Recent Physics Results

Transcription

1 第九届粒子物理 核物理和宇宙学前沿问题研讨会 (2010 年 7 月 日 ) Recent Physics Results from pp Collisions with ALICE at LHC 蔡 勖 华中师范大学, 粒子物理研究所 LHC SPS PS 1

2 Large Hadron Collider at CERN ALICE 0.9, 2.36, 7TeV ALICE 0.9TeV ALICE Size: 16 x 26 meters Weight: 10,000 tons

3 ALICE Collaboration ~ 1000 Members ~ 100 Institutes CROATIA MEXICO CHINA ARMENIA USA UKRAINE INDIA ROMANIA S. KOREA ITALY ~ 30 Countries JINR FRANCE RUSSIA CERN SWITZERLAND FINLAND DENMARK GREECE NETHERLANDS UK PORTUGAL SWEDEN NORWAY SLOVAKIA POLAND CZECH REP. HUNGARY GERMANY 3

4 ALICE / Internal Note Contributed from CCNU ALICE / Internal Note (2007) Contributed from CCNU (1993 年 ) (1995 年 ) (1996 年 ) The ALICE experiment at the CERN LHC (2008) 4

5 First published paper with ALICE (2010) 5

6 First proton-proton collisions at LHC as observed with the ALICE detector: Measurement of the charged-particle pseudorapidity density at s=900 GeV ALICE collaboration Eur. Phys. J. C (2010) 65: 111; arxiv: v2[hep-ex] 1 Dec 2009 LHC s=900gev based on 284 events 6

7 phase diagram of strongly interacting matter early universe T T c (LHC) 250 T 0 2T c (RHIC) Chemical Temperature Tch [MeV] Lattice QCD CERN-SPS BNL-AGS hadron gas critical point? GSI-SIS chemical freeze-out curve quark-gluon plasma atomic nuclei deconfinement chiral restoration neutron stars Baryonic Potential μ B [MeV] 7

8 phase transition of strongly interacting matter Lattice QCD, μ B = 0 both statistical and lattice QCD predict that nuclear matter will undergo a phase transition at a temperature of T ~ 170 MeV and energy density ε ~ 1 GeV/fm 3 8

9 Normal hadronic matter quarks confined in baryons or mesons Quark-Gluon Plasma nuclear matter melts into a plasma of free quarks and gluons under extreme conditions of temperature and/or density

10 High Energy Heavy-Ion Experiments at BNL and CERN Fixed-target experiments AGS ( BNL ) 28 Si, 197 Au E lab 18 GeV/n SPS ( CERN ) 32 S, 207 Pb E lab 200 GeV/n Colliding experiments 10 RHIC ( BNL ) 197 Au Au s 200 GeV/n L = cm -2 s Approved for construction LHC ( CERN ) 2000 Start 207 Pb of +physics 207 Pb run s 5.5 TeV/n L = cm -2 s Approved for construction

11 超高能重离子实验国际合作中的部分中国成员单位 AGS program E815: CCNU(Wuhan), IHEP(Beijing), SXNU(Linfeng) E863: CCNU(Wuhan) SPS program EMU01: EMU12: RHIC program CCNU(Wuhan), IHEP(Beijing), SXNU(Linfeng) CCNU(Wuhan), IHEP(Beijing), SXNU(Linfeng) PHENIX: STAR: LHC program ALICE: CIAE(Beijing) SINAP(Shanghai), USTC(Hefei), Tsinghua(Beijing) IHEP(Beijing), CCNU(Wuhan), IMP(Lanzhou) CCNU(Wuhan), CIAE(Beijing), HUST(Wuhan) CCNU 华中师范大学 CIAE 中国原子能院 HUST 华中科技大学 IHEP 北京高能物理所 IMP 兰州近代物理所 SINAP 上海应用物理所 SXNU 山西师范大学 Tsinghua 清华大学 USTC 中国科技大学 11

12 V f (fm 3 ) t QGP (fm/c) t 0 (fm/c) Cai Xu: First Physics Results from pp Collisions with ALICE at LHC expect conditions to be significantly different Central collisions s 1/2 (GeV) SPS 17 dn ch /dy e (GeV/fm 3 ) t0=1fm s [GeV] 超高能核 - 核碰撞的实验环境 10 3 <1 ~1 AGS SPS RHIC ~0.5 RHIC LHC Y cm LHC < 0.2 Significant gain in e, V, t» 10 SPS LHC» 3-5 RHIC LHC 碰撞初态系统 - 能量 更高 - 核核 更重 碰撞末态系统 - 温度 更热更密 体积更大 寿命更长 产生粒子更多 - 密度 12

13 Observables Jets Open charm, beauty

14 瞎子摸象 bulk properties CGC soft physics high density high tempreture high pressure jet quenching hard probe chiral symmetry multiplicity distribution perfect liquid 14

