PDF《2015年终工作总结》

博四:李树清 导师:李世渊教授 2016.

1.25 Study of forward spectra for pp collision at LHC within quark combination model 2015年终工作总结 Phy. Rev. D86,092001(2012)arXiv:1205.4578 outline Background and motivation

1 Results within quark combination model

3 Summary

4 2 Experimental data analysis and MC simulation Background and motivation 1. One of the important tasks of strong-interaction Physics. 3. a useful benchmark: hadronic interaction model that are used for the simulation of UHECR air showers Quantum chromodynamics(QCD) :hard and soft Forward π0 production in pp collision Experiment measurement:LHCf detectors MC simulation : hadronic interaction model Approach 2. A high priority :analyzing forward π0 production experimental data provide key information for an as yet un-established hadronic interaction theory at the TeV energy scale.

4 Experimental data and MC simulation The LHCf detectors:Arm1 and Arm2 have been installed in the instrumentation slots of the target neutral absorbers (TANs) located ±140m from the ATLAS interaction point (IP1) and at zero degree collision angle.

5 A. Experimental data of π0 pT spectra Experimental pT spectra of Arm1 and Arm2 detector. The two detectors give consistent results

6 B. Analysis of π0 pT spectra ?The LHCf data are combined π0 pT spectra of Arm1 and Arm2 detectors. ?The LHCf data have been corrected for the influences of the detector responses, event selection efficiencies and geometrical acceptance efficiencies. LHCf data: DPMJET 3.04, QGSJET II-03, SIBYLL2.1, EPOS 1.99, PYTHIA 8.145 Hadronic interaction models MC simulation results:

7 the LHCf data compared with the predicted pT spectra by hadronic interaction model

8 Ratio of the LHCf data to the predicted pT spectra by hadronic interaction model

9 Discussion: 1. DPMJET3.04 and PYTHIA 8.145 show overall agreement with the LHCf data for 9.2 < y < 9.6 and pT < 0.2GeV, while the expected π0 production rates by both models exceed the LHCf data as pT becomes large. The latter observation can be explained by the baryon/meson production mechanism that has been employed in both models. More specifically, the "popcorn model" is used to produce baryons and mesons through string breaking, and this mechanism tends to lead to hard π0 spectra. 2. SIBYLL 2.1 is also based on the popcorn model, also predicts harder π

0 spectra than the LHCf data, although the expected π0 yield is generally small. 3. QGSJET II-03 predicts π0 spectra that are softer than the LHCf data and the other models. This might be due to the fact that only one quark exchange is allowed in this model. The remnants produced in a pp collision are likewise baryons with relatively small mass, so fewer π0 s with large energy are produced. 4. EPOS 1.99 shows the best overall agreement with the LHCf data. However EPOS 1.99 behaves softer than the data in the low pT region, pT < 0.4GeV in 9.0 < y < 9.4 and pT < 0.3GeV in 9.4 < y < 9.6, and behaves harder in the large pT region.

10 C. Average transverse momentum 1) An exponential distribution: 2) A Gaussian distribution: 3) Numerically integrating approach obtained by these three methods discussed are in general agreement. ybeam = 6.50 ybeam = 8.92 Δ y ≡ ybeam ? y

11 ? spectra derived by LHCf and UA7 mostly appear to lie along a common curve, and agree with the expectation of EPOS 1.99. other. ? , of the combined pT spectra is consistent with typical values for soft QCD processes. ? , is taken from the weighted mean of obtained by the exponential fit and the Gaussian fit for the rapidity range 8.9