3 Improved analysis At last collaboration meeting 87.6% of background was rejected for 200±20 MeV/c beam at 99.9% signal efficiency. Since then, hard work has gone into improving fits and analysis. –Also some changes to geometrical setup. EMCal closer to TOF2. Both detectors wide enough to catch all muons. TOF2 4 cm thick. Now: Diffused Aug’05 beam gives 99.0% background rejection at 99.9% signal efficiency. I.e ~12 times as low miss identified background! –40-50 times more powerful than basic requirement. –More on this during analysis session.
4 Purpose of the calorimeter The EMCal is not necessarily used to measure energy! Main objective: –Provide separation capability between muons and decay positrons. Secondary objectives: –Separate muons from other form of background. Pions X-rays Electrons –Give independent information on particle momentum. Through range, barycenter, energy etc.
5 Design principles Relative energy resolution gets worse with lower energy. For high energy, resolution is lost by energy leakage. –Longitudinal leakage is worse than transversal. -> Increase dE/dx by inhomogeneous designs. (sampling calorimeters) ATLAS
6 Sampling calorimeters Sampling fluctuations dominate energy resolution! For best energy resolution, the passive material should 1.be as thin as possible 2.be made of as high Z material as possible U excellent, Pb more practical. Problem with channeling. H1 SPACAL
7 Sampling vs non-sampling If energy is low: –More sensitive to sampling fluctuations. –Range is shorter. If the shorter range allows leakage prevention with a homogeneous (non- sampling) calorimeter, it will give better energy resolution. MICE is not a HEP experiment!
8 EMCal Back end, layer 1-10, of EMCal Sandwich design is non sampling, fully active. Front end, layer 0, is sampling (lead & SciFi) to induce EM showers for electrons. –Low energy muons get stuck in layer 0, and if pure lead we would not have any information on their energy.
9 Few words on EMCal analysis More than only energy reconstruction. For example: –Looks for Bragg peak, compare with track parameters. –Looks for how continous the signal is to the Bragg peak. –Barycenter. –Two TDC peaks means muon decay @ t<t_gate.
10 Longitudinal size Layer 0 –4cm thick which is appropriate for showering electrons without losing too much energy of muons. Layers 1-10 –In total 70 cm thick, which makes longitudinal leakage small.
11 Longitudinal segmentation Normally muons are stopped in EMCal. –No energy leakage gives good energy resolution. –Range and barycenter become powerful tools for PID. Range resolution is dominated by thickness of layer at stopping position / track length. –Use thinner layers in the front. Rates are higher in the front. –Again, use thinner layers in the front. With layer thicknesses 1,2,3,4,6,8,10,12,12,12 cm
12 Transversal size Calorimeter should capture any muons which 1.Are contained within tracker active volume. 2.Are hitting TOF2. 3.Are within momentum region of interest. –(= good muons) In addition, question have been raised about muons hitting cryostat after tracker. End Coil 2 Estimated positions
13 Transversal size Not meaningful to define calorimeter transversal size before size of TOF2 is defined. –However results already existing give a good notion. TOF2 PMTs need shielding from magnetic fields. –So could also be the case for calorimeter. –Double shields help for TOF2, and this option has also been examined for calorimeter. –As next slides show, a split design (to allow for 3 rd shield) would require a larger calorimeter.
15 Full phase space beam, non split 63 k events
16 Transversal segmentation I have kept the number of channels fixed to the KLOE light design proposal (240 channels). With 10 plastic layers, that gave 9 cells per layer. Studies suggest full width of calorimeter should be ~1 m. –Each cell is ~1 dm high.
17 Summary Refined analysis shows dramatically improved performance. Calorimeter design has been tailored for special MICE conditions. Longitudinal size and segmentation chosen with muon range and momentum in mind. Transversal size needs decision on TOF2 size to be finalized.