Revisiting EW Constraints at a Linear Collider Work done by S. - - PowerPoint PPT Presentation

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Revisiting EW Constraints at a Linear Collider Work done by S. - - PowerPoint PPT Presentation

Jun 06, 2023 318 likes •544 views

Revisiting EW Constraints at a Linear Collider Work done by S. Heinemeyer P. Rowson U. Baer G. Weiglein M. Woods + many others K. Moenig B. Schumm R. Hawkings D. Gerdes G. Wilson L. Orr Lawrence Gibbons Cornell University Why improve

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SLIDE 1

Revisiting EW Constraints at a Linear Collider

Work done by

  • S. Heinemeyer P. Rowson
  • U. Baer
  • G. Weiglein
  • M. Woods

+ many others

  • K. Moenig
  • B. Schumm
  • R. Hawkings
  • D. Gerdes
  • G. Wilson
  • L. Orr

Lawrence Gibbons Cornell University

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SLIDE 2

7 Jan 2002 Chicago LC Workshop 2

Why improve EW parameters?

❚ Dominant theory limitations

❙ Mt ❙ ∆α = αQED(MZ)-αQED(0)

❚ Three key measurements

❙ tt threshold: Mt ❙ Z pole: sin2 θeff ❙ W+W- threshold: MW

80.25 80.30 80.35 80.40 80.45 80.50

MW [GeV]

0.23125 0.23150 0.23175 0.23200 0.23225 0.23250

sin

2θeff

  • S. Heinemeyer (LC Physics Resource Book)

68% CL: present theory range LEP/SLC/Tevatron

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SLIDE 3

7 Jan 2002 Chicago LC Workshop 3

80.25 80.30 80.35 80.40 80.45 80.50

MW [GeV]

0.23125 0.23150 0.23175 0.23200 0.23225 0.23250

sin

2θeff

  • S. Heinemeyer (LC Physics Resource Book)

68% CL: p r e s e n t t h e

  • r

y r a n g e LEP/SLC/Tevatron ∆α mt MH = 180 GeV 150 GeV 120 GeV LHC/LC GigaZ

Why improve EW parameters?

❚ Dominant theory limitations

❙ Mt ❙ ∆α = αQED(MZ)-αQED(0)

❚ Three key measurements

❙ tt threshold: Mt ❙ Z pole: sin2 θeff ❙ W+W- threshold: MW

❚ Indirect prediction power

❙ MW to ±4 MeV ❙ MH to +- 8%

❚ Caveat: must improve ∆α

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SLIDE 4

7 Jan 2002 Chicago LC Workshop 4

tt threshold: Mt

❚ Kinematic reconstruction

❙ Hadronic machines systematics limited

R Mt to ~ ±2-3 GeV

❙ Measures ~ pole mass

❚ Pole mass ill-defined in QCD

❙ Nonperturbative ambiguity

  • f O(ΛQCD) in definition

344 346 348 350 352 √s (GeV) R(E) LO NLO NNLO 0.25 0.5 0.75 1 1.25 1.5 1.75

  • O. Yakovlev (LC Physics Resource Book)

❙ Eg., poorly-behaved perturbation series for threshold cross-section

❚ Want short-distance mass, eg. Mt(Mt)

❙ EW constraints, ∆MB, …

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SLIDE 5

7 Jan 2002 Chicago LC Workshop 5

tt threshold: Mt

❚ Large Γt (~1.4 GeV) a boon

❙ Γt >> ΛQCD ⇒ no narrow resonances, smooth line shape ❙ Allows calc. in pert. QCD

R infrared cutoff, smearing

346 347 348 349 350 351 352 353 354

  • √s
  • Ge

V 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 R

LL NLL NNLL

(LC Physics Resource Book)

❚ A few short-distance mass def’s near threshold

❙ 1S peak position stable to ~200-300 MeV ❙ Masses related to MS mass via pert. QCD series

