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Effect of beam energy spread on precision measurements of m t and m H

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on precision measurements of mt and mH

Cornell University

July 13-16, 2003

- Beam instrumentation goals
- Top mass: 200 ppm (35 MeV)
- Higgs mass: 200 ppm (25 MeV for 120 GeV Higgs)
- W mass: 50 ppm (4 MeV) ??
- ‘Giga’-Z ALR: 200 ppm (20 MeV) (comparable to ~0.25% polarimetry)
- 50 ppm (5 MeV) (for sub-0.1% polarimetry with e+ pol) ??

The beam energy spectrometers measure <E>,

but for physics we need to know <E>lum-wt.

Effect I am considering today is the beam energy spread.

At NLC, s(E) ~ 0.3% rms, and at TESLA it is ~ 0.1% rms.

(3000 ppm) (1000 ppm)

- MatLIAR-generated files from Andrei Seryi
- LIAR+DIMAD+Matlab used to generate files
- Tools developed by NLC Accelerator physics group
- Files were used for TRC studies
- They were obtained with non-perfect machines:
- LCs were initially misaligned and then brought
- back to ~nominal luminosity by one-to-one
- correction in the linac.
- generates distributions of incoming beams at IP
- 6 files each for NLC-500 and TESLA-500 machines
- Electron and positron beams are symmetric;
- ie. similar spotsizes, bunch lengths, charge
- Guinea-Pig simulation
- ISR and Beamstrahlung turned off
- electron.ini and positron.ini files from MatLIAR simulation
- beam1.dat and beam2.dat files for outgoing beam distributions
- lumi.dat file for distribution of particles that make luminosity

Summary of Results for energy spread effect

Note: energies are given in units

of ppm, ie. the deviation from the

nominal energy, for example:

E1, E2 and Ecm all come from

The Guinea-Pig file lumi.dat

~500ppm effect for NLC

~ 50ppm effect for TESLA

Kink instability is dominant cause for energy bias effect

- tail of the bunch is disrupted in y
- energy-z correlation of the incoming bunches exacerbates effect

- Can consider collision of opposing bunches to be:
- head-head collisions (high ECM)
- head-tail collisions (nominal ECM)
- tail-tail collisions (low ECM; lower luminosity due to disruption)

- Why effect is larger for NLC than TESLA:
- large E-z correlation results from having to reduce
- wakefields in the warm machine by performing a phase
- space rotation to shorten the bunch length and increase
- the energy spread
- large energy spread (for same reason to mitigate wakefields)

Comparing “kink instability” for e+e- and e-e- at NLC-500

e+e-

e-e-

(NLC-G has beam parameters

with uncorrelated,

gaussian distributions)

“kink instability” for e-e- at NLC-500; effect of E-z correlation

- With E-z
- correlation

e-e-

2. Without E-z

correlation

(made z dist’n

uncorrelated with

120 mm rms)

e-e-

(deflection angles)

NLC-6 e+e-

TESLA-6 e+e-

NLC-6 e-e-

TESLA-6 e-e-

‘sharp’ deflection curve will make beam-based

feedback/feed-forward difficult

NLC-6 e-e-

NLC-6 e-e-

Maximum luminosity occurs at

zero deflection angle,

not zero offset

- Kink instabilityreduced luminosity
- bias in energy determination
- - large for e+e- at NLC due to large
- E-z correlation and large espread
- - large for e-e- at both NLC and TESLA
- minimizing deflection angle reduces effect

- Energy bias for e+e- collisions at NLC is ~500ppm
- large compared to desired precision on energy determination of <200ppm
- need to understand associated systematics and compare to other sources
- need to see if 500ppm effect can be reduced

- For e-e- collisions at NLC and TESLA
- deflection scans indicate that beam-based feedbacks will be difficult
- need to find more optimal collision parameters than those used for e+e-

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