Emerging detector concept

1
Emerging detector concept

• 2 main components
• electron detection in forward direction (?lt400)
• final state detection and hadron identification
  in proton direction (? gt 1400 ?)
• some low resolution energy measurement for
  central angles
• vertex detection (resolution better than 100 ?m)
• plus
• electron detection at very low angles (how?)
• detection of recoiling neutron and proton
  (maximum acceptance)
• plus
• luminosity measurement with accuracy of 1
• polarization measurements with accuracy of 1
  (both electron and ion !)

(from ep summary_at_EIC08 meeting)
2
1H(e,ep)n Scattered Electron Kinematics

• Most electrons scatter at angles lt25
• More forward angles correspond to (very) low Q2 ?
  not likely that good resolution is needed ?
  solenoid may be o.k. for electron side.
• BUT access to the high Q2 region of interest for
  GPD studies requires larger electron angles

3
1H(e,ep)n Scattered Pion Kinematics
Q2 (GeV2)
P (GeV)
Pion Lab Angle (deg)
Pion Lab Angle (deg)

• The pion cross section is peaked in the direction
  of the proton
• At larger Q2 pion angles and momenta are smaller
• Ansatz lt1 momentum resolution for p 5 GeV

4
Emerging detector concept

• Open questions (certainly not complete)
• what is the optimal magnetic field
  configurations for such a detector ?
• simple solenoid most likely NOT sufficient
• solenoid plus toroid or solenoid plus dipole ?
• what angular/momentum resolution do we need for
  the electron?
• what angular resolution do we need in the hadron
  detection?
• what about jet physics ???
• what about e-A ?
• any other processes not yet considered ?
• how do we get a real handle on backgrounds
  from beam gas events ?

(from ep summary_at_EIC08 meeting)
5
Magnetic Fields

• Options and comparison with existing magnets

6
General Considerations

• Solenoid is easy field, but not much field at
  small scattering angles
• Toroid would give better field at small (5
  degrees) angles with an asymmetric acceptance
• Improves acceptance for positive hadrons
  (outbending)
• Improves detection of high Q2 electrons
  (inbending)
• May limit acceptance for pp- detection
• Vary Solenoid field to see how far one can push
  and compare with toroidal field
• Could also add central toroidal or dipole field
  to solenoid

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Solenoid Fields - Overview
Conclusion 4-5 Tesla fields, with length scale
inner diameter scale o.k.
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General Solenoid Field

• BT B sin ? (from v x B)
• pT p sin ?

?0
Initial solenoid B4T, L5m, D2.5m

• ?0 tan-1(x/L)
• L (L/2)/cos?, ?lt?0
• L (x/2)/sin?, ?gt?0

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Formulas
Multiple scattering contribution Intrinsic
contribution (first term)

• z charge of particle
• L total track length through detector (m)
• ? angle of incidence w.r.t. normal of detector
  plane
• nr.l. number of radiation lengths in detector

msc

• Bcentral field (T)
• srfposition resolution (m)
• Llength of transverse path through field (m)
• Nnumber of measurements

intr

• Assumptions
• circular detectors around interaction point
• nr.l. 0.03 (from Hall D CDC)

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dp/p angular dependence
p 50 GeV
p 5 GeV
Can improve resolution at forward angles by
offsetting IP
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Multiple scattering contribution
p 50 GeV
p 5 GeV
Multiple scattering contribution dominant at
small angles (due to BT term in denominator) and
small momenta
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Easier Solenoid Field 2T vs. 4T?
p 50 GeV
p 5 GeV
B2T
B4T

• Intrinsic contribution 1/B
• Multiple scattering contribution 1/B

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Include dipole field
p 50 GeV
p 5 GeV
As expected, substantially improves resolutions
at small angles
14
Or include CLAS12 toroidal field
(add dipole)
(add toroid)
p 50 GeV
p 50 GeV
Does the same trick, but would get acceptance
loss at small angles
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CLAS12 Toroid
Calculation GEANT4 simulation ? estimates o.k.
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Remaining puzzle
Formalism often given in terms of pT resolution
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Transverse Momentum Formulas
Multiple scattering contribution Intrinsic
contribution (first term)

• z charge of particle
• L total track length through detector (m)
• ? angle of incidence w.r.t. normal of detector
  plane
• nr.l. number of radiation lengths in detector

msc

• Bcentral field (T)
• srfposition resolution (m)
• Llength of transverse path through field (m)
• Nnumber of measurements

intr

• Assumptions
• circular detectors around interaction point
• nr.l. 0.03 (from Hall D CDC)