❚ Modest luminosity required

❙ 10 fb-1 → ±40 MeV stat. uncertainty

332 0.4 0.6 0.8 0.2 σeff (pb ) 336 340 s (GeV) 344

1 fb–1/point

mt=170 GeV

Mt to ±200 MeV Mt to ±200 MeV

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SLIDE 6

7 Jan 2002 Chicago LC Workshop 6

Other top measurements

❚ Threshold

❙ Total top width

R Peak σ ~ 1/Γt R 100 fb-1 → ~2% uncertainty

❙ Yukawa coupling

R 115 GeV Higgs → 5-8% increase in threshold σ R 2-3% uncertainty in predicted cross section

  • 14-20% on Yukawa

coupling

R Sensitivity drops for increasing Higgs mass

❚ High energy

❙ Yukawa coupling

R e+e- → tth → W+W-bbbb R 800 GeV (1000 fb-1): ~5.5% R 500 GeV: ~4x worse

❙ All neutral and charged current couplings

R Measure/limit mostform factors at 1% level

  • 500 GeV, 100-200 fb-1

R ttZ couplings unique to LC

  • production polarization asymm.

❙ Test QCD, EW radiative corr.

R σ(e+e- → tt → lνjjbb) to < 1%

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SLIDE 7

7 Jan 2002 Chicago LC Workshop 7

sin2θW status

❚ At Z pole: dominated by

❙ LEP b quark Ab

FB

❙ SLD ALR ❙ Ab

FB: not in best agreement

w/ SM

❚ Lower energy scales

❙ Recent NUTEV result

❘ “3σ high”

❙ atomic parity violation

❘ ~2 σ low

10 2 10 3 0.23 0.232 0.234

Preliminary

sin2θ

lept eff

mH [GeV]

χ2/d.o.f.: 12.8 / 5

A

0,l fb

0.23099 ± 0.00053 Al(Pτ) 0.23159 ± 0.00041 Al(SLD) 0.23098 ± 0.00026 A

0,b fb

0.23226 ± 0.00031 A

0,c fb

0.23272 ± 0.00079 <Qfb> 0.2324 ± 0.0012 Average 0.23152 ± 0.00017

∆αhad= 0.02761 ± 0.00036 ∆α(5) mZ= 91.1875 ± 0.0021 GeV mt= 174.3 ± 5.1 GeV

LEPEWWG: summer 2001

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SLIDE 8

7 Jan 2002 Chicago LC Workshop 8

Giga-Z

❚ Revisit Z pole with a linear collider

❙ Expect L ~ 5 x 1033 cm-2s-1 ❙ 109 Z decays in ~ 107 s

R Could contemplate interruption of high energy program

❙ 1010 Z decays: 3-5 year program

R Would need simultaneous low energy/high energy running R Mainly heavy flavor program benefits

❙ Polarization

R 80% electron polarization a given R positron polarization an enormous boon: achievable?

  • 60% polarization desirable
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SLIDE 9

7 Jan 2002 Chicago LC Workshop 9

Z pole scan

❚ Current measurements systematics limited

❙ 2x improvement on eff. syst. (no th’y improvement for L)

R 4x Rl, 30% σ0 improvements

❙ δEbeam/ Ebeam: potentially 10-5 w/ Moller spectrometer?

R 2x ΓZ improvement

❙ Energy spread: beamstrahlung to O(2%): further study needed

R ΓZ, ρl limited otherwise R monitor with Bhabha acolinearity? 5 point scan?

❚ Measured

❙ MZ ❙ ΓZ ❙ σ0 ∝ ΓhadΓll/ ΓZ

2

❙ Rl = Γhad/Γll

❚ Extracted

❙ MZ: ±2 MeV → LC E scale ❙ αS(MZ

2): ±0.0027 → ±0.0009

❙ ρl: ±0.001 → ±0.0005 ❙ Nν: ±0.008 → ±0.0004

→

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SLIDE 10

7 Jan 2002 Chicago LC Workshop 10

ALR → sin2θW

❚ ALR the most sensitive variable to sin2θW

❙ GigaZ = 2000x SLD

❘ SLD: ALR=0.1514±0.0022

ALR = 1 P

−

NL −NR NL + NR = Ae = 2 1− 4sin2 θW

eff

1 + 1 −4sin2 θW

eff

( )

