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Standard Model Physics at the LHC

Discover the fundamental aspects of Standard Model physics at the Large Hadron Collider (LHC) through an in-depth exploration of Parton Distribution Functions, Electroweak Physics, and Cross Sections of SM Processes. Gain insights into jet physics and the sensitivity of W/Z production to PDF variations. Learn about the significance of measuring boson properties and gauge couplings, with implications for precision tests of the SM. Uncover the latest findings in di-boson and lepton-pair production, and delve into the intriguing world of WWγ couplings. Dive into the realm of high-energy physics and unravel the mysteries of the universe.

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Standard Model Physics at the LHC

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  1. Standard Model Physics at the LHC Joachim Mnich RWTH Aachen J. Mnich: SM Physics at the LHC

  2. Standard Model Physics at the LHC • Outline: • Perspectives on • Parton distribution functions • QCD + jet physics • Electroweak physics (Z/W bosons) • Top physics • Will not cover other SM physics topics, e.g. • Higgs • B-physics • Tau physics • Diffraction, luminosity, ... J. Mnich: SM Physics at the LHC

  3. Standard Model Physics at the LHC CMS ATLAS Atlas protons protons J. Mnich: SM Physics at the LHC

  4. Cross Section of Various SM Processes • Low luminosity phase • 1033/cm2/s = 1/nb/s • approximately • 200 W-bosons • 50 Z-bosons • 1 tt-pair • will be produced per second! • The LHC uniquely combines the • two most important virtues of • HEP experiments: • High energy 14 TeV • and high luminosity • 1033 – 1034/cm2/s J. Mnich: SM Physics at the LHC

  5. Parton Distribution Functions (PDF) y = pseudorapidity DGLAP evolution qq  W  l • LHC is a proton-proton collider • But fundamental processes are • the scattering of • Quark – Antiquark • Quark – Gluon • Gluon – Gluon Examples: gg  H • need precise pdf(x,Q2) + QCD corrections (scale) J. Mnich: SM Physics at the LHC

  6. PDF from W/Z production • pT and rapidity distributions are very sensitive to pdf • particularly sensitive variable: • ratio of W+/Wcross section measures u(x)/d(x) Example: study for 0.1 fb-1, i.e. 2·106 W produced Sensitive to small differences in sea quark distribution J. Mnich: SM Physics at the LHC

  7. PDF of s, c and b quarks Generator level study: Isolated high pT + jet with incl.  Isolated high pTe/  + jet with incl.  Estimate 5-10% accuracy on pdf Limited by fragmentation functions Analyses only suited for low luminosity phase J. Mnich: SM Physics at the LHC

  8. Parton Distribution Functions (PDF) Advertisement for the ongoing HERA/LHC workshop: Recipe for measurements of PDFs from SM processes: J. Mnich: SM Physics at the LHC

  9. Jet Physics Atlas • Measure jet ET spectrum, rate varies over 11 orders of magnitude • Test QCD at the multi-TeV scale Inclusive jet rates for 300 fb-1: J. Mnich: SM Physics at the LHC

  10. QCD Atlas • Measurement of s at LHC limited by • PDF (3%) • Renormalisation & factorisation scale (7%) • Parametrisaton (A,B) • 10% accuracy s(mZ) from incl. jets • Improvement from 3-jet to 2-jet rate? • Verification of running of s and • test of QCD at the smallest distance scale • s = 0.118 at mZ • s  0.082 at 4 TeV (QCD expectation) J. Mnich: SM Physics at the LHC

  11. Electroweak Physics: Properties of W and Z bosons Atlas Measurement of the W mass at the LHC mW is important parameter in precision tests of the SM 2004: mW = 80 425  34 MeV LEP & Tevatron Run I 2007: mW  80 ...  20 MeV (2.5 ·10-4) incl. Tevatron Run II Improvement at the LHC requires control of systematic error to 10-4 level • Take advantage from • large statistics • Z  e+e, + • Combine channels & • experiments •  mW  15 MeV J. Mnich: SM Physics at the LHC

  12. Drell-Yan Lepton-Pair Production q e, /Z pT > 6 GeV || < 2.5 e+, + q Inversion of e+e qq at LEP LHC 1 fb-1 Z pole • Total cross section • pdf • parton lumi • search for Z, extra dim. , ... • Much higher mass reach as • compared to Tevatron J. Mnich: SM Physics at the LHC

  13. Drell-Yan Lepton-Pair Production • Forward-backward asymmetry • estimate quark direction • assuming xq > xq • Measurement of sin2W effective • 2004: LEP & SLD • sin2W = 0.23150  0.00016 • AFB around Z-pole • large cross section at the LHC • (Z  e+e)  1.5 nb • stat. error in 100 fb-1 • incl. forward electron tagging • (per channel & expt.) • sin2W  0.00014 • Systematics (probably larger) • PDF • Lepton acceptance • Radiative corrections Atlas [%] J. Mnich: SM Physics at the LHC

  14. Di-Boson Production h1 dim6,  s3/2 CP h2 dim8,  s5/2 CP h3 dim6,  s3/2 CP h4 dim8,  s5/2 CP f4 dim6,  s3/2 CP f5 dim6,  s3/2 CP Measuring Triple Gauge Couplings (TGC) & testing the gauge boson self couplings of the SM • WW and WWZ vertices do exist in the SM Requiring C,P and elm. gauge invariance  5 coupling parameters • ZZ and ZZZ vertices do NOT exist in the SM • Requiring Lorentz & elm. • gauge invariance • & Bose symmetry • 12 coupling parameters hiV, fiV (V= ,Z) Deviations from SM amplified by high energies! J. Mnich: SM Physics at the LHC

