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1 PHYSICS AT THE LHC Marina Cobal University of Udine & INFN Trieste.

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1 1 PHYSICS AT THE LHC Marina Cobal University of Udine & INFN Trieste

2 “Giovanotto, se io fossi in grado di ricordarmi il nome di tutte queste nuove particelle avrei fatto il botanico e non il fisico.” (Enrico Fermi) All of them elementary particles? Too many discoveries?

3 Today we have a quite simple framework to describe the constituents of matter and their interactions: the Standard Model. According to the SM, the elementary constituents of the whole Universe are 12, grouped in 3 families, each of one containing 2 quarks and 2 leptons. Anti-matter has to be added (for each particle a corresponding anti-particle with opposite charge The Standard Model

4 " Three quarks for Muster Mark! Sure he hasn't got much of a bark and sure any he has it's all beside the mark." — James Joyce, Finnegan's Wake Murray Gell-Mann finds a mechanism to explain the common sub-structures of all the discovered hadrons … Barions: 3 quark Anti-barions: 3 anti-quark Mesons: 1 quark and 1 anti-quark Charges: u +2/3, d –1/3, s –1/3 Quarks

5 Forces in Nature ForceIntensityBosonsHappens in: Nuclear force~ 1Gluons (no mass) Electromagnetic~ Photons (no mass) Weak nuclear~10 -5 W +,W -,Z 0 (heavy) beta radioactive decay Gravitation~ Gravitons (?)

6 The Standard Model makes very accurate predictions about the nature of matter, nucleus, atoms, stars, you and me It is compatible with all the measurements performed But: The answers to these questions can be found in new experiments, like the LHC! 9 It is based on an element not yet observed: the Higgs It presents some mathematical difficulties It does not include gravity It does not explain the existence of dark matter Beyond the Standard Model?

7 The answer of Peter Higgs  A scottish physicist who, more than 40 years ago, proposed a mechanism for particles to acquire a mass.  Higgs supposed that the vacuum contains a field which can “slow down” particles.  This force field is generated by a particle yet undiscovered: the higgs boson To slow down a particle corresponds to give it a mass  Bigger or smaller  If the particle is insensitive to this force, the particle remains massless

8 8 In quantum mechanics every particle has an associated wavelength:  ∝ 1/p  high energy particles will allow to investigate at shorter distances Fixed target Colliders larger choice of particles and targets energy is partly wasted maximizes energy limited choice of particles (charged and stable  ions, e , p) 1 eV= energy of an electron accelerated from a potential of 1V 1 GeV= eV 1 GeV=0.016 g (m/s) 2 Microscopes in high energy physics The ability of ‘seeing’ things depends on the incident light and the goodness of the eye. The smallest resolvable details have dimensions comparable with the incident light wavelength. Resolving power ∝ 1/ 

9 Accelerators Campo elettrico: accelera. Campo magnetico: curva Unita di misura energia: eV e-e- E = 1 eV

10 The LHC magnets are the most powerful mankind can build today on industrial scale. They use superconductivity at 1.9 o K (- 271 o C) in a bath of superfluid He. Spin-off: research on superconductivity (cables, alloys). LHC magnets

11 LHC tunnel m 12

12 Lucio Rossi – ASC 2006 – dipoli principali magneti correttori multipoli LHC tunnel 2006

13 Two different interactions: Soft collisions The proton participates to the collision Proton-proton collisions

14 Hard collisions The protons are made of quarks and gluons and these head on collisions may bring away quarks ~1000 charged particles/interaction LHC detector: quick response radiation resistance Proton-proton collisions

15 15 Bunch Crossing 4x10 7 Hz (40 millions per second) 7x10 12 eV Beam Energy cm -2 s -1 Luminosity 2835Bunches/Beam Protons/Bunch 7 TeV Proton Proton Collisions 10 9 Hz Parton Collisions New Particle Production 10 5 Hz 7.5 m (25 ns) The energy of a single proton accelerated to 7 TeV corresponds to the kinetic energy of a flying mosquito The energy of the LHC beam equals the kinetic energy of tons trucks at a speed of 100 Km/h A beam has protons ! or of a Boeing 777 (50 tons) at takeoff (450 Km/h) Colliders: the case of the LHC

16 Collisions!

17 17 CMS ATLAS you are here

18 18 We want to measure: direction, energy, momentum, electric charge, identity. The detector must be able to take the ‘picture’ of the event before the next bunch crossing. This is very demanding at the LHC (25 ns). Statistical distributions give information on average behaviour/properties. Tracking: measure trajectories of charged particles (as lighter as possible) Calorimeters: measure deposited energy (dense, must stop particles) Muon chambers: measure charged particles not stopped by the other detectors (only muons are known to do so) Magnetic field to bend charged particles Detectors on colliders

19 Wouter Verkerke, NIKHEF Measure p of charged particles Silicon & gas based tracking detectors in B field Measure E of all particles Calorimeters convert absorbed energy in light Measure p of muons Tracking Particle detection

20 20 Event reconstruction  Beams cross every 25 ns !  Every beam crossing there are ~25 interactions of ‘minimum-bias’ (MB).  A ‘good’ event (for instance H → ZZ →  ) is always accompanied by ~25 overlapping MB events. F F thousands of particles every triggered event, mostly with low E → All this (not the Higgs event, though) repeats after every 25 ns ! Properties of particles are then determined on a statistical basis

