salvatore fazio bnl university of washington – int seattle, wa – usa november 1-13, 2010...
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Salvatore Fazio BNL
University of Washington – INT Seattle, WA – USA
November 1-13, 2010
Simulation of DVCS with an EICusing MILOU
p p
Planing of the talk
The eRHIC accelerator and an EIC
detector compared to HERA
Strategy of a DVCS measurement
Hera results
Extension to EIC
DVCS simulation for an EIC
Summary
Nov. 9, 2010 2S. Fazio: INT-workshop, Univ. of Washington, Seattle
27.5 GeV electrons/positrons on 920 GeV protons →√s=318 GeV
2 colliding experiments: H1 and ZEUS
Total lumi collected at HERA: 500 pb-1, polarization of electrons/positrons at HERA II
Detectors not originally designed for forward physics, Roman pots added later
From HERA to an EIC collider
20 - 30 GeV electrons on 325 (125) GeV protons (nuclei). Polarization of electrons and protons (nuclei)
Lumi: 1.4 x 1034 cm-2s-1
For exclusive diffraction the concept is similar to HERA but:
• Dedicated forward instrumentation• Higher tracker coverage • Very High lumi!
STAR
ePHEN
IX
6 pass 2.5 GeV ERL
Coherent
e-cooler
Beam-dump
Polarized e-gun eRHIC
detector
EIC/eRHIC
HERA
Nov. 9, 2010 3S. Fazio: INT-workshop, Univ. of Washington, Seattle
Important (as respect of HERA) improvements:• Central Tracking Detector• better em calorimeter resolution• Very forward calorimetry • Rear Trackers! • Roman pots from the early biginning
The EIC detector
ep/N
FORW
ARDREAR
Nov. 9, 2010 4S. Fazio: INT-workshop, Univ. of Washington, Seattle
Similarities with HERA detectors:• Hermetic• Asymmetric
22 44 66 88 1100
2.5 m2.5 m
3.5 3.5
mm
1212 1144
90 mm90 mm
5.75 m5.75 m
1616IPIP
Dipole:Dipole:2.5 m, 6 T2.5 m, 6 T=18 mrad=18 mrad
4.5 m4.5 m=18 mrad=18 mrad
=10 mrad=10 mrad
Estimated Estimated **≈ 8 cm≈ 8 cm
=44 mrad
=44 mrad
6.3 cm6.3 cmZDCZDC
pp cc/2.5/2.5
15.7 cm15.7 cm
6 mrad6 mrad11.2 cm11.2 cm
4.5 cm4.5 cmneutronsneutronsppcc/2.5/2.5
ee
Quad Gradient: Quad Gradient: 200 T/m200 T/m
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 5
0.4
4 m
0.4
4 m
90 m90 m
10 mrad10 mrad 0
.329
m0.3
29
m3.67 mrad3.67 mrad
60 m60 m1010 2020 3030
0.1
88
036
m0.1
88
036
m
18.8
18.8
mm16.8
16.8
mm
6.33 mrad
6.33 mrad4 m4 m
DipoleDipole
© D.Trbojevic© D.Trbojevic
30 GeV e30 GeV e--
325 GeV p325 GeV p
125 GeV/u ions
125 GeV/u ions SpinSpin
rotatorrotator
GPD
GPD
p p
γγ*
Deeply Virtual Compton ScatteringVM (ρ, ω, φ, J/ψ, Υ) DVCS (γ)
Q2Q2 + M2Scale:
DVCS properties:• Similar to VM production, but γ instead of VM in the final state
• No VM wave-function involved
• Important to determine Generalized Parton Distributions sensible to
the correlations in the proton
• GPDs are an ingredient for estimating diffractive cross sections at
LHC
IPp p
Vγ*
Nov. 9, 2010 6S. Fazio: INT-workshop, Univ. of Washington, Seattle
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 7
theoretically very cleantheoretically very clean DVCSDVCS ( (): H, E, H, E): H, E, H, E VMVM ( ( H E H E info on quark flavorsinfo on quark flavors PS mesonsPS mesons ( (: H E : H E
~~
~~ ~~
~~
quantum number of final state quantum number of final state selects different GPDs:selects different GPDs:
0 2ud
2ud
ρ0 2ud, 9g/4
ω 2ud, 3g/4
s, g
ρ+ ud
J/ψ g J
qz
1
2x dx H q E q
1
1
t 0
J
qz
1
2q
q L
qz
q
1
2J
qz J
gz
1
2q
q L
qz
q J
gz
Accessing the GPDs
Nov. 9, 2010 8
BHDVCS
p p
ee
Wrong-sign sample: a negative track match to the second candidate
sample: no tracks matching to the second candidate
e sample: a track match to the second candidate
(DVCS+BH)
(BH+ dilepton + J/)
(dilepton + J/)
DVCS @ ZEUS - Strategy
S. Fazio: INT-workshop, Univ. of Washington, Seattle
Q2 dependence for the W slope not clear within the uncertainties!
