LOW-MASS ππ ENHANCEMENT IN BARYONIC ππ PRODUCTION: ABC EFFECT REVISED BY EXCLUSIVE MEASUREMENTS

2007 ◽  
Vol 22 (02n03) ◽  
pp. 625-628 ◽  
Author(s):  
◽  
M. Bashkanov ◽  
O. Khakimova ◽  
T. Skorodko ◽  
C. Bargholtz ◽  
...  
Keyword(s):  
Mass Spectrum ◽  
Invariant Mass ◽  
Bound States ◽  
Invariant Mass Spectrum ◽  
High Mass ◽  
Crucial Importance ◽  
Threshold Enhancement ◽  
Model Predictions ◽  
Low Mass ◽  
Mass Enhancement

The ABC effect - a puzzling threshold enhancement in the ππ invariant mass spectrum of double-pionic fusion to nuclear bound states - has been investigated since 40 years by inclusive measurements without providing a conclusive interpretation. First exclusive measurements to this topic have now been carried out at CELSIUS-WASA. They confirm a huge ππ threshold enhancement, prove it to be of scalar-isoscalar nature, i.e., a σ-channel phenomenon and reveal the theoretically predicted high-mass enhancement in inclusive spectra to be of πππ rather than of ππ nature - falsifying thus corresponding model predictions for the ABC effect. From the kinematically complete data samples we infer that the interaction between the two Δ particles created in this process is of crucial importance.

OBSERVATION OF THE ABC EFFECT IN THE FIRST EXCLUSIVE MEASUREMENTS OF pn → dπ0π0

2007 ◽  
Vol 22 (02n03) ◽  
pp. 617-620 ◽  
Author(s):  
◽  
O. Khakimova ◽  
M. Bashkanov ◽  
T. Skorodko ◽  
C. Bargholtz ◽  
...  
Keyword(s):  
Mass Spectrum ◽  
Invariant Mass ◽  
Bound States ◽  
Fundamental System ◽  
Theoretical Models ◽  
Invariant Mass Spectrum ◽  
High Mass ◽  
Threshold Enhancement ◽  
Low Mass ◽  
Mass Enhancement

The reaction pn → dπ0π0 constitutes the most fundamental system for the study of the ABC effect - a puzzling threshold enhancement in the ππ invariant mass spectrum of the ππ system in double-pionic fusion to nuclear bound states. The first exclusive measurements of this reaction have now been carried out at CELSIUS-WASA. They exhibit a striking low-mass enhancement in the ππ invariant mass spectrum, prove it to be a σ-channel phenomenon and falsify conventional theoretical models, which predict an associated high-mass enhancement not present in the new exclusive data. In the kinematically complete data sample we observe a ΔΔ excitation, where the interaction between the two Δ obviously plays a crucial role for the generation of the ππ low-mass enhancement.

WHAT IS THE NATURE OF THE ABC EFFECT?

2011 ◽  
Vol 26 (03n04) ◽  
pp. 627-629
Author(s):  
◽  
M. BASHKANOV ◽  
H. CLEMENT
Keyword(s):  
Mass Spectrum ◽  
Total Cross Section ◽  
Invariant Mass ◽  
Cross Section ◽  
Pion Production ◽  
Invariant Mass Spectrum ◽  
Fusion Reactions ◽  
Nuclear Fusion Reactions ◽  
Low Mass ◽  
Mass Enhancement

The ABC effect — an intriguing low-mass enhancement in the ππ invariant mass spectrum — is known from inclusive measurements of two-pion production in nuclear fusion reactions. Exclusive measurements have been carried out at CELSIUS/WASA and WASA-at-COSY for the fusion reactions leading to d, 3 He and 4 He . They all reveal this effect to be of isoscalar nature and associated with a narrow Lorentzian-shaped structure in the total cross section. The latter could point to the formation of an isoscalar resonance, which couples to the pn channel as well as to an intermediate ΔΔ state.

scholarly journals Observation of a Threshold Enhancement in thepΛ¯Invariant-Mass Spectrum

2004 ◽  
Vol 93 (11) ◽  
Author(s):  
M. Ablikim ◽  
J. Z. Bai ◽  
Y. Ban ◽  
J. G. Bian ◽  
X. Cai ◽  
...  
Keyword(s):  
Mass Spectrum ◽  
Invariant Mass ◽  
Invariant Mass Spectrum ◽  
Threshold Enhancement

OBSERVATION OF $p\bar{p}$, $p\bar{\Lambda}$, $K^-\bar{\Lambda}$ NEAR-THRESHOLD ENHANCEMENT AT BES

2005 ◽  
Vol 20 (08n09) ◽  
pp. 1985-1989 ◽  
Author(s):  
◽  
HONGXUN YANG
Keyword(s):  
Mass Spectrum ◽  
Invariant Mass ◽  
Confidence Level ◽  
Invariant Mass Spectrum ◽  
Total Width ◽  
S Wave ◽  
Threshold Enhancement ◽  
Peak Mass ◽  
Near Threshold

