Biomedical subjects

G W Hoffmann

Publications and source records attributed to G W Hoffmann.

At least 19 recordsLinked to original sources

PubMed2003

Three-pion Hanbury Brown-Twiss correlations in relativistic heavy-ion collisions from the STAR experiment.

Data from the first physics run at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory, Au+Au collisions at sqrt[s(NN)]=130 GeV, have been analyzed by the STAR Collaboration using three-pion correlations with charged pions to study whether pions are emitted independently at freeze-out. We have made a high-statistics measurement of the three-pion correlation function and calculated the normalized three-particle correlator to obtain a quantitative measurement of the degree of chaoticity of the pion source. It is found that the degree of chaoticity seems to increase with increasing particle multiplicity.

Journal Article↗

PubMed2003

Narrowing of the balance function with centrality in Au+Au collisions at the square root of SNN = 130 GeV.

The balance function is a new observable based on the principle that charge is locally conserved when particles are pair produced. Balance functions have been measured for charged particle pairs and identified charged pion pairs in Au+Au collisions at the square root of SNN = 130 GeV at the Relativistic Heavy Ion Collider using STAR. Balance functions for peripheral collisions have widths consistent with model predictions based on a superposition of nucleon-nucleon scattering. Widths in central collisions are smaller, consistent with trends predicted by models incorporating late hadronization.

Journal Article↗

PubMed2003

Disappearance of back-to-back high-pT hadron correlations in central Au+Au collisions at sqrt[s NN ] =200 GeV.

Azimuthal correlations for large transverse momentum charged hadrons have been measured over a wide pseudorapidity range and full azimuth in Au+Au and p+p collisions at sqrt[s(NN)]=200 GeV. The small-angle correlations observed in p+p collisions and at all centralities of Au+Au collisions are characteristic of hard-scattering processes previously observed in high-energy collisions. A strong back-to-back correlation exists for p+p and peripheral Au+Au. In contrast, the back-to-back correlations are reduced considerably in the most central Au+Au collisions, indicating substantial interaction as the hard-scattered partons or their fragmentation products traverse the medium.

Journal Article↗

PubMed2003

Azimuthal anisotropy and correlations in the hard scattering regime at RHIC.

Azimuthal anisotropy (v(2)) and two-particle angular correlations of high p(T) charged hadrons have been measured in Au+Au collisions at sqrt[s(NN)]=130 GeV for transverse momenta up to 6 GeV/c, where hard processes are expected to contribute significantly. The two-particle angular correlations exhibit elliptic flow and a structure suggestive of fragmentation of high p(T) partons. The monotonic rise of v(2)(p(T)) for p(T)<2 GeV/c is consistent with collective hydrodynamical flow calculations. At p(T)>3 GeV/c, a saturation of v(2) is observed which persists up to p(T)=6 GeV/c.

Journal Article↗

PubMed2002

Coherent rho(0) production in ultraperipheral heavy-ion collisions.

The STAR Collaboration reports the first observation of exclusive rho(0) photoproduction, AuAu-->AuAurho(0), and rho(0) production accompanied by mutual nuclear Coulomb excitation, AuAu-->Au*Au*rho(0), in ultraperipheral heavy-ion collisions. The rho(0) have low transverse momenta, consistent with coherent coupling to both nuclei. The cross sections at sqrt[s(NN)]=130 GeV agree with theoretical predictions treating rho(0) production and Coulomb excitation as independent processes.

Journal Article↗

PubMed2002

Centrality dependence of high-p(T) hadron suppression in Au+Au collisions at sqrt[s(NN)]=130 GeV.

Inclusive transverse momentum distributions of charged hadrons within 0.2<p(T)<6.0 GeV/c have been measured over a broad range of centrality for Au+Au collisions at sqrt[s(NN)]=130 GeV. Hadron yields are suppressed at high p(T) in central collisions relative to peripheral collisions and to a nucleon-nucleon reference scaled for collision geometry. Peripheral collisions are not suppressed relative to the nucleon-nucleon reference. The suppression varies continuously at intermediate centralities. The results indicate significant nuclear medium effects on high-p(T) hadron production in heavy-ion collisions at high energy.

Journal Article↗

PubMed2002

Azimuthal anisotropy of K(0)(S) and Lambda+Lambda production at midrapidity from Au+Au collisions at sqrt[s(NN)]=130 GeV.

We report STAR results on the azimuthal anisotropy parameter v(2) for strange particles K(0)(S), Lambda, and Lambda at midrapidity in Au+Au collisions at sqrt[s(NN)]=130 GeV at the Relativistic Heavy Ion Collider. The value of v(2) as a function of transverse momentum, p(t), of the produced particle and collision centrality is presented for both particles up to p(t) approximately 3.0 GeV/c. A strong p(t) dependence in v(2) is observed up to 2.0 GeV/c. The v(2) measurement is compared with hydrodynamic model calculations. The physics implications of the p(t) integrated v(2) magnitude as a function of particle mass are also discussed.

