Basics of QCD Lecture 1: the core ingredients Gavin Salam CERN Theory Unit ICTP{SAIFR school on QCD and LHC physics July 2015, S~aoPaulo, Brazil [What is QCD] QCD QUANTUM CHROMODYNAMICS The theory of quarks, gluons and their interactions It's central to all modern colliders. (And QCD is what we're made of) Gavin Salam (CERN) QCD Basics 1 2 / 24 [What is QCD] QCD predictions v. data for many processes Status: March 2015 dt Standard Model Production Cross Section Measurements L 1 Reference R[fb− ] pp 8 8 10− Nucl. Phys. B, 486-548 (2014) total ATLAS Preliminary × Jets R=0.4 0.1 < pT < 2 TeV arXiv:1410.8857 [hep-ex] y <3.0 4.5 | | Dijets R=0.4 0.3 < mjj < 5 TeV JHEP 05, 059 (2014) y <3.0, y <3.0 Run 1 √s = 7, 8 TeV 4.5 | | ∗ W PRD 85, 072004 (2012) total 0.035 Z 0.035 PRD 85, 072004 (2012) total t¯t 4.6 Eur. Phys. J. C 74: 3109 (2014) fiducial 20.3 Eur. Phys. J. C 74: 3109 (2014) PRD 90, 112006 (2014) tt chan 4.6 −total 20.3 ATLAS-CONF-2014-007 WW 4.6 PRD 87, 112001 (2013) total 20.3 ATLAS-CONF-2014-033 γγ JHEP 01, 086 (2013) fiducial 4.9 Wt 2.0 PLB 716, 142-159 (2012) total 20.3 ATLAS-CONF-2013-100 WZ 4.6 EPJC 72, 2173 (2012) total 13.0 ATLAS-CONF-2013-021 ZZ 4.6 JHEP 03, 128 (2013) total LHC pp √s = 7 TeV 20.3 ATLAS-CONF-2013-020 Wγ 4.6 PRD 87, 112003 (2013) fiducial Theory arXiv:1407.1618 [hep-ph] WW+WZ JHEP 01, 049 (2015) fiducial Observed 4.6 stat Zγ stat+syst 4.6 PRD 87, 112003 (2013) fiducial arXiv:1407.1618 [hep-ph] t¯tW 20.3 ATLAS-CONF-2014-038 total 95% CL upper limit LHC pp √s = 8 TeV t¯tZ 4.7 ATLAS-CONF-2012-126 total 20.3 ATLAS-CONF-2014-038 ¯ Theory ttγ 4.6 arXiv:1502.00586 [hep-ex] fiducial Observed Zjj EWK stat 20.3 JHEP 04, 031 (2014) fiducial stat+syst H γγ 20.3 Preliminary fiducial→ Wγγ arXiv:1503.03243 [hep-ex] fiducial, njet=0 20.3 W±W±jj EWK 20.3 PRL 113, 141803 (2014) fiducial 95% CL upper limit ts chan 0.7 ATLAS-CONF-2011-118 −total 95% CL upper limit 20.3 arXiv:1410.0647 [hep-ex] 3 2 1 1 2 3 4 5 6 11 10− 10− 10− 1 10 10 10 10 10 10 10 0.5 1 1.5 2 σ [pb] observed/theory Gavin Salam (CERN) QCD Basics 1 3 / 24 [What is QCD] QCD for Higgs physics QCD is especially relevant in order to deduce information about the Higgs boson. [cf. lectures by Andre Sznajder & Claude Duhr] Gavin Salam (CERN) QCD Basics 1 4 / 24 [What is QCD] QCD for Higgs physics ATLAS Input measurements Individual analysis ± 1σ on µ mH (GeV) +0.27 Overall: µ = 1.17 125.4 → γγ -0.27 H ggF: µ = 1.32+0.38 -0.38 125.4 VBF: µ = 0.8+0.7 -0.7 125.4 WH: µ = 1.0+1.6 -1.6 125.4 ZH: µ = 0.1+3.7 -0.1 125.4 Overall: µ = 1.44+0.40 125.36 H → ZZ* -0.33 ggF+ttH: µ = 1.7+0.5 -0.4 125.36 VBF+VH: µ = 0.3+1.6 -0.9 125.36 +0.24 Overall: µ = 1.16 125.36 H → WW* -0.21 QCD is especially relevant in +0.29 ggF: µ = 0.98 -0.26 125.36 VBF: µ = 1.28+0.55 -0.47 125.36 order to deduce information VH: µ = 3.0+1.6 -1.3 125.36 Overall: µ = 1.43+0.43 125.36 -0.37 H → ττ +1.5 about the . ggF: µ = 2.0 125.36 Higgs boson -1.2 VBF+VH: µ = 1.24+0.59 -0.54 125.36 Overall: µ = 0.52+0.40 125.36 → -0.40 VH Vbb +0.65 WH: µ = 1.11 125 [cf. lectures by Andre Sznajder -0.61 ZH: µ = 0.05+0.52 -0.49 125 & Claude Duhr] H → µµ µ +3.7 Overall: = -0.7 -3.7 125.5 → γ H Z Overall: µ = 2.7+4.5 -4.3 125.5 bb: µ = 1.5+1.1 125 ttH -1.1 Multilepton: µ = 2.1+1.4 -1.2 125 γγ: µ = 1.3+2.62 -1.75 125.4 -1 − s = 7 TeV, 4.5-4.7 fb 2 0 2 4 s = 8 TeV, 20.3 fb-1 Signal strength (µ) Gavin Salam (CERN) QCD Basics 1 4 / 24 [What is QCD] QCD and searches for new physics Search for stop squarks 19.4 fb-1 (8 TeV) 140 CMS Data tt/W→ τ +X 120 hadr tt/W→ e,µ+X Z→νν Identification and/or exclusion of 100 ~ ∼0 t→ tχ (500, 100) ~ ∼0 t→ tχ (650, 50) potential new physics relies in 80 diverse ways on a QCD-based Events / 50 GeV understanding of signals and 60 backgrounds. 40 20 0 2 1 miss 0 p [GeV] -1 T -2 Data 200 250 300 350 400 450 500 Data - MC pmiss [GeV] T Gavin Salam (CERN) QCD Basics 1 5 / 24 [What is QCD] QCD and searches for new physics Summary of CMS SUSY Results* in SMS framework ICHEP 2014 m(mother)-m(LSP)=200 GeV m(LSP)=0 GeV ~ ∼ 0 g → qq χ SUS 13-019 L=19.5 /fb ~ ∼ 0 g → bb χ SUS-14-011 SUS-13-019 L=19.3 19.5 /fb ~ ∼ 0 g → tt χ SUS-13-007 SUS-13-013 L=19.4 19.5 /fb ~ ~ ∼ 0 g → t(t → t χ ) SUS-13-008 SUS-13-013 L=19.5 /fb ~ ∼ ± ∼ 0 x = 0.20 g → qq(χ → Wχ ) SUS-13-013 L=19.5 /fb x = 0.50 0 gluino production ~ ~ ∼ ± ∼ g → b(b → t(χ → Wχ )) SUS-13-008 SUS-13-013 L=19.5 /fb ~ ∼ 0 q → q χ SUS-13-019 L=19.5 /fb squark ~ ∼ 0 t → t χ SUS-14-011 L=19.5 /fb ~ ∼ + ∼ 0 x = 0.25 x = 0.50 t → b(χ → Wχ ) SUS-13-011 L=19.5 /fb x = 0.75 ~ ∼ 0 ∼ 0 t → t b χ ( χ → H G) SUS-13-014 L=19.5 /fb ∼ 0 stop ~ ~ t → ( t → t χ ) Z SUS-13-024 SUS-13-004 L=19.5 /fb ~2 ~1 ∼ 01 t → ( t → t χ ) H SUS-13-024 SUS-13-004 L=19.5 /fb 2 1 1 ~ ∼ 0 b → b χ SUS-13-018 L=19.4 /fb ~ ∼ 0 b → tW χ SUS-13-008 SUS-13-013 L=19.5 /fb ~ ∼ 0 sbottom b → bZ χ SUS-13-008 L=19.5 /fb ∼ 0 ∼ ± ∼ 0 ∼ 0 x = 0.05 χ χ → lll ν χ χ SUS-13-006 L=19.5 /fb x = 0.50 2 x = 0.95 ∼ +∼ - + ∼ 0∼ 0 χ χ → l l-ν ν χ χ SUS-13-006 L=19.5 /fb ∼ 0 ∼ 0 ∼ 0 ∼ 0 χ χ → Z Z χ χ SUS-14-002 L=19.5 /fb ∼ ±2∼ 02 ∼ 0 ∼ 0 χ χ → W Z χ χ 2 SUS-13-006 L=19.5 /fb CMS Preliminary ∼ 0 ∼ 0 ∼ 0 ∼ 0 χ χ → H Z χ χ SUS-14-002 L=19.5 /fb 2 2 ∼ ± ∼ 0 ∼ 0 ∼ 0 For decays with intermediate mass, χ χ → H W χ χ SUS-14-002 L=19.5 /fb ∼ 0 ∼ ±2 ∼ 0 ∼ 0 x = 0.05 χ χ → llτ ν χ χ x = 0.50 ⋅ ⋅ EWK gauginos 2 SUS-13-006 L=19.5 /fb x = 0.95 m = x m +(1-x) m ∼ 0 ∼ ± ∼ 0 ∼ 0 intermediate mother lsp χ χ → τττ ν χ χ SUS-13-006 L=19.5 /fb 2 ~ ∼ 0 l → l χ SUS-13-006 L=19.5 /fb slepton ~ g → qllν λ 122 SUS-12-027 L=9.2 /fb ~ g → qllν λ SUS-12-027 L=9.2 /fb ~ 123 g → qllν λ 233 SUS-12-027 L=9.2 /fb ~ g → qbtµ λ ' 231 SUS-12-027 L=9.2 /fb ~ g → qbtµ λ ' SUS-12-027 L=9.2 /fb ~ 233 g → qqb λ '' 113/223 EXO-12-049 L=19.5 /fb ~ g → qqq λ '' EXO-12-049 L=19.5 /fb ~ 112 g → tbs λ '' 323 SUS-13-013 L=19.5 /fb ~ g → qqqq λ '' SUS-12-027 L=9.2 /fb ~ 112 q → qllν λ 122 SUS-12-027 L=9.2 /fb ~ q → qllν λ 123 SUS-12-027 L=9.2 /fb ~ → ν λ q qll RPV SUS-12-027 L=9.2 /fb ~ 233 q → qbtµ λ ' 231 SUS-12-027 L=9.2 /fb ~ q → qbtµ λ ' SUS-12-027 L=9.2 /fb ~ 233 q → qqqq λ '' R 112 SUS-12-027 L=9.2 /fb ~ t → µ e ν t λ R 122 SUS-13-003 L=19.5 9.2 /fb ~ t → µ τν t λ SUS-12-027 L=9.2 /fb ~R 123 t → µ τν t λ R 233 SUS-13-003 L=19.5 9.2 /fb ~ t → tbtµ λ ' R 233 SUS-13-003 L=19.5 /fb 0 200 400 600 800 1000 1200 1400 1600 1800 *Observed limits, theory uncertainties not included Mass scales [GeV] Only a selection of available mass limits Probe *up to* the quoted mass limit Gavin Salam (CERN) QCD Basics 1 6 / 24 [What is QCD] Aims of the course The school will cover many aspects of QCD, from the advanced calculation techniques to the experimental consequences.