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

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Effect of beam energy spread

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) ??


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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)


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Energy Spread Study

  • 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


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NLC-500 Results

Tail

Head



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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


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  • 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)


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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)


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Comparing “kink instability” for e-e- at NLC-500, TESLA-500

e-e-

e-e-


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“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-


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e+e-

(NLC-6)

Outgoing e-

Outgoing e-

Lumi-wted

ECM

Outgoing e-


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e-e-

(NLC-6)

Outgoing e-

Outgoing e-

Lumi-wted

ECM

Outgoing e-


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Y Deflection Scan

(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


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Y Deflection Scan

(luminosity)

NLC-6 e-e-

TESLA-6 e-e-

NLC-6 e+e-

TESLA-6 e+e-


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Y Deflection Scan

NLC-6 e-e-

NLC-6 e-e-

Maximum luminosity occurs at

zero deflection angle,

not zero offset


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Summary

  • 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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