Fisica ai collisionatori adronici
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Fisica ai collisionatori adronici C. Gemme (INFN Genova) Corso di Dottorato 2014. Outline del corso. Collisionatori ( adronici ) Motivazioni LHC Rivelatori ai collisionatori Anatomia del rivelatore (ATLAS) Trigger Operazione Performance. Osservabili e Analisi dati

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Fisica ai collisionatori adronici C. Gemme (INFN Genova) Corso di Dottorato 2014

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Fisica ai collisionatori adronici c gemme infn genova corso di dottorato 2014

Fisica ai collisionatori adronici

C. Gemme (INFN Genova)

Corso di Dottorato 2014


Outline del corso

Outline del corso

  • Collisionatori (adronici)

    • Motivazioni

    • LHC

  • Rivelatoriaicollisionatori

    • Anatomia del rivelatore (ATLAS)

    • Trigger

    • Operazione

    • Performance

  • Osservabili e Analisi dati

  • Misure di standard model

    • Introduzione

    • EW: fit, W/Z, top

  • Higgs

    • Richiami teorici

    • La scoperta

    • Higgs gg

    • Proprieta’ dell’Higgs

    • Aspettative dei prossimi run

  • Oltre il modello standard

    • Supersimmetria

    • “Esotici”

Slides: www.ge.infn.it/~gemmec/talks/Didattica/

LHCP 2014: https://indico.cern.ch/event/279518/

ICHEP 2014: http://ichep2014.es/ (this week!)

ATLAS: https://twiki.cern.ch/twiki/bin/view/AtlasPublic/WebHome

CMS: https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResults


Fisica ai collisionatori adronici c gemme infn genova corso di dottorato 2014

W/Z bosons

Fisica ai Collisionatori Adronici


W z bosons

W/Z bosons

  • Last time we have seen how to identify Z/W boson.

  • Next:

    • W mass

    • W/Z Production

    • W/Z + jets Production

    • Z4l

    • Diboson production

    • Measurement of aTGC

~20% nn , ~10% ll, 70% hadrons

~67% hadrons, ~33% ln

Fisica ai Collisionatori Adronici


W mass

W mass

  • World measurement by Tevatron and LEP:

    • Analysis being performed with full Tevatron dataset (~10 fb-1):

      • CDF ~10 MeV, D0 ~ 15 MeV total uncertainty projection;

    • More LHC measurement to come

With MW

Without MW


W z production

W/Z production

  • W/Z production studied (mainly) in the leptonic modes:

    • W boson signature (~33% lv, ~67% hadrons): one high pT lepton and missing energy

    • Z boson signature (~20% inv, ~10% ll, ~70% hh): two high pT opposite charge, same flavour leptons

Phys. Rev. D85 (2012) 072004

  • First step is to measure the fiducial cross-section

    • Where N are the candidate events in data, B background events computed using data and simulation, Lint the integrated luminosity corresponding to data and trigger used. CW/Z is correction factor measuring the efficiency in the fiducial region determined by the selection cuts, for instance pT> xx GeV, etc…

NMC,rec events after simulation, reconstruction and selection

NMC,gen,cut events at the generation in the fiducial cuts

Fisica ai Collisionatori Adronici


W z production1

W/Z production

  • The fiducial cross-section is dependent on the analysis cuts, therefore not very useful for comparisons with other results or theoretical expectations.

  • The total cross-section in the leptonic channel is instead given:

    • where the acceptance AW/Zis used to extrapolate the cross-section measured in the fiducial volume, σfid, to the full kinematic region:

Phys. Rev. D85 (2012) 072004

NMC,gen,cut events at the generation in the fiducial cuts

NMC,gen,all events at the generation

√s = 7 TeV, L = 36 pb-1, electron channel

√s = 7 TeV, L = 33 pb-1, muon channel


W z production2

W/Z production

  • Once the cross-sections in the electron/muon channels are measured, the ‘leptonic’ result is given, properly accounting for the common systematics errors:

Phys. Rev. D85 (2012) 072004

√s = 7 TeV

  • Measurements already limited by sys and lumi uncertainties

  • Good agreement with NNLO prediction

  • Discriminating power against different PDF sets


W z production3

W/Z production

  • Measuring the ratio between e and muon channel is a measurement of the branching ratio between the two channels

  • Total cross-section vs cms energy

Fisica ai Collisionatori Adronici


W z production pdf

W/Z production  PDF

  • Cross-sections and mainly the differential cross-sections provide discrimination power for the PDFs.

    • Sensitive to gluon PDF

  • 10 bins in pT(Z) and 8 bins in Y(Z): CMS PAS SMP-13-013

Fisica ai Collisionatori Adronici


W z production with jets

W/Z production with jets

  • Production of jets in association with vector bosons allow to test pQCD

    • Difficult to provide NLO predictions at high multiplicities

    • PDFs probe region of high Q2 and low x

  • Important background for many searches of new physics

  • Sensitive to renormalization scales, PDFs and hard partonradiation at large angles.

