Particle Detector Example: a Magnetic Spectrometer

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Particle Detector Examplea Magnetic Spectrometer
Just as light of different colors is bent
differently by a prism...
Nature lets us measure the momentum of a
charged particle by seeing how much its path is
deflected by a magnet.
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Example Hall C at Jlab (CEBAF)
HMS
SOS
They form specialized magnetic optical
instruments that analyze the momentum of the
scattered charged particles from the experimental
target
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HMS as Optics Example
Detector Hut/Focal Plane
D
QQQD Design
Q1
Q2
Q3
Target
Use three quadrupole magnets to focus more
particles into detectors (increase the solid
angle). In the end, the solid angle is limited by
the actual magnet sizes (or, where one can
physically put magnets) and the quadrupole
gradients (or, how well one can still focus at a
certain momentum).
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Magnets Dipoles and Quadrupoles and Sextupoles
Correctors
Achieving the desired beam optics sometimes
requires a variety of different magnets
Sextupole
Dipole Steer
Quadrupole Focus
Octupole
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Quadrupole Lenses (Magnets)
Recall the Right Hand Rule The focusing force
increase linearly with the off-axis displacement
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Halls A/B/C Base Equipment
Hall A (2 HRS)
Hall C (SOS/HMS)
Hall B (CLAS)
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Putting Everything TogetherA (Magnetic)
Spectrometer

• Magnetic Field for Momentum Measurement
• Scintillators for Triggering and Timing
• Drift Chambers for Tracking
• Particle Identification by
• Gas/Liquid/Lucite Cerenkov Counters
• Time-of-Flight
• Lead-Glass or Scintillator Calorimetry

Hall-A HRSL / HRSR Hall-B CLAS Hall-C
HMS, SOS
The Base Equipment in all three Halls is
composed of optimized arrangements of the same
fundamental detector technologies
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Putting Everything Together (I)A Detector System
B
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Putting Everything Together (I)A Detector System
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Putting Everything Together (I)A Detector System
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HMS Design
Rigid connection to pivot rail system ? Only
takes a few minutes (3 degrees/minute) to reach
a different spectrometer angle. Simple optics
design of SHMS flat acceptance
? Spectrometer knowledge transfers easily
to different angles and momenta Angle rotation
allows for (e,p) elastic and (e,e) DIS checkout
everywhere! Result Reproducible,
well-understood system!
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HMS Performance
(Q2 12 GeV2)
Took 3 Years to understand optics/acceptance, gt3
Years for 10 cm target, 19 dp/p acceptance
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Matrix Representation of Magneto-OpticsUsing
Jlab HMS Spectrometer as Example

• Coordinate Matrices
• At target Xt (xt, xt, yt, yt, 0, ?p),
• xt yt 0 for point target
• At focal plane Xfp (xfp, xfp, yfp, yfp, L,
  ?p),
• measured at the focal plane
• x and y are the angles in dispersion and
  non-dispersion planes
• ?p is momentum in with respect to the central
  momentum
• Transportation Matrices Representing the
  Optical Character of the Spectrometer System
• M Forward optical matrix from target to focal
  plane
• M-1 Backward optical matrix from focal plane to
  target
• Matrix Representation of Optical Transport and
  Reconstruction
• Forward Xfp M Xt Backward Xt M-1 Xfp

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Matrix Representation of Magnetic Spectrometer
A 1st tracking detector plane measures (x1,y1,z1)
A 2nd tracking detector plane measures (x2,y2,z2
) An nth tracking detector plan
measures (xn,yn,zn) ? Can determine (xfp, xfp,
yfp, yfp) (and time)
Need to know at target (x,x,y,y,Dp)
Note z and y are correlated from spectrometer
point of view
Miss one measurement to determine 5 quantities
Solution 1) get Dp from xfp assume x
0 (Dp,x,y,y) M-1(xfp,xfp,yfp,yfp)
better, get x from some other
measurement, and 2) Taylor expansion
corrects for small x (Dp,xa,x,y,y)
M-1(xfp,xfp,yfp,yfp,a)
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Optics Example SHMS Small-Solid-Angle Tune Model
Detector plane
Point-point focus
Side View (COSY Model)
Choose point-to-point tune to obtain reproducible
hour-glass
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HMS Optics
The HMS is the same spectrometer between 0.5 and
5 GeV! ? One set of matrix elements over the full
momentum range
Its point-point tune has allowed for detailed
consistency checks, here one example is given
The sieve spectra (at the detector plane) were
found to differ slightly at low momentum
This small difference in optics at various (low)
HMS momenta was traced to an 0.2A difference
between set and read back currents of Q3 (Dave
Potterveld, 1999), and subsequently corrected.
The HMS Monte Carlo reproduces the effect very
well.
x (cm) ?
Y (cm) ?
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HMS Optics
The HMS is the same spectrometer between 0.5 and
5 GeV! Its point-to-point tune has allowed for
detailed consistency checks.
B/p (norm.) ?
I/p (norm.) ?
With similar procedures, checking where the focus
of HMS was by detailed MC and data comparisons,
we found that the dipole has no saturation
effects yet up to 5 GeV.
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HMS Kinematics Stability
Many years of elastic (e,p) data fit with one
momentum offset and no angle offset
d(e,e)d
Gets online elastic (e,d) right and various
resonance/missing mass peaks!
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HMS Kinematics Stability
Many years of elastic (e,p) data fit with one
momentum offset and no angle offset
July, 2003
July, 1999
DW (MeV)
DW (MeV)
QHMS (degree)
QHMS (degree)
Position of elastic peak stable to lt1 MeV over
many years
Just one of 5 variables we typically look at with
(e,p)
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Comparison with Worlds Data
DIS H(e,e)X
Elastic H(e,e)p
Excellent agreement, to better than 1
0.4 lt E lt 5 GeV/c, 10.5o lt Q lt 80o, all regions
of acceptance
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HMS Pointing Accuracy
HMS Pointing has proven to be reproducible over
6 years due to accurate rotation system based on
rails and pivot connection
Small recent discrepancy at small angles (lt15o)
due to addition of concrete for G0, etc?
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HMS Pointing Accuracy