Journal Article↗

PubMed2002

Midrapidity Lambda and Lambda(macro) production in Au+Au collisions at the square root of [s(NN)]=130 GeV.

We report the first measurement of strange (Lambda) and antistrange (Lambda macro) baryon production from square root of [s(NN)]=130 GeV Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC). Rapidity density and transverse mass distributions at midrapidity are presented as a function of centrality. The yield of Lambda and Lambda; hyperons is found to be approximately proportional to the number of negative hadrons. The production of Lambda; hyperons relative to negative hadrons increases very rapidly with transverse momentum. The magnitude of the increase cannot be described by existing hadronic string fragmentation models alone.

Journal Article↗

PubMed2001

d Macro and (3)He macro production in square root of s(NN) = 130 GeV Au+Au collisions.

The first measurements of light antinucleus production in Au+Au collisions at the Relativistic Heavy-Ion Collider are reported. The observed production rates for d macro and (3)He macro are much larger than in lower energy nucleus-nucleus collisions. A coalescence model analysis of the yields indicates that there is little or no increase in the antinucleon freeze-out volume compared to collisions at CERN SPS energy. These analyses also indicate that the (3)He macro freeze-out volume is smaller than the d macro freeze-out volume.

Journal Article↗

PubMed2001

Measurement of inclusive antiprotons from Au+Au collisions at square root of s(NN) = 130 GeV.

We report the first measurement of inclusive antiproton production at midrapidity in Au+Au collisions at square root of s(NN) = 130 GeV by the STAR experiment at RHIC. The antiproton transverse mass distributions in the measured transverse momentum range of 0.25<p( perpendicular)<0.95 GeV/c are found to fall less steeply for more central collisions. The extrapolated antiproton rapidity density is found to scale approximately with the negative hadron multiplicity density.

Journal Article↗

PubMed2001

Multiplicity distribution and spectra of negatively charged hadrons in Au+Au collisions at square root of (sNN) = 130 GeV.

The minimum-bias multiplicity distribution and the transverse momentum and pseudorapidity distributions for central collisions have been measured for negative hadrons ( h(-)) in Au+Au interactions at square root of ([s(NN)]) = 130 GeV. The multiplicity density at midrapidity for the 5% most central interactions is dN(h(-))/d(eta)/(eta = 0) = 280+/-1(stat)+/-20(syst), an increase per participant of 38% relative to pp collisions at the same energy. The mean transverse momentum is 0.508+/-0.012 GeV/c and is larger than in central Pb+Pb collisions at lower energies. The scaling of the h(-) yield per participant is a strong function of p( perpendicular). The pseudorapidity distribution is almost constant within /eta/<1.

Journal Article↗

PubMed2001

Pion Interferometry of square root of (s(NN)) =130 GeV Au + Au collisions at RHIC.

Two-pion correlation functions in Au+Au collisions at square root of [s(NN)] = 130 GeV have been measured by the STAR (solenoidal tracker at RHIC) detector. The source size extracted by fitting the correlations grows with event multiplicity and decreases with transverse momentum. Anomalously large sizes or emission durations, which have been suggested as signals of quark-gluon plasma formation and rehadronization, are not observed. The Hanbury Brown-Twiss parameters display a weak energy dependence over a broad range in square root of [s(NN)].

Journal Article↗

PubMed2001

Midrapidity antiproton-to-proton ratio from Au+Au collisions at sqrt [s(NN)]=130 GeV.

We report results on the ratio of midrapidity antiproton-to-proton yields in Au+Au collisions at sqrt[s(NN)] = 130 GeV per nucleon pair as measured by the STAR experiment at RHIC. Within the rapidity and transverse momentum range of /y/<0.5 and 0.4<p(t)<1.0 GeV/c, the ratio is essentially independent of either transverse momentum or rapidity, with an average of 0.65+/-0.01((stat))+/-0.07((syst)) for minimum bias collisions. Within errors, no strong centrality dependence is observed. The results indicate that at this RHIC energy, although the p-p pair production becomes important at midrapidity, a significant excess of baryons over antibaryons is still present.

Journal Article↗

PubMed2001

Energy loss of fast quarks in nuclei.

We report an analysis of the nuclear dependence of the yield of Drell-Yan dimuons from the 800 GeV/c proton bombardment of 2H, C, Ca, Fe, and W targets. Employing a new formulation of the Drell-Yan process in the rest frame of the nucleus, this analysis examines the effect of initial-state energy loss and shadowing on the nuclear-dependence ratios versus the incident proton's momentum fraction and dimuon effective mass. The resulting energy loss per unit path length is -dE/dz = 2.32+/-0.52+/-0.5 GeV/fm. This is the first observation of a nonzero energy loss of partons traveling in a nuclear environment.

