SLD Collaboration Meeting, Chateau La Cresta … OF CONTENTS SLD and Run Status J . Huber SLC and...
122
Work supported by Department of Energy contract DE–AC02–76SF00515. SLD Collaboration Meeting, Chateau La Cresta Saratoga, CA, February 15-17, 1995 SLAC-WP-064
Transcript of SLD Collaboration Meeting, Chateau La Cresta … OF CONTENTS SLD and Run Status J . Huber SLC and...
Work supported by Department of Energy contract DE–AC02–76SF00515.
SLD Collaboration Meeting, Chateau La Cresta Saratoga,CA, February 15-17, 1995
SLAC-WP-064
Volulr
Collaboration Meeting Chateau La Cresta Saratoga, California
February 15-17,1995
Stanford Linear Accelerator Center Stanford, California
I
1
TABLE OF CONTENTS
SLD and Run Status ................................................................................................. J . Huber ........................ SLC and Laser Wireplans ....................................................................................... M . Ross ........................
Polarimetry ............................................................................................................... M . Woods ..................... 143 VXD3 Overview: Schedule, Budget, Progress ........................................................ J . Brau .......................... 173 Mechanical Design ................................................................................................... K . Skarpaas .................. 187 VXD3 CCDs and Related Issues .............................................................................. C . Damerell .................. 197 VXD3 Electronics & Tests ........................................................................................ J . Hoeflich ..................... 223 EndCap Tracking ...................................................................................................... S . Willocq ..................... 239 Software Issues ........................................................................................................ A . Johnson ................... 279
1 53
Polarization Improvements ....................................................................................... T . Maruyama ................ 119 . .
BaBar Detector Plans .............................................................................................. D . Hitlin ......................... 297 NLC Plans ................................................................................................................ C . Baltay ....................... 351
QCD PHYSICS ............... Introduction ....................................................................... P . Burrows ................... 359
Charged Particle Multiplicities in b, c, and uds Events ............................................. H . Masuda .................... 399 Measurement of the b-quark Fragmentation Function ............................................. E . Church ..................... 417 Multiplicity Moments: Comparison with QCD Expectations .................................... J . Zhou ......................... 437 Theoretical Expectations for 'Event Handedness' .................................................... L . Dixon ........................ 467 Experimental Results on 'Event Handedness' .......................................................... T . Maruyama ................ 483
.. Search for g q 9 g Events in the 1993 Data ......................................................... M . Strauss .................... 365
Three-Jet Event Orientation and Tests of Scalar, Vector. and Tensor Gluons ........ H . Hwang ...................... 509 Production Fractions of Pions. Kaons. Protons at the Z ........................................... T . Pave1 ........................ 521 Production of KO, Lambdas in Light.Quark. Heavy Quark. and Gluon Jets ............ K . Baird ......................... 545 Summary and Outlook ............................................................................................. D . Muller ....................... 569
HEAVY FLAVOR PHYSICS ........ Introduction .......................................................... Rb from Lifetime Double Tag ................................................................................... Ab from Jet-charge & MC B Decay Model Improvements ........................................ Ab. Ac from Leptons & Lepton ID ............................................................................. Ac from D*, D+ & 94 Beam Position ........................................................................ Inclusive B Lifetime Summary ..................................................................................
Topological Vertex Finding & Applications ...............................................................
Bd & Bs Mixing with SLD ..........................................................................................
. . ZB +/ZBo Measurement .............................................................................................
Prospect of an Exclusive BS Lifetime Measurement ................................................
TAU PHYSICS ............... Introduction ....................................................................... Tau Lifetime Measurements ..................................................................................... Tau Neutrino Mass Limit ........................................................................................... Anomalous Zn: Couplings ....................................................................................... Study of Trigger Efficiency for Tau Pairs ..................................................................
. . . .
ELECTROWEAK PHYSICS ........ Introduction .......................................................... Parameters of the Standard Model ........................................................................... Progress in ALR Analysis .......................................................................................... Proposal for Measuring Positron Polarization ..........................................................
