Introduction to PHENIX Beam Beam Counter (BBC)

Introduction to PHENIX Beam Beam Counter (BBC)
Yuji Tsuchimoto for the PHENIX/BBC group (Hiroshima Univ.) Let me start today’s PHENIX Focus, introduction of beam beam counter. I am Yuji Tsuchimoto from Hiroshima University.

Purpose of PHENIX BBC Collision Vertex initial point of charged particle tracking Centrality Determination Impact Parameter Determination with ZDC Beam-Beam counter has 5 major purpose in PHENIX experiment. One is collision vertex measurement. Almost all shift clew watch BBC vertex distribution on online monitor during the run. Second, BBC provides minimum bias trigger. It is called BBLL1. Almost all data of Run4 is this BBLL1 minimum bias triggered event. Third, BBC provides start timing of Time-of-Flight measurement with ToF or EMC. And BBC charge information is used to determine centrality with ZDC energy information. And BBC charge information is also used for reaction plane determination. Minimum Bias Trigger Level1 Trigger with Online Vertex Cut Time-Zero Determination Start Timing for ToF Measurements Reaction Plane Determination Direction of Impact Parameter Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Level1 Trigger (efficiency )
Contents HV Offline Correction TDC ADC Collision Timing Timing Information Vertex Position Front-end Electronics (calibration) Counter Reaction Plane Charge Information Centrality Particle Level1 Trigger (efficiency ) Let me introduce beam-beam counter elements at first. Simulation Study Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

- Yuji Tsuchimoto - PHENIX Focus - BBC -
Where is PHENIX BBC? BBC is installed on about one and a half meters from the center of PHENIX detector for both North and South arm along beam axis. BBC covers between 3.1 and 4.0 of pseudo rapidity, and 2 pi of azimuthal angle. It detects relatively high momentum charged particles which velocity is greater than 70% of light speed in the forward. North South cm ⊿η = 3.1 ~ 4.0 ⊿φ = 2π Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Hardware Component BBC has 64 elements for North and South arm. BBC has 64 elements in each arm. The bottom figure shows one element of counter. This element was assembled by hexagonal quartz Cherenkov radiator and meshed dynode photomultiplier. Quartz has 2.5 cm of width and 3 cm of length. Threshold velocity of Cerenkov emitting is 0.7. Typical Operational HV is 1.5 to 2 kV. Each element is assembled by Quartz Cherenkov radiator(bth=.7) and meshed dynode PMT. Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Contents HV Offline Correction TDC ADC Collision Timing Timing Information Vertex Position Front-end Electronics (calibration) Counter Reaction Plane Charge Information Centrality Particle Level1 Trigger (efficiency ) Next I will show high voltage and front-end electronics. Simulation Study Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Readout Analog signal (PMT output) from BBC
Digitized at Front End Module (FEM) TDC0 (for ADC gate) TDC1 (for Local Level1) ADC Accumulated in AMU Data Collection Module (DCM) Event Builder PHENIX Raw Data Format other subsystem data BBC Local Level 1 Global Level 1 decision Minimum bias at Run4 (Au+Au) ( BBCN>=2 & BBCS>=2 & BBCZ<36 [cm] ) & ( ZDCN & ZDCS ) BBLL1 Selected (ZDC&BBLL1) ZDC triggered Photomultiplier outputs analog pulse. Raw signals are accumulated by Front End Modules via about 8 meter of cables. This cables are called as “Andrew Cable”. The signal velocity in the Andrew Cable is about 80% of light speed in the vacuum. This is one FEM board. It was developed by Navis Group. One board has 8 channels of inputs. Therefore we have 16 boards for 128 PMTs. Front End Module contains 1 ADC and 2 TDC for each channel. This ADC is high-speed charge sensitive ADC. And this is self gate ADC. The gate is opened by TDC0. And TDC1 provides timing information for local level 1. Then TDC0 threshold is set lower than TDC1. Digitized data is accumulated by DCM, and processed by common event builder. On the other hand, BBC FEM provides BBLL1 information. This BBLL1 information is used for Global Level 1 decision. The BBLL1 information contains online prompt vertex information. This is offline vertex distribution measured by BBC. But those events were triggered by ZDC. The blue region is selected events by BBLL1 online vertex cut within 36cm. Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

