Luminosity Analysis - espace.cern.ch

Giulia Papotti (BE-OP-LHC)

After fruitful discussions with:

M. Lamont, W. Herr,M. Ferro-Luzzi, G. Sterbini, G. Rumolo,

W. Venturini Delsolaro, T. Mertens

Chamonix 2011 LHC Performance Workshop, 27th Jan 2011

Luminosity Analysis

Chamonix 2011 - 2giulia papotti (BE/OP/LHC)

outline

• look only at protons, and only ATLAS + CMS • eases the analysis and allows double-checks

• theory reminders

• historical overviews from 25 bunches to bunch trains• data from end of July (fill 1251)

• luminosity / intensity / emittance lifetimes comparison– for bunch trains

• bunch-by-bunch (bbyb) analysis on a “clean” fill (1440)

• others– fill 1459: 50 ns spaced beams

– fill 1372: hump on and off

• Machine Development ideas


reminder

2221

22

21

210

2 vvhh

b fnNNL

• luminosity decreases with time– beam size

• elastic scattering at IPs and from residual gas, IBS

• noise in PCs, RF (phase and amplitude)

• LR beam-beam

• non-linear resonances

• hump, e-cloud

– intensity• due to interaction of the two beams at the IPs

– luminosity burn-off

– from beam-beam

• other causes – scattering on residual gas

– IBS and Touschek effect (mostly through emittance growth)

– overlap region from orbit drifts


2010 performance

• we have seen these many times

• but they only tell us that we were increasing nb


peak luminosity per collision

• given that rMPP limits the nb, how much Lpeak per bunch?

• luminosity burnoff• L/coll = 0.4 1030 cm-2s-1; 3 collisions / bunch; 100 mb x-section

– dN/dt = 1.2 105 p/s

• Total Losses, after 10 hours: 4.3e9 protons lost…

– 5% (~1 pilot) after 10 hours, or tburnoff ~ 227.5 h

peak luminosity / nb

[1030 cm-2s-1]

pre

pare

d b

y G

. Tra

d


statistics across fills

average bunch

intensity[1011 ppb]

average specific

luminosity[107 cm-2s-1]

calculated emittance

[mm]

fill number

5

2

0.8

1.2

pre

pare

d b

y G

. Tra

d


bunch-by-bunch losses

50 100 150 2005

6

7

8

9

10

11

time [min]

inte

nsity [

1e10 p

+/b

unch]

fill 1299 - beam 1

put in collisions

50 100 150 2005

6

7

8

9

10

11

time [min]

inte

nsity [

1e10 p

+/b

unch]

fill 1299 - beam 2

50 100 150 2000

5

10

15

20

25

30

time [min]

losses [

%]

fill 1299 - beam 1

50 100 150 2000

5

10

15

20

25

30

time [min]

losses [

%]

fill 1299 - beam 2

2h 2h

• take bbyb intensity starting before collisions– calculate % loss from

there• @ time=0: 0% losses

– colour code from head on collisions

• problems start at collisions– before, single beam

lifetimes are excellent

• next: cut 2 hours after collisions to compare fills

IPs: 1 5 2 8 - 1 5 8 - 1 5 2- 1 5 - 2 8 - 8 - 2


bbyb losses summaries – 1

1251 1253 1257 1258 1260 1262 1263 1266 1267 1268 1271 1283 1284 1285 1287 1295 1298 1299 1301 1303 1308 13090

5

10

15

20

25

30

fill number

losses 2

hrs

aft

er

coll.

[%]

• history of fills until 50 bunches/ring (fills longer than 2h)

– tune split until 1258• DQ1x,y= -0.0025; beam 1 always on a bad tune!

