between Correlations photons and charged particles at large transverse momenta in pp and dAu collisions at sNN=200 GeV Subhasis Chattopadhyay, for the STAR Collaboration. Variable Energy Cyclotron Centre, 1/AF, Salt Lake, Kolkata 700 064 India
INTRODUCTION
In High Energy collisions,
jets are produced due to the scattering of
Partons. Energy loss of partons in the medium modifies the jet fragmentation function, most sensitive at high pT (high z) In heavy ion collisions, reconstruction of jets is almost impossible. 2-particle correlations probe the intra-jet (same side) and b-to-b jet (away-side) structures in detail It is essential to study the initial-state nuclear effects from p+p and d+Au At RHIC energy correlations have been measured with charged particles (upto pT of 6 GeV/c).
In present study the range extends to higher energy using EMC trigger for pp and dAu. (AuAu will be studied next run).
What is High Tower Correlation? Few Towers in EMC have large energy deposition from high energy photons (0s) High Towers with Large Energy are used as Trigger for high pT particles. Provide information on photon (0) tagged dijets up to very large energy. Approach: Select Highest Tower = Tower with Max Energy. Energy >4.5 GeV up to 10.5 GeV. * Measure distributions of ALL charged tracks (associated
T
tracks; 2GeV/c< pT <E ) wrt Highest Tower.
T
Investigate Correlations for various Etrig and associated P cuts.
EMC High Towers
Measured correlation Function := (1/Ntrig (asso)) dN/d
0
trigger
incoming partons
associated h
These trigger photons deposit high Energy on a tower and Used as trigger Tower
BEMC (L0) trigger
High Tower trigger
Highest tower in patch
T rig g e r p a tc h (4 x 4 to w e rs )
Tow er M o d u le 3 M o d u le 2 M o d u le 1
Patch sum trigger
Sum over 16 towers 16 bits->6 bits convertion
Linear lookup table Extremely high threshold
High-pt trigger
Photons, electrons and 0 150 (half of BEMC) trigger patches
4 x 4 towers (, ) ~ (0.2, 0.2) Highest tower in patch (HT) 0.5 GeV energy resolution
Jet trigger
Sum over patches in 10 modules Under HIGH commissioning
Only TOWER Trigger used for this analysis
STAR PRELIMNARY
Normalized spectra
Data
3.9 M Triggered events. (Scale-down as was used during run) (all errors shown here are statistical)
Events are isolated from possible trigger tower caused By interacting hadrons No Track pointing to the trigger tower (Single tower isolation)
Effect of Isolation, ratio studied with and without isolation
T(asso)
dAu Correlation Functions (P
>2 GeV/c)
STAR PRELIMNARY
Pedestal subtracted correlation functions are shown here. Peaks are fitted with gaussian
T(asso)
dAu Correlation Functions (P
>3 GeV/c)
STAR PRELIMNARY
T(asso)
Peak of gaussian fitting for various Etrig and P
STAR PRELIMNARY
Width of Gaussian fitting
trig Tassociated
Narrower for higher E
and for higher p
Fitted Sigma
STAR PRELIMNARY
pT of Associated particles
CONCLUSIONS:
1. Clear peaks characteristics of jets observed in correlation functions up to 10.5 GeV. 2. Far angle peaks are wider compared to the near angle peaks 3. Peak heights and widths decrease with increase in associated pT 4. Peak heights decrease faster than width 5. Peak height goes up with increase in Etrigger, correlation becomes narrow. Width of pp is similar to dAu. 7. Pedestal of the correlation functi...