Twarde procesy ekskluzywne i partonowa struktura nukleonu Andrzej Sandacz Instytut Problemów Jądrowych, Warszawa Seminarium Fizyki Wielkich Energii, Uniwersytet Warszawski 11 stycznia 2008 DVCS – głęboko wirtualne rozpraszanie Comptona Spinowa asymetria w produkcji ρ 0 z poprzecznie spolaryzowaną tarczą Ekskluzywna produkcja mezonów wektorowych na akceleratorze HERA Projekt pomiarów DVCS i produkcji mezonów w COMPASS-ie Ekskluzywna produkcja pionów
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Twarde procesy ekskluzywne i partonowa struktura nukleonu
Twarde procesy ekskluzywne i partonowa struktura nukleonu. Andrzej Sandacz. Instytut Problemów Jądrowych, Warszawa. DVCS – głęboko wirtualne rozpraszanie Comptona. Ekskluzywna produkcja mezonów wektorowych na akceleratorze HERA. - PowerPoint PPT Presentation
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Twarde procesy ekskluzywne i partonowa struktura nukleonu
Andrzej SandaczInstytut Problemów Jądrowych, Warszawa
Seminarium Fizyki Wielkich Energii, Uniwersytet Warszawski
11 stycznia 2008
DVCS – głęboko wirtualne rozpraszanie Comptona
Spinowa asymetria w produkcji ρ0 z poprzecznie spolaryzowaną tarczą
Ekskluzywna produkcja mezonów wektorowych na akceleratorze HERA
Projekt pomiarów DVCS i produkcji mezonów w COMPASS-ie
Ekskluzywna produkcja pionów
GGeneralizedeneralized P Partonarton D Distributionsistributions
GPDs
x+ x-
p (P1, s)
hard
soft
* Factorisation:Q2 large, -t<1 GeV2
t
4 Generalised Parton Distributions : H, E, H, Efor each quark flavour and for gluons
depending on 3 variables: x, x, , t, t~~
for DVCS gluons contribute only at higher orders in αs
p (P2, s’)
≈ xB/(2-xB )
GPDs properties and links to ‘standard’ physics
'~
, ssHH qq
'~
, ssEE qq
for P1 = P2 recover usual parton densities
0)()0,0,(~
),()0,0,( xforxqxHxqxH qq
no similar relations; these GPDs decouple for P1 = P2
0)()0,0,(~
),()0,0,( xforxqxHxqxH qq
0~
, qq EE needs orbital angular momentum between partons
)(),,( 1 tFtxHdx qq
)(),,( 2 tFtxEdx qq
)(),,(~
tgtxHdx qA
q
)(),,(~
tgtxEdx qP
q
Dirac axial
pseudoscalar Pauli
GPD= a 3-dimensional picture of the partonic nucleon structure or spatial parton distribution in the transverse plane H(x, =0, t) → H(x,, rx,y ) probability interpretation Burkardt
‘Holy Grails’ or the main goals
x P
x
y
r
z
t
p p
q q
E
Contribution to the nucleon spin puzzle
E related to the orbital angular momentum
2Jq = x (Hq (x,ξ,0) +Eq (x,ξ,0) ) dx
½ = ½ ΔΣ + ΔG + < Lzq > + < Lz
g >
The imaginary part of amplitude T probes GPD at x =
1
1
1
1
( , , ) +
( , ,
- i + ( , )
, )
DVCS
GPD x t
GPD x tT dx
x
GPD x tdx
i
P x
The real part of amplitude T depends on the integral of GPD over x
for the first time ρ0 TTSA extracted separately for γ*L and γ*
T
ρ0 transverse target spin asymmetry from HERMES
in a model dependent analysis data favours positive Ju
in agreement with DVCS results from HERMES
ρ0 transverse target spin asymmetry from COMPASS
Transversely polarised deuteron target (6LiD), PT ≈ 50% 2002-2004 data
2
2
)]sin(1[
)]sin(1[
)()(
)()(
)()(
)()()(
du
du
du
du
aa
aa
NN
NNDRin bins of ϑ = φ – φS:
)]sin(41[ C
obtained using Double Ratio Method
)sin( SUTA
raw asymmetry ε from the fit to DR(η)
TUT Pf
A S )sin(
dilution factor f ≈ 0.38
u (d) are for upstream (downstream) cell of polarised targetarrows indicate transverse polarisation of corresponding cells
ρ0 transverse target spin asymmetry from COMPASS
asymmetry for deuteron target consistent with zero
ongoing work on:
longitudinal/transverse separation separation of incoherent/coherent
in 2007 data taken with transversely polarised proton target (NH3)
new
Exclusive π+ production from HERMES
σL VGG LO σL VGG LO+power corrections σT + ε σL Regge model (Laget)
