Phenomenology. Gavin P. Salam. BUSSTEPP Ambleside, August LPTHE, Universities of Paris VI and VII and CNRS

Transcription

1 Phenomenology Gavin P. Salam LPTHE, Universities of Paris VI and VII and CNRS BUSSTEPP Ambleside, August 2005

2 Phenomenology Lecture 2 (Searching for the Higgs)

3 Phenomenology: lecture 2 (p. 27) High-energy colliders Collider Process max s experiments status SLC e + e 100 GeV SLD closed 1998 LEP e + e 208 GeV Aleph, Delphi, L3, Opal closed 2000 HERA e ± p 330 GeV H1, ZEUS (& Hermes) running Tevatron p p 1.96 TeV CDF, D/0 running LHC pp 14 TeV Atlas, CMS, LHCb, Alice starts 2007

4 Phenomenology: lecture 2 (p. 28) Production (e + e ) Higgs production at LEP Production channels, e.g. e e + e e + Z Z 10 3 H e, ν e 1 Z,W 10-1 H 10-2 Z,W 10-3 e +, ν e σ (pb) e + e - hadrons Born e + e - µ + µ - WW e + e - HZ ZZ 60 m h = 70 GeV s [GeV]

5 Phenomenology: lecture 2 (p. 29) Decay modes Higgs decay modes Easily calculate widths (for tree-level decays, cf. question sheet) Γ(H f f ) = CG F m 2 f M H 4π 2 ( ) 3 1 4m2 2 f MH 2 C = N c = 3 for quarks, C = 1 for leptons. Proportional to mf 2 because Hf f vertex contains m f. Γ(H W + W ) = G F M 3 H 8π 2 Γ(H ZZ) = G F M 3 H M2 W 16π 2M 2 Z ( 1 4M2 W M 2 H ( 1 4M2 Z M 2 H ) 1 2 ( 1 4M2 W M 2 H ) 1 2 ( 1 4M2 Z M 2 H ) + 12 M4 W MH M4 Z M 4 H Widths grow as M 3 H : strong coupling of longitudinal modes at large M H. )

6 Phenomenology: lecture 2 (p. 29) Decay modes Higgs decay modes Easily calculate widths (for tree-level decays, cf. question sheet) Γ(H f f ) = CG F m 2 f M H 4π 2 ( ) 3 1 4m2 2 f MH 2 C = N c = 3 for quarks, C = 1 for leptons. Proportional to mf 2 because Hf f vertex contains m f. Γ(H W + W ) = G F M 3 H 8π 2 Γ(H ZZ) = G F M 3 H M2 W 16π 2M 2 Z ( 1 4M2 W M 2 H ( 1 4M2 Z M 2 H ) 1 2 ( 1 4M2 W M 2 H ) 1 2 ( 1 4M2 Z M 2 H ) + 12 M4 W MH M4 Z M 4 H Widths grow as M 3 H : strong coupling of longitudinal modes at large M H. )

7 Phenomenology: lecture 2 (p. 29) Decay modes Higgs decay modes Easily calculate widths (for tree-level decays, cf. question sheet) Γ(H f f ) = CG F m 2 f M H 4π 2 ( ) 3 1 4m2 2 f MH 2 C = N c = 3 for quarks, C = 1 for leptons. Proportional to mf 2 because Hf f vertex contains m f. Γ(H W + W ) = G F M 3 H 8π 2 Γ(H ZZ) = G F M 3 H M2 W 16π 2M 2 Z ( 1 4M2 W M 2 H ( 1 4M2 Z M 2 H ) 1 2 ( 1 4M2 W M 2 H ) 1 2 ( 1 4M2 Z M 2 H ) + 12 M4 W MH M4 Z M 4 H Widths grow as M 3 H : strong coupling of longitudinal modes at large M H. )

8 Phenomenology: lecture 2 (p. 29) Decay modes Higgs decay modes Easily calculate widths (for tree-level decays, cf. question sheet) Γ(H f f ) = CG F m 2 f M H 4π 2 ( ) 3 1 4m2 2 f MH 2 C = N c = 3 for quarks, C = 1 for leptons. Proportional to mf 2 because Hf f vertex contains m f. Γ(H W + W ) = G F M 3 H 8π 2 Γ(H ZZ) = G F M 3 H M2 W 16π 2M 2 Z ( 1 4M2 W M 2 H ( 1 4M2 Z M 2 H ) 1 2 ( 1 4M2 W M 2 H ) 1 2 ( 1 4M2 Z M 2 H ) + 12 M4 W MH M4 Z M 4 H Widths grow as M 3 H : strong coupling of longitudinal modes at large M H. )

