Hi I think the meson paper has wonderful results, but I agree with Dieter and Flemming that the Landau and Bjorken discussion is not so good. First my understanding of the two pictures. They use the same relativistic hydrodynamic developed by Landau, only the initial state is different. In coordinate space they are similar = very narrow and the size of the overlap=pancake. In velocity space they both have initially vT=0 BUT Landau assumes that v_z is also initially 0, while Bjorken assumes the V_z propto z and the energy density as a function of z is boostinvariant leading to a very simple expansion, i.e., seen form any CM like frame the energy density is constant so the pressure is 0. This might be a wrong understanding (especially the Landau), but I miss a clearer description in the paper of what the difference is (at least what Caruther assume contra Bjorken) - this is for me extremely important since we spend a lot of the paper on this discusion. For me: 1) The pion data are gaussian. The other fits have more parameters and no physics basis. 2) The Landau model has a prediction that is 20 years old and that predicts that the shape is Gaussian and predicts the width of the data within 5% from AGS to RHIC and what is the actual systematic error on our width. In principle the MRS points and FS points bothe have a roughly 5-10% uncorrelated freedom to move from the efficiencies. 3) The Bjorken model has no prediction (about this) except that the yields should be flat in a rapidity interval around mid-rapidity, and is used by most theoreticisians (I believe) to reduce the 3d hydro to a 2d hydro (only transverse) assuming the the simple beam direction scaling, so I guess that new hydromodels don't make predictions either. I think our data supports the Landau prediction. Maybe Landau initial conditions are wrong, but the results suggests that the initial conditions are not so simple as Bjorken said and then it is up to the theoreticians to explain why. Again we see that forward rapidity is not just mid-rapidity;) Other comments: * I think the second sentence in paragraph 1 is a bit unclear. * Why say a) competing ... when we don't refer to a) and b) later * Table on page 2 is a bit uninteresting why not just quote gaussian * Should we say Landau picture or caruthers picture? and in formula (1) we should use the subscript Landau if that is what we mean * Fig 3. I guess this should be Caruthers prediction * I think that the energy loss of 72% might not be able to tell us if Landaus initial conditions are very wrong or not for calculating pions, but it is clear that the bulk net-protons being far from the bulk pions in rapidity shows that there must be more to RHIC than a single source at y=0. * The sentence "In the Landau picture..." is weird. Initially we all think of the beam particles as pancakes, so what does this mean? I guess the initial conditions for the hydro calculation is not highly Lorentz contracted or are they? Another thing (that I was told by Igor Mishustin since the article is in russian;) is that Landau in his paper wanted to calculate everything from before the collision so that he calculated the initial state from the collision of two relativistic drops etc, is this what is meant here? Cheers, Peter -- ***** Peter H L Christiansen Email : Peter.Christiansen@cern.ch Office : 23-R-014 (77283) Mobile : 160425 ***** On Tue, 9 Mar 2004, flemming videbaek wrote: > Hi Djamel > > (and anyone else on the list). > Some of the issue that are raised in the points to a discussion we have had > several times w/o coming to a conclusion. > Do our data in dn/dy support Bjoerken or not? \ > Taken at face value with the syst errors (point to point) > I will tend to agree with Dieter that the y<1 are consistent both with being > flat (Bjoerken like) as also the Star data in similar rapidity ranage says, > but is also consistent with a near Gaussian. > This tells me that we should not focus on the part of the data where it is > hard and difficult to say anything clearcut; > (albeit anyone can certainly promote either in talks) but should focus on > the overall dependence as the paper the paper > does so nicely. This is our strong point as also said in the second par of > the paper. > > Some comments to the comments by Dieter. > > par 1) > Chemical composition.. I is certainly true that Chem comp. cannot prove > equilibration, but could also come from mainly > phase-space dominance (Koch)- it is albeit a necessary condition. I think > the introduction should give general arguments > why it is important to measure particle abundances (after all this is why we > designe Brahms). It is a tool in this sense for both therm. models as well > for dynamical models to get this right. > page 2) > feed-down correction? has anyone done this ? I know that for the dn/deta the > pions from k0s decay are essentailly counnted, and will suspect that the pi > from Lambda are not due to vertex cuts , but w/o a detailled MC it is not > known. > > Figure 2. > The caption say the curves are fit to the data. Which one has been plotted > G1,G2 or WS? (as ref I would ask this question). I assume it is either G2 or > WS since the fit to fig 3 which is a Gaussian is slightly off; > The point for Fig 3 is