LO calculations strongly underestimate the data
data support magnitude of the power corrections (kt and soft overlap)
Regge calculations provides good description of the magnitude of σtot
and of t’ and Q2 dependences
at leading twist σL sensitive to GPDs H and E ~ ~
at small |t’| E dominates as it contains t-channel pion-pole~
L/T separation not possible at HERMES, σT expected to be supressed as 1/Q2
e p → e n π+
Beam spin asymmetry in exclusive π0 production from CLAS
a fit α sinφ Regge model (Laget) pole terms (ω, ρ, b1) + box diagrams (cuts)
first measurement of BSA for exclusive π0 production above resonance region
sizeable BSA (0.04 – 0.11) indicate that both T and L amplitudes contribute necessity for L/T separation and measurements at higher Q2
prelim
inary
at leading twist σL sensitive to GPD H
no t-channel pion-pole (in contrast to exclusive π+ production) any non-zero BSA would indicate L-T interference, i.e. contribution not described
in terms of GPD’s
~ e p → e p π0
Cross sections for exclusive π0 production from JLAB HALL A DVCS Collab.
from P. Bertin, Baryon-07
t-slope close to 0, maybe even small negative
E00-110
dt
dh
dt
d
dt
d
dt
d
dt
d
ddt
dTLTLTTLTpp '*
2
sin)1(2cos)1(22cos2
10
h = ±1 is the beam helicity
dashed – prediction for σL from VGG model using GPDs
Vanderhaeghen, Guichon, Guidal
Summary for existing measurements
New precise data on cross sections and asymmetries → significantly more stringent constraints on the models for GPDs
To describe present data on DVMP, both at large and small x, including power corrections (or higher order pQCD terms) is essential
First experimental efforts to constrain GPD E and quark orbital momentum
Results on DVCS promissing;
good agreement with NLO for HERA data
indication of scaling and handbag dominance in valence region
Generalized Parton Distributions @
Roadmap:
Now with 6LiD or NH3 polarized target and no recoil detector
After 2010 with H2 or D2 target with a recoil detector and an additional calorimetry
« Expression of Interest » SPSC-EOI-005 and presentation to SPSC
writing of the proposal, preparation of the future GPD program ~2010
E=
190,
100
GeV
HERA
Competition in the world and COMPASS role
Gluons valence quarks valence quarks and sea quarks and gluons
COMPASS JLab 12 GeV, FAIR,… 2010 2014
Ix2
COMPASS at CERN-SPS
High energy muon beam100/190 GeV
μ+ or μ- change once per day
polar(μ+)=-0.80polar(μ-)=+0.80
2.108 μ per SPS cycle
in 2010 ?new Linac4 (high intensity H- source)as injector for the PSB + improvements on the muon line
dσ(μpμp) = dσBH + dσDVCSunpol
+ Pμ dσDVCSpol
+ eμ aBH Re ADVCS + eμ Pμ aBH Im ADVCS
Twist-3 M01
)coscos()()(
),,(
2
21021
2BHBHBHBBH cCc
PP
tQxd
DVCS + BH with polarized and charged leptons and unpolarized target
Twist-2 M11 Twist-2 gluon M-11
known
DVCSBH Aa m
DVCSBH Aa e
eμ Pμ
eμ
Pμ
>>
)sinsin()()(
221
213
6IntInt ss
PtPxye
φ
θμ’μ
*
p
)coscos( 221022
6DVCSDVCSDVCSDVCS
unpolcCc
Qye
d
)sin( DVCSDVCSpol
sQy
ed
122
6
μ
pμ
pBH calculableDVCS
+
Belitsky,Müller,Kirchner
)coscoscos()()(
323210
213
6IntIntIntInt cccc
PtPxye
)~)(( EHH22211 4
Fmt
FFF m e
Int
Int
sc
1
1
11 e
ξx
t)ξ,H(x,dxP H
t)ξ,ξ,H(x H mq
q qe HH 2
F1H dominance with a proton target
F2E dominance with a neutron target (F1<<) very attractive for Ji’s sum rule study
with
Both c1Int and s1
Int accessible at COMPASS with + and -
Q2
xBj
7
6
5
4
3
2
0.05 0.1 0.2
6 month data taking in 201025 % global efficiency
Muon Beam Asymmetry at E = 100 GeV
COMPASS predictionWith a 2.5m H2 target
μ’μ
*
p
μ’μ
*
p
Muon Beam Asymmetry at E = 100 GeV
COMPASS prediction
model 1: H(x,ξ,t) ~ q(x) F(t)
VGG: double-distribution in x,
<b2> = α’ ln 1/x
H(x,0,t) = q(x) e t <b
2> = q(x) / xα’t
α’ slope of Regge traject.
