Font for next slides: CERN, BNL, Fermilab, Nobel Lectures, Wikipedia, Dieter Haidt, L. Di Lella and Carlo Rubbia, W. de Boer in 60 Years at CERN, Bettini, ATLAS and CMS Let‘s write then the Feynman rules for a weak charged interaction with a lepton and let‘s take as example the decay of the muon. The matrix element is 2 given by (here q <

In the Fermi 4-fermion interaction

From the analogy of the two, one derives that the Fermi constant

For a massive boson of a mass ~80 GeV, g~e or viceversa 2 3 Kurie plot in

4 Font: Perkins Pauli invented the neutrino in 1930, becoming a tool to investigate weak interactions “ I have today done something terrible which no theoretician ever should do and proposed something which never will be possible to be verified experimentally”. Soon after: • Fermi formulated his theory of � decay • Bethe-Peierls calculated the neutrino cross-section, it was small! • Pontecorvo realized that nuclear plants had high fluxes of anti-neutrinos • Cowan and Reines (1956) detected the first neutrino reactions at the Savannah River reactor

5 200 lt of water with cadmium chloride The positron annihilates in water with an electron giving two photons of 0.511 MeV; followed by the neutron reacting with Cadmium and giving an additional higher energy photon

Telegram to Pauli “We are delighted to tell you that we have definitley found neutrinos through observing inverse of beta-decay” Pauli answered: “Everything comes to him who knows how to wait” Reines Nobel prize in 1995 6 • Pontecorvo et al.: idea of high energy neutrino beams from pion decays in muons. • In 1962 Lederman, Schwarz and Steinberger established that more than one type of neutrino exists by first detecting interactions of the muon neutrino (Nobel Prize in 1988).

Schwarz and the spark chamber at BNL 7 Wu’s experiment It suggested a V-A type of interaction in the (1957): Parity is Lagrangian, with a weak intermediate vector violated in weak boson. interactions For instance matrix element for W decay:

It already raised interests in big labs to 8 search for this vector boson At the end of the 1950s V-A theory was the "standard model" of weak interactions. • In the mid-1960s Glashow-Weinberg-Salam model formulated a gauge theory of weak interactions with charged (W±) and neutral (Z) intermediate vector bosons. • The invention of the Higgs mechanism (1964) solved the problem of having both a gauge theory and massive mediators of weak interactions. • Martinus Veltman and Gerard 't Hooft proved the renormalizability of the theory. So by 1972 weak neutral currents were established in theory.

Proposal at CERN: use the intense beams at PS to produce neutrino beams and detect neutrino interactions using a heavy-liquid bubble chamber.

Large heavy-liquid bubble chamber (Gargamelle) in a magnetic field, at CERN. Started neutrino program at CERN, ”big” collaboration. Initially to solve question of two possible neutrinos, but BNL arrived first.

9 However after the GSW model predicted NC, Gargamelle bubble chamber, Gargamelle took the initiative to search for these 1973 events. A very large heavy liquid (freon) chamber, 4m long, in 2T B field

10 The discovery of neutral currents marked a milestone in experimental verification of the electroweak interactions and triggered new projects at CERN and everywhere else, both in theory and experiments, both on the experimental and theoretical sides. The mass values for the W,Z were better predicted around 80-90 GeV, and this brought CERN to start 11 a project looking for W,Z directly. 12 There was a pressure in mid 70’s to look for the W and Z bosons directly and in 1976 CERN made the decision for a proton- antiproton colliders.

At that time the SPS collider was a relatively new machine.i n 1976 CERN's SPS began operating with particle beams of energies up to 350-400 GeV onto a fixed target, i.e. with centre-of-mass energies of √s ~30 GeV, which was insufficient for W and Z production. There was a resistance to turn the machine into an proton-antiproton collider that The SppS complex at CERN at that time. could have not worked at all, but: Two experiments proposed and • Determination of Carlo Rubbia, with a clear accepted UA1, UA2. understanding of the machine and physics • Stochastic cooling of Simon van der Meer

In addition there was a lot of experience at 13 CERN on hadron-hadron colliders from ISR. Each quark would have ~1/3*1/2 of the beam energy. Putting the knowledge of parton densities in those days and c.m. energy ~540 GeV:

From this cross section, an instantaneous luminosity of at least 1028 cm-2 sec-1 was required to have a meaningful number of events. 14 Font: Bettini This was achieved by the stochastic cooling of van der Meer, reducing the beam emittance of the antiproton beam.