FEM Calibration (ADC, TDC)
details in PHENIX Technical Note 393 charge [ch] DAC value charge [pC] ADC [ch] TDC [ch] delay [ps] ADC pedestal was obtained by extrapolation to zero DAC value of internal charge scanning. ADC Pedestal : 700~1000ch ADC conversion factor [pC/ch] was obtained by external charge injection. Conversion factor : ~0.4 [pC/ch] Dynamic range : ~1200pC TDC conversion factor [ns/ch] was measured using test pulse. Conversion factor : ~7 [ps/ch] Dynamic range : ~21 [ns] Those ADC and TDC has 12 bits resolution. Our FEM has internal pulse injector for calibration at each channels. It is called “Test Pulse” The top figure shows internal charge scanning. We can change pulse height of internal charge injector. The horizontal axis is an arbitrary unit of pulse height. And vertical axis is measured ADC. We calibrate ADC pedestal by extraction at zero point of the line. The typical pedestal is around 1000 channel. Then the ADC has about 3000 channels of dynamic range. The middle figure shows external charge scanning. We cannot measure absolute pulse height of internal test charge. Then we calibrate ADC conversion factor using external charge injector. The typical conversion factor is 0.4 pico coulomb per channel. And its dynamic range is about 1.2 nano coulomb. The bottom figure shows internal timing scan. We can change timing delay of the test pulse. The timing tick is known and can be determine as pico second. The vertical axis is measured TDC value. We calibrated TDC conversion factor by the slope. The typical dynamic range is 21 nano second. Now the internal charge and timing scan are also taken by shift clew. Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

details in PHENIX Technical Note 393
HV configuration details in PHENIX Technical Note 393 Calibrate PMT gain using MIP peak measured at physics run Gain curve was obtained by HV scan with laser. Shift the curve at single particle peak Adjust HV to 40(outer) or 30(inner) pC/MIP Inner PMTs are operated at lower HV due to avoid ADC overflow Averaged HV in HV sharing group (operational Voltage) Single particle peak 40 Let me show how to decide operational HV for BBC. This is a typical ADC spectra of one PMT. But some special cut was applied on this spectra. I required no hit around one hit PMT to reject injection to boundary of photomultipliers. As introduced previous slide, TDC0 opens ADC gate. Then ADC spectra has threshold around 30 channel. We calibrate PMT gain using the single particle peak in Physics event. Sometimes this single particle is called MIP. As you know, BBC isn’t detect ionization. We fit this spectra by Gaussian function with empirical background shape like the red line. In this case, the single particle peak is at around 120 channel. It is corresponding to 50pC. And this PMT was operated 1801V. Then we can plot this green triangle point. Second, we took HV scanning data with PPG laser. The laser peaks are plotted by green circle. Then we got gain curve of the PMT. Next we shift the gain curve to the MIP point. Normally PMT gain are adjusted as 40 or 30 pC/MIP. It is required by that MIP peak is higher than ADC threshold, and most multiplicity events should not be overflow. The outer PMTs are operating as 30pC/MIP, and inner PMTs are operation as 40pC/MIP. Because inner PMTs have relatively higher multiplicity than outer. Now we got gain curve of MIP peak at 40pC/MIP in this PMT’s case. Its best HV is 1.78 kV. But PMTs are sharing HV with 7 to 10 tubes. Finally we took average of HV sharing PMTs. This is blue triangle point. Of course, we grouped similar gain tubes. Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Contents HV Offline Correction TDC ADC Collision Timing Timing Information Vertex Position Front-end Electronics (calibration) Counter Reaction Plane Charge Information Centrality Particle Level1 Trigger (efficiency ) Next I will show timing measurements. Simulation Study Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Slewing Correction (Reference time) – (PMT hit time) of typical PMT
