new results on diffraction at heralevonian/papers/qcd2016.pdf6 selected new results x = e /el n p. ....
TRANSCRIPT
S. Levonian, DESY
New Results on Diffraction at HERA
) GeVπ) - m(Ksππm(K0.14 0.145 0.15 0.155 0.16 0.165
N(D*
)
0
50
100
150
200
250
300
350
400
D* in diffractive DIS
H1 Preliminarydatasignalbackground
Wγπ [GeV]
σ(γπ
+--- >
ρ0 π+)
[µb]
10 20 30 400
1
2
3
4
5
Wγπ [GeV]
σ(γπ
+--- >
ρ0 π+)
[µb]
10 20 30 400
1
2
3
4
5
Wγπ [GeV]
σ(γπ
+--- >
ρ0 π+)
[µb]
10 20 30 400
1
2
3
4
5H1 data H1
)2 (GeV2Q0 10 20 30 40 50 60 70 80
R
0
0.2
0.4
0.6
0.8(1S)ψJ/σ
(2S)ψσR =
-1ZEUS 468 pb
-1H1 27 pb
-1p: 6.3 pbγH1
HIKT: GBW-BT
HIKT: GBW-LOGAR: b-CGC
AR: IP-Sat
= 0δKMW: FFJS
KNNPZZLM
= 2δKMW:
ZEUS
2 HERA: The World’s Only ep Collider
Days of running
H1
Inte
grat
ed L
umin
osity
/ p
b-1
Status: 1-July-2007
0 500 1000 15000
100
200
300
400electronspositronslow E
HERA-1
HERA-2
• 1998 Ep upgrade: 820 ⇒ 920 GeV(√s : 301 ⇒ 319 GeV)
• 2001 HERA-2 upgrade: L × 3, Polarised e+/e−
(〈P 〉 = 40%)
HERA-1 (1993-2000) ≃ 120 pb−1
HERA-2 (2003-2007) ≃ 380 pb−1
Final Data samples
H1+ZEUS: 2 × 0.5 fb−1
3 Diffraction at HERA. Factorisation properties
pp
X (M )X
e
QCD collinearfactorisation at
fixed x , t
(b)
(x )IP
(t)
e
(Q )2g*
}
}
IP
γ
ppIP
IPq
qγ
ppIP= x
QCD versus Regge factorisation
QCD factorisation(rigorously proven for
DDIS by Collins et al.):
Regge factorisation(conjecture, e.g. RPM
by Ingelman,Schlein):
σD(4)r ∝ ∑
i σ̂γ∗i(x,Q2) ⊗ fDi (x,Q2;xIP , t)
• σ̂γ∗i – hard scattering part, same as in inclusive DIS
• fDi
– diffractive PDF’s, valid at fixed xIP , t which obey (NLO) DGLAP
FD(4)2 (xIP , t, β,Q
2) = Φ(xIP , t) · F IP2 (β,Q2)
• In this case shape of diffractive PDF’s is independent of xIP , t
while normalization is controlled by Regge flux Φ(xIP , t)
4 Selection of Diffractive Events
5 Diffraction at HERA: Some old Results
Inclusive Diffraction and DPDFs: gluon dominated IP
]2 [GeV2Q10 210
D(3
)rσ
IP .
xl 3
-210
-110
1
10
210
310
410=0.005 (l=11)β
=0.008 (l=10)β
=0.013 (l=9)β
=0.02 (l=8)β
=0.03 (l=7)β
=0.05 (l=6)β
=0.08 (l=5)β
=0.13 (l=4)β
= 0.2 (l=3)β
=0.32 (l=2)β
= 0.5 (l=1)β
= 0.8 (l=0)β
=0.01IPx < 1.6 GeV)
YH1 LRG (M
H1 FPS HERA-II x 1.2
H1 2006 DPDF Fit B
(extrapol. fit)
H1 0
0.2
0.4
0.6
0.8
0.2 0.4 0.6 0.8z
z⋅gl
uon(
z)
gluonµf
2=25 GeV2
H1
0
0.05
0.1
0.15
0.2
0.2 0.4 0.6 0.8z
z⋅si
ngle
t(z)
singletµf
2=25 GeV2
H1
5 Diffraction at HERA: Some old Results
Inclusive Diffraction and DPDFs: gluon dominated IP
]2 [GeV2Q10 210
D(3
)rσ
IP .