ZEUS: JHEP05(2009)108H1: Phys.Lett.B659:796-806,2008
Nov. 9, 2010 9S. Fazio: INT-workshop, Univ. of Washington, Seattle
Fit: σ ~ Wδ
DVCS @ HERA
t ~ PT2 +PTe
2
2
t measured indirectly:
Fit :ddt
e b |t |
No evidence for W dependence of bby roman pots!
Nov. 9, 2010 10
b = 4.5 ± 1.3 ± 0.4
dσ/dt measured for the first time by a direct measurement of the outgoing proton 4-momentum using the LPS spectrometer
The ZEUS result is in agreement with H1
…nevertheless it seems to suggest a lower trend!
t dependence
S. Fazio: INT-workshop, Univ. of Washington, Seattle
W-dependence: summary
Summary of the W,t-dependence for all VMs + DVCS measured at HERA
Nov. 9, 2010 11S. Fazio: INT-workshop, Univ. of Washington, Seattle
Fit: σ~ Wδ
Fit :ddt
e b |t |
Exclusive production of VMs can be a golden measurement for an EIC
To successfully measure t indirectly from the electron and photon candidates
it is important:
Tracker coverage (tracker has higher momentum resolution than Cal!) Reso of the CTD @ ZEUS: σ(pT)/pT =0.0058pT 0.0065 0.0014/p⊕ ⊕ T
High resolution em calorimetry (crucial! Remember that one particle is a photon!)
For ZEUS it was σ(E)/E=0.18/√E
Measuring t indirectly with an EIC
CTD acceptance @ ZEUS
DVCS/BH BHAlways measure a track when we can -> better momentum resolution but not only… More acceptance for DVCS!
Nov. 9, 2010 12S. Fazio: INT-workshop, Univ. of Washington, Seattle
t ~ PT2 +PTe
22
Direct t measurement at EIC
But… is an indirect measurement of t really an issue for EIC?
We’ll get roman pots in the forward region at EIC!
L = 27.77 pb-1
55 events (DVCS + BH)
for eRHIC: 1.4 1034* Ep/325 cm-2s-1 assuming 50% operations efficiency one week corresponds to:L(1 w)= 0.5 * 604800(s in a week) * (1.4x1034 cm-2s-1) = 4*1039 cm-2 = 4000pb-1
+ Roman Pots ~ 8000 events/week !! assuming the same acceptance ad LPS (~2%)Calculations are absolutely not rigorous! But give an idea…
Silicon micro-stripsresolution: 0.5% for PL ; 5 MeV for PT
Nov. 9, 2010 13S. Fazio: INT-workshop, Univ. of Washington, Seattle
EIC lumi
t vs proton scattering angle
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 14
4 GeV el x 50 GeV prot 4 x 100
4 x 250
very strong correlation between t and “recoiling” proton angle Roman pots need to be very well integrated resolution on t!
t=(p4-p2)2 = 2[(mpin.mp
out)-(EinEout - pzinpz
out)]
t=(p3–p1)2 = mρ2-Q2 - 2(Eγ*Eρ-px
γ*pxρ-py
γ*pyρ-pz
γ*pzρ)
1414
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle
MILOU
d3DVCS
dxdQ2dt
2 3s 1 1 y 2 2xR2Q6 e b t F2
2 x,Q2 12
Based on: Frankfurt, Freund and Strikman (FFS) [Phys. Rev. D 67, 036001 (1998). Err. Ibid. D 59 119901 (1999)]
FFS
GPDs-basedBased on: A. Freund and M. McDermott
All ref. in: http://durpdg.dur.ac.uk/hepdata/dvcs.html
• GPDs, evolved at NLO by an indipendent code which provides tables of CFF
- at LO, the CFFs are just a convolution of GPDs:
15
H (,Q2,t) =ei
2
1 x i
Hi x,,Q2,t dx
1
1u,d,s
• Old model: written before data came out! • Used by H1 and ZEUS for their DVCS measurements• The ALLM parametrization for F2 is used
The code MILOU contains two different models for DVCS simulation:Written by E. Perez, L Schoeffel, L. Favart [arXiv:hep-ph/0411389v1]
• provide the real and imaginary parts of Compton form factors (CFFs), used to calculate cross sections for DVCS and DVCS-BH interference.
• The B slope is allowed to be costant or to vary with Q2:
• Proton dissociation (ep → eγY) can be included
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 16
MILOU
ddxdyd | t | dd
= 3xB y
16 2Q2 1 2
Ie3
= N l
= T N
2xmN
Q
I BH
2
e6
x 2y 2(1 2)22P1()P2()c0
BH cnBH cos n s1
BH sin n1
2
I DVCS
2
e6
y 2Q2 c0DVCS cn
DVCS cos n snDVCS sin n
n1
2
I 2 e6
xy 32P1()P2()c0
I cnI cos n s1
I sin n1
3
d d t exp B Q2 t ; with : B Q2 ln Q2
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle
• 1.5 < Q2 < 100 GeV2
• 10-4 < x < 0.1• 0.01 < y < 0.85• 0 < |t| < 1.5 GeV2
• Radiative corrections: OFF• t slope: B = 5.00 (costant)• GPDs evolved at NLO• ALLM param. used for F2 (FFS model)
30 X 325:• E_el = 10 GeVep -> ep)= 0.186 nb (FFS_ALLM)ep -> ep)= 0.376 nb (GPDs)
20 X 250:• E_el = 5 GeVep -> ep)= 0.16 nb (FFS_ALLM)ep -> ep)= 0.32 nb (GPDs)
10 X 100:• E_el = 0 GeVep -> ep)= 8.1*10-2 nb (FFS_ALLM)ep -> ep)= 0.16 nb (GPDs)
17
5 X 50:• E_el = 0 GeVep -> ep)= 8.1*10-2 nb (FFS_ALLM)ep -> ep)= 0.16 nb (GPDs)
Phase space
eRHIC Luminosity
100 k event generated for each config.