details in PHENIX Technical Note 393 (Reference time) – (PMT hit time) of typical PMT ADC [ch] before correction after correction Slewing effect was corrected by this empirical function Intrinsic time resolution : 40±5ps To calculate hit-timing from TDC, we correct slewing effect. As you know, PMT has a correlation between ADC and TDC. This slot is a typical slewing structure. The horizontal axis is ADC, and the vertical axis is difference between reference time uncorrected hit time. This reference time means average of corrected hit time of all hit PMTs in the same arm. After correction, we got corrected hit-time. For run2 configuration, average intrinsic resolution is 40 pico second. In principle, it is same as Run4. a, b, c : constant ADC : after pedestal subtraction Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Z-Vertex and Time zero BBC South BBC North L Vertex position TS TN BBLL1 Selected (ZDC&BBLL1) ZDC triggered Z-Vertex Time zero Let me show how to calculate the collision timing and the collision vertex position in Z axis. BBC measures timing of charged particles from collision vertex. We can calculate vertex position by difference of both hit timing like this. And we can also calculate colliding time by average hit-time and path length. This is Run4 vertex distribution measured by BBC. After online vertex cut at BBLL1, BBC can triggered blue region. Those small peaks at plus minus 1.5m are particles from outside of BBC like this. In this case, BBC cannot measure where did particle come from in principle. It may be doe to beam-gas interaction or so on. At before run, we had large number of beam-gas events, but at Run4, RHIC is providing better beam. TN/S : average hit time, c : light velocity, L : cm Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Resolution at RUN2 (Au+Au)
BBCZ - PCZ BBCZ - ZDCZ PCZ - ZDCZ PHENIX has 3 detectors to measure vertex. Those are BBC, ZDC and Pad chamber. If all measurements are independent. Intrinsic vertex resolution for each detector can be extracted by solving those equations. These plot shows the difference of vertex between BBC and PC, BBC and ZDC, PC and ADC respectively. We got 20[ps] of BBC intrinsic time resolution. It is corresponding to 6mm of vertex resolution at the circum stance of high multiplicity. Time Zero : 20 [ps] Z-Vertex : 0.6 [cm] ( at Run2 ) Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Time of Flight Resolution
TOF – TOF expected [ns] H. Masui Resolution of time zero (start timing) by BBC is 20 [ps] Resolution of Time of Flight is 113 [ps] Resolution of TOF detector (stop timing) is 111 [ps]   ~ 113 ps K p Now we got 20ps of BBC time resolution. BBC time zero is used as start timing. Stop timing was measured by TOF counter. This figure shows correlation between time-of-flight and momentum. This momentum is measured by drift chamber. We can see clear line of proton, kaon, pion, muon, electron and takion? I don’t know what is this line beyond light speed. The top figure shows measured mass spectra by BBC and ToF. We got 113 ps of timing resolution by fitting of pion peak. Using the 20 ps of BBC timing resolution, ToF stop timing resolution is 111ps. As you know, EMC can be used for stop counter. It is used for particle identification including anti-neutron. Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Contents HV Offline Correction TDC ADC Collision Timing Timing Information Vertex Position Front-end Electronics (calibration) Counter Reaction Plane Charge Information Cectrality Particle Level1 Trigger (efficiency ) Next I will show simulation study. Simulation Study Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

