WAI KEE HOLDINGS LIMITED惠记集团有限公司惠记集团有限公司惠记集团有限公司惠记集团有限公司.pdf
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1、owing in d+Au collisions 11,2426. The fi rst, Sj P,WS, assumes that shadowing is proportional to the local density, A(r), Sj P,WS(A,x,Q 2, s,z) = 1 + NWSSj P(A,x,Q 2) 1A(r) A(0) ,(6) where r= s2 + z2,A(0) is the central density and NWSis chosen so that (1/A) R d2sdzA( s,z)Sj P,WS = Sj P. When r RA,
2、the nucleons behave as free particles while, at the center of the nucleus, the modifi cations are larger than Si P. If, instead, shadowing stems from multiple interactions of the incident parton 27, parton-parton interactions are spread longitudinally over the coherence length, lc= 1/2mNx, where mNi
3、s the nucleon mass 28. For x RAfor any A and the incident parton interacts coherently with all the target partons in its path so that Sj P,(A,x,Q 2, s,z) = 1 + NSj P(A,x,Q 2) 1 R dzA( s,z) R dzA(0,z) .(7) The integral over z includes the material traversed by the incident nucleon. The normal- izatio
4、n requires (1/A) R d2sdzA( s,z)Sj P, = Sj P with N NWS. At large x, lc RAand shadowing is proportional to the local density, Eq. (6). While there are three homogeneous FGS parameterizations, only two inhomogeneous parameterizations are provided. No spatial dependence is given for FGS1, the case with
5、 the strongest gluon shadowing. We have checked the available dependencies against those calculated using Sj FGS1,WS and Sj FGS1, and found that, at similar values of the homogeneous shadowing ratios, Sj FGS1, is quite compatible with the available FGS inhomogeneous param- eterizations. Therefore, t
6、o characterize the spatial dependence of FGS1, we use Sj FGS1,. 5 The fragmentation functions, Dh/k(zc,Q2), describe the production of hadron h from parton k with zc= ph/pk. The produced partons are fragmented into charged pions, kaons and protons using the LO KKP fragmentation functions 29, fi t to
7、 e+e data. The fi nal-state hadrons are assumed to be produced pairwise so that (+)/2, K (K+K)/2, and p (p + p)/2. The equality of p and p production obviously does not describe low energy hadroproduction well. At higher energies, however, the approximation that p = p may be more reasonable. The pro
8、duced hadrons follow the parent parton direction. The minimum Q2in the KKP fragmentation functions is Q2 Fr0 = 2 GeV2, similar to but somewhat lower than the minimum Q2of the shadowing parameterizations. Thus the minimum pT of our calculations is 2 GeV. We assume the same scale in the parton densiti
9、es and the fragmentation functions, Q2= Q2 Fr = p2 T. A larger scale, p 2 T/z 2 c, is sometimes used in the parton densities but where zcis large, as is the case here, changing the scale does not signifi cantly alter the calculated ratios. The largest contribution to the total fi nal-state charged p
10、article production is from the charged pions, followed by the kaons. The proton contribution is the smallest even though, in d+Au collisions at RHIC, (p + p)/h 0.24 0.02 where h = h+ hfor 2 7.5 GeV, antiquarks are predominantly produced by valence quark induced processes since these are large at hig
11、h x. Because we begin to approach the edge of phase space with increasing , the pTdistri- butions steepen, especially for antiquark and gluon production. Quark production, which includes the valence contribution, dominant at high pTand , remains harder overall. Thus quark production will come to dom
12、inate all fi nal-state hadron production. This eff ect, in- creasingly important at high pT and , is refl ected in the relative contributions to pion, kaon and proton production by quarks, antiquarks and gluons. At | 0.2, pion production is dominated by produced gluons up to pT 9 GeV where pion prod
13、uction by quarks be- comes larger. Gluon production of kaons is rather small, similar to the quark contribution at pT QFr0but dropping below the antiquark contribution at pT 3.5 GeV. Quark pro- duction is most important for protons at pT 3.5 GeV. As increases, quark production of fi nal-state hadron
14、s becomes increasingly dominant. Already at = 1, more than half of all kaons and protons are produced by quarks for pT 2.5 GeV. At higher , antiquarks and gluons make negligible contributions to low pTkaon and proton production at = 2.2 and 7 3.2. Quarks also dominate pion production for pT 6.5, 3 a
15、nd 1.5 GeV with = 1, 2.2 and 3.2 respectively. We have calculated the average Au ion momentum fraction, hx2i, and the average deuteron momentum fraction, hx1i, for 2 p T 12 GeV. However, the largest acces- sible pTdecreases to 9.5 GeV at = 3.2 due to phase space. The results are shown in Table I.Sin
16、ce these are average x2values, the actual x2for each event can be smaller or larger than these averages. The minimum and maximum hx2i correspond to the lowest and highest pTvalues respectively. Both the minimum and maximum values decrease as increases so that the minimum hx2i is reached at = 3.2. Ho
17、wever, the maximum hx2i increases relative to more central values due to the reduction of phase space at high pT. Note that as 0, hx2i 1. The averages are not very sensitive to changes in the parton densities or the choice of factorization, renormalization or fragmentation scales. The total hadron y
18、ield closely follows that of the pions.There is little variation of hx2i between hadron species although the proton averages are generally somewhat smaller than those of the mesons. A small diff erence between the partonic contributions to h_ there any pandas in the mountains? A. IsB. Are () 14. Apr
19、il is the _ month of a year. A. fourthB. four () 15. Which season do you like best?I like summer _. A. bestB. / () 16. _ do you do on the weekends? A. WhenB. WhatC. Where () 17. _ season do you like best? A. WhichB. WhatsC. Whichs () 18. Why do you like winter?_ I can skate. 7 A. BecauseB. YesC. But
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