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Fisica ai collisionatori adronici
C. Gemme (INFN Genova) Corso di Dottorato 2014
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Outline del corso Collisionatori (adronici)
Motivazioni LHC Rivelatori ai collisionatori 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: LHCP 2014: ICHEP 2014: (this week!) ATLAS: CMS:
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Fisica ai Collisionatori Adronici
W/Z bosons Giugno 2014 Fisica ai Collisionatori Adronici
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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 Z4l Diboson production Measurement of aTGC ~20% nn , ~10% ll, 70% hadrons ~67% hadrons, ~33% ln Giugno 2014 Fisica ai Collisionatori Adronici
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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 Giugno 2014
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Fisica ai Collisionatori Adronici
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) 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 Giugno 2014 Fisica ai Collisionatori Adronici
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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/Z is used to extrapolate the cross-section measured in the fiducial volume, σfid, to the full kinematic region: Phys. Rev. D85 (2012) 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
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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) √s = 7 TeV Measurements already limited by sys and lumi uncertainties Good agreement with NNLO prediction Discriminating power against different PDF sets
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Fisica ai Collisionatori Adronici
W/Z production Total cross-section vs cms energy Measuring the ratio between e and muon channel is a measurement of the branching ratio between the two channels Giugno 2014 Fisica ai Collisionatori Adronici
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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 Giugno 2014 Fisica ai Collisionatori Adronici
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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 parton radiation at large angles. Giugno 2014 Fisica ai Collisionatori Adronici
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W/Z production with jets
Up to 7 jets measured (17 events) Giugno 2014 Fisica ai Collisionatori Adronici
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Rare processes, an example: Z4l
arXiv: Giugno 2014 Fisica ai Collisionatori Adronici
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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 Giugno 2014 Fisica ai Collisionatori Adronici
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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 s 7/8 TeV cross sections: from 10s of fb to 10s of pb Giugno 2014 Fisica ai Collisionatori Adronici
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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 Giugno 2014 Fisica ai Collisionatori Adronici
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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! Giugno 2014 Fisica ai Collisionatori Adronici
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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 Giugno 2014 Fisica ai Collisionatori Adronici
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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) Giugno 2014 Fisica ai Collisionatori Adronici
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Fisica ai Collisionatori Adronici
The big picture Giugno 2014 Fisica ai Collisionatori Adronici
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Fisica ai Collisionatori Adronici
Top quark Giugno 2014 Fisica ai Collisionatori Adronici
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By Grannis, Tevatron Legacy@ LHCP2014
Giugno 2014 Fisica ai Collisionatori Adronici
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Fisica ai Collisionatori Adronici
Giugno 2014 Fisica ai Collisionatori Adronici
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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 Giugno 2014 Fisica ai Collisionatori Adronici
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Fisica ai Collisionatori Adronici
Top production Top production at Tevatron vs LHC: complementary information! Top-antitop Single top t-chan tW-chan s-chan Single top quarks produced by EW interaction has been observed at Tevatron in 2009 Giugno 2014 Fisica ai Collisionatori Adronici
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Top decay Each top decays ~100% tWb Top pair production decays
~67% hadrons, ~33% ln Top pair production decays
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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… Giugno 2014 Fisica ai Collisionatori Adronici
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Top-antitop cross-sections: summary
* Representative exp. uncertainty: 7 TeV; 8 TeV per experiment; 5% Tevatron * Prediction in agreement with observed data
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Fisica ai Collisionatori Adronici
Single top production Small cross sections: very small yields and overwhelming background ttbar W+jets (t-channel) Z+jets (tW-channel) QCD multijet, dibosons Giugno 2014 Fisica ai Collisionatori Adronici
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Fisica ai Collisionatori Adronici
Single top production Small cross sections: very small yields and overwhelming background ttbar, W/Z+ jets, QCD multijet, dibosons Giugno 2014 Fisica ai Collisionatori Adronici
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Single top production: Summary
No significant deviation from SM observed Giugno 2014 Fisica ai Collisionatori Adronici
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Fisica ai Collisionatori Adronici
Top mass Top mass world combination: mtop = ± 0.76 GeV ATLAS-CONF / CDF note 11071 CMS PAS TOP / D0 note 6416 Giugno 2014 Fisica ai Collisionatori Adronici
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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. Giugno 2014 Fisica ai Collisionatori Adronici
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