9 Phenomenology: lecture 2 (p. 29) Decay modes Higgs decay modes Easily calculate widths (for tree-level decays, cf. question sheet) Γ(H f f ) = CG F m 2 f M H 4π 2 ( ) 3 1 4m2 2 f MH 2 C = N c = 3 for quarks, C = 1 for leptons. Proportional to mf 2 because Hf f vertex contains m f. Γ(H W + W ) = G F M 3 H 8π 2 Γ(H ZZ) = G F M 3 H M2 W 16π 2M 2 Z ( 1 4M2 W M 2 H ( 1 4M2 Z M 2 H ) 1 2 ( 1 4M2 W M 2 H ) 1 2 ( 1 4M2 Z M 2 H ) + 12 M4 W MH M4 Z M 4 H Widths grow as M 3 H : strong coupling of longitudinal modes at large M H. )

10 Phenomenology: lecture 2 (p. 30) Decay modes Higgs decays cont. bb ττ gg cc hep ph/ WW ZZ tt BR(H X ) = Γ(H X )/Γ tot Most features can be understood based on previous page s formulae: b is strongest decay channel at low masses (width m 2 f ). rapid dominance of W, Z at higher masses (width M 3 H v. M H for f f ) once they re kinematically allowed. NB: Not just tree-level decays, e.g. H gg and H γγ:

11 Phenomenology: lecture 2 (p. 30) Decay modes Higgs decays cont. bb ττ gg cc hep ph/ WW ZZ tt BR(H X ) = Γ(H X )/Γ tot Most features can be understood based on previous page s formulae: b is strongest decay channel at low masses (width m 2 f ). rapid dominance of W, Z at higher masses (width M 3 H v. M H for f f ) once they re kinematically allowed. NB: Not just tree-level decays, e.g. H gg and H γγ:

12 Phenomenology: lecture 2 (p. 30) Decay modes Higgs decays cont. bb ττ gg cc hep ph/ WW ZZ tt BR(H X ) = Γ(H X )/Γ tot Most features can be understood based on previous page s formulae: b is strongest decay channel at low masses (width m 2 f ). rapid dominance of W, Z at higher masses (width M 3 H v. M H for f f ) once they re kinematically allowed. NB: Not just tree-level decays, e.g. H gg and H γγ: H t g g

13 Phenomenology: lecture 2 (p. 31) Decay modes Comment on τ versus charm? Beware: plots like those of previous page often contain subtleties... Expect Γ(H c c) Γ(H τ + τ ) N cm 2 c m 2 τ But actual ratio 0.5. Why? 2 (for m c = 1.5 GeV, m τ = 1.8 GeV) Masses are not constants. Like coupling constants, they run with scale (i.e. have anomalous dimensions). QCD gives significant running effects for quark masses Q 2 m Q 2 = γ m(α s )m(q 2 ), γ m = α s π + O ( α 2 ) s. In expression for Higgs width use m q (MH 2 ). Since m/ Q2 < 0 this reduces Γ(H c c). question on problem sheet. [NB: also other higher-order effects, but generally more modest]

14 Phenomenology: lecture 2 (p. 31) Decay modes Comment on τ versus charm? Beware: plots like those of previous page often contain subtleties... Expect Γ(H c c) Γ(H τ + τ ) N cm 2 c m 2 τ But actual ratio 0.5. Why? 2 (for m c = 1.5 GeV, m τ = 1.8 GeV) Masses are not constants. Like coupling constants, they run with scale (i.e. have anomalous dimensions). QCD gives significant running effects for quark masses Q 2 m Q 2 = γ m(α s )m(q 2 ), γ m = α s π + O ( α 2 ) s. In expression for Higgs width use m q (MH 2 ). Since m/ Q2 < 0 this reduces Γ(H c c). question on problem sheet. [NB: also other higher-order effects, but generally more modest]

15 Phenomenology: lecture 2 (p. 31) Decay modes Comment on τ versus charm? Beware: plots like those of previous page often contain subtleties... Expect Γ(H c c) Γ(H τ + τ ) N cm 2 c m 2 τ But actual ratio 0.5. Why? 2 (for m c = 1.5 GeV, m τ = 1.8 GeV) Masses are not constants. Like coupling constants, they run with scale (i.e. have anomalous dimensions). QCD gives significant running effects for quark masses Q 2 m Q 2 = γ m(α s )m(q 2 ), γ m = α s π + O ( α 2 ) s. In expression for Higgs width use m q (MH 2 ). Since m/ Q2 < 0 this reduces Γ(H c c). question on problem sheet. [NB: also other higher-order effects, but generally more modest]