We observe a narrow enhancement near 2mp in the invariant mass spectrum of [Formula: see text] pairs from radiative [Formula: see text] decays. In the case of S-wave fit, the peak mass is below 2mp at [Formula: see text] and the total width is Γ<30MeV at the 90% confidence level. And we also find near-threshold enhancement in the invariant mass spectrum of [Formula: see text] in [Formula: see text] decays. The mass is m=2075±12(stat)±5(syst)MeV and width is Γ=90±35(stat)±9(syst)MeV. A [Formula: see text] near-threshold enhancement is also studied and it has m=1.50~1.65GeV, Γ=70~110MeV with [Formula: see text].

scholarly journals FINAL STARE INTERACTION ENHANCEMENT EFFECT ON THE NEAR THRESHOLD $p\bar p$ SYSTEM IN $B^\pm\to p\bar p \pi^\pm$ DECAY

2007 ◽  
Vol 22 (29) ◽  
pp. 5401-5411 ◽  
Author(s):  
VINCENZO LAPORTA
Keyword(s):  
Mass Spectrum ◽  
Invariant Mass ◽  
Enhancement Effect ◽  
P System ◽  
B Decays ◽  
Final State ◽  
Final State Interactions ◽  
Low Mass ◽  
Three Body ◽  
Mass Enhancement

We discuss the low-mass enhancement effect in the baryon–antibaryon invariant mass in three-body baryonic B decays using final state interactions in the framework of Regge theory. We show that the rescattering between baryonic pair can reproduce the observed mass spectrum.

DOUBLE-PION PRODUCTION IN NUCLEON COLLISIONS ON FEW-BODY SYSTEMS — THE ABC EFFECT AND ITS POSSIBLE ORIGIN

2009 ◽  
Vol 24 (02n03) ◽  
pp. 255-262
Author(s):  
◽  
MIKHAIL BASHKANOV
Keyword(s):  
Mass Spectrum ◽  
Cross Section ◽  
Intermediate State ◽  
Pion Production ◽  
Invariant Mass Spectrum ◽  
Fusion Reactions ◽  
Double Pion ◽  
Nuclear Fusion Reactions ◽  
Low Mass ◽  
Mass Enhancement

The ABC effect – an intriguing low-mass enhancement in the ππ invariant mass spectrum – is known from inclusive measurements of two-pion production in nuclear fusion reactions. Exclusive measurements have been carried out at CELSIUS/WASA and WASA@COSY for the fusion reactions leading to d, 3 He and 4 He . They all reveal this effect to be a σ channel phenomenon combined with a resonance-like behavior in the total cross section. The latter points to the formation of an isoscalar dibaryonic resonance, which couples to the pn channel as well as to a ΔΔ intermediate state.

scholarly journals Dielectrons and Direct Virutal Photons at RHIC-STAR

2020 ◽  
Vol 235 ◽  
pp. 02002
Author(s):  
Chi Yang
Keyword(s):  
Mass Spectrum ◽  
Invariant Mass ◽  
Virtual Photon ◽  
Invariant Mass Spectrum ◽  
Heavy Ion ◽  
Relativistic Heavy Ion Collisions ◽  
Dense Medium ◽  
Model Calculations ◽  
Ion Collisions ◽  
Low Mass

Electromagnetic probes are unique probes of the hot and dense medium cre- ated in relativistic heavy-ion collisions due to their minimal interactions with the partonic and hadronic medium. They can be produced at all stages of a collision, thus they provide unique ways to study the medium properties of the whole collision evolution. We present the dielectron invariant mass spectrum at √sNN = 27, 39, 39, and 62.4 GeV. Comparing to hadronic cocktail simulation, significant excesses of dielectron invariant mass spectrum at low mass are observed. The direct virtual photon invariant yields derived from the low-mass e+e− continuum in Au+Au collisions at √sNN = 200 GeV is presented and the excesses from thermal photons in low transverse momentum (pT) have been observed. Model calculations can simultaneously describe both dielectron low mass excesses and direct virtual photon low pT excesses.

STUDY OF THE DIJET INVARIANT MASS IN W + JETS EVENTS BY THE DØ COLLABORATION

2012 ◽  
Vol 27 (01) ◽  
pp. 1230002
Author(s):  
JADRANKA SEKARIC
Keyword(s):  
Mass Spectrum ◽  
Invariant Mass ◽  
Experimental Verification ◽  
Hadron Collider ◽  
Mass Range ◽  
Invariant Mass Spectrum ◽  
Dijet Production ◽  
Dijet Mass ◽  
Two Jets ◽  
Recent Claim

The recent claim by the CDF Collaboration of a possible anomalous dijet resonance in their data required experimental verification from other hadron collider experiments. We present a study of the dijet invariant mass spectrum in events with two jets produced in association with a W→ℓν boson at the DØ experiment. We investigate the dijet mass range between 110 GeV /c2 and 170 GeV /c2 and find no evidence for any resonant dijet production.

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