrian Buzatu - Povestea descoperirii unui boson Higgs 43

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