Su Dong ....................... 579 H . Neal ......................... 585 T . Junk ......................... 613 G . Mancinelli ................. 655 S . Wagner .................... 703
N . Krishna .................... 729 M . Strauss .................... 749
D . Jackson ................... 777
Su Dong ....................... 799 G . Zapalac .................... 817
M . Daoudi ..................... 841 E . Etzion ....................... 845 N . Allen ......................... 883 T . Barklow .................... 903
J . Quigley ..................... 921
P . Rowson .................... 947 M . Swartz ..................... 951 E . Torrence .................. 965
B . Schumm ................... 999
SLD and Run Status
J. Huber
SLD andRun Status
Jenny Huber SLD Collaboration Meeting February 15, 1995 Chateau La Cresta
3 v
-#
4
Outline
1.) Run Status
2.) Detector Systems
3.) Data Integrity
4.) Shifts
G
s1/1 911: 82/21 6W1 01:/21: 1/21 ZZ/T 1 €TI1 1 VI1 1 92/01 LII01
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8
VXD
Ladder w/ preamp connector contact problem South door open Sept 29 to fix short Bad again; Nov 2-Dec 28 left dead OK since Jan '95 (more solid fix w/ plastic wedges separating connectors)
CCDs: 1 extra permanently dead CCD (hot column) 4-5 flaky CCD's (large noise for 30 min-1 day; 1 didn't recover so suppressed since Jan 26)
VABs: 2 incidents of power dip & FB power
868 (0) offline 2s lost
suppy failure -> damaged 33 (10) VABs (multiplexer chips cooked)
Offline alignment: Many FF triplet movements -> headaches VXD geometry between quick, successive moves unreliable => lost -550 Z's for analysis sensitive to impact parameter resolution
E==-- I --
I d=
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23 I SMM INNER RAD BEAHPIPE r I ,--CONE (-Z DIRECTION)
FLAT
LAYER 2--/
LAYER 3
Figure 17. End view of the vertex detector showing the three layers seated in their mounts in the beryllium endplates. Note the shingling arrangement that guarantees complete azimuthal coverage.
12
LUM,
Hardware Status and Historv: 1 dead tower south; outside fiducial region (dead preamp channel, - no effect on Bhabhas).
October '94 = present: 1 south EM1 octant silicon unbiased (Can't fix ground until access silicon; little effect).
Nov 15-22 '94 (after power crash): North LUM noisy.
Jan 3-5 '95 (door opening): No LV to south system+upper daughterbrds (open developed from bad connector+door close).
Future Plans: New LUM Commisioner:Matt Langston 12/94,
New online Bhabha time history plots soon.
Removal of MASiC and LUM after run; reinstall LUM with new cabling, and redesign and build new cooling system (accommodate laser wire).
13
I "
Bhabha Energy Distribution (North detector) 0.12
L
0.06 -
-
- -
0.04 - -
-
- 0.02 -
-
+ before noise - after noise
t
0 10 20 30 40 50 60 70 80 90 ..- . . \ .-
95/02/14 11.53 Matt Langston
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Bhabha Energy Distribution (North detector) 0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
I +
+ before noise - '95 data
I 0 10 20 30 40 50 60 70 80 90
1
95/02/14 13.45 Matt Lancston
15
e
e
1991 ('engineering run')
.fLdt=l4.4&0.5nb -1
1992 total:
/Ldt = 420.86 k 2.56 $- 4.23nb-1
1993 total:
1994 June - December 31 (preliminary):
(post - Sep t: 1 9 6 0.5 ,+ 5.5nb-1)
i 6
7 0 cn w a_ Z I 0 0
>- I-
cr) 0 7
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4
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CDC
Electronics Problems: 1 dead motherboard; (Bi-stable, need to recalibrate to recover)
Some holes in efficiency (northkouth) (No matching pairs of holes; due to boards lifted off pins during various RODS)
Gas Problems: none' Gas prequalified before use during run
Improvements (compare to '93 and early '94) Laser PES system now operating
Dark currents less
No spontaneously tripping layers
New beam dumper module => minimize number of beam related CDC trips
Many more working mother boardkells
18
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EDC
Hardware All 4 chambers up and running. A few HV issues lurking
New CAEN firmware installed to cure (fix exists if problems develop).
readfail problem.
Gas Quite stable. 0 2 levels -60-80 ppm.
Electronics 1 motherboard goes intermittently bad.
Data Full detector readout for energy triggers:
Installed October 1 1994, >Run 28601. Intent: catch tau pair events in endcap (source of stiff, clean tracks).