of course it is a Gaussian with Landau values and > therefore in my opinion worth to keep even if the data are the same Just > showing sigma's would not convey the message as strongly. > > > the 72% question: > I think that it in fact impossible from inclusive distribution to determine > if the scenario is 'transparency' or ' near full stopping+longitudinal > expansion' . As is > implied in the paper most of the 72% do in fact end up > in long. energy. At eta=-1,1 only about .5*600*1.5*2 GeV == 900 GeV ~1 TeV > out of a total of 350*.72*200== 50TeV is present in the final state; > > I would think it serves the paper best just to state at end that it is > consistent with Landau and leave out the > (fairly obvious ) reservations about other possibilities. They have been > (and should be) qualified in the main text before > then. > > regards > Flemming > > PS excuse my sometimes missing 'd''s due to my keyboard > > > > > ---------------------------------------------------------------- > Flemming Videbaek > Physics Department > Brookhaven National Laboratory > > e-mail: videbaek@bnl.gov > phone: 631-344-4106 > > > > > > > Dear Djamel, > > > > my comments. Most of them are a repetition of what I have sent around > > earlier within the paper comittee. > > > > > > Abstract: > > Why did you remove our numerical results? Now the abstract contains no > > information at all. > > > > P.1, first par.: > > remove "The chemical composition (abundances) of > > the produced particles constitute an important tool to > > test if equilibrium occurs in the course of the collision." > > > > The statement is wrong. See the discussion at QM'02 in Nantes, > > chaired by Koch. Elliptic flow might prove equilibrium; but not > > particle ratios. > > > > > > p2, second par.: > > > > be more specific about the amount of particles from > > Lambda and K0 decays. This is important in order to use our data > > for thermal model fits. > > > > p3, figure 3: > > > > exchange figure with inset. The figure itself contains no new information > > in addition to fig.2 and eqn. 1. > > > > > > p3, second column, 2. par: > > > > The statement > > "As mentioned, collisions at RHIC > > are neither fully stopped nor fully transparent, although > > a relatively high degree of transparency is observed [3] > > corresponding to an average rapidity loss of the colliding > > hadrons of about y 2.2." > > > > contradicts the statement (same page) > > "The analysis of nuclear stopping in central Au+Au collisions at > > psNN = 200 GeV [3] has demonstrated that about 72% > > of the participant energy is lost during the collision and > > potentially available for particle production, ..." > > > > I would not call 72% stopping a "relatively high degree of transparency". > > Remove the sentence. > > > > > > p3, second column, 2. par.: > > > > remove: "The fact that the obs. dist. are flatter at mid-rapidity and > > wider ...may point in this direction." > > > > Don't try to educate the PRL reader that a wider Gaussian is automatically > > flatter around y0. That's the whole point of a Gaussian. > > > > p4, sec. colummn, last par.: > > > > remove > > "although the overall width and the behaviout of the distr. > > around mid-rapidity suggest increased longitudinal expansion at > > RHIC energies reminiscent of the Bjorken picture." > > > > The distributions are Gaussian, punktum. Small deviations > > can easily be explained by our contaminations from weak decays. > > There is no "behaviour around mid-rapidity". > > > > What is an "increased longitudinal expansion"?? > > This makes no sense. > > > > > > With best wishes, > > Dieter > > > > > > > > On Fri, 5 Mar 2004, Djamel Ouerdane wrote: > > > > > Hi, > > > > > > You can find the latest draft of the meson paper here: > > > > > > http://www.nbi.dk/~ouerdane/mesonAuAu.ps > > > http://www.nbi.dk/~ouerdane/mesonAuAu.pdf > > > http://www.nbi.dk/~ouerdane/mesonAuAu.tex > > > > > > or you can get it from CVS: > > > > > > cvs -d /afs/rhic/brahms/BRAHMS_CVS co papers/mesonAuAu200 > > > > > > > > > The plan is to make an announcement soon, and submit it next Friday. > > > Please make final comments and corrections so that we can do it as I > > > mentioned. > > > > > > Thanks, > > > Djam > > > > > > > > > > > > > -- > > -------------------------------------------------------------------- > > Dieter Roehrich | > > Institutt for fysikk og teknologi | Email: Dieter.Rohrich@ift.uib.no > > Universitetet i Bergen | Tel: +47-555-82722 > > Allegt. 55 | Fax: +47-555-89440 > > N-5007 Bergen, Norway | http://www.ift.uib.no/~dieter > > > > > > > > > > _______________________________________________ > > Brahms-l mailing list > > Brahms-l@lists.bnl.gov > > http://lists.bnl.gov/mailman/listinfo/brahms-l > > > > > _______________________________________________ > Brahms-l mailing list > Brahms-l@lists.bnl.gov > http://lists.bnl.gov/mailman/listinfo/brahms-l > -- :-) --------------------------- )-: Peter H L Christiansen pchristi@nbi.dk / (+45)40840492 :-D --------------------------- \-: _______________________________________________ Brahms-l mailing list Brahms-l@lists.bnl.gov http://lists.bnl.gov/mailman/listinfo/brahms-lReceived on Wed Mar 10 05:01:39 2004
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