Marta Ruspa, "Inclusive diffraction", DIS 20041 Inclusive diffraction Diffractive cross section and...
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![Page 1: Marta Ruspa, "Inclusive diffraction", DIS 20041 Inclusive diffraction Diffractive cross section and diffractive structure function Comparison with colour.](https://reader036.fdocuments.us/reader036/viewer/2022062317/5a4d1afd7f8b9ab0599852ee/html5/thumbnails/1.jpg)
Marta Ruspa, "Inclusive diffraction", DIS 2004 1
Inclusive diffraction
Diffractive cross section and diffractive structure function
Comparison with colour dipole models
NLO QCD fit
Marta Ruspa Univ. of Eastern Piedmont-Novara and INFN-Torino (Italy)
XII International Workshop on Deep Inelastic Scattering
Strbske Pleso, High Tatras, Slovakia April 14-18, 2004
on behalf of
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Marta Ruspa, "Inclusive diffraction", DIS 2004 2
IP
Q2
W MX
e’
p’
*e
p
Q2 = virtuality of photon = = (4-momentum exchanged at e vertex)2
t = (4-momentum exchanged at p vertex)2
typically: |t|<1 GeV2
W = invariant mass of photon-proton system
MX = invariant mass of photon-Pomeron system
xIP = fraction of proton’s momentum taken by Pomeron
ß = Bjorken’s variable for the Pomeron = fraction of Pomeron’s momentum carried by struck quark = x/xIP
xIP
t
Inclusive diffraction γ*p Xp
Exchange of an object with the vacuum q. n. Proton almost intact after the collision
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Marta Ruspa, "Inclusive diffraction", DIS 2004 3
(Breit frame)
Diffractive DIS in the Breit frame
Diffractive Deep Inelastic Scattering probes the diffractive PDFs of the proton relevant when the vacuum quantum numbers are exchanged
)ˆ 2iγIP
2pi
* Q(z,σt),x,Q(z,f~Xp)pσ(γ *
fi/pD(z,Q2,xIP,t): probability to find in a proton, with a probe of
resolution Q2, parton i with momentum fraction z, under the condition that the proton remains intact and emerges with small energy loss, xIP, and momentum transfer,t
HARD SCATTERING FACTORISATION
DIS of a pointlike virtual photon off the exchanged object PDFs
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Marta Ruspa, "Inclusive diffraction", DIS 2004 4
Diffractive DIS in the colour dipole picture
We can learn more about the structure of the proton by studying DDIS in a frame in which the virtual photon is faster than the proton
(γ* much faster than p)
• Lifetime of dipoles very long due to large γ boost (E γ ~ W2 ~ 1/x 50TeV ! ) it is the dipole that interacts with the proton !
• Transverse size of dipoles proportional to can be so small that the strong interaction with proton can be treated perturbatively !
)M(Q1/ _qq22
2 gluon exchange: LO QCD realisation of vacuum q.n.
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Marta Ruspa, "Inclusive diffraction", DIS 2004 5
Diffractive DIS in the colour dipole picture
BEKW model : at medium β; at small β
saturation model : (colour transparency)
as Q2 0, growth tamed by saturating
22qq
1/Qrσ _
_qq
σ
β)β(1~FTqq γT
gqqβ)(1~F _
_qq
σ
We can learn more about the structure of the proton by studying DDIS in a frame in which the virtual photon is faster than the proton
(γ* much faster than p)
2 gluon exchange: LO QCD realisation of vacuum q.n.
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Marta Ruspa, "Inclusive diffraction", DIS 2004 6
e pExchange ofcolor singletproducing a
GAPin the
particle flow
Inclusive diffraction γ*p Xp
No activity in the forward direction
Proton suffers only a small energy loss
MX method
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Marta Ruspa, "Inclusive diffraction", DIS 2004 7
Diffr. Non-diffr.
c, b from fit n.d. events subtracted
contamination from reaction epeXN
Selection of events γ*p Xp with Mx method
Properties of Mx distribution: - exponentially falling for decreasing Mx for non-diffractive events - flat vs ln Mx
2 for diffractive events
Forward Plug Calorimeter (FPC):
CAL acceptance extended by 1 unit in pseudorapidity from η=4 to η=5 higher Mx and lower W if MN > 2.3 GeV deposits EFPC > 1 GeV recognized and rejected!
Diffr. Non-diffr.
