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


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


W/Z bosons

Fisica ai Collisionatori Adronici


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

  • 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 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 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 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 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

  • 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

  • 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 jets

  • Up to 7 jets measured (17 events)

Fisica ai Collisionatori Adronici


Rare processes, an example: Z4l

arXiv:1403.5657

Fisica ai Collisionatori Adronici


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,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

    • 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

    • 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

    • 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 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

    Fisica ai Collisionatori Adronici


    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

    Fisica ai Collisionatori Adronici


    Fisica ai Collisionatori Adronici


    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 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

    • Each top decays ~100% tWb

    ~67% hadrons,

    ~33% ln

    • Top pair production decays


    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

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

    5% @ 8 TeV per experiment; 5% Tevatron

    * Prediction in agreement with observed data


    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 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

    No significant deviation

    from SM observed

    Fisica ai Collisionatori Adronici


    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 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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