Dear collaboration, I've been quite silent on the analysis going on at high rapidities but now comes the time to share the preliminary results, discuss the good and the not-that-bad-that-could-be-improved, etc. What follows is of course preliminary. Take a look at these plots : http://www.nbi.dk/~ouerdane/spectra. They mainly deal with rapidities around 3 where I put much of my effort. Why this rapidity ? 1- because the further from mid-rap., the better The idea is to check if the physics there is a bit?, somewhat?, a lot?, really?, extremely? different from mid-rap. 2- because spectrometer acceptances are easier to deal with (smaller y range for p and K than around y = 2) 3- the excellent PID from the RICH 4- the different tracking efficiencies were all calculated for these runs. There's no need to combine several PID detectors (in particular C1, which efficiency is not well-know right now, the RICH is being treated by Pawel as I'm writing now). The good : ---------- Qualitatively, the data looks good. I selected 4 and 3 degree runs at different field settings to cover as much acceptance as possible. When corrected for the geometrical acceptance AND tracking efficiencies, there is consistency between the different settings, although some mismatch remains on yields from setting to setting (taking into account the RICH efficiency should help). The pt spectra can be fitted quite nicely with an exponential fit. This fit returns effective temperature estimations that are consistent with the ratio story, i.e. : * pion slope comparable with mid-rapidity (not affected by flow throughout the whole rapidity range) * kaon and proton slopes lower than at mid-rap, consistent with a lower transverse flow which is not very suprising * increase of K+/pi+ and constance of K-/pi- when compared with mid-rap. (K-/pi-) / (K+/pi+) is consistent with our K-/K+ ratio (hurrah:) * lower particle yields (dn/dy) of course, and increase of the net protons (from y = 0 to y = 3) The not-so-good-that-would-like-to-be-good : ------------------------------------------ * Quantitatively : In general, yields (dn/dy) are roughly speaking 2 times lower than the dn/deta results already published. I've been struggling to understand why for a long long time. This factor of 2 was originally much bigger. It goes in the right direction but it still needs to be lowered. More worrysome, I think, is the fact that doing fits in mt - m will give yields even lower than in pt. I don't understand why but I might miss something here. Maybe it affetcs only the extrapolated yields. I'll check the yields under the fit range, it should be the same... Combining different settings to have overlap between pi and K is not an easy task. Depending on the y bin you work in, the slopes can change by 30 to 50 MeV, which change the pt dependence of e.g. K/pi, though (K-/pi-) / (K+/pi+) remains ok. This fluctuations can be associated to : - edge effect due to small acceptances, fluctuations introduced by non smooth acceptance correction maps (my acceptance correction maps were produced with 5 million events only to speed up their production, it takes quite some time to run the full FS spectrometer with brag and scan the output files, only a small fraction of the tracks can make it from the vtx to the RICH) - lack of high statistics in the data, the chosen fit range in pt influences the result from a bit to pretty much. - efficiencies particle specie dependent (the assumption is that it's independent, except for the RICH in momentum, reason why Pawel is producing an efficiency curve as a function of the gamma factor) or simply not treated correctly by me. I tried two methods which give teh same results : one is to build an average efficiency of your data sample in pt or mt - m and then, use this average on the before final spectrum, the other one is to weight each track by this efficiency factor right at the beginning when I fill my spectrum histograms. - the underlying physics itself, (I doubt about it though) : why should the dynamics of the fragmentation region afterall behave smoothly from 2.8 to 3.5 ? - centrality dependence : if I analyse data from 0 to 10 and 10 to 20 % central, I'll see changes in yield scales that seem ok. Exploring 0 to 5 and 5 to 10% gave me no significant variation (and I must say that the small variation went the wrong way). I do not trust the centrality from 0 to 5. I haven't got the time to put more but it will show up soon (I'll do my best for that). I need first your impression on these plots and then comments, suggestions, etc for improving it. I've spent days AND nights with the forward spectrometer data to get a descent story. I'm almost there but I need new forces from others. I also have to put together my talk (which won't take much time since we've gone through the structure with the NBI guys). Djam PS: if you wonder about the striking flatness of the K/pi ratio while the spectra show sligtly different slopes, it's because I've made the ratios with a bigger rapidity bin and produced the plot first. -- Djamel Ouerdane ------------------------------------------o | Niels Bohr Institute | Home: | | Blegdamsvej 17, DK-2100 Ø | Jagtvej 141 2D, | | Fax: +45 35 32 50 16 | DK-2200 Copenhagen N | | Tel: +45 35 32 52 69 | +45 35 86 19 74 | | http://www.nbi.dk/~ouerdane | | ouerdane@nbi.dk | o---------------------------------------------------------o
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