Journal Article↗

PubMed1998

Second symmetry in the BALB/c-C57BL/6 (B6) system, and anti-antiself antibodies in ageing B6 mice.

Using an ELISA assay and inhibition of antibody mediated cytotoxicity we found that there was a higher level of anti-antiself activity in B6 anti-BALB/c alloimmune mice than in BALB/c anti-B6 mice. In contrast, when an inhibition of cellular cytotoxicity assay was used to assay for the activity, similar levels of anti-antiself antibodies were seen in B6 anti-BALB/c and BALB/c anti-B6 sera. Anti-antiself antibodies in alloimmune sera are not absorbed by the cellular immunogen as readily as are anti-foreign antibodies. These results are interpreted in terms of anti-antiself antibodies being directed mainly against T cell receptors specific for self. Anti-antiself antibodies are found also in old B6 mice, that are also known to make autoantibodies.

Absorption↗

PubMed1996

Similar abnormalities of idiotype and immunoglobulin light chain expression and of cell-mediated cytotoxicity in HIV-infected humans and simian immunodeficiency virus (SIV)-infected rhesus macaques.

The pathogenesis of AIDS in simian immunodeficiency virus (SIV)-infected rhesus macaques models the pathogenesis of human AIDS. We investigated whether certain immunological abnormalities associated with HIV infection and implicated in disease progression also occur in SIV infection. We observed striking parallels between the rhesus macaque humoral immune response to SIV and unusual features of the human humoral immune response to HIV infection. Anti-SIV envelope antibodies from SIV-infected macaques exhibited skewed kappa/lambda L chain usage relative to the ratio of kappa/lambda L chain usage detected on total plasma Ig. In addition, the same idiotope conserved on human anti-HIV gag, pol and env antibodies was detected with a similar distribution pattern on macaque anti-SIV env, gag and pol antibodies. Skewed Ig L chain representation and selection of a highly conserved possible dominant regulatory idiotope on antibodies against key neutralizing antigens raise the possibility that the progressive failure of the humoral immune response to SIV and HIV involves skewed oligoclonal humoral immunity. We also found that SIV-infected macaques, like HIV-infected humans, have elevated levels of CD8+ lymphocyte-mediated cytotoxicity. Cytotoxicity against human B cells was higher in CD8+ effector lymphocytes from SIV-infected macaques than in those from uninfected macaques (P < 0.05). Cell-mediated cytotoxicity against human NK cell targets was not elevated in effector lymphocytes from the SIV-infected macaques, suggesting that CTL activity was selectively elevated. Two out of seven SIV-infected macaques tested had CD8+ cytotoxic lymphocytes that selectively killed activated uninfected CD4+ macaque lymphocytes. Oligoclonal B cell responses and persistently elevated CD8+ lymphocyte-mediated cytotoxicity are consistent features of primate retroviral infections leading to AIDS. Understanding immune predispositions to these features triggered by HIV and SIV may advance new prophylactic and therapeutic strategies.

Animals↗

PubMed1995

The T cell receptor and AIDS pathogenesis.

An idiotypic network model of AIDS pathogenesis is described in which the T cell receptor plays a role both in infection and as a target of autoimmunity. This is an extension of a previously published autoimmunity model, and provides explanations for several otherwise puzzling aspects of AIDS pathogenesis. In the model HIV-specific T cells are preferentially infected, and HIV, acting as an antigen, stimulates the expansion of the infectable pool of T cells. The HIV variants that are most strongly selected are those that are recognized by the most helper T cells. HIV and suppressor T cells are subject to the same selective environment, and consequently undergo a process of convergent selection to resemble each other more and more with time. Eventually immunity against HIV cross-reacts with suppressor T cell idiotypes, disrupting the normal regulation of helper T cells. Autoimmunity ensues. The model leads to novel vaccine and therapy approaches involving the targeting and elimination of HIV-specific T cells.

AIDS Vaccines↗

PubMed1994

Co-selection in immune network theory and in AIDS pathogenesis.

Co-selection is a term used to denote the mutual positive selection of individual members from within two diverse populations, such that selection of members within one population is dependent on interaction with (recognition of) one or more member(s) within the other population. Co-selection is a recurring theme of the idiotypic network model that my colleagues and I have developed. This paper discusses the role that co-selection plays in basic symmetrical network theory and in a network model that resolves the I-J paradox. It proposes that co-selection of helper T cells and HIV variants plays a role in the pathogenesis of AIDS. The AIDS model involves a role for the T cell receptor in the infection of T cells. Finally, a way in which a co-selection process may potentially be used in the prevention and therapy of harmful forms of immunity is described.

Acquired Immunodeficiency Syndrome↗