Quads pulled backward
Model Fit to 1995 1995
(Quads forward)
Concrete in Hall for G0, etc
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Recall Extracting the (e,e) cross section
e'
NN (cm-2)
Ne
e
(??e, ?pe)
Scattering probability or cross section
?
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Acceptance Corrections

• Whether a scattered electron reaches the
  detectors or is stopped by hitting the edge of
  the collimator or one of the other various
  aperture systems in the HMS magnet system and
  beam pipe, is dependent on several factors,
  including
• The electron momentum,
• The in-plane and out-of-plane scattering angles,
  and
• The vertex position

However, the physics depends only upon the
momentum and full scattering angle, Q
cos-1cos(x)cos(Qc-y), with Qc the spectrometer
central angle. So, consider only the momentum (E
pc(1Dp) with pc the spectrometer central
momentum).
Using a model of the spectrometer, the fractional
acceptance, A(E,Q), is calculated by generating
Monte Carlo events and taking the ratio of the
number of detected events to the number of
generated events for each (E,Q) bin covering the
spectrometer acceptance (or phase space). That is
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Acceptance Corrections
Defined here as probability
Obviously, the probability for an electron to be
detected will be reasonably large within the
expected solid angle dW of the spectrometer, and
small beyond. ? Define the effective solid
angle dWeff(E,Q) as
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HMS Acceptance
6.74 msr (Collimator Size)
Beyond Collimator, losses due to Detector
size Magnet Vacuum Can in Hut Apertures
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HMS Acceptance
6.74 msr (Collimator Size)
Beyond Collimator, losses due to Detector
size Magnet Vacuum Can in Hut Apertures
Result excellent (lt2) agreement with models for
known inclusive (e,e) cases
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HMS Acceptance
6.74 msr (Collimator Size)
Beyond Collimator, losses due to Detector
size Magnet Vacuum Can in Hut Apertures
Regions of overlap agree to 1 (from -9 to 10
? essentially the full momentum acceptance!)
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HMS Tracking Efficiency Robust

• Rate dependence well understood on basis of
  Poisson statistics
• DC TDCs have wider window than hodoscope TDCs
  (difference fit with 77 ns)
• varying width of DC TDC window ? find same
  corrected yield!

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HMS Tracking Efficiency Robust
One-event display showing a two electron event
(selected with calorimeter)

• Rate dependence well understood on basis of
  Poisson statistics
• DC TDCs have wider window than hodoscope TDCs
  (difference fit with 77 ns)
• varying width of DC TDC window ? find same
  corrected yield!
• 2 electron tracks ? tracking efficiency 70 /-
  3 (cant find track for two electrons
• close-by, like in plot on right) agrees well
  with number found from TDC window study
• Important to have device with well-defined rates
  and aperture

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Rosenbluth Separations
Hall C E94-110 a global survey of longitudinal
strength in the resonance region...