– 1260: tune split inverted

– 1263: tunes +0.002

– afterwards: no tune split and chroma corrected to ~1/2 units

– 48 bunches/ring: some bunches have very high losses• bunches with LR (33m) in IP 2 and 8

– then changed to 50 bunch scheme

25 48 50n bunches

be

am

1b

ea

m 2

IPs:1 5 2 8

1 5 81 5 2

1 52 8

82


bbyb losses summaries – 2

• history of 150 ns spacing fills + 50 ns fill (fills longer than 2h)

– 1364, 1366: Alice had wrong polarity

– 1393: b2 a mystery, high losses at collisions

– 50 ns fill (1459) losses out of scale (up to 50% for some bunches)

• nb: little statistics for “luminosity analysis”

– start with 11 fills longer than 8 hours, can use only 6• remove 1366 (wrong Alice pol), 1372 (with hump), 1373 (with hump), 1393

(strange losses), 1450 (RF module trips)

IPs:1 5 2 8

1 5 81 5 2

1 52 8

82

24 56 104 152 200 248 312 368 109

n bunches


• using:

• good agreement on whole fill

– luminosity decay is explained by emittance growth and intensity decay

– orbit stability is good• no overlap issues

lifetimes

tb1 tb2 th tv tL,calc tL,publ

81.3 103.3 44.9* 53.5* 15.911.9o

11.0x

106.1 86.12x30.6o

2x29.5x

2x36.6o

2x35.9x

19.6o

19.3x

18.3o

18.3x

0 100 200 300 400 500 6003.6

3.8

4

4.2

4.4

tota

l in

tensity [

101

3 p

pb]

time after stable beams [h]

0 100 200 300 400 500 6000

2

4

6


em

itta

nce [m

m]

0 100 200 300 400 500 600100

150

200

250

lum

inosity [

103

0cm

-2H

z]


beam 1

beam 2

ATLAS

CMS

xATL

yATL

xCMS

yCMS

firs

t 1

00

0 s

(M.

La

mo

nt)

wh

ole fill

vhbbL ttttt

11111

21

* BSRT, o ATLAS, x CMS, all t’s in hours

fill 1440

tota

l in

tensi

ty [

10

13

p]


luminosity lifetime summary

13661372 1373 13751397 14001408 1418 1427 143914401450 145314590

50

100

150

200

fill number

a [

103

2cm

-2H

z]

13661372 1373 13751397 14001408 1418 1427 143914401450 145314590

5

10

15

20

25

30

fill number

b [

h]

fit to y=ae-x/b

ATLAS

CMS

• compare different fills

– initial value (a) follows nb increase

– lifetimes (b) slowly descending

• very similar even removing first 1 h or 2 h

• 50 ns fill: not particularly good


intensity lifetime summary

• compare different fills

– initial value (a) follows nb

increase

– lifetimes (b) beam 2 often worse than beam 1

• very similar even removing first 1 h or 2 h

– lifetime lowest for 50 ns• later: 1 slide on losses

13661372 1373 13751397 14001408 1418 1427 143914401450 145314590

1

2

3

4

5

fill number

a [

101

3p/b

unch]

intensity, fit to y=ae-x/b

13661372 1373 13751397 14001408 1418 1427 143914401450 145314590

50

100

150

fill number

b [

h]

beam 1

beam 2

a [

10

13

p]


intensity lifetimes• single beam lifetimes

– not so easy to recalculate– squeezed + not colliding,

lasts <10 minutes vs tens of hours lifetimes

– most of the time: >100 h• can’t give a number!

• in collisions, add all causes:

INJECT RAMP SQUEEZE

FILL 1393

INJECTRAMP

SQUEEZECOLLIDE

COLLIDE

FILL 1381

1 h

1 h

125 h

125 h

beam 1 – beam 2

– calculated tburnoff ~230 h

– for tgas need a measurment– 100 h in Design Report

– losses on collimators, Mike predicts tcoll ~ 120 h• from D. Wollmann’s presentation in Evian, proton loss rate ~ 1.e8 p/s

