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Where Machine and Detector Meet
APS/DPF Joint April Meeting April 5th, 2003 Philadelphia

Eric Torrence University of Oregon Special thanks to Tom Markiewicz
http://physics.uoregon.edu/~torrence/talks/
Eric Torrence 1/29 April 2003


Interaction Point Detector View

Machine View

Eric Torrence

2/29

April 2003


IP Requirements

High Luminosity · Stability · Instrumentation · Crossing angle (NLC/JLC)

Background Protection · Collimation · Shielding from collision products · Extraction to dump

Collision Properties · Polarization · Beam Energy · Luminosity

Large overlap between traditional detector, accelerator, and analysis camps...
Eric Torrence 3/29 April 2003


IR Geometry

Tesla Design
· Short focal length (L* ~ 3-5 m) · Large conical mask (~ 50 mRad) · Integrated instrumentation
Eric Torrence 4/29 April 2003


Beam-Beam Interactions Tesla 500 N x y z 2.0 â10 5 nm 300 µm
10

NLC/JLC 500 0.75 â10 3 nm 110 µm
10

550 nm

250 nm

Beams strongly attraced to each other! y

z · Spot size reduced (higher lumi ~ x2) · Outgoing beam highly disrupted · Pinch produces `beamstrahlung' photons
Eric Torrence 5/29 April 2003


Beamstrahlung Beamstrahlung Photons Outgoing `Beam' NLC 1 TeV · · · · N/Ne ~ 1.5 E /Ebeam ~ few percent confined to 1 mRad cone secondary e+e- pairs

Charged Particles · Long E tail after IP · Radiative Bhabhas · Beam-beam pairs 77 kW E < 50% Enom 4 kW lost (.25%) to dump (NLC 1 TeV)
Eric Torrence 6/29 April 2003


Detector Backgrounds

IP Backgrounds · Disrupted primary beam · Beamstrahlung (BSL) photons ·e+e- pairs from BSL s · Hadrons from BSL or · Neutrons from e+e- pairs · Radiative Bhabhas These scale with Luminosity (Good) Shield from detectors

Machine Backgrounds · · · · Neutron back-shine from dump Synchrotron radiation Muon production Collimator scraping These don't scale with Lumi (Bad) Avoid near IP

Eric Torrence

7/29

April 2003


e+e- Pairs

PT from opposing bunch

pairs `curl up' in large solenoid field

NLC Simulation

must absorb without scattering into detector...

Eric Torrence

8/29

April 2003


Pair Simulations

Tesla Simulation ~ 1 â10 per second (1 Watt) Pairs also make good monitor of luminosity and collision parameters...
Eric Torrence 9/29 April 2003

9


Other Backgrounds Two Photon

Barrel

Endcap

Mask

~ 0.5 hadron events/NLC train average 6 GeV in barrel + endcap, 10 tracks ~ 30 GeV in forward mask... Neutrons · Expect 0.5 â10 n/cm2/yr at VXD (NLC SD) · Dominated by beam-beam pairs · Small backshine from dump Tolerate 3 â10 n/cm2/yr for pixel detector
9 9

Eric Torrence

10/29

April 2003


e+e- Electroweak

had [nb]



0

40
ALEPH DELPHI L3 OPAL

30

20
measurements, error bars increased by factor 10



Z

10

from fit QED unfolded

M

Z

86

88

90

92

E
· mZ , · mW · sin
2 Z

cm

[GeV]
Lumi

94

(LEP I) (LEP II) (SLC)

Energy Energy

w

Polarization

Dependent upon Beam Instrumentation
Eric Torrence 11/29 April 2003


Physics Beam Instrumentation

Beam Energy · Absolute energy scale · Beam energy width Polarization · Electron polarization scale · Positron polarization (if available) Luminosity · dL / dE (luminosity spectrum) · L dt (total integrated luminosity) Ensure instrumentation for physics needs!

Combination of beam-based and physics-based measurements!
Eric Torrence 12/29 April 2003


Beam Energy at LEP II Production Threshold
[pb]
WW

LEP
20
RacoonWW / YFSWW 1.16

Preliminary

15

10
18

YFSWW 1.16 RacoonWW

5

17

16

0

160

170

180
E
cm

[GeV]

190

200

210

Kinematic Fits

3500 3000 2500 2000
Hadronic Mass

WW

qql

2C Kinematic Fit

1500 1000 500 0 40 50 60 70 80 90 100 Invariant Mass (GeV) M W E Beam ------------ -----------------MW E Beam
April 2003

Common Scale Uncertainty
Eric Torrence 13/29


Beam Energy Energy Needs · Target 200 ppm from 2 m t < s < 1 TeV m t , m H ~ 50 MeV · Recognize desire for < 50 ppm at 2 m
W

Improved precision always welcome...