21 21 Heavy gauge bosons (Z  ) Extra dimensions GUT theories Mini-black holes 1 fb –1 100 pb –1 10 pb –1 Integrated luminosity Initial detector and trigger synchronisation, commissioning, calibration & alignment, material Search for extraordinary new physics signatures Accurate in-situ alignment and EM/jet/E T,miss calibrations Understand SUSY and Higgs backgrounds from SM Initial SUSY and MSSM Higgs sensitivity (E T → ~2 TeV) Higgs discovery sensitivity (M H = 130 ~ 500 GeV) Explore SUSY and new resonances to O(TeV) Time LHC startup Test beams, cosmic runs, pre- alignment and calibration, data distribution dress rehearsals Physics potential at LHC

22 22 Signs of the Higgs boson HIGGS (hopefully spectacular)

23 23 SM Higgs couples to m f 2 FDecays into the heaviest fermion or boson fermion or boson  Final state depends on M higgs  Ready to cover all possibilities Needed ingredients:  charged lepton tagging (including  ), photon reconstruction, jet reconstruction and b tagging, reconstruction, jet reconstruction and b tagging, missing E T reconstruction missing E T reconstruction  Need of a general purpose detector p p q q q q g g g g     H H p p q q q q W W W W H H Z Z Z ZProduction Decay Higgs production and decay

24 24 The Higgs in the detector

25 25 Higgs coverage No holes in m H coverage ! Discovery happens early in the game (just 30/fb needed) In several cases a few months at nominal luminosity are adequate for a proper 5  observation CMS/ATLAS can probe the entire set of allowed SM Higgs mass values  analyze all possible decays 99.7%

26 26 Signs of new physics

27 27 Supersymmetry New symmetry between fermions (matter) and bosons (force). For each particle p with spin s: SUSY partner p with spin s-½ ~ 100% 100% 30% In the decay chain the final products are fermions and the undetected LSP  Typically many jets + missing E T Spectacular signatures Spectacular signatures  Many additional parameters to describe the model model  The masses of SUSY particles are unknown, but the cross-sections are predicted to be big but the cross-sections are predicted to be big (~100 events/day at low luminosity (~100 events/day at low luminosity for ) for )  Fast discovery for the LHC  The challenge is to measure the particle spectrum spectrum

28 28 Spectacular evidence with full statistics Different final states depending on the parameters and the model  Discovery possible up to sparticle masses of 3 TeV with 300/fb Supersymmetry reach300/fb Time period Luminosity [cm –2 s –1 ] squark/gluino masses 1 month1033~1.3 TeV 1 year1033~1.8 TeV 1 year1034~2.5 TeV Ultimate  = 300 fb –1 ~2.5–3 TeV D0 & CDF  = 0.3 fb –1 > (2  ) 0.35 TeV m ~ 1 TeV,  ~ 1 pb → 10 4 events/year at low L

29 29 Stars and galaxies are moving too fast to just be subject to gravitational force of what is visible. Example: rotational velocity of galaxies SUSY could provide a good candidate for dark matter Approximately just 5% of what we ‘see’ (meaning that can emit EM radiation) represents the mass of the universe.  Embarassing, isn’t it? A good candidate for dark matter

30 30 Understanding gravity: extradimensions Much theoretical interest in models with extra dimensions:  All SM particles (us!) confined in a 4D world  Only gravity ‘sees’ the other dimensions  Gravity has the same strength than other forces, but is diluted in extra dimensions forces, but is diluted in extra dimensions  Solves the so-called hierarchy problem  Gravitons can be coupled to ordinary particles, might be visible at the LHC

31 31 Gravitons at the LHC Gravitons as final particles:  they escape in extradimensions  observed as missing energy  signatures: jet + missing energy  + missing energy Gravitons as virtual particles:  extra production of standard particles  observed as extra events  possible presence of resonances ADD Dominant backgrounds 100 fb –1

32 32 Black holes at the LHC Extra dimensions have very small radius and imply that gravity is much stronger at shorter distances Get more than ~TeV of energy into a small ‘enough’ region and a black hole forms spontaneously (impossible if only 4D) They decay instantaneously on the LHC time scales, and evaporate because of the Hawking radiation  Classically nothing escapes  In Quantum Mechanics they radiate ! ‘Normal’ BH: mass: ~ m sun size: ~ Km T: ~ 0.01 K Lifetime: ~forever ‘Mini’ BH: mass: ~ 1000 m p size: ~ m T: ~ K Lifetime: s

33 33 Black Holes at LHC Black hole universally and spherically evaporating into leptons, photons and jets in ATLAS. Final state multiplicity increases with M BH

34 34  Too many things we do not know/understand.  Any good high energy physicist cannot believe the SM is the end of the story.  We are asking some of the most fundamental questions in modern physics. To answer, the needed tools are of incredible complexity.  Still, one of the most exciting intellectual adventures of mankind The LHC should help the next step in the understanding of fundamental aspects of the infinitely small and the infinitely large After it, our view of (particle) physics could change forever (Personal) conclusions

35 35 Conclusions M. Mangano


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