April 1 Minutes

Mikhail's Slides
Mikhail showed results from a study whose goal was to see what kind of things must be changed in order to get a target which could survive 2MW of proton power. For two interaction lengths of solid material with a 1mm sigma (in x and y) proton beam, the temperature change due to the beam was too high. But by increasing the beam spot size to 2.5 or 3mm, and increasing the target transverse size also to something like 3 times the beam sigma, then the target can survive, or at least the temperature rise is much lower and the target won't break, or submilmate. The pion yield (for 6-7 GeV pions) per unit proton power doesn't change by more than about 10% for this modification. For the record, the temperature for the shock wave limit is 2200-2400 degrees C, and the sublimation temperature is 3600 degrees C (I think this is for graphite). The graphite-graphite composite material only survives up to 1600 degrees C. This study is promising, and Fritz asked if a cooling scheme was included in this study--it hasn't, but the study does indicate that perhaps the cooling requirements will not be too tough, although some cooling will be necessary. It was also suggested that Mikhail look into beam sweeping.
Mayda Velasco's Slides
http://lotus.phys.nwu.edu/~mvelasco/april_1/ This talk showed some of the optimization studies (optimizing L/E...looking at results from different L's or different E's) that Mayda and Michal have done, using the geant-based NUMI beam monte carlo. Michal's talk (described below) optimized the signal reach by increasing the signal efficiency at the expense of background rejection, and by putting air between the various layers of steel and scintillator. On page 6 of this file you can see a summary of the different beams considered: 10km off axis at 735km, 12.5km off axis at 735km, 11.5km off axis at 900km, and the last combination in antineutrino running. All these configurations are for medium energy position of the target and horns. The numbers in the quotients correspond to the number of events per (kton-3.8x10^20 POT ), where the numerator is after all cuts (with oscillation probabilities included) and the denominator is before cuts (but still with the oscillation probabilities included, no matter effects, and I don't recall what value of theta_13, but delta m^2 is 3x10^-3eV^2.

The signal efficiencies range between 38 and 44%, and the NC backgrounds are for most cases, about the same size as the beam nu_e backgrounds. (except for the case of L=735 and off-axis distance=12.5km, where the nc backgrounds after all cuts are only about 40% of the beam nu_e backgrounds.).

Doug's question was, how well do we need to know delta m^2 before picking a site for the far detector? (this was addressed in a later message from Mayda, but not shown in this meeting--but really we could debate this one a long time!).

Brajesh's question was: can further optimize the flux by changing the beam optics? Stan last week showed that a third horn probably wouldn't help much, and the medium energy configuration was really where things were optimal for the off-axis flux.
Mikhal Szleper, Detector Optimization Michal reported on his study on optimizing the detector geometry. Recall that earlier he did studies with single pi0's and electrons to determine the best transverse and longitudinal segmentation. That study provided the numbers of 4.5mm for the thickness of the steel plates, and 2cm wide readout cells.

Now he's extending the study by simulating neutrino neutral current interactions, and varying the amount of air between the consecutive plates. (direct quote "Nice feature of air...it's free" which isn't exactly true since it means you have to build a bigger building). Originally there were 1.9cm air gaps between the consecutive plates (a "feature" of the original MINOS monte carlo). There the nue efficiency achieved was 20%, but the nc contamination was only 1/4 as large as the intrinsic nue background. Air gaps increase the effective radiation length so there is better separation of 2 close tracks. On the other hand, individual showers get wider and more scattered, so track fitting gets worse.

There are two ways to do the analysis: minizing the background at the expense of the signal, or "just" getting the background to where it's comparable to the nu_e background, and keeping signal efficiency as high as possible. Air gaps tested ranged from 0cm to 3cm, with the best results for 3cm. For the "no nc background" analysis, the signal efficiency ended up being 24%, the nc background was 0.08% The second way to do the analysis was to maximize the efficiency...so for that the efficiency was 33% and the nc efficiency was 0.5%. However, by looking at the events which survived Michal estimated that the efficiencies could be as high as 38% and a NC background of <=0.3%. (for 10km off-axis beam at 735km, and the LE beam). Michal showed some plots of event displays, and showed how one could even see the recoil proton in some of the events.

The list of cuts (for the low efficiency analysis) are as follows:
Steve Geer's Slides
Nu_Roadmap.pdf.pdf Steve broke up the goals for this field into two categories: 1) those goals which are independent of whatever gets measured in the next few years, and 2) those which depend on the outcomes of a few future experiments. He suggests that we need to be as quantative as we can be in this "consensus" document.
Maury Goodman's Slides
Slide 1 (jpeg version)
Slide 2 (jpeg version)
Slide 3 (jpeg version)
Slide 4 (jpeg version)
Or Get the whole file here... http://www.hep.anl.gov/mcg/mapmap.ppt Maury gave the analogy that in order to get from north america to south america (by land) you have to go through panama--and for us, Panama is theta_13. How big that is determines how well you can achieve various other goals in this field. He showed an email from Lincoln Wolfenstein (forwarded to this group) stating the same thing-- we need to really focus on getting to a measurement of theta_13. One big question in all of this (mentioned above) is how well do we need to know delta m^2_23 to get too far in the planing for future possible experiments?
Deborah Harris
Last modified: Tue Apr 9 13:34:23 CDT 2002