Energy Proposal · BPM-style at upstream 1mRad bend RT monitor, possible absolute scale · WISRD-style at post-IP chicane RT monitor, possible absolute scale Energy width? · Forward tracking 200-500 mRad Lumi-weighted absolute scale ( µ + µ - )
Eric Torrence 14/29 April 2003


BPM Spectrometer LEP II Spectrometer
Quad
Wire Position Sensors

Steel Dipole

Synchrotron Absorbers

Quad

BPM Pickups

NMR Probes 0m 10m

· 4.8 mRad Bend 1 µm BPM resolution · Stability maintained for less than 8 hours ~200 ppm achieved (relative) RF Spectrometer
RF BPM Triplets ~1 meter

· 200 µRad Bend < 100 nm BPM resolution · Move the BPMs to the beam · In situ alignment Upstream of IP only!
Eric Torrence 15/29 April 2003


Meet the WISRD
Spectrometer Magnet Quadrupole Vertical Doublet eHorizontal Bends for Synchrotron Radiation

E

beam

l = -- B dl x



Dump Synchrotron Light Monitor

e+



B dl = 3.05 T m

l = 15 m x = 27 cm at 50 GeV

Operated for 8 years ~250 ppm achieved NLC Questions · Improved detector? · Downstream operation? · Energy distribution? Photon Rate 1/E In Collision Out of Collision

Transverse Position
Eric Torrence 16/29 April 2003


Radiative Returns at LEP f e+eff f
Number of Events / 1 GeV
Data qq M.C. reweighted M.C. background 183 GeV Data MZ = 91.172 ± 0.098 GeV

1 2

sin 1 + sin 2 ­ sin ( 1 + 2 ) s' -- = -----------------------------------------------------------------------sin 1 + sin 2 + sin ( 1 + 2 ) s

Statistics
Channel Ebeam

L3

300

qq µµ ee

~ 18 MeV ~ 40 MeV ~ 70 MeV

200

LEP Potential Statistics Only 2.7 fb-1

100

0 70

80

90

100

110

m

inv

[ GeV]
Estimates Ebeam ~ 70 MeV Ebeam ~ 20 MeV Ebeam ~ 80 MeV
April 2003

Systematics
· Theoretical Description · Hadronization Uncertainties · Detector Understanding Need absolute measurement!
Eric Torrence 17/29

Opal qq µµ ee


Radiative Returns at NLC
cos 1 0.9 0.8 0.7 0.6 0.5 200 300 400 500 600 800 1000 Collision Energy (GeV)
2 Symmetric production: s = m Z , 1 = 2

e+eµµ

1 2

Collision Energy 2 mW 2 mt 500 GeV 1 TeV

cos 0.522 0.875 0.937 0.984

(mRad) 1000 500 360 180

Need precision and accuracy at small 0. 1 % per event ( Z limit) 100ppm accuracy (20 µm @ 2 meters)
Eric Torrence 18/29 April 2003


Polarization Physics

Process WW qq ll

Events per 80 fb-1 560 k 250 k 120 k

ALR 99% 45% 10%

dA // A

(stat) in % 0.07 0.5 3.2

Also WW background suppression, SUSY, new physics, etc.
Eric Torrence 19/29 April 2003


Polarized Positron Physics Slepton Production e e
-

Z/
+

~ e ~ e
L

e e

- +

~

~ e
0

~ e

~~ s-channel: e L e ~~ t-channel: e L e

or

R

~ e ~ and e

RR RL

~ e ~ e

only also

1000

1000

100

100

10

10

-1

-0.5

0

0.5

1

-1

-0.5

0

0.5

1

[G. Moortgat-Pick, H. Steiner, 2000]

Unique manipulation of helicity states

Eric Torrence

20/29

April 2003


Compton Polarimetry
532 nm Frequency Doubled YAG Laser e­ Mirror Box Pockels Cell Left or Right Circularly Polarized Photons Focusing and Steering Lens Mirror Box (preserves circular polarization) Compton Back Scattered e­ Analyzing Bend Magnet
1-93 7268A1

e+

SLD e­ Laser Beam Analyzer and Dump "Compton IP"

Cerenkov Detector Proportional Tube Detector

Multiple Detectors ·ãerenkov counter - scattered e- asymmetry · Photon counter - integral E asymmetry · Quartz fiber calorimeter - transverse asym.