Backgrounds 50% more hits in random events compared to 1993.
21
CRID
Running smoothly
2 TPC switched off: 1 broke a wire during run 1 faulty right from point of replacement
TPC's opened during Christmas shutdown still have lower ELM lifetime (although on-line information is OK)
New RTH plots show Cherenkov signal!
22
C r i d l i q a n g l e s (CANGLE) #CALLS= 0 19890 5836 D(UND HIST OVR)
3 - I I 1
- <X>=(623d +- 1 6 ) ~ - 4 ' sD=(2281'+- - - - - - - -
2 - - 1 iqui d - - - - - - -
1 - - -
0.0 0.2 0.4 0.6 0.8 1.0 U C h . Angle
Crid gas angles (CANGLE) +CALLS= 0 2 1 2 9 4693 (UND HIST OVR)
1.2
Gcc-S
0.2
0.0 0.00 0.02 0.04 0.06 0.08 0.10
23 Gas Ch. Angle pllr
3.b
DRIFT VELOCITY = f(E/p) -- C. Sirnopoulos
-
/974 :
4.395 1 - i -1
4.390 - I ' " ' ' I ' I I t I 1 I 1
0.524 0.525 0.526 0.527 0.526 0.559 E/P (V/cm)/Torr
E/P __________------------------------------------ In the 1993 run we did not see a s imple correlation, probably due to a nickel filter use.
24
ECCRID
Detectors:
TPC49 is now fully functional
All endcap TPC's taking data for first time since start of SLD
Radiator System:
C4Flo flow increased from 2 Urn to 3 llm per endcap
Future Plans:
Work on TMAE bypass system (in progress)
Need to heat drift gas plumbing on vessel
25
ad
I J
v I . . . . . . . . I
LAC
Hardware status: essentially no change since Dec '94 LAC/LUM review.
High Voltage All OK, no recent problems.
Low Voltage All OK now. One supply died, was replaced. Fans will be replaced on all LV supplies after run.
Dead Channels HV: -290 shorted towers Daughterboard electronics: -370 dead channels (1%); no completely dead preamp and CDU hybrids.
(0.8%).
27
WIC
WIC Strips: GAS
OK now. Had problem with bad connection to Isobutane flow controller.
HV OK. 407 disconnected modules (almost 5%). A few extra shorted modules or bad HV boards.
Strips OK. -1% dead channels. No dead daisy chains (a few need resets).
WIC Pads: 99.3% of channels working w/o problems.
Minor problems: 2 failures of TCM fibre-optic drivers (replaced). 6 hot towers (suppressed in displays). 1 CDM pillaged for LAC (shortage of spare CDMs, replaced).
Backgrounds much higher than 1993 28
Compton Polarimeter Hardware and Operations Status
1. Laser and Optics Systems
i) Laser Svstem - 2 lasers exist--one in operation and one as a spare - replace flashlamps about every 3 weeks - we have swapped lasers 3 times (iune, sept.,jan.)
- first 2 swaps required Spectra to refurbish laser and correct a contamination problem in flow system
- last swap due to a damaged Q-sw Pockels cell - have a continuing unresolved problem with damage
to optics in doubling crystal assembly; often exchange some of these optics when flashlamps are changed
ii) Optics Svstem - in July, August had trouble with damaged optics in laser transport line--in particular with optics at end of the line in the SFF
- in September down, modified system to flow N2 at a low rate and added more filtering (oil, water, particulates) at input
- only one optic replaced since September
2. Cherenkov Detector
- phototubes slowly age and gain decreases during run - one phototube (out of 9) replaced in September
-> plan to replace some or all phototubes during '95 down and add cooling for the detector
3 . Data Acquisition
- Kinetic Systems 2160 driver partially failed in early december. Spare was found to be broken. This driver communicates between the polarimeter microvax and the polarimeter camac crates.
