Search for New Physics at the Large Hadron Collider

Transcription

1 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 1 Search for New Physics at the Large Hadron Collider Babes-Bolyai University, Cluj-Napoca, 17 March 2011 Dezső Horváth horvath@rmki.kfki.hu KFKI Research Institute for Particle and Nuclear Physics, Budapest and Institute for Nuclear Research, Debrecen

2 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 2 Outline Elementary Particles: Leptons and Quarks Interactions and Gauge Bosons LHC and its Experiments Search for the Higgs Boson Search for Supersymmetry What Is It Good for?

3 The Zoo of the Standard Model colored quarks colorless composite hadrons hadrons = mesons (qq) + baryons (qqq) Nucleons (I = 1 2 ): p = (uud) n = (udd) p = (uud) Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 3

4 Glory Road of the Standard Model Status 2010 Includes hundreds of measurements of all experiments Expt theory expt. uncertainty Slightly deviating quantity changes from year to year Now it is forward-backward asymmetry of e + e Z b b LEP Electroweak Working Group: Measurement Fit O meas O fit /σ meas α (5) had (m Z ) ± m Z [GeV] ± Γ Z [GeV] ± σ 0 had [nb] ± R l ± A 0,l fb ± A l (P τ ) ± R b ± R c ± A 0,b fb ± A 0,c fb ± A b ± A c ± A l (SLD) ± sin 2 θ lept eff (Q fb ) ± m W [GeV] ± Γ W [GeV] ± m t [GeV] ± July 2010 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 4

5 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 5 Spontaneous symmetry breaking mass Free fermion Higgs boson David J. Miller and CERN: djm/higgsa.html

6 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 6 Where is the Higgs boson? By-product of spontaneous symmetry breaking of the SM Most wanted particle of physics as the only missing piece of the Standard Model. Experimentally not (yet?) observed, LEP: M(H) > GeV It was in that my life as a boson really began Peter Higgs: My Life as a Boson: The Story of The Higgs, Int. J. Mod. Phys. A 17 Suppl. (2002)

7 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 7 Accelerators of CERN LHC: Large Hadron Collider SPS: Super Proton Synchrotron AD: Antiproton Decelerator ISOLDE: Isotope Separator On Line DEvice PSB: Proton Synchrotron Booster PS: Proton Synchrotron LINAC: LINear ACcelerator LEIR: Low Energy Ion Ring CNGS: Cern Neutrinos to Gran Sasso

8 LHC and its main experiments Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 8

9 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 9 Steering magnets of LHC 1232 superconducting magnets (before installation) (L=15 m, M = 35 t, T = 1.9 K, B=8.3 T)

10 Dipole magnets of LHC: cross section Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 10

11 Dipole magnets of LHC in the tunnel Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 11

12 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 12 LHC: the Good, the Bad and the Ugly Good Great discovery potential: high energy, many kinds of collisions (steel balls vs. cheese dumplings), enormous luminosity. Bad Terrible SM background, rate of interesting new phenomena is Ugly Under any interesting event there are more p-p collisions giving combinatorial background

13 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 13 CMS: Compact Muon Solenoid ton digital camera: 100 M pixel, 40 M pictures/sec, 1000 GB/sec data Store max 400 pictures/sec intelligent filter!!

14 Work on 160 muon chambers ATOMKI, Debrecen Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 14

15 Very forward calorimeter of CMS Cherenkov calorimeter: quartz fibers in steel RMKI, Budapest Calibration Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 15

16 CMS: the World s Largest SC Magnet Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 16

17 LICE: A Large Ion Collider Experiment Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 17

18 ATLAS: A Toroidal Lhc ApparatuS Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 18

19 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 19 What is measured: cross section Bombarding particle beam Target σ = W/Φ transition probability/flux Unit: 1 barn = m 2 (1 pb = m 2 ) Flux = particle density velocity in beam: Φ=n b v b = particles/surface/sec

20 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 20 Higgs boson production at LHC g q H g gluon fusion q q _ q W,Z _ q H vector boson fusion

21 Sensitivity of SM to Higgs mass SM fit to hundreds of data, 2010): +35 M H = GeV Lower limit (uncertainty of theory and expt): M H < 158 GeV (95 % CL) χ July 2010 Theory uncertainty α (5) α had = ± ± incl. low Q 2 data m Limit = 158 GeV LEP search: M H > GeV Tevatron (2010): excl GeV Free for the Higgs mass: < M H < 158 GeV 2 1 Excluded Preliminary m H [GeV] LEP Electroweak Working Group ( CMS and ATLAS should improve it in 2011 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 21

22 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 22 Decay of the SM Higgs boson SM Higgs mass: GeV, bad region for LHC

23 Search for the Higgs boson at LHC Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 23

24 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 24 CMS, H γγ: m H < 140 GeV Simulation! Good identification, very low rate ( ) Most efficient for a light Higgs boson The electromagnetic calorimeter of CMS is designed for detecting such photon pairs

25 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 25 CMS: elektromagnetic calorimeter PbWO 4 scintillators

26 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 26 H γγ (simulation) We need a lot more data for that, maybe in

27 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 27 Problems of the Standard Model Naturalness (hierarchy): Mass of the Higgs boson quadratically diverges due to radiative corrections. Eliminated if fermions and bosons exist in pairs. Cold dark matter: 20% of the energy of Universe. What is CDM that we observe its gravity only? Gravity: does not fit in system of gauge interactions (strong, electromagnetic, weak) Convergence of interactions: in SM the three gauge couplings get close at GeV, but do not meet All problems are purely theoretical, SM beautifully describes all experimental data. They would be solved by a universal fermion boson supersymmetry (SUSY).

28 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 28 Supersymmetry: partner particles Charges (electric, color, fermion) identical SUSY partners of fermions Leptons (S= 1 2 ) scalar leptons (S=0) e, µ, τ ẽ, µ, τ ν e, ν µ, ν τ ν e, ν µ, ν τ Quarks (S= 1 2 ) scalar quarks (S=0) u, d, c, s, t, b ũ, d, c, s, t, b Antiparticle antipartner X L, X R X 1, X 2

29 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 29 SUSY partners of bosons Elementary boson spin SUSY partner spin 1 photon: γ 1 photino: γ 2 1 weak bosons: 1 zino: Z 2 Z, W +, W 1 wino: W +, W gluons: g 1,... g gluinos: g 1,... g Higgs fields 0 higgsinos 2 H 0 1, H0 2, H+ 1, H 2 H 0 1, H 0 2, H + 1, H 2 3 graviton 2 gravitino 2 Two Higgs doublets 5 Higgs bosons: h, H, A, H +, H

30 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 30 Supersymmetry? Supersymmetry is obviously broken: no such particles, or maybe with much larger masses What is a broken symmetry good for? Higgs mechanism: symmetry violating field masses, renormalisation Higgs field violates an existing symmetry SUSY introduces a non-existing one All this for a rational, consistent theory

31 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 31 Unification of gauge interactions Standard Model: Gauge couplings get close, but do not converge at high energies SUSY: Convergence at GeV extra particles corrections Frank Wilczek: Nature 433 (2005) 239

32 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 32 Supersymmetry: + and Naturalness of theory + Cold dark matter of the Universe ( 20%) lightest SUSY-particle (LSP) Unification of interactions Can include gravitation BUT: Mechanism of SUSY breaking?? Many different models Many new parameters Not seen below m 100 GeV SUSY is almost 50% discovered!! (we see half of all SUSY particles (except 1) )

33 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 33 Search for SUSY particles Creation in pairs, decay to ordinary and SUSY particles Properties depend on models and parameters Lightest SUSY particle (LSP) unobservable missing energy observed Which one is LSP? Model dependent. SUSY (and Higgs) search at CERN: Large Electron-Positron collider (LEP), ; Large Hadron Collider (LHC), 2009

34 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 34 First year of the LHC: Tune the LHC: energy, intensity, stability 2. Tune the detectors: operation, trigger, calibration 3. How good is the simulation? Does it describe the known reactions and the detector? Agrees with data? 4. Do we see deviations? New phenomena or poor simulation of physics or of detector? 5. Beam time is shared between accelerator development and physics Nov. 2010: Pb ions circulating in LHC 7 Nov. 2010: Revolution starts in heavy ion physics!

35 LHC operation: bunches 312 bunches in LHC: 295, 16, 295, 295 collisions Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 35

36 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 36 Data collection: Data received and collected by CMS at 7 TeV linear scale logarithmic scale Horizontal regions: machine development Increase of 8 orders of magnitude in 8 months! To reach design values: 1000* intensity, 2*energy (2014?)

37 Multi-quark CMS event at 7 TeV Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 37

38 CMS-event: muon + missing momentum Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 38

39 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 39 CMS event: ZZ µ + µ µ + µ M(ZZ)= 200 GeV (Higgs candidate with too high mass)

40 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 40 The first paper of 7 TeV: CMS, QCD Text: 5 pages, 2324 authors: 8 pages Significant Hungarian contribution: Ferenc Siklér, Gábor Veres and Krisztián Krajczár (Budapest)

41 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 41 Measuring angular correlations at CMS Test pair correlations: angular differences between any two particles Difference in axial angle: η, in azimuthal: Φ Higher multiplicity weaker correlation??

42 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 42 New observation at CMS Any multiplicity High multiplicity (N > 110) p T > 0.1 GeV/c 1< p T < 3 GeV/c

43 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 43 ew phenomenon in p-p collisions at CMS High energy and multiplicity ridge in 2-particle angular correlation Low energy, few particles: peaks at 0, theory OK In multiparticle reactions at any η max. Φ initial state interaction like with heavy ions (it was observed at RHIC in Cu Cu collisions) Significant contribution by Gábor Veres (Eötvös U.)

44 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 44 ATLAS: Pb-Pb collisions Jet quenching in central Pb-Pb collisions Formation of colored medium at high energy. For 2-jet events from central collisions only the quark or gluon formed near the surface can escape, its counterpart will be absorbed. Also observed by CMS (naturally -:)

45 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 45 What all this is good for? Curiousity driven fundamental research, no direct applications BUT it produces useful by-products, e.g. World Wide Web: CERN, World, 1993 Muon Spin Resonance (chemistry, solid state physics) Positron Emission Tomography (PET) in medical diagnostics At present particle accelerators on Earth. Cca. 120 in particle physics, 7000 in medicine (mostly cancer therapy), rest in materials science. Grid computer networking: LHC data practical applications (meteorology, statistics for insurance, medical diagnosis)

46 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 46 SUMMARY LHC started in 2009 with low luminosity at TeV We hope for discoveries from 2011 on Even 7 TeV collision energy is enough for many things: Higgs boson(s), SUSY particles For precise studies one needs an e + e collider: International Linear Collider (ILC) LHC design started before LEP construction ILC plans are developing worldwide

47 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 47 SUMMARY 2 "There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. "There is another theory which states that this has already happened." Douglas Adams: The Restaurant at the End of the Universe

48 Dezső Horváth: Search for New Physics at the LHC, UBB, Cluj-Napoca, p. 48 Thanks for your attention Detector control room of CMS 16 Dec at 18.00