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