15 pp Physics with ALICE ALICE detector performs very well in pp very low-momentum cutoff (<100 MeV/c) new xt - regime (down to 4 10^(-6)) pt - reach up to 100 GeV/c excellent particle identification efficient minimum-bias trigger additional triggers provides important reference data for heavy-ion programme multiplicity distribution baryon transport measurement of charm cross section major input to pp QCD physics Start-up some collisions at 900 GeV connect to existing systematics Ldt = 3 10^(30) cm ^(-2) s^(-1) 10^(7) s 30 pb-1 for pp run at 14 TeV Npp collisions = 2 10^(12) collisions minimum-bias triggers: 20 events pile-up (TPC) Npp minb = 10^(9) collisions high-multiplicity trigger: reserved bandwidth ~ 10Hz muon triggers: ~ 100% efficiency, < 1kHz electron trigger: ~ 25% efficiency of TRD L1

16 ALICE data summary (2010) 10 9 pp events reached before the end of pp run 16

17 The first 6 publications of ALICE published in EPJ C 3 accepted by PRL 1 submitted to PL B 1 charged-particle multiplicity and pseudorapidity density transverse momentum spectra of charged particles midrapidity antiproton-to-proton ratio two-pion Bose-Einstein correlations 17

18 pseudorapidity density and multiplicity distribution at 0.9, 2.36, and 7 TeV (ALICE) arxiv:

19 dn ch /dη arxiv: arxiv: consistent with UA5 (only 900 GeV) UA5: only stat. uncertainty shown consistent with CMS (only NSD) does not include charged leptons ~1.5 % difference 19

20 Comparison to Monte Carlo simulat Pythia D6T and Perugia-0 match neither INEL, NSD, INEL>0 at all three energies Pythia Atlas CSC and Phojet reasonably close with some deviations at 0.9 and 2.36 TeV Only Atlas CSC close at 7 TeV

21 dn ch /dη vs. s arxiv: power law dependence fits well (points at the same energy slightly shifted) arxiv: significantly larger increase from 0.9 to 7 TeV than in MCs Increase in dn ch /dη in η < 1 s ALICE (%) MCs (%) TeV 23.3 ± for INEL > TeV 57.6 ±

22 Predictions for LHC Energies dn ch 7 TeV predictions range from 4.3 to 6.4 Extrapolations of trends at lower s Just for average multiplicities For the multiplicity distribution Gluon saturation models (Armesto et al, Kharzeev et al) Dual Parton Model / Quark-Gluon String Model Monte Carlo generators Pythia (pqcd + soft phenomenology) with all its tunes Phojet (based on DPM/QGSM) Epos (allows mini-plasma in p+p) NSD arxiv:

23 Multiplicity Distributions arxiv: arxiv: distributions in limited η-regions the average multiplicity of the distribution reproduces the dn ch /dη measurement within 1% consistent with UA5 fits with one NBD work well in limited η-regions difference between INEL and NSD in low-multiplicity region 23

24 Multiplicity Distributions arxiv: arxiv: Fits with one NBD work also at 2.36 and 7 TeV 24

25 Comparison to Monte Carlo simulations arxiv: arxiv: arxiv: Phojet provides a good description at 900 GeV fails at 2.36 and 7 TeV Pythia Atlas CSC fails at 0.9 TeV reasonably close at 2.36 and 7 TeV but deviations around Pythia D6T and Perugia-0 far from the distribution at all energies 25

26 Transverse momentum spectra at 900 GeV Compared with ATLAS, CMS data Compared with UA1 data Hagedorn fit Power law fit Energy dependence of the average transverse momentum 26

27 Comparison to Monte Carlo simulations n acc : number of accepted particles in η <0.8, p T >0.15 GeV/c n ch : number of all primaries in η <0.8, p T >0 Hagedorn fit Average transverse momentum as a function of n_acc (left) and n_ch (right) 27

28 Midrapidity antiproton-to-proton ratio Comparison to Monte Carlo simulations antiproton-to-proton ratio is independent of both rapidity and transverse momentum 28

29 two-pion Bose-Einstein correlations Distribution of pair momentum difference, C(q)=A(q)/B(q), q=p_2 p_1 A(q) from same event, B(q) from different events HBT radii 29

30 First pp run important pp reference data for heavy ions unique physics to ALICE minimum-bias running fragmentation studies baryon-number transport heavy-flavor cross sections Summary & Outlook First few heavy-ion collisions global event characteristics important bulk properties First long heavy-ion run quarkonia measurements Jet-suppression studies flavour dependences Outlook High luminosity heavy ion running dedicated high pt electron triggers jets > 100 GeV (EMCAL) ϒ states γ - jet correlations pa & light ion running Next Physics: Pb-Pb collisions in November, 2010; pp at 14 TeV in 2013?! 谢谢!