SMOG: an internal gas target in LHCb?

Transcription

1 System for Measuring the Overlap with Gas SMOG: an internal gas target in LHCb? intro: LHCb/VELO luminosity calibration what we use the SMOG for hardware implementation operational aspects impact on LHC possible extensions? Disclaimer: this talk and these slides have not been approved by the LHCb Collaboration. workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 1

2 LHCb location pp s 0.9 TeV 2.76 TeV 7 TeV 8 TeV p-pb s NN 5 TeV LHCb AFTER@LHC workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 2

3 LHCb: single arm spectrometer at LHC point 8 Core program: study of b and c hadrons (CP, rare decays,...) But also: W/Z boson production, forward searches, QCD,... beam1 beam2 crucial: displaced IP 11.25m AFTER@LHC workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 3

4 VErtex LOcator Essential role in all measurements with SMOG workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 4

5 VELO sensors: R and Phi silicon microstrips "Performance of the LHCb Vertex Locator", LHCb Collaboration, J. Instrum. 9 (2014) P09007, arxiv AFTER@LHC workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 5

6 A crucial item: the "RF Boxes" beam side coated with NEG (reduction of Secondary Electron Yield) workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 6

7 Result excellent impact parameter resolution feature used for beam-gas imaging workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 7

8 SMOG's primary role: luminosity measurement Idea: measure individual beam profiles and calculate the overlap Beam shapes, positions, angles measured by reconstructing beamgas and beam-beam interaction vertices and fitting all distributions with a model AFTER@LHC workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 8

9 LHCb beam-gas imaging Beam-gas imaging method, proposed in 2005, for luminosity calibration Successfully tried for first time in 2009, pp collisions at 0.9 TeV ~15% Phys. Lett. B 693 (2010) beam 1 beam 2 lumi Achieved 3.5 % in 2010, agreement with van der Meer method J. Instrum. 7 (2012) P01010 P.Hopchev CERN-THESIS Now 1.43% (2012 pp data 8 TeV), lots of info from that... AFTER@LHC workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 9

10 Latest result of LHCb BGI luminosity calibration Every data point is a bunch pair averaged over 20 min repeated over several periods of time and many different bunch pairs Detailed analysis reveals subtle effects of non-factorizability (XY) AFTER@LHC workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 10

11 BGI / LHCb: most recent results CERN-THESIS arxiv (accepted by JINST) AFTER@LHC workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 11

12 Pumping up the beam-gas rates 2009: use pure residual gas p ~ 1e-9 mbar of more or less unknown composition and VELO was not closed around the beams : increased rate by turning off the ion pumps in the VELO vacuum system (beam vacuum) => p ~ 5e-9 mbar of more or less unknown composition 2012: increase drastically the rate by injecting Neon gas into the VELO vacuum (of course with ion pumps switched off) => p ~ 1.5e-7 mbar of Neon AFTER@LHC workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 12

13 LHCb vacuum system layout workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 13

14 This is SMOG restriction workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 14

15 factor ~4 more for Ne Rate and luminosity (for beam-gas interactions) bunch revolution frequency protons per bunch z-dependent acceptance factor Neon gas density profile inelastic p-ne cross section luminosity L Hz/cm 2 per p ~ mbar this is everything we know now about the target density... AFTER@LHC workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 15

16 4TeV proton beams VELO acceptance for beam1-gas and beam2-gas is visible here workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 16

17 Beam-gas imaging can do a lot Transverse beam sizes/distributions full beam and b-by-b Ghost charge compare rate in bunch slots and empty slots crucial for precision lumi calib Relative bunch charges compare rates between bunch slots Beam positions and angles Longitudinal distribution if time info is added (order of ~0.1ns resolution) AFTER@LHC workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 17

18 See P.Hopchev s talk at DITANET Workshop 9th DITANET Topical Workshop on Non-Invasive Beam Size Measurement for High Brightness Proton and Heavy Ion Accelerators, 16 April 2013 AFTER@LHC workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 18

19 Ghost charge LHC DCCT measure total circulating current (all protons in ring) LHC FBCT measures relative bunch population in each of 3564 LHC 25ns slots population must be above above a given threshold (of order ~1e9) sum of FBCT signals is then normalized to the total current (DCCT) How many protons are not seen by the FBCT? Measured by LHCb with beam-gas rates pp 8TeV pp 2.76TeV AFTER@LHC workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 19

20 First SMOG gas injection test with beams (nov 2011) Done with Pb beams (no collisions in IP8) VELO ion pumps are off during gas injection Pressure is back to normal within minutes after stopping injection and restarting ion pumps workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 20

21 Q1 Current vacuum configuration compensator magnet for LHCb dipole ion pump VELO (+SMOG) powerful ion pumps ion pump Be pipe sections NEG coating on warm beam pipe sections needed for reduction of SEY (not much for pumping) including VELO RF boxes Q1: cryo!! warm-to-cold transition! SS pipe sections Q1 workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 21