– still missing: longitudinal losses, …

– but only tburnoff and tcoll give already tb1 ~ 80 h

• need controlled experiment: measure single beam lifetime

...1111

1

collgasburnoffb tttt


136613721373137513971400140814181427143914401450145314592

2.5

3

3.5

fill number

emittance from lumiregions

ah [m

m]

136613721373137513971400140814181427143914401450145314590

20

40

60

fill number

bh [

h]

fits to y=ae-x/b

136613721373137513971400140814181427143914401450145314592

2.5

3

3.5

fill number

av [m

m]

136613721373137513971400140814181427143914401450145314590

20

40

60

fill number

bv [

h]

CMS

ATLAS

growth summary• compare different fills, from lumi regions

– tv (bv) generally worse than th (bh)• v would be better than h if IBS dominated• hump probably• something else maybe? with

humpgood

fill


• emittance growth times from Design Report (7 TeV)– longitudinal: tIBS~ 63 h– horizontal: th,IBS~ 105 h

– from theory:• factor 2 from g• smaller than nominal

– scaling from DR: th,IBS~ 37.5 h

• from V. Lebedev th,IBS(2.5mm, 3.5 TeV) ~ 38.6 h

IBS

***0

1

lvh

ppbN

gt

136613721373137513971400140814181427143914401450145314592

2.5

3

3.5

fill number

emittance from lumiregions

ah [m

m]

136613721373137513971400140814181427143914401450145314590

20

40

60

fill number

bh [

h]

fits to y=ae-x/b

136613721373137513971400140814181427143914401450145314592

2.5

3

3.5

fill number

av [m

m]

136613721373137513971400140814181427143914401450145314590

20

40

60

fill number

bv [

h]

CMS

ATLAS

• IBS does not explain the whole blow up– noise? beam-beam? hump?

– need controlled experiment: estimate IBS at least


0 2 4 6 8 10100

120

140

160

180

200

220


lum

inosity [

103

0cm

-2H

z]

fill 1440 - fit to y=ae-x/b

R2=98.178%

b=18.3 h

a=196.4 h

ATLAS

fit

luminosity lifetime

• fill 1440, from ATLAS total instantaneous luminosity

• long fill and very clean data sets

– exponential fit: not very good fit

– overall: lifetime ~18.3 hours• first 30’: lifetime ~10.9 h• at around 2h: lifetime ~13.8 h• at around 6h: lifetime ~24.0 h• at around 10h: lifetime ~31.4 h


luminosity lifetime

0 5 10100

150

200


lum

inosity [

103

0cm

-2H

z]

fill 1440 - fit to y=ae-x/b

R2=98.178%

b=18.3 h

0 5 10100

150

200


lum

inosity [

103

0cm

-2H

z]

fit to y=ae-x/b+ce-x/d

R2=99.997%

b=3.0 h

d=28.7 h

0 5 100

50

100

150

200


lum

inosity [

103

0cm

-2H

z]


a=44

c=164

• e.g.: from ATLAS total lumi

• much better with 2 exponentials instead of 1

– y = a e-x/b + c e-x/d

• a+c = Lpeak

• b, d time constants

• …can do the same on bbyb lumi data

– works also for single beam lifetimes


bbyb lumi lifetimes

0 1000 2000 30000.08

0.1

0.12

0.14

0.16

a [

103

0cm

-2H

z]

fill 1440, ATLAS

25ns slot

0 1000 2000 30002.6

2.8

3

3.2

3.4

3.6

b [

h]

25ns slot

0 1000 2000 30000.35

0.4

0.45

0.5

0.55

c [

103

0cm

-2H

z]

25ns slot

0 1000 2000 300024

26

28

30

32

d [

h]

25ns slot

0 1000 2000 300099.992

99.994

99.996

99.998

100

R2 [

%]

