KIT – Universität des Landes Baden-Württemberg und nationales Forschungszentrum in der...
-
Upload
david-booker -
Category
Documents
-
view
217 -
download
0
Transcript of KIT – Universität des Landes Baden-Württemberg und nationales Forschungszentrum in der...
KIT – Universität des Landes Baden-Württemberg undnationales Forschungszentrum in der Helmholtz-Gemeinschaft
Institut für Experimentelle Kernphysik
www.kit.edu
W. de Boer
Measurements of the strong coupling constant:History and Prospects for Grand Unified Theories
Outline
Measurements of s
Prospects for GUTs
2Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
Incomplete History of the SM (1972-2012)
pp
QCD at TeV scaleHiggs at 126 GeV
LHC
ep
HERA
e+e-(+fixed target)
c,b,tau,gluon3 neutrinos
SUSY unification
PEP, PETRA, TRISTANSLC, LEP
THEPARTICLEPHYSICSTRIUMF
pp
top quarkW,Z bosons
TevatronSPS
-
Lattice non-pert.
QCD
Electro-Weak
Unification
HiggsMechanism
.QCD
AsymptoticFreedom
3Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
History of s measurements
From PDB 1992 From PDB 2012
0.113 0.003
(170+45 ) -30
Factor 4 improvement in s error in last 20 yrs
Phys. Rev. D86, 010001 (2012)
4Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
HERA
5Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
Alpha_s from DIS
DIS
Fractional energy of parton in protoncan be determined from electron energy:
Cross section only dependent on x in parton model,if parton probability distribution (PDF) independentof Q2 (Bjorken scaling).However, at larger Q2 more gluons resolved,thus enhancing x-section at small x and decreasingit at large x (scaling violation). Scaling violationdependent on alpha-s, but strongly correlated withgluon PDF
DIS with measurement of onlylepton is inclusive measurement.since integrated over all jetmultiplicities. Exclusive measurement of jet multiplicities also depende on alpha-s. Combining incl. and excl. meas. decorrelate gluon PDF and alpha_s (ZEUS).
6Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
Legacy measurements from HERA
Larger x-range, equal Q2
Non-pert propt 2/Q2
Calc. In NLO only
T. Schorner-Sadenius, arXiv1111.7290, for HERA combination group
Scale dependence (4%) dominant in NLO
7Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
e+e-fragmentation
8Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
Alpha_s from scaling violation in e+e- annihilation
DIS e+e-
Pro: no PDF of proton involved same range of Q2 (LEP=104 GeV2)
Con: much smaller range of x (CM=LAB, so low energy particles inside beam pipe) b-quark prod. higher at Z0) (have to parametrize heavy quark fragm., light quark fragm. and gluon fragm.)
Results: using lund string fragm. fct. as parametrization of fragm. fcts and integrating O(s
2) ME: s(MZ)=0.118 0.005 (DELPHI,1993) polynomial param. of fragm. fct. and DGLAP eqns: s(MZ)=0.126 0.009 (ALEPH,1994) s(MZ)=0.124 0.0060.009 (DELPHI,1997) (error dominated by scale dep. In NLO, as in DIS)
crossing
9Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
e+e-event shapes
10Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
PRD, arXiv:1006.3080, World data on Thrust reanalysed in NNLO.Systematics? QCD at parton level is NOT experiment at hadron level!
Event shapes in e+e- annihilation (PDG 2012)
11Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
LHC
12Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
LHC electroweak production x-sections in NNLO QCD
excl. n-jets
13Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
LHC electroweak production x-sections in NLO QCD
14Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
Inclusive is one of the most elementary measurements at hadron colliders.– Inclusive jet cross sections at Tevatron/LHC test pQCD over 8-9 orders of magnitude up to 2 TeV– Primary and powerful source of PDF constraint!– LHC experiments are covering larger phase space in jet pT and |y| than Tevatron (probedown to x 0.5x10-3, well studied earlier by DIS) but still have less sensitivity at high x.m
QCD at Hadron Colliders
15Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
With ~5/fb per experiment of 2011 data, jet physics extended to the TeV rangeDijet mass leads the way in highest energy reach, with highest masses 4 TeVExcellent confirmation of perturbative QCD up to the very highest scales!