What does BBC detect? beam pipe Z-direction R-direction Collision point (b) BBC (a) : Internal track coming from collision : External track not coming from collision inner ring middle ring outer ring RING ID BBC 50% of external track was estimated compared to all injected particles using HIJING Au+Au 130GeV events inner ring = 43% middle ring = 52% outer ring = 57% Main background source is beam pipe Beryllium (thickness 1.02 [mm]) : < 75 [cm] Stainless Steal (thickness 1.24 [mm]) : < 200 [cm] BBC signal contains some background from materials inside BBC. I categorized injected particles to BBC for 2 groups. One is initially toward BBC. The others is not directed to BBC originally. According to our GEANT simulation, around a half of injected particles are coming from scattering in materials like (b). But main background source is from beam pipe of stainless steal. Its pass length is not so different from (a). Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

BBC Response in Simulation
Implemented for BBC Response PMT gains based on observed MIP peak One sigma width of observed MIP peak ADC pedestal value ADC conversion factors [pC/ch] TDC overflow value TDC RMS of overflow value TDC conversion factors [pC/ch] TDC threshold value Slewing effect and parameters PMT intrinsic time resolution Relative time offset between North and South We implemented variable constants to simulate BBC reaction as real as possible. Almost all constants were based on real data by physics run. It is applied for the GEANT output to obtain the trigger efficiency of BBC. Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Events for Trigger Efficiency
HIJING 1.35 (Au+Au 200GeV) with default options was used to obtain trigger efficiency of BBC at Run2 (Au+Au). impact parameter < 25 [fm] sqrt(sNN) = 200 [GeV] dN/dy in HIJING events are modified to evaluate systematic uncertainty because of trigger biases is model dependent. Z-Vertex distribution was adjusted to real data of run# The exactly same Level 1 emulator was applied to this simulated data. We used HIJING 1.35 (Au+Au 200GeV) as event generator. We used default options for HIJING. It was used to obtain trigger efficiency of BBC at Run2 (Au+Au). dN/dy in HIJING events are modified to evaluate systematic uncertainty because the trigger bias depends on some model. For example, default HIJING provides somewhat small number of multiplicity for BBC. It is shown as blue line in the charge sum distribution. We enhanced multiplicity by about 10% as same as real data. It is shown as green line. The vertex distribution was adjusted to real data of run# And we used exactly same Level 1 emulator in this simulation. details in PHENIX Analysis Note 107 Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Definition of Trigger Efficiency
Efficiency required only BBC Local Level 1 Efficiency required BBC Local Level 1 and offline vertex cut Let me show the definition of trigger efficiency. The BBLL1 trigger efficiency is defined like this function. This study was for Run2 trigger efficiency. Then we cut 75 cm of online BBLL1 vertex. Next I want to know the real trigger efficiency after 30 cm of offline vertex cut. We got about 90% of trigger efficiency for Run2. At this Run4, we are using 36 cm of BBLL1 vertex cut. It may reduce trigger efficiency a little because of edge of prompt online vertex cut. Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Trigger Efficiency details in PHENIX Analysis Note 107 Systematic uncertainties BBLL1 cut : 75cm ( in Run2 case ) Offline Vertex cut : 30cm 1) Input dN/dy used modified HIJING events as controlled samples ±1.29% 2) Input Z-vertex distributions due to cutting edge of BBLL1 vertex cut ± 0.56% 3) Trigger threshold on TDC1 ±0.75% Considering those uncertainty of multiplicity and vertex distribution, We god 93.1% of BBLL1 trigger efficiency for Run2. It is not so different for Run4. 1)As for the item 1, we prepared modified HIJING events where North/South side tracks were flipped each other and certain fraction of those flipped tracks in one side were merged to original tracks in another side in each collision. Figure shows dN/dy of those generated HIJING event samples where the normal, 10% increased, and 20% increased samples are plotted with blue, green and pink curve, respectively. 2) Concerning the item 2, there should be almost no dependence on Z-vertex distribution, since our definition of the trigger efficiency should cancel out the Z-vertex position dependence. However, the vicinity of cutting edges of the BBLL1 vertex cut, the enhancement of trigger efficiency is seen due to contaminations from other true vertex bins. 3) As for the item 3, we applied 50% increased and 50% reduced threshold values from the default one for the evaluation of threshold dependence. This 50% includes uncertainties on the true hardware threshold values and the PMT gains. Trigger Efficiency : 93.1% ± 0.4%(stat.) ± 1.6%(syst.) Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Contents HV Offline Correction TDC ADC Collision Timing Timing Information Vertex Position Front-end Electronics (calibration) Counter Reaction Plane Charge Information Centrality Particle Level1 Trigger (efficiency ) Next I will show impact parameter determination. Simulation Study Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

BBC ChargeSum p+p (Run3) d+Au (Run3) Au+Au (Run4) BBC charge sum is related to number of participant It has also anti-correlation with ZDC energy sum. Those are ChargeSum correlation between North and South. Charge Sum means the summation of 64 tubes in one arm. There is no correlation at proton-proton run. In contract, there is strong correlation at gold-gold run. BBC charge sum is related with number of participant. In the gold-gold case, when beam is collided, the interacted region is participant, and the blue region is spectator. BBC can detect forward scattered participants. And ZDC can detected neutral spectator. Then there is anti correlation between BBC charge sum and ZDC energy sum. participants go into BBC go into ZDC spectator Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Centrality Determination
Event characterization in terms of impact parameter (b) in Au+Au collisions. Large : peripheral collision Small : central collision Coincidence between BBC and ZDC. Determine collision centrality. 93 % of inelastic cross section can be seen. Extract variables using Glauber Model Number of participants (Npart). Number of nucleons participate in a collision. Represents centrality. Related with soft physics. Number of binary collisions (Nbinary). Number of Nucleon-Nucleon collisions. Related with hard physics. Incoherent sum of N-N collisions becomes a baseline for A-A collisions. 0-5% 15-20% 10-15% 5-10% We can determine centrality using correlation between BBC charge sum and ZDC energy sum. And we got 93% of BBLL1 trigger efficiency. It means most peripheral events are 93% of centrality. We are using radially selection of centrality like this figure. If we assume some model like a Glauber Model, We can estimate number of collisions and number of participants. Those are event characterizations with respect to impact parameter b. Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Contents HV Offline Correction TDC ADC Collision Timing Timing Information Vertex Position Front-end Electronics (calibration) Counter Reaction Plane Charge Information Centrality Particle Level1 Trigger (efficiency ) At last, I will show reaction plane determination Simulation Study Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