• Spread of points about the
• linear fits is Gaussian with
• s 1.6 consistent with
• the estimated point-point
• experimental uncertainty
• (1.1-1.6)
• a systematic tour de force

Residuals
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Rosenbluth Separations (cont.)
10 of Hall Cs Rosenbluth Separations. The
kinematics represent all regions of the HMS
acceptance
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Point-to-Point Systematic Uncertainties
Compare with SLAC E140X (DIS) 1 x 10-3 0.3 1 x
10-3 0.2 0.1 mr 0.3 0.3 0.3 0.2 0.2 0.
3 0.3 0.1 0.1 0.2 0.2 0.5 0.5 1.0 1
.0 1.3
Total point-to-point systematic uncertainty for
E94-110 is 1.6.
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Shield Hut Essential for Small High-Energy Cross
Sections

• HMS 25o bend
• 2 types of background
• I) Neutrals hit the inside
• of the dipole iron, and
• produce secondaries.
• II) Background enters the
• front collar of the hut

II
I
Vacuum can at HMS hut entrance
I) x gt 1 run, bad good
II) good
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HMS is the same spectrometer between 0.5 and 5
GeV, and extremely well understood, highlighted
by gt200 precision Rosenbluth L/T separations
(close to 1,000 kinematics) performed to date in
Hall C. Lessons learned Essential to have
highly reproducible optics tune, rigid mechanical
system, flat acceptance function, and allowance
for detailed cross-checking.
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Jefferson Labs Experimental Hall C
Hall C AT PRESENT (6 GeV)
AFTER the 12-GeV Upgrade

• Hall Cs High Momentum Spectrometer, Short Orbit
  Spectrometer and specialized equipment to study
• The strange quark content of the proton
• Form factors of simple quark systems
• The transition from hadrons to quarks
• Nuclei with a strange quark embedded

• Add a Super-High Momentum (11 GeV) Spectrometer
  tostudy
• Super-fast quarks
• Form factors of simple quark systems
• The transformation of quarks into hadrons
• Quark-quark correlations

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SHMS Design
Rigid connection to pivot rail system ? Only
takes a few minutes (3 degrees/minute) to reach
a different spectrometer angle. Simple optics
design of SHMS flat acceptance
? Spectrometer knowledge transfers easily
to different angles and momenta Angle rotation
allows for (e,p) elastic and (e,e) DIS checkout
everywhere! Result Reproducible,
well-understood system!
39
SHMS Design
Rigid connection to pivot rail system ? Only
takes a few minutes (3 degrees/minute) to reach
a different spectrometer angle. Simple optics
design of SHMS flat acceptance
? Spectrometer knowledge transfers easily
to different angles and momenta Angle rotation
allows for (e,p) elastic and (e,e) DIS checkout
everywhere! Result Reproducible,
well-understood system! 12 GeV physics requires
even better understanding of systematics than
present case - Energy grows x 2 - Smaller
angles (for electrons s 1/Q4)
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SHMS Design
Rigid connection to pivot rail system ? Only
takes a few minutes (3 degrees/minute) to reach
a different spectrometer angle. Simple optics
design of SHMS flat acceptance
? Spectrometer knowledge transfers easily
to different angles and momenta Angle rotation
allows for (e,p) elastic and (e,e) DIS checkout
everywhere! Result Reproducible,
well-understood system! 12 GeV physics requires
even better understanding of systematics than
present case - Energy grows x 2 - Smaller
angles (for electrons s 1/Q4) Strategy 8 GeV _at_
SLAC ? HMS _at_ Hall C ? SHMS
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End Station A _at_ SLAC with 8 GeV
QQDDQ system
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Hall C _at_ JLab with HMS (7.3 GeV)
QQQD system
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Recall JLab Data Reveal Deuterons Size and Shape
Hall A
Combined Data -gt Deuterons Intrinsic Shape
The nucleon-based description works down to lt 0.5
fm
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2H(e,e)2H elastic scattering
2H spin-1 ? 3 form factors
to disentangle
Solution measure tensor polarization in
2H(e,ed)
T20 experiment used HMS to detect the scattered
electrons and a QQQD magnetic spectrometer on the
floor to detect the
recoiling deuteron and measure its tensor
polarization
1st large installation experiment 1997
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Motivation for Hall C Upgrade

• Pion and nucleon form factors at high Q2
• Deep inelastic scattering at high Bjorken x
• Semi-inclusive scattering at high hadron momenta
• Polarised and unpolarised scattering on nuclei

• Highest Luminosity (L1038 nucleons/cm2/s)
• Pair of magnetic spectrometers
• Detection of charged particles with highest
  momenta
• Accuracy and reproducibility
• Small angle capability
• Very good particle identification
• Compatibility with all target configurations

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Hall C at 12 GeV HMS SHMS

• Charged particle detection with momentum up to
  beam energy z Eh/n 1
• Small angle capability essential to measure
  charged particle along momentum transfer
  qh // q few o
• Precision L/T separations
• High Luminosity L 1038

s G(sT esL e cos(2f)sTT
e(e1)/21/2cos(f)sLT)

• Exclusive and Semi-Inclusive Reactions (z gt 0.3)
  at high Q2
• Separation of Polarized and Unpolarized Structure
• Functions over large range of x and Q2
• ?Small Cross Sections