xl 3
-210
-110
1
10
210
310
410=0.005 (l=11)β
=0.008 (l=10)β
=0.013 (l=9)β
=0.02 (l=8)β
=0.03 (l=7)β
=0.05 (l=6)β
=0.08 (l=5)β
=0.13 (l=4)β
= 0.2 (l=3)β
=0.32 (l=2)β
= 0.5 (l=1)β
= 0.8 (l=0)β
=0.01IPx < 1.6 GeV)
YH1 LRG (M
H1 FPS HERA-II x 1.2
H1 2006 DPDF Fit B
(extrapol. fit)
H1 0
0.2
0.4
0.6
0.8
0.2 0.4 0.6 0.8z
z⋅gl
uon(
z)
gluonµf
2=25 GeV2
H1
0
0.05
0.1
0.15
0.2
0.2 0.4 0.6 0.8z
z⋅si
ngle
t(z)
singletµf
2=25 GeV2
H1
αIP(t)=α(0)+α′t
VM: soft vs hard IP
soft
hard
transition from soft to hard regime at µ2 ≃ 4÷5 GeV2
6 Selected new Results
x = E /EL pn
. .
γ π+
π−
π+
0
t’
t
γ Wγ
+πW
p
PI
ρ
p
π
n
� Diffractive Photoproduction of Isolated Photons [ZEUS-prel-2015]
� D∗ Meson Production in Diffractive DIS at HERA [H1-prel-2016]
� Cross-section Ratioσψ(2S)σJ/ψ(1S)
in Exclusive DIS [ZEUS-pub-2016]
� Exclusive ρ0 Meson Photoproduction with a Leading Neutron [H1-pub-2016]
Isolated Photons in Diffractive Photoproduction
8 Isolated Photons in Diffractive PHP
4 < Eγt < 15 GeV
−0.7 < ηγ < 0.9
• Use energy-weighted e.m. cluster width 〈δZ〉to distinguish γ from π0, η background
• Diffraction: LRG signature, and xIP < 0.03
9 Isolated Photon+ Jet: Data vs MC model
Photon Jet All well described,except highest zIPComparison with NLO QCD to follow
D* in Diffractive DIS at HERA
11 D∗ Production in Diffractive DIS: Data sample
) GeVπ) - m(Ksππm(K0.14 0.145 0.15 0.155 0.16 0.165
N(D
*)
0
50
100
150
200
250
300
350
400
D* in diffractive DIS
H1 Preliminarydatasignalbackground
[nb]
eY
X(D
*)→
ep
σ0
0.2
0.4
D* in diffractive DIS
H1 Preliminarydata
scale variation⊕ cmNLO QCD, H1 2006 Fit B
scale variation⊕ cmNLO QCD, H1 2006 Fit B
scale variation⊕ cmNLO QCD, H1 2006 Fit B
2 < 100 GeV25 < Q < 0.03IPx
0.02 < y < 0.65 < 1.6 GeVYM
> 1.5 GeVT,D*
p 2|t| < 1 GeV
< 1.5D*
η-1.5 <
Based on 280 pb−1 HERA-2 data
Open charm tagged with D∗
D∗+ →D0π+slow→(K−π+)π+
slow + C.C.