16 Phenomenology: lecture 2 (p. 31) Decay modes Comment on τ versus charm? Beware: plots like those of previous page often contain subtleties... Expect Γ(H c c) Γ(H τ + τ ) N cm 2 c m 2 τ But actual ratio 0.5. Why? 2 (for m c = 1.5 GeV, m τ = 1.8 GeV) Masses are not constants. Like coupling constants, they run with scale (i.e. have anomalous dimensions). QCD gives significant running effects for quark masses Q 2 m Q 2 = γ m(α s )m(q 2 ), γ m = α s π + O ( α 2 ) s. In expression for Higgs width use m q (MH 2 ). Since m/ Q2 < 0 this reduces Γ(H c c). question on problem sheet. [NB: also other higher-order effects, but generally more modest]

17 e + e eµν e ν µ What can experiments detect? e + e b b (secondary vertex) e + e µ + µ γγ e + e q q

18 e +e µ+ µ γγ e+

19 e + e eµνe νµ e+

20 e + e q q

21 e + e b b (secondary vertex)

22 Phenomenology: lecture 2 (p. 33) LEP LEP Higgs search Searches in various channels (e + e HZ) H b b, Z q q H b b, Z ν ν H b b, Z l + l H τ + τ, Z q q Must reduce backgrounds e.g. ee Z b bgg. Call the jets 1,2,3,4, require M 34 M Z ee Z( b b)z( q q). Require M 34 M Z and M 12 M Z Example event (from Aleph): Centre-of-mass energy GeV NN value b-tag probabilities HZ hypothesis M H = GeV M Z = 93.3 GeV ZZ hypothesis M Z = 102 GeV M Z = 91.7 GeV

23 Phenomenology: lecture 2 (p. 33) LEP LEP Higgs search Searches in various channels (e + e HZ) H b b, Z q q H b b, Z ν ν H b b, Z l + l H τ + τ, Z q q Must reduce backgrounds e.g. ee Z b bgg. Call the jets 1,2,3,4, require M 34 M Z ee Z( b b)z( q q). Require M 34 M Z and M 12 M Z Example event (from Aleph): Centre-of-mass energy GeV NN value b-tag probabilities HZ hypothesis M H = GeV M Z = 93.3 GeV ZZ hypothesis M Z = 102 GeV M Z = 91.7 GeV

24 Phenomenology: lecture 2 (p. 33) LEP LEP Higgs search Searches in various channels (e + e HZ) H b b, Z q q H b b, Z ν ν H b b, Z l + l H τ + τ, Z q q Must reduce backgrounds e.g. ee Z b bgg. Call the jets 1,2,3,4, require M 34 M Z ee Z( b b)z( q q). Require M 34 M Z and M 12 M Z Example event (from Aleph): Centre-of-mass energy GeV NN value b-tag probabilities HZ hypothesis M H = GeV M Z = 93.3 GeV ZZ hypothesis M Z = 102 GeV M Z = 91.7 GeV

25 Example Higgs candidate ALEPH DALI_F1 ECM=206.7 Pch=83.0 Efl=194. Ewi=124. Eha=35.9 BEHOLD Run=54698 Evt=4881 Nch=28 EV1=0 EV2=0 EV3=0 ThT= :32 Detb= E3FFFF Gev EC (φ 138)*SIN(θ) 5 Gev HC o o o o x x x o x o o x oo ox o x x o RO TPC 0.3cm 0.6cm Y" 1cm 0 1cm X" P>.50 Z0<10 D0<2 F.C. imp. µ oo xo o o o o o o x x o x o x x o o o 15 GeV x θ=180 θ=0 x o o x Made on 29-Aug :06:54 by DREVERMANN with DALI_F1. Filename: DC054698_004881_000829_1706.PS_H_CAND

26 Phenomenology: lecture 2 (p. 35) LEP Data v. expected signal & background Events / 3 GeV/c LEP s = GeV Data Background Signal (115 GeV/c 2 ) all > 109 GeV/c 2 Data Backgd Signal Loose Events / 3 GeV/c LEP s = GeV Data Background Signal (115 GeV/c 2 ) all > 109 GeV/c 2 Data 18 4 Backgd Signal Tight m H rec (GeV/c 2 ) m H rec (GeV/c 2 ) LEP Higgs WG conclusions: statistical analysis: signal at 1.7 standard dev., corresponding to M H 116 GeV