  15. WW Couplings Atlas Test CP conserving anomalous couplings at the WW vertex  and  • W final states • W  e and  • pT spectrum of bosons pT () spectrum for SM couplings & current limits , at 1.5 TeV Sensitivity to anomalous couplings from high end of the pT spectrum J. Mnich: SM Physics at the LHC

  16. Sensitivity to WW Couplings LEP 2004 Atlas 30 fb-1 • At LHC limits depend on energy scale  • Large improvement wrt LEP • in particular on  due to higher • energy J. Mnich: SM Physics at the LHC

  17. ZZ Couplings Example: Couplings at the ZZ vertex hi • Z final states • Z  e+e– and +– • pT spectrum of photons and mT(ll) Spectra for SM couplings compared to current limits on anomalous couplings ( = 1.5 TeV): J. Mnich: SM Physics at the LHC

  18. Triple-Boson Production SM anomalous QGC Atlas Sensitive to quartic gauge boson couplings (QGC) 30 W signal events in 30 fb-1 J. Mnich: SM Physics at the LHC

  19. Top Physics • tt production • 87% gluon fusion 13% quark annihilation • Approx. 1 tt-pair per second at 1033/cm2/s • LHC is a top factory! Inverse ratio of production mechanism as compared to Tevatron • Top decay:  100% t  bW • Other rare SM decays: • CKM suppressed t  sW, dW: 10-3 –10-4 level • tbWZ: O(10-6) • difficult, but since mt mb+mW+mZ sensitive to mt • & non-SM decays, e.g. t  bH+ J. Mnich: SM Physics at the LHC

  20. Measurement of the Top Mass: Motivation t W+ W+ b H W,Z 1-r  (1- )(1-rW) rW  (mt2-mb2)  Top mass from Tevatron: rW  log mH J. Mnich: SM Physics at the LHC

  21. Top Mass from Semi-Leptonic Events Atlas • Easiest channel tt  bb qq l • Large branching ratio • Easy to select tt  bb qq  events from CMS & ATLAS J. Mnich: SM Physics at the LHC

  22. Top Mass from Semi-Leptonic Events j1 W j2 t b-jet Atlas Reconstruct mt from hadronic W decay Constrain two light quark jets to mW J. Mnich: SM Physics at the LHC

  23. Top Mass from Semi-Leptonic Events • 3.5 million semileptonic events in 10 fb-1 • (first year of LHC operation) • Error on mt  1 – 2 GeV • Dominated by • Jet energy scale (b-jets) • Final state radiation J. Mnich: SM Physics at the LHC

  24. Top Mass from Other Channels • Di-lepton events: • BR  5% • low background • but two neutrinos in final state • mt  1.7 GeV • Fully hadronic events: • BR  45% • difficult jet enviroment • mt  3 GeV J. Mnich: SM Physics at the LHC

  25. Top Mass from J/ channel 1000 events/y @ 1034 • Method: • Partial reconstruction of top • J/ + lepton • independent of jet energy scale • limited by b fragmentation • & needs high luminosity • Estimated ultimate precision: • mt 1 GeV J. Mnich: SM Physics at the LHC

  26. W Polarization Massive gauge bosons have three polarization states • At LEP in e+e W+W : • determine W helicity from lepton (quark) decay angle in W rest frame  • (1  cos )2 transverse • sin2 longitudinal  • Fraction of longitudinal W • in e+e  W+W • 0.218  0.031 • SM: 0.24 • Tevatron: • Longitudinal W in top decays • 0.91  0.52 CDF • 0.56  0.31 D0 • SM: 0.7 J. Mnich: SM Physics at the LHC

  27. W Polarization in Top Decays Standard Model prediction: detector simulation & acceptance • precision on fraction of long. pol. W:  0.023 (stat)  0.022 (sys) J. Mnich: SM Physics at the LHC

  28. tt Spin Correlation • Very short lifetime, • no top bound states • Spin info not diluted by hadron formation • Distinguishes between • quark annihilation • A = -0.469 • and gluon fusion • A = +0.431 Use double leptonic decays tt  bb l l A= 0.311  0.035  0.028 (using 30 fb-1) J. Mnich: SM Physics at the LHC

  29. Single Top Production • direct measurement of Vtb • observable by Tevatron in Run II • LHC t  1.5 t • Selection: • t  bW  b e () • b-jet + high pT lepton • reconstruction of top mass • Background from tt • signal to bkgd. 3.5 : 1 Production mechanisms and cross sections:  245 pb  60 pb  10 pb experimental determination of Vtb to percent level (with 30 fb-1) J. Mnich: SM Physics at the LHC

  30. Determination of Top Charge Qt = +2/3 Qt = -4/3 Atlas • Top charge: • Qt = +2/3 not yet established t  W+b • Qt = -4/3 not yet excluded t  W–b • LHC: • Determine charge from rate of radiative tt events • pT spectrum of photons for 10 fb-1: J. Mnich: SM Physics at the LHC

  31. Measurement of tt cross section • Total cross section: • At 14 TeV interesting in itself • Sensitive to top mass tt  1/mt2 • Differential cross sections: • d/dpT checks pdf • d/d checks pdf • d/dmtt sensitive to production of heavy object decaying to top-pairs Xtt 1.6 TeV resonance xBR required for a discovery 30 fb-1 σxBR [fb] 300 fb-1 Mtt mtt [GeV/c2] J. Mnich: SM Physics at the LHC

  32. Summary & Conclusions • SM physics at the LHC • Very important in initial phase • to check detector • to check generators (pdf) • to prepare discoveries • Large potential for precision measurements • large cross sections • precision limited by systematics • use as many different strategies as possible Credits: Marina Cobal, Matt Dobbs, Fabiola Gianotti, Alexander Oh, Dominique Pallin, Sergey Slabospitsky J. Mnich: SM Physics at the LHC

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