LRG selection of diffraction (∼ 1100D∗)
12 D∗ Production in Diffractive DIS: Data vs NLO
• NLO QCD by HQVDIS in FFNS
(H1 DPDF-2006, mc = 1.5GeV,
µ2r = µ2
f = m2c + 4Q2)
in good agreement with data
• Charm fragm.func. as determined
in H1 non-diffractive D∗ analysis
works here ⇒ supports
universality of charm fragmentation
• Data could be used as
additional input to the global
DPDF fit
Cross−section Ratio in DISσψ(2S)σJ/ψ(1S)
14 Motivation
pQCD predictions: R(Q2 = 0) ≃ 0.17 and rises withQ2
15 Data samples and Decay channels
(GeV)µµM2 3 4 5
Ent
ries
10
210
310
410
-1ZEUS 468 pb
Background fit
ZEUS
(1S)ψJ/
(2S)ψ
5<Q2<80GeV2 L = 468pb−1
16 Results: σψ(2S)/σJ/ψ(1S) vs Q2, W and |t|
)2 (GeV2Q10 20 30 40 50 60 70 80
com
bR
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
-1ZEUS 468 pb
ZEUS
W (GeV)40 60 80 100 120 140 160 180 200
com
bR
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
-1ZEUS 468 pb
ZEUS
)2|t| (GeV0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
com
bR
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
-1ZEUS 468 pb
ZEUS
)2 (GeV2Q0 10 20 30 40 50 60 70 80
R
0
0.2
0.4
0.6
0.8(1S)ψJ/σ
(2S)ψσR =
-1ZEUS 468 pb
-1H1 27 pb
-1p: 6.3 pbγH1
HIKT: GBW-BT
HIKT: GBW-LOGAR: b-CGC
AR: IP-Sat
= 0δKMW: FFJS
KNNPZZLM
= 2δKMW:
ZEUS
• Ratio rises with Q2 and
is constant in W and |t|
• HERA data in qualitative agreement
with pQCD models
• Some discriminating power
(albeit statistically limited)
Rho−0 with a Leading Neutron at HERA
18 HERA as a ‘4P ’ facility
HERA enables to study structure of
Proton – F2, FL, ...Photon – g/γ
Pomeron – FD2 , F
DL
Pion – F π2
0.2
0.4
0.6
0.8
1
410 310 210 110 1
HERAPDF2.0 NLO uncertainties: experimental model parameterisation HERAPDF2.0AG NLO
x
xf 2 = 10 GeV2f
µ
vxu
vxd
0.05)×xS (
0.05)×xg (
H1 and ZEUS
0
1
2
3
4
5
-1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0
log10(xγ)
x γ g(x
γ)/α
H1 1993 (dijet events)
H1 1994 (high pT track events)
GRV-LO
LAC1-LO
SAS1D-LO
‹pT2› = 38 (GeV/c)2ˆ
0
0.2
0.4
0.6
0.8
0.2 0.4 0.6 0.8z
z⋅gl
uon(
z)
gluonµf
2=25 GeV2
H1
18 HERA as a ‘4P ’ facility
HERA enables to study structure of
Proton – F2, FL, ...Photon – g/γ
Pomeron – FD2 , F
DL
Pion – F π2
0.2
0.4
0.6
0.8
1
410 310 210 110 1
HERAPDF2.0 NLO uncertainties: experimental model parameterisation HERAPDF2.0AG NLO
x
xf 2 = 10 GeV2f
µ
vxu
vxd
0.05)×xS (
0.05)×xg (
H1 and ZEUS
0
1
2
3
4
5
-1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0
log10(xγ)
x γ g(x
γ)/α
H1 1993 (dijet events)
H1 1994 (high pT track events)
GRV-LO
LAC1-LO
SAS1D-LO
‹pT2› = 38 (GeV/c)2ˆ
0
0.2
0.4
0.6
0.8
0.2 0.4 0.6 0.8z
z⋅gl
uon(
z)
gluonµf
2=25 GeV2
H1
ρ 0 + p
+πγ n
W
W
0
π+γ
γπ
p
t
x = E /En
t’
pL
γ
π+
π
π+
−
.
ρ
p n
IP
Here for the first time we investigate the reaction involving all these objects simultaneously:
No hard scale present ⇒ Regge framework is most appropriate
19 ρ0 with Leading Neutron: S/B decomposition
x = E /EL pn
.
γ π+
π−0
t’
π+*
γ π+
−0
t’
