From: Jens Jørgen Gaardhøje (gardhoje@nbi.dk)
Date: Fri Oct 18 2002 - 17:43:30 EDT
> Dear friends, > > The problem at hand that Marco is struggling with concerns estimating the > corrections to p, pbar, d and anti-d in view of > correcting the raw measured B_2 and B_anti-2 derived from the basic yields > of these particles after acceptance correction etc. > All for the MRS and for now at 90 deg. > > Let me try to summarize my understanding of these corrections and of their > relative importances for the sake of discussion. > All input is welcome. > > The experimental quantity B_A is proportional to the ratio (dN_A/dp_A) / > (dN_p/dp_p)**A, neglecting energy dep. prefactors. > Thus is follows directly from the measured yields of identified particles > after correction for geometrical acceptance, contamination from > secondary particles (produced and due to decays), absorption (in material > between the collision vertex and the final PID detector) and decay losses > (not applicable here). > > Production contribution: > to protons: > These can be ejected from the beam pipe and produced in secondary reactions > with other detectors, magnets etc... They can originate from knock-out > reactions on nuclei or from pair production in a dense medium. Both pi, K, > and p (and their antiparticles) can contribute to this. Thus the effect can > be simulated by generating particles in the MC according to spectra > distributions with slopes and yields close to those which we have measured > in the MRS. > to deuterons: > I would expect that there is a finite (but small) contribution to the > deuteron yields from knock out from very light nuclei (mainly the Be pipe). > The energy required to produce a d and d-bar pair (4GeV) is so large that > the yield from this source must be vanishing. > to antiprotons: > since there are not antiprotons present in the material surrounding the > experiment the only contribution can be pair production.. this requires at > least 2 GeV of primary energy, thus the effect must be relatively much > smaller than for protons. > to antideuterons: > Since there is no knock out possible, the only contribution is from > pairproduction. It is presumably of exactly the same magnitude as for d. > > Decay (feed down) contributions: > to protons: > These originate mainly from the decay of baryonic resonances (hyperons > etc..). STAR has measured the Lambda yield (Lamda/p=1/2 ?). The contribution > from protons from such decays in our acceptance needs to be estimated. This > may be the most important contribution to the B2 corrections. > to antiprotons: > Similar. Star has measured antilambda/lambda (= 3/4 ?). > to deuterons and antideuterons: > unimportant. Only source I could think of is fragmentation of heavier (and > rarer) clusters. > > Absorbtion contributions: > to protons: > absorption in pipe and in air mostly. > to deuterons: > idem. The main effect is presumably the larger cross section of the > deuteron. Some estimate of this can be optained by looking in the review of > part. physics p. 208 and following. At E_p > 1Gev the pd cross section is a > factor of two larger than for pn collisions. So roughly the deuterons is > twice the size of the nucleon - not surprisingly. > to antiprotons: > significant contribution due to absorbtion in the pipe and in air (at low > momenta) > to antideuterons: > the absorbtion contribution should resemble that for antiprotons, but with a > higher cross section. I would expect that for large antideuteron energies > ( > 1 GeV) the absorption is twice that for antiprotons (in relative terms). > At lower energies the Coulomb interaction plays a dominant role. But, a > reasonable approximation is probably still to take the antiproton absorbtion > and multiply by two (for comparable CM energies) since the neutron does not > contribute to the total charge. > > All of these corrections are momentum dependent, i.e. dependent on the input > momentum of the particles. > > Since we have a good Monte Carlo description of the experiment, the natural > course of action seems to me to create a full calculation with a mix of the > approximately correct yields and spectrum slopes of the original particles > and antiparticles, letting decays be operational, and then for each particle > type (p, d, pbar, dbar) of interest to take the ratio of the input spectrum > and the accepted/reconstructed spectrum after PID in TOFW. This results in > the momentum dependent correction factors to be applied to the spectra > before calculating the B2. As mentioned above the antideuterons present a > problem, but I would probably apply the antiproton correction up to 0.5 GeV > ( the antiproton dominates the Coulomb part) and then twice that at higher > energies (above 1GeV). > > This could either be done with a mix of thermal spectra or with a large > HIJING sample of events (we know that HIJING is quite OK at mid-rapidity). > HIJING events are probably too small to allow for a reasonable d study. > > hope