CMS: CMS PAS QCD-11-004 Atlas: arXiv:1112.6297
Di-jet masses at 7 TeV
CMS: CMS PAS QCD-11-004 Atlas: arXiv:1112.6297
16Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
Correlated uncertainties look better: typical veto, NNLO ~ 15%.Stewart, Tackmann
Errors at LHC dominated by higher orders
Alphas measurements at hadron colliders:D0 from pT dependence of inclusive jet cross section :αs(M2Z) = 0.1161+0.0041−0.0048 (NLO) arXiv:0911.2710CMS from ttbar x-section (NLO): aS(mZ) = 0.1178+0.0048-0.0042,
17Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
LATTICEQCD
18Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
LATTICE QCD (WILSON 1974)
Discretise space time on lattice with V=L3xt
Lattice spacing a small compared with nucleon size
Quarks exist on lattice points,
Gauge fields on links
Path Integrals solved on supercomputers.
QCD Scale fixed by masses and mass splittings
n
axd 44
19Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
QUENCHED APPROXIMATION
In the quenched approximation vacuum polarization effects of quark loops are turned off.
Popular approximation in past (reduces computation time by about 103-105)
Nowadays 2+1 approximation, i.e. 2 light quarks + s-quark in loop
What are remaining errors?R. Gupta, “Introduction to Lattice QCD”, arXiv:hep-lat/9807028
20Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
21Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
From Kronberg in Alphas Workshop, arXiv:1110.0016v3
Alphas values from lattice QCD
Variation: 0.117-0.121s(MZ)=0.1190.002?
22Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
Tau decays and e+e- hadronic
x-sections
23Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
Baikov, Chetyrkin, Kühn, 0801.1821
5-loop calculations in QCD (20.000 diagrams)
C
Theor. errors from non-pert. contr. at M dominate. O(s5)=0.005 at Mtau.Errors reduced by evolution.
Errors dominated by experiment.. O(s4) term =+0.005 at MZ.Errors reduced by evolution
24Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
Calculation up to NNNLO
Non-perturbative regime(Q2=M=1.7 GeV)
Different approaches fortreatment of the perturbative expansion (fixed-order or “contour-improved”)
SM review rescales errorsto get 2/dof=1
Extrapolation to MZ reducesrelative error:
s(MZ)=0.1200.002
Alpha_s from tau decays
PDG 2012
25Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
e+e-hadronic x-sections
26Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
G.~D'Agostini, W.~de Boer and G.~Grindhammer, %``Determination Of Alpha-s And The Z0 Mass From Measurements Of The Total Hadronic Cross-section In E+ E- Annihilation,'' Phys.\ Lett.\ B {\bf 229} (1989) 160.
R ratio in e+e-
Simultaneous fit of s, MZ and sin2W: MZ=89.41.3 GeV, s=0.
27Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
Electroweak fits from different programs
ZFITTER, Bardin et al. , used by electroweak working group
GAPS, J. Erler, , used in PDB
GFITTER, . 0811.0009, used by GFITTER Group:
All consistent with:
Why experimental error so large? Very simple exp.: number counting withhigh statistics in 4 independent LEP experiments!
Answer: 2 hardly compatible alphas measurements at LEP!!! alphas from hadronic x-section: alphas=error dominated byluminosity errr
28Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
Global electroweak fits and gauge coupling unification. Wim de Boer, Christian Sander Phys.Lett. B585 (2004) 276-286 hep-ph/0307049
29Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
Jadach, hep-ph/0306083
Theoretical uncertainties in LEP luminosity (BHLUMI)
30Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
Summary of alphas at Mz
NNNLO, theor. error dominates
NNLO, theor. error?
NNNLO, theor. error negligible
Average completely dominatedby lattice gauge theory, if onebelieves error and NNNLO negl.
My estimate: 0.1200.001
31Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
32Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
33Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
34Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
s=0.118
s=0.116
Heavy Higgs masses near GUT scale strong function of s
.Minimal Supersymmetric SU(5) and Gauge Coupling Unification at Three Loops, W. Martens, L. Mihaila, J. Salomon, M. Steinhauser. Phys.Rev. D82 (2010) 095013 , arXiv:1008.3070 [
35Wim de Boer, Quantum Chromodynamics: History and Prospects, Oberwölz, Sep. 3-8., 2012
Prospects from GigaZ linear collider
Gfitter Group, 0811.0009
Hope to have enough statistics to measure alphas from Rl INDEPENDENT of Lumiand settle hadronic vacuum polarization at 10-4 level! (Input for lattice QCD, g-2 and gauge coupling unification !)