1. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 1/24 PID at high p T with the ALICE TPC The ALICE experiment –The ALICE TPC Motivation for PID at high pT –STAR results with TPC PID –Gluon vs quark energy loss Calibrating the TPC PID –Test beam results –Model comparison Conclusions

2. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 2/24 The ALICE experiment PHOS Muon arm TOF TRD HMPID PMD ITS BergenBratislava CERNCopenhagen Darmstadt TUFrankfurt GSI DarmstadtHeidelberg KIP Heidelberg PIKrakow Lund The ALICE TPC Collaboration

3. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 3/24 ALICE TPC design Minimize multiple scattering –Composite materials for field cage High occupancy –High readout segmentation (3D) Online reduction of data –Neon gas (fast ion drift velocity limits space charge effects) –CO 2 quencher (small diffusion and good aging properties) Small signal (Small pads, low density gas) –Low noise electronics (<1000e) –High gain (~10 4 ) Non-transparent gate (<10 -4 ) Good space point resolution –Small field distortions  E/E  10 -4 (field cage precision) –Temperature stability<0.1K gradient (Non-saturated gas)

4. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 4/24 E 510 cm E 88µs 560 cm LARGE DATA VOLUME: 570 132 (pads) x 500 (time bins) 356 MB/event (NO 0-suppression!) Pb – Pb  60 MB/event (after 0-) p-p  1-2 MB/event (suppres.) ALICE TPC: Layout 4 cylinders! CO 2 high voltage isolation volume. GAS VOLUME: 95 m 3 DRIFT GAS: Ne-CO 2 –N 2 (86-9-5)

5. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 5/24 Pb+Pb central event in ALICE Pb+Pb event (dN/dy = 8000)  = 2 o slice only! (~500 tracks) TOF HMPID PHOS TRD ITS TPC Up to 40% occupancy (N ABOVE / N ALL ) Clusters at the innermost pad row of the TPC

6. ﾧ TPC in June ‘06 Outer ROC (OROC) Inner ROC (IROC)

7. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 7/24 Side view OROC IROC First Cosmic Ray Data 3-dimensional view of a shower induced by cosmic rays

8. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 8/24 TPC status ALICE TPC has been assembled and completely instrumented on ground. ALICE TPC has been assembled and completely instrumented on ground. It was running with gas and HV drift field from April to November ’06 It was running with gas and HV drift field from April to November ’06 Commissioning, two sectors at a time, with cosmic and laser tracks from June to November ’06. Commissioning, two sectors at a time, with cosmic and laser tracks from June to November ’06. Preliminary results show many features achieve the expected performance: Preliminary results show many features achieve the expected performance: Gas quality: excellent stability! Noise < 1000 e Signal well separated from noise (“S/N” > 30 for MIP) Space point resolution ~ 1mm after 2.5m of drift Jan – Mar ’07: installation underground in the ALICE Detector Apr – Oct ’07: commissioning of the TPC in its final position in ALICE Apr – Oct ’07: commissioning of the TPC in its final position in ALICE November ’07: first LHC p-p collisions November ’07: first LHC p-p collisions

9. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 9/24 PID in ALICE PID in ALICE ALICE PPR CERN/LHCC 2003-049  1σ K p e The TPC provides PID track by track at low momentum (p<1) The TPC can PID on a statistical basis at intermediate (3 < p < 50) if the resolution and/or calibration is sufficient.

10. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 10/24 STAR TPC PID The PID on the relativistic rise is an added benefit, i.e., it was not originally thought of as feasible! P= 0.1 1 10 100GeV/c STAR PID using dE/dx (high momentum!)  top 5%  40-80% PID from TPC

11. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 11/24 The physics of PID at high pT Elliptic flow (v2) kinetic energy scaling High pT suppression (vs event plane) Baryons and mesons shows different suppression patterns Gluon jets vs Quark jets? –Mechanisms of suppression And much more.... –p/pi ~ 10?

12. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 12/24 Quark vs gluon energy loss (modified QM summary slide) STAR, L. Ruan PRL 97, 152301 (2006) Curves: X-N. Wang et al PRC70(2004) 031901 p T (GeV/c) p/  STAR, B. Mohanty STAR results with TPC PID Model calculations very interesting: –90% of p from gluons –40% of pi from gluons –But cited papers does not contain relevant information!!!

13. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 13/24 Baryon production in quark and gluon jets in string models. q QUARK JET: _ _ Needs diquark (q q - q q) string break to make a leading baryon. (suppressed by 1/10 vs q-q breaking) q g GLUON JET (KINK): 2 possibilities for diquark breaking => 2/10 NB! gluon jets are softer than quark jets q _q_q _ q _ q _q_q_q_q _ q or q _ q or q _ q or q q q

14. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 14/24 Delphi results on quark and gluon jets (Eur. Phys. J C17(2000)207) 3 jet events: e + -e - -> Z 0 -> q + q-bar + g Select Y-events –Require 150-15 deg < θ 2,3 < 150+15 deg (Ignore jet1) –Compare identified particle yield in quark (jet2) and gluon (jet3) This ensures that quark and gluon have similar kinematics –Gluon jet is identified by angle or history assigment (?)

15. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 15/24 Identified particles in quark and gluon jets from Y events Trivial, since pions dominate Leading baryon effect (will decrease with jet energy!) Enhanced overall particle prod. in gluon jets (NB! but less at high p) Baryon production is enhanced wrt charged particle production, but mostly at high p where gluon particle productions is suppressed! quark jetsgluon jetsg/q g/q / Nch(g)/Nch(q)

16. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 16/24 TPC proto field cage with IROC Test beam setup with Inner ROC at CERN PS T10 Beam parameters 1 < p < 7 GeV/c Online monitor: Single track PID @ p=3GeV/c

17. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 17/24 Energy loss resolution of identified particles Energy loss resolution for the truncated charge C is ~9% (IROC~47cm out of IROC+OROC~160cm)  Estimated final energy loss resolution (160 cm track): Minimum Ionizing Particle (MIP) 9.0%/  3.3~ 5.2% (low multiplicity e.g. p+p)

18. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 18/24 Truncated charge C vs βγ The truncated mean dependence on β  is similar to what was observed by Aleph (used in sim/TDR) and NA49. This confirms that there is the expected separation!

19. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 19/24 Model calculations of energy loss straggling functions PAI (Allison and Cobb model). Cross sections from Berkowitz. Hans Bichsel operates with different straggling functions: Energy loss Δ (Theoretical) Energy deposit & ionization Electron drift and amplification Final ADC value (Experimental) Monte Carlo simulation data from Hans Bichsel showing the Bichsel straggling function, and the Landau straggling function. NIM A 562 p.154 (big review) NIM A 566 p.1 (ALICE sim comment)

20. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 20/24 First Comparison Qualitative agreement between data and calculation (100% Neon at correct gas density) – –1 parameter: 1 ADC ~ 3 eV Calculations predicts an energy resolution σ C ~8.1% while for the data we find 9.3%! (Discrepancy of 15%) 7.5 mm Neon 60* 7.5 mm Ne

21. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 21/24 Energy resolution derived from straggling function The resolution derived from the experimental straggling function is 7.6% and NOT the measured 9.3%! Signals in neighboring rows show a correlation of +33%.   Information loss due to charge sharing that reduces the resolution The straggling function does not contain all information! σ=7.6 %! Generate tracks with 60 samples Exp. straggling dataDerived truncated mean

22. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 22/24 Simulation: Detector effects Simulation (include charge sharing detector effect) : –Input E (from Bichsel’s energy loss straggling function) –Convert to total electrons N = E/W (W=30eV) –Diffuse (220µm/  cm) and Amplify (exp.) each electron Other detector effects not included: –Capacitive coupling between neighboring rows (signal sharing) –Delta-electrons (small effect) Normalized

23. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 23/24 Final comparison 3 params: 2*gain (<3% diff)& W Proton 1GeV/cProton 3GeV/c

24. High p T - workshop in Jyväskylä - P. Christiansen (Lund) 27.3-2007 24/24 Conclusions and Outlook From the test beam results we concluded – –σ C / ~ 5% (p+p) -> (PbPb central) – –C(beta-gamma) according to expectations –Consistent with model calculations The results (and model calculations) can be used to calibrate the ALICE TPC simulation and improve the PID description Test beam: NIM A 565 p. 551 PID: physics/0703097