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The experimentalist's task

This talk is on the experimental evidence of this fundamental (?) particle (theory in the previous talk). The experimentalist's task. Theory: A small number of general equations with some parameters (unknown or poorly known) Observables:

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The experimentalist's task

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  1. TTdF – Seminario - DFO Milano-Bicocca

  2. TTdF – Seminario - DFO Milano-Bicocca This talk is on the experimental evidence of this fundamental (?) particle (theory in the previous talk)

  3. TTdF – Seminario - DFO Milano-Bicocca The experimentalist's task • Theory: • A small number of general equations with some parameters (unknown or poorly known) • Observables: • Cross-sections (probability of interaction), branching ratios, lifetimes • Experiments: • Inquire about what nature does • Imperfect measurement of a (set of) particle interactions in a (set of) detector(s). Compare measurements to observables

  4. TTdF – Seminario - DFO Milano-Bicocca Theory… e.g. the standard model • Has parameters • Coupling constants(electric charge and weak charge) • Masses • Predicts: • Cross-sections • Branching ratios • Lifetimes • … Adapted from G.Dissertori

  5. TTdF – Seminario - DFO Milano-Bicocca … and experiment Raw data 2×107 GB / year at the LHC (over 1 millionDVDs) Adapted from G.Dissertori

  6. TTdF – Seminario - DFO Milano-Bicocca … and experiment • Interactions  Electric signals Digitization  Hits  Track  p= (px,py,pz)  • Event (a unique happening): • List of (stable) particles with: E, p, charge and other information • Higher level reconstruction: e, μ, γ, hadrons (jets) Raw data Address: where the detector element took the reading ✚ Values: what the electronics wrote out ✚ ✚ ✚ pT=eBR Adapted from G.Dissertori

  7. TTdF – Seminario - DFO Milano-Bicocca … and experiment • Interactions  Electric signals Digitization  Hits Track  p= (px,py,pz)  • Event (a unique happening): • List of (stable) particles with: E, p, q and other information • Higher level reconstruction: e, μ, γ, hadrons (jets) ✚ ✚ • A measurement: data and theory prediction (convolved with detector response) ✚ ✚

  8. TTdF – Seminario - DFO Milano-Bicocca Any definite prediction? • The standard model (SM) of EWK interactions: • Non-abelian gauge theory: SU(2)L x U(1)Y • With spontaneous symmetry breaking • New unequivocal predictions: • A neutral massive boson (Z-boson) and its couplings • A massive scalar field (Higgs boson) of unpredicted mass • 1954 - Yang & Mills non-abelian gauge theory • 1961 - Sh. Glashow, SU(2)xU(1) with mass-less bosons • 1964 - P. Higgs + Brout & Englert – Symmetry breaking • 1967/68 - S.Weinberg / A.Salam :

  9. TTdF – Seminario - DFO Milano-Bicocca However… LEP/SLC/Tevatron • 1973 – Discovery of neutral currents • 1982 – Discovery of W/Z bosons • 1989-2000 – Over 100 tests of the standard model with no sign of inconsistency … • … and yet no (direct) sign of a Higgs boson mH > 114.4 GeV (95% CL)

  10. TTdF – Seminario - DFO Milano-Bicocca More about the Higgs boson • Gauge bosons : • MW2 = ¼ g2 v • MZ2 = ¼ (g2+g’2) v • Theory constraint: (MZ/MW)2 = g2/(g2+g’2) • Strong indication of a ‘Higgs mechanism’ through the independent measurement of boson masses and EWK coupling constants • Fermions : • m = λv / √2 • Unconstrained by theory • Higgs mass unknown, but: • mH> 114 GeV LEP direct bound • mH< 152 GeV Indirect bound from SM precision tests • mH< 1 TeV Theory bound (e.g. WW scattering) • gHVV = 2MV2/v • gHVV = mf/v

  11. TTdF – Seminario - DFO Milano-Bicocca The Large Hadron Collider • Primary objectives: • Search for the SM Higgs boson up to 1 TeV • Characterize it, if found • Search for phenomena beyond the standard model • New gauge bosons, ‘new physics’ at the 1 TeV scale • Dark matter candidate • Centre of mass energy: • 7-8 TeV (2010-2012) • 14 TeV (design) • 18 km/27 km of superconducting dipoles • B = 8.3 T • T = 1.9 K (120 ton of L-He) • 80 MW (+ 30 MW for the experiments) Approved in 1994 First collisions in 2009

  12. TTdF – Seminario - DFO Milano-Bicocca Detectors at the LHC

  13. TTdF – Seminario - DFO Milano-Bicocca The Compact Muon Solenoid

  14. TTdF – Seminario - DFO Milano-Bicocca The Compact Muon Solenoid charged tracks Jets (originated by partons) Pixel / Tacker detector Electromagnetic Calorimeter Hadron Calorimeter Solenoid Muon detector hadrons (π,K,p,n,…) made by quarks photons/electrons muon

  15. TTdF – Seminario - DFO Milano-Bicocca The Compact Muon Solenoid • Milano-Bicocca in CMS Hγγ candidate γ2 γ1 Electromagnetic calorimeter: cooling system, commissioning, calibration and monitoring, project coordination (2011-2012) Pixel detector: construction commissioning, data monitoring Data analysis: Hγγ, HWW, Hττ, Search for heavy gauge and scalar bosons, Heavy flavour physics Computing: INFN coordination