reaction plain (Ψ) by BBC
Reaction Plane details in PHENIX Analysis Note 151 : S. Esumi et al. (Univ. of Tsukuba) Reaction plane Target Projectile b:impact parameter Reaction plane reaction plain (Ψ)　by BBC The reaction plane is defined by the direction of the impact parameter and the beam direction. BBC charge distribution can be used for determination of the reaction plane using this function. It is like Fourier transform. The reaction plane angle phi is the azimuthal angle between the reaction plane and horizontal axis of the laboratory. The reaction is a one of the event characteristics related to event anisotropic analysis, e.g. collective flow, hard processes, jet-quenching and HBT source radii etc.. The reaction plane could be measured by BBC using ADC value of each PMT for both arm respectively. initial geometry final momentum anisotropy ADCi : calibrated ADC of each PMT Φi : azimuthal location of each PMT n : order of harmonics collective flow, hard processes, Jet-quenching and HBT radii, etc… Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Corrected Reaction plane correlation
Reaction Plane by BBC details in PHENIX Analysis Note 151 : S. Esumi et al. (Univ. of Tsukuba) -- no correction -- ring-by-ring gain correction -- average subtraction (shift correction) -- fluttening Corrected Reaction plane correlation azimuthal angle Φ Dead PMT in South Several collections are applied to measured raw reaction plane. First, ring-by-ring gain collection because of pseudo rapidity is a little bit different in BBC ring-by-ring. Second, average of whole event was subtracted. And last, correct remaining component using flattering method. This plot shows the correlation of reaction plane between obtained by BBC North and South after those correction. It is used for variable v2 measurements. Unfortunately we have one dead PMT in South. But fortunately those 4 PMTs are not used for determination of reaction place to keep hexagonal symmetry doe to providing better reaction plane resolution. Ignore 4 PMT To keep hexagonal symmetry Ψ (BBC South) Ψ (BBC North) Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

BBC Guys DC : Toru Sugitate contact person Kensuke Homma Tomoaki Nakamura Takashi　Hachiya Yuji Tsuchimoto Kenta Shigaki Finally, let me introduce the current member of BBC staff. Kota Haruna Hiroyuki Harada Akitomo Enokizono Ryota Kohara Feb - Yuji Tsuchimoto - PHENIX Focus - BBC - BBC mailing list

Backup Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Contents What’s BBC? Where’s BBC in PHENIX? Detector and Electronics Calibration and Correlation What does BBC detected? What can BBC measure? Collision Timing Vertex Point Level-1 trigger Centrality Determination with ZDC Reaction Plane Measurement Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Purpose of PHENIX BBC Minimum Bias Trigger BBC & (ZDC or NTC)
Centrality Determination with ZDC Beam-Beam counter has various purpose in PHENIX experiment. 1) One of them is a minimum bias trigger with ZDC or NTC. 2) Second, charge sum information measured by BBC is used for centrality determination as event characteristics. 3) Then, timing difference between north and south BBC provides start timing for time-of-flight measurement. 4) And the last, BBC can determine collision vertex. This information is used as initial point of charged particle tracking. Time Zero 　 start timing for time-of- flight measurement Collision Vertex initial point of charged particle tracking Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Multiplicity dependence of Intrinsic time resolution
Typical PMT Resolution [ns] Intrinsic time resolution is getting worth decreasing multiplicity, because of ambiguity of reference time. The reference time, which is used for slewing correction is not confident at the low multiplicity. Number of required hit PMT Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Injected particles to BBC
HIJING Au+Au √s 130 A GeV minimum bias ( 0<b<14 fm ) Initial velocity > 0.7 c ・Inner Ring (2.98 < |η| < 3.50) ・Middle Ring (3.20 < |η| < 3.50) ・Outer Ring ( 3.50 < |η| < 3.92) HIJING emits 0~900 particles in the acceptance of BBC. Fig. 1 : (Number of Particles vs. Impact Parameter) by PID Fig. 2 : (Number of Particles vs. Impact Parameter) ring by ring of BBC ・All Particles ・π+, π- ・π0 (Fig. 2) (Fig. 1) Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Background Source This is all vertex position of each secondary particles that are injected to BBC. Fig.10 is electron or positron at each vertex position. Fig.11 is charged pion. Almost of electron and positron are produced at beam pipe of Stainless steal. electron, positron at each position (Fig. 10) π+, π- at each position (Fig. 11) Beam Pipe Stainless steal BBC inner edge of central magnet (Fig. 12) MVD Beryllium pipe Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Material Contribution
contents of particle for charge sum ring by ring charge sum inner ring middle ring outer ring Inner ring Middle ring Outer ring (# of particles) Ratio Ratio of external particles (External/All Injected) vs. Number of particles per one PMT HIJING Au + Au √s = 130 A GeV minimum bias (0<b<14 fm) Z-Vertex ( 0 cm) (Fig. 15) (Fig. 16) (MIP) Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Z-Vertex distribution Distance from BBC to Z-Vertex (cm)
Z-vertex dependence Ratio of external particles (External/All Injected) vs. Distance from BBC to Z-Vertex point (cm) HIJING Au + Au √s = 130 A GeV minimum bias (0<b<14 fm) Z-Vertex (RMS = 30 cm) Z-Vertex distribution for the same events Inner ring Middle ring Outer ring Distance from BBC to Z-Vertex (cm) Ratio (Fig. 17) (Fig. 18) Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

