1. How to detect protons from exclusive processes
E.C. Aschenauer
EIC INT Program, Seattle Week 8

2. Kinematics of elastic diffraction
no cuts:
4x100
4x50
4x250
cuts: Q2 > 0.1 GeV && y < 0.9 GeV
decay products of r & J/ψ
go more and more
forward with
increasing
asymmetry in
beam energies
E.C. Aschenauer
EIC INT Program, Seattle Week 8

3. Diffractive Physics: p’ kinematics
t=(p4-p2)2 = 2[(mpin.mpout)-(EinEout - pzinpzout)]
4 x 50
t=(p3–p1)2 = mρ2-Q2 - 2(Eγ*Eρ-pxγ*pxρ-pyγ*pyρ-pzγ*pzρ) ?
Diffraction: p’
4 x 100
4 x 250
need “roman pots”
to detect the protons
and a ZDC for
neutrons
E.C. Aschenauer
EIC INT Program, Seattle Week 8

4. How to detect exclusive protons
Detector concepts
Roman Pots for protons / charged particles
Zero Degree Calorimeters (ZDC) for neutrons
Preshower & ECal for photons, important for eA  e’A’g
Challenges
angular emittance of the beam
eRHIC: 0.1 mrad
how close to the beam can the roman pots go
normally 10s  1mrad
geometric acceptance of magnets
need thin exit windows for particles
need most likely more than one place to put roman pots
E.C. Aschenauer
EIC INT Program, Seattle Week 8

5. eRHIC Detector Concept
Forward / Backward
Spectrometers:
minimum angle for “elastic protons”
to be detected in the main detector
10 mrad  pt = 1 GeV 2m 4m
central detector acceptance: very high coverage -5 < h < 5
Tracker and ECal coverage the same
crossing angle: 10 mrad; Dy = 2cm and Dx = 2/4cm (electron/proton direction)
Dipoles needed to have good forward momentum resolution and acceptance
DIRC, RICH hadron identification  p, K, p
low radiation length extremely critical  low lepton energies
precise vertex reconstruction (< 10 mm)  separate Beauty and Charmed Meson
E.C. Aschenauer
EIC INT Program, Seattle Week 8

6. EIC INT Program, Seattle 2010 - Week 8
IR-Design-Version-I
eRHIC - Geometry high-lumi IR with β*=5 cm, l*=4.5 m and 10 mrad crossing angle
Assume 50% operations efficiency
 4fb-1 / week D5 Q5 Q4
Spin
rotator
325 GeV p
125 GeV/u ions
4 m
Dipole
0.44 m
6.33 mrad
3.67 mrad
18.8 m
0.329 m
16.8 m m
10 mrad
30 GeV e- 10 20 30
60 m
90 m
© D.Trbojevic
E.C. Aschenauer
EIC INT Program, Seattle Week 8

7. A detector integrated into IR – Version 1
space for
e-polarimetry
and luminosity
measurements
ZDC
FPD
FED
for ERL solution need not to measure electron polarization bunch by bunch
need still to integrate luminosity monitor
need still to integrate hadronic polarimeters, maybe at different IP
E.C. Aschenauer
EIC INT Program, Seattle Week 8

8. Can we detect DVCS-protons and Au break up p
track the protons through solenoid, quads and dipole with hector
beam angular spread 0.1mrad at IR
Quads +/- 5mrad acceptance; geometric acceptance: 1.5cm
Proton-beam: p’z> 0.9pz
100 GeV: ptmax < 0.45 GeV
 suboptimal as we loose intermediate pt (0.4 – 1.2 GeV)/ t range
solution could be to do the same as for the electrons swap the
dipole and quads  lumi goes down  see next slides
proton track Dp=10%
proton track Dp=20%
proton track Dp=40%
Equivalent to fragmenting
protons from Au in Au optics
(197/79:1 ~2.5:1)
E.C. Aschenauer
EIC INT Program, Seattle Week 8

9. IP configuration for eRHIC – Version-II
4.5 cm
pc/2.5
Estimated b*≈ 8 cm
neutrons
90 mm
11.2 cm
6 mrad
3.5 m
q=44 mrad
pc/2.5
2.5 m
15.7 cm
5.75 m
q=18 mrad
4.5 m
ZDC
6.3 cm
q=10 mrad e IP 2 4 6 8 10 12 14 16
Dipole:
2.5 m, 6 T
q=18 mrad
Quad Gradient:
200 T/m
E.C. Aschenauer
EIC INT Program, Seattle Week 8

10. IP configuration for eRHIC – Version-II
q= mrad Q4 Q5 D5
4 m
11.9 m
q=18 mrad m m m
5.75 m
10 mrad
5.75 cm
4.5 10 20 30
17.65 m m m
E.C. Aschenauer
EIC INT Program, Seattle Week 8

11. Can we detect “exclusive” protons
lets see acceptance now
beam angular spread 0.1mrad at IR
Dipole +/- 10 mrad; geometric acceptance: +/ cm
Quads +/- 3 mrad acceptance; geometric acceptance: < 1.5cm
Proton-beam: p’z> 0.9pz  lets assume pz = pbeam
maximal pt
100 GeV: ptmax < 1 GeV
50 GeV: ptmax < 0.8 GeV
minimal pt  assume 10s distance of roman pot to beam
100 GeV: ptmin ~ 100 MeV
50 GeV: ptmin ~ 50 MeV
Looks much more promising than v-I, need to do full particle ray tracing
E.C. Aschenauer
EIC INT Program, Seattle Week 8

12. How to measure coherent diffraction in e+A ?
Beam angular divergence limits smallest outgoing Qmin for p/A that can be measured
Can measure the nucleus if it is separated from the beam in Si (Roman Pot) “beamline” detectors
pTmin ~ pzAtanθmin
For beam energies = 100 GeV/n and
θmin = 0.1 mrad
Large momentum kicks, much larger
than binding energy (~8 MeV)
Therefore, for large A, coherently diffractive nucleus cannot be separated from beamline without breaking up
species (A)
pTmin
(GeV/c)
d (2)
0.02
Si (28)
0.22
Cu (64)
0.51
In (115)
0.92
Au (197)
1.58
U (238)
1.90
E.C. Aschenauer
EIC INT Program, Seattle Week 8

13. How to measure coherent diffraction in e+A ?
Purity
Efficiency
rapidity
Rely on rapidity gap method
simulations look good
high eff. high purity
possible with gap alone
~1% contamination
~80% efficiency
depends critical on detector
hermeticity
improve further by veto on
breakup of nuclei (DIS)
Very critical
mandatory to detect nuclear
fragments from breakup
E.C. Aschenauer
EIC INT Program, Seattle Week 8

14. EIC INT Program, Seattle 2010 - Week 8
BACKUP
E.C. Aschenauer
EIC INT Program, Seattle Week 8

15. EIC INT Program, Seattle 2010 - Week 8
6.5 T magnet, 2.5 m long
4.5 cm
E.C. Aschenauer
EIC INT Program, Seattle Week 8

16. EIC INT Program, Seattle 2010 - Week 8
Quads for β*=5 cm
© B.Parker
E.C. Aschenauer
EIC INT Program, Seattle Week 8