27 Phenomenology: lecture 2 (p. 35) LEP Data v. expected signal & background Events / 3 GeV/c LEP s = GeV Data Background Signal (115 GeV/c 2 ) all > 109 GeV/c 2 Data Backgd Signal Loose Events / 3 GeV/c LEP s = GeV Data Background Signal (115 GeV/c 2 ) all > 109 GeV/c 2 Data 18 4 Backgd Signal Tight m H rec (GeV/c 2 ) m H rec (GeV/c 2 ) LEP Higgs WG conclusions: statistical analysis: signal at 1.7 standard dev., corresponding to M H 116 GeV

28 Phenomenology: lecture 2 (p. 36) LEP LEP limit LEP s highest (sustained) energy was s 206 GeV. Threshold: s M Z + M H, so M H,max s M Z = 115 GeV Higgs signal at 115 GeV, i.e. right at kinematic limit. Possible because there is only one reaction at a time: takes all energy and is clean. So why not increase s? Synchrotron energy loss too large: E loss E 4 beam R 1 m 4 e, ( 2.5 GeV per turn) Next generation e + e collider will be linear. Not before For now have hadron colliders (at same energy, synchrotron energy loss (m e /m p ) smaller).

29 Phenomenology: lecture 2 (p. 36) LEP LEP limit LEP s highest (sustained) energy was s 206 GeV. Threshold: s M Z + M H, so M H,max s M Z = 115 GeV Higgs signal at 115 GeV, i.e. right at kinematic limit. Possible because there is only one reaction at a time: takes all energy and is clean. So why not increase s? Synchrotron energy loss too large: E loss E 4 beam R 1 m 4 e, ( 2.5 GeV per turn) Next generation e + e collider will be linear. Not before For now have hadron colliders (at same energy, synchrotron energy loss (m e /m p ) smaller).

30 Phenomenology: lecture 2 (p. 36) LEP LEP limit LEP s highest (sustained) energy was s 206 GeV. Threshold: s M Z + M H, so M H,max s M Z = 115 GeV Higgs signal at 115 GeV, i.e. right at kinematic limit. Possible because there is only one reaction at a time: takes all energy and is clean. So why not increase s? Synchrotron energy loss too large: E loss E 4 beam R 1 m 4 e, ( 2.5 GeV per turn) Next generation e + e collider will be linear. Not before For now have hadron colliders (at same energy, synchrotron energy loss (m e /m p ) smaller).

31 Phenomenology: lecture 2 (p. 36) LEP LEP limit LEP s highest (sustained) energy was s 206 GeV. Threshold: s M Z + M H, so M H,max s M Z = 115 GeV Higgs signal at 115 GeV, i.e. right at kinematic limit. Possible because there is only one reaction at a time: takes all energy and is clean. So why not increase s? Synchrotron energy loss too large: E loss E 4 beam R 1 m 4 e, ( 2.5 GeV per turn) Next generation e + e collider will be linear. Not before For now have hadron colliders (at same energy, synchrotron energy loss (m e /m p ) smaller).

32 Phenomenology: lecture 2 (p. 36) LEP LEP limit LEP s highest (sustained) energy was s 206 GeV. Threshold: s M Z + M H, so M H,max s M Z = 115 GeV Higgs signal at 115 GeV, i.e. right at kinematic limit. Possible because there is only one reaction at a time: takes all energy and is clean. So why not increase s? Synchrotron energy loss too large: E loss E 4 beam R 1 m 4 e, ( 2.5 GeV per turn) Next generation e + e collider will be linear. Not before For now have hadron colliders (at same energy, synchrotron energy loss (m e /m p ) smaller).

33 Phenomenology: lecture 2 (p. 36) LEP LEP limit LEP s highest (sustained) energy was s 206 GeV. Threshold: s M Z + M H, so M H,max s M Z = 115 GeV Higgs signal at 115 GeV, i.e. right at kinematic limit. Possible because there is only one reaction at a time: takes all energy and is clean. So why not increase s? Synchrotron energy loss too large: E loss E 4 beam R 1 m 4 e, ( 2.5 GeV per turn) Next generation e + e collider will be linear. Not before For now have hadron colliders (at same energy, synchrotron energy loss (m e /m p ) smaller).

