Introduction to Particle Physics I orientation_higgs. Risto Orava Spring 2015

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1 Introduction to Particle Physics I orientation_higgs Risto Orava Spring

Higgs as predicted by the standard model. It's On!

2 NEWS in September November 2009: Tevatron tightens up the race for the Higgs...by early 2011 they will have recorded enough data to allow them to either find or rule out the Higgs as predicted by the standard model. It's On! "God Particle" Race Intensifies as Obama Tries to Keep Particle Smasher in Hunt Fermilab to Receive Additional $60.2 Million in Recovery Act Funding for High Energy Physics 2

3 Higgs News from Fermilab 3 hep_experiments Risto Orava Helsinki

1 to 175 GeV W, Z bosons with masses of 80-90 GeV

4 The Standard Model of Particle Physics quark masses vary: 0.1 to 175 GeV W, Z bosons with masses of GeV (neutrino masses??) lepton masses between 0.1 to 1.8 GeV b-quark, t-quark and ν τ discovered at Fermilab 4

5 The Standard Model of Particle Physics Particle masses are built up in a dynamic process. radiative corrections The Higgs mechanism is a consistent way to give spin-1 particles a mass - the W and Z bosons masses in the standard model. The Higgs boson remains as a remnant of the process. Quark & lepton masses come as a bonus. 5

cosmic superconductor: Weak fields screened

6 Higgs Mechanism A single scalar field spontaneously acquires a vacuum expectation (v) value to generate boson and fermion masses. physical Higgs boson modes eaten by W,Z v A cosmic superconductor: Weak fields screened within fm Brout, Englert, Guralnik, Hagen, Higgs, Kibble (1964) 6

7 Internal Symmetry Breaking V ( φ) = ( φ v ) V ( φ) = ( φ v ) V ( φ) = ( φ v ) φ real φ real φ real φ im V ( φ) = ( φ v ) φ im V ( φ) = ( φ v ) φ im V ( φ) = ( φ v ) φ real φ real φ real φ im φ im φ im The potentials live in every point of space and waves of fluctuations move through entire space. 7

8 There are many open questions: gravity dark matter & dark energy cosmological inflation neutrino masses unification of gauge interactions... The idea is to try to find out what drives the electroweak symmetry breaking. 8

9 Quantum Mechanics and Special Relativity At the colliders, kinetic energy is converted to mass (E = mc 2 ). Particles are excitations of quantized fields the fields are fundamental. We are searching for fields that fill spacetime by seeing what particle states they excite. ħ = c = 1 9

10 How to find it? Higgs boson couples strongly to heavy fields and weakly to light fields (interactions are proportional to mass). Problem: We have to use light particles (that don t decay too soon!) in colliders. Large number of collisions needed. (In CDF 400,000 proton-antiproton collisions took place per second!) In a hard collision 1,96 TeV of kinetic energy could get packed into a volume as small as (1 am) 3. Many background particles and quanta are emitted. 10

11 Indirect information of the Higgs Boson is available: precise measurement of electroweak interactions Step 1: Measure 3 electroweak parameters extremely well QH(all)E or (g-2) e µ lifetime Step 2: Compute quantum corrections to other observables depend on plus LEP1 (Helsinki group in DELPHI) was the only unknown in SM Higgs sector 11

12 Most important corrections are to W/Z propagators For most observables, find: strong, quadratic dependence on m t weak, logarithmic dependence on m H Precise value of m W = (0.044) GeV and m t = (1.58) GeV by CDF/D0 experiments. 12

13 Combine precision observables for m H Most likely m H 90 GeV, excluded m H 114 GeV, upper limit (95% C.L.) m H 160 GeV. concentrate searches on light Higgs: 114 GeV < m H < 160 GeV 13

14 DIRECT SEARCH 14

15 THE TEVATRON COLLIDER COMPLEX proton-antiproton collisions at 1,96 TeV L peak = cm -2 s -1 weekly integrated lumi 50 pb -1 yearly integrated lumi 2 fb -1 total luminosity by mid September fb -1 6 fb -1 on tape today 15

16 THE TEVATRON COLLIDER COMPLEX Some 40 miles to Chicago Antiproton source Booster CDF Main injector & recycler Tevatron Some miles to California... 16

17 CDF and D0 EXPERIMENTS AT THE TEVATRON vertex detection and jet measurement in key roles 17

18 Luminosity: N events = L σ Tevatron performance now by far exceeds the initial expectations: L dt 2 fb -1 18

19 CDF Standard Model Higgs Searches l l l CDF aim was to find/exclude Higgs. 21 different final states for the Standard Model Higgs analyses. l Some of the final states subjects to more than one active analysis. Also 8 different Beyond The Standard Model Higgs searches. 19

20 Proton-(Anti)Proton Cross Sections σ(gg H o bb) σ(pp bb) 10-9 antip-p vs. pp! 20

21 Which processes to look at 1.96 TeV? Production through couplings to heavy objects (top/w/z) Signal/Background ratios! 1000 fb 5 fb Signatures? 200 fb 70 fb Cross sections for m H = 120 GeV 21

