1 Measurement of heavy flavour production in p-p and d-Au collisions at RHIC by the detection of the inclusive muons Ju Hwan Kang (Yonsei Univ.) for the PHENIX collaboration Lake Louise Winter Institute 2004 Lake Louise, Alberta, Canada 15-21, February, 2004

2 Motivation l Heavy flavour production in pp collisions at s 1/2 = 200 GeV/c Differential production cross section: How good is the description by pQCD-driven parton model at this energy? Charge asymmetry (non-perturbative effect): How big is the effect of higher twist (recombination)? l Heavy Flavor production in dAu and AuAu collisions Nuclear modification factor (R cp ): Does "binary scaling (by number of nucleon-nucleon binary collisions)" work for these systems? Evolution of charge asymmetry: How does the non-perturbative dynamics evolve from p+p to these systems? l Study of the forward/backward hadron production in dAu Probe different “x” ranges: (anti)shadowing/saturation(CGC). central peripheral

3 d  [A+B  X] =  ij f i/A  f j/B  d  [ij  cc+X]  D c  H +... J.C.Collins,D.E.Soper and G.Sterman, Nucl. Phys. B263, 37(1986) Factorization theorem for charmed hadron production f i/A,  f j/B : distribution fuction for parton i,j D c  H : fragmentation function for c d  [ij  cc+X] : parton cross section +... : higher twist (power suppressed by  QCD /m c, or  QCD /p t if p t ≫ m c ) : e.g. "recombination" PRL, (2002) f i/Au  79 f i/p f i/n  197 f i/N f i/d  f i/p + f i/n  2 f i/N Application to nuclei: An example: Does "binary scaling" work? d+Au Au+Au Binary scaling not working for high pt particles in central AuAu collisions! PHENIX: PRL, 91, (2003)

4 Muon Production l Origins of muons PYTHIA √s=200GeV low P T : light hadron decays high P T : Heavy quark decays Muon P T distribution Direct reconstruction of open charm is ideal, but difficult. Open charm and bottom can be measured via single muons. By removing muons from  /K decays, heavy quark production can be measured.

5 RHIC at Brookhaven National Laboratory Dedicated (relativistic) heavy ion collider: P+P (can be polarized) at  s = 200 GeV or  s = 500 GeV A+A (d+Au, Au+Au, …) at  s = 200 GeV 4 Exp's: PHENIX STAR PHOBOS BRAHMS

6 The PHENIX Experiment (12 Countries; 58 Institutions; 480 Participants as of January 2004) Two central arms for measuring hadrons, photons and electrons Two forward arms for measuring muons Event characterization detectors in middle The data for this talk is from the muon arms

7 The PHENIX Muon Arms l Detect muons with p tot > 2 GeV/c -1.2 >  > -2.2 (South Arm) or 1.2 <  < 2.4 (North Arm) l Muon Tracker (MuTr) Measure momentum of muons with cathode-readout strip chambers at 3 stations inside Muon Magnet l Muon Identifier (MuID)  /µ separation with 5-layer sandwich of chambers (Iarocci tubes) and steel Trigger muons MuID MuTr Muon Magnet Beam Pipe IP

8 1 : Hadrons, interacting and absorbed (4λ or 98%) 2 : Charged  /K's, "decaying" before absorber ( ≤1%) 3 : Hadrons, penetrating and interacting ("stopped") 4 : Hadrons, "punch-through" 5 : Prompt muons, desired signal Tracker Identifier Absorber Collision range Collision Muon Hadron Absorber Symbols Detector Major Sources of Inclusive Tracks Items 2 and 4 are small fraction of the original hadrons, but are more than prompt muon signal 5.

9 Case 2, Decaying hadrons * We need to understand “Decaying hadrons” to determine background to “Prompt Muons” * Daughter muons from the hadrons can be measured separately from other sources using the dependence of yields on the location of collision points. The longer the distance from the collision point to the front absorber, the more daughter muons from hadrons. Almost linear dependence: Flight distance is much smaller compared to the mean decay length. e -L/λ ~ (1-L/λ)=(1+Z coll /λ) Arbitrary unit

10 Measured decay muons with the expectation Green band represents systematic uncertainty. Red and blue dotted lines correspond to expectation. Red and blue lines show statistical uncertainty. μ -μ - μ +μ +

11 Tracks reaching the second last (4 th ) MuId layer exclusively are made up of stopping tracks & interacting hadrons. Stopping tracks Interacting hadrons Stopping (range-out) tracks: Lose all of its energy by ionization and stop before reaching the last MuId layer. Interacting hadrons: Even when hadrons have large momenta to reach the last MuId layer, they can undergo hadron interaction in the last absorber layer to stop before reaching the last MuId layer. Momentum distribution of the tracks with DEPTH 4 Use of interacting hadrons for data driven punch-through estimation? Case 4, Punch-through hadrons

12 Extraction of Interaction Length There is relation between hadon flux at collision point (I 0 ) and hadron flux at depth 4 (I 4 ) obtained in the previous page. In simplified picture, assume hadrons experience damping by an exponential absorption, exp(-L  as they propagate through the absorber material. Then, simplified picture works to the 1st order: some differences exist due to the details of hardon propagation (decay, shower, uncertainty on hadron interaction) I 0 : Flux at collision I 3 : Flux at 3 rd ID layer I 4 : Flux at 4 th ID layer I 5 : punch-through's I0I0 I4I4 I5I5 I3I3 Estimate punch-through by extrapolating to depth 5

13 d Au Phenix Preliminary Central Depletion on the d-going side ( low x partons in Au) : Shadowing/suppression region (depletion of low x in Au compared to nucleon) As a by-product, measured backgrounds (abundant hadrons, especially stopped hadrons in MuId) also lead to an interesting physics (study of shadowing/saturation). Backgrounds is also Signals ! Rcp: nuclear modification factor

14 Prompt muon production: In Progress Remaining to the measurement of the prompt  yields, N inclusive – N decay – N punch through = N prompt + N background In ControlIn Evaluation (about 10-20%) Expected plot No absolute value yet; final efforts in progress

15 Summary l Systematic study of heavy flavor production at RHIC can be possible by measuring single muons resulting from semi-leptonic decays of heavy flavour. l From this study, perturbative and non-perturbative aspects of collisions (p+p, d+Au, Au+Au) can be explored. As major sources of backgrounds,  decays and punch-through's of the abundant hadrons were identified. As a by-product, measured backgrounds (abundant hadrons; mostly  )  also lead to an interesting physics (study of shadowing/saturation by measuring Rcp in different x). l Final efforts to estimate non-trivial sources of backgrounds (10 ~ 20%) and determine prompt muon production is in progress.

16 Backup Slides

17 X  p mean  Dominance of multiple scattering suggests is distributed as where  is 0.13 (GeV/c). DATA How do we quantify purity of the selected tracks? We utilize multiple scattering!

18 Observation of interests : 1. Large charge asymmetry in interacting hadrons is seen in data and simulation. This is mostly due to penetrating power of the K + particles according to the GEANT. 2. While data and simulations with different interaction models show qualitative agreement, quantitative description shows substancial difference. Comparison with Models

19 Probed “ x ” region of Au Saturation? shadowing enhancement EMC effect Fermi Effect Blue band: d direction Shadowing/suppression regime Yellow band: Au direction Anti-shadowing/Cronin regime