25ns slot


• factor 10 between time constants

– fast component with effect from collisions schedule

• superpacman bunches

• fast+slow component also in other fills

IPs: 1 5 2 8 - 1 5 8 - 1 5 2 - 1 5


0 1000 2000 3000

0

0.5

1

1.5

a [

101

1ppb]

fill 1440, ATLAS

25ns slot

0 1000 2000 3000

0

50

100

150

b [

h]

25ns slot

0 1000 2000 3000

0

0.5

1

1.5

c [

101

1ppb]

25ns slot

0 1000 2000 3000-500

0

500

d [

h]

25ns slot

0 1000 2000 300099.85

99.9

99.95

100

R2 [

%]

25ns slot


intensity lifetimes in collisions

• need the 2-exp model– single exp not good

• much more variation– no simple correlation

with collision schedule

– some correlation with injection pattern

• a lot of variation across different fills

IPs: 1 5 2 8 - 1 5 8 - 1 5 2 - 1 5


bbyb growth – 1

• bbyb luminosities from experiments

• combine with fBCT to get specific luminosities

• unfold emittance

– assumes very small orbit drifts• verified in few occasions with end-of-fill lumi scans

0 200 400 600

0.1

0.2

0.3

0.4

0.5

lum

i per

bunch [

103

0cm

-2H

z]

time after StableBeams [min]

fill 1440, CMS

0 200 400 6001.5

2

2.5

3

3.5

4

4.5

5

specific

lum

i [1

07cm

-2H

z]


Nbu

= 368 bu/ring

0 200 400 6001

2

3

4

5

6

calc

ula

ted e

mitta

nce [m

m]


growth = 4%/h (0.09 mm/h)

mean = 3.35

mean = 2.31

IPs: 1 5 2 8 – 1 5 8 – 1 5 2 – 1 5


bbyb growth – 2• ATLAS vs CMS: good agreement on average emittance

– use end-of-fill lumi scans for emittance cross-check– quite some spread on bbyb luminosity, from experiments

0 200 400 600

0.1

0.2

0.3

0.4

0.5

lum

i per

bunch [

103

0cm

-2H

z]


fill 1440, CMS

0 200 400 6001.5

2

2.5

3

3.5

4

4.5

5

specific

lum

i [1

07cm

-2H

z]


Nbu

= 368 bu/ring

0 200 400 6001

2

3

4

5

6

calc

ula

ted e

mitta

nce [m

m]



mean = 3.35

mean = 2.31

0 200 400 600

0.1

0.2

0.3

0.4

0.5

lum

i per

bunch [

103

0cm

-2H

z]


fill 1440, ATLAS

0 200 400 6001.5

2

2.5

3

3.5

4

4.5

5

specific

lum

i [1

07cm

-2H

z]


Nbu

= 368 bu/ring

0 200 400 6001

2

3

4

5

6

calc

ula

ted e

mitta

nce [m

m]



mean = 3.30

mean = 2.26

AT

LA

SC

MS

IPs: 1 5 2 8 – 1 5 8 – 1 5 2 – 1 5


estimation vs lumireg

0 100 200 300 400 500 6001

1.5

2

2.5

3

3.5

4

4.5

5

5.5

6


em

itta

nce [m

m]

fill 1440, ATLAS, fit to y=ae-x/b+ce-x/d

lumireg: a=2.9mm b=-44.5h c=-0.5mm d=1.9h R2=90.0%

lumi+fBCT: a=2.7mm b=-55.3h c=-0.5mm d=3.3h R2=100.0%

0 100 200 300 400 500 6001

1.5

2

2.5

3

3.5

4

4.5

5

5.5

6


em

itta

nce [m

m]

fill 1440, CMS, fit to y=ae-x/b+ce-x/d

lumireg: a=2.9mm b=-36.1h c=-0.5mm d=1.6h R2=63.9%

lumi+fBCT: a=2.8mm b=-61.2h c=-0.5mm d=4.1h R2=100.0%

• compare

– emittance calculated from luminosity + fBCT

– luminous region (average)

• good agreement!