this is of some use > cheers > jj > > ____________________________________________________________ > Jens Jørgen Gaardhøje, Assoc. Prof., Dr. Sc. > Niels Bohr Institute, Blegdamsvej 17, 2100 Copenhagen, Denmark. > Tlf: (+45) 35 32 53 09, secr. (+45) 35 32 52 09, Fax: (+45) 35 32 50 16. > UNESCO Natl. Comm., secr. (+45) 33 92 52 16. > Email: gardhoje@nbi.dk. > ____________________________________________________________ > > > ----- Original Message ----- > From: <murray@comp.tamu.edu> > To: <brahms-dev-l@bnl.gov> > Sent: Friday, October 18, 2002 12:23 AM > Subject: Re: deuterons in brag > > > > Can one not take the approach that if the dbar hits anything hard it > > will split up into an nbar and pbar. Thus one could create a dbar in > > GEANT and then check everytime GUHADR if it is scheduled to have a > > hadronic interaction. At that point one could kill it and transform into > > a pbar and nbar. > > Alternatively one can do the analysis separely for dbars and nbars > > at least when you are out of the magnetic fields. > > Michael > > > > Quoting Flemming Videbaek <videbaek@sgs1.hirg.bnl.gov>: > > > > > Hi > > > To the best of my knowledge anti-deuterons are not defined in geant ! > > > One can certainly define a particle being a anti-deuteron, and one can > make > > > it behave properly in regard > > > to multiple scattering, energy loss and tracking - but NOT for hadronic > > > integraction (and absorbtion) which > > > requires a proper interface to the tracking part of hadronic > interaction. > > > Good but tough problem. > > > > > > Flemming' > > > ------------------------------------------------------ > > > Flemming Videbaek > > > Physics Department > > > Brookhaven National Laboratory > > > > > > tlf: 631-344-4106 > > > fax 631-344-1334 > > > e-mail: videbaek@bnl.gov > > > ----- Original Message ----- > > > From: "Marco Germinario" <germina@hilux17.nbi.dk> > > > To: "Flemming Videbaek" <videbaek@sgs1.hirg.bnl.gov> > > > Sent: Thursday, October 17, 2002 4:35 PM > > > Subject: Re: deuterons in brag > > > > > > > > > > > > > > Hi Flemming, > > > > I've been looking at the Geant manual, and the deuteron number is > 45.Th > > > > e problem is I can't find out how to throw antideuterons,and how to > > > > rethreive them,if f ex i want to find the ratio between thrown and > > > > accepted antideuterons. And at which point I should issue the command > > > > cont/print part 0 ? > > > > Thanks > > > > Marco > > > > > > > > > > > > > > > > > > > > On Tue, 15 Oct 2002, Flemming Videbaek wrote: > > > > > > > > > This kind of stuff can be looked up in the Geant html description - > or > > > when > > > > > running brag > > > > > issue an cont/print part 0 that will print all the particles that > geant > > > > > knows of. > > > > > Deuteron are '42' > > > > > > > > > > > > > > > ------------------------------------------------------ > > > > > Flemming Videbaek > > > > > Physics Department > > > > > Brookhaven National Laboratory > > > > > > > > > > tlf: 631-344-4106 > > > > > fax 631-344-1334 > > > > > e-mail: videbaek@bnl.gov > > > > > ----- Original Message ----- > > > > > From: "Marco Germinario" <germina@hilux03.nbi.dk> > > > > > To: <brahms-dev-l@bnl.gov> > > > > > Sent: Tuesday, October 15, 2002 2:36 PM > > > > > Subject: deuterons in brag > > > > > > > > > > > > > > > > > > > > > > I'm making some knock out simulations for the beam pipe in > brag,and > > > have > > > > > > to look at protons and > > > > > > deuterons produced, vs pt.Does someone know which is the id number > > > for > > > > > > deuterons,if brag take it into account,or if some special > procedure > > > before > > > > > > to launch the simulation has to be taken? > > > > > > Thanks, > > > > > > Marco > > > > > > > > > > > > -- > > > > > > > > > > > > Marco Germinario > > > > > > -------------------------------------------------- > > > > > > University address : Personal address > > > > > > : > > > > > > Niels Bohr Institute : Noerre Alle' 75,518 > > > > > > Blegdamesvej 17,Ta-2 : Egmont kollegium > > > > > > Copenhagen, Danmark : 2100 Copenhagen > > > > > > Mail: germina@nbi.dk : Danmark > > > > > > Tlf : + 45 35325305 : Tlf: +45 82320518 > > > > > > > > > > > > Mob: +45 26720446 > > > > > > --------------------------------------------------- > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > > Marco Germinario > > > > -------------------------------------------------- > > > > University address : Personal address > > > > : > > > > Niels Bohr Institute : Noerre Alle' 75,518 > > > > Blegdamesvej 17,Ta-2 : Egmont kollegium > > > > Copenhagen, Danmark : 2100 Copenhagen > > > > Mail: germina@nbi.dk : Danmark > > > > Tlf : + 45 35325305 : Tlf: +45 82320518 > > > > > > > > Mob: +45 26720446 > > > > --------------------------------------------------- > > > > > > > > > > > > > > > > > ------------------------------------------------- > > This mail sent through IMP: http://horde.org/imp/ > > > > > > >
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