- temporary solution includes: - truncate data list (ex. no PTD, no GCAL, no
- slow laser firing to 1/9 of 120 Hz (was 1/7) - read out only 1 background pulse for every
TDCs)
laser pulse
-> plan to replace polarimeter microvax, driver and camac crate controllers with new system using smart crate controllers in ‘95 down
4. Backgrounds
- have had intermittent problems with bad backgrounds. In particular for channels 1-4; 5-9 much quieter
- this continues to be studied. Have recently added some lead shielding to protect against a possible source from a fixed collimator
30
2 0 v)
J
0 03 a * P4 0 0 0 0 0 0
WHAT’S NEW IN BEL LAND
DATA FLOW System is now fully pipelined and fully buffered. Deadtime is typically < 2.5%. For trigger rates < ~ H z , the deadtime is about - 80msec/readout, i.e. deadtime = 8% at 1 Hz. Bhabha trigger (since it does not readout the wire systems) has, in practice, no deadtime. Improvements have allowed energy trigger to have a full readout.
RELIABILITY Have not had a slave bugcheck in a long time.
Now have 0 - 3 AEB bugchecks per day. Better than
b Any residual slave bugchecks are the result of the AEB
before because ... 0 Additions to AEB ucode’s FASTBUS library, allowing reduced interrupt contention 0 Elimination of some hardware retry logic which
apparently corrupts the inner workings of the AEB 0 General cleansing of the software of low level bugs. Hardware reliability has been very good, particularly after November. 4 CDMs, WSMs & SIs holding up nicely.
corrupting them.
TRIGGERS Have new Bhabha trigger b During clean running, it is close to100% pure. Endcap muon trigger defeated by abundance of SLC muons. Got rid of the veto on the HADRON trigger. Decrease the discriminator threshold of CDC @ reduce inefficiency in the vertical plane of CDC.
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33
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1.10 1.05 1.00 0.95 0.90 0 .85 0 .80 0.75 0 . 7 0
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- - - - - - - - - - -
I
- I 1 1 !
35
Outline
1.) Run Status
2.) Detector Systems
-> 3.) Data Integrity
4.) Shifts
36
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39
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n
good :: POCAz<2cm PV > 0.2GeV
X2/& 5. cos0 < 0.8
20 40 60 Number of Tracks per Event
L - ID IW 2 - Enrrira 40 MEM 17.59 RMS 5.061
0 'E: V 0.08 F -5 'S 0.07
6 0.06
8 0.04 2 rn b 0.05
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0 0 10 20 30 40 Number of Good Linked Tracks per Event
u O 10 20 30 40 Number of Good Tracks per Event
ID la, 0.5 Enrriri M
0.4
0.3
0.2
0.1
- I -0.5 0 0.5 I Number of Good Tracks per Event vs cos0
0
42
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- -
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Number of Linked VXD Hits per Track
0 2 4 6 8 10
Chi2 for CDC+ W f i t
3
2.5
2
1.5
I
0.5
0
I
0.8
0.6
0.4
0.2
0 20 40 60 80 0
Number of CDC Track Hits
Comparison of Impact Parameters for Good Tracks
0.6
0.4
0.2
-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 Signed Impact Parameters(6)
- 1
: - -
- - 1993 datal1994 data 1 - -
1 1 1 1 1 1 1 1 I I I I I I l l 1 I I I I I I I I 1 1 1 1 , I I I I I
44
Outline
l e ) Run Status
2.) Detector Systems
3.) Data Integrity
'-> 4.) Shifts
L
4 .
I.m.0.I
eldoad 40 requrnu
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80
70
60
50
40
30
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0 0 15
S h i f t Point Dis t r ibu t ion in 1993 R u n r
....
....
....
i 1:
Tr
... ̂ .....
...-....
._..__
..
& 30
T-F . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.......... -....
................
--..---*.--- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.......... ̂ __.
..........
..... & 45
. . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..........-... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... ~ ..... ..-- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......... ̂... . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . .
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60 75
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105 120 Total Points
47
S 0
0
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2
48
Ir, 6 c
4 F L
rc 0
Grad Student Shift Participation in 1993 Run ,-.a
SLC and Laser Wire Plans
M. Ross
53
SLC and Laserwire Plans M. Ross, Februaq 15,1995
Performance Summary
Progress made in recent months
Linac long range wakes
Mechanic a1 stability
e+ -> e- crosstalk
Linac quad mounting
IP scan position correction Use of linac BPMs to stabilize deflection scan results
Dispersion-free linac steering
Thermal linac phase sensitivity (?) SLED cavity tuning
Feedback Problems
Spot size optimization between linac and IP
Discrepancy between SLD Z’s on tape and SLC 1 uminosi ty estimator
Damping Rings
Plans for the coming downtime
Laserwire and Other
Reliability and Thermal
1993 Performance
Intesrated Luminositv God:
> 5 0 K Z % -> SLD
Total : > 50000 2' on taPe with 63 % polarization
Flat beam optics S t r a i d lattice cathode
-> 2000-2500 Zo/week on t a D e
Status:
> 700 Zo/dav on tape Best 1992 was 315
4400 Zo/week on tape Best 1992 was 1300
averape 2500 Zo/week
56 N. Phinney 2/13/95
1994 Performance
Integrated Luminosity
Total : - 90000 2" on taDe with 80 % polarization
DR and FF upgrades lo0 nm Strained lattice cathode
Goal:
Status:
> 1500 Z"/dav on time Best 1993 was 122
> 7500 Z"/week on tape Best 1993 was 4400
averace - 4000Z"Iweek
N. Phinney 2/14/95 \Po 57
1994 Run
Polarization Status
Improvements 100 nm Stra id lattice cathode
Ti : Sapphire laser upgraded for higher power Used for E143 and A p l Moller runs
atGun > 8 0 %
Polarization transmission to IP
Extraction line Moller experiment in April
Compton agrees with Extraction line Moller Comparison with Lifnac Miiiller measurements
indicate 1-3% depolarization through Arc
Orbit bumps in Arc =e used to orient spin and reduce depolarization
at IP - 80 a/,
Polarized source status
Accidental gun vent in November - rebuild Vacuum leak on gun vent in May - rebake
Gun 2 (used in 1993) installed on SLC in May Small area cathode but 4.0 1010 OK
Gun 3 (used in 1992) in preparation Large area cathode for > 4.0 10'0 Could be installed mid-run (3 days)
N. Phinney 2/14/95
1994 Luminosity Beam Intensity
DamDine Ring Vacuum Chamber
Successes: “Sawtooth” imta?dhty threshold > 4.5 1010 Shorter bunch length
Problems: Evidence for new, weaker instability > 2.5 1010
Present performance: High-current operation established > 4 1010 per pulse in Damping Ring 3.5 1010 per pulse at IP
Bunch OvercomDression
Overcompression produces tighter energy distribution with
Energy tails clipped in RTL -> 15 % beam loss less tails
Present performance: Energy spread 0.1 - 0.2 % Less background in SLD
Emittances
Stronger BNS damping for higher currents Improved linac alignment
Present performance: Good emittances achievable (4.0 x 0.5 E-5) Beam jitter and emittance stability a proMem
s9 0 N. Phinney 2/13/95
1994 Luminositv
Beam Size
Final Focus ODtics UDerade
Successes:
quadrupoles for fit11 n ~ c h i n g UT wire scanaers #w emi&mce measurement
FT quadruples to reduce 3rd order aberrations FT sextupoles to cancel triplet aberrations
UT
commissioned)
Expected performance: Vertical beam size 0.5 micron Peak 2,-> 10
Problems: Vertical emittance gowth through Arcs
Larger than expected Indepencknt o € b intensity
Vertical beam size measured at TP * 2 too large Position and beam size jitter Problems with measurement technique Possible onset of disruption
Achieved at low current (1010): Vertical beam size < 0.5 micron Peak 2" > 12
Typical values at high current (3.5 10")): Vertical beam size < 1.0 micron Peak Zn > 8 (Average Z n = 4-6)
(to be
N. Phinney 2/13/95 60
I
3 A
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
- m 8 b a I n * 0 a c O
Ill t s cy cy / 1 (Y
Q, Q,
0 0 0 0
0 0 0
0 0 0 d 0 O O
0 0 0 L n v
0 cu
,O 0 0 (0
0 0 0 0 0 0
a2 b
z
100%
90%
80%
709
60%
50%
40%
30%
20%
10%
0%
I SLC UpTime
62 N. Phinney 2/13/95
1992 - 1994 SLC Average Z/hour
70 T P
4 0
30
20
10
0
i h,
1992 1993
f
i
3994
- N. Phinney 2/13/95
1994 Run Schedule Februarv 7 - Mav 31 --> Strict limits on electricity usage
30 Hz, no SLD solenoid On
Commission DR aad FF upgrades + SLC turnon ASSET installation and run - 1-2 weeks FFrBm144nUrs- 3-4 weeks Extraction line Moller runs - 1 week