34 Moonrise over LEP Fall of 1992 : The historic tide experiment! Beam Energy (MeV) Nov. 11th 1992 Tide prediction :00 2:00 6:00 10:00 14:00 18:00 22:00 2:00 Daytime The total strain is 4 x 10-8 ( C = 1 mm) J.Wenninger - LEP fest 8

35 Success in the Press! J.Wenninger - LEP fest 9

36 The Crack in the Model Spring of 1994 : the beam energy model seemed to explain all observed sources of energy fluctuations... EXCEPT : An unexplained energy increase of 5 MeV was observed in ONE experiment. Beam Energy (MeV) August 29th :00 6:00 10:00 14:00 18:00 22:00 2:00 It will remain unexplained for two years (After Tide correction) Expected evolution Daytime J.Wenninger - LEP fest 11

37 Pipebusters The explanation was given by the Swiss electricity company EOS... I blast your pipes! DC railway Vagabond currents from trains and and subways Source of electrical noise and corrosion (first discussed in 1898!) ~20% ~80% Vagabond (Earth) current J.Wenninger - LEP fest 13

38 TGV for Paris November 1995 : Measurements of The current on the railway tracks The current on the vacuum chamber The dipole field in a magnet correlate perfectly! Because energy calibrations were usually performed : At the end of fills (saturation) During nights (no trains!) we missed the trains for for many years!! Voltage on rails [V] Voltage on beam pipe [V] Bending field [Gauss] November 17th 1995 Geneve Railway Tracks LEP Beam Pipe LEP NMR TGV Meyrin Zimeysa 16:50 16:55 Time J.Wenninger - LEP fest 15

39 Phenomenology: lecture 2 (p. 42) Hadron colliders Basics of hadronic collisions Protons are composite objects. Only a fraction of energy (e.g. 1 of 3 quarks) goes into the hard collision need higher s to generate a given process x 1 p 1 Z σ H x 2 p 2 σ = dx 1 f q/p (x 1, µ 2 ) p 1 p 2 dx 2 f q/ p (x 2, µ 2 ) ˆσ(x 1 p 1, x 2 p 2, µ 2 ), ŝ = x 1 x 2 s Momentum fractions x 1 and x 2 are different in each collision C.O.M. frame not easily identifiable (ambiguous kinematic reconstruction)

40 Phenomenology: lecture 2 (p. 42) Hadron colliders Basics of hadronic collisions Protons are composite objects. Only a fraction of energy (e.g. 1 of 3 quarks) goes into the hard collision need higher s to generate a given process x 1 p 1 Z σ H x 2 p 2 σ = dx 1 f q/p (x 1, µ 2 ) p 1 p 2 dx 2 f q/ p (x 2, µ 2 ) ˆσ(x 1 p 1, x 2 p 2, µ 2 ), ŝ = x 1 x 2 s Momentum fractions x 1 and x 2 are different in each collision C.O.M. frame not easily identifiable (ambiguous kinematic reconstruction)

41 Phenomenology: lecture 2 (p. 43) Hadron colliders Basics of hadronic collisions (cont.) There is QCD radiation from initial-state partons Z H collision environment is dirty x 1 p 1 σ x 2 p 2 p 1 p 2 remnants from protons fragment & can also interact collision environment is even dirtier quarks and gluons interact via QCD (strong); Higgs & some other new physics, via EW (weak). Backgrounds (from QCD) are enhanced relative to (some) signals of new physics

42 Phenomenology: lecture 2 (p. 43) Hadron colliders Basics of hadronic collisions (cont.) There is QCD radiation from initial-state partons Z H collision environment is dirty x 1 p 1 σ x 2 p 2 p 1 p 2 remnants from protons fragment & can also interact collision environment is even dirtier quarks and gluons interact via QCD (strong); Higgs & some other new physics, via EW (weak). Backgrounds (from QCD) are enhanced relative to (some) signals of new physics

43 Phenomenology: lecture 2 (p. 43) Hadron colliders Basics of hadronic collisions (cont.) There is QCD radiation from initial-state partons Z H collision environment is dirty x 1 p 1 σ x 2 p 2 p 1 p 2 remnants from protons fragment & can also interact collision environment is even dirtier quarks and gluons interact via QCD (strong); Higgs & some other new physics, via EW (weak). Backgrounds (from QCD) are enhanced relative to (some) signals of new physics

44 Phenomenology: lecture 2 (p. 44) Hadron colliders Example: Tevatron Higgs search Largest production channel: gg H, with decay H b b (for M H 135 GeV) gg >h SM qq >h SM qq gg,qq _ >h SM tt _ gg,qq _ >h SM bb _ bb _ >h SM σ(pp _ >h SM +X) [pb] s = 2 TeV M t = 175 GeV CTEQ4M qq _ >h SM W qq _ >h SM Z g g t H For 115 GeV Higgs, production cross section is 1 pb. [1 barn (b) = m 2 ] [1 mb 2.56 GeV 2 ( hc) 2 ] M h [GeV ] SM

45 Phenomenology: lecture 2 (p. 45) Hadron colliders b b background b m b b 115 GeV E T 50 GeV b Cross section 1 nb Background is 10 3 signal.

