Diffrazione ad HERA IFAE 2004 Torino 1315 aprile 2004
Diffrazione inclusiva ad HERA DiffPDF Produzione di mesoni vettori
DVCS Marcella Capua INFN e Universita della Calabria Slide 2 IFAE04
Torino aprile 2004 Marcella Capua INFN e Universita' della Calabria
2 X W Q2Q2 e (k) e(k) P (p) P(p) t IP x IP * (q) Diffraction:
exchange of color singlet producing a rapidity GAP in the particle
flow Q2Q2 W Standard Deep Inelastic Scattering in a frame in which
the proton is very fast (Breit frame): x = fraction of protons
momentum carried by struck quark Q 2 /W 2 W = photon-proton centre
of mass energy fraction of the p momentum carried by the IP:
fraction of the IP momentum carried by the struck quark:
Diffractive *p interactions at HERA Slide 3 IFAE04 Torino aprile
2004 Marcella Capua INFN e Universita' della Calabria 3 Flux of
Pomerons Pomeron structure function F 2 D(4) f IP (x IP,t) F 2 IP (
,Q 2 ) Naively, if IP were particle: diffractive * p cross section:
diffractive structure function (assumes ): Inclusive diffraction *p
Xp DIS probes the partonic structure of the proton Structure
function: X W Q2Q2 e (k) e(k) P (p) P(p) t IP x IP * (q) Q2Q2 W
Slide 4 IFAE04 Torino aprile 2004 Marcella Capua INFN e Universita'
della Calabria 4 Large Rapidiy Gap method X system and e measured
System Y not measured, some theoretical and experimental
uncertanties Integrate over t2 GeV, x IP 2 G"> IFAE04 Torino
aprile 2004 Marcella Capua INFN e Universita' della Calabria 12 QCD
fit describes data fractional gluon momentum is M X >2 GeV, x IP
2 GeV 2 NLO DGLAP fit Regge factorisation assumption possible for
this small data set initial scale Q o 2 =2 GeV 2 NLO DGLAP QCD fits
to the ZEUS data Similar to H1! Slide 13 IFAE04 Torino aprile 2004
Marcella Capua INFN e Universita' della Calabria 13 Lifetime of
dipoles very long it is the dipole that interacts with the proton
Transverse size 1/ (Q 2 + M qq 2 ) This is why can do diffraction
in ep collisions ! Virtual photon fluctuates to qq, qqg states
(colour dipoles) Transverse size of incoming hadron beam can be
reduced at will. Can be so small that strong interaction with
proton becomes perturbative (colour transparency) ! The colour
dipole picture ** ** Two models : Saturation Model (Golec-Biernat
and M. Wusthoff) BEKW model (Bartels, Ellis, Kowalski and Wsthoff)
Slide 14 IFAE04 Torino aprile 2004 Marcella Capua INFN e
Universita' della Calabria 14 Saturation vs data (LPS) (Bartels,
Golec-Biernat, Kowalski) Q2Q2 x IP F 2 D(3) F2F2 Inclusive
diffraction: Inclusive DIS: Data well described by BGK saturation
model Slide 15 IFAE04 Torino aprile 2004 Marcella Capua INFN e
Universita' della Calabria 15 Main features of the data described
by BEKW parametrization (x IP