Fisica ai Collisionatori Adronici


W z production with jets1

W/Z production with jets

  • Up to 7 jets measured (17 events)

Fisica ai Collisionatori Adronici


Rare processes an example z 4l

Rare processes, an example: Z4l

arXiv:1403.5657

Fisica ai Collisionatori Adronici


Diboson production ww zz wz w g z g gg

Diboson production (WW,ZZ,WZ,Wg,Zg, gg)

  • At the LHC dibosons measurements allow Precision tests of Standard Model and searches of new physics:

    • The major background to many Higgs channels

    • Background to many BSM searches

    • Probes of anomalous gauge boson self-interaction

      • Sensitive to BSM physics

      • Closely related to Higgs/EWSB mechanism

  • The electroweak Lagrangian of the SM allows for triple gauge couplings:

    • Leads to two bosons in the final state

  • Fisica ai Collisionatori Adronici


    Diboson production ww zz wz w g z g gg1

    Diboson production (WW,ZZ,WZ,Wg,Zg, gg)

    • In the boson production:

      • Largest LO contributions :

        • s-channel with triple gauge vertex

        • qqbar t- and u-channel (without triple coupling!)

    • Gluon-gluon:

      • typically a few % of the s7/8 TeV cross sections: from 10s of fb to 10s of pb

    Fisica ai Collisionatori Adronici


    Anomalous triple gauge couplings

    Anomalous Triple Gauge couplings

    • SM(+Higgs): Existence and strength of Triple and Quartic gauge boson couplings fully constrained

      • Deviations = New Physics!

    • However, physics beyond the SM could allow for ”anomalous” Triple Gauge Couplings (aTGCs)

      • Search for an excess in high energy tails where SM backgrounds are small

    Fisica ai Collisionatori Adronici


    Parametrization of atgcs

    Parametrization of aTGCs

    • Non-SM processes can affect TGCs:

      • aTGCs modify total production rate as well as event kinematics

      • Possible vertices using an effective Lagrangian with a parametrization:

    For ZZZ and ZZg couplings (forbidden!):

    For WWZ and WWg couplings:

    No deviation from SM expectation found!

    Fisica ai Collisionatori Adronici


    Diboson production

    Diboson production

    • Example: measurement of ZZ production at 8 TeV

      • Reconstructed Z in both e+e- and m+m-

      • Small background contamination

    Fisica ai Collisionatori Adronici


    Diboson production1

    Diboson production

    • Example: measurement of ZZ production at 8 TeV

      • Reconstructed Z in both e+e- and m+m-

      • Small background contamination

    Measurements are

    slightly above theory

    expectations (but in

    agreement within 1s)

    Fisica ai Collisionatori Adronici


    The big picture

    The big picture

    Fisica ai Collisionatori Adronici


    Fisica ai collisionatori adronici c gemme infn genova corso di dottorato 2014

    Top quark

    https://indico.cern.ch/event/279518/session/27/contribution/37/material/slides/0.pdf

    Fisica ai Collisionatori Adronici


    By grannis tevatron legacy@ lhcp2014

    By Grannis, Tevatron Legacy@ LHCP2014

    Fisica ai Collisionatori Adronici


    Fisica ai collisionatori adronici c gemme infn genova corso di dottorato 2014

    Fisica ai Collisionatori Adronici


    Top quark is special

    Top Quark is special!

    • Its mass is much larger than any other fermion  only quark that has weak decay in real W, rather than a virtual W.

    • The decay width is large: decay happens before any strong bound may be formed as happens for c and b  measure quark properties before hadronization.

    Latest results:

    ΔMtop/Mtop <1%

    Best relative precision available for any of the quark masses

    Fisica ai Collisionatori Adronici


    Top production

    Top production

    Top production at Tevatron vs LHC: complementary information!

    Top-antitop

    Single top

    t-chan

    s-chan

    tW-chan

    Single top quarks produced by EW interaction

    has been observed at Tevatron in 2009

    Fisica ai Collisionatori Adronici


    Top decay

    Top decay

    • Each top decays ~100% tWb

    ~67% hadrons,

    ~33% ln

    • Top pair production decays


    Top antitop cross sections at lhc

    Top-antitop cross-sections at LHC

    • Cross-sections are measured in all the channels, despite the S/B being different between them.

    • Similar for 8 TeV, results are coming…

    Fisica ai Collisionatori Adronici


    Top antitop cross sections summary

    Top-antitop cross-sections: summary

    * Representative exp. uncertainty: ~8% @ 7 TeV;

    5% @ 8 TeV per experiment; 5% Tevatron

    * Prediction in agreement with observed data


    Single top production

    Single top production

    • Small cross sections: very small yields and overwhelming background

      • ttbar

      • W+jets (t-channel) Z+jets (tW-channel)

      • QCD multijet, dibosons

    Fisica ai Collisionatori Adronici


    Single top production1

    Single top production

    • Small cross sections: very small yields and overwhelming background

      • ttbar, W/Z+ jets, QCD multijet, dibosons

    Fisica ai Collisionatori Adronici


    Single top production summary

    Single top production: Summary

    No significant deviation

    from SM observed

    Fisica ai Collisionatori Adronici


    Top mass

    Top mass

    • Top mass world combination: mtop = 173.34 ± 0.76 GeV

    ATLAS-CONF-2014-008 / CDF note 11071

    CMS PAS TOP-13-014 / D0 note 6416

    Fisica ai Collisionatori Adronici


    Top and calibration

    Top and calibration

    • Top final states involve all types of particles...

      • light-quark and b jets, missing transverse energy (ν), electrons, muons, tau decays products

    • The whole detector is involved: used for detector commissioning and calibration

      • Example: a method to perform a b-tagging calibration exploits the very high purity of the tt pairs with both W’s decaying leptonically.

      • The b-tagging efficiency can be computed either with tag-and-probe or applying b-tagging algorithm to both jets and comparison with simulation.

    Fisica ai Collisionatori Adronici


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