46 Phenomenology: lecture 2 (p. 46) Hadron colliders Actual searches Final State Modes and Backgrounds Signal Production and Final State: p p pp pp gg H bb WH qq' bb WH νbb ZH qqbb + pp ZH pp bb ZH ννbb Primary Background Processes: QCD Dijet Background Huge QCD Jet Background/W+jets W+bb/cc, Single top, tt QCD Jet Background/W+jets W/Z+bb/cc, tt (Poor BR) W/Z+bb/cc, tt, QCD Jets Essentials: Lepton Acceptance, b-tagging eff/acceptance, dijet Mass Resolution April 2, 2004 Moriond QCD: B. L. Winer Page 3

47 tt Event Rates/fb -1 Rates determined from a combination of MC and data. WH Signal(115) ZH Signal(115) Total Signal t(w*) t(wg) W/Z bb WZ/ZZ QCD Total Bkg S / B S / B No Mass Window April 2, 2004 Moriond QCD: B. L. Winer Page Mass Window Missed Chg Lepton

48 Phenomenology: lecture 2 (p. 48) Hadron colliders Tevatron Higgs search: prospects Express results of studies in terms of luminosity needed in order to see a Higgs signal, as function of M H. Dip at 160 GeV: H W + W (easier to identify, smaller backgrounds). Currently Tevatron has 1 fb 1. For full details, see joint theoretical-experimental Report of the Tevatron Higgs working group, hep-ph/ (For luminosity progress, see:

49 Phenomenology: lecture 2 (p. 48) Hadron colliders Tevatron Higgs search: prospects Express results of studies in terms of luminosity needed in order to see a Higgs signal, as function of M H. Dip at 160 GeV: H W + W (easier to identify, smaller backgrounds). Currently Tevatron has 1 fb 1. For full details, see joint theoretical-experimental Report of the Tevatron Higgs working group, hep-ph/ (For luminosity progress, see:

50 Phenomenology: lecture 2 (p. 48) Hadron colliders Tevatron Higgs search: prospects Express results of studies in terms of luminosity needed in order to see a Higgs signal, as function of M H. Dip at 160 GeV: H W + W (easier to identify, smaller backgrounds). Currently Tevatron has 1 fb 1. For full details, see joint theoretical-experimental Report of the Tevatron Higgs working group, hep-ph/ (For luminosity progress, see:

51 Phenomenology: lecture 2 (p. 48) Hadron colliders Tevatron Higgs search: prospects Express results of studies in terms of luminosity needed in order to see a Higgs signal, as function of M H. Dip at 160 GeV: H W + W (easier to identify, smaller backgrounds). Currently Tevatron has 1 fb 1. For full details, see joint theoretical-experimental Report of the Tevatron Higgs working group, hep-ph/ (For luminosity progress, see:

52 Phenomenology: lecture 2 (p. 49) Hadron colliders LHC Higgs search: prospects Signal Significance L dt=10 fb VBF H WW VBF H ττ H γγ (inclusive + VBF) H ZZ 4l (with K-factors) H ZZ 4l (no K-factors) tth,h bb H WW lν lν H ZZ llbb VBF H ZZ llqq Combined 5σ 1 M H (GeV) Les Houches Physics at Tev Colliders 2003, hep-ph/

53 Phenomenology: lecture 2 (p. 50) Hadron colliders NB Higgs is one of the main high-priority searches. Involves far more work than could possibly be done justice to in 1 lecture. e.g. recent NNLO QCD calculations of gg H Aim was to explain principles behind searches these are similar regardless of what you re looking for. Identify how new particle or phenomenon (e.g. BH) can be produced. Identify how it decays. Choose production and decay channels so as to minimize backgrounds. Exploit experimental detector capabilities in choice of channels. Very different strategies may be needed in e + e v. hadronic colliders. Don t forget that it isn t enough to discover it. Then you have to prove it really was what you were looking for in the first place. E.g. for Higgs Yukawa couplings to fermions. Couplings to other gauge bosons. Self-couplings (reconstruct potential).

