Vector Meson Production and DVCS from H1 at HERA. K.Hiller, DESY - for the H1 Collaboration. Introduction r and J/ y in Photo & Electroproduction - W- dependence - t – dependence - effective Regge trajectories - Q 2 – dependence - PowerPoint PPT Presentation
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Consistent with H1/HERA-1 data, ZEUS data at low W a bit higher…typical hard process at low |t|
K.Hiller, DESY 21Lowx Meeting, Lisbon 2006
DVCS – Models versus Q2 / W (4)
GPD - model Dipole - model
Band for b-range 5.26 < b < 6.4 GeV-2, no Q2 dependence of b
Both models reproduce general trend quite well,smaller errors needed for model discrimination
K.Hiller, DESY 22Lowx Meeting, Lisbon 2006
Summary
Vector Mesons
New high-statistics -measurement at Q2 ~ 0 New publication of -photoproduction at high |t| Soft to hard transition visible W0.2 W1 Regge parametrization alive, but no universal Pomeron Violation of SCHC for , not for J/ pQCD models describe the trend, need improvements in details (… helicity at high |t|)
DVCS Theoretical interest to extract generalized PDFs First HERA-2 measurement performed, confirms HERA-1 data Models based on GPDs and color dipoles reproduce trend
K.Hiller, DESY 23Lowx Meeting, Lisbon 2006
Spare slides …
K.Hiller, DESY 24Lowx Meeting, Lisbon 2006
Photoproduction (2)
Data & Monte Carlo
Generator DIFFVM: Pomeron exchange plus VM dominance
d/dMY2 ~ MY -2(1+) with 0.08
low-|t|: d/dt ~ exp(- b|t|) with b = 11.4 / 6.5 GeV-2
for elastic/p-dissociative
high-|t|: d/dt ~ |t|-n
with n = 23 / 8.5 for elastic /p-dissocitive
Monte Carlo reproduces well-known features of diffractive vector meson production
K.Hiller, DESY 25Lowx Meeting, Lisbon 2006
Photoproduction at large |t| (2)
What about d/d|t| ?
Standard low-|t|exponential fails,
d/dt ~ |t|-n , with n ~ 4.3
QCD-Models: 2-gluon model fixed/running as fails
BFKL / gluon ladders better, but undershoots at highest |t|
High |t| range nice fortuning of QCD models
K.Hiller, DESY 26Lowx Meeting, Lisbon 2006
b(W) = b0 + 4’ ln(W/W0)
Photoproduction’ = (0.164 ± …) GeV-2
Electroproduction’ = (0.019 ± …) GeV-2
J/Photo & Electroproduction (3)
Slope of the exp(-b|t|) in dependence on W …
Photoproduction: b increases with W … shrinkage
Electroproduction:b ~ constant
K.Hiller, DESY 27Lowx Meeting, Lisbon 2006
J/Photo & Electroproduction (5)
Use r0004 to separate L and T …
at low Q2 dominates T, at large Q2 more L
pQCD predictions*: at large Q2 sensitive to gluon PDFs
(M2 J/ + Q2) –n
n = 2.486 ± 0.080 ± 0.068
*) Martin, Ryskin, Teubner
tot = L + T
K.Hiller, DESY 28Lowx Meeting, Lisbon 2006
Vector Mesons & pQCD
[x g(x,Q2)]2
with x 1/W2
VM production sensitive to g(x,2)
At hard scales, large MVM or Q2 or |t|, pQCD reproduces general features
K.Hiller, DESY 29Lowx Meeting, Lisbon 2006
DVCS – Models versus W (4)
GPD - model Dipole - model
Band for b-range 5.26 < b < 6.4 GeV-2, no Q2 dependence of b
Consistent with H1/HERA-1 dataZEUS data at low W a bit higherBoth models reproduce trend, MRST2001 ~ 50% off
K.Hiller, DESY 30Lowx Meeting, Lisbon 2006
Again: both models give reasonable predictions,MRST2001 seems to overshoot the data
Band for b-range 5.26 < b < 6.4 GeV-2, no Q2 dependence of b