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Compare both formalisms
Must include angular dependence term (pT psinQ)
Puzzling why results are not identical, something
missing?
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Resolution Studies

• Test magnet performance with exclusive reactions

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Mx Resolution fixed target
Cross-check simulation w. 6 GeV JLab
dp/p0.5
Hall B CLAS6
dMx16.2 MeV
dp/p1 Fixed T
Fixed target Ee5.7 GeV
dMx15.6 MeV
Conclusion in good agreement with data ?
simulation o.k.
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Simulated dMx2 distributions for 5 on 50
kinematics
Tp lt 30
CLAS12 (toroid) dMx211 GeV2
Hall D (solenoid) dMx251 GeV2
Conclusion MX2 resolution technique alone is
never good enough to guarantee exclusivity
Ideal Solenoid (4T) dMx26 GeV2
Hall D (scaled to 4T) dMx231 GeV2
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Why?
Missing Mass Resolution in Collider Kinematics

• Consider two cases
• pin gtgt pout (e.g. 5 on 50)
• pin0, stotEin2

Asymmetric collider, e.g. 5 on 50 Symmetric
collider
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Result Mx Resolution scales like stot
Conclusion relying on Mx2 resolution only fails
miserably at EIC energies

• Need to guarantee exclusivity by measuring all
  particles

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1H(e,ep)n Scattered Neutron

• Low t neutrons are emitted at very small angles
  with respect to the beam line, outside the main
  detector acceptance
• A separate detector placed tangent to the proton
  beam line away from the intersection region is
  required not clear how to do yet

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Interaction Region
120 m
200 GeV
COMPASS
10 m
CLAS
11 GeV
8 m
EIC
10 on 250 GeV

• Available space makes things challenging

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Emerging detector cartoon
8 meters (for scale)
140 degrees
Offset IP
TOF
HCAL
PbWO4 ECAL
Tracking
dipole
RICH
HCAL
Needed?
solenoid
Issues 1) would need to change (E)TOF with HTCC
if 500 MHz operation 2) need addl Particle Id.
(RICH/DIRC) for large angle p/K/p? 3) conflict
with charm measurements that require low central
field?
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Similar to PANDA Detector Concept
See PANDA Technical Progress Report also here
discussions of solenoid vs. solenoid dipole vs.
solenoid toroid.
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Charge Symmetry Plans
Assumed u up dn d dp un
Valid at lt 1 (Mn Mp)/Mp 0.1
duv(x) uvp dvn ddv(x) dvp - uvn
Figure from Rodionov et al., Int. J. Mod. Phys.
Lett. A9 (1994) 1799 Similar to MRST, Eur. Phys.
J. C35 (2004) 325
Accessible by comparison of ed with e-d charged
current cross sections
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Charge Symmetry Plans
Assumed u up dn d dp un
Valid at lt 1 (Mn Mp)/Mp 0.1
duv(x) uvp dvn ddv(x) dvp - uvn
For the sea alone, CSV may be large! MRST
obtained
Accessible through charge symmetry sum rule
defined by Ma (Phys. Lett. B274 (1992) 111)
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Backup
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Detector Considerations _at_EIC
(status_at_EIC06 meeting)

• Open Charm Production (Glue, Glue, Glue!)
• Dominant reaction mechanism through glue at small
  x ? e/ion momentum mismatch not so relevant and
  created nearly at rest ? Decay products at large
  angles.
• Background reduction critical issue ? requires
  lt100 m vertex resolution ? drives vertex detector
• Decay products have typical momenta between 0-2
  GeV ? Need good particle id in this region and
  good track capability in large rate region ? for
  the former, use dE/dx plus TOF of hodoscope?
  (with 100 ps timing resolution, 3.2 meters gives
  3s p/K separation)
• HERA typical momentum cutoff of 5 GeV, studies
  show can push down to Field (in Tesla) of
  Solenoid. STAR has only 0.5 T field and lower
  cut-off of 0.4 GeV ? Need low T (about 0.5)
  magnetic field in central region.

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CLAS12 Solenoid - Example
Field calculation for ¼ solenoid
Note the distribution of currents in the
Solenoids winding pack was determined such that
the requirements imposed on the generated
magnetic field inside and outside the Solenoid
were satisfied 5 Tesla and 10-4 Homogeneity and
limited field (35 G) at HTCC PMTs.
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CLAS12 Solenoid - Example
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Compare w. Hall D Solenoid
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Include angular dependence (MS)