The anti-proton accumulator

The machine started in 1981 just few years after its conception, with the so-called “jet- 15 run”, to see 2-jet events in the detectors. Event display in UA1 with the large central tracker (drift chamber). Tracks had resolution of 100-300 um in the bending plane and up to 180 hits.

An event in UA1 From the first run in December 1982

UA1, one of the first multipurpose detectors, tracker, e.m. calorimeter (lead-scintillator,27 X0), hadronic calorimeter Fe-Sci, (4.5 �) and muon chambers. It was hermetic! 16 Central tracker, visible at Microcosm, CERN 17 Ua2: more centred on calorimetry, was optimized for electrons, could not detect muons.

18 In December 1982 the machine had reached enough int luminosity and UA1 oberved the first W event in electron+missing transverse energy.

The event had a track point to a high Et cluster and large missing Et

A W in enu event in UA1. The low energy Carlo Rubbia and Simon van tracks are due der Meer at the celebration to parton of the discovery spectator interactions.

19 Saclay selection: an ECAL cluster of > 15 GeV, a hard isolated track of pt > 7 GeV/c roughly pointing to the cluster, missing Et > 14 GeV, and no jet within 30° back-to-back in the plane transverse to the electron candidate. 6 clear events found, Confirmed by another selection later, in publication.

Seminar at CERN 20 January 1983, announcement of the discovery. Few days later Rubbia said “They look like Ws, they feel like Ws, they smell like Ws, they must be Ws”. 20 Few months later: discovery of Z

21 Font: Symmetry Nobel prize for Rubbia and van der Meer in 1984

Press conference at CERN

22 Font: CERN Jacobian peak (M(W)=83±3 ��� measured by Ua1 :

23 () ����= () At tree level

By measuring the two masses:

The SM is over-constrained. By measuring its parameters in different experiments, we can tests its consistency, i.e.: • Z mass at LEP • W mass at LEP2, Tevatron*

• Weinberg angle in neutrino experiments, LEP (AFB, etc..)

24 2 Brand new result appeared yesterday sin (θW) =0.22324±0.00033, Tevatron combination, arXiv:1801.06283 i.e. in neutrino experiments:

CHARM2 experiment at CERN in the 80-90’s

25 Where the couplings to the fermions differ for leptons/quarks and up-type/down-type

26 27 The weak interaction is based on the symmetry group SU(2)L where L indicates left- handed particles which transform under the gauge transformation. The weak „charge“ in this case in the weak isospin. Transitions between the weak isospin doublets

are mediated by W exchange. Right-handed particles are singlet and are „neutral“ for what concerns the weak isospin and therefore do not interact with the W. Let‘s now try to write down the Lagrangian density:

with 28 Let‘s apply now a local gauge transformation under SU(2):

T are 3 2X2 matrices, the generators of the group Similarly to QED and QCD, the local transformation are not invariant, so we apply the covariant derivative:

W are 3 new vector fields

The last term is the interaction between the doublets and29 the W For the Lagrangian to be local gauge invariance, adding the kinetic term for the W and their transformation, one gets (passages left out):

30 The Lagrangian that we have introduced has a problem: it does not contain mass terms for the W and Z bosons, which we know to be massive. Massive terms in that Lagrangian would not be gauge invariant. This was solved by the electroweak unified model of Glashow-Weinberg- Salam + the Higgs mechanism

Covariant derivative

in U(1)Y X SU(2)L

31 32 After the discovery of Z/W two projects started on electron-positron collisions to make precision physics at the Z peak: LEP (circular machine) at CERN and SLC (linear machine, with polarized beams) at Stanford.

Electron-positron collider 1989-2000 √s= M(Z) ÷ 209 GeV

LEP cavity in exposion at CERN

33 Startup of LEP 14th July 1989 L3 34 35 Font for this part: P. Zerwas At the peak:

Radiative corrections decrease the peak and broaden the shape.

