Transverse Target Moments of SIDIS Vector Meson Production at HERMES

The on-going analysis of the transverse target ( A UT ) moments of the non-collinear cross section for SIDIS dihadron production at Hermes is discussed. These moments access the transversity ( h 1 ), pretzelocity ( h _ 1T ), and Sivers ( f _ 1T ) distribution functions convoluted with the unpolarized ( D 1 ) and Collins ( H 1 ) dihadron fragmentation functions. This measurement allows greater insight into the flavor decomposition and factorization of these functions. Additionally, the results will test the Lund/Artru fragmentation model, which predicts a sign change in the Collins function between pseudo-scalar mesons and certain partial waves of vector mesons. In preparation for this analysis, a new Monte Carlo generator has been written, and non-collinear fragmentation functions have been computed in a spectator model. Additionally, an alternate partial wave expansion is presented, providing a complementary interpretation of the fragmentation functions and allowing computation of the next-to-leading twist cross section.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90826/1/1742-6596_295_1_012044.pd

Connecting the underlying event with jet properties in pp collisions at s\sqrt{s} = 7 TeV with the ALICE experiment

A preliminary study of the fragmentation properties of charged particle jets as a function of the Underlying Multiplicity (UM) is presented. The UM is defined such that it can be related to the global soft event characteristics by excluding the contribution due to jet fragmentation. The measurement of jet properties as a function of the UM might be connected to the impact parameter dependence of the transverse nucleon structure as described via Generalized Parton Distributions. The results from the studies are compared to Monte Carlo (MC) models.Comment: Proceedings submitted for the 28th Winter Workshop on Nuclear Dynamics, Puerto Rico, April 7-14, 201

Proces hadronizacije u duboko-neelastičnom raspršenju u eksperimentu HERMES

The influence of the nuclear medium on lepto-production of hadrons was studied in the HERMES experiment at DESY in semi-inclusive deep-inelastic scattering of 27.6 GeV and 12 GeV positrons off deuterium, and off light and heavy targets. The differential multiplicity for nuclei relative to that of deuterium has been measured for the first time for various identified hadrons (π +, π −, π 0 , K+, K−, p and ¯p) as a function of the virtual photon energy ν, the fraction z of this energy transferred to the hadron, and the hadron transverse momentum squared p 2 t .Proučavamo utjecaj nuklearne tvari na leptonsku tvorbu hadrona u mjerenju HERMES u DESYu poluinkluzivnim duboko-neelastičnim raspršenjem pozitrona energije 27.6 GeV i 12 GeV u deuteriju, te lakim i teškim metama. Načinili smo prva mjerenja omjera diferencijalne višestrukosti za jezgre u odnosu prema deuteriju za više utvrđenih hadrona (π +, π −, π 0 , K+, K−, p and ¯p) u ovisnosti o virtualnoj energiji fotona ν, dijela te energije z predane hadronu i kvadrata poprečnog impulsa pt2

Spinska fizika na HERMESU: nedavni rezultati

The HERMES experiment at DESY has been designed to study the spin structure of the nucleon. Impressive results have been obtained not only from inclusive processes but also for semi-inclusive and exclusive processes in deep-inelastic lepton scattering, helping to clarify the spin puzzle of the nucleon.Eksperiment HERMES u DESY bio je postavljen radi proučavanja spinske strukture nukleona. Dojmljivi rezultati postignuti su ne samo inkluzivnim procesima, već i polu-inkluzivnima i ekskluzivnima u duboko-neelastičnom raspršenju leptona, što pomaže rasvjetljavanju spinske zagonetke nukleona

Okusno razdvojene kvarkovske polarizacije u HERMESU

Recent HERMES results are presented on the flavor decomposition of the sea quark helicity distributions in the nucleon from semi-inclusive deep inelastic scattering. For the first time, a five component decomposition of quark helicity distributions using flavor tagging has been performed. The helicity distributions of the up and down quarks confirm the results obtained from inclusive deep inelastic scattering, however, there is no evidence for either a negative strange quark polarization or for a flavor asymmetry in the light sea polarization.Predstavljamo nedavne ishode mjerenja HERMES za okusno razdvajanje raspodjela heliciteta kvarkovskog mora u nukleonu zasnovane na polu-inkluzivnom dubokoneelastičnom raspršenju. Načinili smo prvo razdvajanje kvarkovskih raspodjela heliciteta na pet sastavnica primjenom označavanja okusa. Raspodjele heliciteta u i d kvarkova potvrđuju ishode mjerenja inkluzivnih duboko-neelastičnih raspršenja, međutim, ne nalazimo znakove niti za negativnu polarizaciju stranih kvarkova niti za asimetriju okusa u polarizaciji lakog mora

Tvrda ekskluzivna elektrotvorba rezonantnih i nerezonantnih parova piona u HERMESu

A selection of recent HERMES results is presented on the hard exclusive electroproduction of resonant and non-resonant π +π − pairs. The ratio of ρ 0 electroproduction cross sections per nucleon on 14N as compared to that on 1H, known as the nuclear transparency, was found to increase (decrease) with increasing coherence length for coherent (incoherent) ρ 0 electroproduction. For a fixed coherence length, a rise of the nuclear transparency with Q2 is observed for both coherent and incoherent ρ 0 production, which is in agreement with theoretical calculations that include the effect of color transparency. The first-order intensity density for exclusive electroproduction of π +π − pairs has been studied as a function of the invariant mass Mππ in the range 0.3 < Mπ+π− < 1.5 GeV. The derived quantities show a dependence of the π +π − invariant mass, which can be understood as due to the interference between pion pairs in relative P-wave (isovector channel) and S,D-waves (isoscalar channel) states.Predstavljamo odabir ishoda nedavnih mjerenja tvrde ekskluzivne elektrotvorbe rezonantnih i nerezonantnih parova π +π −. Nalazimo da omjer udarnih presjeka elektrotvorbe ρ 0 po nukleonu u 14N i 1H, poznat kao nuklearna prozirnost, raste (opada) s povećanjem koherentne duljine za koherentnu (nekoherentnu) elektrotvorbu. Za određenu koherentnu duljinu, opaža se porast sa Q2 za koherentnu kao i za nekoherentnu tvorbu ρ 0 , što je u skladu s teorijskim računima koji uključuju učinke prozirnosti boje. Proučavali smo gustoću intenziteta za ekskluzivnu elektrotvorbu parova π +π − u prvom redu, kao funkciju invarijantne mase Mππ u području 0.3 < Mπ+π− < 1.5 GeV. Izvedene veličine pokazuju ovisnost invarijantne mase π +π −, što se može shvatiti posljedicom interferencije među pionskim parovima u relativnim P-valnim (izovektorski kanal) i S,D-valnim stanjima (izoskalarni kanal)