π+
π
W. .
γ π+
π−
π+
0
t’
t
γ Wγ
+π
γ+
−0
t’
ππ
Y
pN
ρ
PI
np
PI
ρ
n n
p
PI
ρ
p
π
n
ρ
PI
p n
M
(a) (b) (c) (d)
20 ρ-meson shape
M(π+π-) [GeV]
dN/d
M [
GeV
-1]
ρ0 with Forward Neutron
0.5 1 1.5
0
400
800
1200
M(π+π-) [GeV]
dN/d
M [
GeV
-1]
ρ0 with Forward Neutron
0.5 1 1.5
0
400
800
1200H1 dataρ0: BWρ0: BW RSx
interference termω reflection
M(π+π-) [GeV]
dN/d
M [
GeV
-1]
ρ0 with Forward Neutron
0.5 1 1.5
0
400
800
1200
full fit
(a)
H1
pT2 [GeV2]
n RS
Exclusive ρ0 photoproduction
0.01 0.1 10
2
4
6
8
fit n 0(pT2+M2)-β
pT2 [GeV2]
n RS
Exclusive ρ0 photoproduction
0.01 0.1 10
2
4
6
8
H1 dataZEUS-1994 (γp ----> ρ0p)
(b)
H1
dN(Mππ)dMππ
∝ BWρ(Mππ)(
Mρ
Mππ
)nRS
M = 764 ± 3 MeV
Γ = 155 ± 5 MeV
Analysis region: 0.6<Mπ+π−<1.1 GeV extrapolated using BW to the full range: 0.28<Mρ0<1.5 GeV
21 Cross sections definitions
0
π+
π+
π
π−
+γ
γ
π
ρ
PI
np
e
e’
f
f /p
/eσγp =σepΦγ
Φγ =∫
fγ/e(y,Q2)dydQ2
σγπ =σγpΓπ
Γπ =∫
fπ/p(xL, t)dxLdt
VMD:
OPE:
. fγ/e(y,Q2) =
α
2πQ2y
[
1 + (1 − y)2 − 2(1 − y)
(
Q2min
Q2− Q2
M2ρ
)]
1(
1 + Q2
M2ρ
)2
. fπ/p(xL, t) =1
2π
g2pπN
4π(1 − xL)
−t(m2
π − t)2exp[−R2
πn
m2π − t
1 − xL]
21 Cross sections definitions
Wγp [GeV]
σ γp [n
b]
20 40 60 80 1000
100
200
300
400
500
Wγp [GeV]
σ γp [n
b]
20 40 60 80 1000
100
200
300
400
500
H1 data
Wγp [GeV]
σ γp [n
b]
20 40 60 80 1000
100
200
300
400
500
POMPYT
Wγp [GeV]
σ γp [n
b]
20 40 60 80 1000
100
200
300
400
500
fit W δ (δ=--0.26+--- 0.06stat+--- 0.07sys)
H1ρ0 with Forward Neutron
Wγπ [GeV]
σ(γπ
+--- >
ρ0 π+)
[µb]
10 20 30 400
1
2
3
4
5
Wγπ [GeV]
σ(γπ
+--- >
ρ0 π+)
[µb]
10 20 30 400
1
2
3
4
5
Wγπ [GeV]
σ(γπ
+--- >
ρ0 π+)
[µb]
10 20 30 400
1
2
3
4
5H1 data H10
π+
π+
π
π−
+γ
γ
π
ρ
PI
np
e
e’
f
f /p
/e
VMD:
OPE:
. fγ/e(y,Q2) =
α
2πQ2y
[
1 + (1 − y)2 − 2(1 − y)
(
Q2min
Q2− Q2
M2ρ
)]
1(
1 + Q2
M2ρ
)2
. fπ/p(xL, t) =1
2π
g2pπN
4π(1 − xL)
−t(m2
π − t)2exp[−R2
πn
m2π − t
1 − xL]
22 Constraining pion flux
xL
dσγp
/dx L
[µb
]
0.4 0.5 0.6 0.7 0.8 0.90
0.2
0.4
0.6
0.8
1H1 data (ϑn<0.75 mrad)
Normalised to data:
xL
dσγp
/dx L
[µb
]
0.4 0.5 0.6 0.7 0.8 0.90
0.2
0.4
0.6
0.8
1
FMSNSSS
xL
dσγp
/dx L
[µb
]
0.4 0.5 0.6 0.7 0.8 0.90
0.2
0.4
0.6
0.8
1
H1
xL
dσγp
/dx L
[µb
]
0.4 0.5 0.6 0.7 0.8 0.90
0.2
0.4
0.6
0.8
1H1 data (ϑn<0.75 mrad)
Normalised to data:
xL
dσγp
/dx L
[µb
]
0.4 0.5 0.6 0.7 0.8 0.90
0.2
0.4
0.6
0.8
1
Bishari-0HoltmannKPPMST
xL
dσγp
/dx L
[µb
]
0.4 0.5 0.6 0.7 0.8 0.90
0.2
0.4
0.6
0.8
1
H1
pT,n2 [GeV2]
d2 σ γp/(
dxLdp
T,n
2) x
3j [
µb/G
eV2]
0 0.1 0.2 0.3
0.1
1
10
100 0.35<xL<0.50 (j=3)
0.50<xL<0.65 (j=2)
0.65<xL<0.80 (j=1)
0.80<xL<0.95 (j=0)
pT,n2 [GeV2]
d2 σ γp/(
dxLdp
T,n
2) x
3j [
µb/G
eV2]
0 0.1 0.2 0.3
0.1
1
10
100
H1 data
Fit: e--bn(x L) p2T,n
H1
ρ0 with Forward Neutron
xL
b n [G
eV-2]