BBC Response (ADC) At Cherenkov detector, number of produced photo electron is calculated by this formula. BBC quartz 1 2 3 4 L : path length of particles in quartz εc : collecting Cherenkov light efficiency εd : quantum efficiency of photo electron conversion β>0.7 and incident angle>±45° Charge value of PMT output is calculated by PMTGainFactor and # of Photoelectron. ADC input value is split in FEM. Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

BBC Response (ADC) Charge value for ADC input is summarized by this constant value. This constant value is tuned by 1 MIP peak of real data for 128 ADC channel. This ADC charge value is randomized by Gauss function with width of 1 MIP, channel by channel. After randomization, charge value is converted to ADC[ch] by ADC conversion factor [pC/ch] and pedestal, which is obtained by internal charge injection. Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

BBC Response (TDC) Time of Flight is extracted from GEANT as fastest track β>0.7 and incident angle>±45 Threshold was applied for each TDC TDC1 (ADC>5pC), TDC1 (ADC>15pC) Slewing effect is implemented Intrinsic timing resolution was added for each channel. Timing offset was added. Global timing offset set to 1500 [ch], which is center of time window of TDC. TDC[ns] = TOF – (SlewParA + SlewParB/ADC_without pedestal + SlewParC*log(ADC without pedestal)) TzeroOffset=(BBC_Zvertex-PC_Zvertex)/2 (North+, South-) TDC[ch] = (TDC+TzeroOffset)/Conversion_factor + GlobalTimingoffset BBC quartz 1 2 3 Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Reaction Plane Resolution
details in PHENIX Analysis Note 151 : S. Esumi et al. (Univ. of Tsukuba) central region : small elliptic flow mid-central region : best resolution peripheral region : low number of tracks The resolution of reaction plane is defined by this equation. Since we cannot know the phi true, so it could be evaluated by sub-event analysis. In the BBC case, phi A and B correspond to North and South. This equation could be expanded like this. The sine term vanishes because of reflection symmetry, that is even function. If we assume resolution of each arm is equal, resolution is obtained by this equation. Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Calibration (HV, Z-offset)
Gain curve of each PMT was obtained by laser. It is scaled to measured output charge of one MIP peak. Operational HV value were determined to 40 pC for one MIP, so that the dynamic range of ADC is 30~35 MIP. BBC cannot provide absolute Z-vertex positions by itself because it is calculated by the hit timings of North and South. Global offset is adjusted to PC-Z at Run2, which is geometrically adjusted center of PHENIX In this case, offset is 1.075cm details in PHENIX Technical Note 393 (BBC Z) - (Pad Chamber Z) [cm] Gain curve of each PMT was obtained by laser. It is scaled to measured output charge of one MIP peak. Operational HV value were determined to 40 pC for one MIP, so that the dynamic range of ADC is ~30 MIP. BBC cannot provide absolute Z-vertex positions by itself because it is calculated by hit timings of North and South. Global Z offset is adjusted to PC-Z at Run2, which is geometrically adjusted center of PHENIX. In this case, offset is 1.075cm. We will determine its offset by using the laser signal. Feb - Yuji Tsuchimoto - PHENIX Focus - BBC -

Introduction to PHENIX Beam Beam Counter (BBC)

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