Very first measurement: the number of „neutrinos“ from the total cross section, i.e. of family generation, at least those neutrinos which are not sterile and light enough and that couple to the Z. 17 millions of Z‘s detected by the 4 experiments. 36 37 LEP: high precision measurements of EWK parameters. Overconstrained, redundacy and possibility to test the consistency of the theory.

From Gfitter (RK) 38 Precision measurements at LEP allowed also predictions of parameters through radiative corrections, like the mass of the top and of the Higgs, before their direct observation (in 1995 and 2012, respectively).

39 Direct search:

40 Indirect constraint through radiative corrections:

41 42 The top quark is special. It is heavy like a golden nucleus, it can decay to a Wb, so it has a short lifetime ~ 10-25 sec and therefore it decays before hadronizing. It does not form bound states, its spin is transferred to its decay products. We can observe a „bare“ quark through its decays.

The top quark was discovered in 1995 at the Tevatron (FNAL) by the CDF and Dzero experiments. 43 1987-2011 at Fermilab (Batavia, IL) Energy 900 GeV- 1.8 TeV

44 45 46 47 48 49 Font: Quigg, PDG 50 By now at the LHC we have ~ 5 millions top pair produced

51 Tevatron combined 1.96 TeV (L ≤ 8.8 fb-1) -1 Aug 2016 CMS eµ* 5.02 TeV (L = 26 pb ) ATLAS+CMS Preliminary ATLAS eµ 7 TeV (L = 4.6 fb-1) -1 LHCtop WG CMS eµ 7 TeV (L = 5 fb ) 3 ATLAS eµ 8 TeV (L = 20.3 fb-1) 10 CMS eµ 8 TeV (L = 19.7 fb-1) LHC combined eµ 8 TeV (L = 5.3-20.3 fb-1) ATLAS eµ 13 TeV (L = 3.2 fb-1) CMS eµ* 13 TeV (L = 2.2 fb-1) ATLAS ee/µµ* 13 TeV (L = 85 pb-1) ATLAS l+jets* 13 TeV (L = 85 pb-1) CMS l+jets* 13 TeV (L = 2.3 fb-1) -1 cross section [pb] CMS all-jets* 13 TeV (L = 2.53 fb ) t 900 * Preliminary 102 800

Inclusive t 700 NNLO+NNLL (pp) NNLO+NNLL (pp) 13 s [TeV] 10 Czakon, Fiedler, Mitov, PRL 110 (2013) 252004 NNPDF3.0, m = 172.5 GeV, α (M ) = 0.118 ± 0.001 top s Z 2 4 6 8 10 12 14 s [TeV]

52 10 CMS 2010, dilepton 175.50 ± 4.60 ± 4.60 GeV JHEP 07 (2011) 049, 36 pb-1 (value ± stat ± syst) CMS Lepton+jets, 19.7 fb-1 (8 TeV) CMS 2011, dilepton 172.50 ± 0.43 ± 1.43 GeV 12000 -1 tt correct Single t EPJC 72 (2012) 2202, 5.0 fb (value ± stat ± syst) W+jets tt wrong Z+jets CMS 2011, all-jets 173.49 ± 0.69 ± 1.21 GeV 10000 tt unmatched QCD multijet EPJC 74 (2014) 2758, 3.5 fb-1 (value ± stat ± syst) Data Diboson 8000 After P selection CMS 2011, lepton+jets 173.49 ± 0.43 ± 0.98 GeV gof -1 JHEP 12 (2012) 105, 5.0 fb (value ± stat ± syst) 6000 CMS 2012, dilepton 172.82 ± 0.19 ± 1.22 GeV This analysis, 19.7 fb-1 (value ± stat ± syst) 4000

CMS 2012, all-jets 172.32 ± 0.25 ± 0.59 GeV 2000 5 Permutations / 5 GeV This analysis, 18.2 fb-1 (value ± stat ± syst)

CMS 2012, lepton+jets 172.35 ± 0.16 ± 0.48 GeV 1.5 This analysis, 19.7 fb-1 (value ± stat ± syst) 1 CMS combination 172.44 ± 0.13 ± 0.47 GeV 0.5