54 Phenomenology: lecture 2 (p. 50) Hadron colliders NB Higgs is one of the main high-priority searches. Involves far more work than could possibly be done justice to in 1 lecture. e.g. recent NNLO QCD calculations of gg H Aim was to explain principles behind searches these are similar regardless of what you re looking for. Identify how new particle or phenomenon (e.g. BH) can be produced. Identify how it decays. Choose production and decay channels so as to minimize backgrounds. Exploit experimental detector capabilities in choice of channels. Very different strategies may be needed in e + e v. hadronic colliders. Don t forget that it isn t enough to discover it. Then you have to prove it really was what you were looking for in the first place. E.g. for Higgs Yukawa couplings to fermions. Couplings to other gauge bosons. Self-couplings (reconstruct potential).

55 Phenomenology: lecture 2 (p. 50) Hadron colliders NB Higgs is one of the main high-priority searches. Involves far more work than could possibly be done justice to in 1 lecture. e.g. recent NNLO QCD calculations of gg H Aim was to explain principles behind searches these are similar regardless of what you re looking for. Identify how new particle or phenomenon (e.g. BH) can be produced. Identify how it decays. Choose production and decay channels so as to minimize backgrounds. Exploit experimental detector capabilities in choice of channels. Very different strategies may be needed in e + e v. hadronic colliders. Don t forget that it isn t enough to discover it. Then you have to prove it really was what you were looking for in the first place. E.g. for Higgs Yukawa couplings to fermions. Couplings to other gauge bosons. Self-couplings (reconstruct potential).

56 Phenomenology: lecture 2 (p. 50) Hadron colliders NB Higgs is one of the main high-priority searches. Involves far more work than could possibly be done justice to in 1 lecture. e.g. recent NNLO QCD calculations of gg H Aim was to explain principles behind searches these are similar regardless of what you re looking for. Identify how new particle or phenomenon (e.g. BH) can be produced. Identify how it decays. Choose production and decay channels so as to minimize backgrounds. Exploit experimental detector capabilities in choice of channels. Very different strategies may be needed in e + e v. hadronic colliders. Don t forget that it isn t enough to discover it. Then you have to prove it really was what you were looking for in the first place. E.g. for Higgs Yukawa couplings to fermions. Couplings to other gauge bosons. Self-couplings (reconstruct potential).

57 Phenomenology: lecture 2 (p. 50) Hadron colliders NB Higgs is one of the main high-priority searches. Involves far more work than could possibly be done justice to in 1 lecture. e.g. recent NNLO QCD calculations of gg H Aim was to explain principles behind searches these are similar regardless of what you re looking for. Identify how new particle or phenomenon (e.g. BH) can be produced. Identify how it decays. Choose production and decay channels so as to minimize backgrounds. Exploit experimental detector capabilities in choice of channels. Very different strategies may be needed in e + e v. hadronic colliders. Don t forget that it isn t enough to discover it. Then you have to prove it really was what you were looking for in the first place. E.g. for Higgs Yukawa couplings to fermions. Couplings to other gauge bosons. Self-couplings (reconstruct potential).

58 Phenomenology: lecture 2 (p. 50) Hadron colliders NB Higgs is one of the main high-priority searches. Involves far more work than could possibly be done justice to in 1 lecture. e.g. recent NNLO QCD calculations of gg H Aim was to explain principles behind searches these are similar regardless of what you re looking for. Identify how new particle or phenomenon (e.g. BH) can be produced. Identify how it decays. Choose production and decay channels so as to minimize backgrounds. Exploit experimental detector capabilities in choice of channels. Very different strategies may be needed in e + e v. hadronic colliders. Don t forget that it isn t enough to discover it. Then you have to prove it really was what you were looking for in the first place. E.g. for Higgs Yukawa couplings to fermions. Couplings to other gauge bosons. Self-couplings (reconstruct potential).

59 Phenomenology: lecture 2 (p. 50) Hadron colliders NB Higgs is one of the main high-priority searches. Involves far more work than could possibly be done justice to in 1 lecture. e.g. recent NNLO QCD calculations of gg H Aim was to explain principles behind searches these are similar regardless of what you re looking for. Identify how new particle or phenomenon (e.g. BH) can be produced. Identify how it decays. Choose production and decay channels so as to minimize backgrounds. Exploit experimental detector capabilities in choice of channels. Very different strategies may be needed in e + e v. hadronic colliders. Don t forget that it isn t enough to discover it. Then you have to prove it really was what you were looking for in the first place. E.g. for Higgs Yukawa couplings to fermions. Couplings to other gauge bosons. Self-couplings (reconstruct potential).