  16. TTdF – Seminario - DFO Milano-Bicocca Higgs boson production at pp colliders Gluon-gluon fusion ~ 500 kevts in data • Higgs couples to quarks, and bosons; initial and final states include composite hadrons  Not an easy problem: (leading theory group in the field at Milano-Bicocca) • Vector boson fusion ~ 40 kevts in data Two forward jets

  17. TTdF – Seminario - DFO Milano-Bicocca Higgs detection at the LHC • Higgs boson mass • from decay products: • “Invariant mass” of final state particles originated by the Higgs boson decay • The Higgs Hunter’s vademecum • Identify decay products • Measure with high resolution the energy and the momentum • Search for a (narrow) peak in the invariant mass spectrum Probability of Higgs boson decay to a final state • Discovery channels: • H  ZZ(*)  4 leptons • H γγ

  18. TTdF – Seminario - DFO Milano-Bicocca Experimental challenges ATLAS • Trigger • Total collision rate 40 MHz • Storage capability ~300 Hz • Must trigger efficiently Higgs boson candidates (and other processes) • Crowded environment • Pileup events affect ‘particle isolation’ and energy reconstruction • Rejection/mitigation of background events: • E.g. in the Hγγ case: • Fake photons from neutral pions in γ+jet, or dijet events • Prompt diphoton production • Fine transverse segmentation • High invariant mass resolution 2010 O(2) collisions per beam crossing 2011 O(10) collisions per beam crossing 2012 O(20) collisions per beam crossing

  19. TTdF – Seminario - DFO Milano-Bicocca The Higgs boson signal: HZZ* • Signal significance • ATLAS: 6.6 standard deviations • MH = 124.3 +/- 0.5 +/- 0.5 GeV • CMS: 6.7 standard deviations • MH = 125.8 +/- 0.5 +/- 0.2 GeV H  ZZ* μ+μ-e+e-

  20. TTdF – Seminario - DFO Milano-Bicocca The Higgs boson signal: H  γγ • Signal significance • ATLAS: 7.4 standard deviations • MH = 126.8 +/- 0.2 +/- 0.7 GeV • CMS: 3.9 standard deviations • MH = 125.4 +/- 0.5 +/- 0.6 GeV H γγ

  21. TTdF – Seminario - DFO Milano-Bicocca Restrospective view • Comparison between HZZ* results and projections from the first LHC Workshop in 1990 (I was a PhD student atin DELPHI though) Simulation for three mass hypotheses Much better than anticipated From MarumiKado

  22. TTdF – Seminario - DFO Milano-Bicocca Is it the SM Higgs boson? • Test, spin, couplings, etc. • Example: Measurement of the modifiers of the SM Higgs coupling to gauge bosons and fermions • All measurements so far consistent with the SM κv kf andκV κf This Higgs boson couples to fermions: not a trivial result!

  23. TTdF – Seminario - DFO Milano-Bicocca Yet, the standard model is not enough • E.g. dark matter: • An experimental evidence that there is more than the standard model • Astrophysical evidence from rotation curves, gravitational lensing, bullet clusters • Six times more abundant than ordinary matter • ¼ of the total energy budget of the Universe • Particle candidates proposed in several models • Detection at LHC: • Jet of hadrons or photon • Missing energy (Dark matter footprint) partpn jet photon Dark matter particles

  24. TTdF – Seminario - DFO Milano-Bicocca Monojet events • No anomalies observed compared to known (SM) processes Adapted from Sh.Rahatlou

  25. TTdF – Seminario - DFO Milano-Bicocca Adapted from Sh.Rahatlou

  26. TTdF – Seminario - DFO Milano-Bicocca Prospects for the next runs • Found a scalar boson: its relatively small mass leaves theoretical puzzles to be addressed: EWK scale ~ 100 GeV ??? Mplanck = 1019 GeV • No evidence of new phenomena • New gauge bosons excluded up to 3 TeV • New fermions excluded up to 0.5 GeV • We have just gone through the first run! • LHC running planned for the next ~20 y (through upgrades) • Resume operation in 2015: • Centre of mass energy: 13 TeV (a factor ~2 more) • Integrated luminosity: 300 fb-1 (10 times more data) • Objectives: • Precision measurements of the Higgs boson properties • Couplings to 5-10% to see deviations from SM Higgs phenomenology • Search for new particles/phenomena at higher mass scales • Rare processes

  27. TTdF – Seminario - DFO Milano-Bicocca Conclusions and outlook • S’io fui del primo dubbio disvestitoper le sorrise parolette brevidentro ad un nuovo più fui irretitoe cominciai: “Già contento requievi,di grande ammirazion, ma ora ammirocom’io trascenda questi corpi lievi”. • Ond’ella, appresso d’un pio sospiro,li occhi drizzò ver me con quel sembiante che madre fa sovra figlio deliroe cominciò: “Le cose tutte quantehan ordine tra loro ……sì come cader si può vederefuoco di nube, sì l’impeto primos’atterra torto da falso piacere… “ • Dante, Paradiso, Canto I • There is a scalar boson compatible with the SM • and nothing else • Still puzzled by the way mass is given to massless particles • There is a higher level symmetry • Spontaneously broken • Let’s check this part of the theory in the next LHC run(s)

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