(value ± stat ± syst) Data/MC 100 200 300 400 Tevatron combination (2014) fit arXiv:1407.2682 174.34 ± 0.37 ± 0.52 GeV mt [GeV] (value ± stat ± syst) World combination 2014 ATLAS, CDF, CMS, D0 173.34 ± 0.27 ± 0.71 GeV arXiv:1403.4427 (value ± stat ± syst) Most precise value today by CMS 0 165 170 175 180 53 mt [GeV] As we have already seen, EW tests are a bit more complex to test at the LHC, due to the fact that the elementary collisions is between partons in the initial proton beams. However 54 several tests has been performed, some highlights in the next slides. May 2017 CMS Preliminary

7 TeV CMS measurement (L ≤ 5.0 fb-1) 5 8 TeV CMS measurement (L ≤ 19.6 fb-1) [pb] 10 13 TeV CMS measurement (L ≤ 35.9 fb-1) σ ≥n jet(s) Theory prediction 4 CMS 95%CL limits at 7, 8 and 13 TeV 10 ≥n jet(s)

103

102 =n jet(s)

10

1

10−1

Production Cross Section, 10−2

10−3

−4 EW EW γγ→ EW EW EW EW VBF 10 W Z Wγ Zγ WW WZ ZZ WVγ Zγγ Wγγ tt t tW t ttγ tZq ttW ttZ tttt ggH VH ttH HH qqW qqZ WW WγjjssWW Zγjj ZZjj t-ch s-ch qqH EW: W→lν, Z→ll, l=e,µ Th. ∆σ in exp. ∆σ All results at: http://cern.ch/go/pNj7 H

Status of SM cross sections measurement at CERN (similar plot exists for ATLAS) 55 May 2017 CMS Preliminary

7 TeV CMS measurement (L ≤ 5.0 fb-1) 5 8 TeV CMS measurement (L ≤ 19.6 fb-1) [pb] 10 13 TeV CMS measurement (L ≤ 35.9 fb-1) σ ≥n jet(s) Theory prediction 4 CMS 95%CL limits at 7, 8 and 13 TeV 10 ≥n jet(s)

103

102 =n jet(s)

10 Tri- boson 1

10−1 top Production Cross Section, 10−2 −3 W,Z Higgs 10 WW,WZ,ZZ −4 EW EW γγ→ EW EW EW EW VBF 10 W Z Wγ Zγ WW WZ ZZ WVγ Zγγ Wγγ tt t tW t ttγ tZq ttW ttZ tttt ggH VH ttH HH qqW qqZ WW WγjjssWW Zγjj ZZjj t-ch s-ch qqH EW: W→lν, Z→ll, l=e,µ Th. ∆σ in exp. ∆σ All results at: http://cern.ch/go/pNj7 H

Status of SM cross sections measurement at CERN (similar plot exists for ATLAS) 56 Z/γ*

57 Based on ~15M W events, 1.6 M Z‘s with 2011 data. New very precise Take ratios to decrease uncertainties, i.e. measurement of the inclusive Z and W luminosity uncertainties cancel. cross sections, with syst. unc. of ~0.6% Some tensions of the W/Z ratio compared (W) and <0.32% (Z) (+1.8% due to to recent PDF parametrizations luminosity determination). In good agreement with theory, NNLO QCD+NLO EW, sensitive to PDFs

Font: ATLAS arXiv:1612.03016 58 m(top) latest ATLAS measurement, mH from combination ATLAS+CMS

ATLAS measurement:

mW = 80370±19 MeV Similar precision to Tevatron Theory NNLO precision 8 MeV CDF: 80389±19 MeV D0: 80375±23 MeV PDG: 80385±15 MeV This plot shows how the Higgs, top and W mass come well together Font: ATLAS 59 LHC has high statistics of diboson events: ZZ, WZ, WW Test of QCD+EW and search for anomalousTCG couplings. Background process for Higgs boson production and new resonant states

60 The cross section for WW production in VBS would go to infinity without the Higgs. It is an indirect measurement for the Higgs boson, a difficult but cute measurement.

Alboteanu,Kilian,Reuter,2008 Selection requires two leptons with same charge, two jets |Δηjj|>2.5, MET,Z/top veto

The yellow region shows evidence for a WWJJ signal as expected from VBS. Observed in CMS with an observed significance of 5.5.