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Parity-Odd Asymmetry in W-Jet Events. Hiroshi Yokoya (Niigata U.). Ref. K.Hagiwara, K.Hikasa, N.Kai , Phys.Rev.Lett.52(1984)1076; K.Hagiwara, K.Hikasa, HY , hep-ph/0604208. RBRC workshop, June 18-23, 2006 “RHIC physics in the Context of the Standard Model”. Contents :. - PowerPoint PPT Presentation
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1
Parity-Odd Asymmetry in W-Jet Events
Hiroshi Yokoya (Niigata U.)
RBRC workshop, June 18-23, 2006
“RHIC physics in the Context of the Standard Model”
Ref. K.Hagiwara, K.Hikasa, N.Kai, Phys.Rev.Lett.52(1984)1076;
K.Hagiwara, K.Hikasa, HY, hep-ph/0604208
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Contents :
• Introduction : W-jet production
• Parity-odd asymmetry in W-jet events
• Phenomenology and Simulation
• Summary
3Introduction
• High-qT W-boson productions at Hadron Collider
UA1, UA2 Collaborations @ CERN
CDF, D0 Collaborations @ FNAL Tevatron
have been measured by
4
CDF (’91)D0 (’98)
• Measurements in Tevatron Run-I
qT-distributions - Experiments -
5qT-distributions - Theory -
• High-qT (qT ~ MW)perturbation is good
complete NLO calc. Arnold,Reno(’89);Gonsalves,Pawlowski,Wai(’89)
(NNLO is modest ) Kidonakis,Vera (’04)
c.f.) small-qT (qT ≪ MW)
Arnold,Kauffman(’91),Ellis,Ross,Veseli(’98),,,
K ~ 1.3, flat behavior
log corrections → qT-resummation
6Lepton Angular Distributions
P-even
P-odd
• Rich information on the polarization of W-boson, i.e.the details of production mechanism can be investigated
Fi : structure functions
7
Collins-Soper frame
(W-rest frame)
W-jet c.m. frame
(parton c.m. frame)
Notice : Both frames are NOT constructible from observables, because of missing neutrino momentum.
Collins-Soper Frame
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P-even parts :LO (tree-level)Chaichian,Hayashi,Yamagishi(’82)
Mirkes,Korner,Schuler(’91),Mirkes(’92)NLO (one-loop)
P-odd parts :LO (one-loop)Hagiwara,Hikasa,Kai(’84)
• pQCD calculation :
Lepton Angular Distributions
9Recent Results from CDF [hep-ex/504020]
• Some of the P-even distributions are measured at Tevatron Run-I, in good agreement with the pQCD prediction in NLO.
• In Run-II, measurements of P-odd distributions may be possible.
We study the simple and practical observables of the P-odd asymmetry, and perform a realistic Monte-Carlo simulation.
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Parity-odd asymmetry
11Parity-odd asymmetry
"for their penetrating investigation of the so-called parity laws which has led to important discoveries regarding the elementary particles"
T.D. Lee and C.N. Yang
The Nobel Prize in Physics 1957
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• β-decay of polarized nucleus :
P
Parity-odd asymmetry
13Parity-odd asymmetry
• Parity transformation :
• Parity-odd observables :
with spin :
without spin :
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• T-transformation :
• T-transformation : (anti-unitary)
Parity-odd and Naïve-T ( T )-odd
~
• P-odd observables without spins are interesting,
because these are at the same time T-odd.~
~
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• Unitarity of S-matrix
Time-reversal violation
• T-odd quantity
→ proportional to the absorptive parts of scattering amplitude
Unitarity and T-odd quantity~
~
absorptive part
16One-loop calculation
Hagiwara,Hikasa,Kai(’84)
• one-loop calculation in pQCD on the absorptive part of scattering amplitude
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with CTEQ6M
Hagiwara,Hikasa,Kai(’84)
One-loop calculation
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Phenomenology and Monte Carlo Simulation
19
Collins-Soper frame
(W-rest frame)
W-jet c.m. frame
(parton c.m. frame)
Notice : Both frames are NOT constructible from observables, because of the missing neutrino momentum.
Collins-Soper Frame
20Two-fold ambiguity
• (longitudinal) neutrino momentum is not observable
→ Two-fold ambiguity in
determining
• W-jet c.m. frame
• Collins-Soper frame
Advantage of CS frame : only the sign of cosθ can’t be determined.
sinθ and φ can be determined.
Laboratory frame
21Realistic Observables
• Pseudo-rapidity difference of lepton and jet, instead of
Laboratory frame
• qT is observable,
from jet transverse momentum
22Monte-Carlo simulation
• Tevatron Run-II :Luminosity :
• “standard” CDF cuts :
• W → lepton detection : • jet identification :
W’s transverse mass :
Jet cone size :
• qT minimum cut :
CDF hep-ex/504020
23Effective Higher-Order enhancement
LO Matrix Elements with “effective” H.O. enhancement
• good as well, for P-even distributionsMirkes,Ohnemus (’94)
settingabsorb the H.O. enhancement into LO result, approximately
• not confirmed for P-odd, because NLO is not known.
Kidonakis,Vera(’04)
24Results : Event yield
• Total number of events for one lepton-flavor ~ 50,000.
c.f.) for Run-I we get: # ~ 16,000.
: 12,676.: 6,941.
CDF
25Results : Observable P-odd asymmetries
• Left-right asymmetry
more than 5σ deviation from zero-asymmetry is expected
• sign(sin2φ) asymmetry
(combining all Δy and qT)
~ 5% at large Δη
+
+
-
-
①
②
④
③
26RHIC case :
• looser cut for qT minimum to use more events
→ perturbation works well?
Perhaps, we need qT-resummation for the azimuthal
angular distributions D.Boer and W.Vogelsang, hep-ph/0604177
pp collision
27RHIC case :
• W+, one-lepton flavor
# of events ~ 11,000.
• Left-right asymmetry →
28Summary
• High-qT W-boson production at Hadron colliders
• P-odd asymmetries in decay-lepton angular distributions
• Monte-Carlo simulation for Tevatron Run-II and RHIC
• well-described by (NLO) pQCD
• lepton angular distributions are measured at
Tevatron
• naïve-T-odd as well• arise from the absorptive part of scattering amplitudes• new test of the pQCD prediction
• two-fold ambiguity → realistic observables
• we proposed observable asymmetries
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