2

2 4 6 8 10 12 14 16 18 20 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

P+ ∆ALR x105 P-=0.8

❚ e+ polarization:

❙ None: δP-/P- dominates uncertainty: 0.25% (optimistically) feasible

❘ ∆ALR to 4x10-4

❙ With: use Blondel scheme (combine NLL,NRR,NLR,NRL)

❘ 60% P+ ↔ effective 95% polarization, don’t need absolute polarization ❘ ⇒ ∆ALR to 10-4

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SLIDE 11

7 Jan 2002 Chicago LC Workshop 11

ALR → sin2θW: experimental issues

❚ polarization

❙ Blondel scheme: need relative L,R polarizations to 10^-4

❘ Appears feasible

❙ Systematics: polarimeters after IP?

  • Difficult w/o crossing angle

❙ Can positron helicity be switched rapidly enough relative to beam stability?

❘ What is the relevant time scale?

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SLIDE 12

7 Jan 2002 Chicago LC Workshop 12

ALR → sin2θW: experimental issues

❚ Z-γ interference: ALR changes rapidly away from pole

❙ Control δE/E to 10-5 ❙ Control of beamstrahlung (effective √s shift)

❘ Ignore: ALR shift of 9x10-4 at TESLA, much worse at NLC ❘ E scale from Z pole scan + LEP MZ. Same beam parameters? ❘ Trade L for reduced beamstrahlung

  • NLC:125→18 MeV E shift for factor 5 L penalty

❚ If beam issues controlled:

sin2θW to ±0.000013 sin2θW to ±0.000013

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SLIDE 13

7 Jan 2002 Chicago LC Workshop 13

Zbb vertex

❚ Ab: 2.5–3.5 σ discrepancy w/ SM persists

❙ Stat’s dominated measurement

❚ Complementary sensitivity to “new physics” than S,T,U ❚ Rb=Γbb/ Γ had

❙ Measure corrections to Zbb vtx

R EW prop., QCD corr. cancel

❙ 5x improvement from b-tagging

❚ Ab(=3/4 AFB,LR)

❙ P+ =60%: 15x improvement ❙ P+ =0: 6x improvement

0.88 0.9 0.92 0.94 0.215 0.216 0.217 0.218 0.219

Rb Ab

LEP/SLD Giga-Z

68% c.l.

+ SM

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SLIDE 14

7 Jan 2002 Chicago LC Workshop 14

b physics at Giga-Z?

❚ Great potential

❙ Production flavor tagging

R εD2~0.6 vs 0.1-0.25 R D=1-2P(mistag)

❙ Large boost

R b’s well-separated R Excellent b tagging

❙ Well-defined initial state:

R ”ν-reconstruction”

❚ Stiff competition

❙ Mainly cross checks others on “standards”

R CKM unitarity angles R ∆ms

1 2 3 4

  • 1
  • 0.8
  • 0.6
  • 0.4
  • 0.2

0.2 0.4 0.6 0.8 1

b quark cos θ dσ/dcosθ

P-=+0.8 P += -0.6 P-= -0.8 P +=+0.6 P-=+0.8 P +=+0.6 P-= -0.8 P += -0.6

event thrust axis cos θ mistag fraction

0.1 0.2 0.3 0.4 0.5

  • 1
  • 0.8
  • 0.6
  • 0.4
  • 0.2

0.2 0.4 0.6 0.8 1

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SLIDE 15

7 Jan 2002 Chicago LC Workshop 15

Some unique b physics

❚ Bs →Xlν rate

❙ Constrain uncontrolled uncertainty in OPE from quark-hadron duality violations

❚ Polarized Λb decays (G. Hiller)

❙ Probe bR→qLγ (SM) vs bL→qRγ (new physics)

R 109 Z’s gives interesting reach in θ(spin,pγ) asymmetry

❚ B→Xsνν

❙ Emiss constraints + well-separated b decays allow access ❙ Non-SM physics affects Xsνν, Xsl+l- differently ❙ reach? B→τν bkg?

