XVIII SEMINARIO NAZIONALE di FISICA NUCLEARE E SUBNUCLEARE
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XVIII SEMINARIO NAZIONALE di FISICA NUCLEARE E SUBNUCLEARE. Fisica dello Spin. Mauro Anselmino Torino University and INFN . Why spin ….?.

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XVIII SEMINARIO NAZIONALE di FISICA NUCLEARE E SUBNUCLEARE

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Xviii seminario nazionale di fisica nucleare e subnucleare

XVIII SEMINARIO NAZIONALE di FISICA NUCLEARE E SUBNUCLEARE

Fisica dello Spin

Mauro Anselmino Torino University and INFN


Xviii seminario nazionale di fisica nucleare e subnucleare

Why spin ….?

Spin is one of the most fundamental concepts in physics, deeply rooted in Poincaré invariance and hence in the structure of space-time itself. All elementary particles we know today carry spin, among them the particles that are subject to the strong interactions, the spin-1/2 quarks and the spin-1 gluons. Spin, therefore, plays a central role also in our theory of the strong interactions, Quantum Chromodynamics (QCD), and to understand spin phenomena in QCD will help to understand QCD itself.

Research Plan for Spin Physics at RHIC, 2005


Xviii seminario nazionale di fisica nucleare e subnucleare

Polarized Deep Inelastic Scattering: exploring the proton longitudinal spin structure

  • Helicity distributions- Δq, Δg -and their QCD evolution

  • Polarized structure functions: g1, g2

  • Data and “spin crisis” (not a real crisis)

  • The spin carried by the gluons

  • Flavour separation

  • Weak interactions

  • Missing information


Xviii seminario nazionale di fisica nucleare e subnucleare

Surprises:Transverse Single Spin Asymmetries(unintegrated polarized parton distributions)

  • Single Spin Asymmetries (SSA) in elastic processes

  • Single Spin Asymmetries in pQCD and in data

  • Parton intrinsic motion and spin

  • Spin - Transverse Momentum Dependent distribution and fragmentation functions

  • Phenomenology of SSA in inclusive processes

  • Mysteries: spin asymmetries in pp → pp processes


Xviii seminario nazionale di fisica nucleare e subnucleare

The last missing piece of the proton structure:transversity

  • The partontransverse spindistribution,h1

  • A partner for h1

  • Transversity inDrell-Yanprocesses

  • Transversity inSIDISprocesses

  • Collins function from e+e- data

  • Hunting strategies forh1


Xviii seminario nazionale di fisica nucleare e subnucleare

Polarized Deep Inelastic Scattering

What do we know, and how, about the proton structure?

l’

l,s

Main source of information is DIS

q

p,S

X

l’,E’

θ

p, S

l,E,s

X


Xviii seminario nazionale di fisica nucleare e subnucleare

parity conserving case (one photon exchange)

current conservation


Xviii seminario nazionale di fisica nucleare e subnucleare

measuring dσ one extracts information on the structure functionsF1, F2, g1andg2

F1,2related toq(x,Q2), g(x,Q2 ) quark, gluon distributions

g1 related to∆q(x,Q2), ∆g(x,Q2)quark, gluonhelicity distributions


Xviii seminario nazionale di fisica nucleare e subnucleare

l’

l

QCD parton model

q

q

p,S

X


Xviii seminario nazionale di fisica nucleare e subnucleare

scheme dependent

coefficient functions

helicity distributions

at LO


Xviii seminario nazionale di fisica nucleare e subnucleare

QCD evolution

splitting functions


Xviii seminario nazionale di fisica nucleare e subnucleare

de Florian, Navarro, Sassot


Xviii seminario nazionale di fisica nucleare e subnucleare

Dirk Ryckbosh, DIS 2005


Xviii seminario nazionale di fisica nucleare e subnucleare

Research Plan for Spin Physics at RHIC

February 11, 2005

Figure 11: Left: results for Δg(x,Q2 = 5GeV2) from recent NLO analyses [1, 2, 36] of polarized

DIS. The various bands indicate ranges in Δg that were deemed consistent with the scaling

violations in polarized DIS in these analyses. The rather large differences among these bands

partly result from differing theoretical assumptions in the extraction, for example, regarding the

shape of Δg(x) at the initial scale. Note that we show xΔg as a function of log(x), in order

to display the contributions from various x-regions to the integral of Δg. Right: the “net gluon

polarization” Δg(x,Q2)/g(x,Q2) at Q2 = 5 GeV2, using Δg of [2] and its associated band,

and the unpolarized gluon distribution of [82].


Xviii seminario nazionale di fisica nucleare e subnucleare

Spin(Jz)sum rule

de Florian, Navarro, Sassot

Direct measure of Δg needed

  • large pT di-hadron production in SIDIS,

  • high pT pions and jets at RHIC,

  • direct photon production at RHIC,

  • charm production at RHIC,

  • role of orbital angular momentum


Xviii seminario nazionale di fisica nucleare e subnucleare

large pT di-hadron production in SIDIS


Xviii seminario nazionale di fisica nucleare e subnucleare

(collinear configurations)

factorization theorem

X

c

a

b

X

FF

PDF

pQCD elementary interactions


Xviii seminario nazionale di fisica nucleare e subnucleare

RHIC


Xviii seminario nazionale di fisica nucleare e subnucleare

polarized case: measure

X

c

a

b

X

Δq, Δg

FF

pQCD elementary asymmetries


Xviii seminario nazionale di fisica nucleare e subnucleare

RHIC proposal 2005


Xviii seminario nazionale di fisica nucleare e subnucleare

prompt photon production at RHIC


Xviii seminario nazionale di fisica nucleare e subnucleare

Flavour separation -W production at RHIC

X

parity violating longitudinal single spin asymmetry

a

b

X


Xviii seminario nazionale di fisica nucleare e subnucleare

Flavour decomposition in SIDIS,

DIS

SIDIS

Unknowns:


Xviii seminario nazionale di fisica nucleare e subnucleare

large x behaviour


Xviii seminario nazionale di fisica nucleare e subnucleare

Charged–Current Deep-Inelastic Scattering (neutrino factory)

S. Forte, M. Mangano, G. Ridolfi

p,S

X


Xviii seminario nazionale di fisica nucleare e subnucleare

LO QCD parton model results

Some combinations of the polarized structure functions are of particular interest. For example:


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