0.4 0.6 0.80
10
20H1 data
xL
b n [G
eV-2]
0.4 0.6 0.80
10
20 Bishari-0HoltmannKPPMSTFMS
H1
ρ0 with Forward Neutron
Failure to describe bn(xL) suggests strong absorptive effects (n rescattering) ⇒ try to quantify
23 Estimate of absorption corrections
Wγπ [GeV]
σ(γπ
+--- >
ρ0 π+)
[µb]
10 20 30 400
1
2
3
4
5
Wγπ [GeV]
σ(γπ
+--- >
ρ0 π+)
[µb]
10 20 30 400
1
2
3
4
5
Wγπ [GeV]
σ(γπ
+--- >
ρ0 π+)
[µb]
10 20 30 400
1
2
3
4
5H1 data H1
γπ γp
(2.33 ± 0.56)µb (9.5 ± 0.5)µb
rel =σγπ→ρ0π
σγp→ρ0p
=
{
0.25 ± 0.06 (exp.extracted)
0.57 ± 0.03 (theo.expected)Kabs = 0.44 ± 0.11
Optical Theorem: dσel
dt|t=0
= belσel ∝ σ2tot
rel = (bγp
bγπ) · (σγπtot/σ
γptot)
2
Eikonal approach: b = 〈R2〉; b12 = b1 + b2
World data: (bpp≃11.7, bπ+p≃9.6, bγp≃9.75) GeV−2
Differential cross section inp2T,ρ
-t' [GeV2]
dσγp
/dt'
[µb/
GeV
2 ]
0 0.2 0.4 0.6 0.8 1
0.01
0.1
1
10
-t' [GeV2]
dσγp
/dt'
[µb/
GeV
2 ]
0 0.2 0.4 0.6 0.8 1
0.01
0.1
1
10
H1 data
-t' [GeV2]
dσγp
/dt'
[µb/
GeV
2 ]
0 0.2 0.4 0.6 0.8 1
0.01
0.1
1
10
Fit: a1eb1t' + a2e
b2t'
b1 = 25.7 +– 3.2 GeV-2, b2 = 3.62 +– 0.32 GeV-2
H1ρ0 with Forward Neutron
q
_q
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R
��������������������
��������������������
����������������
����������������
π
γ
ISR
M(nπ)/GeV
Geometric interpretation: 〈r2〉 = 2b1·(~c)2 ≃ 2 fm2 ⇒ (1.6Rp)2 ⇒ ultra-peripheral process
DPP explanation: low mass π+n state → large slope, high masses → less steep slope
25 Summary
� Diffraction is an important part of HERA physics landscape.Despite overall consistent picture, the field is challenging, as it representsa complicated interplay of soft and hard phenomena.
� Statistically limited channels have been studied with full HERA data sample.Whenever a hard scale is present, pQCD calculations are successful.
� The data show sensitivity to some QCD models parameters.They can also be used to further constrain DPDF, especially at high zIP .
� Photon-pion elastic cross section is extracted experimentally (in OPE ap-proximation) for the first time.
� Strong absorptive effects are confirmed in Leading Neutron production.Since the nature of these is non-perturbative, exp. results are essential fortuning models of ‘Survival Gap Probability’.
Backup Slides
27 Open questions
� FD(4)2 from HERA-II VFPS data and final DPDF determination without as-
sumption on Regge factorisation.
� Explain factorisation breaking mechanizm in PHP, in particular indepen-dence of Gap Survival Probability on xγ.
� Multiscale problem: (Q2, ET ,MV , t).
� Where is an Odderon ?
� Can one observe Glueball in a double Pomeron reaction in PHP?γp → (IPIP ) → MX (MX =
√xIP1xIP2Wγp = 2 ÷ 4 GeV)
HERA has finished, but not DIS physics.What’s next? eRHIC ? LHeC ?