Motivation:

How does underlying event multiplicity, average pT change with Leadiing jet pT?

CMS publication: arxiv.org/abs/1507.07229
CDF publication: arxiv.org/abs/1508.05340

Grant Webb's study on p+p 500 GeV data: drupal.star.bnl.gov/STAR/blog/gdwebb/underlying-event-run-9-pp-500-gev
Zilong Change's study on PYTHIA p+p 500 GeV: drupal.star.bnl.gov/STAR/blog/zchang/underlying-event-study-4


Here is Li Yi's first step to study the underlying event in p+p 200 GeV. 

See follow-up on mono-jet as direction angle at  drupal.star.bnl.gov/STAR/blog/yili/underlying-event-activity-pp-200-gev-mono-jet-2015-10-02-0


See Master Page: drupal.star.bnl.gov/STAR/blog/yili/master-page-underlying-event-pp-200-gev

Data:

p+p 200 GeV
Run 12 
filetype=daq_reco_MuDst,events!=0,trgsetupname=pp200_production_2012,filename~st_physics,production=P13ib,storage!=hpss,sanity=1

triggerid: 370541,370542,370351 
for  BHT0*BBCMB*TOF0, BHT0*BBCMB*TOF0, MTD*BHT3


Cuts:

|Vz|<30 cm
|eta|<1
|dca|< 1 cm 
NFIt > 20 points
NFit/NFitPossible > 0.52
Track Pt or Tower Et<1000GeV

no pileup removal

anti-kT algorithm
R = 0.4
ghost area 0.01

Dijet |Δφ-π|<0.4

14M events, found 0.027 M dijet pairs (no jet pT requirement) 


Method:

1. Search for dijet pair to define the φ_dijet = ( φ_Leading-φ_SubLeading )/ 2 . Should be φ_dijet = ( φ_Leading +(π-φ_SubLeading ))/ 2.
Both TPC tracks and BEMC towers are used for jet reconstruction by fastjet pacakge.  

2. Loop over tracks (charged particles only) 

|φ-φ_dijet|<60 degree --> Leading jet direction
|φ-φ_dijet|>120 degree --> SubLeading jet direction
60 degree<|φ-φ_dijet|<120 degree --> transverse direction

For the two transverse directions, the one with larger pT sum of the charged particle is defined as TranMax. The other is TranMin. 

3. Sum the multiplciity in various directions.
Calucate the average pT in various directions. 


Code:
http://www.star.bnl.gov/cgi-bin/protected/cvsweb.cgi/offline/users/yili/code/run12/underlyingevent/?sortby=rev#dirlist
version 1.1


Result:

1. Leading jet Pt Distribution:

2. SubLeading Jet Pt vs Leading Jet Pt

3. Ntrk in Leading Jet Direction vs Leading Jet Pt
 (number of charged particles in |φ-φ_dijet|<60 degree, including the particles belongs to leading jet) :

4. Sum of charged particle pT in Leading Jet Direction vs Leading Jet Pt. The title in the plot was wrong: it is sum not mean <pT>.
 (in |φ-φ_dijet|<60 degree, including the particles belongs to leading jet) : 


5. Ntrk in SubLeading Jet Direction vs Leading Jet Pt
(number of charged particles in |φ-φ_dijet|>120 degree, including the particles belongs to subleading jet) :

 
6. Sum of particle pT in recoil side of Jet Direction vs Leading Jet Pt. The title in the plot was wrong: it is sum not mean <pT>.
(in |φ-φ_dijet|>120 degree, including the particles belongs to subleading jet) : 


7. Ntrk in Transverse direction vs Leading Jet Pt

8. <pT> in transverse direction vs Leading Jet Pt

9. Ntrk in TranMax vs Leading Jet Pt


10. <pT> in TranMax vs Leading Jet Pt


11. Ntrk in TranMin vs Leading Jet Pt


12 <pT> in TranMin vs Leading Jet Pt





All the plots show a dip at Leading Jet Pt  ~ 12 GeV