Measuring the Luminosity Spectrum Bhabha to the rescue! • Why? • Detector-based measurement • Beamline spectroscopy • Goals Both essential
TESLA TDR parameters, 350 GeV Beamstrahlung Initial State Radiation BHWIDE Machine spread Beamstrahlung CIRCE s/2Eb Why? The LC is not like LEP calculable how to measure? p/p0.1%, TESLA 0.3%, NLC/GLC; nongaussian, with jitter and timewalk? how to measure?
Physics Needs TDR, Black Book, JLC report all claim we can do:- * mh 100 Mev, using beam energy constraint. * mt < 100 Mev, from threshold scan. * And we want mW 6 Mev, at GigaZ. Needs p/p to a few 10-5. The job after next! Needs p/p to a few 10-4 QCD systematicsmt theory ~50 MeV. Experiment must match, ormt dominates EW precision measurements [Heinemeyer et al (hep-ph/0306181)].
current MW Why mt < 100 Mev? Heinemeyer et al (hep-ph/0306181) LC’s precision programme!
A , small A p+ BUTwhile p- Calorimetry to >1%, Not good enough! Acollinearity to <10-4 Detector-based part Reference process should: 1. be based on real events – to represent the physics samples. 2. have better statistics than the physics channels. 3. have energy resolution to match the mass resolution required. Measurement of Bhabha acollinearity in the endcap region ( milliradians) meets all 3 criteria. Nothing else does (, Z rates ~ physics rates; Z less use at high √s) Basic Principle
First Results from acollinearity method (Boogert, Montpellier, BDI and top sessions) Shift from true mean x to reconstructed mean x. Reconstruction assumes only 1 gamma lost along beam. Will improve with unfolding; to ~10-4. (Next job) Modelled correlation effects, c.f. Boogert/DJM Jeju note. Much more to do, but we have the tools (Guinea Pig and detector simulation) and the effort (PPARC willing). (Finite crossing angle also seems manageable to ~10-4)
Effect on top threshold First attempt at fit gives shift of ~40MeV in mt. Much more to do, but we have the tools (Guinea Pig for beam-beam, Brahms detector simulation, Topik for tt ). (Finite crossing angle also seems manageable to ~10-4) Bhabha acollinearity looks as if it will work to ~10-4
Need Spectrometry too! 3 kinds:- • Energy jitter (~0.1%) in real time; measure to 10-4. Match to Bhabha events. • - Absolute average energy to 10-4 for mt (10-5 for MW). Check with e+e-Z. • Shape (non gaussian) of lumi-weighted energy spread.
Absolute and Jitter Spectrometer Mike Hildreth suggesting “bump” spectrometer insert, upstream, in BDS. Reverts to straight-ahead when currents turned off. Blue discs are bpms on precision movers. Follow the beam as it deflects. Picture is LEP version. LC longer(P.T.), more, smaller bends Tradeoffs - bpm bandwidth - bpm resolution - length of insertion - bend angle Jitter within train? Emittance dilution urgent. Do precision RF bpms work in a beamline? Will only find out if we try.
Spectrometry, continued Spectral Shape Measurement * Synchrotron swathes from a pair of bends (downstream only, like SLD WISRD?) * Laserwire at dispersed focus for spectrum, maybe even upstream so could use all the time, not just pulse sampling? Building a collaboration for beam tests Talking to Mike Woods(SLAC), Mike Hildreth(Notre Dame), Eric Torrence(Oregon), Stan Herzbach(Amherst), David Ward(Cambridge) about a test-beam campaign using SLAC End Station A. Heinz-Jurgen Schreiber(Zeuthen) and collaborators have DESY based plans. All of us striving for funds to do proper experiments.
Goals We need a well engineered spectrometry design before the Beam Delivery System is finalised. It would be wise to prove we can measure mt and mh to the claimed precision before funding agencies send referees to check in 2006, ahead of final approval. So we had better start the spectrometry tests soon to match progress on Bhabha acollinearity. We will also need a strategy for p/p~10-5 measurements before anyone will fund a GigaZ upgrade. There are not enough of us; happy if Asia can join in.