A measurement of dielectron production in proton-proton (pp) collisions at ffiffiffi s p ¼ 13 TeV, recorded with the ALICE detector at the CERN LHC, is presented in this Letter. The data set was recorded with a reduced magnetic solenoid field. This enables the investigation of a kinematic domain at low dielectron (ee) invariant mass mee and pair transverse momentum p T;ee that was previously inaccessible at the LHC. The cross section for dielectron production is studied as a function of mee , p T;ee , and event multiplicity dNch=dη. The expected dielectron rate from hadron decays, called hadronic cocktail, utilizes a parametrization of the measured η=π0 ratio in pp and proton-nucleus collisions, assuming that this ratio shows no strong dependence on collision energy at low transverse momentum. Comparison of the measured dielectron yield to the hadronic cocktail at 0.15 < mee < 0.6 GeV=c2 and for p T;ee < 0.4 GeV=c indicates an enhancement of soft dielectrons, reminiscent of the “anomalous” soft-photon and soft-dilepton excess in hadron-hadron collisions reported by several experiments under different experimental conditions. The enhancement factor over the hadronic cocktail amounts to 1.61 0.13ðstatÞ 0.17ðsyst; dataÞ 0.34ðsyst; cocktailÞ in the ALICE acceptance. Acceptance-corrected excess spectra in mee and p T;ee are extracted and compared with calculations of dielectron production from hadronic bremsstrahlung and thermal radiation within a hadronic many-body approach
Soft-Dielectron Excess in Proton-Proton Collisions at $\sqrt{s}$ = 13 TeV / Acharya, S., Adamová, D., Adler, A., Adolfsson, J., Aglieri Rinella, G., Agnello, M., Agrawal, N., Ahammed, Z., Ahmad, S., Ahn, S.U., Ahuja, I., Akbar, Z., Akindinov, A., Al-Turany, M., Alam, S.N., Aleksandrov, D., Alessandro, B., Alfanda, H.M., Alfaro Molina, R., Ali, B., et al.. - In: PHYSICAL REVIEW LETTERS. - ISSN 1092-0145. - 127:4(2021). [10.1103/PhysRevLett.127.042302]
Soft-Dielectron Excess in Proton-Proton Collisions at $\sqrt{s}$ = 13 TeV
L. CunqueiroMembro del Collaboration Group
;
2021
Abstract
A measurement of dielectron production in proton-proton (pp) collisions at ffiffiffi s p ¼ 13 TeV, recorded with the ALICE detector at the CERN LHC, is presented in this Letter. The data set was recorded with a reduced magnetic solenoid field. This enables the investigation of a kinematic domain at low dielectron (ee) invariant mass mee and pair transverse momentum p T;ee that was previously inaccessible at the LHC. The cross section for dielectron production is studied as a function of mee , p T;ee , and event multiplicity dNch=dη. The expected dielectron rate from hadron decays, called hadronic cocktail, utilizes a parametrization of the measured η=π0 ratio in pp and proton-nucleus collisions, assuming that this ratio shows no strong dependence on collision energy at low transverse momentum. Comparison of the measured dielectron yield to the hadronic cocktail at 0.15 < mee < 0.6 GeV=c2 and for p T;ee < 0.4 GeV=c indicates an enhancement of soft dielectrons, reminiscent of the “anomalous” soft-photon and soft-dilepton excess in hadron-hadron collisions reported by several experiments under different experimental conditions. The enhancement factor over the hadronic cocktail amounts to 1.61 0.13ðstatÞ 0.17ðsyst; dataÞ 0.34ðsyst; cocktailÞ in the ALICE acceptance. Acceptance-corrected excess spectra in mee and p T;ee are extracted and compared with calculations of dielectron production from hadronic bremsstrahlung and thermal radiation within a hadronic many-body approach| File | Dimensione | Formato | |
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