W. Morse GamCal 1

GamCal: a Beam-strahlung Gamma Detector for Beam

Diagnostics

William M. MorseBrookhaven National Lab

W. Morse GamCal 2

GamCal Detector

• W. Morse (BNL): Coordinator• M. Ohlerich et al. (Zeuthen): beam-

strahlung simulations• B. Parker (BNL): Machine interface issues• M. Zeller, G. Atoian, V. Issakov, A.

Poblaguev (Yale): GamCal detector design

• Y. Nosochkov (SLAC): Extraction line issues

W. Morse GamCal 3

RDR: Luminosity Feedback Detectors BeamCal and GamCal

W. Morse GamCal 4

Beam-strahlung Gammas

• F = e(E + cB)• E = 0, Bmax 1KT• P 2% Pe 0.3MW• N 1.5Ne 31010 /BX

mcFrP

32 220

yzx

xycNeB

0

W. Morse GamCal 5

Beam-strahlung Pairs

• Bethe-Heitler: e → e e+e-

BH 38 mb• <E> 1GeV• Landau-Lifshitz: ee → ee e+e-

LL 19 mb• <E> 0.15GeV

W. Morse GamCal 6

Beam-strahlung Pairs

0.1m low Z

W. Morse GamCal 7

Bethe-Heitler Pairs

e → e e+e-

oy

ox

oe

oBH

ee

NNN

o

yox

oeBHee N

NN

For left and right detectors separately: N+/xy and N-/xy.

oy

ox

oo NNL

W. Morse GamCal 8

Vertical Offset E_pairs (BCAL) and E_photon

0

20

40

60

80

100

120

140

160

180

200

-300 -200 -100 0 100 200 300

offset_y/2 (nm)

E_pa

irs

(BC

AL,

TeV)

0

2

4

6

8

10

12

14

16

E_ph

oton

(MTe

V)

Ratio of Energies (BCAL)

0

0,02

0,04

0,06

0,08

0,1

0,12

0,14

-300 -200 -100 0 100 200 300

offset_y/2 (nm)E_

pairs

(BCAL)

/E_g

amm

a (1

0̂-6

)

0

0,5

1

1,5

2

Lum

inos

ity (1

0̂34

cm̂

-2/

s)

M.Ohlerich

complementary information from1. total photon energy vs

offset_y2. BeamCal pair energy vs

offset_y

ratio of E_pairs/E_gam vs offset_y is proportional to the luminosity

similar behaviour for angle_y, waist_y …see also: EUROTeV-Memo-2006-011

W. Morse GamCal 9

GamCal and BeamCal

• Measuring the beam-strahlung pairs and gammas provides robust complementary information

• Ratio of pairs to gammas is largely proportional to the instantaneous luminosity

W. Morse GamCal 10

BeamCal

• .003 < < .02 rad3.5m from IR• Pairs curl in the magnetic field• Measure the 104 beam-strahlung e+e-

pairs/BX for beam diagnostics• The distribution of the pairs on the

BeamCal contains rich information on the beam parameters of the collision (beam sizes, emittances, etc.)

W. Morse GamCal 11

GamCal Detector 180m from IR 10-4 X0 to convert beam-strahlung gammas into

e+e- pairs• Converter could be gas jet or a thin solid

converter• Dipole magnet with PT kick 0.25 GeV/c separates

the pairs from beam electrons• Calorimeters outside vacuum after magnet

measure the 1-10 GeV positrons

W. Morse GamCal 12

Statistical Error for BXN pairs and gammas full intensity

0.E+00

2.E+03

4.E+03

6.E+03

8.E+03

0 20 40 60 80 100

y angle (urad)

pairs

3.E+05

4.E+05

5.E+05

6.E+05

gam

mas

BeamCal

GamCal

W. Morse GamCal 13

Start-up?10% beam intensities

0

5

10

15

20

25

0 20 40 60 80 100

y angle (urad)

pairs

3.E+03

4.E+03

5.E+03

6.E+03

gam

mas

BeamCal

GamCal

W. Morse GamCal 14

Beam-strahlung Ze+e-Z

0

5

10

15

20

0 2 4 6 8 10 12 14 16 18 20

E (GeV)

E dN

/dE

W. Morse GamCal 15

GamCal Backgrounds from Beam Electrons

Process Background/signal

Bremsstrahlung <1%

Delta rays <1%

Landau-Lifshitz 6%

production <0.1%

W. Morse GamCal 16

Ratio of ZeeZ vs. eZ eZee

0

7

14

21

-1 0 1

log_10 (E)

Ratio

W. Morse GamCal 17

W. Morse GamCal 18

Yale IBS Design

W. Morse GamCal 19

Beam Diagnostics Detectors Conclusions

• BeamCal and GamCal provide robust complimentary information.

• GamCal backgrounds look OK – needs simulations.• Can measure, and then subtract, the GamCal

background by accelerating only one beam. • Ratio of the beamstrahlung pairs (BeamCal) to gammas

(GamCal) is largely proportional to the instantaneous luminosity.

• There is much rich information from pair distributions on BeamCal and IBS camera, which we are studying.

W. Morse GamCal 20

Extra Slides

W. Morse GamCal 21

Feed-back with Luminosity Detectors

P.N. Burrows GDE/MDI Vancouver 19/7/06

Intra-train y + y’ IP feedback simulations

0 100 200 300 400 500 6000

1

2

3x 10

34

Bunch #

Lum

inos

ity /

cm-2s-1

y position FB:restore collisionswithin 100 bunches

1 seed:

post-BBA

+ GM

+ wakes

y position scan:optimise signal in pair monitor

y angle scan

OPTIMALLUMINOSITY

W. Morse GamCal 22

BNL Magnet Division Position Stability

W. Morse GamCal 23

Achieving the ILC Luminosity Will Be a Challenge

• Bunch P- (t) {N, x, y, z, xy, x, y}• Bunch P+(t) {N, x, y, z, xy, x, y}• Instantaneous Luminosity:

oy

ox

oo NNtL

)(

x

y

W. Morse GamCal 24

IBS Camera

W. Morse GamCal 25

IBS Camera

W. Morse GamCal 26

1 2

0

21

yE

0

21

yB

+ -

0

221

212

01

2

eyeyF

y

z

W. Morse GamCal 27

Perfect Collisions

zx

NE 2

2

zyx

eeNE

3

3

W. Morse GamCal 28

Bunch width

0

100

200

300

400

500

600

400 500 600 700 800 900

Bunch width (nm)

Ener

gy in

gam

mas

(MTe

V)O

0

10

20

30

40

50

60

gammas

pairs

W. Morse GamCal 29

Bunch Width

0

5

10

15

20

25

30

400 500 600 700 800 900

Bunch width (nm)

Lum

inos

ity (1

0^33

cm

^-2/

s)

0

0.02

0.04

0.06

0.08

0.1

0.12

Lum

R

W. Morse GamCal 30

GamCal Backgrounds

Gammas

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

1.E+09

-2 -1 0 1 2

log(E)

dN/d

log(

E)

BeamstBrem

1

10

100

1000

-2 -1 0 1 2log(E)

dN/d

log(

E) Delta RaysBeamst e

W. Morse GamCal 31

ZeeZ vs. eZ eZee

• Electron carries virtual gammas• Landau Lifshitz conversion of virtual

gammas

211.1ln12

minbc

ddN

W. Morse GamCal 32

Production Compared to ee

p eep 10 mbp N 0.5 mb on peak of Δ

resonancep N 0.1 mb E > 4GeV• ep e N 10-3 mb • Thus ep e N is negligible