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 18
vs E
30 X 325
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 19
vs E
20 X 250
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 20
vs E
10 X 100
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 21
vs E
5 X 50
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 22
t-xsec (ep -> p)FFS - 30 X 325
by roman pots!
L = 0.54 fb-1
EIC lumi: 4 fb-1/month @ 30x325 • Precision enormously improved• Roman pots acceptance not yet
included in the simolation
• 1.5 < Q2 < 100 GeV2
• 10-4 < x < 0.1• 0.01 < y < 0.8
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 23
t-xsec
GPDs conv. - 30 X 325
• 1.5 < Q2 < 100 GeV2
• 10-4 < x < 0.1• 0.01 < y < 0.8
Systematics will dominate!!
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 24
20 X 250 10 X 100 5 X 50
t-xsec
dominated by gluon contributionsdominated by gluon contributions EIC will provide sufficient luminosity to bin in multi-dimensionsEIC will provide sufficient luminosity to bin in multi-dimensions wide x and Qwide x and Q22 range needed to extract GPDs range needed to extract GPDs
… … we can do a fine binning in Q2 and W!we can do a fine binning in Q2 and W!
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 25
Scanning the phase space…
Logarithmic bins:
1 < Q2 < 100 GeV2
10-4 < x < 0.1
y = 0.85
y = 0.
01
y = 0.85
y = 0.85
y = 0.85
y = 0.
01
20 X 250
10 X 100
30 X 325
5 X 50
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 26
Scanning the phase space…
y = 0.
01
y = 0.
85
y = 0.
01
y = 0.
85
y = 0.
85
y = 0.
85
30 X 325 20 X 250
10 X 100 5 X 50
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 27
30x325-t-xsec
Veri precice scan!
y = 0.
85
y = 0.
01
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 28
20x250-t-xsec
GPD FFS
y = 0.
01
y = 0.
85
y = 0.
01
y = 0.
85
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle 29
10x100 5x50 t-xsec
y = 0.
85y =
0.85
The phi angle
AC =d+ d
d+ +d
DVCS: the beam-charge asymmetry
At EIC:Possible if a positron beam Thanks to a good tracker coverage
Nov. 9, 2010 30S. Fazio: INT-workshop, Univ. of Washington, Seattle
AC =d d
d+ +d Re ADVCS
AI Re ADVCS +Im ADVCS Interference term:
Beam charge asymmetry:
A 2 = ADVCS 2 + ABH 2 + AI 2 DVCS and BH: identical final state → they Interfere
31
How does the nuclear environment modify parton-parton correlations? How does the nuclear environment modify parton-parton correlations? How do nucleon properties change in the nuclear medium?How do nucleon properties change in the nuclear medium?
(Bethe-Heitler)(Bethe-Heitler)
Nuclear GPDs ≠ GPDs of free nucleonNuclear GPDs ≠ GPDs of free nucleon Enhancement of effect when leaving forward limit? Enhancement of effect when leaving forward limit?
caused by transverse motion of partons in caused by transverse motion of partons in nuclei?nuclei?
important role of mesonic degrees of freedom?important role of mesonic degrees of freedom? manifest in strong increase of real part of τmanifest in strong increase of real part of τDVCS DVCS
with atomic mass number A? with atomic mass number A?
DVCS in coherent region: DVCS in coherent region: new insights into ‘generalized EMC effect’?new insights into ‘generalized EMC effect’?
Nov. 9, 2010 S. Fazio: INT-workshop, Univ. of Washington, Seattle
DVCS on nuclear targets
MC simulation for DVCS on nuclei coming soon thanks to an updated version of MILOU code
Summary A lot of experience carried over from HERA
Simulation shows how an EIC forward program can sensibly improve HERA
results and go beyond
Uncertainties will be dominated by systematics
Large potential for diffractive-DIS studies using polarized and unpolarized
protons and nuclei
Outlook:
Simulation of asymmetries
Simulation of DVCS on nuclei
Updating the MILOU code to status of art (Re_Amp, NNLO…)
Nov. 9, 2010 32S. Fazio: INT-workshop, Univ. of Washington, Seattle
Back up
Nov. 9, 2010 33S. Fazio: INT-workshop, Univ. of Washington, Seattle