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• Physics needs for SHMS
• Spectrometer momentum up to beam energy (11 GeV)
• To detect particles up to the highest momenta
  possible
• 2) Spectrometer can reach forward angles, down
  to 5.5o,
• even with HMS at forward angles (12o?) too.
• To do (e,em) coincidence reactions (m p, K)
• 3) Detailed understanding of acceptance
  function,
• and easy reproducibility
• To perform accurate longitudinal-transverse
  separations
• Well-shielded detectors
• To measure the smallest cross sections (high
  luminosity required!)
• 5) Scattering angles up to 35-40o desirable
• To have flexible device

Optics needs for SHMS A) Point-to-point optics
tune (3) B) Angle of focal plane w.r.t. detector
plane gt 5o (3) C) Vertical acceptance 2-3 x
Horizontal acceptance (2) The latter three
requirements impose a QQQD design!
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Hall C _at_ 12 GeV add SHMS (11 GeV)
HMS an extremely well understood device
Small horizontal bender (d) to facilitate angles
down to 5.5o
SHMS emulates the essential features of HMS A
rigid connection to the pivot, a precision rail
system, vacuum, a simple and reproducible
point-to-point optics design, a flat and easily
understood acceptance, and a heavily shielded hut
with redundant detectors allowing for detailed
cross checks.
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New SHMS Design  
SHMS
Q1
HB
Q1
HMS
target chamber
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SHMS at 5.5 degrees (HMS at 12 degrees)
SHMS at 40 degrees (HMS at 12 degrees)
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Shield Hut Essential for Small High-Energy Cross
Sections

• HMS 25o bend
• 2 types of background
• I) Neutrals hit the inside
• of the dipole iron, and
• produce secondaries.
• II) Background enters the
• front collar of the hut

II
I

• SHMS 18o bend
• 2 types of background
• I) 4.5 msr vs. 8 msr,
• 3o horizontal bend!
• II) Dipole shields front
• collar of the hut

detectors
D
Q2
Q3
Q1
HB
II
I
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Technical Issues with Proposed Experiments

• Copy main properties of well-understood HMS into
  SHMS design
• Pivot
• Rail System
• Point-Point Optics Design
• Flat Acceptances
• Shield House
• Redundancy in Detectors

Emphasize Reproducibility and Ability to
Cross-Check
(PR12-06-101, PR12-06-104, PR12-06-111)
Good acceptance between -10 and 22 (30 cm
target)
Reasonably flat for 30 cm target (as viewed at
90o)
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Technical Issues with Proposed Experiments
Several experiments (PR12-06-101, PR12-06-104,
PR12-06-111, LOI12-06-106) require good tracking
efficiency knowledge at 1 MHz rate. HMS tracking
efficiency is robust, but we typically still
restrict rates to lt 0.5 MHz

• Rate dependence well understood on basis of
  Poisson statistics
• DC TDCs have wider window than hodoscope TDCs
  (difference fit with 77 ns)
• varying width of DC TDC window ? find same
  corrected yield!
• 2 electron tracks ? tracking efficiency 70 /-
  3 (cant find track for two electrons close-by)
  agrees well with number found from TDC window
  study
• Important to have device with well-defined rates
  and aperture

SHMS Design incorporates Quartz hodoscope (?
cleaner event selection), well-defined apertures,
and multi-hit TDCs ? Good knowledge _at_ 1 MHz
probable (but lot of work)
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Design Parameters 
Based on similar MC for SHMS as used for HMS
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SHMS/HMS Detector Systems
Quartz Hodoscope
Space for aerogel, etc.
(for p/e at high E only, otherwise vacuum)
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SHMS Particle Identification Summary
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SHMS/HMS Detector Systems
Option Replace Cherenkov with Focal Plane
Polarimeter
Quartz Hodoscope
Space for aerogel, etc.
(for p/e at high E only, otherwise vacuum)
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Revolutionized Polarized Beam Experiments!
Precise access to (small) charge form factor of
proton utilizing polarization transfer
technique e p ? e p
Focal Plane Polarimeter
GE Px (Ei Ef) Qe GM
Pz 2m 2
__ __ _____ __
- tan

• No error contributions from
• analyzing power
• beam polarimetry

 
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at 12 GeV
Magnetic Spectrometer Pair Capable to Handle Full
12 GeV Energy Luminosity
(Note 12 GeV means 11 GeV to Halls A/B/C)
HMS has been successfully used for many precision
L/T separation measurements, which represent the
worlds state-of-the-art, largely due to its
highly reproducible optics tune, rigid mechanical
system, flat acceptance function, and allowance
for detailed cross-checking.
SHMS has been designed with similar properties in
mind.
HMS SHMS Momentum Range 0.4 - 7.3 2
11 Angle Range 10.5 90 5.5
40 Solid Angle 8 msr 5 msr Momentum
Acceptance 20 32 Target
Length_at_90o 10 cm 30 cm