- e 15
Switch to 120 Hz, SLD solenoid On Tune up luminosity, backgrounds
June 15 - -r 1 SLD Physics Run
Goal: > 50 Z/ hour (peak)
SeDtember
FTTBLE14-4 Run - 2+ weeks 60 Hz limit due to budget
CtObe r - March 15
SLD Physics Run
Goal: > 100 Z/ hour (peak) except 2 week break at Christmas (2 days FFTB)
* -
F'FTBLEl4.4 Run - 1.5 - 2 weeks
N. Phinney 2/13/95
SLC PROJECTIONS
1993 Run %t Beam optics
Average 2SK 2"s / wk
> 5 0 K Z 0 s -> SLD
1994 Run DR vacuum chamber and FF optics
4 month turn-on, 2 month m, 6 month SLD run
Average 4 5 K Zos / wk
> 100 K Z"S -> SLD
Future SLD Runs When full benefit of upgrades is achieved
Possible increase from new DR and FF improvements
Average 8-10K 2"s / wk
250 K zos / 6-7 Month Run
N. Phinney 2/13/95
- E cc
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( W R ELEC)
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16-OEC-94 25166:- -0 DISABLED xa
-1 /4/95
e+Kl'cK e' f(t) = A * sin (2nft) QeE~Lk\w*q n A=-400 mm, f=4142.0, 4144.5 MHz
Time Ins]
Time [ns] 63
Possible Solutions
1 . Less jitter in positrons
2 . Structure:
dimple cell 3,4,5 to reach 4144.5 MHz on average for dipole mode frequency e.g. 4142.5, 4144.5, 4146.5 MHz (down time)
[temperature would effect fundamental mode too much]
3. Different phase advance for electrons and positrons
a) different energy profile(weak)
b) split tune lattice: +/- 3-5 % for focussing/defocussing quadrupoles no resonant excitation-
4 . Expected performance of Split-Tune-Lattice:
a) Reduction of cross-talk by factor of 2-3
b) Chromatic emittance blow-up 5 8 % (mainly Li04)
c) More sensitive to bunch length changes
F 1 N T r n A l . 1
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SLC/SLD Laserwire December 20, 1994
Laserwire Project Staff: D. Amett, R. Alley, E. Bong, S . Davies, J. Frisch, K. Job, M. Ross, M. Scheeff, J. Turner, S . Wagner
The laser-based SLC/SLD Interaction Region Beam Size Monitor is a challenging, ground-breaking project directed primarily toward improving SLC Luminosity.
Outline SLC and its tuning challenges
Why is this device needed and how it will be used
Performance expectations Laser spot sizes
Tolerances Rates
Resolution Components and Specifications
Hardware Technical challenges
The SLAC Linear Collider is unique among operating high energy accelerators in its reliance on (semi) automated optimization.
Intensity 3 . 6 ~ 1010
Continual optimization is required to keep good performance in the face of thermal, mechanical and other instabilities, both short and long term.
Linac Emittance Beam size (a) 3 x 0.3 x 10-5 m-rad 2.2 x OSpm
Most optimization is done online, with minimal or no interruption, using the IP ‘beam-beam
deflection’ luminosity estimator At very low intensities, a 4 p diameter C
wire may also be used
Luminosity from the above: 120 Zo/hr (1984 design 600) 11/94 performance average 55 za/hr with peaks up to 80 - difference due to 30% larger oy Problems with the beam-beam scan:
Inability to attribute changes to e+ or e- 4
Inter-beam roll - tilt in colliding large aspect ratio beams Instability in results of deflection scan
Is beam position or size changing? Inaccuracy of position monitor fits - poor knowledge of IP transverse location
Reduce difference between peak and average Luminosity
88
The IP wire scanner is limited to ‘round’ beams (uX - ~ y ) with I5 0.15 IO
The carbon wire breaks at 1/02 >1 x 1010/2pm2 Minimum measurable spot - 1.4pm (3 x nom.) Tuning and optimization is straightforward Wire scanner technology does not appear to be extendible to higher I or smaller size
4
What will the laserwire do? Measure single beam sizes with an accuracy of 10% to below realizable SLC sizes (0.4pm)
Measurements of position with accuracy SO. 1 pm possible
Allow tuning from ‘wire’ currents to nominal using a single device
Study intensity dependent effects Detailed studies of optics with nominal
input emittances Turn-on after shutdown (upcoming runs
must have reduced turn-on time)
- All other final focus beam diagnostics are in the other direction in phase space
Provide a tool for understanding instabilities
The laserwire is a device that places an ‘optical scattering structure’ inside the SLD/SLC beam pipe about 29cm away from the e+/e- collision point.