50 ns spaced beam

50 100 150 200 250 3000

5

10

15

20

25

30

time [min]

losses [

%]

fill 1459 - beam 1 - 108 bu/ring

50 100 150 200 250 3000

5

10

15

20

25

30

time [min]

losses [

%]

fill 1459 - beam 2

50 100 150 200 250 3005

6

7

8

9

10

11

time [min]

inte

nsity [

1e10 p

+/b

unch]

fill 1459 - beam 1 - 108 bu/ring

50 100 150 200 250 3005

6

7

8

9

10

11

time [min]

inte

nsity [

1e10 p

+/b

unch]

fill 1459 - beam 2

• fill 1459

• 9 trains of 12– summer to winter time change in the

middle of the fill, some problems with data extraction

• very sudden losses for some bunches– mid-train bunches

• seem due to initial parameters

– had no extra LR

– e-cloud?

• no statistics: only 1 fill!

IPs: 1 5 2 8 - 1 5 8 - 1 5 2 - 1 5 - 2 8 - 8 - 2

tLumi [h] th [h] tv [h]

ATLAS 13.2 153.9 19.7

CMS 12.1 25.9 15.5


a fill with the hump – 1

0 5 10 150

5

10

15

20

25

30

35

40

inst

lum

inosity [

1030cm

-2H

z]


fill 1372

0 5 10 150

2

4

6

8

10


em

itta

nce [m

m]

CMS

ATLAS

x CMS

y CMS

x ATLAS

y ATLAS

• fill 1372

• particularly bad vertical blow up– emittances from lumi region

• clear correlation with instantaneous luminosity slope changes


0 5 10 1510

15

20

25

30

35

40

45

inst

lum

inosity [

103

0cm

-2H

z]


ATLAS published

calc(N1, N

2,

x,

y)

calc(N1, N

2,

x,

x)

calc(N1, N

1,

x,

x)

12

3

4

0 5 10 150

10

20

30

40

50

inst

lum

inosity [

103

0cm

-2H

z]


CMS published

calc(N1, N

2,

x,

y)

calc(N1, N

2,

x,

x)

calc(N1, N

1,

x,

x)

12

3

4

a fill with the hump – 2• difference in integrated luminosity with / without extra V blow up

• 3 calculated curves– with h,v from luminous regions (ATLAS or CMS)

– N1, N2 average intensity beam 1 and beam 2

• integral(3) - integral(2) = 25% (ATLAS) / 27% (CMS)

• integral(3) - integral(1) = 15% (ATLAS) / 18% (CMS)

• 20% integrated luminosity lost due to the hump!


used and requests

• data used for this analysis– machine measurements (always available)

• fBCT: bbyb intensities• single beam lifetime

– from experiments (only for stable beams, in LPC folders)• single bunch luminosities• average luminous region size

– looking forward to BSRT bbyb emittance

• requests for Machine Developments– “hands off” squeezed beams for machine time constants

• few hours for tens of hours time constants?

• and IBS studies?– if after a test ramp… only net time for the measurement

– possibly on a day with no hump

– tune scans! • working point almost never optimized so far

– end-of-fill VdM scans for emittance measurement, bbyb emittance and orbit differences


conclusions• 150 ns spaced beam lifetimes

– luminosity lifetime (~20 h)• decay explained by emittance growth and intensity decay• fast and slow component

– fast component dependence on collision pattern

– intensity lifetime (~90 h)• single beam lifetime is excellent, need a hard number• drops after collisions

– dependence on collision pattern

– emittance grows (x: ~ 30 h; y: ~ 20-40 h)• minimum overlap/orbit drifts

– also verified with end-of-fill lumi scans

• need to look at causes– probably not only IBS

• many fills have different characteristics• fill 1459: with 50 ns spacing, very fast losses• fill 1372: hump caused loss of 20% of integrated lumi

• nb: results are preliminary due to the lack of statistics

Date post:	30-Jun-2022
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