Unique systematics help reduce errors P / P = 0.5% achieved at SLD
Eric Torrence 21/29 April 2003


Polarization Precision Electron polarization only · absolute scale limiting factor · IP depolarization significant Lum Weighted != Polarimeter 0.25% per beam possible (not proven)

Positron polarization also
P
eff

= ( P+ + P- ) / ( 1 + P+P- )

0.1% precision achievable Blondel scheme gives lumi-weighted P+, PLL RR LR RL 10% `wrong'

90% `correct'

· Lose some luminosity (or don't gain as much) · Still need = P L ­ P R , relative Lumi · Precision depends upon P+ reversal freq.
Eric Torrence 22/29 April 2003


Direct Polarization

W

Z/



W W

W

= 7 pb at s = 500 GeV
A
LR

1

0.8

s = 800 GeV

0.6

= 1.007 Z = 1.01 SM

0.4

-1

-0.5

0

0.5

1 cos

[K. MÆnig, Snowmass 2001]

P / P < 0.15 % for 500 fb-1 at 500 GeV (9/1 L ratio) Similar with e- pol only
Eric Torrence 23/29 April 2003


Beyond ISR
1 350 GeV Machine + ISR + Beamstrahlung + 0.3% Linac

10

-1

NLC Simulation Gaussian energy spread Core

10

-2

Tail
10
-3

10

-4

300

310

320

330

340

350

360

Collision Energy (GeV)

Highly dynamic distribution... Linac energy spread dn / dE


E
Eric Torrence 24/29 April 2003


Physics Example tt
1.00 Bare (Peskin+Strassler, m = 174.0 GeV, = 1.42 GeV, = 1) +ISR 0.75 +Beamstrahlung +Linac
(tt) (pb)

0.50

0.25

0.00 335

340

345 2*Ebeam (GeV)

350

355

[D. Cinabro]

Flat tail + Gaussian core R = A

tail

/A

core

dm t / dR = 40 MeV / 1% d t / dR = 100 MeV / 1% Comparable to other systematics
Eric Torrence 25/29 April 2003


The Uncertainty of it all

Key Reactions · Threshold scans (top mass) · Mass reconstruction (Higgs mass) Plus many, many more...

Highly dynamic distribution · Variance: increased statistical errors · Uncertainty: increased systematic errors Both need consideration

Rough physics needs · Scans mostly need shape (tails to 1%) · Mass analyses need mean s' (200 ppm)

New instrumentation problem for e+eEric Torrence 26/29 April 2003


Bhabha Acolinearity 1 s' / s 1 ­ -- -----------2 sin 0 Bhabha rates · Forward · Intermediate · Barrel (180-300 mRad) ~ 200 R (300-800 mRad) ~ 100 R (> 800 mRad) ~ 8R
s'

0 E b / sin
0

Need rates from forward events, but not too far forward... Forward Tracker (Tesla design)
TPC SIT VTX
50cm 100cm

Pixels

25

o

30cm

Strips
7
o

20cm 10cm 150cm

Silicon planes 100 - 400 mRad
Eric Torrence 27/29 April 2003


dL/dE concerns Acolinearity Limitations · Bhabha analysis measures boost not s' · Other inputs (e.g. energy width, asymmetry) · Detector alignment systematics Area of active study...

Beamstrahlung Correlations · Dispersion effects · Early-late correlations · Banana tail effects

Higher L, less tail

Lower L, more tail

Can't trust simulation alone... Need data-tuned models integrated into generators
Eric Torrence 28/29 April 2003


Summary

The Linear Collider Interaction Region must be carefully planned between accelerator, detector, and analysis-minded people.

New challenges exist for the LC environment · · · · Nanometer-sized beams, IP stability Large beam disruption Large e+e- pair background Uncertain luminosity spectrum

Old challenges for e+e- also exist · Beam energy/width · Beam polarization · Absolute luminosity scale

Lots of interesting work going on NOW! Plenty of work still to be done...
Eric Torrence 29/29 April 2003