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ISS meeting UCIrvine 21 August 2006 Alain Blondel 1 Evaluation of « optimal » segmentation for neutrino factory far detectors A. magnetized iron sampling calorimeter for muon charge measurement (not too controversial) B. segmented fine grained detector with external magnetic field (ex: LARG, ECC, TASD) for electron charge measurement (very very approximate) caution: results obtained with analytic formulae and some approximations. Determine scaling laws outlines issues (and initiate discussion) Excel Worksheet ==> can be updated online.

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ISS meeting UCIrvine 21 August 2006 Alain Blondel 2 muon charge measurement in magnetized iron sampling calorimeter

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ISS meeting UCIrvine 21 August 2006 Alain Blondel 3 curvature curvature error due to measurement curvature error due to multiple scattering We have a system with N planes of iron of thickness t and density d interspaced with N planes of scintillator of thickness t’ and density d’ of point measurements with precision tracking formulae from PDG

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ISS meeting UCIrvine 21 August 2006 Alain Blondel 4 The average density is d0 = (d.t+d’.t’)/(t+t’) The equivalent average energy loss Ê such that Ê0 (t+t’)d0 = Êtd+Ê’t’d’ Ê0= (Êtd+Ê’t’d’) /(dt+d’t’) The average magnetic field is B’’ = B iron t/(t+t’) The average radiation length is (t+t’) /X’’ = t/X iron + t’/X scint he total length of detector is N(t+t’) and mass is A*N(t*d + t’*d’)

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ISS meeting UCIrvine 21 August 2006 Alain Blondel 5

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6 Results A. resolution as a function of momentum t = 1cm iron t’= 2cm scint B= 1.4 T space resolution= 1cm t = 10 cm iron t’= 2cm scint B= 1.4 T space resolution= 1cm Notes: improvement with high momentum comes from number of points on longer tracks. MS always dominates. Range measurement not used.

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ISS meeting UCIrvine 21 August 2006 Alain Blondel 7 resolution as a function of iron plate thickness (t’=2cm) Best is [ P/P ~37% at 1 GeV] for 2-3 cm plates. remains within 10% of this for 1

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ISS meeting UCIrvine 21 August 2006 Alain Blondel 8 electron charge separation

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ISS meeting UCIrvine 21 August 2006 Alain Blondel 9 Electron charge separation Assume a fully active medium (Larg or TASD) with a given two-track resolution ’. The tricky question is to evaluate the probability that the tracking software is confused by secondary photons and cannot follow the primary electron in an electromagnetic shower. Gimmick: an electron will get confused if a HE photon (k >= E/3) materializes within a transverse distance less than ’ of the primary electron. Then in addition the track measurement resolution must be better than about 40%-50% over this length.

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ISS meeting UCIrvine 21 August 2006 Alain Blondel 10 The typical length for radiating one photon with k> kmin = f.E is d1 ~ X0 / F(f) PDG: F(f)= N ( d=X0, kmax=1, kmin= f.E) for f=0.3, F(f)= 0.29 Typical distance for materializing is 9/7 X0 ==> the typical length is L 0 = X0 (9/7+1/F) ~ 4.7 X0 and the typical distance from the primary electron track will be = L 0 2 /2/R = L 0 2. B. 0.3/2/E which has to be compared with ’ this is the critical number!

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ISS meeting UCIrvine 21 August 2006 Alain Blondel 11 If we wish to measure the sign of a significant electrons up to an energy Emax, B must be such that = L 0 2 /2/R = L 0 2. B. 0.3/2/Emax > ’ or B >~ 2 Emax ’ X0) 2 The fractional resolution over this distance will be given by the previous formulae for tracking over this distance ! careful that this means that a fraction of electrons of energy Emax will be measurable (typically 1-1/e = 30%)

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ISS meeting UCIrvine 21 August 2006 Alain Blondel 12 What Emax? I will take Emax = 10 GeV as it is sufficiently large to cover the first oscillation maximum (5 GeV at 2500 km) with good resolution and efficiency.

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ISS meeting UCIrvine 21 August 2006 Alain Blondel 13 Results 1. TASD with scintillator (X0=43 cm) 1 measurement every t’= 3cm point resolution epsilon = 1cm two track separation epsilon’= 3cm 2. AIR-TASD of variable fraction f of length occupied with scint. same assumptions as above t’=3cm/f X0=43cm/f 3. Liquid Argon (X0=14cm) 1 measurement every 3mm point resolution 1mm two track separation 3mm or whatever number we would like to have above.

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ISS meeting UCIrvine 21 August 2006 Alain Blondel 14 1. TASD with scintillator (X0=43 cm) 1 measurement every t’= 3cm point resolution epsilon = 1cm two track separation epsilon’= 3cm B needed for meast at 10 GeV is 0.52T resolution dominates badly.

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ISS meeting UCIrvine 21 August 2006 Alain Blondel 15 2. AIR-TASD of variable fraction f of length occupied with scint. same assumptions as above resolution = 1cm, ttsep = 3cm t’=3cm/f X0=43cm/f f= 0.5: B-Field required for meast at 10 GeV is 0.13 T and this scales as 1/f 2 resolution still dominates

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ISS meeting UCIrvine 21 August 2006 Alain Blondel 16 3. Liquid Argon (X0=14cm) 1 measurement every 3mm point resolution 1mm two track separation 3mm B = 0.49 T for measurability of electrons up to 10 GeV good match MS-resolution MS dominates slightly

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ISS meeting UCIrvine 21 August 2006 Alain Blondel 17 A better TASD would have better two track separation and resolution -- suppose we could improve these numbers by factor 2? result: B(10 GeV) required for full TASD is 0.26 T B(10 GeV) required for 50% TASD is 0.065 T etc… ex: 50% TASD ttsep=1.5cm res=0.5cm B=0.065T much better matched!

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ISS meeting UCIrvine 21 August 2006 Alain Blondel 18 Main conclusions magnetized iron-scintillator detector -- fairly reliable results -- MS dominates, and -- the thickness of plates need not decrease below ~2-4 cm Electron charge ID -- not very reliable results: assumptions about ability of tracking program to follow an electron in the shower -- scaling law B >~ 2 Emax ’ X0) 2 -- assumptions on resolutions etc… need to be checked -- for air+f.TASD, B scales down as 1/f 2 -- TASD: better resolution would pay off quickly -- Larg: seems well matched for B field~0.5 T

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