60 Phenomenology: lecture 2 (p. 50) Hadron colliders NB Higgs is one of the main high-priority searches. Involves far more work than could possibly be done justice to in 1 lecture. e.g. recent NNLO QCD calculations of gg H Aim was to explain principles behind searches these are similar regardless of what you re looking for. Identify how new particle or phenomenon (e.g. BH) can be produced. Identify how it decays. Choose production and decay channels so as to minimize backgrounds. Exploit experimental detector capabilities in choice of channels. Very different strategies may be needed in e + e v. hadronic colliders. Don t forget that it isn t enough to discover it. Then you have to prove it really was what you were looking for in the first place. E.g. for Higgs Yukawa couplings to fermions. Couplings to other gauge bosons. Self-couplings (reconstruct potential).

61 Phenomenology: lecture 2 (p. 50) Hadron colliders NB Higgs is one of the main high-priority searches. Involves far more work than could possibly be done justice to in 1 lecture. e.g. recent NNLO QCD calculations of gg H Aim was to explain principles behind searches these are similar regardless of what you re looking for. Identify how new particle or phenomenon (e.g. BH) can be produced. Identify how it decays. Choose production and decay channels so as to minimize backgrounds. Exploit experimental detector capabilities in choice of channels. Very different strategies may be needed in e + e v. hadronic colliders. Don t forget that it isn t enough to discover it. Then you have to prove it really was what you were looking for in the first place. E.g. for Higgs Yukawa couplings to fermions. Couplings to other gauge bosons. Self-couplings (reconstruct potential).

62 Phenomenology: lecture 2 (p. 50) Hadron colliders NB Higgs is one of the main high-priority searches. Involves far more work than could possibly be done justice to in 1 lecture. e.g. recent NNLO QCD calculations of gg H Aim was to explain principles behind searches these are similar regardless of what you re looking for. Identify how new particle or phenomenon (e.g. BH) can be produced. Identify how it decays. Choose production and decay channels so as to minimize backgrounds. Exploit experimental detector capabilities in choice of channels. Very different strategies may be needed in e + e v. hadronic colliders. Don t forget that it isn t enough to discover it. Then you have to prove it really was what you were looking for in the first place. E.g. for Higgs Yukawa couplings to fermions. Couplings to other gauge bosons. Self-couplings (reconstruct potential).

63 Phenomenology: lecture 2 (p. 50) Hadron colliders NB Higgs is one of the main high-priority searches. Involves far more work than could possibly be done justice to in 1 lecture. e.g. recent NNLO QCD calculations of gg H Aim was to explain principles behind searches these are similar regardless of what you re looking for. Identify how new particle or phenomenon (e.g. BH) can be produced. Identify how it decays. Choose production and decay channels so as to minimize backgrounds. Exploit experimental detector capabilities in choice of channels. Very different strategies may be needed in e + e v. hadronic colliders. Don t forget that it isn t enough to discover it. Then you have to prove it really was what you were looking for in the first place. E.g. for Higgs Yukawa couplings to fermions. Couplings to other gauge bosons. Self-couplings (reconstruct potential).

64 Phenomenology: lecture 2 (p. 51) Hadron colliders Things swept under the carpet... We talked about quark production and discussed it perturbatively, but experiments see jets of (non-perturbative) hadrons. What s the relation? Are we justified in making the connection? Is it well-defined? We talk about hard interactions between partons from the proton. But proton is non-perturbative. To what extent are we allowed to do this? When you calculate them in detail many cross sections seem divergent.... What s going on? Subject of the remaining two lectures

65 Phenomenology: lecture 2 (p. 51) Hadron colliders Things swept under the carpet... We talked about quark production and discussed it perturbatively, but experiments see jets of (non-perturbative) hadrons. What s the relation? Are we justified in making the connection? Is it well-defined? We talk about hard interactions between partons from the proton. But proton is non-perturbative. To what extent are we allowed to do this? When you calculate them in detail many cross sections seem divergent.... What s going on? Subject of the remaining two lectures

66 Phenomenology: lecture 2 (p. 51) Hadron colliders Things swept under the carpet... We talked about quark production and discussed it perturbatively, but experiments see jets of (non-perturbative) hadrons. What s the relation? Are we justified in making the connection? Is it well-defined? We talk about hard interactions between partons from the proton. But proton is non-perturbative. To what extent are we allowed to do this? When you calculate them in detail many cross sections seem divergent.... What s going on? Subject of the remaining two lectures

67 Phenomenology: lecture 2 (p. 51) Hadron colliders Things swept under the carpet... We talked about quark production and discussed it perturbatively, but experiments see jets of (non-perturbative) hadrons. What s the relation? Are we justified in making the connection? Is it well-defined? We talk about hard interactions between partons from the proton. But proton is non-perturbative. To what extent are we allowed to do this? When you calculate them in detail many cross sections seem divergent.... What s going on? Subject of the remaining two lectures