α’=0.8 α’=1.1
model 2 and 2*: correl x and t
Guzey: Dual parametrization model 3: also Regge-motivated
t-dependence with α’=1.1
Design :2 concentric barrels of 24 scintillators counters read at both sides
Goals: Detect protons of 250-750 MeV/c t resolution => TOF < 300 ps exclusivity => Hermetic detector
European funding through a JRA for studies and construction of a prototype ( Bonn, Mainz, Saclay, Warsaw )
Recoil detector design
Recoil Detector Prototype Tests (2006)
i
CHTarget
Inner Layer
Outer Layer
A0
A1
A2
B0
B1
25cm
110cm
15°
All scintillators are BC 408A: 284cm x 6.5cm x 0.4cm Equiped with XP20H0 (screening grid)B: 400cm x 29cm x 5cm Equiped with XP4512
Use 1GHz sampler (300ns window) Design by CEA-Saclay/LAL-Orsay
Trigger:A&B coincidencesfinger pairs
Installed downstream of COMPASS
Resolution on TOFCenter 340ps HV lowCenter 310ps HV high Expected resolution 280 ps
Light brought by LS fibers to Avalanche Micro-Pixel PhotodiodeVery Challenging development for new and cheap AMPDs - magnetic field, low threshold detection, high rate environment
Studies for a new ECAL0 (Dubna,…)
ECAL0 modules dimesions: ~ 50x50 mm2 (inner), ~ 70x70 mm2 (middle and outer)Inner part - 1200 modules (7200 AMPDs) Middle part - 980 modules (3920 AMPDs)Outer part - 1372 modules (4116 AMPDs)The first scint – 3552 AMPDsTotal 3552 modules (15236+3552=18788 AMPDs)
requiremens on ECAL0
large transverse size:
small depth: ~ 25 cm
~ 400 x 400 cm2
geometry
The AMPD (1)The AMPD (1)
~ 1 mm
Depletion region ~ 2 m Substrate
Si Resistor
substrate p+
p-
Guard ring n-
Al conductorp+ n+Vbias
• High Gain (105~106)• Good Photon Detection Efficiency (15~65%)• Compact (package size ~ a few mm)• Relatively Low Cost • Magnetic-field tolerant• High dark noise
(order of 100-1000 kHz)• Response against input light yield is non-linear
Conclusions & prospects for future COMPASS measurements
• Possible physics ouput– Sensitivity to total spin of partons : Ju & Jd
– Sensitivity to spatial distribution of partons– Testing a variety of GPD models (VGG, Müller, Guzey, FFS-
Sch) to quantify the Physics potential of DVCS and HEMP
• Experimental challenges– Recoil Detection for proton (and neutron) – High performance and extension of the EM calorimetry
• Roadmap– Now with the transversely polarized targets: 6LiD ( 2006) and NH3 (2007)– 2008-9: A small RPD and a liquid H2 target will be available for the hadron program (ask for 2 shifts + and -)– > 2010: A complete GPD program at COMPASS with a long RPD + large liquid H2 target
before the availability of JLab 12 GeV, FAIR, EIC…