The laser spot must have features smaller than or similar in size to the electron or positron beam
e+/e- focus must be moved +/- 29 cm to laser (easily done for wire scanner; 15% of
final lens - IP distance) Not possible to have e+/e- collisions there
Compton scattered photons and e+ or e- are detected as the particle beam is systematically steered across the laser spot on a succession of machine pulses (1 20Hz)
e+/e- shape is reconstructed from the number of scattered particles at each step of
the scan
The laser must pulse at (or near) the full accelerator rate (120Hz) and must be synchronized to the passage of the 0.5mm long particle bunch
The laserwire ‘compton IP’ is inaccessible because of the surrounding SLD hardware
During the coming summer it will be opened for the VXD upgrade - the only
opprtunity to install this device
90
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92
How can the smallest laser spot be achieved? (at fixed A) Start with a diffraction limited laser
High power spatial filter at the source
tight optical tolerances Maintain phase front through transport
Optimize angular divergence at laserwire IP entrance
F#; mode size at final optic Diffraction and steering effects modeled
Which mode (00 or 01) should be used for best performance?
What are the spot’s characteristics? Rayleigh range, ‘tails’, power lost on
defining apertures Since it is easy to switch between 00 and 01, both will be used
How do you know what the spot size is? The power is too high and the spot too small for easy, conventional diagnosis
Our approach is to: understand spot behavior, test at low power and calibrate during operation with electron beam
SOKJlcm2 at focus
Several types of laser spot structures can be generated: (proposed A = 350nm; limited by damage concerns)
Simple gaussian profile wire (00 mode) Smallest size ~ y - A (F2, 99% transmission)
length - 20 A May have tails due to aberrations
Oe from 40Onm up
Easy to generate
Uses optical structures identical to 00 mode Spacing between peaks indicates focus
Sensitive to background May provide resolution down to A/4
(with S/N= 100) Oe from 25Onm to 5oOnm
Fringe spacing W2 Sensitivity from 3L/2 to WlO
Sensitive to background Can be done with retro-reflector
Transverse dipole mode (01 mode)
Interference fringes (Shintake; FFTB)
Oe from 4Onm to 13Onm (below SLC) One device can monitor a wide range of sizes 00 and 01 mode provide an ideal range for SLC 95->
94
Three laser spot structures:
Fundamental '0' Mode Gaussian 'wire'
az= 5Omm
Spherical Retro- reflector with fringe pattern
Spacing U2
Transverse Dipole mode O(m0dL
Y5
. . .
8 ” 1
00 mode spot size as a function of lens system f# and aperture (approximation):
d o = 2 p A for
do = 2 wo ; 99% transmission so for m f2 system; wo - 2h.
nominal spot length (2 Rayleigh range) = 2% 2 ~ r - 2 ~ p 2 A
As incoming size is increased, the IP spot size is decreased slightly but diffraction tails are generated.
01 mode is described by: x2e -xzo2
The spacing between the peaks is 21/20
Electron beam size is estimated using a fit to the convolution of a gaussian and the (known) 01 distribution
Optimum spot can be estimated using the same tools
Rayleigh range correction is required for large aspect ratio particle beams (both for 00 and 01 modes)
I O 3 97
I
E Q) U CA
Laser System Focus (TMO1 LikeBern) Final Optics Final AperJture, radius=3mm
('I'M01 LikeMode)
Fourier Transformer, continued
. - - e G iz
('I'M01 like mode) 90% Transmission Aperature
Fourier Transformer
;@l 01 (Phase Modulated TMOO) 3 @ed
08
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Ratio center/side peaks vs ellaser Sig rat& 1. I
0.9 _ 0 8 ......................................................
.....................................................
.....................................................
x 3
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..........................................................
..........................................................
..........................................................
..........................................................
....................................................
I I
1 0.5 e+/- to laser sigma ratio
.........