22 Possible Fixted-Target usage of SMOG Target thickness measurement: Currently, LHCb is not measuring the density of the target gas This could be done with relatively simple appendages 5% precision? just a guess... transverse distribution not changing significantly over the beam size longitudinal distribution can be measured Target type: Distinguish between two "categories" of gases: getterable (N 2, CO 2, etc) or non-getterable (He, Ne, Ar, Kr, Xe) Pay attention to impact on LHC (dynamic surface effects) Luminosity (target thickness) amplitude: Now (Neon): L ~ Hz/cm 2 = 1 b -1 /s for a full LHC p-beam (i.e p) Limited by pressure interlocks. Levels could be scrutinized. An increase by a small factor (5-10) is not excluded. AFTER@LHC workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 22

23 Issues to be aware of when injecting gas into LHC(b) LHCb: beam-gas background cohabitation with beam-beam LHCb physics? Use of the non-colliding bunches? radiation damage: there is margin (pp luminosity is much higher) Getterable gases: NEG saturation (RF boxes and beam pipe) NEG is there primarily to reduce beam-dynamic surface effects, not so much for pumping. A monolayer-saturated NEG is not necessarily a problem, depending on what type of atoms are deposited. Non-getterable gases: cryosorption at Warm-to-Cold transition again, beam-dynamic surface effects to be addressed Beam life time: there is margin! For LHCb/SMOG the beam-gas induced life time is O(10 8 s) AFTER@LHC workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 23

24 Secondary Electron Yield of noble gases Ne Kr Ar Xe Measurements of the Secondary Electron Emission from Rare Gases at 4.2K, Y. Bozhko, J. Barnard, N. Hilleret (Submitted on 10 Feb 2013) workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 24

25 LHCb can do (is doing) ion physics Already published by LHCb Collaboration: "Study of J/ψ production and cold nuclear matter effects in ppb collisions at s NN = 5 TeV", J. High Energy Phys. 02 (2014) 072 "Study of Υ production and cold nuclear matter effects in ppb collisions at s NN = 5 TeV", J. High Energy Phys. 07 (2014) 094 "Observation of Z production in proton-lead collisions at LHCb", J. High Energy Phys. 09 (2014) 030 More publications and more measurements coming: continue p-pb considering also extensions of physics program with SMOG (fixed target, Pb-Ar, p-ar, Pb-Ne, p-ne...) AFTER@LHC workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 25

26 Polarized internal target? (what nuclei...?) 1 H, 2 H, 3 He? VELO alcove challenges: - space - magnetic stray fields AFTER@LHC workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 26

27 Space around VELO: seen from alcove entrance Fun video from Moedal Collaboration showing space around VELO workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 27

28 Space around VELO: seen from inside alcove Fun video from Moedal Collaboration showing space around VELO workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 28

29 Summary LHCb has pioneered the use of gaseous fixed target in the LHC for beam-gas imaging, luminosity calibration, ghost and bunch charge measurements This was based on a simple appendage to the VELO vacuum system and on a pretty nice detector LHCb has extended its physics program well beyond its original scope (flavour physics) and is likely to continue extending it Some extensions involving just the measurement of distributions of particles from beam-gas interactions are straightforward (could already be done) New target types would require some minimal studies and changes Extensions requiring knowledge of the gas density (for normalization) would require some new, yet still quite simple, hardware Extensions involving target polarization would require much bigger investments and long studies AFTER@LHC workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 29

30 workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 30

31 LHCb extended use of SMOG (being considered) Look at PbAr collisions to study charmonium suppression in these collisions, with several states (J/psi, chi_c and psi(2s)). This allows to probe the quark gluon plasma (QGP), which is formed in these collisions (this we know from NA50) The centre of mass energy is 72 GeV per nucleon. The LHCb rapidity coverage is (in the nucleon centre of mass frame): -1.8 < y* < 0.2 and thus includes the central region where QGP effects are larger. For a gas pressure of 10-6 mbar, the integrated luminosity for one month running is 0.7 nb-1. That means 1.4x10^5 J/psi produced in the LHCb acceptance per month. A realistic efficiency is about 30% to reconstruct them, that corresponds to the samples collected usually in fixed target experiments like NA50, but we can do more measurements than what was done (like chi_c, B production, etc...) The gas pressure has a big role in these numbers (the number of J/psi depends linearly on it) so the higher the better :) A Neon target is also interesting, the energy density is smaller so may be not enough for QGP. And the other important points are that we can have par collisions for reference, and that the multiplicity in PbAr fixed target are much smaller than these in PbPb collisions, and manageable for LHCb. AFTER@LHC workshop 17-Nov-2014 CERN Massimiliano Ferro-Luzzi 31