1. Identified hadron production in d+Au and p+p collisions at RHIC
Hongyan Yang
for the BRAHMS Collaboration
University of Bergen, Norway

2. Outline Experimental overview
Preliminary results - particle spectra - particle yields and ratios - nuclear modification factor - net-protons
Summary
2019/1/14
Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

3. Motivations
rapidity dependence of particle spectra in p+p and d+Au: a reference for heavy ion collisions
particle spectra in p+p collisions: a test of pQCD
nuclear modification factor for nuclear effect, initial state effect?
rapidity distribution of net-protons: stopping in elementary collisions
2019/1/14
Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

4. 2019/1/14
Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

5. Identified particle spectra in p+p collisions
2019/1/14
Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

6. Spectra at forward rapidity (pp collisions) – comparison to NLO pQCD
Calculations
by W. Vogelsang
BRAHMS Preliminary
Same fragmentation functions as used for the PHENIX comparison at mid-rapidity. mKKP: KKP has only 0 fragmentation. Modifications were needed to calculate charged pions. K: fragmentation function by Kretzer
NLO pQCD describes data also at forward rapidities
2019/1/14
Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

7. Spectra at forward rapidity ( p+p collisions ) pT-dependence of ratios
Red: p/+ Blue: p-bar/ -
e+e-: p+p-bar/++ - (ALEPH)
BRAHMS Preliminary
Ratios y=3.0 and 3.3
Excess of positive pions: ratio ->1/2 (valence quark counting)
Small p/p ratio eliminates possible strong g -> p or p fragmentation
The difference between protons and anti-protons indicates another mechanism besides fragmentation that puts so many protons at high pT.
2019/1/14
Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

8. RdAu - for hadrons, suppression was seen at forward rapidity
PRL 93, (2004)
RdAu
- for hadrons, suppression was seen at forward rapidity
- Pions are suppressed, while protons are not
2019/1/14
Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

9. Extraction of particle yields (p+p)
d2N/2ppTdpTdy
2019/1/14
Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

10. Rapidity distributions
2019/1/14
Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

11. like-particle ratios (p+p)
2019/1/14
Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

12. K/p, p/p ratios (p+p)
Open symbols: positive particles
Closed symbols: negative particles
All ratios decrease with increasing rapidity , except p/p+
2019/1/14
Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

13. Net-proton distribution
pT [GeV/c]
BRAHMS Preliminary
p+p 200GeV
dN/dpT
Subtraction of p-bar yield from proton yield for each pT bin
A Boltzmann function is used to fit the data
2019/1/14
Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

14. p+p 200GeV
2019/1/14
Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

15. Net-proton distribution (d+Au)
d+Au 200GeV
2019/1/14
Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

16. Summary
NLO pQCD describes pT spectra at forward rapidities in p+p collisions
RdAu: suppression of h- yields at forward rapidities confirmed by identified hadrons spectra
Strong suppression of pions
No suppression of protons
HIJING/B describes the net-protons in p+p better than PYTHIA
Net-protons are piled up at mid-rapidity in central d+Au collisions
2019/1/14
Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

17. BRAHMS Collaboration
I. C. Arsene12, I. G. Bearden7, D. Beavis1, S. Bekele12, C. Besliu10, B. Budick6,
H. Bøggild7, C. Chasman1, C. H. Christensen7, P. Christiansen7, H.Dahlsgaard7,
R. Debbe1, J. J. Gaardhøje7, K. Hagel8, H. Ito1, A. Jipa10, E.B.Johnson11, J. I. Jørdre9, C. E. Jørgensen7, R. Karabowicz5, N. Katrynska5 ,E. J. Kim11, T. M. Larsen7,
J. H. Lee1, Y. K. Lee4,S. Lindahl12, G. Løvhøiden12, Z. Majka5, M. J. Murray11,
J. Natowitz8, C.Nygaard7B. S. Nielsen8, D. Ouerdane8, D.Pal12, F. Rami3, C. Ristea8, O. Ristea11, D. Röhrich9, B. H. Samset12, S. J. Sanders11, R. A. Scheetz1, P. Staszel5, T. S. Tveter12, F. Videbæk1, R. Wada8, H. Yang9, Z. Yin9, I. S. Zgura2
1. Brookhaven National Laboratory, Upton, New York, USA
2. Institute of Space Science, Bucharest - Magurele, Romania
3. Institut Pluridisciplinaire Hubert Curien et Université Louis Pasteur, Strasbourg, France
4. Johns Hopkins University, Baltimore, USA
5. M. Smoluchkowski Institute of Physics, Jagiellonian University, Krakow, Poland
6. New York University, New York, USA
7. Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
8. Texas A&M University, College Station, Texas, USA
9. University of Bergen, Department of Physics and Technology, Bergen, Norway
10. University of Bucharest, Romania
11. University of Kansas, Lawrence, Kansas, USA
12. University of Oslo, Department of Physics, Oslo, Norway
2019/1/14
Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

18. Backup slides
2019/1/14
Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)

19. Particle Identification
MRS by TOFW
FS by RICH
Two plots (just flash...) - one is for MRS (TOFW) - another is for FS (RICH)
2019/1/14
Identified particle production in d+Au and p+p collisions at RHIC (QM2006 Shanghai, China)