❚ Production flavor tagged B→π0π0

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SLIDE 16

7 Jan 2002 Chicago LC Workshop 16

W+W- threshold: MW

❚ Potential indirect precision: δMW ~ ±4 MeV

❙ Tevatron/LHC: expect 15-20 MeV precision (syst. limited)

❚ EW constraints: can LC approach indirect precision?

❙ Ebeam, beamstrahlung appear to be most serious issues

R high energies: direct reconstruction needs Ebeam constraint

  • E scale likely to be pinned via MZ
  • Beamstrahlung scales as (Ebeam) 2

❙ Threshold needs:

R Ebeam to 10-5: potentially e+e- → γZ, Z → µµ,ee?

  • Stat’s for √s vs time?

R Beamstrahlung: control shape distortion to 0.12%↔±2 MeV

  • Bhabha acolinearity?

R Theory: cross section shape to 0.12%

⇒ explore threshold region

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SLIDE 17

7 Jan 2002 Chicago LC Workshop 17

W+W- threshold: MW

❚ 100 fb-1 → ±5 MeV (stat)

❙ 60% e+ polarization ❙ ~107 sec

❚ Strategy: t-channel dominates

❙ 75% e+

Re- L

❙ 15% e+

Le- R (~ no W+W-)

❙ 10% other

❚ Polarization

❙ 0.25% absolute or e+e- → γZ + Blondel scheme ❙ P+=0: doubles L required

80.39 GeV 80.47 GeV

Centre-of-mass Energy (GeV) Event Rate / Cross Section

0.95 0.96 0.97 0.98 0.99 1 1.01 1.02

80.31 GeV

1.03 1.04 1.05 160 162 164 166 168 170

Generated MW= 80.36 GeV Fit MW: –5 MeV

  • G. Wilson

e- e+ W- W+

ν

MW to ±7 MeV MW to ±7 MeV

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SLIDE 18

7 Jan 2002 Chicago LC Workshop 18

EW reach summary (U. Baer et al, hep-ph/0111314)

Run IIB: 15 fb-1 Run IIB*: 30 fb-1

LC improvement in sin2θeff:

dedicated fixed target Moller scattering exp.

GigaZ improvement in Mt:

from improved αs (Z pole scan)

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SLIDE 19

7 Jan 2002 Chicago LC Workshop 19

Constraint potential: S,T,U

❚ S,T,U

❙ Parameterize effect of new physics on W, Z vacuum pol. ❙ EW variables linear fcn’s of STU

❚ Sensitivity (now→LC/GigaZ)

❙ S: ±0.11 → ±0.05 (±0.02 w/ U=0) ❙ T: ±0.14 → ±0.06 (±0.02 w/ U=0) ❙ U: ±0.15 → ±0.04

❚ Peskin,Wells (PRD 64, 093003)

❙ Survey models w/ heavy Higgs:

R Significant dev’s in S,T from SM

  • bservable w/ GigaZ
  • M. Peskin, J. Wells

❚

  • eg. technicolor

❙ S, T > ~0.1 ❙ 5σ deviation from SM

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SLIDE 20

7 Jan 2002 Chicago LC Workshop 20

Constraint potential: SUSY

❚ MSSM Higgs, light scalar top seen at Tevatron/LHC/LC

❙ at LC yields

R mass, stop-sector mixing to 1%

❚ Various MSSM constraints

❙ sin2θW vs MW predicted vs. measured ❙ Mh predicted vs measured ❙ Constraint on mass of heavy scalar top

  • S. Heinemeyer, G. Weiglein

e+e- →

~

t1

~

t1

*

~

t1

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SLIDE 21

7 Jan 2002 Chicago LC Workshop 21

Conclusion

❚ Low energy program adds great value to the overall LC and general HEP program

❙ Powerful constraints provide

R Self-consistency checks for interpretation of new particles R Extension of effective mass reach

❙ Unique flavor physics contributions a bonus

❚ Beam energy and polarization issues need further study

❙ Solutions will involve monitoring instrumentation that must be allowed for in baseline designs