22 Higgs-strahlung (Bjorken process) Signature: a lepton (e or µ), missing E T, a pair of b-jets 22

23 Higgs decays to W + W - pairs are easy to see experimentally Signature: two leptons (e or m), 2 x missing E T 23

24 CDF Standard Model Higgs searches l Associated Higgs production l WH e/µ ν, bb (Helsinki: Timo Aaltonen)* l ZH νν, bb l ZH ll, bb l WH l ν, bb l VH jj, ll l ZH νν, ll l ZH ll, νν l ZH νν, bb, γγ l VH jj bb (Helsinki: Petteri Mehtälä)* l WH WWW l VH ZWW l VH, H ZZ *Important improvements in analysis algorithms, jet energy calibration and background rejection 24

25 CDF Standard Model Higgs searches l Single Higgs production l H WW eν l ν, µνl ν, qq l ν l H WW (eν/µν/qq ) qq l gg H WW eν/µν qq bb l gg H bb l gg H ll l gg H WW l ν l ν l gg H ZZ l gg H YZ (?) Central Diffractive Production pp p + H o + p (validation for the LHC) 25

26 A Higgs at CDF?: ZH ννbb could look like this! Many Higgs-like events have been seen in CDF & D

Higgs likes to decay into heavy objects: m H 140 GeV to bb pairs, m H > 140 GeV W + W - pairs SM decay probabilities (branching ratios) completely determined by m H

27 Higgs likes to decay into heavy objects: m H 140 GeV to bb pairs, m H > 140 GeV W + W - pairs SM decay probabilities (branching ratios) completely determined by m H Experimentally: b-quarks appear as jets of particles difficult to measure b jet energies precisely m H = 140 GeV W s appear as e/µ ν pairs measure e/µ + missing E T 27

28 Weak Boson Fusion: qq qqh o Signature: forward-backward pair of quarks with large p T s + central pair of jets (W s, τ s,...) 28

29 Top quark events represent the most serious backgrounds Signature: two leptons (e or µ), a pair of b- jets,2xmissing E T 29

30 General Principles of Detection Beam s Eye View 30

31 Can we see a quark? (3) Electrons, photons and hadrons turn into cascades in calorimeters. (2) Quark-antiquark pairs are emitted in the colour fields; they combine into colour neutral particle states (mainly p-mesons). The fastest ones form collimated showers jets. (1) Lorentz contracted packages of quarks & gluons collide. Hard collisions between quarks/gluons occasionally happen. The rest of proton/antiproton constituents remain as spectators or create multiple collisions. 31

32 b- quarks are important in discriminating against the backgrounds b-quarks are bound to hadron states that decay very quickly (10-13 sec) Special relativity (time dilatation) helps in getting more leverage. Helsinki group has b-tagging as its speciality. 32

An example: VH, H bb at the Tevatron - lepton tag removes most of the QCD background - top quark final states remain: t Wb l + jj - QCD WW l + bb - ISR give extra jets look into angular distributions

33 An example: VH, H bb at the Tevatron - lepton tag removes most of the QCD background - top quark final states remain: t Wb l + jj - QCD WW l + bb - ISR give extra jets look into angular distributions of b-jets and leptons ZH, WZ, ZZ, Wbb, Zbb, QCD+top WH, W/Z, Wbb, top 10 fb fb -1 WH signal! WZ Wbb top top m jj (GeV) - top quark pair and di-boson backgrounds peak close to the Higgs mass - shapes of the mass distributions similar σ signal possible - need to understand the QCD backgrounds and detector response in detail m jj (GeV) 33

34 New: Hki Group & Adaptive Informatics Research Centre,HUT 34

35 Multivariate analysis tools The Helsinki Group: Novel multivariate analysis approaches. 35

36 B-jet energy correction, flavor separator 4-5% Neural Network b-jet energy correction to improve Higgs mass resolution. Made by Helsinki. Neural Network flavor separator. Validation with new tracking algorithms driven by Helsinki. 36

37 95% C.L. exclusion for SM Higgs with m H = GeV Yesterday For 115 GeV Higgs: Expected limit: 1.9 x σ SM Observed limit: 2.8 x σ SM 37

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40 A SUMMARY 40

41 Higgs at the LHC - main difference vs. tevatron: the step in energy (2 14 TeV) - LHC is a gluon collider! 41

42 VBF BECOMES ATTRACTIVE VBF covers most of the mass range 42

43 NEXT:Introduction to Particle Physics I acceleration " Risto Orava " Spring

How To Find The Higgs Boson

How To Find The Higgs Boson Dezső Horváth: Search for Higgs bosons Balaton Summer School, Balatongyörök, 07.07.2009 p. 1/25 Search for Higgs bosons Balaton Summer School, Balatongyörök, 07.07.2009 Dezső Horváth MTA KFKI Research