Please see the plot and the message/explanation below from Chuyu Liu for his calculation about luminosity reductions (within z= +/-
10 cm or outside)
for pp.
Kin
From: Liu, Chuyu <cliu1 AT bnl.gov>
Sent: Thursday, September 21, 2023 12:19 PM
To: Yip, Kin <kinyip AT bnl.gov>; Hock, Kiel <khock AT bnl.gov>
Cc: Fischer, Wolfram <wfischer AT bnl.gov>; Minty, Michiko <minty AT bnl.gov>; Drees, Angelika <drees AT bnl.gov>; Huang, Haixin <huanghai AT bnl.gov>
Subject: Re: [Sphenix-run-l] Fwd: [request for input] sPHENIX crossing angle with PP in Run24
Here's the plot along with some key messages:
-
The reduction in luminosity for polarized protons is milder compared to AuAu, primarily because of the shorter
proton bunch length, resulting in a reduction factor of 4 compared to a reduction factor of 6 for AuAu with 2 mrad crossing angle.
-
Luminosity within a range of +/- 10 cm accounts for 20% of the total luminosity when there is no crossing angle.
-
When a 1 mrad crossing angle is introduced, the luminosity within +/- 10 cm is 94.0% of the luminosity without
a crossing angle.
-
Similarly, with a 2 mrad crossing angle, the luminosity within +/- 10 cm is 79.4% of the luminosity without a
crossing angle.
Chuyu Liu
Collider Accelerator Department,
Brookhaven National Lab, Upton, NY
Work: +1 631 344-4431
Cell: +1 631 202-7823
Yes , I think that is what Tony asks (for now at least).
-------- Original message --------
Date: 9/21/23 07:35 (GMT-05:00)
Subject: Re: [Sphenix-run-l] Fwd: [request for input] sPHENIX crossing angle with PP in Run24
Sure, I can work on that. I will plot total luminosity and
+/-10 cm luminosity VS crossing angle, similar to what wolfram did before. Would that be sufficient?
Chuyu Liu
Collider Accelerator Department,
Brookhaven National Lab, Upton, NY
Work: +1 631 344-4431
Cell: +1 631 202-7823
Hello Chuyu and all,
As Tony asked below, do you have a way to estimate how much luminosity is inside +/- 10 cm ?
You've got non-Gaussian shapes of beam profiles etc. in your simulation. I think, you have had some knowledge of beam profiles/sizes. Can you please do your luminosity calculations for just
+/- 10 cm and give us the results ?
Kin
On 9/19/23 15:48, Anthony Frawley wrote:
For most of the sPHENIX physics program, the usable luminosity is from collisions inside the MVTX acceptance (z = +/- 10 cm). Increases in luminosity
that occur outside the acceptance of our silicon do not help that program, but they contribute background in the TPC that is harmful.
It is important to understand by how much the luminosity inside z = +/- 10 cm would increase with a reduced crossing angle.
Thanks for sharing, this was really interesting. One thing that's not clear to me, when it is said that we aren't able to get the luminosity that we had in previous runs "after
so many years", do we really understand the issue? Is it a training issue - I understand that a large fraction of C-AD operators up until Run 23 hadn't been around for top energy running. Is it something in the RHIC ring itself? AGS? Since the luminosity
is so important both to the program we can have in sPHENIX and for the EIC, I'd like to understand it a bit better.
Chuyu Liu
Collider Accelerator Department,
Brookhaven National Lab, Upton, NY
Work: +1 631 344-4431
Cell: +1 631 202-7823
Hi,
Our polarization experts such as Ralf Seidl and Sasha
have had some email discussion about the polarization effect with crossing angles.
-
What is at stake here? Do we have guidance from CAD on crossing angle vs maximum luminosity?
In the RHIC Retreat, basically, C-AD (Chuyu Liu and Wolfram Fischer) told us that what we saw ( a factor of 6-7) is “right” and
real.
Their previous calculation assuming Gaussian only profile is wrong. After the RHIC Retreat, I asked Chuyu and he
sent us this file for his new calculation :
https://bnlbox.sdcc.bnl.gov/index.php/s/9oDpcep7ZD5Ciyk
Kin
This seems like a very important question that we should make sure to get right.
What is at stake here? Do we have guidance from CAD on crossing angle vs maximum luminosity?
Hi Stefan,
Ralf has calculations of the expected impact of the cross angle on polarization. I haven't seen any calculations like that from STAR people. So, they are talking qualitatively (yes, the effect may be there), but we are talking quantitatively (the effect is
small).
I think Ralf may give more details and/or correct my understanding.
Sasha.
On 9/18/23 10:09 AM, Stefan Bathe wrote:
Hi All,
Please see Kiel’s message below. I don’t feel qualified to answer this by myself. So I’m asking for input. But I’d like to turn this around within 24
h.
I think the answer to the question why we are not concerned about running polarized protons with a crossing angle is quantitative: in principle it’s a
concern, but quantitatively we think we can live with it. But I don’t know what the actual evidence is.
I think there’s no reasonable chance we’d switch to a zero crossing angle except in a disaster scenario (luminosity so low that we don’t need a crossing
angle; or no tracking).
-
---------------------------------------------------------------------------------
Stefan Bathe
Professor of Physics
Baruch College, CUNY
and RIKEN Visiting Scientist
Baruch: BNL:
17 Lexington Ave Bldg. 510
office 940 office 2-229
phone 646-660-6272 phone 631-344-8490
----------------------------------------------------------------------------------
Subject: sPHENIX crossing angle with PP in Run24
Date:
September 18, 2023 at 09:20:48 EDT
* This email originates from a sender outside of CUNY. Verify the sender before replying or clicking on links and
attachments. *
To support intensities at RHIC above 2.1e11 protons/bunch, a crossing angle at sPHENIX is needed.
Is there a reason why sPHENIX is not concerned about having a crossing angle for polarized protons where STAR is?
Is there a possibility that sPHENIX will change to a zero crossing angle during the run, which would limit the maximum intensity?
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Email: shura AT bnl.gov
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