Cross Sections and Spin Asymmetries in Hadronic Scattering
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Transcript of Cross Sections and Spin Asymmetries in Hadronic Scattering
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Cross Sections and Spin Asymmetries in Hadronic
Scattering
Werner VogelsangBNL Nuclear Theory
KEK, 03/10/2007
Dedicated to Jiro
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• QCD perturbation theory in hadronic collisions
• Some NLO phenomenology at RHIC
• Phenomenology of resummation in hadronic collisions
• Conclusions
Outline:
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Jiro’s work has had a big impact onthe development of this area:
some of the early seminal papers of the field polarized-DIS & RHIC programs
QCD spin physics:
proposals and studies for processes at RHIC
open the door to beyond-LL resummation
QCD resummation:
brought young people into field
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I. Introduction
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pp jet Xpp Xpp X, …
Polarized and unpolarized protons
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Such reactions :
0
10
20
30
40
50
60
70
80
90
1st Qtr 2nd Qtr 3rd Qtr 4th Qtr
EastWestNorth
important tests of our understanding of QCD, need for higher orders, resummations, power corrections, …
important insights into proton structure
short-distance interaction perturbation theory
One prime example: at RHIC to measure
baseline for heavy-ion collisions, New Physics searches, …
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short-distance:perturbation theory
universal pdf’s
: factorization/ren. scale
(good up to corrections suppressed as )
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II. Some NLO phenomenology Example: pp at RHIC
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K
RHIC
(Aversa et al.; de Florian)
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Scales varied between pT/2 < < 2 pT
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STAR
Jäger, Stratmann, WV
(NLO calculation assumes “narrow” jet cone)
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Aurenche et al.; Baer et al.; Gordon, WV
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−=Lg1
−=Lg1
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The gluon distribution g
“axial anomaly” Altarelli et al.
Not much information until recently:
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Ultimately: “global analysis” to really extract g and its integral
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III. Phenomenology of resummation in hadronic scattering
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A long-standing problem :
…well described by NLO at RHIC …but data much higher than NLO at fixed-target energies !
Aurenche et al.; Bourrely, Soffer
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higher-order corrections beyond NLO ?
(without rapidity integration: )
Real emission inhibted Only soft/collinear gluons allowed
“threshold” logarithms
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• convolution with PDFs :
emphasized, in particular as
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• work began in the late ‘70sDokshitzer et al.; Parisi Petronzio;Collins, Soper, Sterman;Kodaira, Trentadue
threshold resummation
qT resummation
Sterman; Catani, Trentadue; …
= Resummation
• will spoil perturbative series - unless taken into account to all orders
• today : high level of sophistication
many other reactions in QCD
towards NNLL
Kidonakis, Sterman; Bonciani et al.;Catani, Mangano, Nason;Laenen, Oderda, Sterman;Catani, Grazzini, de Florian;Moch, Vogt, Vermaseren; Aybat, Dixon, Sterman;
“joint resummations” Li; Laenen, Sterman, WV
other formalisms Becher, Neubert; Ji, Ma, Yuan
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Resummation usually done in “transform space”:
In our case, Mellin moments in
Exponentiation
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• : soft-collinear emission off “observed” partons. LL+…
• J : collinear (soft/hard) emission off “unobserved” recoiling “jet” LL+…
• (int) : large-angle soft emission (matrix problem) NLL+…
Kidonakis, Sterman; Bonciani, Catani, Mangano, Nason; Aybat, Dixon, Sterman
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Kodaira, Trentadue
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Jet function:
expect large enhancement ! de Florian, WV
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de Florian, WV
E706
(use “Minimal Prescription” of )Catani, Mangano, Nason, Trentadue
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WA70
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subleading terms important at collider energies
resummation effects much smaller
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Application to prompt photons:
“direct” contributions:
“fragmentation” contributions:
Relatively small resum. effects
a bit like 0 production,but less gggg (because Dg
is smaller)
(Catani et al.; Sterman, WV; Kidonakis, Owens)
de Florian, WV
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de Florian, WV
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de Florian, WV
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Application to jet production: de Florian, WV
Jet cone
• “ observed” jet: involves integration over jet mass
• “unobserved” jet: becomes massless at threshold
no double logs Kidonakis, Sterman
• can be explicitly verified by comparison to “analytical” NLO calculation in small-cone approximation Jäger, Stratmann,WV
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Tevatron 1800 GeV RHIC 200 GeV
de Florian, WV
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Drell-Yan @ J-PARC
Yokoya, WV
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• good understanding of high-p cross sections at colliders
• gives confidence for analysis of spin asymmetries at RHIC
Conclusions
• progress in fixed-target regime through soft-gluon resummation
• generally, resummation techniques important with regard to hadron colliders: J-PARC to RHIC to Tevatron to LHC
• Jiro’s contributions crucial throughout this physics