Quark Matter 2017

Reconstruction of neutral-triggered full recoil jets in sNN=200 GeV p+p collisions at the STAR experiment

Not scheduled

2h 30m

Hyatt Regency Chicago

Board: J20

Poster Poster Session

Speaker

Mr Derek Anderson (Cyclotron Institute, Texas A&M University)

Description

In heavy-ion collisions, the study of recoil jets tagged by high transverse-momentum "direct photons" (${\gamma }_{dir}$) should provide a measurement of the partonic energy loss in the hot, dense medium produced in such collisions\footnote{X.-N. Wang, Z. Huang, and I. Sarcevic, Phys. Rev. Lett. 77, 231 (1996)}. Since a ${\gamma }_{dir}$ does not interact strongly with the medium, it closely approximates the initial energy of the recoiling parton. It is also interesting to compare the recoil jets tagged by ${\gamma }_{dir}$ to those tagged by high transverse-momentum ${\pi }^0$. In contrast to the ${\gamma }_{dir}$, high transverse-momentum ${\pi }^0$ are assumed to be biased towards being produced near the surface of the medium. Moreover, the production mechanisms of ${\gamma }_{dir}$ favor recoiling quarks over gluons, but the production mechanisms of ${\pi }^0$ show no such preference. Thus the comparison of ${\gamma }_{dir}$-tagged recoil jets to ${\pi }^0$-tagged recoil jets may shed light on the path-length and color-factor dependence of in-medium partonic energy loss.

To establish a vacuum fragmentation reference, we present the measurement of the yields of full recoil jets (recoil jets consisting of both charged and neutral particles) in p+p collisions. The yields are measured using the STAR Time Projection Chamber and Barrel Electromagnetic Calorimeter in p+p collisions at $\sqrt{s_{NN}}=200$ GeV tagged by neutral-particle triggers recorded during the running year 2009. The neutral-particle triggers satisfy $9<E_T^{trig}<20$ GeV and $|{\eta }^{trig}|<1$, and are separated into a sample of identified ${\pi }^0$ triggers and a sample of triggers with an enhanced fraction of ${\gamma }_{dir}$. Jets are reconstructed from charged tracks and neutral towers with $p_T>0.2$ GeV/c and $E_T>0.2$ GeV respectively and $|\eta |<1$ using the anti-$k_T$ algorithm for resolution parameter $0.3\le R\le 0.6$. To assay the effect of reconstructing full jets versus charged-only jets in such studies, the yields of charged recoil-jets are compared to the yields of full recoil-jets. The data are corrected for instrumental effects and compared to Pythia simulations\footnote{T. Sj\"ostrand, S. Mrenna and P. Z. Skands, Comput. Phys. Commun. 178 (2008) 852 [arXiv:0710.3820 [hep-ph]]}.

Presentation materials

Anderson_QM2017.v4.pdf