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Marta Ruspa, "Inclusive diffraction", DIS 2004 8
e pExchange ofcolor singletproducing a
GAPin the
particle flow
Inclusive diffraction γ*p Xp
No activity in the forward direction
Proton suffers only a small energy loss
LPS method
MX method
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Marta Ruspa, "Inclusive diffraction", DIS 2004 9
Free of p-diss background Low acceptance
low statistics
z
zIP p
p'x1
Selection of events γ*p Xp with LPS
Diffractive peak
IPx1
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Marta Ruspa, "Inclusive diffraction", DIS 2004 10
97 LPS sample
0.03 < Q2 < 100 GeV2
25 < W < 280 GeV
1.5 < Mx < 70 GeV
xIP < 0.1
Higher xIP region
99-00 FPC sample(Mx method)
22 < Q2 < 80 GeV2
37 < W < 245 GeV
Mx < 35 GeV
MN < 2.3 GeV
Higher β region
Data samples
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Marta Ruspa, "Inclusive diffraction", DIS 2004 11
diffractive γ*p cross section
dWdMdQ
σd
)y)(α(WπQ
dM
dσ
X
De'Xp'ep
X
Dpγ*
2
3
2
2
11
diffractive structure function (assumes ) 0)3( D
LF
IP
XpeepD
IPD
dxdQdd
yyQ
xQF2
''22
42)3(
2 )2/1(4),,(
Cross section and structure function
xIP dependence of F2D(3)
andW dependence of dσ/dMX
- extraction of αIP
- Regge factorisation
Q2 dependence of F2D(3)
and dσ/dMX
-sensitivity to diffractive PDFs
comparison to BEKW model and to saturation model
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Marta Ruspa, "Inclusive diffraction", DIS 2004 12
xIP dep. of F2
D(3) equivalent to W dep. of dσ/dMx
F2D(3) xIP
dependence
Data agree with Regge factorisation assumption in the region of the fit
)(02.0)(02.016.1)0( sysstatIP
(LPS)
Regge fit (xIP<0.01):
),()( 22
)3(2 QFxfF IP
IPIPD
dtx
exftIP
t
IP
tb
IPIP
1)(2)(
with
tt IPIPIP ')0()(
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Marta Ruspa, "Inclusive diffraction", DIS 2004 13
p-dissociation events with MN<2.3 GeV included
MX< 2 GeV: weak W dep.
MX> 2 GeV: d/dMX rises rapidly with W
Cross section W dependence (Mx method)
power-like fit
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Marta Ruspa, "Inclusive diffraction", DIS 2004 14
fit to total cross section data:
fit to diffractive cross section data:
Evidence of a rise of IPdiff with
Q2 mild Regge factorisation violation .
αIP from diffractive and total γ*p scattering
IPdiff higher than soft Pomeron
Similar W dep. of diffractive and total cross section
(Mx method)
(0)αtotIP
(0)αdiffIP
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Marta Ruspa, "Inclusive diffraction", DIS 2004 15
BUT
low MX : strong decrease of
diff/tot with increasing Q2 high MX : no Q2 dependence !
ratio ~ flat in W
Regge expectation:
19.01)0(2
222
*
*
)()(/
WWWdMd
IP
IP
totp
XD
p
at W=220 GeV: diff(MX<35 GeV)/tot
~ 20 % Q2= 2.7 GeV 10 % Q2= 27 GeV
σdiff/ σtot W dependence(Mx method)
Explained by saturation model
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Marta Ruspa, "Inclusive diffraction", DIS 2004 16
Main features of the data described by BEKW parametrization (xIP<0.01)
Cross section Q2 dependence
Transition to a constant cross section as Q20(similar to total cross section )
qqg fluctuations dominant at low Q2
(Bartels, Ellis, Kowalski and Wüsthoff)
medium β
small β
)1(~ TqqF
)1(~ TqgqF
totp*
(LPS)
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Marta Ruspa, "Inclusive diffraction", DIS 2004 17
F2D(3) Q2 dependence(LPS)
Data well described by BGK saturation model (xIP<0.01)
Positive scaling violation at all values of β QCD fit
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Marta Ruspa, "Inclusive diffraction", DIS 2004 18
QCD fit describes data
fractional gluon momentum is at initial scale
NLO QCD fit on LPS+charm data
))%(9)(882( sysstat
)36/9.37/( 2 ndf
[F2D(3)cc from DESY-03-094, see N. Vlasov
talk]
• xIP <0.01• QCDNUM• Regge factorisation assumption possible for this small data set• DL flux• initial scale Q2=2 GeV2
• zf(z)=ΣPi(1-x)a at initial scale• other PDFs parametrisation tried• Thorne-Robert variable-flavour- number-scheme
(LPS)
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Marta Ruspa, "Inclusive diffraction", DIS 2004 19
LPS QCD fit compared to Mx data
Main discrepancies at high β, where no LPS data available
NB: fits scaled by 0.69to account for p-dissbackground in Mx data
Mx method data described by the fit in the region of overlap LPS-Mx method
ZEUS (MX method)
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Marta Ruspa, "Inclusive diffraction", DIS 2004 20
xIP.F2D(3)/F2
Q2 and xBJ dependences(LPS) (LPS)
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Marta Ruspa, "Inclusive diffraction", DIS 2004 21
Recent data from ZEUS with improved precision and extended kinematic range
Data described by colour dipole models (BEKW, saturation)
Data described by a NLO QCD fit (+model)
Possible indication that αIP increases with Q2 in diffraction
W dep. of diffractive and total cross section similar at high Q2
Summary