marta ruspa, "inclusive diffraction", dis 20041 inclusive diffraction diffractive cross...
DESCRIPTION
Marta Ruspa, "Inclusive diffraction", DIS (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 f i/p D (z,Q 2,x IP,t): probability to find in a proton, with a probe of resolution Q 2, parton i with momentum fraction z, under the condition that the proton remains intact and emerges with small energy loss, x IP, and momentum transfer,t HARD SCATTERING FACTORISATION DIS of a pointlike virtual photon off the exchanged object PDFsTRANSCRIPT
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
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
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
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.
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.
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
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.
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
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
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
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
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()(
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
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
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
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)
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
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)
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)
Marta Ruspa, "Inclusive diffraction", DIS 2004 20
xIP.F2D(3)/F2
Q2 and xBJ dependences(LPS) (LPS)
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