(00
I .5
Expected laser spot sizes including errors
Approximation No diffraction, 1% clipping on aperture No diffraction, 10% climing
0 (=20) 70Onm 46Onm
Ideal lens, diffraction a&h& I66Onm Lens ray-trace (on axis) aberrations Lens rav-trace (lo) aberrations
8Onm 22onm
II \ I I
Surface f i m e contribution (estimate) lx1.2 Estimated sDot size for calculations I75Onm The system resolution will scale linearly with the spot size
Expected Resolution: I P&cle Spot size (a) lL&er mode shape00 101
Assuming 10% error in knowledge of laser spot size and 1 % background contamination for 01 mode minimum
Background contamination will depend on detector performance and external sources
Laser IP spot can be ‘calibrated’ using low emittance, low intensity beams
Mknimum expected spot is 300nm Small enough to characterize 01 mode to
10%
4
e x 3 f S 0 u Q
e
F
1 I
- 0 I
0
How are the compton scattered e-/e+ y detected?
Performance with 01 mode depends strongly on contamination other signal sources (background) Monitors: BSM (both sides); Radiative Bhabha luminosity monitor (N) and Compton polarimeter 6)
With one beam only, the background in each of these monitors is quite small
compared to the expected signal of 5K degraded beam particles per 1010 per pm. Signal to noise strengths of 1OOOO:l have
been achieved in other parts of the accelerator (at the end of the linac and at the
entrance to the fiial focusj
1U6
System components:
High power pulsed laser and support controls and utilities. This is to be located on the CEH floor. Transport line to bring light to the laserwire IP 3Ocm from the e+/e- IP on the south side. Internal optics bench with focusing elements, mirrors and diagnostics
Technical challenges
FS In vacuum~5OOOx demagnification optics
High reliability internal optics In vacuum testing required before assembly
No possibility for repair after construction Optical damage issues
Vibration
Precision, stable, internal optical alignment
Rigid, very low mass structure required Extremely cramped regions
Near the end of the triplet and inside SLD CDC
Control of beam EM1 inside SLD
FT Filter
rl Evacuatq Trat?sport
Laser Room
I Schematic 1
E Z 2 D i a g n o s t i C Mirror\
(3 moveable)-
Brewstu angle polarizer for
1 switching x<+y
108
0
\
209
. .
I Q,
Optical Damage Mechanisms ~~ ~
Commercial operation lJ/cm2 at 355nm, 611s (with
lOOmJ/cm2 200MW/cm2 at 355nm; E144 2OOGW/cm2 at 1053nm
scaling) ->
Mechanism Laserwire Expected lOmJ/cm2
1 SOMWcm2
Thermal damage from energy density
Electric field damage from peak intensity
Damage caused by contamination Damage from optical "Ghosts" and sputtering Multi-photon damage *
< 3 ~ ~ ~ j ~ ~ 2 - too low for sputtering <O.lnJ 3rd order ghost
proportional to E2; N shots
* most worrisome effect
I .00E-11
1 .OOE-12
,O 1.00E-13
1.00E-14
5 1.00E-15
0 c
Q
0 1.00E-16
1.00E-17
Nonlinear damage rate
0 2 4 6 a
Measureddamagerates
A Commercial YAG laser
0 Required damage rate
photon energy in ev
114 H
J 41 I m
1
I
Cavity mimx R-2480mm
Pockels Cell (electro-optic switch) T
Regene rat ive Amplifier Layout
1/4 wave plate
Optical cavity length 1 26mm, (1 1 9 MHz).
Brewster polarizer
Mode-matching telescope
Faraday rotator (isolator)
1/4 wave plate
doping
(diffuse)
Telescope for thema1 .,,$. lensing compensation .. .. >ss;;;... 'V( *. .-...... ................... ......... I :?!?!?TY%c ...... .. ...... ....
Output -5mJ
116
I
2
I 1 ' 1 U
Conclusions: The goal of a 10% measurement should be achievable with both 00 and 01 laser spots Challenge is to construct a reliable, long lifetime device
Laserwires for NLC +
Timing wide dynamic range/thickness
other, parasitic, laser uses
cost systematics from laser spot aberrations
High power required
Should be ubiquitous in NLC ring->linac ->FF systems
Simple system for DR
