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ILC Meeting Vancouver July 2006 1
What Does Beam-strahlung Tell Us?
William Morse - BNL
ILC Meeting Vancouver July 2006 2
Achieving the Design Luminosity Will Be a Challenge
• Bunch P- (t) {N, E, x, y, z, x, y, z, xy, x, y}
• Bunch P+(t) {N, E, x, y, z, x, y, z, xy, x, y}
• Instantaneous Luminosity:
oy
ox
oo NNtL
4)(
x
y
ILC Meeting Vancouver July 2006 3
Run Time Measurements
• Beam-beam deflections (pickup electrodes)
• Beam-strahlung gammas (GamCal)
• Beam-strahlung pairs (BeamCal)
• We need robust and complementary information
ILC Meeting Vancouver July 2006 4
Beam-strahlung• F = e(E + B). Bmax 1KT• Instantaneous power radiated:• P 3% Pe N 1.5Ne
• Bethe-Heitler: e → e e+e-
BH 38 mb• <E> 1GeV• Landau-Lifshitz: ee → ee e+e-
LL 19 mb• <E> 0.15GeV• Other processes much smaller• C. Rimbault et al., Phys Rev ST AB 9,034402 (2006).
mc
FrP
3
2 220
ILC Meeting Vancouver July 2006 5
Bethe-Heitler Pairs
e → e e+e-
oy
ox
oe
oBH
ee
NNN
oy
ox
oeBHee N
N
N
oy
ox
oeee N
E
E
For left and right detectors separately: N+/xy and N-/xy. Question: How well does this really work? Answer: Needs simulation.
ILC Meeting Vancouver July 2006 6
Landau-Lifshitz Pairs
• ee → eee+e-
oy
ox
ooLLLL
ee
NNN
For left and right detectorequally
1 GeV
ILC Meeting Vancouver July 2006 7
Simulations
• W. Morse (BNL)
• W. Lohman and M. Ohlerich (DESY Zeuthen)
• Submitted as an ILC Note
• Guinea Pig simulations varying some of the 500 GeV ILC bunch parameters around nominal values
ILC Meeting Vancouver July 2006 8
Vertical offset
0
50
100
150
200
-200 -100 0 100 200
offset/2 (nm)
ener
gy
in g
amm
as (
MT
eV)
0
5
10
gammas
pairs
E BeamCal (TeV)
ILC Meeting Vancouver July 2006 9
Vertical Offset
0
5
10
15
20
-200 -150 -100 -50 0 50 100 150 200
offset/2 (nm)
Lu
min
osi
ty (
10^
33 c
m^
-2/s
)
0
0.05
0.1
Lum
R
R (10-6)
ILC Meeting Vancouver July 2006 10
Bunch Width
0
100
200
300
400
500
600
400 500 600 700 800 900
Bunch width (nm)
Energ
y in g
amma
s (MT
eV)O
0
10
20
30
40
50
60
gammas
pairs
0
5
10
15
20
25
30
400 500 600 700 800 900
Bunch width (nm)
Lumi
nosit
y (10
^33 c
m^-2/
s)0
0.02
0.04
0.06
0.08
0.1
0.12
Lum
R
BeamCal E (TeV)
R 10-6
ILC Meeting Vancouver July 2006 11
Comparison• Sign of dE/d(bunch characteristic) at design values. Note that all five
lines are different, which means complementary information.
Parameter Pairs Gammas Ratio
X offset 0 (max) 0 (max) 0 (max)
z - - 0
y0 (max) 0 0 (max)
x - - -Y offset 0 (max) 0 (min) 0 (max)
ILC Meeting Vancouver July 2006 12
Bunch Height
0
40
80
120
160
200
240
3 5 7 9 11
Bunch height (nm)
Energ
y in g
amma
s (MT
eV)
0
4
8
12
16
gammas
pairs
0
2
46
8
10
1214
16
18
3 5 7 9 11
Bunch height (nm)
Lum
inos
ity (1
0^33
cm^-
2/s)
0
0.02
0.04
0.06
0.08
Lum
R
ILC Meeting Vancouver July 2006 13
Bunch Length
0
50
100
150
200
250
300
350
150 200 250 300 350 400
Bunch Length (um)
gam
ma e
nerg
y (MT
eV)
0
5
10
15
20
25
gammas
pairs
0
2
46
8
10
1214
16
18
150 200 250 300 350 400
Bunch length (um)
Lum
(10^
33 cm
^-2/s
)0
0.02
0.04
0.06
0.08
Lum
R
ILC Meeting Vancouver July 2006 14
Is There More Info in BeamCal?
• T.Tauchi,K.Yokoya• Phys Rev E51,6119(95)• 6<r<7cm azimuthal dist• But, Moliere dia. 2cm!• Also, 1 Bhabha/BX!• Thus we need more
simulation to show that it is robust enough.
normalized
0.001
0.01
0.1
0 1.57 3.14
theta (radians)
1/E
dE
/ds
(0.8
cm)^
-1
sig_y
2sig_y
ILC Meeting Vancouver July 2006 15
Radiative Bhabha Detector?
• After TESLA quadrupole magnet (ILC space issues)
• O. Napoly and D. Schulte,• Luminosity Monitor Studies for Tesla• DESY TESLA 97-17:• “Because of its sensitivity to the beam-
beam effect, the radiative Bhabha signal within a fixed kinematical acceptance is no longer proportional to the luminosity.”
ILC Meeting Vancouver July 2006 16
GamCal Design
• Can we only measure the large angle (1mrad) gammas?
• Too sensitive to the beam-beam effect
• 0.1GeV/250GeV = 0.4mrad
• Just started thinking about detector design (BNL-Yale).
• Collect Cerenkov light from H2O Dump?
ILC Meeting Vancouver July 2006 17
Clever Idea: Measure Polarization Vector of Visible Beam-strahlung Light
ILC Meeting Vancouver July 2006 18
Being Tested Now at CESR
CESR Detector = 11.5 mrad (z 12mm)ILC z 0.3mm, ie. much shorter than CESR
ILC Meeting Vancouver July 2006 19
Robust and Complementary
Detector X offset Y offset x y
PUE x y Normal Normal
E GamCal Low High Low Normal
E BeamCal Low Low Low Low
Luminosity, ie. R, is low. Note that all columns are different, ie. complementary information.
ILC Meeting Vancouver July 2006 20
Conclusions
• We need robust, redundant information:• Beam-beam deflections• Beam-strahlung gammas• Beam-strahlung pairs• E(pairs)/E(gammas) particularly valuable• Largely proportional to instantaneous
luminosity• We need a “White Paper”, in my opinion.
ILC Meeting Vancouver July 2006 21
Extra Slides
ILC Meeting Vancouver July 2006 22
1 2
0
21
y
E
0
21
y
B
+ -
0
221
212
01
2
eyey
F
y
z
ILC Meeting Vancouver July 2006 23
Can We Correct?
N
NN
E
ER
ELLo
BHoy
ox
oee
032
5
R
c
dt
dN
Needs more study.
ILC Meeting Vancouver July 2006 24
Perfect Collisions
zx
NE
2
2
zyx
ee
NE
3
3